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APPROVED ENG STORM REPORT BLD2019-0951March 25, 2020 Edmonds Apartments Drainage Report 23830 Edmonds Way SDA Project #410-002-18 ! . 1 77777, Prepared for: Constantine Korovkin PACE 23830 Edmonds Way Edmonds, WA 98026 An Engineering Services Company CIVIL ENGINEERING I PROJECT MANAGEMENT I PLANNING 1724 W. Marine View Drive, Suite 140, Everett, WA 98201 1 425.486.6533 1 www.sdaengineers.com Edmonds Apartments Drainage Report Prepared For: Constantine Korovkin 23830 Edmonds Way Edmonds, WA 98026 Prepared By: PACE/SDA Engineers 1724 West Marine View Drive, Ste 140 Everett, WA 98201 (425) 486-6533 a~AL'ft41 wnsyl�� sC 1 33747 �46 SIONAL .403-25-20 Last save by: Travis Stanley on 3/25/20 R:\Projects\410 (LZG Construction)\002-18 (Edmonds Apt)\Technical\Reports\2020-02-21\2020-02-21 - EW Drainage Report _updated.docm Edmonds Apartments Drainage Report TABLE OF CONTENTS EXECUTIVE SUMMARY • Executive Summary • Vicinity Map SECTION 1 - PREPARATION OF STORMWATER SITE PLANS • Step 1: Site Analysis: Collect and Analyze Information on Existing Conditions • Step 2: Prepare Preliminary Development Layout • Step 3: Perform an Off -Site Analysis • Step 4: Determine and Read the Applicable Minimum Requirements • Step 5: Prepare a Permanent Stormwater Control Plan • Step 6: Prepare a Construction Stormwater Pollution Prevention Plan • Appendix 1 A — Existing Condition Summary Documents • Appendix 1 B — Downstream Flowpath Analysis • Appendix 1 C — Geotechnical Report SECTION 2 — CONSTRUCTION STORMWATER POLLUTION PREVENTION (SWPP) • 1.0 - Introduction • 2.0 - Site Description • 3.0 - Construction Stormwater BMPs • 4.0 - Construction Phasing and BMP Implementation • 5.0 - Pollution Prevention Team • 6.0 - Site Inspections & Monitoring • 7.0 - Reporting & Recordkeeping • Appendix 2A - Site Plan with BMP Measures • Appendix 2B - SWPPP Project Summary • Appendix 2C - Alternative BMPs • Appendix 2D - General Permit • Appendix 2E - Site Log & Inspection Forms SECTION 3 — SOURCE CONTROL OF POLLUTION • Source Control of Pollution SECTION 4 - PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND OUTFALLS • Natural Drainage Course Description SECTION 5 - ON -SITE STORMWATER MANAGEMENT • Performance Standards • Existing Site Hydrology • Developed Site Hydrology • Appendix 5A — Basin Mapping Edmonds Apartments Drainage Report • Runoff Treatment SECTION 7 - FLOW CONTROL • Existing Site Hydrology Synopsis • Developed Site Hydrology Synopsis • Flow Control Performance Standards • Appendix 7A —Flow Control Design Calculations • Appendix 7B — Conveyance Calculations SECTION 8 - WETLANDS PROTECTION SECTION 9 — OPERATION & MAINTENANCE Edmonds Apartments Drainage Report EXECUTIVE SUMMARY Edmonds Apartments Drainage Report EXECUTIVE SUMMARY The project proposes the construction of an apartment building on a single existing parcel occupying approximately 0.36-ac on the southwest side of Edmonds Way. The project is located in the SW '/4 of Section 31, Township 27 N, Range 4 E, W.M. More specifically, the project is located at 23830 Edmonds Way, and occupies Snohomish County Tax Parcel No. 0043601000302. A vicinity map has been included as Figure 1 of this document. The site is currently developed and appears to contain two residential buildings as well as an accessory structure. The remainder of the project contains some ornamental trees and traditional residential lawn and landscaping. The project site is triangular in shape and bounded on the northeast side by Edmonds Way (SR 104). The project is bounded on the northwest and south sides by existing residential parcels. The underlying topography generally falls moderately to the north and northwest. Surface runoff can be expected to follow this topography, following the existing slope to the north and northwest. The project appears to be within a single threshold discharge area, as all runoff from the site appears to be intercepted within the Edmonds Way right-of-way within a short distance of the site. The USDA Web Soil Survey identifies the underlying soil unit as a "till' variety of soil, which typically will not support infiltration of surface runoff. The project is subjected to the provisions of Chapter 18.30 of the City of Edmonds Stormwater Code Supplement to Edmonds Community Development Code, which is supplemented to the Washington State Department of Ecology Stormwater Management Manual for Western Washington (2014 amended edition). The project will add more than 5,000 square feet of new impervious, thus minimum requirements 1-9 apply to this project, including both flow control and water quality requirements. The project will utilize underground stormwater detention to meet the flow control requirements and a wet vault to meet the water quality requirements. The project is required to utilize on -site stormwater management techniques, and is proposing to utilize detention to meet this requirement. The project is unable to collect and mitigate all of the frontage area, and therefore the project proposes to bypass this area which is discussed further in Section 7 of this report. Basin mapping is provided in Appendix 5A. Figure 1 Vicinity Map Edmonds Apartments Drainage Report SECTION 1 PREPARATION OF STORMWATER SITE PLANS (Minimum Requirement #1) Edmonds Apartments Drainage Report PREPARATION OF STORMWATER SITE PLANS The project is required to provide stormwater management techniques consistent with Chapter 18.30 of the Edmonds Community Development Code (ECDC). This code generally adopts the 2014 Edition of the WA Dept. of Ecology's Stormwater Management Manual for Western Washington, with an addendum issued by the City dated 12/21/2016. These two documents will be referred to throughout this report as "DOE Manual" and "City Addendum", respectively. This report, along with the accompanying plans, is intended to satisfy the site plan preparation requirements outlined in the regulatory documents listed above. Stormwater site plans are prepared by completing the steps below, as outlined in Volume 1, Chapter 3 of the DOE Manual: Step 1: Site Analysis: Collect and Analyze Information on Existing Conditions A boundary/topographic survey was prepared for the project site, and was used as a basis for the engineering plans. The USDA Web Soil Survey identifies the underlying soil unit as "McKenna gravelly silt loam". McKenna soils are typically considered to be a glacially -consolidated till soil, with a hardpan layer. These soils typically exhibit moderate runoff rates and very little capacity for infiltration. The map also shows a very small portion of the site as being underlain by "Alderwood-Urban Land Complex", which is another till unit. There may be an interface between these two soil units at or near the site, but both can be expected to exhibit similar hydrologic responses. A USDA Web Soil Survey map is provided in Appendix 1A of this report. A geotechnical report by Gary A. Flowers, PLLC provided a recommendation to not provide infiltration as the site is underlain with hardpan soil. This documentation has been provided in Appendix 1C. FEMA identifies the project site on Flood Insurance Rate Map (FIRM) Panel #53061 C1315, which is a non -printed panel. The project site is not expected to be within a flood hazard area. A portion of the FIRM map is provided in Appendix 1A of this report. The City's GIS database identifies an erosion hazard area on the site, due to a slope that ranges between 15% and 40%. This slope extends through the middle of the site, essentially being a step between the two existing building pads on -site. The slope is less than 10-ft high, and the proposed apartment building will be constructed over this slope, so the erosion hazard is not expected to remain following the proposed development. The project will create a 2H:1 V slope along the southern boundary of the site, which can be stabilized with vegetation. No other critical areas were identified on or near the site. A critical areas map is provided in Appendix 1A of this report. Step 2: Prepare Preliminary Development Layout A set of engineering plans are being provided to the City with this report to depict the proposed development layout. Step 3: Perform an Off -Site Analysis A site visit was conducted on January 31, 2019, and the conditions were clear and cool, with no significant rainfall having occurred within the previous couple of days. No surface runoff was observed at the project site or the nearby downstream flowpath. The site topography generally falls to the north and northwest, and is ultimately tributary to the public storm drainage network in Edmonds Way. The public drainage network extends northwesterly beneath Edmonds Way for the entire'/4-mile downstream analysis zone. The downstream flowpath is depicted on a map in Appendix 1 B. Edmonds Apartments Drainage Report The entire'/4-mile downstream flowpath is contained within an underground pipe network. From surface - visible observation, the downstream pipes appear to be concrete, ranging from 12-inch to 36-inch in diameter. No significant issues or concerns were noted during the field investigation. The project site appears to lie near a relative high -point in the area. A small portion of the adjacent parcel to the south will fall toward the site. The project proposes a french drain to collect this runoff and route it to the project's frontage, essentially conveying it around the site. Step 4: Determine and Read the Applicable Minimum Requirements The project proposes more than 5,000 square feet of new/replaced hard surface, and therefore, all minimum requirements from the City Addendum are applicable to all new/replaced hard surfaces and converted vegetation areas. This requires preparation of Category 2 Stormwater Site Plans, as prescribed by the City Addendum. Step 5: Prepare a Permanent Stormwater Control Plan A set of engineering plans are being provided to the City with this report to depict the proposed development layout. Step 6: Prepare a Construction Stormwater Pollution Prevention Plan The accompanying engineering plans include an erosion & sediment control plan for the project. That drawing, along with Section 2 of this report are intended to be the stormwater pollution prevention plan for this project. The project site proposes less than 1-acre of disturbance, so a DOE Construction Stormwater Permit will not be required for this project. Edmonds Apartments Drainage Report APPENDIX 1A EXISTING CONDITION SUMMARY DOCUMENTS Edmonds Apartments Drainage Report 3 Ny N 548590 47' 46 58" N 47° 46 55" N 548590 548600 548610 548620 548630 548640 548650 3 v N Map Scale: 1:504 if printed on A landscape (11" x 8.9') sheet Meters N 0 5 10 20 30 Feet 0 20 40 80 120 Map projection: Web Mercator Comer 000rdinates: WGS84 Edge tics: UTM Zone ION WGS84 USDA Natural Resources Web Soil Survey Conservation Service National Cooperative Soil Survey Soil Map —Snohomish County Area, Washington (Edmonds Apartments) o N 548600 548610 54862D 548630 548640 548650 548660 548670 548680 548690 54866D 548670 548680 54869D 47' 4658" N �n N �i 3 N H 2/19/2019 Page 1 of 3 47° 46 55" N MAP LEGEND Area of Interest (AOI) Area of Interest (AOI) Soils 0 Soil Map Unit Polygons rwr Soil Map Unit Lines Soil Map Unit Points Special Point Features Ua Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp + Mine or Quarry Miscellaneous Water Perennial Water 1W Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip oa Sodic Spot Soil Map —Snohomish County Area, Washington (Edmonds Apartments) ,-;;i Spoil Area 15 Stony Spot Very Stony Spot Wet Spot Other .� Special Line Features Water Features Streams and Canals Transportation t_" Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography MAP INFORMATION The soil surveys that comprise your AOI were mapped at 1:24, 000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 20, Sep 10, 2018 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 7, 2014—Jul 8, 2014 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. USDA Natural Resources Web Soil Survey 2/19/2019 Conservation Service National Cooperative Soil Survey Page 2 of 3 Soil Map —Snohomish County Area, Washington Edmonds Apartments Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 6 32 Alderwood-Urban land complex, 8 to 15 percent slopes 0.0 0.2% 99.8% McKenna gravelly silt loam, 0 to 8 percent slopes 0.5 Totals for Area of Interest 0.5 100.0% usDA Natural Resources Web Soil Survey 2/19/2019 Conservation Service National Cooperative Soil Survey Page 3 of 3 30 4 ZONE X 224TH STREET APPROXIMATE SCALE IN FEET 1000 0 1000 ! 00 ® NATIONAL FLOOD INSURANCE PROGRAM 28TH STREET 228TH ST m m FIRM 230Tr STREET sw FLOOD INSURANCE RATE MAP :E SNOHOMISH COUNTY, m WASHINGTON AND 4 INCORPORATED AREAS PANEL 1315 OF 1575 =4 (SEE MAP INDEX FOR PANELS NOT PRINTED) 234TH STREET WEST J = CONTAINS: COMMUNITY NUMBER PANEL SUFFIX ® � 31 236TH STREET WEST EDMONDS, CITY OF 530153 1315 E Mou L4K TRACE CITY OF 530170 iais E WOODWAY, TOWN OF 530306 I315 E FT]F J = SNOHOMISH COUNTY, UNINCORPORATED AREAS 53553 135 E ZONE X < m m 238TH STREET SW m I e CITY OF EDMONDS MAP NUMBER 530163 53061C1315 E 240TH S SW 2 0 D ay � v EFFECTIVE DATE: '�� = NOVEMBER 8,1999 ww4 242ND z a STREET 2 Federal Emergency Management Agency D w LU m This is an official copy of a portion of the above referenced flood map. It Cc was extracted using F-MIT On -Line. This map does not reflect changes ® or amendments which may have been made subsequent to the date on the title block. For the latest product information about National Flood Insurance ..� Program flood maps check the FEMA Flood Map Store at www.nnsc.ferna.gov City of Edmonds Edmonds Apartments \ 23725 M \ 00 O 00 r jL [V i, 8615 85 ,j •. i.: ,nrtiake 00 ace fV — Legend 23 8TH ST SW = Creeks ® Seismic Hazard Areas $82fi 1111110� 23800 88628 23 Earth Subsidence and Landslide L _ Minimum Buffer Adjacent to Hai ❑ 23802 8606 Wetlands 23804 0 23810 D �, 23 Wetlands Boundary -.- Wetland Boundaries Not Complete) s, 2'381.2 7s — Wetland Known Extents 882.8 23808 23814 to 38 ® Floodplains Landslide Hazard Area 40% 23816 ��y — '�� r9 ❑ Severe Erosion Hazard 15%-40% ❑ Erosion Hazard Areas 15%-40% 617-382b-ftV1' 123822 23824 T 8801 117ik 23904 829Ln N 88 8717 87q,5 N 8629 � 88 y $721 1 00 Notes 1. 2,257 Critical Areas Map 0 94.04 188.1 Feet This map is a user generated static output from an Internet mapping site and is for WGS_1984_Web-Mercator _Auxiliary -Sphere reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. © City of Edmonds THIS MAP IS NOT TO BE USED FOR DESIGN OR CONSTRUCTION APPENDIX 1 B DOWNSTREAM FLOWPATH ANALYSIS Edmonds Apartments Drainage Report " City of Edmonds Downstream Flowpath 19 .u0 Iron �- _ +j - _ -- 23321 r _ 2 -' ! '° .► r E�325 F� gf•,y .�1 i .n 2 a 4TH 5'D I m N m 23329 -!� Smonas _ 9 30 o ' 2i4C3 2'4� r ► I i ■ 2 4oa ■ ® � n m Legend 23411 2i451 O 23409 254,0 -� .,� •iyjO'_ 23 L1 23414 234,� 212 23415 23416 2341 + PD16-$:' Storm Catch Basins ❑ <all other values> .- 23420 � 422 2 1 1 6J1 23419 -❑Y cv! � 43 3426� 2343.1 23430� 3 ■ I , .. .. w m _ �; •jr �-- � m J 23425 Storm Manholes p <all other values> ■--� 35 3508 23 23 ` _ly 8721 Ir ];;R 23506= 8423 ..p«, .a Yes 516 T5 235 235 235 23� ' 90, . 1. 9 1 TF�- �. ^. ry. 6705 86 8 235 '�, L SW �� Itih��' P Detention Facilities n m 9 23 ® 9 91 1 r .... PD16-9 4 - 8717 8729 ¢ 1 235 J PD-6-81 -� Culvert • <all other values> • Yes 235 a a 9205 9 8923 805 8715 w I 6423 8505 m L �. 23525 �' Q Facility Feature PD1.6=7 0 D'� Creeks PI) f PD76-72 o imv,76,77 23 Q 914 V. Storm Line <all other values> m oo 23611 I - 1 O 23601 — Yes 23� b 0 622 °° 8614 sq 67 8606 23 6M 0 504 236 2 23603 23605 23607 Facilit Lines y C' 1 37MW ® 862 8506 3627s 23619 23625 Storm Ditch Contour Lines PD1 6-45� h� r r,7 10 23713 ' 1 � z 8 23706 PD�16=72 �� 50 100 CPD1 6=T4� � 4W0 O 0 ` e N 7 0 s a 2372o PD1fi�2 -2 IL 9 �8 9 �i,. s.9o1 i PDQ �. °° . �'A_O ♦ O : D = 26 `1 PD16-25 s PD15 4i1' ♦�,_ n P�16-22 1 OQ n� RD7.s 28 PD16=28a�,�/]- — - - T §,., �...F.■ 826— 23 0 , "t!+' ,p>n 81A - 7 f : D16-27 23805 8606 n 8_ 85 0 23gr;n q, a 9112 �tib � 23804 16 ;3r8+00 , �- 2 ��=•"1a�� i 23 m PD16}24 TS1, CD L 6912 � 822 1 2362� 7�g3"A �g 3616 \ 3sz �' a 3822 'S�`L Nv PD766 23 O 91D�5' 88 7 8239574 l�9 23904 � a$A ` � K RE:AN PRES TE 1 ' 23914 — J PD1 fi-77 8821* 03 88 87� C LJRC PD1s=62 2s•�I�� 9109 901 629 3 3920 88 PD16 0 PD7s-s7 - im � � 2 � r 1: 4, 514 'aa2, "`Zzz�_ PD15 21 4A-,- P-D760 PD16'--31 5 y Notes - .9 9216 � 9016 841 C• 401 752.3 0 376.17 752.3 Feet This map is a user generated static output from an Internet mapping WGS_1984_Web_Mercator_Auxiliary_Sphere site and is for reference only. Data layers that appear on this map may © City of Edmonds THIS MAP IS NOT TO BE USED FOR DESIGN OR CONSTRUCTION r y :, �• a p - As ,,.yam {: �u .� •, r-�-��?= ..`ter, P: - '= JECT SITE. . . .F .ti.s i rr : .' "• v } -ley {�t.��44 �' i y � � 3: �r yy t � z Photo #3 Looking northwest, approx. 600-ft downstream of site Photo #4 Looking northwest, approx. 900-ft downstream of site Edmonds Apartments Drainage Report APPENDIX 1 C GEOTECHNICAL REPORT Edmonds Apartments Drainage Report Gary A. Flowers, PLLC Geological & Geotechnical Consulting 5205 23rd Avenue W Everett, WA 98203 June 8, 2019 Project No. 18019 Constantin Korovkin Principal Rnk Eastside, LLC 2603 78th Ave NE Medina, WA 98039 Subject: Geotechnical Services Report — Edmonds Apartments 23830 Edmonds Way Edmonds, Washington This report summarizes the results of our geological and geotechnical evaluation of the property located at the above noted address in Edmonds, WA. It is our understanding that the existing structures on the property will be demolished and a new 10-unit apartment building will be constructed on the site. EXISTING CONDITIONS The property is currently developed with 3 single family residences. Two of the residences are located on the lower, western portion, of the site. The third structure is located on an upper bench level, about 6 feet higher in elevation than the other two structures. Egress to all the existing residences is off of Edmonds Way. Single family residences are present to the west, southwest and south, an automotive repair business is located to the east/southeast and Edmonds Way borders the property to the north. The upper portion of the property is located on the north end of a slight north -south trending ridge that terminates at the north end of the property. The area around the residence on the upper portion is generally flat lying at an approximate elevation of 404 feet. The property slopes gently down to the north and northeast to approximate elevation 400 feet. The lower, western, portion of the property is generally flat lying at an approximate elevation of 396 feet. The western descending slope between the upper and lower portion of the property is on the order of 5 to 6 feet tall and is relatively steep. Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington At the time of our field study there was no evidence of standing or flowing water on the property. Vegetation consists primarily of landscape bushes and grass, several small deciduous trees and multiple large evergreen trees. Subsurface Exploration In order to confirm subsurface conditions on the property a series of 5 exploration pits were excavated on the property on October 8, 2018. Logs of the exploration pits are attached with this report. Generally, very dense glacial till was observed on the western and northeastern portions of the site (EP-1 and EP-2. Significant quantities of fill soils were observed in all of the exploration pits on the upper portion of the site. The fill extended to a maximum depth of 5 feet and was underlain by loose recessional outwash sediments. Significant organics and ash was observed within some of the fill soils. In the northwest corner (EP-2) large gravels up to 4 inches in diameter were encountered. Ground water seepage was not observed in any of the exploration pits. Moderate caving conditions was observed within the loose fill soils. Mappings According to the Draft Composite Geologic Map of the Sno-King Area, Central Puget Lowland, Washington, by Booth, Cox, Troost and Shimel, January 5, 2004, the site is mapped as Vashon age glacial till. Our explorations are in agreement with the published geology map of the area. Seismic Hazards Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture; 2) seismically induced landslides; 3) liquefaction; and 4) ground motion. The nearest known fault zone is the South Whidbey Island fault that is located several miles north of the property. No surficial faulting has been noted anywhere near this area and the potential for surficial ground rupture during the lifespan of the residences is considered to be low. Due to the lack of significant slopes near the site the potential for seismically induced landslides is considered to be very low. The underlying glacial till soils are not subject to liquefaction. Based on the encountered site conditions, seismic design criteria should follow 2015 International Building Code recommendations for Site Class C soils. Gary A. Flowers, PLLC. 5205 23" Avenue W Everett, Washington 98203 206-819-4304 2 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington CONCLUSIONS AND RECOMMENDATIONS Based on the results of our site reconnaissance, subsurface investigation and literature review it is our opinion that the site is suitable for the planned development. Planned finish floor elevation for the new structures will be 399.5 which will require removal of much of the encountered fill soils on the upper portion of the site. In areas where the existing fill is not fully removed it will be necessary to further excavate to extend the foundations to suitable bearing soils. It should also be noted that loose recessional outwash sediments were observed underlying the fill soil. These loose soils are also not suitable for foundation support and must either be recompacted to a medium dense or better condition or removed down to the underlying glacial till sediments. Grading of the site will expose loose fill soil or loose native sediments along the south property line. In order to not adversely impact the adjacent properties to the south it may be necessary to provide temporary shoring to support the slope until the buildings are constructed and the foundation walls fully backfilled. We anticipate that ecology blocks or Ultrablocks can be used for this purpose, but sloughing soils could mandate other shoring methods as well. Excavation along the south property line will also likely impact a large evergreen tree that is located very near the south property line. An arborist should be consulted to determine whether or not this tree will be considered a hazard tree or how the excavation can proceed without damaging the tree. The observed fill soils are generally granular in nature and where organics are not present can generally be re -used as structural or nonstructural fill around the site. Excavation safety is incumbent on the contractor as they are on site on a continual basis. However, for planning purposes we do not recommend that temporary excavations in the loose fill or loose native sediments should be planned any steeper than 1H:1V. Even at this inclination some sloughing could occur and the slopes should be protected from storm water. Foundations Based on our field explorations suitable bearing soils will be encountered at a relatively shallow depth after the site is final graded. The foundation should be designed for an allowable soil bearing of 2,000 psf. An increase of one-third will be appropriate for short term wind or seismic loading conditions. The planned wall along the west property line will be constructed atop fill soils utilized for detention vault wall backfill. The backfill must be placed and compacted as structural fill. Lateral resistance will be provided be soil pressure against the footings and foundation walls and/or by friction between building elements and the soil. We recommend a passive resistance value of 200 pcf and a soil friction value of 0.30 for this site. These values are allowable and have a minimum factor of safety of 1.5. Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington Bearing soils will be easily disturbed and must be protected from disturbance during grading. No footing should be placed on existing fill soil. Any loose native soil that is naturally loose or has been disturbed during grading operations must either be removed or suitably recompacted to a medium dense or better and unyielding condition. Overexcavation or re -compaction of the soils must extend outward from the footing line a distance equal to the depth of excavation on each side of the footing. In other words, if a 2-foot overexcavation is required to reach suitable bearing, and the excavation will be backfilled with structural fill to footing subgrade elevation, or can be recompacted to a suitable density, the overexcavated trench or area of re -compaction must extend 2 feet outward from each side of the footing. Due to the variability of the onsite soils and depth to bearing soils all footing subgrade soils must be approved by a representative of this office prior to concrete placement. Floor Support Recommendations The observed native sediments, or granular fills soils, will provide suitable support for slab -on -grade floors provided that they are re -compacted to a medium dense or better and unyielding condition. Compaction should be attained with a hoe-pac, walk behind vibratory compactor, jumping jack or large sled compactor. Small sled compactors used for surficial leveling and compaction are not suitable for this purpose. Suitable compaction should be verified by the geotechnical professional prior to concrete placement. If any unsuitable soils are observed during excavation and/or compaction they should be removed and replaced with appropriate structural fill material. Following compaction and approval of the slab bearing soils, a capillary break layer consisting of a minimum of 4 inches of washed pea gravel, washed crushed rock or clean, coarse grained, granular soils and a heavy duty (minimum 10 mil), polyethylene plastic vapor barrier should be provided under any floor slabs where moisture intrusion is a concern. If the vapor barrier becomes compromised in any way during construction it should be replaced or an additional layer added. Penetrations through the vapor barrier should be wrapped and taped. All seams should be overlapped a minimum of 2 feet. Retaining Walls Foundation or basement retaining walls that are free to rotate at least .001 percent of their height should be designed for an active equivalent fluid pressure of 35 pcf. Wall that are not free to rotate should be designed for an at rest pressure of 50 pcf equivalent fluid pressure. These pressures are for a condition of level backflll and suitable wall drainage to eliminate hydrostatic pressure. Drainage Storm water from impermeable surfaces should be collected and discharged into a city approved storm water drainage system. Footing drains should be installed around the exterior footings with discharge to a catch basin and ultimately into the storm drain system. The footing drains should Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 4 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington consist of 4-inch diameter, perforated pvc pipe, bedded in washed drain rock and covered entirely with washed drain rock that is wrapped in geotextile filter cloth. The drains should be placed at the bottom of the footings and sloped to gravity drain to the catch basin. Appropriate cleanouts should be installed to allow for periodic maintenance of the drainpipes. Foundation walls taller than 3 feet should be provided a wall drain to reduce the potential for hydrostatic pressure buildup against the wall. The wall drain should consist of either a minimum of 12 inches of washed drain rock, wall backfill containing less than 3% fines or a geotextile drainage mat such as MiraDrain or DeltaDrain. The wall drains must hydraulically connect to the footing drain system. All drainage material should extend to within 18 inches of ground surface before being capped in order to prevent surface water from entering the wall drain. Infiltration of Storm Water We understand that infiltration of storm water may be considered for the project. We further understand that an infiltration facility, if feasible, would be located on the western portion of the site. During our subsurface exploration we encountered very dense glacial till soils at shallow depth on the western portion of the site and in the northeast corner of the site and they most likely underlie the entire site. The presence of shallow glacial till soils means that infiltration is not a feasible alternative for the site. Erosion Control Suitable best management practice (BMP) erosion control measures should be implemented for the project. The site will be graded nearly level which will aid in reducing the amount of potential sediment laden runoff from the parcel. A silt fence should be installed as per city of Edmonds requirements along the lower portions of the site. Soil stockpiles should be covered with plastic sheeting to contain in -situ moisture and prevent storm water runoff. Areas of disturbance should be limited to necessary construction areas. A rocked construction should be provided in order to reduce sediment impacts to the adjacent streets. The exposed soils should be covered with geotextile filter fabric prior to rock placement. The construction entrance will likely require maintenance and additional rock depending upon local weather conditions. Detention Vault A large detention vault is planned for the western portion of the site. Bottom elevation of the vault floor is planned at 385 feet, Footing excavation will be on the order of 1 foot deeper for a total excavation to approximate elevation 384 feet. Ground surface elevation ranges from 396 to 398 feet in this area. This will require an excavation on the order of 14 feet deep. The excavation will be located approximately 5 feet from the west property line. Our subsurface excavation in this area only extended to approximate elevation 391 feet due to utilizing smaller limited access equipment to access the site. Dense glacially consolidated soils Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 5 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington were observed in exploration pit EP-1. These sediments are typically capable of standing in temporary vertical excavations when ground water is not present. For planning purposes it is likely that an 8 foot or taller vertical cut can be established and then slope to the property line. However, it will be necessary to obtain additional subsurface information in order to verify subsurface soil and ground water conditions. We recommend that, at the time of demolition, when larger equipment will be on site, that several additional exploration pits be excavated at least to elevation 384 feet. If soils or ground water conditions are encountered at that time that are not suitable for the required vertical excavation, it will be necessary to provide temporary shoring to support the cut face. A design for a soldier pile wall would then be required. Temporary Shoring — South Property Line The required cut slopes along the south property line will encounter loose fill and/or native soils that will require temporary shoring unless a temporary construction easement is obtained from the adjacent property owner(s). We strongly recommend trying to obtain the temporary construction easement as the loose nature of the soils in this area are problematic. Also, the large evergreen tree along the south property line as discussed above will likely have multiple large roots that must be cut to make room for the block wall. The cut in this area will only be about 5 feet tall. Should temporary shoring be necessary, it is our opinion that either ecology blocks or Ultrablocks may be utilized for the temporary shoring. The face of the cut should be as far away from the property line as is feasible to allow space for the blocks and workers who will be forming the footings and foundation walls. The face of the cut slope should be continually densified with the bucket of the trackhoe as the excavation proceeds. The blocks should be installed with a small batter on the order of 5 degrees. The larger Ultrablocks (2.5'x2.5' x5') could support the cut with only 2 blocks while ecology blocks (2'x2'x6')will require 3 blocks. The bottom block must be embedded a minimum of 6 inches into bearing soils. The blocks must be staggered such that each block sits atop the two lower blocks. A minimum 4- inch-thick, crushed rock leveling pad must be placed and graded prior to block placement to establish level and batter. Any annular space behind the blocks must be immediately filled with pea gravel, sand or crushed rock in order to provide continuous contact between the back of the blocks and the excavation cut surface. The excavation should not be cut until the blocks are on site and available for use. The excavation should be staged such that no more than 10 feet is open at a time without being shored. A representative of this firm should monitor the excavation and wall building activities and periodically monitor the wall until such time as the permanent building walls are constructed and backfilled. This temporary shoring wall will be sacrificial and remain in place after the building walls are constructed and backfilled. During initial grading operations several exploratory excavations should be made near the south property line to further evaluate whether or not the loose soils will stand temporarily while the Gary A. Flowers, PLLC. 5205 23rd Avenue W Everett, Washington 98203 206-819-4304 0 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington temporary shoring is installed. Should the caving be excessive, and if no temporary construction easement can be attained, it may be necessary to redesign the temporary shoring system to avoid adversely impacting the adjacent property. Alternative methodology would likely involve some type of pile supported temporary wall. SUMMARY The conclusions and recommendations presented in this report are based on our interpretation and evaluation of soil conditions on this site based on visual observation, literature research and subsurface exploration. If changed conditions are observed during construction, we should be immediately contacted to further evaluate the changes and make suitable recommendations. Our findings and recommendations provided in this report were prepared in accordance with generally accepted principles of engineering geology and geotechnical engineering as practiced in the Puget Sound area at the time this report was submitted. We make no other warranty, either express or implied. Thank you for the opportunity to be of service. Should you have any questions please do not hesitate to contact our office. Respectfully submitted, `eoE Wash;' y� �I prr�ring Gedopfq �. '�P 105fi �'•`' qs�d Geo�o Gary A. Flowers Gary A. Flowers, P.G., P.E.G. Principal Engineering Geologist Attachments: Exploration Pit Logs Site & Exploration Plan Robert M. Pride, P.E. Geotechnical Engineer Gary A. Flowers, PLLC. 5205 23" Avenue W Everett, Washington 98203 206-819-4304 7 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington EXPLORATION PIT LOGS 23830 Edmonds Way Edmonds, WA EP-1 Approximate elevation 396 feet. 0.0' — 0.3' Forest duff and highly organic topsoil 0.3' — 2.3' Dense, moist, brownish -gray, silty SAND with occasional gravel — highly oxidized (weathered glacial till) 2.3' — 5.0' Very dense, moist, gray, silty SAND with gravel (unweathered glacial till) Bottom of pit at 5.0 feet on 10/8/2018. No ground water. No caving. EP-2 Approximate elevation 403 feet. 0.0' — 3.5' Loose, moist, gray and brown, silty SAND with large gravel to 4" diameter — 2 old drainpipes with large diameter drain rock on NW side of pit (fill) 3.5' — 4.5' Dense, moist, gray, silty SAND with gravel (glacial till) Bottom of pit at 4.5 feet on 10/8/2018. No ground water. No caving. EP-3 Approximate elevation 403 feet. 0.0' — 0.3' Grass sod and organic topsoil 0.3' — 5.0' Very loose, dry, brown, silty SAND with gravel and probable ash (fill) 5.0'— 7.0' Loose, moist, brown, silty SAND (fill or recessional outwash) Bottom of pit at 7.0 feet on 10/8/2018. No ground water. Moderate caving throughout pit. Surrounding ground loose and very spongy with many fine organics to a depth of 3 feet. EP-4 Approximate elevation 403 feet. 0.0' 2.0' Very loose, dry, brown, silty SAND with occasional gravel (fill) 2.0' — 3.0' Loose, dry, brown, gravelly SAND with silt (recessional outwash) Bottom of pit at 3 feet on 10/8/2018. No ground water. Moderate caving. Gary A. Flowers, PLLC. 5205 23" Avenue W Everett, Washington 98203 206-819-4304 Rnk Eastside, LLC Property Geotechnical Services Report 23830 Edmonds Way, Edmonds Washington EP-5 Approximate elevation 402 feet. Off— 3.0' Very loose, dry, brown, silty SAND with occasional gravel and ash (fill) 3.0' — 6.0' Loose, dry, brown, fine to medium SAND with gravel, trace silt (recessional outwash) Bottom of pit at 6 feet on 10/8/2018. No ground water. Moderate caving. Gary A. Flowers, PLLC. 5205 23" Avenue W Everett, Washington 98203 206-819-4304 9 THE NW 1/4 OF THE SW 1/4 OF SEC. 31, T 27 N., R 4E. 00I \ \ \ \ \ \ \ IN, \ \ \ \ \ IN, \ \ \ \ IN, I \ I \ T� ACT TR I 3 ti� N 10 CB I \\ \ RIM 393.64 IE(14") 389.31 SE -NW \ IE(8") 389.91 SW EX. SSMH\ \ \� RIM 395.15 CP \\ I s\ IE(MC) 388.1�\� \ I I 5.5' \ I / / I � \ s I � s\ 2.4 \ � \ 6 4 \ ` 41 4010 96 / ro \ l; \ /011 S.F.R. �,J� A \ s1952 Av \ ±SQ.ET. �J, ,' �` / o AD 1 I '� 402-241L- �V A / 6.6' 0.7' S.F.R. \q---------------- ----' \ \' s 964 BUILDING / 12 1 516 _ 8. o ( I r —� I / — 6' WOOD FENC N89"44'52"E 255.96' ( \ \ FENCE CRN. 9.5' \ 6.�' 3.5' W, 0.6' N \ 77//77/7/� s /moo SDMW RIM RIM 398.32 IE(24") 388.32 NE -SE IE(MC; IE(12") 390.28 SW I I I I I I I I I , I I I I I SITE 16,957 sq.ft.± 0.38 Acr± 20' 0 20' 40' 1 "= 20' Scale Feet APPROVED FOR CONSTRUCTION CITY OF EDMONDS DATE: z 0 Cn W W In m� m '2 41 in '0 d � 4) N 'y m > I oX a Z p Z a p� . a U� Q 0 a N d 0 ofz m 00 T 1 v M N z O C> N N 0 �i I N II 2 1 > 1W (L N 01 U 0 0) C C ° m 3 E0) � rn 3N N LL �} 0 a W U 01 •o = C 10 v U CL � LO <n v > a 3 LL m 10 00 0 z Y > W O Ix z O W rn Y � C W Z ao z W rn z p n Z V co 0 C W N W Z L�J Z 0 0 0 Z W x W C 1.2 Know what's below. Call before you dig. R:\Projects\410 (LZG Construction)\002-18 (Edmonds Apt)\Dwg\sheets\EW-exO1.dwg 36x24 AIM CITY ENGINEERING DIVISION SECTION 2 CONSTRUCTION STORMWATER POLLUTION PREVENTION (Minimum Requirement #2) Edmonds Apartments Drainage Report CSWPPP ANALYSIS & DESIGN This section, along with the Temporary Erosion and Sediment Control (TESC) Plan contained in the engineering drawings, is intended to serve as the construction Stormwater Pollution Prevention Plan (SWPPP) for the project. The SWPPP is outlined in conformance with the Washington State Department of Ecology's Stormwater Management Manual for Western Washington (DOE Manual). 1.0 — INTRODUCTION An introductory overview of the project has been provided in the Executive Summary of this report. 2.0 — SITE DESCRIPTION A general site description has been provided in the Executive Summary of this report. Additional detailed information is provided through the rest of this report. 3.0 — CONSTRUCTION STORMWATER BMPs 3.1 — 12 BMP ELEMENTS Element #1— Mark Clearing Limits To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land -disturbing activities begin. Trees that are to be preserved, as well as all sensitive areas and their buffers, shall be clearly delineated, both in the field and on the plans. In general, natural vegetation and native topsoil shall be retained in an undisturbed state to the maximum extent possible. The BMPs relevant to marking the clearing limits are identified in Appendix 2B. Alternate BMPs for marking clearing limits are included in Appendix 2C as a quick reference tool for the onsite inspector in the event the primary BMPs) are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix 2D). To avoid potential erosion and sediment control issues that may cause a violation of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. Element #2 — Establish Construction Access Construction access or activities occurring on unpaved areas shall be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads, and wheel washing, street sweeping, and street cleaning shall be employed to prevent sediment from entering state waters. All wash wastewater shall be controlled on site. The specific BMPs related to establishing construction access that will be used on this project are identified in Appendix 2B. Alternate construction access BMPs are included in Appendix 2C as a quick reference tool for the onsite inspector in the event the primary BMP(s) are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix 2D). To avoid potential erosion and sediment control issues that may cause a violation of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. Edmonds Apartments Drainage Report Element #3 - Control Flow Rates In order to protect the properties and waterways downstream of the project site, stormwater discharges from the site will be controlled. The specific BMPs for flow control that shall be used on this project are identified in Appendix 2B. Alternate flow control BMPs are included in Appendix 2C as a quick reference tool for the onsite inspector in the event the primary BMP(s) are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit. To avoid potential erosion and sediment control issues that may cause a violation of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. In general, discharge rates of stormwater from the site will be controlled where increases in impervious area or soil compaction during construction could lead to downstream erosion, or where necessary to meet local agency stormwater discharge requirements (e.g. discharge to combined sewer systems). Element #4 - Install Sediment Controls All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP before leaving the construction site or prior to being discharged to an infiltration facility. The specific BMPs to be used for controlling sediment on this project are identified in Appendix 2B. Alternate sediment control BMPs are included in Appendix 2C as a quick reference tool for the onsite inspector in the event the primary BMP(s) are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix 2D). To avoid potential erosion and sediment control issues that may cause a violation of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs at the first sign that existing BMPs are ineffective or failing. In addition, sediment will be removed from paved areas in and adjacent to construction work areas manually or using mechanical sweepers, as needed, to minimize tracking of sediments on vehicle tires away from the site and to minimize wash off of sediments from adjacent streets in runoff. Whenever possible, sediment laden water shall be discharged into onsite, relatively level, vegetated areas (BMP C240 paragraph 4, Volume II page 116). In some cases, sediment discharge in concentrated runoff can be controlled using permanent stormwater BMPs (e.g., infiltration swales, ponds, trenches). Sediment loads can limit the effectiveness of some permanent stormwater BMPs, such as those used for infiltration or biofiltration; however, those BMPs designed to remove solids by settling (wet ponds or detention ponds) can be used during the construction phase. When permanent stormwater BMPs will be used to control sediment discharge during construction, the structure will be protected from excessive sedimentation with adequate erosion and sediment control BMPs. Any accumulated sediment shall be removed after construction is complete and the permanent stormwater BMP will be restabilized with vegetation per applicable design requirements once the remainder of the site has been stabilized. Edmonds Apartments Drainage Report Element #5 - Stabilize Soils Exposed and unworked soils shall be stabilized with the application of effective BMPs to prevent erosion throughout the life of the project. The specific BMPs for soil stabilization that shall be used on this project are identified in Appendix 2B. Seeding will be used on disturbed areas that have reached final grade or that will remain unworked for more than thirty days. Plastic Covering will be used on the temporary stock pile areas and elsewhere on the site as needed. Dust control will be implemented as needed, to prevent it being required all roadways and driveways to be paved will receive early application of gravel base. Alternate soil stabilization BMPs are included in Appendix 2C as a quick reference tool for the onsite inspector in the event the primary BMP(s) are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix 2D). To avoid potential erosion and sediment control issues that may cause a violation of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. The project site is located west of the Cascade Mountain Crest. As such, no soils shall remain exposed and unworked for more than 7 days during the dry season (May 1 to September 30) and 2 days during the wet season (October 1 to April 30). Regardless of the time of year, all soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on weather forecasts. In general, cut and fill slopes will be stabilized as soon as possible and soil stockpiles will be temporarily covered with plastic sheeting. All stockpiled soils shall be stabilized from erosion, protected with sediment trapping measures, and where possible, be located away from storm drain inlets, waterways, and drainage channels. Element #6 - Protect Slopes All cut and fill slopes will be designed, constructed, and protected in a manner than minimizes erosion. The specific BMPs that will be used to protect slopes for this project are identified in Appendix 2B. Alternate slope protection BMPs are included in Appendix 2C as a quick reference tool for the onsite inspector in the event the primary BMP(s) are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix 2D). To avoid potential erosion and sediment control issues that may cause a violation of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. Element #7 - Protect Drain Inlets All storm drain inlets and culverts made operable during construction shall be protected to prevent unfiltered or untreated water from entering the drainage conveyance system. However, the first priority is to keep all access roads clean of sediment and keep street wash water separate from entering storm drains until treatment can be provided. Storm Drain Inlet Protection (BMP C220) will be implemented for all drainage inlets and culverts that could potentially be impacted by sediment -laden runoff on and near the project site. The inlet protection measures to be applied on this project are identified in Appendix 2B. Edmonds Apartments Drainage Report If the primary BMP options are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix 2D), or if no BMPs are listed above but deemed necessary during construction, the Certified Erosion and Sediment Control Lead shall implement one or more of the alternative BMP inlet protection options. Element #8 - Stabilize Channels and Outlets Where site runoff is to be conveyed in channels, or discharged to a stream or some other natural drainage point, efforts will be taken to prevent downstream erosion. The specific BMPs for channel and outlet stabilization that shall be used on this project are identified in Appendix 2B. Alternate channel and outlet stabilization BMPs are included in Appendix 2C as a quick reference tool for the onsite inspector in the event the primary BMP(s) are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix 2D). To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. The project site is located west of the Cascade Mountain Crest. As such, all temporary on - site conveyance channels shall be designed, constructed, and stabilized to prevent erosion from the expected peak 10 minute velocity of flow from a Type 1A, 10-year, 24-hour recurrence interval storm for the developed condition. Alternatively, the 10-year, 1-hour peak flow rate indicated by an approved continuous runoff simulation model, increased by a factor of 1.6, shall be used. Stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches shall be provided at the outlets of all conveyance systems. Element #9 - Control Pollutants All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well -organized, and free of debris. Any required BMPs to be implemented to control specific sources of pollutants are identified in Appendix 2B. The contractor shall implement the following measures as much as is practicable, in order to mitigate pollutant impacts from vehicles, construction equipment, and/or petroleum product storage/dispensing: • All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills. • On -site fueling tanks and petroleum product storage containers shall include secondary containment. • Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. • In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle. Edmonds Apartments Drainage Report • Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. • The contractor shall implement the following concrete and grout pollution control measures: • Process water and slurry resulting from concrete work will be prevented from entering the waters of the State by implementing Concrete Handling measures (BMP C151). The contractor shall implement the following Solid Waste pollution control measures: • Solid waste will be stored in secure, clearly marked containers. Element #10 - Control Dewatering Foundation, vault, and trench de -watering water, which shall have similar characteristics to stormwater runoff at the site, shall be discharged into a controlled conveyance system prior to discharge to a sediment trap, pond, or other specified facility. Channels must be stabilized as specified in Element #8. Clean, non -turbid de -watering water, such as well -point groundwater, can be discharged to systems tributary to state surface waters, provided the de -watering flow does not cause erosion or flooding of receiving waters. These clean waters should not be routed through stormwater sediment ponds. Highly turbid or contaminated dewatering water shall be handled separately from stormwater. Element #11 - Maintain BMPs All BMPs should be monitored and maintained regularly to ensure adequate operation. A TESC supervisor shall be identified at the beginning of the project to provide monitoring and direct the appropriate maintenance activity. As site conditions change, all BMPs shall be updated as necessary to maintain compliance with local regulations. Temporary BMPs can be removed when they are no longer needed. All temporary erosion and sediment control BMPs shall be removed within 30 days after construction is completed and the site is stabilized. Element #12 - Manage the Project Erosion and sediment control BMPs for this project have been designed based on the following principles: • Design the project to fit the existing topography, soils, and drainage patterns. • Emphasize erosion control rather than sediment control. • Minimize the extent and duration of the area exposed. • Keep runoff velocities low. • Retain sediment on site. • Thoroughly monitor site and maintain all ESC measures. Edmonds Apartments Drainage Report • Schedule major earthwork during the dry season. As this project site is located west of the Cascade Mountain Crest, the project will be managed according to the following key project components: Phasina of Construction • The construction project is being phased to the extent practicable in order to prevent soil erosion, and, to the maximum extent possible, the transport of sediment from the site during construction. • Revegetation of exposed areas and maintenance of that vegetation shall be an integral part of the clearing activities during each phase of construction, per the Scheduling BMP (C 162). Seasonal Work Limitations • From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted if shown to the satisfaction of the local permitting authority that silt - laden runoff will be prevented from leaving the site through a combination of the following: o Site conditions including existing vegetative coverage, slope, soil type, and proximity to receiving waters; and o Limitations on activities and the extent of disturbed areas; and o Proposed erosion and sediment control measures. • Based on the information provided and/or local weather conditions, the local permitting authority may expand or restrict the seasonal limitation on site disturbance. • The following activities are exempt from the seasonal clearing and grading limitations: o Routine maintenance and necessary repair of erosion and sediment control BMPs; o Routine maintenance of public facilities or existing utility structures that do not expose the soil or result in the removal of the vegetative cover to soil; and o Activities where there is 100 percent infiltration of surface water runoff within the site in approved and installed erosion and sediment control facilities. Coordination with Utilities and Other Jurisdictions • Care has been taken to coordinate with utilities, other construction projects, and the local jurisdiction in preparing this SWPPP and scheduling the construction work. Inspection and Monitorina All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Site inspections shall be conducted by a person who is knowledgeable in the principles and practices of erosion and sediment control. This person has the necessary skills to: o Assess the site conditions and construction activities that could impact the quality of stormwater, and o Assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. Edmonds Apartments Drainage Report • A Certified Erosion and Sediment Control Lead shall be on -site or on -call at all times. • Whenever inspection and/or monitoring reveals that the BMPs identified in this SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, appropriate BMPs or design changes shall be implemented as soon as possible. Maintaining an Updated Construction SWPPP • This SWPPP shall be retained on -site or within reasonable access to the site. • The SWPPP shall be modified whenever there is a change in the design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state. • The SWPPP shall be modified if, during inspections or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) days following the inspection. 3.2 — SITE SPECIFIC BMPs Site specific BMPs are shown on the TESC plan sheet(s) in Appendix 2A. 4.0 — CONSTRUCTION PHASING AND BMP IMPLEMENTATION The BMP implementation schedule will be driven by the construction schedule. The list below provides an estimate of the anticipated construction schedule. The project site is located west of the Cascade Mountain Crest. As such, the dry season is considered to be from May 1 to September 30, and the wet season is considered to be from October 1 to April 30. 5.0 — POLLUTION PREVENTION TEAM 5.1 ROLES AND RESPONSIBILITIES The pollution prevention team consists of personnel responsible for implementation of the SWPPP, including the following: • Certified Erosion and Sediment Control Lead (CESCL) — primary contractor contact, responsible for site inspections (BMPs, visual monitoring, sampling, etc.); to be called upon in case of failure of any ESC measures. • Resident Engineer — For projects with engineered structures only (sediment ponds/traps, sand filters, etc.): Site representative for the owner that is the project's supervising engineer responsible for inspections and issuing instructions and drawings to the contractor's site supervisor or representative. • Emergency Ecology Contact — Individual to be contacted at Ecology in case of emergency. • Emergency Owner Contact — Individual that is the site owner or representative of the site owner to be contacted in the case of an emergency. • Non -Emergency Ecology Contact — Individual that is the site owner or representative of the site owner that can be contacted if required. Edmonds Apartments Drainage Report • Monitoring Personnel — Personnel responsible for conducting water quality monitoring; for most sites this person is also the CESCL. 5.2 TEAM MEMBERS Names and contact information for those identified as members of the pollution prevention team are provided in the project summary in Appendix 213. 6.0 — SITE INSPECTIONS AND MONITORING Monitoring includes visual inspection, monitoring for water quality parameters of concern, and documentation of the inspection and monitoring findings in a site log book. A site log book will be maintained for all on -site construction activities and will include: A record of the implementation of the SWPPP and other permit requirements; Site inspections; and, Stormwater quality monitoring. For convenience, the inspection forma and water quality monitoring forms included in Appendix 2E of this report include the required information for the site log book. This SWPPP may function as the site log book, if desired, or the forms may be separated and included in a separate site log book. However, if separated, the site log book must be maintained on -site or within reasonable access to the site and be made available upon request to Ecology or the local jurisdiction. 6.1 SITE INSPECTION All BMPs will be inspected, maintained, and repaired as needed to assure continued performance of their intended function. The inspector will be a Certified Erosion and Sediment Control Lead (CESCL) per BMP C160. The name and contact information for the CESCL is provided in Section 5 of this SWPPP. Site inspection will occur in all areas disturbed by construction activities and at all stormwater discharge points. Stormwater will be examined for the presence of suspended sediment, turbidity, discoloration, and oily sheen. The site inspector will evaluate and document the effectiveness of the installed BMPs and determine if it is necessary to repair or replace any of the BMPs to improve the quality of stormwater discharges. All maintenance and repairs will be documented in the site log book or forms provided in this document. All new BMPs or design changes will be documented in the SWPPP as soon as possible. 6.1.1 Site Inspection Frequency Site inspections will be conducted at least once a week and within 24 hours following any rainfall event which causes a discharge of stormwater from the site. For sites with temporary stabilization measures, the site inspection frequency can be reduced to once every month. 6.1.2 Site Inspection Documentation The site inspector will record each site inspection using the site log inspection forms provided in Appendix 2E. The site inspection log forms may be separated from this SWPPP document, but will be maintained on -site or within reasonable access to the site and be made available upon request to Ecology or the local jurisdiction. Edmonds Apartments Drainage Report 6.2 Stormwater Quality Monitoring 6.2.1 Turbidity Sampling Monitoring requirements for the proposed project will include turbidity sampling to monitor site discharges for water quality compliance with the 2010 Snohomish County Drainage manual and Snohomish County Code Title 30.63A NPDES Construction Stormwater General Permit (Appendix 2D). Sampling will be conducted at all site discharge points at least once per calendar week. Turbidity monitoring will follow the analytical methodologies described in Section S4 of the 2005 Construction Stormwater General Permit (Appendix 2D). The key benchmark values that require action include 25 NTU and 250 NTU for turbidity. If the 25 NTU benchmark for turbidity is exceeded, the following steps will be conducted: 1. Ensure all BMPs specified in this SWPPP are installed and functioning as intended. 2. Assess whether additional BMPs should be implemented and make revisions to the SWPPP as necessary. 3. Sample the discharge location daily until the analysis results are less than 25 NTU (turbidity) or 32 cm (transparency). If the turbidity is greater than 25 NTU but less than 250 NTU for more than 3 days, additional treatment BMPs will be implemented within 24 hours of the third consecutive sample that exceeded the benchmark value. Additional treatment BMPs will include, but are not limited to, off -site treatment, infiltration, filtration and chemical treatment. If the 250 NTU benchmark for turbidity is exceeded at any time, the following steps will be conducted: 1. Notify Ecology by phone within 24 hours of analysis. 2. Continue daily sampling until the turbidity is less than 25 NTU. 3. Initiate additional treatment BMPs such as off -site treatment, infiltration, filtration and chemical treatment within 24 hours of the first 250 NTU exceedance. 4. Implement additional treatment BMPs as soon as possible, but within 7 days of the first 250 NTU exceedance. 5. Describe inspection results and remedial actions that are taken in the site log book and in monthly discharge monitoring reports. 6.2.2 pH Sampling Stormwater runoff will be monitored for pH starting on the first day of any activity that includes more than 40 yards of poured or recycled concrete, or after the application of "Engineered Soils" such as, Portland cement treated base, cement kiln dust, or fly ash. This does not include fertilizers. For concrete work, pH monitoring will start the first day concrete is poured and continue until 3 weeks after the last pour. For engineered soils, the pH monitoring period begins when engineered soils are first exposed to precipitation and continue until the area is fully stabilized. Edmonds Apartments Drainage Report Stormwater samples will be collected daily from all points of discharge from the site and measured for pH using a calibrated pH meter, pH test kit, or wide range pH indicator paper. If the measured pH is 8.5 or greater, the following steps will be conducted: 1. Prevent the high pH water from entering storm drains or surface water. 2. Adjust or neutralize the high pH water if necessary using appropriate technology such as CO2 sparging (liquid or dry ice). 3. Contact Ecology if chemical treatment other than CO2 sparging is planned. 7.0 — REPORTING AND RECORDKEEPING 7.1 RECORDKEEPING 7.1.1 Site Log Book A site log book will be maintained for all on -site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements; • Site inspections; and, • Stormwater quality monitoring. For convenience, the inspection form and water quality monitoring forms included in Appendix 2E of this report include the required information for the site log book. 7.1.2 Records Retention Records of all monitoring information (site log book, inspection reports/checklists, etc.), this Stormwater Pollution Prevention Plan, and any other documentation of compliance with permit requirements will be retained during the life of the construction project and for a minimum of three years following the termination of permit coverage in accordance with permit condition S5.C. 7.1.3 Access to Plans and Records The SWPPP, General Permit, Notice of Authorization letter, and Site Log Book will be retained on site or within reasonable access to the site and will be made immediately available upon request to Ecology or the local jurisdiction. A copy of this SWPPP will be provided to Ecology within 14 days of receipt of a written request for the SWPPP from Ecology. Any other information requested by Ecology will be submitted within a reasonable time. A copy of the SWPPP or access to the SWPPP will be provided to the public when requested in writing in accordance with permit condition S5.G. 7.1.4 Updating the SWPPP In accordance with Conditions S3, S4.13, and S9.B.3 of the General Permit, this SWPPP will be modified if the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site or there has been a change in design, construction, operation, or maintenance at the site that has a significant effect on the discharge, or potential for discharge, of pollutants to the waters of the State. The SWPPP will be modified within seven days of determination based on inspection(s) that Edmonds Apartments Drainage Report additional or modified BMPs are necessary to correct problems identified, and an updated timeline for BMP implementation will be prepared. 7.2 REPORTING 7.2.1 Discharge Monitoring Reports Discharge Monitoring Report (DMR) forms will not be submitted to Ecology because water quality sampling is not being conducted at the site. 7.2.2 Notification of Noncompliance If any of the terms and conditions of the permit are not met, and it causes a threat to human health of the environment, the following steps will be taken in accordance with permit section S5.F: 1. Ecology will be immediately notified of the failure to comply. 2. Immediate action will be taken to control the noncompliance issue and to correct the problem. If applicable, sampling and analysis of any noncompliance will be repeated immediately and the results submitted to Ecology within five (5) days of becoming aware of the violation. 3. A detailed written report describing the noncompliance will be submitted to Ecology within five (5) days, unless requested earlier by Ecology. In accordance with permit condition S2.A, a complete application form will be submitted to Ecology and the appropriate local jurisdiction (if applicable) to be covered by the General Permit. Edmonds Apartments Drainage Report APPENDIX 2A SITE PLAN WITH BMP MEASURES Edmonds Apartments Drainage Report \ I \ P/ �pT S CB`�� \ / RIM 393.64 I ��W'•'�L��♦♦ \ IE(14") 389.31 SE -NW �'�.♦♦ \ IE(8") 38991 SW� II / 902 TEMPORARY SEDIMENT TRAP / / - FOR CATCH BASINS TYP / / / I /# I / / \ \w 6.6' /f 900 FILfER FABRIC FENCs - F TRATION SYSTEMS / \ I12�` BULL LNG / 51 ±SQ. T. 8.0' - / -� I FENCE CRRN 3.5' W, 0.6' N 2' v 2' WOOD/STEEL FlLTER FABRIC SECURED TOrxr 14 CA WIRE FABRIC EQUAL 4 NATIVE BACKFlU, MTERW. I e. USE STAPLESIFFOORR TIIIWIRE RINGS TO -ACH FABRIC TO WIRE 2' • 2' wOOD/SiUL POSTS .1 rWIPLA E MESH FENCE Q tT0 SUPPORT FILTER FABRIC '6 BURY �TTUM OF FILLER IMTERUL B' TO 12" 1. CONIMCTOP/OEVELOPER SHALL MMNTNN MID ENSURE PROPER EROSION COMMI, THROUGHOUT PROTECT. CRY INSPECTION RELIUIRED ON 2. SILT FENCE TO BE FLACED DOWNSUME OF CONSTRUCTION ALL EROSION CONTROL METHODS AcmTrr, BEFORE OTHER WORI( CAN BEGIN REVISION ROTE CITY OF EDMONDSLFILTEFABRIC FENCEION SYSTEMS PUBLIC WORKS STANDARD DEPARTMENT DETAIL Es r89° R. ENGUSH ER-900 �L S.F.R. 1952 ±SQ.FT. THE NW 1/4 OF THE SW 1/4 OF SEC. 31, T 27 N., R 4E. \wm I AG TS�'VO "0 \ \ O `\\ EX. SMS H \ \w '9� RIM 395.1��\ \ IE(MC) 388.1 \ ate\ .. ( \ \ \ y�\ �♦ a\`` a \`4AO b61 . ' \♦♦ s9 � \�♦ \ RAJ � \ \ / IS.F.R. / 964 / tSQ.FT. I STOCKPILE aa LOCATION 255.98' I el DETAIL NOTES: 1O TIE MINIMUM UEI*CM S14WL BE EXTENDED AS NECESE— TO ENSURE MTERUL R NOT TRACKED OFF SITE AND/OR INTO THE PUBIJC RIGHT-CF-WAY. O2 ATB OPNEW'AY WIMP AND/OR SITE ACCEBS ROAD 15' WICE MIN. SEE TRBIE NOTES: BELOW FOR REQUIRED I.ENGM. 1. SURFACE WATER -ALL SURFACE WATER FLOWING OR DNERTED TOWARD CONSTRUCTION ENTRANCES SHALL BE PIPED ACROSS TIE EMMMICE. IF PIPING IS IMPPAC11T1L, A MOUN-BLE BERM WIM 5:1 SLOPES WILL BE PERMRIED. 2. MNNTE— - ME ENTRANCE SHALL BE —NED IN A CONDRION WHICH WILL PREVENT TUCKING OR FLOWING OF SEDIMENT OFF SITE AND/OR ONTO PUSUC RIGHT-OF-WAY. THIS MAY REQUIRE PERIODIC TOP DRESSING WRH ADOIIIDNAL QUARRY SPACES AS CONDITIONS DEMAND AND REPAIR AND/OR CLEANOUT OF PLAY MEASURES USED TO TRAP SEDIMENT. ALL SEIMENT SPI—i CROPPED, —NED OR TRACKED RIGHT-OF-WAY MUST BE REMOVED IMMEDIATELY. OFF SITE AND/OR dR0 PUB= 3. WHEELS SHNL BE C-NEO TO REMCVE SEDIMENT PRIOR TO LEAVING ME BE DONE ON M AREA STABIUZED WM WMRY SE—S AND WHICH DRNNS DEVIOE 4. INSPECTION MID NEEDED MNHTENANCE SHALL BE PROVIDED AFTER EACH SRE. WHEN WASHING IS USED, IT SHALL INTO AN APPROVID SEDIMENT TRAPPING MIN. PROJECT MIN "" M OF (FEET) •PROWDE AM OR ASPHALT SIZE QUARRY SPALL9 TRANSITION WHERE FRONTAGE < 1/4 ACRE 30 ROMD IS AN ARIE - IENGTx TO BE OEIERMINED 1 AORE SO BY CTTY INSPECTOR. CITY INSPECTION RELIUIRED ON < S ACRE 1. ALL EROSION CONTROL METHODS > 3 IDRE 1. BEFORE OTHER WORT( CAN BEGIN REVISION M1E CITY OF EDMONDS STABILIZED CONSTRUCTION JAHUARr tole ENTRANCE PUBLIC WORKS STANDARD DEPARTMENT DETAIL �sr, 189° APPROVED BY: R. ENGMSH ER-901 STABILIZED CONSTRUCTION ENTRANCE -----xxx----- EXISTING CONTOUR w - - PROPERTY LINE o - - - - - - - - - N CLEARING/GRADING LIMITS w FILTER FABRIC FENCE D: X X X X X X X EX. STRUCTURE TO BE REMOVED ❑ SEDIMENT TRAP FOR CATCH BASIN NOTE INSTALL AND MAINTAIN ALL TESC MEASURES ACCORDING TO APPROVED PLANS, CITY OF EDMONDS STANDARD DETAILS, AND ALL OTHER MEASURES THAT MAY BE REQUIRED DURING CONSTRUCTION. I i I GMIE FlLTER SOLK WDN ��JJ/ OVER ROW H0I&S mP) CA1DH BASIN �/ `CATCH &SINNOTES- 1 CON—CTOR,lDEVELOPER SWYL MAINTNN THIS MPL1— N AT A TIMES DURING CONSTRUCTION PERIOD. 2. ANY SEDIMENT IN CATCH BASIN INSERT SNNL BE REMOVED WHEN INSERT IS ONE -VITRO NLL 3. CITY INSPECTION REQUIRED ON ALL EROSION COTTROL METHODS BEFORE OTHER WORK CAN BEGIN. TEMPORARYS CITY OF EDMONDS EDIMENT TRAP PUBLIC WORKS FOR CATCH BASINS HER-902 DEPARTMENT APPROVED BY: R. ENGUSX 15. Know what's below. Call before you m �11- u a • a I yzo3 U 3 < I: o I0 alz O W D Z x ME m h W Z m > O1 F < = 3 � y ~ < a n m O Z m W U E// H��\\i a r Z SW L W Q Q J Cl- a N Q u V /Q V / (1) cl W ~ Z 20' 0 20' 40, Q 1'= 20 CC Scale Feet G APPROVED FOR CONSTRUCTION W CITY OF EDMONDS DATE: BY: CITY ENGINEERING DIVISION C2.0 m APPENDIX 2B SWPPP PROJECT SUMMARY Edmonds Apartments Drainage Report PROJECT TEAM MEMBERS: Title Certified Erosion & Sediment Control Lead Name(s) Phone Number Resident Engineer Bill Helsley (425) 486-6533 Emergency Ecology Contact Puget Sound Office (425) 649-7000 Emergency Owner Contact Non -Emergency Ecology Contact Northwest Region (425) 649-7000 Monitoring Personnel ESTIMATED CONSTRUCTION SCHEDULE: • Construction Start Date TBD • Install ESC Measures TBD • Construction End Date TBD CONSTRUCTION BMP LIST: • High Visibility Plastic or Metal Fence (BMP C103) • Temporary and Permanent Seeding (BMP C120) • Plastic Covering (BMP C123) • Topsoiling (BMP C125) • Dust Control (BMP C140) • Materials on Hand (BMP C150) • Interceptor Dike and Swale (BMP C200) • Check Dams (BMP C207) • Storm Drain Inlet Protection (BMP C220) • Silt Fence (BMP C233) • Straw Wattles (BMP C235) • Detention Pond Or Vault Edmonds Apartments Drainage Report APPENDIX 2C ALTERNATIVE BMPs Edmonds Apartments Drainage Report The following includes a list of possible alternative BMPs for each of the 12 elements not described in the main SWPPP text. This list can be referenced in the event a BMP for a specific element is not functioning as designed and an alternative BMP needs to be implemented. Element #1 - Mark Clearing Limits • High Visibility Plastic or Metal Fence (BMP C103) Element #2 - Establish Construction Access • Wheel Wash (BMP C106) Element #3 - Control Flow Rates • (none) Element #4 - Install Sediment Controls • Straw Bale Barrier (BMP C230) • Vegetated Strip (BMP C234) • Materials on Hand (BMP C150) Element #5 - Stabilize Soils • Dust Control (BMP C140) • Topsoiling (BMP C125) • Sodding (BMP C124) Element #6 - Protect Slopes • Straw Wattles (BMP C235) • Grass -Lined Channels (BMP C201) Element #7 - Protect Drain Inlets • (none) Element #8 - Stabilize Channels and Outlets • Level Spreader (BMP C206) Element #10 - Control Dewatering • (none) Edmonds Apartments Drainage Report APPENDIX 2D GENERAL PERMIT Edmonds Apartments Drainage Report Construction Stormwater General Permit The project proposes a disturbance less than 1-acre, so a DOE Construction Stormwater General Permit is not required. Edmonds Apartments Drainage Report APPENDIX 2E SITE LOG & INSPECTION FORMS Edmonds Apartments Drainage Report Site Inspection Forms (and Site Lo The results of each inspection shall be summarized in an inspection report or checklist that is entered into or attached to the site log book. It is suggested that the inspection report or checklist be included in this appendix to keep monitoring and inspection information in one document, but this is optional. However, it is mandatory that this SWPPP and the site inspection forms be kept onsite at all times during construction, and that inspections be performed and documented as outlined below. At a minimum, each inspection report or checklist shall include: a. Inspection date/times b. Weather information: general conditions during inspection, approximate amount of precipitation since the last inspection, and approximate amount of precipitation within the last 24 hours. c. A summary or list of all BMPs that have been implemented, including observations of all erosion/sediment control structures or practices. d. The following shall be noted: i. Locations of BMPs inspected, ii. Locations of BMPs that need maintenance, iii. The reason maintenance is needed iv. Locations of BMPs that failed to operate as designed or intended, and V. Locations where additional or different BMPs are needed, and the reason(s) why. e. A description of stormwater discharged from the site. The presence of suspended sediment, turbid water, discoloration, and/or oil sheen shall be noted, as applicable. f. A description of any water quality monitoring performed during inspection, and the results of that monitoring. g. General comments and notes, including a brief description of any BMP r repairs, maintenance or installations made as a result of the inspection. h. A statement that, in the judgment of the person conducting the site inspection, the site is either in compliance or out of compliance with the terms and conditions of the SWPPP and the NPDES permit. If the site inspection indicates that the site is out of compliance, the inspection report shall include a summary of the remedial actions required to bring the site back into compliance, as well as a schedule of implementation. i. Name, title, and signature of person conducting the site inspection; and the following statement: "I certify under penalty of law that this report is true, accurate, and complete, to the best of my knowledge and belief'. When the site inspection indicates that the site is not in compliance with any terms and conditions of the NPDES permit, the Permittee shall take immediate action(s) to: stop, contain, and clean up the unauthorized discharges, or otherwise stop the noncompliance; correct the problem(s); implement appropriate Best Management Practices (BMPs), and/or conduct maintenance of existing BMPs; and achieve compliance with all applicable standards and permit conditions. In addition, if the noncompliance causes a threat to human health or the environment, the Permittee shall comply with the Noncompliance Notification requirements in Special Condition S5.F of the permit. Edmonds Apartments Drainage Report Site Inspection Form General Information Project Name: Inspector Name: Title: CESCL # : Date: Time: Inspection Type: ❑ After a rain event ❑ Weekly ❑ Turbidity/transparency benchmark exceedance ❑ Other Weather Precipitation Since last inspection In last 24 hours Description of General Site Conditions: Inspection of BMPs Element 1: Mark Clearing Limits BMP: Location Inspected Functionin Problem/Corrective Action Y I N I Y N NIP :�►VAI9 Location Inspected YunNtio ing Problem/Corrective Action NIP Element 2: Establish Construction Access BMP: Location Inspected Functi ning Problem/Corrective Action Y N Y N NIP Location Inspected ing Problem/Corrective Action YunNtio NIP Edmonds Apartments Drainage Report Element 3: Control Flowrates BMP: Location Inspected Functionin Problem/Corrective Action Y I N I Y N NIP 9M Location In Functioning Problem/Corrective Action lected NIP Element 4: Install Sediment Controls BMP: Location Inspected Functionin Problem/Corrective Action Y I N I Y N NIP Ma Location Inspected ing Problem/Corrective Action YunNtio NIP Element 5: Stabilize Soils BMP: Location Inspected Functionin Problem/Corrective Action Y I N I Y N NIP Ma Location Ins ing Problem/Corrective Action lected YunNtio NIP Edmonds Apartments Drainage Report Element 6: Protect Slopes BMP: Location Inspected Functionin Problem/Corrective Action Y I N I Y N NIP 9M Location In Functioning Problem/Corrective Action lected NIP Element 7: Protect Drain Inlets BMP: Location Inspected Functionin Problem/Corrective Action Y I N I Y N NIP Ma Location Inspected ing Problem/Corrective Action YunNtio NIP Element 8: Stabilize Channels and Outlets BMP: Location Inspected Functionin Problem/Corrective Action Y I N I Y N NIP Ma Location Ins ing Problem/Corrective Action lected YunNtio NIP Edmonds Apartments Drainage Report Element 9: Control Pollutants BMP: Location Inspected Functi ning Problem/Corrective Action Y N Y N NIP BMP: Location In ing Problem/Corrective Action lectevd Yunicvtio NIP Element 10: Control Dewatering BMP: Location Inspected Functioning Problem/Corrective Action Y N Y N NIP 2M Location In Funicvtio ing Problem/Corrective Action lectevd NIP Stormwater Discharges From the Site Observed? Problem/Corrective Action Y N Location Turbidity Discoloration Sheen Location Turbidity Discoloration Sheen Edmonds Apartments Drainage Report Water Quality Monitoring Was any water quality monitoring conducted? ❑ Yes ❑ No If water quality monitoring was conducted, record results here: If water quality monitoring indicated turbidity 250 NTU or greater; or transparency 6 cm or less, was Ecology notified by phone within 24 hrs? ❑ Yes ❑ No If Ecology was notified, indicate the date, time, contact name and phone number below: Date: Time: Contact Name: Phone #: General Comments and Notes Include BMP repairs, maintenance, or installations made as a result of the inspection. Were Photos Taken? ❑ Yes ❑ No If photos taken, describe photos below: Edmonds Apartments Drainage Report SECTION 3 SOURCE CONTROL OF POLLUTION (Minimum Requirement #3) Edmonds Apartments Drainage Report Source Control of Pollution The project is not classified as a high -use site, and no hazardous materials requiring source control BMPs are proposed to be stored on -site. Edmonds Apartments Drainage Report SECTION 4 PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND OUTFALLS (Minimum Requirement #4) Edmonds Apartments Drainage Report PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND OUTFALLS The project lies at a relative high point, and generally discharges runoff to the north and northwest. All runoff from the site can be expected to follow this topography and discharge runoff to Edmonds Way, along the northern edge of the site. The project proposal will collect on -site runoff, provide detention & treatment, then discharge to the public storm drainage system within Edmonds Way. The downstream flowpath beyond this point will be the same as it was prior to development. Edmonds Apartments Drainage Report SECTION 5 ON -SITE STORMWATER MANAGEMENT (Minimum Requirement #5) Edmonds Apartments Drainage Report Existing Site Hydrology The project site occupies a single drainage basin which flows northerly toward Edmonds Way. For hydrologic modeling purposes, the existing site conditions are assumed to be fully forested, to represent the historic conditions that existed prior to any previous development of the site. A map depicting the existing site hydrology is provided in Appendix 5A. Developed Site Hydrology The proposed development activity will involve site grading to accommodate the proposed apartment building, and associated driveways, parking areas, hardscape and landscape features. Surface runoff from the site will be collected via roof drains and catch basins and will be routed to an underground stormwater detention facility. That facility will ultimately discharge to the public storm drainage system within Edmonds Way. A map depicting the developed site conditions is provided in Appendix 5A. Performance Standards The project is required to provide stormwater management techniques consistent with Chapter 18.30 of the Edmonds Community Development Code (ECDC). This code generally adopts the 2014 Edition of the WA Dept. of Ecology's Stormwater Management Manual for Western Washington, with an addendum issued by the City dated 1/1/2017. These two documents will be referred to throughout this report as "DOE Manual" and "City Addendum", respectively. For Minimum Requirement #5, the City Addendum refers to Section 18.30.060.D.5 of the Edmonds Community Development Code (ECDC). This section of the ECDC identifies the project as a Category 2 project, since it will discharge to the public storm drainage system. As such, it is required to satisfy all nine minimum drainage requirements. It must also evaluate the feasibility of several low -impact stormwater management features, and implement them to the greatest practical extent. The required feasibility evaluation is provided below: Surface On -site BMP Feasibility Analysis Manual Reference Post -Construction Soil FEASIBLE - This BMP will be utilized by retaining the duff layer in an undisturbed state Lawn & Quality &Depth where no grading is needed. In areas where grading is expected to occur, the existing Landscape (BMP T5.13) topsoil shall be removed and stockpiled in a designated location, and reapplied to other portions of the site upon reaching the finished grade. Full Dispersion (BMP T5.30) NOT FEASIBLE — This BMP requires 65% of the site to be protected in a (BMP T5.30) native (forested) condition. This project site was previously cleared of native vegetation, and 65% of the site is not available to be set aside for dispersion. - or - —or— Downspout Full Roofs Infiltration (BMP T5.10A) NOT FEASIBLE — The portions of the site scheduled for development are (BMP T5.10A) underlain by a dense till soil unit which is not expected to support infiltration. NOT FEASIBLE — The underlying soil in the development area is identified as a till soil unit Bioretention which is not likely to support infiltration. With this in mind, the facility would require an (Vol. V, Ch. 7) underdrain to collect and convey runoff. The bioretention soil media allows percolation of runoff to the underdrain at a rate which does not provide any meaningful flow control benefit. Edmonds Apartments Drainage Report Downspout Dispersion NOT FEASIBLE — The project is incapable of providing a dedicated dispersion area due to (BMP T5.10B) site layout constraints. Perforated Stub -out NOT FEASIBLE —A perforated stub -out is considered infeasible, as it appears the project (BMP T5.10C) cannot provide the required 1-foot of separation to groundwater. Detention Vaults/Pipes FEASIBLE — Detention will be utilized on this project and is considered feasible. A detention discussion is provided in Section 7 of this report. Full Dispersion NOT FEASIBLE — This BMP requires 65% of the site to be protected in a native (forested) (BMP T5.30) condition. This project site was previously cleared of native vegetation, and 65% of the site is not available to be set aside for dispersion. Permeable Pavement NOT FEASIBLE — The portions of the site scheduled for development are underlain by a dense till soil unit which is not expected to support infiltration. NOT FEASIBLE — The underlying soil in the development area is identified as a till soil unit Bioretention which is not likely to support infiltration. With this in mind, the facility would require an (Vol. V, Ch. 7) underdrain to collect and convey runoff. The bioretention soil media allows percolation of runoff to the underdrain at a rate which does not provide any meaningful flow control Other Hard benefit. Surfaces Sheet Flow Dispersion (BMP T5.12) (BMP T5.12) NOT FEASIBLE — The project is incapable of providing a dedicated dispersion area due to site layout constraints. - or - —or— Concentration Flow Dispersion (BMP T5.12) NOT FEASIBLE — The project is incapable of providing a dedicated (BMP T5.11) dispersion area due to site layout constraints. Detention Vaults/Pipes FEASIBLE — A detailed stormwater detention design is discussed in Section 7 of this report. Edmonds Apartments Drainage Report APPENDIX 5A BASIN MAPPING Edmonds Apartments Drainage Report Y T m a U) 0 J Q 00 rn 0 N C ro U O LEGEND BASIN BOUNDARY \ I s \ 10o \S `b 402 \ No \\ ;1 \ ------------- ------------------------- \\� N TOTAL ON -SITE BASIN AREA = 17999 SF (0.41 AC) (ASSUME FULLY FORESTED) 0 20 1 "= 20' Scale Feet 4 MEOW \1 O R:\Projects\410 (LZG Construction)\002-18 (Edmonds Apt)\Dwg\figures\TIR Figures\EW—Predeveloped (KJM).dwg 11x17 O to U O I I I I I l 6 1� i Imo,♦,.,♦ % �� 11 ON -SITE BASIN SUMMARY N ROOF AREA (INCL. OVERHANGS) = 3948 SF (0.09 AC) PAVEMENT/WALKWAY AREA = 8466 SF (0.19 AC) TOTAL IMPERVIOUS AREA = 12414 SF (0.28 AC) LANDSCAPE/LAWN AREA = 5585 SF (0.13 AC) TOTAL ON —SITE BASIN AREA R:\Projects\410 (LZG Construction)\002-18 17999 SF (0.41 AC) 0 20 1 "= 20' Scale Feet monds Apt)\Dwg\figures\TIR Figures\EW—Developed (KJM).dwg 11x17 NKJ Design NKJ Drawn 6/28/1 g Date 410-002-18 Project No. ®®® civil Engineering Project Management Planning 1724 W. Marine View Drive, Suite 140; Everett, Washington 98201 Office:425A86.6533 Foc 425.486.6593 v w vsdoengineers.com EDMONDS APARTMENTS DEVELOPED BASIN MAP I sheet: 3 SECTION 6 RUNOFF TREATMENT (Minimum Requirement #6) Edmonds Apartments Drainage Report RUNOFF TREATMENT Surface runoff from the site will be collected and routed to an underground stormwater detention vault. The lower portion of this vault will contain a wetpool storage component intended to provide basic treatment, as prescribed by the DOE Manual. The primary goal of basic treatment is to remove sediment, and the wetpool storage acts as a plug -flow vessel, which provides sufficient residence time to promote settlement of suspended sediment prior to discharge. Sidewalks and roof areas are not typically considered to be pollution -generating surfaces if runoff from those surfaces can be separated from the rest of the site. However, runoff from this entire project site will be collected and routed to the underground stormwater vault. Since all site runoff will be combined prior to treatment, it is all considered to be from pollution -generating surfaces. Wetpool sizing calculations are included in the flow control calculations, provided in Appendix 7A of this report. A brief summary of the water quality treatment design parameters is provided below: Pollution -Generating Impervious Surface Area = 12,414-sf (0.28-ac) Pollution -Generating Pervious Surface Area = 5,585-sf (0.13-ac) Total Tributary Basin Area = 17,999-sf (0.41-ac) Required Wetpool Volume = Provided Wetpool Volume = 1,269-cf (see Appendix 7A) 7,296-cf (24' x 76' x 4') Edmonds Apartments Drainage Report SECTION 7 FLOW CONTROL (Minimum Requirement #7) Edmonds Apartments Drainage Report FLOW CONTROL The project is required to provide flow control mitigation for the project, as prescribed in the 2014 edition of the Stormwater Management Manual For Western Washington (SWMMWW), issued by the Washington State Department of Ecology. This is intended to protect downstream waterways and properties from flooding, erosion, and sedimentation. Surface runoff from the site will be collected and routed to an underground stormwater detention vault. The lower portion of this vault will contain a wetpool storage component, and the remainder of the vault will be utilized for stormwater detention. Prior to discharge from the underground vault, water will pass through a multiple -orifice flow -control riser, which is intended to release flows at rates and durations that approximately mimic those that existed historically. The project intends to collect all on -site runoff and convey it to the stormwater detention/treatment vault. The project will also involve frontage improvements, including the installation of a sidewalk, and a looped driveway to provide access to the site. The sidewalk will reside in the public right-of-way, but will be installed to slope toward the site (away from the fronting street), so that runoff from the sidewalk improvements can be managed on -site. There is currently no storm drainage system within the Edmonds Way right-of-way across the project's frontage, so all right-of-way runoff in the vicinity is currently conveyed along the existing flowline. The project intends to install a frontage conveyance system in order to provide a future drainage connection for a parcel to the south. With that in mind, the frontage conveyance improvements are considered to be an off -site utility improvement, which are not typically required to provide mitigation for flow control, per Vol. 1, Section 2.2 of the SWMMWW. This exemption in the SWMMWW is primarily intended for stand-alone utility projects which intend to replace the ground surface with in -kind material, however this project is managing all other on -site and frontage sidewalk, so the fronting drainage improvements are isolated from the rest of the project in that sense. Additionally, the City has indicated that the project frontage is already being managed by a separate off -site facility, so there does not appear to be a need to provide additional mitigation for those improvements. There will be a very small portion of new pavement at the entrance to the project which lies too low to be mitigated on - site, as well as a small portion of off -site sidewalk. However, those areas total less than 0.1-acres and are expected to have a negligible effect on the downstream drainage system, so it has not been incorporated into the project design. Stormwater detention pond and control riser design has been performed using MGS-Flood hydrologic modeling software. This software utilizes a locally -calibrated continuous runoff simulation, and is approved by the WA Dept. of Ecology for the design of stormwater management facilities. Flow control design calculations are provided in Appendix 7A of this report. A brief summary of the site parameters is provided below. Proposed Impervious Surface Area = Proposed Landscape/Lawn Area = Total Tributary Basin Area = Required Detention Volume = Provided Detention Volume = 12,414-sf (0.28-ac) 5,585-sf (0.13-ac) 17,999-sf (0.41-ac) 7,296-cf (see Appendix 7A) 7,296-cf (see Plans) The design calculations for the stormwater detention facility indicate that a lower -orifice diameter less than '/z-inch is required. Small orifices are more prone to plugging so the City (and State) regulations typically do not allow orifices less than '/z-inch. Per guidance from City of Edmonds, the City will accept an orifice below '/z an inch in size at the engineer's discretion if an appropriately sized debris screen is proposed around the bottom of the riser. Therefore, a debris screen is proposed, and a detail is provided on the plan set. Edmonds Apartments Drainage Report CONVEYANCE SYSTEM The conveyance system for the project will consist of a series of catch basins and storm pipe to collect and convey the runoff from the project to the stormwater facility. In the event of an overflow, the facility will connect into the existing conveyance system on Edmonds Way where it matches the historic flowpath. Appendix 7B of this report provides an evaluation of the conveyance elements proposed for the project. These are generally split into two distinct conveyance analyses as described below. An on -site conveyance figure is provided to depict the individual sub -basins tributary to each proposed structure. The figure also tabulates the land cover conditions within each of those sub -basins. That tabulation is then used in a rational -method evaluation of the flowrates generated by each sub -basin. The rational method calculations are then followed by a direct -step backwater analysis demonstrating that sufficient capacity exists to fully -contain the peak flows from a 100-yr design storm event. A separate conveyance analysis has been provided for the proposed frontage improvements. This analysis is not intended to be a detailed direct -step backwater evaluation because a determination of the downstream tailwater conditions would require a comprehensive regional drainage study that is beyond the scope of this project analysis. However, an open -channel capacity evaluation of the flattest proposed frontage pipe is provided. This was performed by mapping the anticipated tributary area, assuming a 70% build -out potential of that basin, and assuming no functioning flow control elements within that fully built -out basin. Using these conservative assumptions, a rational -method estimate of the peak flowrates tributary to that pipe was performed. That flowrate estimate was then used in a Manning's-equation analysis to verify that it is less than the full -flow capacity of the pipe. Edmonds Apartments Drainage Report APPENDIX 7A FLOW CONTROL DESIGN CALCULATIONS Edmonds Apartments Drainage Report Existing Basin Conditions Subbasin Developed Basin Conditions Subbasin 7 Vault fo Subbasin land Use - Subbasin 1 l o 0 Edit Runoff Components Area lac) ❑A700 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.4100 Ok Cancel Su66asin 1 C-1-Kail Type TII Forest Till Pasture PH Grass Outwash Forest Outwash Pasture Outwash Grass wetland Green Roof User user 2 User 3 Impervious Total [acres] ** Subbasin land Use - Subbasin 1 0 0 Edit Runoff Components Area lac) 0.0000 0.0000 0.13W 0.0000 0.0000 0.0000 U.UaUU 0.0000 0.0000 0.0000 0.0000 0.2SW 0.4100 Ok Cancel Subbasin1 Co rlSoil Type Till Forest Till Pasture Till Grass Outwash Forest Outwash Pasture Outwash Grass Wetland Green Roof User 1 User 2 User 3 Impervious Total [acres] Edmonds Apartments Drainage Report MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.46 Program License Number: 201110001 Project Simulation Performed on: 10/30/2019 11:35 AM Report Generation Date: 10/30/2019 11:35 AM Input File Name: 2019-10-29.fid Project Name: Edmonds Apts Analysis Title: Detention Vault Comments: PRECIPITATION INPUT Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 14 Full Period of Record Available used for Routing Precipitation Station : 96003605 Puget East 36 in_5min 10/01/1939-10/01/2097 Evaporation Station 961036 Puget East 36 in MAP Evaporation Scale Factor 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.410 0.410 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.410 0.410 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 -- -------Area (Acres) -- Till Forest 0.410 Subbasin Total 0.410 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 -- -------Area (Acres) -- Till Grass 0.130 Impervious 0.280 Subbasin Total 0.410 Edmonds Apartments Drainage Report ************************* LINK DATA ***************************** ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 Link Name: Vault Link Type: Structure Downstream Link: None Prismatic Pond Option Used Pond Floor Elevation (ft) Riser Crest Elevation (ft) Max Pond Elevation (ft) Storage Depth (ft) 4.00 Pond Bottom Length (ft) Pond Bottom Width (ft) Pond Side Slopes (ft/ft) Bottom Area (sq-ft) Area at Riser Crest El (sq-ft) (acres) Volume at Riser Crest (cu-ft) (ac-ft) Area at Max Elevation (sq-ft) (acres) Vol at Max Elevation (cu-ft) (ac-ft) Massmann Infiltration Option Used Hydraulic Conductivity (in/hr) Depth to Water Table (ft) Bio-Fouling Potential Maintenance Riser Geometry Riser Structure Type Riser Diameter (in) Common Length (ft) Riser Crest Elevation Number of Devices: 3 389.90 393.90 394.40 76.0 24.0 L1= 0.00 1824. 1,824. 0.042 7,296. 0.167 1824. 0.042 8,208. 0.188 L2= 0.00 W 1= 0.00 W2= 0.00 0.00 100.00 Low Average or Better Circular 12.00 0.000 393.90 ft ---Device Number 1 --- Device Type Circular Orifice Control Elevation (ft) 389.90 Diameter (in) 0.28 Orientation : Horizontal Elbow : Yes ---Device Number 2 --- Device Type Circular Orifice Control Elevation (ft) 392.60 Diameter (in) 0.50 Orientation : Horizontal Elbow : Yes Edmonds Apartments Drainage Report ---Device Number 3 --- Device Type Circular Orifice Control Elevation (ft) 393.10 Diameter (in) 0.50 Orientation : Horizontal Elbow : Yes **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ********** Link: Vault ********** Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) -------------------------------------- -------------------------------------- 1.05-Year 391.157 1.11-Year 391.282 1.25-Year 391.519 2.00-Year 392.127 3.33-Year 392.595 5-Year 392.845 10-Year 393.278 25-Year 393.562 50-Year 393.643 100-Year 393.763 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perind Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) Subbasin: Subbasin 1 62.662 Total: 62.662 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) Subbasin: Subbasin 1 Link: Vault Total: 14.968 0.000 14.968 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.397 ac-ft/year, Post Developed: 0.095 ac-ft/year Edmonds Apartments Drainage Report ***********Water Quality Facility Data ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 Link: Vault ******** Basic Wet Pond Volume (91 % Exceedance): 1269. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 1904. cu-ft Infiltration/Filtration Statistics -------------------- Inflow Volume (ac-ft): 130.89 Inflow Volume Including PPT-Evap (ac-ft): 130.89 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 130.85 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Subbasin 1 Scenario Postdeveloped Compliance Link: Vault *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position F Req'd WQ Treatment Volume Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ------------------------------------------------------------------------------------------------------------ 2-Year 6.715E-03 2-Year 2.987E-03 5-Year 1.145E-02 5-Year 6.562E-03 10-Year 1.570E-02 10-Year 1.155E-02 25-Year 2.101 E-02 25-Year 1.435E-02 50-Year 2.815E-02 50-Year 1.501 E-02 100-Year 3.080E-02 100-Year 1.593E-02 200-Year 4.630E-02 200-Year 1.621 E-02 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals **** Flow Duration Performance **** Excursion at Predeveloped 50%Q2 (Must be Less Than or Equal to 0%): -42.5% PASS Maximum Excursion from 50%Q2 to Q2 (Must be Less Than or Equal to 0%): -1.0% PASS Maximum Excursion from Q2 to Q50 (Must be less than 10%): 1.1% PASS Percent Excursion from Q2 to Q50 (Must be less than 50%): 2.5% PASS MEETS ALL FLOW DURATION DESIGN CRITERIA: PASS Edmonds Apartments Drainage Report aAs a� a� aj3s aA1 aAa 1 Ae-v Flog Duration Plot a2 50%02 1 lae-M 1 Ae-M 10R-U 1 Ae-W 110e-M 1 Oe-01 1 Ae+aa Exceedance Probability Predeveloped Postdeveloped Edmonds Apartments Drainage Report APPENDIX 7B CONVEYANCE CALCULATIONS Edmonds Apartments Drainage Report 0 M U 0 \�9 6'\ J \11 \ I �\ ♦ BA IN I � a°� \ 398 \sue LEGEND PROPOSED BUILDING ROOF AREA \ i s\ PROPOSED PAVEMENT AREA PROPOSED CONCRETE/WALK AREA �\ s\ PROPOSED FRENCH DRAIN \ PROPOSED CHANNEL DRAIN BASIN BOUNDARY 1 os os s\ 1 BASIN #4 `\ 1 `S 110, 1 `s \S R `s 1 O � ad \ \\ \ \S, a \ \ a J`\ 1 \ AS\FN #9 CONVEYANCE BASIN SUMMARY BASIN # IMPERVIOUS AREA LANDSCAPE AREA TOTAL AREA 4 2595 SF (0.06 SF) 1411 SF (0.03 SF) 4006 SF (0.09 SF) 5 2927 SF (0.07 SF) 339 SF (0.01 SF) 3266 SF (0.07 SF) 7 1921 SF (0.04 SF) 779 SF (0.02 SF) 2700 SF (0.06 SF) 8 3948 SF (0.09 SF) 0 SF (0.00 SF) 3948 SF (0.09 SF) 9 966 SF (0.02 SF) 3114 SF (0.07 SF) 4080 SF (0.09 SF) KJ M Civil Engineering Project Management ®®® Planning 1724 W. Marine View Drive, Suite 140; Everett, Washington 98201 Ke Mg n Drawn 10/30/19 Date 410-002-18 Office;425A86.6533 Foc 425.486.6593--,doengineeo.com Project No. 0 20 1 "= 20' Scale Feet EDMONDS APARTMENTS CONVEYANCE EXHIBIT I sheet: R:\Projects\410 (LZG Construc 002-18 (Edmonds Apt)\Dwg\figures\TIR Figures\EW—Conveyance (KJM).dwg 11x17 Made by: Date: Project: Rational Method Flowrate Calculations (per KCSWDM Section 32.1) Checked by: Date: Project No: PACE An Fngineering Services Company Backchecked by: Date: Sheet No: Edmonds Apartments Design Storm Event: 100-yr Rational Coefficients: aR = 2.61 bR = 0.63 Total Precipitation (PR) = 3.00 in Unit Peak Rainfall Intensity (iR) = 0.82 Peak Rainfall Intensity (IR) = 2.46 in Design Notes: 1. Runoff Coefficients (C) per KCSWDM T. 3.2.1.A 2. Rational Coefficients per KCSWDM T. 3.2.1.6 3. Unit Peak Rainfall Intensity OR) per KCSWDM Eq. 3-4 assuming a minimum travel time of 6.3 min. 4. Precipitation per Isopluval Maps (KCSWDM Fig's 3.2.1.A - 3.2.1.D) S. Peak Rainfall Intensity OR) per KCSWDM Eq. 3-3 (ac) (ac) (ac) (ac) (cfs) 4 0.06 0.90 0.03 0.25 0.09 0.68 0.15 5 0.07 0.90 0.01 0.25 0.08 0.82 0.16 7 0.04 0.90 0.02 0.25 0.06 0.68 0.10 8 0.09 0.90 0.00 0.25 0.09 0.90 0.20 9 0.02 0.90 0.07 0.25 0.09 0.39 0.09 Frontage 0.97 0.90 0.41 0.25 1.38 0.71 2.39 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) Outlet Inlet Appr ti El Pipe Pipe Manning's MENEENI Vel Friction HGL Head Cntrl Cntrl Vel Head Head HW board 0 7FromTo . . . . . •B (cfs) (ft) I (in) (ft) I (ft) I (ft) (°) (ft) (ftz) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) ~ Vault .. 0.70 4 12 0.012 391.66 391.70 397.96 88 393.90 0.79 0.01 0.00 393.90 0.01 393.92 392.18 0.01 0.01 0.00 393.92 4.04 ai 6 5 0.60 67 12 0.012 391.70 392.10 395.60 88 393.92 0.79 0.01 0.02 393.94 0.00 393.95 392.54 0.00 0.00 0.00 393.95 1.65 a 5 8 0.29 40 12 0.012 392.10 392.50 396.46 25 393.95 0.79 0.00 0.00 393.96 0.00 393.96 392.80 0.00 0.00 0.00 393.96 2.50 N 8 9 0.09 36 6 0.012 392.50 393.00 396.72 0 393.96 0.20 0.00 0.01 393.97 0.00 393.97 393.20 0.00 0.00 0.00 393.97 2.75 C v ;: a 5 4 0.15 22 12 0.012 392.60 393.66 395.16 0 393.95 0.79 0.00 0.00 394.66 0.00 394.66 393.85 0.00 0.00 0.00 394.66 0.50 Y a co � a Q 6 7 0.10 43 12 0.012 391.70 393.95 397.45 0 393.95 0.79 0.00 0.00 394.95 0.00 394.95 394.10 0.00 0.00 0.00 394.95 2.50 Q Q a U C u o G Q m W 01 ai O N O M O1 \ O1 N a N N t N a Y U N U Y U U m LEGEND BASIN #4 Ir li A. �16- 61 0Amr i 1 i BASIN TRIBUTARY TO PROJECT FRONTAGE IMPERVIOUS BASIN AREA = 0.97 AC (ASSUME 70% IMPERVIOUS) KJM LANDSCAPE/LAWN AREA = 0.41 AC Design e Mg n Civil Engineering ® Project management Drawn Planning (ASSUME 30% LANDSCAPE/LAWN) 10/30/19 1724 W.Marinevlew Drive, Suite 140; Everett, Washington 98MI TOTAL BASIN AREA = 1.38 AC Date Office:425A86.6533 Foc 425.486.6593 v—vsdoengineers.com 410-002-18 Project No. BASIN BOUNDARY I 0 20 1 "= 20' Scale Feet EDMONDS APARTMENTS FRONTAGE CONVEYANCE sheet: R:\Projects\410 (LZG Construction)\002-18 (Edmonds Apt)\Dwg\figures\TIR Fig ures\EW—Frontage Conveyance (KJM).dwg 11x17 Open Channel Flow Calculator For Circular Pipes PACE An Engineering Services Company Project Name Description: Edmonds Apartments Frontage Conveyance Check Pipe Diameter (D) = 12 in Pipe Slope (S) = 0.60 Flow Depth (y) = 1.00 ft Flowrate (Q) = 3.00 cfs Mannings Coeff. (n) = 0.012 Theta Angle (0) = 6.28 rad Wetted Area (A) = 0.79 ft2 Wet. Perimeter (P) = 3.14 ft Hydraulic Radius (R) = 0.25 cfs Top Width (T) = 0.00 ft Flow Velocity = 3.82 fps LON Formulas: Theta Angle (0): If y r : B = 2/c — 2a cos( y — r ) r - Ify<_r: B = 2acos( ry) r Wetted Area (A): A = 8 (B — sin O)d 2 Wetted Perimeter (P): P _ 1 Od _2 Hydraulic Radius (R): R = A P Top Width (T): T = sin (% Project No.: 410-002-18 Date: 10/31/2019 Calc. By: KJM I where: r = Pipe Radius where: r = Pipe Radius SECTION 8 WETLANDS PROTECTION (Minimum Requirement #8) Edmonds Apartments Drainage Report WETLANDS PROTECTION There are no wetlands identified on -site, or within the downstream flowpath, so this requirement is not applicable. Edmonds Apartments Drainage Report SECTION 9 OPERATION & MAINTENANCE (Minimum Requirement #9) Edmonds Apartments Drainage Report OPERATIONS AND MAINTENANCE Stormwater facilities and BMPs shall be inspected, operated and maintained in accordance with Sections 18.30.060.D.9 of the Edmonds Community Development Code (ECDC). The following is a selection of operations/maintenance recommendations specific to the site, obtained from the current DOE Manual. Edmonds Apartments Drainage Report No. 3 — Closed Detention Systems (Tanks/Vaults) Maintenance Defect Conditions When Maintenance is Needed Results Expected Component When Maintenance is Performed Storage Area Plugged Air Vents One-half of the cross section of a vent is Vents open and blocked at any point or the vent is damaged. functioning. Debris and Sediment Accumulated sediment depth exceeds 10% All sediment and of the diameter of the storage area for 1/2 debris removed from length of storage vault or any point depth storage area. exceeds 15% of diameter. (Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than 1/2 length of tank.) Joints Between Any openings or voids allowing material to All joint between Tank/Pipe Section be transported into facility. tank/pipe sections are sealed. (Will require engineering analysis to determine structural stability). Tank Pipe Bent Out Any part of tank/pipe is bent out of shape Tank/pipe repaired or of Shape more than 10% of its design shape. (Review replaced to design. required by engineer to determine structural stability). Vault Structure Cracks wider than 1/2-inch and any Vault replaced or Includes Cracks in evidence of soil particles entering the repaired to design Wall, Bottom, structure through the cracks, or specifications and is Damage to Frame maintenance/inspection personnel structurally sound. and/or Top Slab determines that the vault is not structurally sound. No cracks more than Cracks wider than 1/2-inch at the joint of any inch wide at the jooinin t of the inlet/outlet inlet/outlet pipe or any evidence of soil pipe. particles entering the vault through the walls. Manhole Cover Not in Place Cover is missing or only partially in place. Manhole is closed. Any open manhole requires maintenance. Locking Mechanism Mechanism cannot be opened by one Mechanism opens Not Working maintenance person with proper tools. Bolts with proper tools. into frame have less than 1/2 inch of thread (may not apply to self-locking lids). Cover Difficult to One maintenance person cannot remove lid Cover can be Remove after applying normal lifting pressure. Intent removed and is to keep cover from sealing off access to reinstalled by one maintenance. maintenance person. Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, Ladder meets design misalignment, not securely attached to standards. Allows structure wall, rust, or cracks. maintenance person safe access. Catch Basins See "Catch Basins" See "Catch Basins" (No. 5). See "Catch Basins" (No. 5) (No. 5). Edmonds Apartments Drainage Report No. 4 - Control Structure/Flow Restrictor Maintenance Defect Condition When Maintenance is Needed Results Expected Component When Maintenance is Performed General Trash and Debris Material exceeds 25% of sump depth or 1 Control structure (Includes Sediment) foot below orifice plate. orifice is not blocked. All trash and debris removed. Structural Damage Structure is not securely attached to Structure securely manhole wall. attached to wall and outlet pipe. Structure is not in upright position (allow up Structure in correct to 10% from plumb). position. Connections to outlet pipe are not watertight Connections to outlet and show signs of rust. pipe are water tight; structure repaired or replaced and works as designed. Any holes --other than designed holes --in the Structure has no structure. holes other than designed holes. Cleanout Gate Damaged or Missing Cleanout gate is not watertight or is missing. Gate is watertight and works as designed. Gate cannot be moved up and down by one Gate moves up and maintenance person. down easily and is watertight. Chain/rod leading to gate is missing or Chain is in place and damaged. works as designed. Gate is rusted over 50% of its surface area. Gate is repaired or replaced to meet design standards. Orifice Plate Damaged or Missing Control device is not working properly due to Plate is in place and missing, out of place, or bent orifice plate. works as designed. Obstructions Any trash, debris, sediment, or vegetation Plate is free of all blocking the plate. obstructions and works as designed. Overflow Pipe Obstructions Any trash or debris blocking (or having the Pipe is free of all potential of blocking) the overflow pipe. obstructions and works as designed. Manhole See "Closed See "Closed Detention Systems" (No. 3). See "Closed Detention Systems" Detention Systems" (No. 3). (No. 3). Catch Basin See "Catch Basins" See "Catch Basins" (No. 5). See "Catch Basins" (No. 5). (No. 5). Edmonds Apartments Drainage Report No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed General Trash & Trash or debris which is located immediately No Trash or debris located Debris in front of the catch basin opening or is immediately in front of blocking inletting capacity of the basin by catch basin or on grate more than 10%. opening. Trash or debris (in the basin) that exceeds 60 No trash or debris in the percent of the sump depth as measured from catch basin. the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Trash or debris in any inlet or outlet pipe Inlet and outlet pipes free blocking more than 1/3 of its height. of trash or debris. Dead animals or vegetation that could No dead animals or generate odors that could cause complaints vegetation present within or dangerous gases (e.g., methane). the catch basin. Sediment Sediment (in the basin) that exceeds 60 No sediment in the catch percent of the sump depth as measured from basin the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. Structure Top slab has holes larger than 2 square Top slab is free of holes Damage to inches or cracks wider than 1/4 inch and cracks. Frame and/or Top Slab (Intent is to make sure no material is running into basin). Frame not sitting flush on top slab, i.e., Frame is sitting flush on separation 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 Fractures or Maintenance person judges that structure is Basin replaced or repaired Cracks in unsound. to design standards. Basin Walls/ Bottom Grout fillet has separated or cracked wider Pipe is regrouted and than 1/2 inch and longer than 1 foot at the secure at basin wall. joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. Settlement/ If failure of basin has created a safety, Basin replaced or repaired Misalignment function, or design problem. to design standards. Vegetation Vegetation growing across and blocking more No vegetation blocking than 10% of the basin opening. opening to basin. Vegetation growing in inlet/outlet pipe joints No vegetation or root that is more than six inches tall and less than growth present. six inches apart. Edmonds Apartments Drainage Report No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed Contamination See "Detention Ponds" (No. 1). No pollution present. and Pollution Catch Basin Cover Not in Cover is missing or only partially in place. Catch basin cover is Cover Place Any open catch basin requires maintenance. closed Locking Mechanism cannot be opened by one Mechanism opens with Mechanism maintenance person with proper tools. Bolts proper tools. Not Working into frame have less than 1/2 inch of thread. Cover Difficult One maintenance person cannot remove lid Cover can be removed by to Remove after applying normal lifting pressure. one maintenance person. (Intent is keep cover from sealing off access to maintenance.) Ladder Ladder Rungs Ladder is unsafe due to missing rungs, not Ladder meets design Unsafe securely attached to basin wall, standards and allows misalignment, rust, cracks, or sharp edges. maintenance person safe access. Metal Grates Grate opening Grate with opening wider than 7/8 inch. Grate opening meets (If Applicable) Unsafe design standards. Trash and Trash and debris that is blocking more than Grate free of trash and Debris 20% of grate surface inletting capacity. debris. Damaged or Grate missing or broken member(s) of the rate is in place and rn Missing. grate. eets design standards. Edmonds Apartments Drainage Report No.12 — Wetvaults Maintenance Defect Condition When Maintenance Results Expected When Component is Needed Maintenance is Performed General Trash/Debris Trash and debris accumulated Remove trash and debris from vault. Accumulation in vault, pipe or inlet/outlet (includes floatables and non- floatables). Sediment Sediment accumulation in vault Remove sediment from vault. Accumulation in bottom exceeds the depth of the Vault sediment zone plus 6-inches. Damaged Pipes Inlet/outlet piping damaged or Pipe repaired and/or replaced. broken and in need of repair. Access Cover Cover cannot be opened or Pipe repaired or replaced to proper Damaged/Not removed, especially by one working specifications. Working person. Ventilation Ventilation area blocked or Blocking material removed or cleared plugged. from ventilation area. A specified % of the vault surface area must provide ventilation to the vault interior (see design specifications). Vault Structure Maintenance/inspection Vault replaced or repairs made so Damage- personnel determine that the that vault meets design specifications Includes Cracks vault is not structurally sound. and is structurally sound. in Walls Bottom, Damage to Frame and/or Top Slab Cracks wider than 1/2-inch at Vault repaired so that no cracks exist the joint of any inlet/outlet pipe wider than 1/4-inch at the joint of the or evidence of soil particles inlet/outlet pipe. entering through the cracks. Baffles Baffles corroding, cracking, Baffles repaired or replaced to warping and/or showing signs of specifications. failure as determined by maintenance/inspection staff. Access Ladder Ladder is corroded or Ladder replaced or repaired to Damage deteriorated, not functioning specifications, and is safe to use as properly, not attached to determined by inspection personnel. structure wall, missing rungs, Replace sign warning of confined has cracks and/or misaligned. space entry requirements. Ladder Confined space warning sign and entry notification complies with missing. OSHA standards. Edmonds Apartments Drainage Report