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APPROVED STM RESUB1 BLD2022-1279+Storm_Drainage_Report+5.17.2023_3.09.22_PM+3552080RESUB May 17 2023 CITY OFEDMONDS BLD2022-1279 DEVELOPMENT SERVICES DEPARTMENT STORMWA TER MAM4GE/NE/VTREPORT (Stormwater Site Plan) GOODMGHTSFR 741 Aloha Street Edmonds, WA 98020 CSP Engineering PFN 22-005 City PFN BLD2022-1279 05-12-22 Revised 05-1 1-23 111SPIT16 ONAL E or) 123 CSp EAl ngineering Civil Engineering Design and Consulting 1037 NE 65v St # 153 Seattle, WA 98115 Phone: 206 406 9965 email@cspengineering.com COMPLIES WITH APPLICABLE CITY STORMWATER CODE www.cspengineering.com 08/14/2023 TABLE OF CONTENTS Section 1- Project Overview Section 2 - Existing Conditions Summary Section 3 - Off -Site Analysis Section 4 - Permanent Stormwater Control Plan Section 5 - Construction Stormwater Control Plan Section 6 - Special Reports and Studies Section 7 - Other Permits Section 8 - Operations and Maintenance Manual Appendix Single family Source Control BMPs Geotechnical Report This document, in conjunction with the Site Development Construction Plans prepared for this project, is intended to satisfy the local governing authority's adopted drainage manual requirements as interpreted and implemented by agency staff. The Site Development Construction Plans supplement the documentation provided in this report and also serve as the construction documents necessary for implementation of the project. Cn&-tinn 1 Project Overview Project Summary A single-family residence is proposed for an undeveloped Site Parcel situated in the Shell Creek watershed. The development proposes 4,216 sf of New/Replaced Hard Surface classifying the Site as a Category 1 Project subject to Minimum Requirements 1-5. The Project Site including right of way improvements totals —0.19 acres. SITE PARCEL DATA SF AC 8,518 0.196 SITE PARCEL EXISTING IMPERVIOUS SURFACE ROOF - - EXISTING IMPERVIOUS SURFACE HARDSCAPE - 0% EXISTING IMPERVIOUS SURFACECOVERAGE PROJECT SITE DATA SF AC 496 0.011 DISTURBED AREA ROW/OFFSITE DISTURBED AREA SITE PARCEL 7,701 0.177 8,197 0.188 TOTAL DISTURBED AREA PROJECT SITE NEW/REPLACED HARD SURFACE SF AC 289 0.007 PGIS ROW PAVEMENT/DRIVEWAY APRON NPGIS ROW SIDEWALK 135 0.003 NPGIS SITE ROOF 2,937 0.067 NPGIS SITE STAIRWELL 29 0.001 PGPS SITE DRIVEWAY 533 0.012 NPGPS SITE WALK/PATIO/EQUIPMENT PAD 293 0.007 TOTAL NEW/REPLACED HARD SURFACEI 4,216 1 0.097 PROJECTSITE IMPERVIOUS SURFACES SF AC PGIS ROW PAVEMENT/DRIVEWAY APRON 289 0.007 NPGIS ROW SIDEWALK 135 0.003 NPGIS SITE ROOF 2,937 0.067 NPGIS SITE STAIRWELL 29 0.001 3,390 0.078 TOTAL IMPERVIOUS SURFACE PROJECTSITE PERVIOUS SURFACES SF AC PGPS SITE DRIVEWAY 533 0.012 NPGPS SITE WALK/PATIO/EQUIPMENT PAD 293 0.007 NPGPS LAWN/LANDSCAPE 3,981 0.091 4,807 0.110 TOTAL PERVIOUS SURFACE Limy- �a EUX Vicinity Map Minimum Requirements Minimum Requirement #1— Preparation of Stormwater Site Plans Applicable —This document and the Site Development Construction Plans satisfy the Stormwater Site Plan requirement. Minimum Requirement #2 — Construction Stormwater Pollution Prevention Applicable - A Construction Stormwater Pollution Prevention Plan is illustrated in the Site Development Construction Plan set. The construction SWPPP narrative and details are delineated in Section 5. Minimum Requirement #3 — Source Control of Pollution Applicable — Single family Source Control BMPs are delineated in the Appendix. Minimum Requirement #4 — Preservation of Natural Drainage System and Outfalls Applicable - The post -developed site will not significantly alter the natural drainage system characteristics and/or outfall location of the Site. Minimum Requirement #5 — On -Site Stormwater Management Applicable - On -Site Stormwater Management BMPs to infiltrate, disperse, and retain stormwater runoff will be implemented from List #1. Section 2 Existing Conditions Summary The subject Site Parcel is situated on a —7.0% average northwest facing slope and is currently undeveloped. Site ground coverage consists of lawn and deciduous/coniferous trees with areas of bare ground. No critical areas, stormwater facilities, surface drainage features, or BMPs are known to exist on the Site Parcel. Stormwater conveyance infrastructure exists in the adjacent right of way and private driveway west and north of the Site Parcel. A storm drain manhole north of the Site Parcel constructed as part of a previous related short plat stubs into the Site to accommodate future development. Site topography directs stormwater runoff northwest via surface sheetflow. Developed parcels exist north, west and east of the Project Site. Site soils types are identified as SM. Existing Conditions Map Section 3 Off -Site Analysis The Site Parcel is situated in an urban residential area bordered on the south by street frontage improvements, on the west/north by a private drive, and on the east by a single-family residence. Precipitation exceeding the infiltration/evaporation capacity of the onsite vegetation is discharged northwest to existing single family residential parcels. Site topography indicates that some upstream runoff from an adjacent residentially developed parcel may enter the Site from the east. Stormwater discharge from the project's Impervious Surfaces and possible overflow from the Permeable Pavement driveway apron will be collected and conveyed to an existing storm system stub located along the north property line. Stormwater runoff is then conveyed east to a stormwater conveyance system flowing north to Caspers Street then west along Caspers Street, crossing 7th Ave N to Shell Creek —0.28 miles downstream of the Project Site. Stormwater runoff exceeding the infiltration capacity of at -grade BMP hardscape surfaces will follow the historical drainage path of the undeveloped site. Accessible portions of the downstream drainage system were visually inspected and no evidence of limited downstream conveyance capacity or erosion was observed and no future issues are anticipated from development of the site. Basin Map Section 4 Permanent Stormwater Control Plan Existing Site Hydrology Existing Impervious Surfaces on the Project Site are conveyed to adjacent vegetated areas for dispersion/infiltration. Precipitation reaching the Site exceeding the infiltration/evaporation capacity of existing vegetated areas sheet flows northwest to existing single-family residential development. Developed Site Hydrology The proposed development will mitigate stormwater runoff utilizing applicable BMPs from List #1 as follows: Lawn and Landscaped Areas: [A] BMP T5.13 Post -Construction Soil Quality and Depth: Feasible Roofs: [A] BMP T5:30 Full Dispersion: Not Feasible The Site cannot meet the 65%/10% native vegetation to Impervious Surface ratio. [B] BMP T5.10A Downspout Full Infiltration: Not Feasible Geotechnical report recommends infiltration not be utilized on the Site. [C] BMP T5.14A Rain Gardens/BMP T7.30 Bioretention: Not Feasible Available siting area cannot meet the minimum 1' separation to high groundwater/impervious layer (-2' below grade). [D] BMP T5.10B Downspout Dispersion Systems: Not Feasible Available siting area cannot meet the required 25' vegetated flow path. [E] Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum: Feasible Required 3' tank diameter length L=0.008(2,937) = 23.5 If Other Hard Surfaces: (Onsite Hard Surfaces at or above existing grade) [A] BMP T5:30 Full Dispersion: Not Feasible The Site cannot meet the 65%/10% native vegetation to Impervious Surface ratio. [B] BMP T5.10A Full Infiltration: Not Feasible Geotechnical report recommends infiltration not be utilized on the Site. [B] BMP T5.15 Permeable Pavement: Feasible Locations of proposed permeable pavement have been reviewed and approved by the geotechnical engineer. Other Hard Surfaces: (ROW Pavement/Sidewalk/Driveway) [A] BMP T5:30 Full Dispersion: Not Feasible The Site cannot meet the 65%/10% native vegetation to Impervious Surface ratio. [B] BMP T5.10A Full Infiltration: Not Feasible Geotechnical report recommends infiltration not be utilized on the Site. [B] BMP T5.15 Permeable Pavement: Not Feasible Permeable Pavement is not an approved surface for use in the right of way. [C] BMP T5.14A Rain Gardens/BMP T7.30 Bioretention: Not Feasible The elevation/location of the surrounding drainage systems cannot accommodate a properly functioning bioretention/raingarden area. [D] BMP T5.12 Sheet Flow Dispersion/BMP T5.11 Concentrated Flow Dispersion: Not Feasible The required vegetated flow path cannot be achieved. [E] Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum: Not Evaluated Area contains less than 1,000 square feet of contributing site Impervious Surfaces that are not managed by other On - Site Stormwater Management BMPs (Total Hard Surface = 424 sf). Other Hard Surfaces: (Basement Stairwell) [A] BMP T5:30 Full Dispersion: Not Feasible The Site cannot meet the 65%/10% native vegetation to Impervious Surface ratio. [B] BMP T5.10A Full Infiltration: Not Feasible Geotechnical report recommends infiltration not be utilized on the Site. [B] BMP T5.15 Permeable Pavement: Not Feasible At depth soils are not suitable for infiltration. [C] BMP T5.14A Rain Gardens/BMP T7.30 Bioretention: Not Feasible Available siting area cannot meet the minimum 1' separation to high groundwater/impervious layer (-2' below grade). [D] BMP T5.12 Sheet Flow Dispersion/BMP T5.11 Concentrated Flow Dispersion: Not Feasible The required vegetated flow path cannot be achieved. [4] Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum: Not Evaluated Area contains less than 1,000 square feet of contributing site Impervious Surfaces that are not managed by other On - Site Stormwater Management BMPs (Total Hard Surface = 29 sf). Performance Standards and Goals Water Quality — Not Applicable The project does not propose more than 5,000 sf of Pollution -Generating Impervious Surface or more than % of an acre Pollution -Generating Pervious Surface. POLLUTION GENERATING PERVIOUS SURFACE SF AC PGPS ROW PAVEMENT/DRIVEWAY APRON PGPS ROW SHOULDER PGPS ROW PAVEMENT/DRIVEWAY APRON - - PGPS SITE DRIVEWAY 533 0.012 533 0.012 POLLUTION GENERATING IMPERVIOUS SURFACE SF AC PGIS ROW PAVEMENT/DRIVEWAY APRON 289 0.007 PGIS SITE DRIVEWAY(S) - - 289 0.007 Flow Control — Not Applicable The project does not exceed the thresholds triggering Flow Control based on the following criteria: • Projects in which the total of effective impervious surfaces is 10,000 square feet or more in a threshold discharge area, or • Projects that convert % acres or more of vegetation to lawn or landscape, or convert 2.5 acres or more of native vegetation to pasture in a threshold discharge area, and from which there is a surface discharge in a natural or manmade conveyance system from the site, or Projects that through a combination of effective hard surfaces and converted vegetation areas cause a 0.10 cubic feet per second increase in the 100-year flow frequency from a threshold discharge area as estimated using the Western Washington Hydrology Model or other approved model and one -hour time steps (or a 0.15 cfs increase using 15- minute time steps) PROJECT SITE IMPERVIOUS SURFACES SF AC PGIS ROW PAVEMENT/DRIVEWAY APRON 289 0.007 NPGIS ROW SIDEWALK 135 0.003 NPGIS SITE ROOF 2,937 0.067 NPGIS SITE STAIRWELL 29 0.001 3,390 0.078 TOTAL IMPERVIOUS SURFACE PROJECT SITE PERVIOUS SURFACES SF AC PGPS SITE DRIVEWAY 533 0.012 NPGPS SITE WALK/PATIO/EQUIPMENT PAD 293 0.007 NPGPS LAWN/LANDSCAPE 3,981 0.091 4,807 0.110 TOTAL PERVIOUS SURFACE Water Quality System Not Applicable Flow Control System Not Applicable Conveyance System Analysis and Design Conveyance systems provided for the project will consist of 4" - 6" diameter pipes. Based on experience with projects of similar size and configuration the proposed conveyance systems are presumed to be adequate without generating detailed calculations. Due to the implementation of onsite stormwater mitigation the downstream conveyance system is not anticipated to be negatively impacted by the proposed development. Section S Construction Stormwater Pollution Prevention Plan The following 13 Construction SWPPP elements are addressed on the Site Development Construction Plans and SWPPP narrative/details. Element 1: Preserve Vegetation/Mark Clearing Limits Element 2: Establish Construction Access Element 3: Control Flow Rates Element 4: Install Sediment Controls Element 5: Stabilize Soils Element 6: Protect Slopes Element 7: Protect Drain Inlets Element 8: Stabilize Channels and Outlets Element 9: Control Pollutants Element 10: Control De -Watering Element 11: Maintain Best Management Practices Element 12: Manage the Project Element 13: Protect Low Impact Development BMPs Narrative - Element 1: Preserve Vegetation/Mark Clearing Limits The area to be graded and cleared shall be marked with visible flagging, orange plastic construction fencing, or filter fabric fencing. C101 Preserve Natural Vegetation C103 High Visibility Plastic or Metal Fence Element 2: Establish Construction Access - Applicable The existing asphalt driveway adjacent to the Project Site will be utilized as a Stabilized Construction Entrance. Element 3: Control Flow Rates - Applicable Flow rates will be controlled by SWPPP Element 4 sediment controls and BMP T5.13 amended soils. Element 4: Install Sediment Controls - Applicable Sediment will be controlled by installation of a silt fence placed on the downhill side of the Site. C233 Filter Fabric Fence Element 5: Stabilize Soils - Applicable No soil shall remain exposed and unworked for more than 2 days from October 1st the April 30th or 7 days from May 1st to September 301h. Once disturbed landscape areas are graded they shall be stabilized via seeding, mulching, or sodding. All stockpiles will be covered with plastic if left unworked. Soil excavated for the foundation will be exported offsite or backfilled against the foundation. C123 Plastic covering C124 Sodding C120 Temporary or Permanent Seeding C121 Mulching Element 6: Protect Slopes - Not Applicable No cut slopes over 4' high will exceed 2:1 slope and no fill slopes over 4' in height will exceed 3:1 slope. Element 7: Protect Drain Inlets - Applicable Storm drain catch basins in the vicinity of the project will be protected during construction activities and remain in place until the entire site has been stabilized. C220 Storm Drain Inlet Protection Element 8: Stabilize Channels and Outlets - Not Applicable No storm drainage channels or ditches will be constructed during the project. Element 9: Control Pollutants - Applicable Any pollutants, chemicals, liquid products and other materials that have the potential to pose a threat to human health or the environment will be kept under cover in a secure location on site and protected from vandalism. Concrete handling, and sawcutting wastewater shall be prevented from discharging pollutants from the site. C151 Concrete Handling C152 Sawcutting and Surfacing Pollution Prevention C153 material Storage, Delivery, and Containment Element 10 Control Dewatering - Not Applicable Dewatering at the site is not anticipated. Element 11— Maintain Best Management Protections - Applicable BMPs will be inspected and maintained during construction and removed within 30 days after the site has been stabilized. Element 12 — Manage the Project - Applicable All BMPs shall be installed as delineated in the Site Development Construction Plans construction sequence and maintained, repaired, and/or replaced as necessary to prevent construction stormwater pollution from leaving the Site. Element 13: Protect Low Impact Development BMPs - Applicable Areas proposed for Permeable Pavement surfacing shall be protected from compaction with orange plastic construction fencing. BMP C101: Preserving Natural Vegetation Propose The purpose of preserving natural vegetation is to reduce erosion wherever practicable. Limiting site disturbance is the single most effective method for reducing erosion. For example, conifers can hold up to about 50 percent of all rain that falls during a storm. Up to 20-30 percent of this rain may never reach the ground but is taken up by the tree or evaporates. Another benefit is that the rain held in the tree can be released slowly to the ground after the storm. Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial and intermittent watercourses or swales, and on building sites in wooded areas. • As required by local governments. • Phase construction to preserve natural vegetation on the project site for as long as possible during the construction period. Design and Natural vegetation can be preserved in natural clumps or as individual Installation trees, shrubs and vines. Specifications The preservation of individual plants is more difficult because heavy equipment is generally used to remove unwanted vegetation. The points to remember when attempting to save individual plants are: • Is the plant worth saving? Consider the location, species, size, age, vigor, and the work involved. Local governments may also have ordinances to save natural vegetation and trees. • Fence or clearly mark areas around trees that are to be saved. It is preferable to keep ground disturbance away from the trees at least as far out as the dripline. Plants need protection from three kinds of injuries: • Construction Equipment - This injury can be above or below the ground level. Damage results from scarring, cutting of roots, and compaction of the soil. Placing a fenced buffer zone around plants to be saved prior to construction can prevent construction equipment injuries. • Grade Changes - Changing the natural ground level will alter grades, which affects the plant's ability to obtain the necessary air, water, and minerals. Minor fills usually do not cause problems although sensitivity between species does vary and should be checked. Trees can typically tolerate fill of 6 inches or less. For shrubs and other plants, the fill should be less. When there are major changes in grade, it may become necessary to supply air to the roots of plants. This can be done by placing a layer of gravel and a tile system over the roots before the fill is made. A tile system protects a tree from a raised grade. The tile system should be Volume H— Construction Stormieater Pollution Prevention - August 2012 4-3 laid out on the original grade leading from a dry well around the tree trunk. The system should then be covered with small stones to allow air to circulate over the root area. Lowering the natural ground level can seriously damage trees and shrubs. The highest percentage of the plant roots are in the upper 12 inches of the soil and cuts of only 2-3 inches can cause serious injury. To protect the roots it may be necessary to terrace the immediate area around the plants to be saved. If roots are exposed, construction of retaining walls may be needed to keep the soil in place. Plants can also be preserved by leaving them on an undisturbed, gently sloping mound. To increase the chances for survival, it is best to limit grade changes and other soil disturbances to areas outside the dripline of the plant. Excavations - Protect trees and other plants when excavating for drainfields, power, water, and sewer lines. Where possible, the trenches should be routed around trees and large shrubs. When this is not possible, it is best to tunnel under them. This can be done with hand tools or with power augers. If it is not possible to route the trench around plants to be saved, then the following should be observed: Cut as few roots as possible. When you have to cut, cut clean. Paint cut root ends with a wood dressing like asphalt base paint if roots will be exposed for more than 24-hours. Backfill the trench as soon as possible. Tunnel beneath root systems as close to the center of the main think to preserve most of the important feeder roots. Some problems that can be encountered with a few specific trees are: • Maple, Dogwood, Red alder, Western hemlock, Western red cedar, and Douglas fir do not readily adjust to changes in environment and special care should be taken to protect these trees. • The windthrow hazard of Pacific silver fir and madrona is high, while that of Western hemlock is moderate. The danger of windthrow increases where dense stands have been thinned. Other species (unless they are on shallow, wet soils less than 20 inches deep) have a low windthrow hazard. Cottonwoods, maples, and willows have water -seeking roots. These can cause trouble in sewer lines and infiltration fields. On the other hand, they thrive in high moisture conditions that other trees would not. • Thinning operations in pure or mixed stands of Grand fir, Pacific silver fir, Noble fir, Sitka spruce, Western red cedar, Western hemlock, Pacific dogwood, and Red alder can cause serious disease problems. Disease can become established through damaged limbs, trunks, roots, Volume H— Construction Stormsrater Pollution Prevention - August 2012 4-4 and freshly cut stumps. Diseased and weakened trees are also susceptible to insect attack. Maintenance Inspect flagged and/or fenced areas regularly to make sure flagging or Standards fencing has not been removed or damaged. If the flagging or fencing has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. If tree roots have been exposed or injured, "prune" cleanly with an appropriate pruning saw or lopers directly above the damaged roots and recover with native soils. Treatment of sap flowing trees (fir, hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier. BMP C103: High Visibility Fence Purpose Fencing is intended to: 1. Restrict clearing to approved limits. 2. Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undisturbed. 3. Limit construction traffic to designated construction entrances, exits, or internal roads. 4. Protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used: • At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared. • As necessary to control vehicle access to and on the site. Design and High visibility plastic fence shall be composed of a high -density Installation polyethylene material and shall be at least four feet in height. Posts for Specifications the fencing shall be steel or wood and placed every 6 feet on center (maximum) or as needed to ensure rigidity. The fencing shall be fastened to the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color shall be high visibility orange. The fence tensile strength shall be 360 lbs./ft. using the ASTM D4595 testing method. If appropriate install fabric silt fence in accordance with BMP C233 to act as high visibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. Maintenance If the fence has been damaged or visibility reduced, it shall be repaired or Standards replaced immediately and visibility restored. Volume II— Construction Stormwater Pollution Prevention - August 2012 4-6 BMP C120: Temporary and Permanent Seeding P,npose Seeding reduces erosion by stabilizing exposed soils. A well -established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use Use seeding throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. The optimum seeding windows for western Washington are April 1 through June 30 and September 1 through October 1. Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is established. Between October 1 and March 30 seeding requires a cover of mulch with straw or an erosion control blanket until 75 percent grass cover is established. Review all disturbed areas in late August to early September and complete all seeding by the end of September. Otherwise, vegetation will not establish itself enough to provide more than average protection. • Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding. See BMP C 121: Mulching for specifications. • Seed and mulch, all disturbed areas not otherwise vegetated at final site stabilization. Final stabilization means the completion of all soil disturbing activities at the site and the establishment of a permanent vegetative cover, or equivalent permanent stabilization measures (such as pavement, riprap, gabions or geotextiles) which will prevent erosion. Design and Seed retention/detention ponds as required. Installation Install channels intended for vegetation before starting major Specifications earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated channels that will have high flows, install erosion control blankets over hydroseed. Before allowing water to flow in vegetated channels, establish 75 percent vegetation cover. If vegetated channels cannot be established by seed before water flow; install sod in the channel bottom —over hydromulch and erosion control blankets. Volume H— Construction Stormwater Pollution Prevention -August 2012 4-13 • Confirm the installation of all required surface water control measures to prevent seed from washing away. • Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 percent tackifier. See BMP C 121: Mulching for specifications. • Areas that will have seeding only and not landscaping may need compost or meal -based mulch included in the hydroseed in order to establish vegetation. Re -install native topsoil on the disturbed soil surface before application. • When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up in contact with the soil surface. This reduces the ability to establish a good stand of grass quickly. To overcome this, consider increasing seed quantities by up to 50 percent. • Enhance vegetation establishment by dividing the hydromulch operation into two phases: 1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in the first lift. 2. Phase 2- Install the rest of the mulch and tackifier over the first lift. Or, enhance vegetation by: 1. Installing the mulch, seed, fertilizer, and tackifier in one lift. 2. Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per acre. 3. Hold straw in place with a standard tackifier. Both of these approaches will increase cost moderately but will greatly improve and enhance vegetative establishment. The increased cost may be offset by the reduced need for: • Irrigation. • Reapplication of mulch. • Repair of failed slope surfaces. This technique works with standard hydromulch (1,500 pounds per acre minimum) and BFM/MBFMs (3,000 pounds per acre minimum). • Seed may be installed by hand if: • Temporary and covered by straw, mulch, or topsoil. • Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil, or erosion blankets. • The seed mixes listed in the tables below include recommended mixes for both temporary and permanent seeding. Volume H— Construction Stormsrater Pollution Prevention - August 2012 4-14 • Apply these mixes, with the exception of the wetland mix, at a rate of 120 pounds per acre. This rate can be reduced if soil amendments or slow -release fertilizers are used. • Consult the local suppliers or the local conservation district for their recommendations because the appropriate mix depends on a variety of factors, including location, exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the local authority may be used. • Other mixes may be appropriate, depending on the soil type and hydrology of the area. Table 4.1.2 lists the standard mix for areas requiring a temporary vegetative cover. Table 4.1.2 Temporary Erosion Control Seed Mix o o A' eight O o Purity % Gerwination Chewings or annual blue grass 40 98 90 Festuca rubra var. commutata or Poa anna Perennial rye - 0 98 90 Lolium perenne Redtop or colonial bentgrass 5 92 85 Agrostis alba or Agrostis tenuis White dutch clover 5 98 90 Trifolium repens • Table 4.1.3 lists a recommended mix for landscaping seed. Table 4.1.3 Landscaping Seed Mix 0 o Weight ht OA Pori % Germination Perennial rye blend 70 98 90 Lolium perenne Chewings and red fescue blend 30 98 90 Festuca rubra var. commutata or Festuca rubra Volume II — Construction Stormwater Pollution Prevention - August 2012 4-15 • Table 4.1.4 lists a turf seed mix for dry situations where there is no need for watering. This mix requires very little maintenance. Table 4.1.4 Low -Growing Turf Seed Mix % NVei ht % PmitN % Germination Dwarf tall fescue (several varieties) 45 98 90 Festuca arundinacea var. Dwarf perennial rye (Barclay) 30 98 90 Lolium perenne var. barclay Red fescue 20 98 90 Festuca rubra Colonial bentgrass 5 98 90 Agrostis tennis • Table 4.1.5 lists a mix for bioswales and other intermittently wet areas. Table 4.1.5 Bioswale Seed Mix* % Weight % Purity °-b Germination Tall or meadow fescue 75-80 98 90 Festuca arundinacea or Festuca elatior Seaside/Creeping bentgrass 10-15 92 85 A ostfs alustris Redto!bentgrass 5-10 90 80 ,OSt15(7l17(I Ot_-la)'OSt7S gla(771tPQ *Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix Volume II — Construction Stormivater Pollution Prevention - August 2012 4-16 • Table 4.1.6 lists a low -growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wetlands. Apply this mixture at a rate of 60 pounds per acre. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable. Table 4.1.6 Wet Area Seed Mix* Weight % Puri % Germination Tall or meadow fescue 60-70 98 90 Festuca arundinacea or Festuca elatior Seaside/Creeping bentgrass 10-15 98 85 Agrostis palustris Meadow foxtail 10-15 90 80 Ale ocurus pratensis Alsike clover 1-6 98 90 Trifolium hybridum Redtop bentgrass 1-6 92 85 Agrostis alba *Modified Briargreen, Inc. Hvdroseeding Guide IT'etlands Seed Mix Table 4.1.7 lists a recommended meadow seed mix for infrequently maintained areas or non -maintained areas where colonization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seeding should take place in September or very early October in order to obtain adequate establishment prior to the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix. Amending the soil can reduce the need for clover. Table 4.1.7 Meadow Seed Mix 0 o R eight 0.o Purity % Germination Redtop or Oregon bentgrass 20 92 85 Agrostis alba or Agrostis ore onensis Red fescue 70 98 90 Festuca rubra White dutch clover 10 98 90 Tri olium re ens Volume II— Construction Stormwater Pollution Prevention - August 2012 4-17 Roughening and Rototilling: • The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track walk slopes before seeding if engineering purposes require compaction. Backblading or smoothing of slopes greater than 411:1 V is not allowed if they are to be seeded. • Restoration -based landscape practices require deeper incorporation than that provided by a simple single -pass rototilling treatment. Wherever practical, initially rip the subgrade to improve long-term permeability, infiltration, and water inflow qualities. At a minimum, permanent areas shall use soil amendments to achieve organic matter and permeability performance defined in engineered soil/landscape systems. For systems that are deeper than 8 inches complete the rototilling process in multiple lifts, or prepare the engineered soil system per specifications and place to achieve the specified depth. • Fertilizers: • Conducting soil tests to determine the exact type and quantity of fertilizer is recommended. This will prevent the over -application of fertilizer. • Organic matter is the most appropriate form of fertilizer because it provides nutrients (including nitrogen, phosphorus, and potassium) in the least water-soluble form. • In general, use 10-4-6 N-P-K (nitrogen -phosphorus -potassium) fertilizer at a rate of 90 pounds per acre. Always use slow -release fertilizers because they are more efficient and have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agitate, more than 20 minutes before use. Too much agitation destroys the slow -release coating. • There are numerous products available that take the place of chemical fertilizers. These include several with seaweed extracts that are beneficial to soil microbes and organisms. If 100 percent cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be necessary. Cottonseed meal provides a good source of long-term, slow -release, available nitrogen. Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix: • On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix (MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre of mulch with approximately 10 percent tackifier. Achieve a minimum of 95 percent soil coverage during application. Numerous products are available commercially. Installed products per manufacturer's instructions. Most products require 24-36 hours to cure before rainfall and cannot be installed on wet or saturated soils. Volume H— Construction Stormseater Pollution Prevention -August 2012 4-18 Generally, products come in 40-50 pound bags and include all necessary ingredients except for seed and fertilizer. BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation establishment. Advantages over blankets include: • BFM and MBFMs do not require surface preparation. • Helicopters can assist in installing BFM and MBFMs in remote areas. • On slopes steeper than 2.5H:1V, blanket installers may require ropes and harnesses for safety. • Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets. Maintenance Reseed any seeded areas that fail to establish at least 80 percent cover Standards (100 percent cover for areas that receive sheet or concentrated flows). If reseeding is ineffective, use an alternate method such as sodding, mulching, or nets/blankets. If winter weather prevents adequate grass growth, this time limit may be relaxed at the discretion of the local authority when sensitive areas would otherwise be protected. • Reseed and protect by mulch any areas that experience erosion after achieving adequate cover. Reseed and protect by mulch any eroded area. • Supply seeded areas with adequate moisture, but do not water to the extent that it causes runoff. Approved as Ecology has approved products as able to meet the requirements of BMP Equivalent C 120. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology's website at hq://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html BMP C121: Mulching Prnhose Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating soil temperatures. There is an enormous variety of mulches that can be used. This section discusses only the most common types of mulch. Conditions of Use As a temporary cover measure, mulch should be used: • For less than 30 days on disturbed areas that require cover. • At all times for seeded areas, especially during the wet season and Volume H— Construction Storm rater Pollution Prevention - August 2012 4-19 during the hot summer months. During the wet season on slopes steeper than 3H:1 V with more than 10 feet of vertical relief. Mulch may be applied at any time of the year and must be refreshed periodically. For seeded areas mulch may be made up of 100 percent: cottonseed meal; fibers made of wood, recycled cellulose, hemp, kenaf; compost; or blends of these. Tackifier shall be plant -based, such as guar or alpha plantago, or chemical -based such as polyacrylamide or polymers. Any mulch or tackifier product used shall be installed per manufacturer's instructions. Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application. Design and For mulch materials, application rates, and specifications, see Table 4.1.8. Installation Always use a 2-inch minimum mulch thickness; increase the thickness Specifications until the ground is 95% covered (i.e. not visible under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive areas or other areas highly susceptible to erosion. Mulch used within the ordinary high-water mark of surface waters should be selected to minimize potential flotation of organic matter. Composted organic materials have higher specific gravities (densities) than straw, wood, or chipped material. Consult Hydraulic Permit Authority (HPA) for mulch mixes if applicable. 31aintenance . The thickness of the cover must be maintained. Standards • Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched. Volume H— Construction Stormivater Pollution Prevention - August 2012 4-20 Table 4.1.8 Mulch Standards and Guidelines Application Mulch Material Quality Standards Rates Remarks Straw Air-dried; free from 2"-3" thick; 5 Cost-effective protection when applied with adequate thicknes_,. undesirable seed and bales per 1,000 Hand -application generally requires greater thickness than coarse material. sf or 2-3 tons per blown straw. The thickness of straw may be reduced by half acre when used in conjunction with seeding. In windy areas straw must be held in place by crimping, using a tackifier, or covering with netting. Blown straw always has to be held in place with a tackifier as even light winds will blow it away. Straw, however, has several deficiencies that should be considered when selecting mulch materials. It often introduces and/or encourages the propagation of weed species and it has no significant long- term benefits. It should also not be used within the ordinary high-water elevation of surface waters (due to flotation). Hydroinulch \o growth Approx. 25-30 Shall be applied with hydromulcher. Shall not be used without inhibituig factors. lbs per 1,000 sf seed and tackifier unless the application rate is at least doubled. or 1,500 - 2,000 Fibers longer than about 3/o-1 inch clog hydromulch equipment. lbs per acre Fibers should be kept to less than 3/o inch. Composted No visible water or 2" thick min.; More effective control can be obtained by increasing thickness Mulch and dust during approx. 100 tons to 3". Excellent mulch for protecting final grades until Compost handling. Must be per acre (approx. landscaping because it can be directly seeded or tilled into soil produced in 800 lbs per yard) as an amendment. Composted mulch has a coarser size accordance with gradation than compost. It is more stable and practical to use in WAC 173-350, wet areas and during rainy weather conditions. Do not use Solid Waste composted mulch near wetlands or near phosphorous impaired Handling Standards. water bodies. Chipped Site Average size shall 2" thick min.; This is a cost-effective way to dispose of debris from clearing Vegetation be several inches. and grubbing, and it eliminates the problems associated with Gradations from burning. Generally, it should not be used on slopes above fines to 6 inches in approx. 10% because of its tendency to be transported by length for texture, runoff. It is not recommended within 200 feet of surface waters. variation, and If seeding is expected shortly after mulch, the decomposition of interlocking the chipped vegetation may tie up nutrients important to grass properties. establishment. Wood -based No visible water or 2" thick min.; This material is often called "hog or hogged fuel." The use of Mulch or Wood dust during approx. 100 tons mulch ultimately improves the organic matter in the soil. Straw handling. Must be per acre (approx. Special caution is advised regarding the source and composition purchased from a 800 lbs. per of wood -based mulches. Its preparation typically does not supplier with a Solid cubic yard) provide any weed seed control, so evidence of residual Waste Handling vegetation in its composition or known inclusion of weed plants Permit or one or seeds should be monitored and prevented (or minimized). exempt from solid waste regulations. Wood Strand A blend of loose, 2" thick min. Cost-effective protection when applied with adequate thickness. Mulch long, thin wood A minimum of 95-percent of the wood strand shall have lengths pieces derived from between 2 and 10-inches, with a width and thickness between native conifer or 1/16 and %-inches. The mulch shall not contain resin, tannin, or deciduous trees with other compounds in quantities that would be detrimental to plant high length -to -width life. Sawdust or wood shavings shall not be used as mulch. ratio. (WSDOT specification (9-14.4(4)) Volume H— Construction Stormwater Pollution Prevention - August 2012 4-21 BMP C123: Plastic Covering Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of Plastic covering may be used on disturbed areas that require cover Use measures for less than 30 days, except as stated below. • Plastic is particularly useful for protecting cut and fill slopes and stockpiles. Note: The relatively rapid breakdown of most polyethylene sheeting makes it unsuitable for long-term (greater than six months) applications. • Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes. • Plastic sheeting may result in increased runoff volumes and velocities, requiring additional on -site measures to counteract the increases. Creating a trough with wattles or other material can convey clean water away from these areas. • To prevent undercutting, trench and backfill rolled plastic covering products. • While plastic is inexpensive to purchase, the added cost of installation, maintenance, removal, and disposal make this an expensive material, up to $1.50-2.00 per square yard. • Whenever plastic is used to protect slopes install water collection measures at the base of the slope. These measures include plastic - covered berms, channels, and pipes used to covey clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a plastic covered slope with dirty runoff from a project. • Other uses for plastic include: 1. Temporary ditch liner. 2. Pond liner in temporary sediment pond. 3. Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel being stored. 4. Emergency slope protection during heavy rains. 5. Temporary drainpipe ("elephant trunk") used to direct water. Design and Plastic slope cover must be installed as follows: Installation 1. Run plastic up and down slope, not across slope. Specifications 2. Plastic may be installed perpendicular to a slope if the slope length is less than 10 feet. 3. Minimum of 8-inch overlap at seams. Volume H— Construction Stormivater Pollution Prevention - August 2012 4-26 4. On long or wide slopes, or slopes subject to wind, tape all seams. 5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top of the slope and backfill with soil to keep water from flowing underneath. 6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them together with twine to hold them in place. 7. Inspect plastic for rips, tears, and open seams regularly and repair immediately. This prevents high velocity runoff from contacting bare soil which causes extreme erosion. 8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be staked in place. • Plastic sheeting shall have a minimum thickness of 0.06 millimeters. • If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall be installed at the toe of the slope in order to reduce the velocity of runoff. Maintenance • Tom sheets must be replaced and open seams repaired. Standards • Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radiation. • Completely remove plastic when no longer needed. • Dispose of old tires used to weight down plastic sheeting appropriately. Approved as Ecology has approved products as able to meet the requirements of BMP Equivalent C 123. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology's website at hqp://www.ecy.wa.goy/programs/wQ/stormwater/newtech/equivalent.html BMP C124: Sodding Pinhole The purpose of sodding is to establish permanent turf for immediate erosion protection and to stabilize drainage ways where concentrated overland flow will occur. Conditions of Use Sodding may be used in the following areas: • Disturbed areas that require short-term or long-term cover. • Disturbed areas that require immediate vegetative cover. • All waterways that require vegetative lining. Waterways may also be seeded rather than sodded, and protected with a net or blanket. Volume H— Construction Stormwater Pollution Prevention - August 2012 4-27 Design and Sod shall be free of weeds, of uniform thickness (approximately 1-inch Installation thick), and shall have a dense root mat for mechanical strength. Specifications The following steps are recommended for sod installation: • Shape and smooth the surface to final grade in accordance with the approved grading plan. The swale needs to be overexcavated 4 to 6 inches below design elevation to allow room for placing soil amendment and sod. • Amend 4 inches (minimum) of compost into the top 8 inches of the soil if the organic content of the soil is less than ten percent or the permeability is less than 0.6 inches per hour. See http://www.ecy.wa.gov/programs/swWorganics/soil.html for further information. • Fertilize according to the supplier's recommendations. • Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface. • Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the direction of water flow. Wedge strips securely into place. Square the ends of each strip to provide for a close, tight fit. Stagger joints at least 12 inches. Staple on slopes steeper than 311:1V. Staple the upstream edge of each sod strip. • Roll the sodded area and irrigate. • When sodding is carried out in alternating strips or other patterns, seed the areas between the sod immediately after sodding. Maintenance If the grass is unhealthy, the cause shall be determined and appropriate Standards action taken to reestablish a healthy groundcover. If it is impossible to establish a healthy groundcover due to frequent saturation, instability, or some other cause, the sod shall be removed, the area seeded with an appropriate nix, and protected with a net or blanket. BMP C150: Materials on Hand Puthose Keep quantities of erosion prevention and sediment control materials on the project site at all times to be used for regular maintenance and emergency situations such as unexpected heavy summer rains. Having these materials on -site reduces the time needed to implement BMPs when inspections indicate that existing BMPs are not meeting the Construction SWPPP requirements. In addition, contractors can save money by buying some materials in bulk and storing them at their office or yard. Conditions of Use • Construction projects of any size or type can benefit from having materials on hand. A small commercial development project could have a roll of plastic and some gravel available for immediate protection of bare soil and temporary berm construction. A large earthwork project, such as highway construction, might have several tons of straw, several rolls of plastic, flexible pipe, sandbags, geotextile fabric and steel "T" posts. • Materials are stockpiled and readily available before any site clearing, grubbing, or earthwork begins. A large contractor or developer could keep a stockpile of materials that are available for use on several projects. • If storage space at the project site is at a premium, the contractor could maintain the materials at their office or yard. The office or yard must be less than an hour from the project site. Volume II — Construction Stormirnter Pollution Prevention -August 2012 4-41 Design and Installation Specifications Maintenance Standards BMP C151 Depending on project type, size, complexity, and length, materials and quantities will vary. A good minimum list of items that will cover numerous situations includes: Material Clear Plastic, 6 mil Drainpipe, 6 or 8 inch diameter Sandbags, filled Straw Bales for mulching, Quarry S alls Washed Gravel Geotextile Fabric Catch Basin Inserts Steel "T" Posts Silt fence material Straw Wattles All materials with the exception of the quarry spalls, steel "T" posts, and gravel should be kept covered and out of both sun and rain. Re -stock materials used as needed. Concrete Handling Prnhose Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, concrete process water, and concrete slurry from entering waters of the state. Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction projects include, but are not limited to, the following: • Curbs • Sidewalks • Roads • Bridges • Foundations • Floors • Runways Design and • Wash out concrete truck chutes, pumps, and internals into formed Installation areas only. Assure that washout of concrete trucks is performed off - Volume H— Construction Stormwater Pollution Prevention - August 2012 4-42 .Specifications site or in designated concrete washout areas. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or streams. Refer to BMP C154 for information on concrete washout areas. • Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site, except in designated concrete washout areas. • Wash off hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels into formed areas only. • Wash equipment difficult to move, such as concrete pavers in areas that do not directly drain to natural or constructed stormwater conveyances. • Do not allow washdown from areas, such as concrete aggregate driveways, to drain directly to natural or constructed stormwater conveyances. • Contain washwater and leftover product in a lined container when no formed areas are available,. Dispose of contained concrete in a manner that does not violate ground water or surface water quality standards. • Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface waters. • Refer to BMPs C252 and C253 for pH adjustment requirements. • Refer to the Construction Stormwater General Permit for pH monitoring requirements if the project involves one of the following activities: • Significant concrete work (greater than 1,000 cubic yards poured concrete or recycled concrete used over the life of a project). • The use of engineered soils amended with (but not limited to) Portland cement -treated base, cement kiln dust or fly ash. • Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for high pH. ?Maintenance Check containers for holes in the liner daily during concrete pours and .Standards repair the same day. Volume II — Construction Stormwater Pollution Prevention - August 2012 4-43 BMP C152: Sawcutting and Surfacing Pollution Prevention Ptnhose Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high pH (concrete cutting), both of which can violate the water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from entering waters of the State. Conditions of Use Utilize these management practices anytime sawcuttmg or surfacing operations take place. Sawcutting and surfacing operations include, but are not limited to, the following: • Sawing • Coring • Grinding • Roughening • Hydro -demolition • Bridge and road surfacing Design and . Vacuum slurry and cuttings during cutting and surfacing operations. Installation Slurry and cuttings shall not remain on permanent concrete or asphalt Specifications pavement overnight. • Slurry and cuttings shall not drain to any natural or constructed drainage conveyance including stormwater systems. This may require temporarily blocking catch basins. • Dispose of collected slurry and cuttings in a manner that does not violate ground water or surface water quality standards. • Do not allow process water generated during hydro -demolition, surface roughening or similar operations to drain to any natural or constructed drainage conveyance including stormwater systems. Dispose process water in a manner that does not violate ground water or surface water quality standards. • Handle and dispose cleaning waste material and demolition debris in a manner that does not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an appropriate disposal site. Maintenance Continually monitor operations to determine whether slurry, cuttings, or Standards process water could enter waters of the state. If inspections show that a violation of water quality standards could occur, stop operations and immediately implement preventive measures such as berms, barriers, secondary containment, and vacuum trucks. Volume H— Construction Stormsrater Pollution Prevention - August 2012 4-44 BMP C153: Material Delivery, Storage and Containment Ptnpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on -site, store materials in a designated area, and install secondary containment. Conditions of Use These procedures are suitable for use at all construction sites with delivery and storage of the following materials: • Petroleum products such as fuel, oil and grease • Soil stabilizers and binders (e.g. Polyacrylamide) • Fertilizers, pesticides and herbicides • Detergents • Asphalt and concrete compounds • Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds • Any other material that may be detrimental if released to the environment Design and The following steps should be taken to minimize risk: Installation Temporary storage area should be located away from vehicular traffic, Specifications near the construction entrance(s), and away from waterways or storm drains. • Material Safety Data Sheets (MSDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. • Hazardous material storage on -site should be minimised. • Hazardous materials should be handled as infrequently as possible. • During the wet weather season (Oct 1— April 30), consider storing materials in a covered area. • Materials should be stored in secondary containments, such as earthen dike, horse trough, or even a children's wading pool for non -reactive materials such as detergents, oil, grease, and paints. Small amounts of material may be secondarily contained in "bus boy" trays or concrete mixing trays. • Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, and within secondary containment. • If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. Volume H— Construction Stormsrater Pollution Prevention - August 2012 4-45 Material Storage Areas and Secondary Containment Practices: • Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities. • Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed container volume of all containers, or 110% of the capacity of the largest container within its boundary, whichever is greater. • Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours. • Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums. These liquids shall be handled as hazardous waste unless testing determines them to be non -hazardous. • Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. • During the wet weather season (Oct 1— April 30), each secondary containment facility shall be covered during non -working days, prior to and during rain events. • Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill clean-up material (spill kit). • The spill kit should include, at a minimum: • 1-Water Resistant Nylon Bag 3-Oil Absorbent Socks 3"x 4' 2-Oil Absorbent Socks 3"x 10' • 12-Oil Absorbent Pads 17"xl9" 1-Pair Splash Resistant Goggles • 3-Pair Nitrite Gloves 10-Disposable Bags with Ties • Instructions Volume H— Construction Stormwater Pollution Prevention - August 2012 4-46 BMP C220: Storm Drain Inlet Protection Purpose Storm drain inlet protection prevents coarse sediment from entering drainage systems prior to permanent stabilization of the disturbed area. Conditions of Use Use storm drain inlet protection at inlets that are operational before permanent stabilization of the disturbed drainage area. Provide protection for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless conveying runoff entering catch basins to a sediment pond or trap. Also consider inlet protection for lawn and yard drains on new home construction. These small and numerous drains coupled with lack of gutters in new home construction can add significant amounts of sediment into the roof drain system. If possible delay installing lawn and yard drains until just before landscaping or cap these drains to prevent sediment from entering the system until completion of landscaping. Provide 18-inches of sod around each fmished lawn and yard drain. Table 4.2.2 lists several options for inlet protection. All of the methods for storm drain inlet protection tend to plug and require a high frequency of maintenance. Limit drainage areas to one acre or less. Possibly provide emergency overflows with additional end -of -pipe treatment where stormwater ponding would cause a hazard. Volume H— Construction Stormseater Pollution Prevention - August 2012 4-79 Table 4.2.2 Storm Drain Inlet Protection Applicable for Type of Inlet Emergency Paved/ Earthen Protection Overflow Surfaces Conditions of Use Drop Inlet Protection Excavated drop inlet Yes, Earthen Applicable for heavy flows. Easy protection temporary to maintain. Large area flooding will Requirement: 30' X 307acre occur Block and gravel drop Yes Paved or Earthen Applicable for heavy concentrated inlet protection flows. Will not pond. Gravel and wire drop No Applicable for heavy concentrated inlet protection flows. Will pond. Can withstand traffic. Catch basin filters Yes Paved or Earthen Frequent maintenance required. Curb Inlet Protection Curb inlet protection Small capacity Paved Used for sturdy, more compact with a wooden weir overflow installation. Block and gravel curb Yes Paved Sturdy, but limited filtration. inlet protection Culvert Inlet Protection Culvert inlet sediment 18 month expected life. trap Design and Excavated Drop Inlet Protection - An excavated impoundment around the Installation storm drain. Sediment settles out of the stormwater prior to entering the Specifications storm drain. • Provide a depth of 1-2 ft as measured from the crest of the inlet structure. • Slope sides of excavation no steeper than 2H:IV. • Minimum volume of excavation 35 cubic yards. • Shape basin to fit site with longest dimension oriented toward the longest inflow area. • Install provisions for draining to prevent standing water problems. • Clear the area of all debris. • Grade the approach to the inlet uniformly. • Drill weep holes into the side of the inlet. • Protect weep holes with screen wire and washed aggregate. • Seal weep holes when removing structure and stabilizing area. Volume H— Construction Stormwater Pollution Prevention - August 2012 4-80 • Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass flow. Block and Gravel Filter - A barrier formed around the storm drain inlet with standard concrete blocks and gravel. See Figure 4.2.8. • Provide a height of 1 to 2 feet above inlet. • Recess the first row 2-inches into the ground for stability. • Support subsequent courses by placing a 2x4 through the block opening. • Do not use mortar. • Lay some blocks in the bottom row on their side for dewatering the pool. • Place hardware cloth or comparable wire mesh with 1/2-inch openings over all block openings. • Place gravel just below the top of blocks on slopes of 2H:1 V or flatter. • An alternative design is a gravel donut. • Provide an inlet slope of 3H:1 V. • Provide an outlet slope of 2H:IV. • Provide al -foot wide level stone area between the structure and the inlet. • Use inlet slope stones 3 inches in diameter or larger. • Use gravel'/z- to'/4-inch at a minimum thickness of 1-foot for the outlet slope. Volume H— Construction Stonnn•ater Polhrtion Prevention - August 2012 4-81 Plan View q Drain Grate 0 0° 00o 0.. 0 opv °oo 04 •o 00 ° o ° o o •��SOa:�b �O Concrete t�oO°a , o Block OOQ��p4 Q0 4�04 0 < c 'moo ,° Gravel 'moo �` ° .o Backfill ° OQ ° �04ov .C]L/� QOL/ A h Section A - A Concrete Block Wire Screen or / Filter Fabric Gravel Backfill overflow 0 Water 0 o Ponding Height _ l Water • po Drop Inlet Notes: 1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas_ (less than 5%) 2. Excavate a basin of sufficient size adjacent to the drop inlet. 3. The top of the structure (ponding height) must be well below the ground elevation downslope to prevent runoff from bypassing the inlet. A temporary dike may be necessary on the downslope side of the structure. Figure 4.2.8 - Block and Gravel Filter Gravel and Wire Mesh Filter - A gravel barrier placed over the top of the inlet. This structure does not provide an overflow. • Use a hardware cloth or comparable wire mesh with t/z-inch openings. • Use coarse aggregate. • Provide a height 1-foot or more, 18-inches wider than inlet on all sides. • Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot beyond each side of the inlet structure. • Overlap the strips if more than one strip of mesh is necessary. Volume H- Construction Stormivater Pollution Prevention - August 2012 4-82 • Place coarse aggregate over the wire mesh. • Provide at least a 12-inch depth of gravel over the entire inlet opening and extend at least 18-inches on all sides. Catchbasin Filters — Use inserts designed by manufacturers for construction sites. The limited sediment storage capacity increases the amount of inspection and maintenance required, which may be daily for heavy sediment loads. To reduce maintenance requirements combine a catchbasin filter with another type of inlet protection. This type of inlet protection provides flow bypass without overflow and therefore may be a better method for inlets located along active rights -of -way. • Provides 5 cubic feet of storage. • Requires dewatering provisions. • Provides a high -flow bypass that will not clog under normal use at a construction site. • Insert the catchbasin filter in the catchbasin just below the grating. Curb Inlet Protection with Wooden Weir — Barrier formed around a curb inlet with a wooden frame and gravel. • Use wire mesh with %2-inch openings. • Use extra strength filter cloth. • Construct a frame. • Attach the wire and filter fabric to the frame. • Pile coarse washed aggregate against wire/fabric. • Place weight on frame anchors. Block and Gravel Curb Inlet Protection — Barrier formed around a curb inlet with concrete blocks and gravel. See Figure 4.2.9. • Use wire mesh with %-inch openings. • Place two concrete blocks on their sides abutting the curb at either side of the inlet opening. These are spacer blocks. • Place a 2x4 stud through the outer holes of each spacer block to align the front blocks. • Place blocks on their sides across the front of the inlet and abutting the spacer blocks. • Place wire mesh over the outside vertical face. • Pile coarse aggregate against the wire to the top of the barrier. Curb and Gutter Sediment Barrier — Sandbag or rock berm (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure 4.2.10. Volume H— Construction Stormwater Pollution Prevention - August 2012 4-83 • Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet. • Construct a horseshoe shaped sedimentation trap on the outside of the berm sized to sediment trap standards for protecting a culvert inlet. Maintenance • Inspect catch basin filters frequently, especially after storm events. Standards Clean and replace clogged inserts. For systems with clogged stone filters: pull away the stones from the inlet and clean or replace. An alternative approach would be to use the clogged stone as fill and put fresh stone around the inlet. • Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly over the surrounding land area or stockpile and stabilize as appropriate. Approved as Ecology has approved products as able to meet the requirements of BMP Equivalent C220. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology's website at http://www.ecy.wa.goy/programs/wq/stormwater/newtech/equivalent.html Volume H— Construction Stormsrater Pollution Prevention - August 2012 4-84 Plan View Back of Sidewalk A Catch Basin 0 2x4 Wood Stud Back of Curb Concrete Block Curb Inlet o, e" • o o� .o • o I IL ill� o � AdaaaS°, ' �rfdp° 4 O O� O b Oe Oe Oe Op� O• � Oyyy � Wire Screen or A Filter Fabric Concrete Block Section A — A ri�2 Drain Gravel ( 20mm) '/" Drain Gravel (20mm) Ponding Height Concrete Block Overflow Curb Inlet \ Wire Screen or / Filter Fabric \\ Catch Basin \\� 4 Wood Stud / (100x50 Timber Stud) NOTES: 1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street segment, where water can pond and allow sediment to separate from runoff. 2. Barrier shall allow for overflow from severe storm event. 3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. Figure 4.2.9 — Block and Gravel Curb Inlet Protection Volume II— Construction Stornn'ater Pollution Prevention - August 2012 4-85 Plan View Back of Sidewalk NOTES: 1. Place curb type sediment barriers on gently sloping street segments, where water can pond and allow sediment to separate from runoff. 2. Sandbags of either burlap or woven 'geotextile' fabric, are filled with gravel, layered and packed tightly. 3. Leave a one sandbag gap in the top row to provide a spillway for overflow. 4. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. Figure 4.2.10 — Curb and Gutter Barrier Volume H— Construction Stormwater Pollution Prevention - August 2012 4-86 BMP C233: Silt Fence Punhose Use of a silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. See Figure 4.2.12 for details on silt fence construction. Conditions of Use Silt fence may be used downslope of all disturbed areas. • Silt fence shall prevent soil carried by runoff water from going beneath, through, or over the top of the silt fence, but shall allow the water to pass through the fence. • Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Convey any concentrated flows through the drainage system to a sediment pond. • Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide an adequate method of silt control for anything deeper than sheet or overland flow. Volume II — Construction Stormivater Pollution Prevention - August 2012 4-88 Joints in filter fabric shall be spliced at posts. Use staples, wire rings or 2"x2" by 14 Ga. wire or equivalent to attach fabric to posts equivalent, if standard I strength fabric used � Filter fabric — 6' max Minimum 4"x4" trench �� i _E ' I N 1 Backfill trench with native soil Post spacing may be increased or 3/4"-1.5" washed gravel to 8' if wire backing is used Design and Installation Specifications 2"x2" wood posts, steel fence posts, or equivalent Figure 4.2.12 — Silt Fence • Use in combination with sediment basins or other BMPs. Maximum slope steepness (normal (perpendicular) to fence line) 1H:1V. • Maximum sheet or overland flow path length to the fence of 100 feet. • Do not allow flows greater than 0.5 cfs. • The geotextile used shall meet the following standards. All geotextile properties listed below are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in Table 4.2.3): Table 4.2.3 Geotextile Standards Polymeric Mesh AOS 0.60 mm maximum for slit film woven (#30 sieve). 0.30 (ASTM D4751) mm maximum for all other geotextile types (#50 sieve). 0.15 ram minimum for all fabric types (#100 sieve). Water Permittivity 0.02 sec-1 minimum (ASTM D4491) Grab Tensile Strength 180 tbs. Minimum for extra strength fabric. (ASTM D4632) 100 lbs minimum for standard strength fabric. Grab Tensile Strength 30% maximum (ASTM D4632) Ultraviolet Resistance 70% minimum (ASTM D4355) Support standard strength fabrics with wire mesh, chicken wire, 2-inch x 2-inch wire, safety fence, or jute mesh to increase the strength of the Volume H— Construction Stormwater Pollution Prevention - August 2012 4-89 fabric. Silt fence materials are available that have synthetic mesh backing attached. • Filter fabric material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum of six months of expected usable construction life at a temperature range of 0°F. to 120°F. • One -hundred percent biodegradable silt fence is available that is strong, long lasting, and can be left in place after the project is completed, if permitted by local regulations. • Refer to Figure 4.2.12 for standard silt fence details. Include the following standard Notes for silt fence on construction plans and specifications: 1. The contractor shall install and maintain temporary silt fences at the locations shown in the Plans. 2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those activities. 3. The silt fence shall have a 2-feet min. and a 2'/2-feet max. height above the original ground surface. 4. The filter fabric shall be sewn together at the point of manufacture to form filter fabric lengths as required. Locate all sewn seams at support posts. Alternatively, two sections of silt fence can be overlapped, provided the Contractor can demonstrate, to the satisfaction of the Engineer, that the overlap is long enough and that the adjacent fence sections are close enough together to prevent silt laden water from escaping through the fence at the overlap. 5. Attach the filter fabric on the up -slope side of the posts and secure with staples, wire, or in accordance with the manufacturer's recommendations. Attach the filter fabric to the posts in a manner that reduces the potential for tearing. 6. Support the filter fabric with wire or plastic mesh, dependent on the properties of the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh securely to the up -slope side of the posts with the filter fabric up -slope of the mesh. 7. Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2-inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric mesh shall be equivalent to or greater than 180 lbs. grab tensile strength. The polymeric mesh must be as resistant to the same level of ultraviolet radiation as the filter fabric it supports. 8. Bury the bottom of the filter fabric 4-inches min. below the ground surface. Backfill and tamp soil in place over the buried portion of the filter fabric, so that no flow can pass beneath the fence and Volume H— Construction Stormseater Pollution Prevention -August 2012 4-90 scouring cannot occur. When wire or polymeric back-up support mesh is used, the wire or polymeric mesh shall extend into the ground 3-inches min. 9. Drive or place the fence posts into the ground 18-inches min. A 12—inch min. depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be reached. Increase fence post min. depths by 6 inches if the fence is located on slopes of 3H:1V or steeper and the slope is perpendicular to the fence. If required post depths cannot be obtained, the posts shall be adequately secured by bracing or guying to prevent overturning of the fence due to sediment loading. 10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a maximum of 6-feet. Posts shall consist of either: • Wood with dimensions of 2-inches by 2-inches wide min. and a Meet min. length. Wood posts shall be free of defects such as knots, splits, or gouges. • No. 6 steel rebar or larger. • ASTM A 120 steel pipe with a minimum diameter of 1-inch. • U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft. • Other steel posts having equivalent strength and bending resistance to the post sizes listed above. 11. Locate silt fences on contour as much as possible, except at the ends of the fence, where the fence shall be turned uphill such that the silt fence captures the runoff water and prevents water from flowing around the end of the fence. 12. If the fence must cross contours, with the exception of the ends of the fence, place gravel check dams perpendicular to the back of the fence to minimize concentrated flow and erosion. The slope of the fence line where contours must be crossed shall not be steeper than 3H:1V. • Gravel check dams shall be approximately 1-foot deep at the back of the fence. Gravel check dams shall be continued perpendicular to the fence at the same elevation until the top of the check dam intercepts the ground surface behind the fence. • Gravel check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. Gravel check dams shall be located every 10 feet along the fence where the fence must cross contours. • Refer to Figure 4.2.13 for slicing method details. Silt fence installation using the slicing method specifications: Volume H— Construction Stormwater Pollution Prevention - August 2012 4-91 1. The base of both end posts must be at least 2- to 4-inches above the top of the filter fabric on the middle posts for ditch checks to drain properly. Use a hand level or string level, if necessary, to mark base points before installation. 2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7- feet apart in standard applications. 3. Install posts 24-inches deep on the downstream side of the silt fence, and as close as possible to the filter fabric, enabling posts to support the filter fabric from upstream water pressure. 4. Install posts with the nipples facing away from the filter fabric. 5. Attach the filter fabric to each post with three ties, all spaced within the top 8-inches of the filter fabric. Attach each tie diagonally 45 degrees through the filter fabric, with each puncture at least 1-inch vertically apart. Each tie should be positioned to hang on a post nipple when tightening to prevent sagging. 6. Wrap approximately 6-inches of fabric around the end posts and secure with 3 ties. 7. No more than 24-inches of a 36-inch filter fabric is allowed above ground level. Compact the soil immediately next to the filter fabric with the front wheel of the tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the upstream side first and then each side twice for a total of four trips. Check and correct the silt fence installation for any deviation before compaction. Use a flat -bladed shovel to tuck fabric deeper into the ground if necessary. Volume H— Construction Stormwater Pollution Prevention - August 2012 4-92 Ponding height POST SPACING: max. 24- 7' maa. on open runs 4' max. on pooling area• Attach bens to ep.n. ra aa. or po,t FLOW ---- Dnre — e.ch .lae of POST DEPTH: slit tense 2 to 4tlm.. As much below ground with d.Ac..""" a. fabric above ground ae P...I. or greater l t00%compectl 100%eerwpactlen No more than 24' of a 36e fabric is allowed above ground. AIIACHMENT DETAILS: • Gather fabric at posts, If needed. e UUN- three ties per post, as whhln top 8' of fabric. • Position each to diaganalty, puncturing holes vonically a rdNrnixn of 1' apan. • Hang each tie on a post nipple and tighten —ety Use cable ties (SObs) m soft wre. Roll of silt fence Post installed after Fabric compaction r 0 gm d Sit Fence � � "�' d✓/ „rF�!�h(f� '�� 200-300frIT Hctiz ntal chisel print Slicing blade (76 mm width) (18 mm width) Completed Installation Vibratory plow is not acceptable because of horizontal compaction Figure 4.2.13 — Silt Fence Installation by Slicing Method Maintenance • Repair any damage immediately. Standards • Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment pond. Check the uphill side of the fence for signs of the fence clogging and acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence or remove the trapped sediment. Volume II — Construction Stornrmater Pollution Prevention -August 2012 4-93 • Remove sediment deposits when the deposit reaches approximately one-third the height of the silt fence, or install a second silt fence. • Replace filter fabric that has deteriorated due to ultraviolet breakdown. Section 6 Special Reports and Studies Cobalt Geosciences February 14, 2022 Geotechnical Evaluation (See Appendix) Section 7 Other Permits No other permits related to stormwater management beyond those issued by the local governing authority are anticipated for this project. Section 8 Operation and Maintenance Manual The facility -specific maintenance standards contained in this section are intended to be conditions for determining if maintenance actions are required as identified through inspection. They are not intended to be measures of the facility's required condition at all times between inspections. In other words, exceedence of these conditions at any time between inspections and/or maintenance does not automatically constitute a violation of these standards. However, based upon inspection observations, the inspection and maintenance schedules shall be adjusted to minimize the length of time that a facility is in a condition that requires a maintenance action. Table V-4.5.2(5) Maintenance Standards - Catch Basins Results Expected Maintenance Conditions When Maintenance is Component Defect Needed When Main- tenance is performed No Trash or debris loc- Trash or debris which is located imme- ated imme- diately in front of the catch basin opening or diately in is blocking inletting capacity of the basin by front of catch more than 10%. basin or on Trash or debris (in the basin) that exceeds grate open- 60 percent of the sump depth as measured ing. from the bottom of basin to invert of the low- No trash or est pipe into or out of the basin, but in no debris in the Trash & case less than a minimum of six inches catch basin. Debris clearance from the debris surface to the invert of the lowest pipe. Inlet and out- let pipes free Trash or debris in any inlet or outlet pipe of trash or blocking more than 1/3 of its height. debris. General Dead animals or vegetation that could gen- No dead erate odors that could cause complaints or animals or dangerous gases (e.g., methane). vegetation present within the catch basin. Sediment (in the basin) that exceeds 60 per- cent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case No sediment Sediment less than a minimum of 6 inches clearance in the catch from the sediment surface to the invert of the basin lowest pipe. Structure Top slab has holes larger than 2 square Top slab is Damage to inches or cracks wider than 1/4 inch. (Intent free of holes Frame and/or is to make sure no material is running into and cracks. Top Slab basin). Frame is sit- 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 838 Table V-4.5.2(5) Maintenance Standards - Catch Basins (continued) Results Expected Maintenance Conditions When Maintenance is Component Defect Needed When Main- tenance is performed Frame not sitting flush on top slab, i.e., sep- ting flush on aration of more than 3/4 inch of the frame the riser rings or top slab from the top slab. Frame not securely and firmly attached attached. Basin Maintenance person judges that structure is replaced or unsound. repaired to Fractures or design stand- rac in Grout fillet has separated or cracked wider ards. Basin Walls/ than 1/2 inch and longer than 1 foot at the g Bottom joint of any inlet/outlet pipe or any evidence Pipe is of soil particles entering catch basin through regrouted cracks. and secure at basin wall. Basin Settlement/ If failure of basin has created a safety, func- replaced or repaired to Misalignment tion, or design problem. design stand- ards. No veget- ation block - Vegetation growing across and blocking more than 10% of the basin opening. ing opening to basin. Vegetation Vegetation growing in inlet/outlet pipe joints No that is more than six inches tall and less veget- than six inches apart. ation or root growth present. Contamination "Detention No pollution and Pollution See Ponds" (No. 1). present. Cover Not in Cover is missing or only partially in place. Catch basin Catch Basin Place Any open catch basin requires main- cover is tenance. closed Cover Locking Mech- Mechanism cannot be opened by one main- Mechanism anism Not itenance person with proper tools. Bolts into opens with 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 839 Table V-4.5.2(5) Maintenance Standards - Catch Basins (continued) Results Expected Maintenance Conditions When Maintenance is Component Defect Needed When Main- tenance is performed Working frame have less than 1/2 inch of thread. proper tools. One maintenance person cannot remove lid Cover can be Cover Difficult after applying normal lifting pressure. removed by to Remove s (Intent is keep cover from sealing off acces one main- tenance per - to maintenance.) son. Ladder meets design stand Ladder Rungs Ladder is unsafe due to missing rungs, not ards and Ladder securely attached to basin wall, mis- allows main - Unsafe alignment, rust, cracks, or sharp edges. tenance per- son safe access. Grate open - Grate opening Grate with opening wider than 7/8 inch. ing meets Unsafe design stand- ards. Metal Grates Grate free of (If Applic- Trash and Trash and debris that is blocking more than trash and able) Debris 20% of grate surface inletting capacity. debris. Grate is in Damaged or Grate missing or broken member(s) of the place and Missing. grate. meets design standards. Table V-4.5.2(22) Maintenance Standards - Permeable Pavement Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) Surface/Wearing Course Permeable 1A, S Runoff from Clean deposited soil or 2014 Stormwater Management Manual for Western Washington Volume V - Chapter - Page 887 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) other materials from per- meable pavement or other adjacent surfacing . Check if surface elevation adjacent per- of planted area is too high, or slopes towards pave - vious areas ment, and can be regraded Pavements, deposits soil, (prior to regrading, protect all mulch or sed- permeable pavement by invent on pav- covering with temporary ing plastic and secure covering in place) . Mulch and/or plant all exposed soils that may erode to pavement surface Clean surface debris from pave- ment surface using one or a com- bination of the following methods: Remove sediment, debris, trash, vegetation, and other debris deposited onto pave Porous ment (rakes and leaf asphalt or A or B None (routine blowers can be used for pervious maintenance) removing leaves) concrete . Vacuum/sweep permeable paving installation using: Walk -behind vacuum (sidewalks) High efficiency regen- erative air or vacuum sweeper (roadways, parking lots) 2014 Stormwater Management Manual for Western Washington Volume V - Chapter - Page 888 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) ShopVac or brush brooms (small areas) • Hand held pressure washer or power washer with rotat- ing brushes Follow equip- ment manufacturer guidelines for when equip- ment is most effective for cleaning permeable pave- ment. Dry weather is more effective for some equip- ment. • Review the overall per- formance of the facility (note that smal I clogged areas may not reduce over- all performance of facility) . Test the surface infiltration Surface is rate using ASTM C1701 as clogged: Pond a corrective maintenance ing on surface indicator. Perform one test or water flows per installation, up to 2,500 A b off the per- square feet. Perform an meable pave - additional test for each addi ment surface tional 2,500 square feet up during a rain to 15,000 square feet total. event (does Above 15,000 square feet, not infiltrate) add one test for every 10,000 square feet. . If the results indicate an infiltration rate of 10 inches per hour or less, then per- form corrective main- 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 889 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) tenance to restore per- meability. To clean clogged pavement surfaces, use one or combination of the following methods: Combined pressure wash and vacuum system calibrated to not dislodge wearing course aggregate. Hand held pressure washer or power washer with rotating brushes Pure vacuum sweep- ers Note: If the annual/biannual routine maintenance stand- ard to clean the pavement surface is conducted using equipment from the list above, corrective main- tenance may not be needed. . Assess the overall per- formance of the pavement system during a rain event. Sediment If water runs off the pave - A present at the ment and/or there is pond - surface of the ing then see above. pavement * Determine source of sed- iment loading and evaluate whether or not the source 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 890 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) can be reduced/eliminated. If the source cannot be addressed, consider increasing frequency of routine cleaning (e.g., twice per year instead of once per year). . Sidewalks: Use a stiff broom to remove moss in the summer when it is dry Moss growth . Parking lots and roadways: inhibits infilt- Pressure wash, vacuum Summer ration or sweep, or use a com- poses slip bination of the two for clean safety hazard ing moss from pavement surface. May require stiff broom or power brush in areas of heavy moss. • Fill potholes or small cracks with patching mixes . Large cracks and set- tlement may require cutting and replacing the pave - Major cracks ment section. Replace in - or trip hazards kind where feasible. Repla- A and concrete cing porous asphalt with spalling and conventional asphalt is raveling acceptable if it is a small percentage of the total facil- ity area and does not impact the overall facility function. . Take appropriate pre- 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 891 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) cautions during pavement repair and replacement efforts to prevent clogging of adjacent porous mater- ials Clean pavement surface using one or a combination of the fol- lowing methods: . Remove sediment, debris, trash, vegetation, and other debris deposited onto pave- ment (rakes and leaf blowers can be used for removing leaves) . Vacuum/sweep permeable paving installation using: Walk -behind vacuum Interlocking (sidewalks) concrete A or B None (routine maintenance) efficiency regen- High e paver blocks erative air or vacuum and aggreg- sweeper (roadways, ate pavers parking lots) ShopVac or brush brooms (small areas) Note: Vacuum settings may have to be adjusted to pre- vent excess uptake of aggregate from paver open- ings orjoints. Vacuum sur- face openings in dry weather to remove dry, encrusted sediment. Ab Surface is . Review the overall per- 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 892 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) clogged: Pond ing on surface or water flows off the per- meable pave- ment surface during a rain event (does not infiltrate) formance of the facility (note that small clogged areas may not reduce over- all performance of facility) . Test the surface infiltration rate using ASTM C1701 as a corrective maintenance indicator. Perform one test per installation, up to 2,500 square feet. Perform an additional test for each addi tional 2,500 square feet up to 15,000 square feet total. Above 15,000 square feet, add one test for every 10,000 square feet. . If the results indicate an infiltration rate of 10 inches per hour or less, then per- form corrective main- tenance to restore permeability. . Clogging is usually an issue in the upper 2 to 3 centimeters of aggregate. Remove the upper layer of encrusted sediment, and fines, and/or vegetation from openings and joints between the pavers by mechanical means and/or suction equipment (e.g., pure vacuum sweeper). 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 893 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) . Assess the over- all per- formance of the /1 Sediment present at the surface of the pavement pave- ment sys- tem during a rain event. If water runs off the pave- ment and/or there is ponding, then see above. Determi- ne source of sed- iment loading and eval- uate whether or not the source can be 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 894 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) reduced/- elim- inated. If the Summer Moss growth inhibits infilt- ration or poses slip safety hazard source cannot be address- ed, con- sider increas- ing fre- quency of routi ne cleaning (e-g-, twice per year instead of once per year). . Side- walks: Use a stiff broom to remove moss in the sum- mer when it is dry 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 895 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) Parking lots and road- ways: Vacuum sweep or stiff broom/ - power brush for cleaning moss fro m pave- ment sur- face Remove indi- vidual dam- aged paver blocks by Paver block hand and A missing or replace or damaged repair per man- ufacturer's recom- mendations Refill per man - lufacturer's Loss of aggregate recom- material mendations between for interlocking paver blocks paver sec- tions Settlement of IMay require 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 896 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) surface resetting . Remove sediment, debris, trash, vegetation, and other debris deposited onto pave - (rakes and leaf A or B None None (routine blowers can be used for maintenance) removing leaves) . Follow equipment man- ufacturer guidelines for cleaning surface. Aggregate is clogged: Pond ing on surface • Use vacuum truck to or water flows remove and replace top off the per- course aggregate A b meable pave- . Replace aggregate in pav- Open-celled ment surface ing grid per manufacturer's paving grid during a rain recommendations with gravel event (does not infiltrate) . Remove pins, pry up grid segments, and replace gravel Paving grid • Replace grid segments A where three or more adja- missing or cent rings are broken or damaged damaged Follow manufacturer guidelines for repairing sur- face. A Settlement of May require resetting surface A Loss of Replenish aggregate material by 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 897 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) spreading gravel with a rake (gravel level should be main - aggregate tained at the same level as the material in plastic rings or no more than 1/4 paving grid inch above the top of rings). See manufacturer's recom- mendations. . Manually remove weeds . Presence of weeds may Weeds indicate that too many fines A present are present (refer to Actions Needed under "Aggregate is clogged" to address this issue) • Remove sediment, debris, trash, vegetation, and other debris deposited onto pave - (rakes and leaf A or B None None (routine blowers can be used for maintenance) removing leaves) • Follow equipment man- ufacturer guidelines for Open -celled cleaning surface. paving grid Aggregate is with grass clogged: Pond ing on surface or water flows A b off the per- Rehabilitate per manufacturer's meable pave- recommendations. ment surface during a rain event (does not infiltrate) 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 898 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) • Remove pins, pry up grid segments, and replace grass Paving grid • Replace grid segments A where three or more adja- missing or cent rings are broken or damaged damaged • Follow manufacturer guidelines for repairing sur- face. A Settlement of May require resetting surface • Restore growing medium, reseed or plant, aerate, and/or amend vegetated Poor grass area as needed A coverage in paving grid •Traffic loading may be inhibiting grass growth; reconsider traffic loading if feasible As needed None (routine Use a mulch mower to mow maintenance) grass • Sprinkle a thin layer of com post on top of grass surface A None (routine (1/2" top dressing) and maintenance) sweep it in • Do not use fertilizer • Manually remove weeds A Weeds • Mow, torch, or inoculate present and replace with preferred vegetation Inlets/Outlets/Pipes Inlet/outlet JA 1Pipe is dam- Repair/replace 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 899 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) aged pipe A Pipe is Remove roots or debris clogged Clean orifice Plant roots, . Jet clean or rotary cut at least bian- sediment or debris/roots from under- nually (may debris redu- drain(s) Underdrain Clean pipe need more cing capacity of underdrain If underdrains are equipped pipe as needed frequent (may cause with a flow restrictor (e.g., cleaning dur- prolonged orifice) to attenuate flows, ing wet sea- drawdown the orifice must be cleaned son) period) regularly Clean orifice . Jet clean or rotary cut at least bian- debris/roots from under - Plant roots, drain(s) Raised sub- Clean pipe need more sediment or If underdrains are equipped surface over as needed frequent debris redu- with a flow restrictor (e.g., flow pipe cleaning dur- cing capacity orifice) to attenuate flows, ing wet sea- of underdrain the orifice must be cleaned son) regularly Sediment, vegetation, or • Clear the blockage Outlet struc- A S debris redu- . Identify the source of the ture cing capacity blockage and take actions of outlet struc- to prevent future blockages to re Native soil is exposed or other signs of Repair erosion and stabilize sur- Overflow B erosion dam- face age are present at dis- charge point 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 900 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) Aggregate Storage Reservoir Water remains in the storage If immediate cause of extended aggregate Ponding is not identified, sched- Observation A' S longer than ule investigation of subsurface port anticipated by materials or other potential design after causes of system failure. the end of a storm Vegetation . Sweep leaf litter and sed- Vegetation invent to prevent surface related fallout clogging and ponding As needed clogs or will potentially • Prevent large root systems clog voids from damaging subsurface Adjacent structural components Vegetation Edging and trimming of planted large shrubs or trees growing bey- areas to control groundcovers Once in May and facility and shrubs from overreaching and Once in edge onto the sidewalks, paths and street September sidewalks, edge improves appearance and paths. and reduces clogging of permeable street edge pavements by leaf litter, mulch and soil. In fall (Octo- ber to Decem Use leaf blower or vacuum to Leaves, ber) after leaf Accumulation blow or remove leaves, ever - needles, drop (1-3 of organic green needles, and debris (i.e., and organic times, debris and flowers, blossoms) off of and debris depending leaf litter away from permeable pavement on canopy cover) Note that the inspection and routine maintenance frequencies listed above are recom- 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 901 Table V-4.5.2(22) Maintenance Standards - Permeable Pavement (continued) Recommended Fre- Condition quency a when Main - Component tenance is Action Needed (Procedures) Inspection Routine Needed Maintenance (Standards) mended by Ecology. They do not supersede or replace the municipal stormwater permit requirements for inspection frequency required of municipal stormwater permittees for "stormwater treatment and flow control BMPs/facilities". a Frequency: A= Annually; B= Biannually (twice per year); S = Perform inspections after) major storm events (24-hour storm event with a 10-year or greater recurrence interval). b Inspection should occur during storm event. Appendix S411 BMPs for Landscaping and Lawn / Vegetation Management Description of Pollutant Sources: Landscaping can include grading, soil transfer, vegetation planting, and vegetation removal. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; and residential lawn/plant care. Proper man- agement of vegetation can minimize excess nutrients and pesticides. 2019 Stormwater Management Manual for Western Washington Volume /V - Chapter 4 - Page 523 Pollutant Control Approach: Maintain appropriate vegetation to control erosion and the dis- charge of stormwater pollutants. Prevent debris contamination of stormwater. Where practicable, grow plant species appropriate for the site, or adjust the soil properties of the site to grow desired plant species. Applicable BMPs: . Install engineered soil/landscape systems to improve the infiltration and regulation of storm - water in landscaped areas. . Select the right plants for the planting location based on proposed use, available main- tenance,soil conditions, sun exposure, water availability, height, sight factors, and space avail- able. • Ensure that plants selected for planting are not on the noxious weed list. For example, but- terfly bush often gets planted as an ornamental but is actually on the noxious weed list. The Washington State Noxious Weed List can be found at the following webpage: https://www.nwcb.wa.gov/printable-noxious-weed-list • Do not dispose of collected vegetation into waterways or storm sewer systems. . Do not blow vegetation or other debris into the drainage system. . Dispose of collected vegetation such as grass clippings, leaves, sticks by composting or recyc- ling. • Remove, bag, and dispose of class A & B noxious weeds in the garbage immediately. . Do not compost noxious weeds as it may lead to spreading through seed or fragment if the composting process is not hot enough. • Use manual and/or mechanical methods of vegetation removal (pincer -type weeding tools, flame weeders, or hot water weeders as appropriate) rather than applying herbicides, where practical. • Use at least an eight -inch "topsoil' layer with at least 8 percent organic matter to provide a suf- ficient vegetation -growing medium. Organic matter is the least water-soluble form of nutrients that can be added to the soil. Composted organic matter generally releases only between 2 and 10 percent of its total nitrogen annually, and this release corresponds closely to the plant growth cycle. Return natural plant debris and mulch to the soil, to continue recycling nutrients indef- initely. . Select the appropriate turfgrass mixture for the climate and soil type. Certain tall fescues and rye grasses resist insect attack because the symbiotic endo- phytic fungi found naturally in their tissues repel or kill common leaf and stem -eating lawn insects. 2019 Stormwater Management Manual for Western Washington Volume IV - Chapter 4 - Page 524 ■ The fungus causes no known adverse effects to the host plant or to humans. ■ Tall fescues and rye grasses do not repel root -feeding lawn pests such as Crane Fly larvae. ■ Tall fescues and rye grasses are toxic to ruminants such as cattle and sheep • Endophytic grasses are commercially available; use them in areas such as parks or golf courses where grazing does not occur. • Local agricultural or gardening resources such as Washington State University Exten- sion office can offer advice on which types of grass are best suited to the area and soil type. • Use the following seeding and planting BMPs, or equivalent BMPs, to obtain information on grass mixtures, temporary and permanent seeding procedures, maintenance of a recently planted area, and fertilizer application rates: BMP C120: Temporary and Permanent Seeding, BMP C121: Mulching, BMP C123: Plastic Covering, and BMP C124: Sodding. . Adjusting the soil properties of the subject site can assist in selection of desired plant species. Consult a soil restoration specialist for site -specific conditions. Recommended Additional BMPs: . Conduct mulch -mowing whenever practicable. • Use native plants in landscaping. Native plants do not require extensive fertilizer or pesticide applications. Native plants may also require less watering. . Use mulch or other erosion control measures on soils exposed for more than one week during the dry season (May 1 to September 30) or two days during the rainy season (October 1 to April 30). . Till a topsoil mix or composted organic material into the soil to create a well -mixed transition layer that encourages deeper root systems and drought -resistant plants. . Apply an annual topdressing application of 3/8" compost. Amending existing landscapes and turf systems by increasing the percent organic matter and depth of topsoil can: • Substantially improve the permeability of the soil. • Increase the disease and drought resistance of the vegetation. • Reduces the demand for fertilizers and pesticides. . Disinfect gardening tools after pruning diseased plants to prevent the spread of disease. . Prune trees and shrubs in a manner appropriate for each species. . If specific plants have a high mortality rate, assess the cause and replace with another more appropriate species. . When working around and below mature trees, follow the most current American National Standards Institute (ANSI) ANSI A300 standards (see 2019 Stormwater Management Manual for Western Washington Volume IV - Chapter 4 - Page 525 http://www.tcia.org/TCIA/BUSINESS/ANSI A300 Standards /TCIA/BUSINESS/A300 Standards/A300_Standards. aspx?hkey=202ff566-4364-4686-b7c1-2a365af59669) and International Society of Arboriculture BMPs to the extent practicable (e.g., take care to min- imize any damage to tree roots and avoid compaction of soil). . Monitor tree support systems (stakes, guys, etc.). • Repair and adjust as needed to provide support and prevent tree damage. • Remove tree supports after one growing season or maximum of 1 year. • Backfill stake holes after removal. . When continued, regular pruning (more than one time during the growing season) is required to maintain visual sight lines for safety or clearance along a walk or drive, consider relocating the plant to a more appropriate location. . Make reasonable attempts to remove and dispose of class C noxious weeds. • Re -seed bare turf areas until the vegetation fully covers the ground surface. . Watch for and respond to new occurrences of especially aggressive weeds such as H im- alayan blackberry, Japanese knotweed, morning glory, English ivy, and reed canary grass to avoid invasions. . Plant and protect trees per BMP T5.16: Tree Retention and Tree Planting. . Aerate lawns regularly in areas of heavy use where the soil tends to become compacted. Con- duct aeration while the grasses in the lawn are growing most vigorously. Remove layers of thatch greater than %-inch deep. . Set the mowing height at the highest acceptable level and mow at times and intervals designed to minimize stress on the turf. Generally mowing only 1/3 of the grass blade height will prevent stressing the turf. • Mowing is a stress -creating activity for turfgrass. • Grass decreases its productivity when mowed too short and there is less growth of roots and rhizomes. The turf becomes less tolerant of environmental stresses, more dis- ease prone and more reliant on outside means such as pesticides, fertilizers, and irrig- ation to remain healthy. Additional BMP Information: . King County's Best Management Practices for Golf Course Development and Operation (King County, 1993) has additional BMPs for Turfgrass Maintenance and Operation. . King County, Seattle Public Utilities, and the Saving Water Partnership have created the fol- lowing natural lawn and garden care resources that include guidance on building healthy soil with compost and mulch, selecting appropriate plants, watering, using alternatives to pesti- cides, and implementing natural lawn care techniques. 2019 Stormwater Management Manual for Western Washington Volume IV - Chapter 4 - Page 526 ■ Natural Yard Care -Five steps to make yourpiece of the planet a healthier place to live (King County and SPU, 2008) ■ The Natural Lawn & Garden Series: Smart Watering (Saving Water Partnership, 2006) ■ Natural Lawn Care for Western Washington (Saving Water Partnership, 2007) ■ The Natural Lawn & Garden Series: Growing Healthy Soil; Choosing the Right Plants; and Natural Pest, Weed and Disease Control (Saving Water Partnership, 2012) . The International Society of Arboriculture (ISA) is a group that promotes the professional prac- tice of arboriculture and fosters a greater worldwide awareness of the benefits of trees through research, technology, and education. ISA standards used for managing trees, shrubs, and other woody plants are the American National Standards Institute (ANSI) A300 standards. The ANSI A300 standards are voluntary industry consensus standards developed by the Tree Care Industry Association (TCIA) and written by the Accredited Standards Com- mittee (ASC). The ANSI standards can be found on the ISA website: www.isa-arbor.- com/education/publications/index.aspx Washington State University's Gardening in Washington State website at http://garden- ing.wsu.edu contains Washington State specific information about vegetation management based on the type of landscape. . Seethe Pacific Northwest Plant Disease Management Handbook (Pscheidt and Ocamb, 2016) for information on disease recognition and for additional resources. COBALT G E O S C I E N C E S February 14, 2022 Brian Goodnight earthtobrian(&vahoo.com RE: Geotechnical Evaluation Proposed Residence 741 Aloha Street Edmonds, Washington Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, Washington 98028 In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to discuss the results of our geotechnical evaluation at the referenced site. The purpose of our evaluation was to provide recommendations for foundation design, grading, and earthwork. Site Description The site is located at 741 Aloha Street in Edmonds, Washington. The site consists of one irregularly shaped parcel (No. 00731400000701) with a total area of about 0.2 acres. The site is undeveloped and vegetated with grasses, other understory bushes/shrubs, blackberry vines, ivy, ferns, and variable diameter evergreen and deciduous trees. The site slopes gently downward from southeast to northwest at magnitudes of 5 to 10 percent and relief of about 7 feet. There is evidence of historic grading at the site, including a low area filled with surface water/precipitation. Some of these areas have steeper magnitudes but very limited relief. The site is bordered to the north by a driveway and residence, to the west by a driveway and residence, to the east by a residence, and to the south by Aloha Street. The proposed development includes a new residence and driveway. Stormwater will include infiltration or other systems depending on feasibility. Site grading may include cuts and fills of 3 feet or less and foundation loads are expected to be light. We should be provided with the final plans to verify that our recommendations remain valid and do not require updating. Area Geology The Geologic Map of the Edmonds East Quadrangle, indicates that the site is underlain by Transitional Beds. Transitional Beds include dense to hard silts, silty -sands, and sandy silts that underlie Vashon Advance Outwash. These materials are usually impermeable and are typically dense to very dense below a weathered zone. Soil & Groundwater Conditions As part of our evaluation, we excavated a test pit within the property, where accessible. The exploration encountered approximately 6 inches of grass and topsoil underlain by approximately 1.5 feet of loose to medium dense, silty -fine to medium grained sand with gravel www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page 2 of 11 Geotechnical Evaluation trace cobbles (Weathered Transitional Beds). These materials were underlain by dense to very dense, silty -fine to fine grained sand trace gravel (Transitional Beds), which continued to the termination depths of the explorations. Groundwater was not encountered during our exploration work; however, the soils were mottled from 6 inches to 1.5 feet below grade. Perched groundwater may develop on the dense till during the winter months. We note ponded runoff in a low area within the property. Water table elevations often fluctuate over time. The groundwater level will depend on a variety of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and soil permeability. Water levels at the time of the field investigation may be different from those encountered during the construction phase of the project. Erosion Hazard The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that the site is underlain by Alderwood-Urban land complex (2 to 8 percent slopes). These soils would have a slight to moderate erosion potential in a disturbed state depending on the slope magnitude. It is our opinion that soil erosion potential at this project site can be reduced through landscaping and surface water runoff control. Typically, erosion of exposed soils will be most noticeable during periods of rainfall and may be controlled by the use of normal temporary erosion control measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The typical wet weather season, with regard to site grading, is from October 31st to April ist. Erosion control measures should be in place before the onset of wet weather. Seismic Hazard The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the International Building Code (IBC). A Site Class D applies to an overall profile consisting of stiff/medium dense soils within the upper too feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for Ss, S,, FQ, and F,,. The USGS website includes the most updated published data on seismic conditions. The following tables provide seismic parameters from the USGS web site with referenced parameters from ASCE 7-10 and 7-16. Seismic Design Parameters (ASCE 7-10) Site Spectral Spectral Site Design Spectral Design Class Acceleration Acceleration Coefficients Response Parameters PGA at 0.2 sec. (g) at 1.o sec. (g) Fa Fv SDS SDl D 1.274 0.499 1.0 1.501 o.849 0.5 0.517 www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page 3 of 11 Geotechnical Evaluation Seismic Design Parameters (ASCE 7-16) Site Spectral Spectral Site Design Spectral Design Class Acceleration Acceleration Coefficients Response Parameters PGA at 0.2 sec. (g) at 1.o sec. (g) Fa F, SDs SD1 D 1.289 0.454 1.0 Null o.86 Null 0.549 Additional seismic considerations include liquefaction potential and amplification of ground motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a high groundwater table. The site has a low likelihood of liquefaction. For items listed as "Null" see Section 11.4.8 of the ASCE. Conclusions and Recommendations General The site is underlain by areas of fill along with weathered and unweathered Transitional Beds which becomes denser with depth. The proposed residential structure may be supported on a shallow foundation system bearing on medium dense or firmer native soils or on structural fill placed on the native soils. Local overexcavation or recompaction of loose weathered native soils may be necessary depending on the proposed elevations and locations of the new footings. Any fill must be removed below new foundation elements. Infiltration is not feasible or recommended due to the presence of the very dense fine grained soils which act as an aquitard. These soils were mottled and there is a chance that groundwater may become perched on the denser soils at shallow depths during the winter months. Additionally, there were areas of ponded surface water in a local excavation on site. We recommend detention with overflow to City infrastructure. We can provide additional recommendations once a civil plan has been prepared. Site Preparation Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich soil and fill. Based on observations from the site investigation program, it is anticipated that the stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below foundation systems and in any areas underlain by undocumented fill. The native soils consist of silty -sand with gravel. Most of the native soils may be used as structural fill provided they achieve compaction requirements and are within 3 percent of the optimum moisture. Some of these soils may only be suitable for use as fill during the summer months, as they will be above the optimum moisture levels in their current state. These soils are variably moisture sensitive and may degrade during periods of wet weather and under equipment traffic. www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page 4 of 11 Geotechnical Evaluation Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of 3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve). Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the ASTM D 1557 test method. Temporary Excavations Based on our understanding of the project, we anticipate that the grading could include local cuts on the order of approximately 4 feet or less for foundation and most of the utility placement. Temporary excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose native soils and fill, 1H:1V in medium dense native soils and 3/4H:1V in dense to very dense native soils. If an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than 2H:1V, where room permits. Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a qualified person during construction activities and the inspections should be documented in daily reports. The contractor is responsible for maintaining the stability of the temporary cut slopes and reducing slope erosion during construction. Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather, and the slopes should be closely monitored until the permanent retaining systems or slope configurations are complete. Materials should not be stored or equipment operated within 10 feet of the top of any temporary cut slope. Soil conditions may not be completely known from the geotechnical investigation. In the case of temporary cuts, the existing soil conditions may not be completely revealed until the excavation work exposes the soil. Typically, as excavation work progresses the maximum inclination of temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental recommendations can be made. Soil and groundwater conditions can be highly variable. Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that the project can proceed and required deadlines can be met. If any variations or undesirable conditions are encountered during construction, we should be notified so that supplemental recommendations can be made. If room constraints or groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed by the WAC, temporary shoring systems may be required. The contractor should be responsible for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences and the project structural engineer review temporary shoring designs prior to installation, to verify the suitability of the proposed systems. Foundation Design The proposed structure may be supported on a shallow spread footing foundation system bearing on undisturbed medium dense or firmer native soils or on properly compacted structural fill placed on the suitable native soils. Any undocumented fill and/or loose native soils should be removed and replaced with structural fill below foundation elements. Structural fill below footings should consist of clean angular rock 5/8 to 4 inches in size. We should verify soil conditions during foundation excavation work. www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page 5 of 11 Geotechnical Evaluation For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively, for continuous wall and isolated column footings supporting the proposed structure. Provided that the footings are supported as recommended above, a net allowable bearing pressure of 3,000 pounds per square foot (psf) may be used for design. A 1/3 increase in the above value may be used for short duration loads, such as those imposed by wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing excavations should be inspected to verify that the foundations will bear on suitable material. Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch. Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most settlement is expected to occur during construction, as the loads are applied. However, additional post -construction settlement may occur if the foundation soils are flooded or saturated. All footing excavations should be observed by a qualified geotechnical consultant. Resistance to lateral footing displacement can be determined using an allowable friction factor of 0.40 acting between the base of foundations and the supporting subgrades. Lateral resistance for footings can also be developed using an allowable equivalent fluid passive pressure of 250 pounds per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12 inches below grade in exterior areas). The frictional and passive resistance of the soil may be combined without reduction in determining the total lateral resistance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the footing excavations, should be removed prior to placing concrete. The potential for wetting or drying of the bearing materials can be reduced by pouring concrete as soon as possible after completing the footing excavation and evaluating the bearing surface by the geotechnical engineer or his representative. Concrete Retaining Walls The following table, titled Wall Design Criteria, presents the recommended soil related design parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall system is used. This has been included for new cast in place walls, if any are proposed. Wall Design Criteria "At -rest" Conditions (Lateral Earth Pressure — EFD+) 55 pcf (Equivalent Fluid Density) "Active" Conditions (Lateral Earth Pressure — EFD+) 35 pcf (Equivalent Fluid Density) Seismic Increase for "At -rest" Conditions (Lateral Earth Pressure) 21H* (Uniform Distribution) 1 in 2,500 year event Seismic Increase for "At -rest" Conditions (Lateral Earth Pressure) 14H* (Uniform Distribution) 1 in 500 year event www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page 6 of 11 Geotechnical Evaluation Seismic Increase for "Active" Conditions 7H ` (Uniform Distribution) (Lateral Earth Pressure) Passive Earth Pressure on Low Side of Wall Neglect upper 2 feet, then 275 pcf EFD+ (Allowable, includes F.S. = 1.5) Soil -Footing Coefficient of Sliding Friction (Allowable; 0.40 includes F.S. = 1.5) 'H is the height of the wall; Increase based on one in 500 year seismic event (io percent probability of being exceeded in 50 years), +EFD — Equivalent Fluid Density The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by water accumulation behind the retaining walls. Uniform horizontal lateral active and at -rest pressures on the retaining walls from vertical surcharges behind the wall may be calculated using active and at -rest lateral earth pressure coefficients of 0.3 and 0.5, respectively. A soil unit weight Of 125 pcf may be used to calculate vertical earth surcharges. To reduce the potential for the buildup of water pressure against the walls, continuous footing drains (with cleanouts) should be provided at the bases of the walls. The footing drains should consist of a minimum 4-inch diameter perforated pipe, sloped to drain, with perforations placed down and enveloped by a minimum 6 inches of pea gravel in all directions. The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should consist of free -draining granular material. All free draining backfill should contain less than 3 percent fines (passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S. Standard No. 4 Sieve with at least 30 percent of the material being retained on the U.S. Standard No. 4 Sieve. The primary purpose of the free -draining material is the reduction of hydrostatic pressure. Some potential for the moisture to contact the back face of the wall may exist, even with treatment, which may require that more extensive waterproofing be specified for walls, which require interior moisture sensitive finishes. We recommend that the backfill be compacted to at least go percent of the maximum dry density based on ASTM Test Method D1557. In place density tests should be performed to verify adequate compaction. Soil compactors place transient surcharges on the backfill. Consequently, only light hand operated equipment is recommended within 3 feet of walls so that excessive stress is not imposed on the walls. Stormwater Management Feasibility The site is underlain by relatively dense Transitional Beds. The unweathered soils were cemented and very fine grained, and act as a restrictive layer. The mottled soils were observed within the upper 18 inches of the ground surface and there was a large area of ponded surface water in a local excavation on site. Widespread infiltration is not feasible due to the dense and fine grained soil conditions at depth and likely shallow groundwater conditions during the wet season. We recommend collection of runoff from new impervious surfaces with connection to City infrastructure. Local permeable pavements and dispersion systems could be feasible depending on their location and elevation. We can provide additional recommendations upon request and once civil plans have been prepared. www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page 7 of 11 Geotechnical Evaluation We should be provided with final plans for review to determine if the intent of our recommendations has been incorporated or if additional modifications are needed. Slab -on -Grade We recommend that the upper 12 inches of the existing native soils within slab areas be re - compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture typically requires the usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers. The American Concrete Institutes ACI 36oR-o6 Design of Slabs on Grade and ACI 302.1R-04 Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. Slabs on grade may be designed using a coefficient of subgrade reaction of 210 pounds per cubic inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and compacted as outlined above. A 4- to 6-inch-thick capillary break layer should be placed over the prepared subgrade. This material should consist of pea gravel or 5/8 inch clean angular rock. A perimeter drainage system is recommended unless interior slab areas are elevated a minimum Of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4-inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perimeter drainage system should discharge by gravity flow to a suitable stormwater system. Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface water flow away from the building and preferably with a relatively impermeable surface cover immediately adjacent to the building. Erosion and Sediment Control Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment control measures should be implemented, and these measures should be in general accordance with local regulations. At a minimum, the following basic recommendations should be incorporated into the design of the erosion and sediment control features for the site: • Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance of the site soils, to take place during the dry season (generally May through September). However, provided precautions are taken using Best Management Practices (BMP's), grading activities can be completed during the wet season (generally October through April). • All site work should be completed and stabilized as quickly as possible. • Additional perimeter erosion and sediment control features may be required to reduce the possibility of sediment entering the surface water. This may include additional silt fences, silt fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration systems. www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page 8 of ii Geotechnical Evaluation • Any runoff generated by dewatering discharge should be treated through construction of a sediment trap if there is sufficient space. If space is limited other filtration methods will need to be incorporated. Utilities Utility trenches should be excavated according to accepted engineering practices following OSHA (Occupational Safety and Health Administration) standards, by a contractor experienced in such work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided. Depending upon the location and depth of some utility trenches, groundwater flow into open excavations could be experienced, especially during or shortly following periods of precipitation. In general, silty soils were encountered at shallow depths in the explorations at this site. These soils have low cohesion and density and will have a tendency to cave or slough in excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations greater than 4 feet deep. All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe manufacturer's recommendations. The contractor is responsible for removing all water -sensitive soils from the trenches regardless of the backfill location and compaction requirements. Depending on the depth and location of the proposed utilities, we anticipate the need to re -compact existing fill soils below the utility structures and pipes. The contractor should use appropriate equipment and methods to avoid damage to the utilities and/or structures during fill placement and compaction procedures. Pavements The near surface subgrade soils generally consist of silty sand with gravel. These soils are rated as good for pavement subgrade material (depending on silt content and moisture conditions). We estimate that the subgrade will have a California Bearing Ratio (CBR) value of 10 and a modulus of subgrade reaction value of k = 200 pci, provided the subgrade is prepared in general accordance with our recommendations. We recommend that at a minimum, 12 inches of the existing subgrade material be moisture conditioned (as necessary) and re -compacted to prepare for the construction of pavement sections. Deeper levels of recompaction or overexcavation and replacement may be necessary in areas where fill and/or very poor (soft/loose) soils are present. The subgrade should be compacted to at least 95 percent of the maximum dry density as determined by ASTM Test Method D1557. In place density tests should be performed to verify proper moisture content and adequate compaction. The recommended flexible and rigid pavement sections are based on design CBR and modulus of subgrade reaction (k) values that are achieved, only following proper subgrade preparation. It should be noted that subgrade soils that have relatively high silt contents will likely be highly www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page 9 of ii Geotechnical Evaluation sensitive to moisture conditions. The subgrade strength and performance characteristics of a silty subgrade material may be dramatically reduced if this material becomes wet. Based on our knowledge of the proposed project, we expect the traffic to range from light duty (passenger automobiles) to heavy duty (delivery trucks). The following tables show the recommended pavement sections for light duty and heavy duty use. ASPHALTIC CONCRETE (FLEXIBLE) PAVEMENT LIGHT DUTY Asphaltic Concrete Aggregate Base* Compacted Subgrade* ** 2.5 in. 6.o in. 12.0 in. HEAVY DUTY Asphaltic Concrete Aggregate Base* Compacted Subgrade* ** 3.5 in. 6.o in. 12.0 in. PORTLAND CEMENT CONCRETE (RIGID) PAVEMENT Min. PCC Depth Aggregate Base* Compacted Subgrade* ** 6.o in. 6.o in. 12.0 in. * 95% compaction based on ASTM Test Method D1557 **A proof roll may be performed in lieu of in place density tests The asphaltic concrete depth in the flexible pavement tables should be a surface course type asphalt, such as Washington Department of Transportation (WSDOT) 1/2 inch HMA. The rigid pavement design is based on a Portland Cement Concrete (PCC) mix that has a 28 day compressive strength of 4,000 pounds per square inch (psi). The design is also based on a concrete flexural strength or modulus of rupture of 550 psi. CONSTRUCTION FIELD REVIEWS Cobalt Geosciences should be retained to provide part time field review during construction in order to verify that the soil conditions encountered are consistent with our design assumptions and that the intent of our recommendations is being met. This will require field and engineering review to: ■ Monitor and test structural fill placement and soil compaction ■ Observe bearing capacity at foundation locations ■ Observe slab -on -grade preparation ■ Monitor foundation drainage placement ■ Observe excavation stability Geotechnical design services should also be anticipated during the subsequent final design phase to support the structural design and address specific issues arising during this phase. Field and www.cobaltgeo.com (206) 331-1097 February 14, 2022 Page 10 of ii Geotechnical Evaluation engineering review services will also be required during the construction phase in order to provide a Final Letter for the project. CLOSURE This report was prepared for the exclusive use of Brian Goodnight and his appointed consultants. Any use of this report or the material contained herein by third parties, or for other than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC. The recommendations contained in this report are based on assumed continuity of soils with those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with final architectural and civil drawings when they become available in order that we may review our design recommendations and advise of any revisions, if necessary. Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is the responsibility of Brian Goodnight who is identified as "the Client" within the Statement of General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences should any of these not be satisfied. Sincerely, Cobalt Geosciences, LLC Pa�"ONry� 54896 SSO STT E�`v�� NAL 2/14/2022 Phil Haberman, PE, LG, LEG Principal www.cobaltgeo.com (2o6) 331-1097 February 14, 2022 Page n of n Geotechnical Evaluation Statement of General Conditions USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its agent and may not be used by any third party without the express written consent of Cobalt Geosciences and the Client. Any use which a third party makes of this report is the responsibility of such third parry. BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this report are in accordance with Cobalt Geosciences present understanding of the site specific project as described by the Client. The applicability of these is restricted to the site conditions encountered at the time of the investigation or study. If the proposed site specific project differs or is modified from what is described in this report or if the site conditions are altered, this report is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the report to reflect the differing or modified project specifics and/or the altered site conditions. STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in accordance with the normally accepted standard of care in the state of execution for the specific professional service provided to the Client. No other warranty is made. INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and statements regarding their condition, made in this report are based on site conditions encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or sampling locations. Classifications and statements of condition have been made in accordance with normally accepted practices which are judgmental in nature; no specific description should be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in situ conditions can only be made to some limited extent beyond the sampling or test points. The extent depends on variability of the soil, rock and groundwater conditions as influenced by geological processes, construction activity, and site use. VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be encountered that are different from those described in this report or encountered at the test locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected conditions are substantial and if reassessments of the report conclusions or recommendations are required. Cobalt Geosciences will not be responsible to any parry for damages incurred as a result of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present upon becoming aware of such conditions. PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next project stage (property acquisition, tender, construction, etc), to confirm that this report completely addresses the elaborated project specifics and that the contents of this report have been properly interpreted. Specialty quality assurance services (field observations and testing) during construction are a necessary part of the evaluation of sub -subsurface conditions and site preparation works. Site work relating to the recommendations included in this report should only be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be responsible for site work carried out without being present. www.cobaltgeo.com (2o6) 331-1097 ; TP-1 Approximate Test Pit N Aerial Image Location 9 Not to Scale Cobalt Geosciences, LLC COBALT741 Proposed Residence Aloha Street Edmonds, Washington g SITE PLAN FIGURE >< P.O. Box 82243 Kenmore, WA 98028 ( ) 33 - 97 www•cobaltgeoeo.com cobaltgeo(&gmail.com Slab on Grade Basement or Shallow Foundation Wall 12" Free Draining Backfill and/or Drainage Mat Attached to Wall Backfill Soils Compacted per Geotechnical Report 4" Diameter Perforated Pipe -- --�H H Native Soils Benched as Required Filter Fabric Over Rock (Mirafi 14oN) 3//4" Washed Rock or Clean Angular Rock Not to Scale Cobalt Geosciences, LLC PO Box 1792 Typical Foundation Drain Detail Attachment North Bend, WA 98045 • _ (2o6) 331-1097 GEOSCIENCES www.cobaltgeo.com Philpcobaltgeo.com Unified Soil Classification System (USCS) MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION Clean Gravels Gw Well -graded gravels, gravels, gravel -sand mixtures, little or no fines Gravels (more than 50% (less than 5% fines) GP Poorly graded gravels, gravel -sand mixtures, little or no fines COARSE GRAINED SOILS of coarse fraction retained on No. 4 sieve) Gravels with Fines (more than 12% fines) GM Silty gravels, gravel -sand -silt mixtures GC Clayey gravels, gravel -sand -clay mixtures (more than 50% retained on Clean Sands :•: sw Well -graded sands, gravelly sands, little or no fines No. 200 sieve) Sands (50% or more of coarse fraction (less than 5% fines) sP Poorly graded sand, gravelly sands, little or no fines passes the No. 4 sieve) Sands with Fines sM Silty sands, sand -silt mixtures (more than 12% fines) sc Clayey sands, sand -clay mixtures ML Inorganic silts of low to medium plasticity, sandy silts, gravelly silts, FINE GRAINED (50% or more Silts and Clays (liquid limit less than 50) Inorganic cL or clayey silts with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays silty clays, lean clays Organic rganic oL Organic silts and organic silty clays of low plasticity passes the MH Inorganic silts, micaceous or diatomaceous fine sands or silty soils, No. 200 sieve) Silts and Clays (liquid limit 50 or more) Inorganic elastic silt CH Inorganic clays of medium to high plasticity, sandy fat clay, or gravelly fat clay Organic OHOrganic clays of medium to high plasticity, organic silts HIGHLY ORGANIC SOILS Primarily organic matter, dark in color, and organic odor PT Peat, humus, swamp soils with high organic content (ASTM D4427) Classification of Soil Constituents MAJOR constituents compose more than 50 percent, by weight, of the soil. Major constituents are capitalized (i.e., SAND). Minor constituents compose 12 to 50 percent of the soil and precede the major constituents (i.e., silty SAND). Minor constituents preceded by "slightly" compose 5 to 12 percent of the soil (i.e., slightly silty SAND). Trace constituents compose o to 5 percent of the soil (i.e., slightly silty SAND, trace gravel). Relative Density (Coarse Grained Soils) Consistency (Fine Grained Soils) N, SPT, Relative N, SPT, Relative Blows/FT Density Blows/FT Consistency 0-4 Very loose Under 2 Very soft 4 -10 Loose 2-4 Soft 10 - 30 Medium dense 4-8 Medium stiff 30 - 50 Dense 8 -15 Stiff Over 50 Very dense 15 - 30 Very stiff Over 3o Hard Grain Size Definitions Description Sieve Number and/or Size Fines <#200 (o.o8 mm) Sand -Fine #200 to #40 (o.o8 to 0.4 mm) -Medium #40 to #10 (0.4 to 2 mm) -Coarse #10 to #4 (2 to 5 mm) Gravel -Fine #4 to 3/4 inch (5 to 19 mm) -Coarse 3/4 to 3 inches (19 to 76 mm) Cobbles 3 to 12 inches (75 to 305 mm) Boulders >12 inches (305 mm) 1 Moisture Content Definitions 1 Dry Absence of moisture, dusty, dry to the touch Moist Damp but no visible water Wet Visible free water, from below water table Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 Soil Classification Chart Figure Ci (2o6) 331-1097 _ www.cobaltgeo.com cobaltgeo(&gmail.com Test Pit TP-1 Date: January 2022 Depth: 4' Groundwater: None Contractor: Client provided Elevation: N/A Logged By: PH Checked By: SC N 0) o Moisture Content (%) u Q E Plastic I Limit I Liquid Limit � � L Material Description DCP Equivalent N-Value o C ? o 0 0 10 20 30 40 50 Cobalt Geosciences, LLC Proposed Residence P.O. Box 82243 COBALT 741 Aloha Street Test Pit Kenmore, WA 98028 (2o6) 331-1097 " Edmonds, Washington Logs www.cobaltgeo.com cobaltgeopgmail.com ------- — -- ss Graand Topsoil --------------------------------- 1 SM Medium dense, silty -fine to medium grained sand with gravel, mottled yellowish brown, moist. (Weathered Trans. Beds) ' SM Dense to ve M Gmail Jeff Haynes - CSP Engineering <jsh@cspengineering.com> Goodnight SFR 741 Aloha 2 messages Jeff Haynes - CSP Engineering <jsh@cspengineering.com> Tue, May 10, 2022 at 2:07 PM To: Phil Haberman <cobaltgeo@gmail.com> Cc: Tom Leren <tom@lerendesign.com>, Brian Goodnight <earthtobrian@yahoo.com> Hi Phil, We would like to place the detention pipe illustrated on the attached plan 4' away from the foundation however the City would like you to sign off on the proposal. Please let me know your thoughts and I will add your email to the end of your geotech report for submittal to the City. FOUNDATION WALL EX GRADE 3' DIA DETENTION PIPE ADS N-12 PROP LINE 85 85 80 ------ -- __ ---— J -----y 80 -------- - — ----------- 75 ---- ----- _ - -- - -T 75 --- - - 70 70 1:1 8.24' 4.00' DETENTION TANK SECTION SCALE I = 10' 8 IF 4-0 S-LOLL[ PVC FIG DRAIN COLLECTION LINE FLOW CONTROL STRUCTURE TYPE-2 60' RM 76.29 IE 7294 (SIN) IE 7294 (NE) IE 7294 (SE) _ IE 7294 (SE) 24 LF 76'0 5=0.50S ADS N-11S0. .t6 DEANWT VERT 0 BOIRAI TANK 9ry o. '(rR) i CONNECPCN PgNT TOR TS` ROOF DOVINSPOUHE t6 MN=79.a5ROCI( DISPERSIDI STRIP y SOCO-2 CLEANOUT RIM 79.83 _ II � R77.39 I. DRY UTILITY CORiWR \ - Thanks Jeff Jeff Haynes PE CSP Engineering Inc. PS 1037 NE 65th St #153 Seattle, WA 98115 206-406-9965 www.espengineering.com jsh@cspengineering.com ,,--4 V 6Y 5=3.00I PVC I I "—Il LF 6'0 S-SOO,T PVC r lfI4Y 5=200F PVC 2.6' CLR as'ryq "--i13 LF 4'0 S=2OOf PVC - $DCO-1 DEAROUT ARM 80.39 F 73.48 —20 IF 4'0S=2DR PVC________ SOAR-1 AREA DRAW RIM M13 N 73." 7 IF 4-/ S=20M PVC SDAD-2 AREA DRAW —RIM 7.R 1.3 on _22-005 CIVIL PLANS-C1.1 CIVIL SITE PLAN TO GEO 2022-05-10.pdf 1453K Phil Haberman <cobaltgeo@gmail.com> Tue, May 10, 2022 at 2:30 PM To: Jeff Haynes - CSP Engineering <jsh@cspengineering.com> Cc: Tom Leren <tom@lerendesign.com>, Brian Goodnight <earthtobrian@yahoo.com> I have no issues with the storm pipe location from the site plan (Sheet Ci.i). Thanks. Regards, Phil Haberman, PE, LG, LEG Principal Cobalt Geosciences, LLC (2o6) 331-1097 IMPORTANT/CONFIDENTIAL: This e-mail message (and any attachments accompanying it) may contain confidential information, including information protected by attorney -client privilege. The information is intended only for the use of the intended recipient(s). Delivery of this message to anyone other than the intended recipient(s) is not intended to waive any privilege or otherwise detract from the confidentiality of the message. If you are not the intended recipient, or if this message has been addressed to you in error, do not read, disclose, reproduce, distribute, disseminate or otherwise use this transmission, rather, please promptly notify the sender by reply e-mail, and then destroy all copies of the message and its attachments, if any. [Quoted text hidden] MG ma i I Jeff Haynes - CSP Engineering <jsh@cspengineering.com> Googdnight SFR - 741 Aloha 2 messages Jeff Haynes - CSP Engineering <jsh@cspengineering.com> To: Phil Haberman <cobaltgeo@gmail.com> Cc: Tom Leren <tom@lerendesign.com>, Lee Michaelis <lee.michaelis@pugetsound plan ning.com>, Brian Goodnight <earthtobrian@yahoo.com> Hi Phil, The City is looking for your concurrence to use permeable pavement as shown below. Thanks / 1E 12' PVC(SE)=169.59 IE 8' PVC(SW)-73.89 IE 6' PVC(S)-72.4J '! I � vl . `'O / r7 -I�• EIS so ' I FOUND RESAR W/CAP .prr-�9 M'L (E) & L 7 m / C&C FENCE LINE 0.5 (W) CORNEROF N 2.15.2 S) SSCO RIM = 79. 11' / INVERT N OBTAINABLE FFE 75.75 _I_ �/ I 1CV1 • \ i NCE i 27032900223100 GAR FEE 85.00 e kv — - - N 89'55 57 E ---_--- 86 CONC. WALK ? CONC. WALK w Jeff Haynes PE CSP Engineering Inc. PS 1037 NE 65th St #153 Seattle, WA 98115 206-406-9965 www.cspengineering.com jsh@cspengineering.com Tue, Apr 25, 2023 at 12:11 PM Phil Haberman <cobaltgeo@gmail.com> Tue, Apr 25, 2023 at 12:39 PM To: Jeff Haynes - CSP Engineering <jsh@cspengineering.com> Cc: Tom Leren <tom@lerendesign.com>, Lee Michaelis <lee.michaelis@pugetsoundplanning.com>, Brian Goodnight <earthtobrian@yahoo.com> Generally not an issue. If a basement, then we'd want to make sure we have nice drainage materials and the ability to recollect any excess or non -infiltrating runoff so it can be routed off site via tightline. Regards, Phil Haberman, PE, LG, LEG Principal Cobalt Geosciences, LLC (2o6) 331-1097 www.cobaltgeo.com IMPORTANT/CONFIDENTIAL: This e-mail message (and any attachments accompanying it) may contain confidential information, including information protected by attorney -client privilege. The information is intended only for the use of the intended recipient(s). Delivery of this message to anyone other than the intended recipient(s) is not intended to waive any privilege or otherwise detract from the confidentiality of the message. If you are not the intended recipient, or if this message has been addressed to you in error, do not read, disclose, reproduce, distribute, disseminate or otherwise use this transmission, rather, please promptly notify the sender by reply e-mail, and then destroy all copies of the message and its attachments, if any. [Quoted text hidden]