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StormWater Report.pdf—AAIHIUI]an associates, illc. M E N G I N E E R I N G z "0 M 9801 Edmonds Way Edmonds, Washington The information contained in this report was prepared by and under direct supervision of the undersigned: Craig Harris PE AAI Engineering 4875 S.W. Griffith Drive Suite 300 Beaverton, Oregon 97005 PH 503.620.3030 FX 503.620.5539 craigh@aaieng.com AAI Project Number: A11182.11 Walgreens SECTIONS Section 1 - Project Overview Section 2 — Existing Conditions Summary Section 3 — Off -Site Analysis Section 4 — Site Classification Section 5 — Permanent Stormwater Control Plan Section 6 — Construction Stormwater Pollution Prevention Plan Section 7 — Other Reports and Studies Section 8 — Other Permits Section 9 — Operation and Maintenance Manual Section 10 — Bond Quantities Worksheet FIGURES Figure 1 — Existing Conditions Figure 2 — Proposed Conditions — New/Replaced PGIS Areas APPENDIX Appendix A —Design Documents Appendix B — Design Calculations and Supporting Information Appendix C — Operations and Maintenance Manual Appendix D — Other Reports and Studies Walgreens Chapter 1— Project Overview The Walgreens project is located at 9801 Edmonds Way in Edmonds, Washington. The existing site (Parcel II) contains an existing building (23,295 SF) as well as —1 1,565SF of existing asphalt paving for vehicle parking and maneuvering areas. The total existing impervious area is 34,860SF (0.80AC). The proposed project will include removing the existing building and constructing a single story structure 14,490SF. There is a plan to construct an additional building to the south 3,373 SF bringing the total proposed building areas to 17,863SF. The total site area of Parcel II is 58,477SF. Parcel I is a shared parking lot (68,018SF) of which—23,025SF will be removed and replaced. The project will also include the construction of new stormwater quality facilities (Rain Gardens) and conveyance system on Parcel I and new conveyance system and Detention facility with a flow control structure on Parcel II. The project has been designed according to the requirements of ECDC 18.30 Storm Water Management and Exhibit "A" Stormwater Supplement. Conveyance pipe sizing for new stormwater piping was performed using Manning's Equation (Q = 0.149 AR 23 S I2 ), Where A is the pipe area (SF), R is the hydraulic radius, S is n pipe slope (ft/ft), and n is the Manning's Coefficient and is based on the pipe material. A value of 0.013 was used for this project as a value for PVC piping. Walgreens Chapter 2- Existing Conditions Summary The existing site (Parcel II) contains an existing building (23,295SF) as well as —11,565SF of existing asphalt paving for vehicle parking and maneuvering areas. The total existing impervious area is 34,860SF (0.80AC). The total site area of Parcel II is 58,477SF. Parcel I is a shared parking lot 68,018SF of which—59,735SF is impervious. There is a retaining wall constructed to the north of the parking lot which is approximately 16' high. Walgreens Chapter 3® ffsite Analysis All storm runoff is proposed to be treated on-site and those areas that require detention will adhere to the Cities Stormwater Requirements, as stated in the Project Overview. With the on-site treatment and flow control measures proposed, the off-site impact to the existing public storm system will be diminished from the current demands placed on it by the existing site conditions. Walgreens Chapter 4 — Site Classification This project has been classified per the Edmonds Stormwater Code Supplement (ESCS). This project proposes to add/replace approximately 71,867SF of impervious area and will disturb —81,250SF. Per the ECSC this is classified as a Large Site Project. All Minimum Requirements that apply to large sites are listed below. 1. Preparation of Stormwater Site Plan. Complete site plans that show the existing and proposed conditions of the project and drainage systems are included. This drainage report summarizes the methods and analysis in the design of the stormwater components. 2. Construction Stormwater Pollution Prevention The Construction Stormwater Pollution Prevention Plan (SWPPP) is a combination of the Temporary Erosion and Sediment Control (TESC) Plan and the Stormwater Spill Prevention Plan (SSPP). The TESC are sheets C2.0 and C2.1 of the construction documents and the SSPP is included in Section 6 of this document. TESC - See Appendix A SSPP — See Section 6 3. Source Control of Pollution All applicable source control BMP's have been applied to this site. The storm runoff is treated on-site in rain gardens (Parcel I) and sumped catchbasins with a baffle (Parcel II). 4. Preservation of Natural Drainage Systems and Outfalls The existing site sheet flows to various collection points on-site. Post construction this sheet flow will be collected in rain gardens designed to treat the water before it is piped to the existing public main (Parcel I). The existing (destination) outfall for the storm runoff is the public stormline in Edmonds Way, after construction all on-site runoff will be conveyed to the same existing main. 5. On -Site Stormwater Management LID techniques have been designed where feasible to handle stormwater runoff. Below is a list of the LID chosen: Rain Gardens — Rain Gardens have been designed in various places in the site to capture, treat storm runoff. See Appendix A locations and details. Compost Amended Soil — In disturbed pervious areas, the soil will be compost amended to restore the water holding capacity of these areas. Walgreens 6. Runoff Treatment This project proposes approximately 71,867SF of pollution generating impervious surface (PGIS). Refer to Figure 2 for the layout of the PGIS associated with this project and Appendix A for runoff treatment methods and details. 7. Flow Control Site runoff from the disturbed impervious areas will be detained onsite and released at per the Cities requirements (0.25cfs per acre of impervious for the 10yr design storm and 045cfs per acre of impervious for the 100yr design storm). Refer to Appendix A for plans and details and Appendix B for design calculations. Detention and Flow Control calculation were performed using HydroCAD10.0 which is a SBUH modeling software. 8. Wetlands Protection No existing wetlands on or adjacent to project site. No on-site or off-site protection required. 9. Operation and Maintenance Operation and Maintenance guidance from Volume V of the 2005 Stormwater Management Manual for Western Washington, for the on-site flow control BMP's are included in Appendix C. 10. Off -Site Analysis and Mitigation All storm runoff is to remain onsite therefore no off-site analysis or mitigation is proposed. 11. Financial Liability This is a commercial project which would normally require a performance bond as a financial guarantee for the stormwater system and BMP's related to the SWPPP. However, since no proposed stormwater improvements are proposed in the Right -of -Way no bond should be required. If the City does require such a bond the owner will submit proper documentation to the City. Walgreens Chapter 5 — Permanent Stormwater Control Plan 5.1 Existing Site Hydrology The existing site consists of the existing building and asphalt vehicle parking and maneuvering areas to the south and west of the existing building located on Parcel II and a steep vegetated hill to the north and east of the building. Parcel I is an existing parking and maneuvering area with a few vegetated islands and the same steep vegetated hill to the north. There is an existing stormwater system serving the existing building and asphalt areas. Please refer to Figure 1 for the Existing Conditions Site Plan 5.2 Proposed Site Hydrology The proposed site will consist of a new retail building, asphalt vehicle parking and maneuvering areas to the south and west of the new building located on Parcel II, a vehicle maneuvering area to the east and west of the proposed building and a new retaining wall to hold back the steep vegetated hill to the north and east of the building. Parcel I will remain relatively un -touched with the exception of the northern and eastern portions which will be removed and replaced to blend the new construction on Parcel II into the existing grades on Parcel I. Additionally some of the parking stalls will be deleted and turned into rain gardens which will serve to treat stormwater runoff in Parcel I. The parking stalls to the South of Parcel I will also be reworked and re -striped to accommodate the construction of a new public sidewalk along the project frontage. Parcel II will be graded to collect runoff in sumped catchbasins that have a baffle to allow sediment to settle out of the flows and also keep floatables (trash and oils) from entering the detention system. Please refer to Appendix A for the Design Documents showing the stated improvements. 5.3 Performance Standards and Goals The proposed water quality/detention facilities have been designed to meet the Cities design Standards. 5AWater Quality System The project proposes approximately 71,867SF of PGIS. Rain garden have been proposed in various places to collect and treat the stormwater runoff from the PGIS that flows to them (Parcel I). Since the areas collected in each rain garden varies, each rain garden has been calculated individually using the Western Washington Hydrology Model version 3.0 (WWHM3). Please refer to Appendix A for On -Site Stormwater Structure Plans, Appendix B for HydroCAD 10.0 Calculations for water quantity flows (Detention), and Appendix C for the Operations and Maintenance Manual for the on-site stormwater components. Walgreens Chapter 6 — Construction Stormwater Pollution Prevention Plan The Construction Stormwater Pollution Prevention Plan (SWPPP) is a combination of the Temporary Erosion and Sediment Control (TESC) Plan and the Stormwater Spill Prevention Plan (SSPP). TESC - See Appendix A In this section we will describe how BMP's will be used during the construction phase of the Walgreens project. There are 12 elements of SWPPP design and they are addressed as follows: #1 Mark Clearing Limits: Natural vegetation will be preserved wherever possible. Sediment fence will be used to mark the limits of construction as shown on the project drawings. #2 Establish Construction Access: A standard Stabilized Construction Entrance will be installed on the eastern edge of the project site as shown on the project drawings and. In addition there will be a concrete washout installed adjacent to the Construction Entrance. The area of the future secondary buiding will be used to park the construction machinery during the project construction period and therefore those areas will be stabilized as well. #3 Control Flow hates: It will be unnecessary to control flow rates off of the project site during this construction, flow increases will be minimal and sediment outflow can be controlled by other means described in later elements. #4 Install Sediment Controls: The primary BMP to be used for Sediment Controls will be a silt fence as shown on the Erosion and Sediment Control Plan, sheet C2.1. In addition the existing off-site and proposed on-site area drains and catch basins will be protected with silt sacks as shown on sheet C2.1 #5 Stabilize Soils: Temporary and permanent seeding will be used at the discretion of the contractor throughout the construction phase of the project. Mulching will be used in conjunction with the temporary and permanent seeding to protect the seeds. Plastic coverings may be used by the contractor at his discretion for short term soil protection. Various dust control methods may need to be used by the contractor's discretion. Walgreens #6 Protect Slopes: Temporary and permanent seeding may be used at the discretion of the Contractor and/or on-site inspecting engineer. #7 Protect Drain Inlets: All Catch Basins and Area Drains put into service during the construction phase shall be protected with Silt Sack protection. Existing area drains and inlets shall be protected with Silt Sacks, Bio Bags or a combination of both prior to site disturbing activities #8 Stabilize Channels and Outlets: There will be no temporary on-site stormwater channeling therefore there is no need for BMP's to address this issue. #9 Control Pollutants: There will be no maintenance of heavy equipment on-site, nor will there be any application of industrial chemical, fertilizers, or insecticides, therefore there is no need for measures to protect against those practices. Sediment will be controlled by the use of the above described BMP's. " #10 Control De -Watering: De -watering process shall be managed by the contractor by pumping or routing by gravity flow to an approved sediment settling or filtration facility prior to discharge. #11 Maintain BMPs: All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with BMP specifications. All temporary erosion and sediment control BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized on site. Disturbed soil resulting from removal of BMPs or vegetation shall be permanently stabilized. #12 Manage the Project: The contractor will maintain a daily presence on the site and will assign a contact person for erosion and sediment control issues. Walgreens BMP's will be in accordance with the Stormwater Management Manual for Western Washington and the City of Edmonds standards unless otherwise noted here. The contractor will be responsible for monitoring and maintaining the erosion control on-site as the project progresses. 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: 1. Site conditions -including existing vegetative coverage, slope, soil type, and proximity to receiving waters; and 2. Limitations on activities and the extent of disturbed areas; and 3. Proposed erosion and sediment control measures. Maintaining an Updated Construction SWPPP The Construction 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. Walgreens Chapter 7 — Other Reports and Studies The following reports are included within Appendix D of this report. Geotechnical Report by Geotech Consultants Inc. dated February 2012. (This report is preliminary and will be replaced with the FINAL version as soon as it has been released by the Geotechnical Engineer.) Walgreens The following reports are included within Appendix D of this report. o Construction Stormwater General Permit NOI (Notice of Intent). (The blank NOI is enclosed as a place holder. A completed NOI will be inserted as soon as the project has progress to the point a contractor has been chosen and before final approval design plans and this report is given) NOTICE OF INTENT (NOI) Check if applicable: moons APPLICATION FORM ❑ Change or Update Permit Information DEPARTMENT OF Construction Stormwater General ❑Modification of Permit Coverage ECOLOGY Permit Permit #WAR State of Washington Please print or tvae all sections of this application. All fields are required unless otherwise marked. (.Operator/Permittee (Party with operational control over plans and specifications or day-to-day operational control of activities which ensure compliance with Stormwater Pollution Prevention Plan (SWPPP) and permit conditions. Ecology will send correspondence and permit fee invoices to the permittee on record. Name: Company: Business Phone: Ext. Unified Business Identifier (UBI): (UBI is a nine -digit number used to identify a business entity. Write "none" if you do not have a UBI number.) Cell Phone (Optional): Fax (Optional): E-mail: Mailing Address: City: State: Zip + 4: ll. Property Owner (The party listed on the County Assessor's records as owner and taxpayer of the parcel[s] for which permit coverage is requested. Ecology will not send correspondence and permit fee invoices to the Property Owner. The Property Owner information will be used for emergency contact purposes.) Name: Company (if applicable): Business Phone: Ext. Unified Business Identifier (UBI): (UBI is a nine -digit number used to identify a business entity. Cell Phone (Optional): Fax (Optional): Write "none" if you do not have a UBI number.) E-mail: Mailing Address: City: State: Zip + 4: III. On-site Contact Person (Typically the Certified Erosion & Sediment Control Lead or Operator/Permittee) Name: Company: Business Phone: Ext. Mailing Address: Cell Phone (Optional) Fax (Optional): City: State: Zip + 4: E-mail: IV. WebDMR Electronic Discharge Monitoring Reporting) You must submit monthly discharge monitoring reports using Ecology's WebDMR system. To sign up for WebDMR, or to register a new site, go to www.ecy.wa.gov/stormwater, and click on the "Construction Stormwater" link. You will find information on WebDMR under the "WebDMR and PARIS" link on the right-hand side. If you are unable to submit your DMRs electronically, you may contact Ecology to request a waiver. Ecology will generally only grant waiver requests to those permittees without internet access. Only a permittee or representative, designated in writing, may request access to or a waiver from WebDMR. To have the ability to use the system immediately, you must submit the Electronic Signature Agreement with your application. If you have questions on this process, contact Ecology's WebDMR staff at WebDMR ec .wa. ov or 360-407-7097. ECY 020-85 (Rev. 03/11) V. Site Information Site or Project Name Site Acreage Total size of your site/project (that you own/control): acres. Street Address or Location Description (If the site lacks a street address, list its specific location. For example, Total area of soil disturbance (grading and/or excavating) for your Intersection of Highway 61 and 34.) site/project over the life of the project: acres. (Note: 1 acre = 43,560 V.) Concrete / Engineered Soils Parcel ID#: (Optional) How many yards of concrete will be poured over the life of the project? -yd' (estimate Type of Construction Activity (check all that apply): ❑ Residential How many yards of recycled concrete will be used over the life of ❑ Commercial the project? yd3 (estimate ❑ Industrial ❑ Highway or Road (city ,county, state) Will any engineered soils be used? (For example: cement treated ❑ Utilities (specify): base, cement kiln dust, etc.) ❑ Other (specify): ❑ Yes ❑ No City (or nearest city): Zip Code: Estimated project start-up date (mm/dd/yy): Estimated project completion date (mm/dd/yy): County: Record the latitude and longitude of the main entrance to the site or the approximate center of site. Latitude: ON Longitude: °W For assistance with latitude and longitude, refer to any of the following websites: www.getlatlon.com or hfp://www.worldatlas.com/aatias/imageg.htm. Please convert all latitude and longitude coordinates into decimal degrees format. For help with this process, go to: http://wwwfcc.gov/mb/audio/bickel/DDDMMSS-decimal.html. VI. Existing Site Conditions 1. Are you aware of contaminated soils present on the site? ❑ Yes ❑ No 2. Are you aware of groundwater contamination located within the site boundary? ❑ Yes ❑ No 3. If you answered yes to questions 1 or 2, will any contaminated soils be disturbed or will any contaminated groundwater be discharged due to the proposed construction activity? ❑ Yes ❑ No ['Contaminated" and "contamination" here mean containing any hazardous substance (as defined in WAC 173-340-200) that does not occur naturally or occurs at greater than natural background levels.] If you answered yes to Question 3, please explain below or on a separate paper in detail the locations, contaminants, and concentrations, and pollution prevention and/or treatment BMPs proposed to control the discharge of soil/groundwater contaminants. Ecology may request a copy of your SWPPP. VII. Stormwater Pollution Prevention Plan SWPPP You must develop a SWPPP prior to starting construction. Do not submit your SWPPP with your application. The exception is that Ecology may request a copy of your SWPPP if you answered yes to the questions in Part VI. ECY 020-85 (Rev. 03/11) /2 VIII. Best Management Practices BMPs You must use the BMPs listed in the Stormwater Management Manual for Western Washington or the Stormwater Management Manual for Eastern Washington or other manuals approved by Ecology. Alternatively, you may use demonstrably equivalent BMPs on the basis of permit condition S9.C.4. If you intend to use a BMP at your site that is not included in these manuals, but that you believe meets the definition of a demonstrably equivalent BMP, you must notify the appropriate regional office. (See Definitions in the Construction Stormwater General Permit).* http://www.ecy.wa.aov/r)roa rams/wg/stormwater/construction/contacts. html *Note that if you receive permit coverage without indicating the preference for a demonstrably equivalent BMP and later decide to use one, you must provide Ecology with notice of the selection of an equivalent BMP no less than 60 days before the intended use of the equivalent BMP. IX. Discharge/Receiving Discharge/ReceivingWater Information Indicate whether your site's stormwater and/or dewatering water could enter surface waters, directly and/or indirectly: ❑ Water will discharge directly or indirectly (through a storm drain system or roadside ditch) into one or more surface waterbodies (wetlands, creeks, lakes, and all other surface waters and water courses). If your discharge is to a storm sewer system, provide the name of the operator of the storm sewer system: (e.g., City of Tacoma): (NOTE: If your stormwater discharges to a storm sewer system operated by the City of Seattle, King County, Snohomish County, City of Tacoma, Pierce County, or Clark County, you must also submit a copy of this NOI to the appropriate jurisdiction.) ❑ Water will discharge to ground with 100% infiltration, with no potential to reach surface waters under any conditions. If your project includes dewatering, you must include dewatering plans and discharge locations in your site Stormwater Pollution Prevention Plan. Location of Discharge into Surface Waterbody Enter the waterbody name and latitude/longitude of the point(s) where the site has the potential to discharge into a waterbody (enter all locations). ® Include the names and locations of both direct and indirect discharges to surface waterbodies, even if the risk of discharge is low or limited to periods of extreme weather. ® Some large construction projects (for example, subdivisions, roads, or pipelines) may discharge into several waterbodies. ® If the creek or tributary is unnamed, use a format such as "unnamed tributary to Deschutes River." ® Attach a separate list if necessary. Surface Waterbody Name Latitude Longitude Decimal Degrees Decimal Degrees °N °W °N °W °N °W °N °W If your site discharges to a waterbody that is on the impaired waterbodies list (i.e., 303[d] list) for turbidity, tine sediment, nigh pH, or pnospnorus, Ecology will require additional documentation before issuing permit coverage and these sites will be subject to additional sampling and numeric effluent limits (per Permit Condition S8). Ecology will notify you if any additional sampling requirements apply. Information on impaired waterbodies is available online at: http://www.ecy.wa..qov/programs/wg/stormwater/construction/impaired.html. ECY 020-85 (Rev. 03/11) X. State Environmental Policy Act (SEPA) This Notice of Intent (NOI) is incomplete and cannot be approved until the applicable SEPA requirements under Chapter 197-11 WAC are met. Who is the SEPA lead agency on your site? Has the SEPA lead agency issued a final decision on your checklist? ❑No ❑Yes ❑ Exempt* If No: The NOI is incomplete. Ecology will hold the application until a final SEPA decision is made or the Construction Stormwater NOI public comment period ends, whichever is later. You must notify Ecology once the lead agency has issued a determination. If Yes: Type of SEPA decision issued: ❑ Determination of Non -Significance (DNS) ❑ Mitigated DNS (MDNS) ❑ Determination of Significance (DS) ❑ Final Environmental Impact Statement (EIS) ❑ Other: Date of final SEPA decision: ® If a supplemental EIS, SEPA addendum, or some other type of additional SEPA review was required, please attach and submit with this form. Date when all SEPA-related comment & appeal periods are exhausted: *If Exempt: Attach written documentation, check type of exemption below, and proceed to Section VII. ❑ Watershed Restoration & Fish Habitat Enhancement Exemption (RCW 43.21 C.0382). ❑ Infill Development Exemption (RCW 43.21C.229). ❑ Planned Action Exemption (RCW 43.21C.031). ❑ Categorical Exemption. Under what section of the SEPA Rule (WAC 197-11-800) is it exempt? (for example, WAC 197-11-800(1) Minor New Construction) More SEPA information is available at. htto.-I www.ecy.wa.gov/programs/sea/sepa/e-review.html. XI. Public Notice You must publish a public notice at least once a week for two consecutive weeks with seven days between publications, in at least a single newspaper of general circulation in the county in which the construction is to take place. Ecology cannot grant permit coverage sooner than the end of the 30 -day public comment period, which begins on the date of the second public notice. Mail or fax (360-407-6426) the NOI to Ecology on or before the first public notice date. If you fax the public notice to Ecology, you must also mail a hard copy. Failure to do so may delay the issuance of your permit. Provide the exact dates (mm/dd/yy) that the first and second public notices will appear in the newspaper(s): First notice: Second notice: / / (Begins 30 -day public comment period.) For example: First notice: 01/01/10 Second notice: 01/08/10 Name of the newspaper(s) publishing the notices: ECY 020-85 (Rev. 03/11) Complete this template using project -specific information and submit to a local newspaper with general circulation within the county where the project is located. The bold language is required by WAC 173-226-130 and must be included in its entirety. (Either use the fill-in template below or attach on a separate sheet of paper, if necessary.) (Note: This section is unprotected so you can delete text in parentheses) (Name of operator/permittee), (address of operator/permittee), is seeking coverage under the Washington State Department of Ecology's Construction Stormwater NPDES and State Waste Discharge General Permit. The proposed project, ,(project name) is located at (street address, intersection, crossroads, or other descriptive site location) in (name of nearest city), in (County). This project involves acres of soil disturbance for construction activities. (List all construction activities, for example, residential, commercial, industrial, highway, utility). Stormwater will be discharged to (List all named and un- named surface waterbodies, or ground water if applicable, waters identified in section IX). Any persons desiring to present their views to the Washington State Department of Ecology regarding this application, or interested in Ecology's action on this application, may notify Ecology in writing no later than 30 days of the last date of publication of this notice. Ecology reviews public comments and considers whether discharges from this project would cause a measurable change in receiving water quality, and, if so, whether the project is necessary and in the overriding public interest according to Tier II antidegradation requirements under WAC 173-201A-320. Comments can be submitted to: Department of Ecology Attn: Water Quality Program, Construction Stormwater P.O. Box 47696, Olympia, WA 98504.7696 XII. Certification of Permittees `7 certify under penalty of law that this document and all attachments were prepared under my direction or supervision in accordance with a system designed to assure that qualified personnel properly gather and evaluate the information submitted. Based on my inquiry of the person or persons who manage the system or those directly responsible for gathering the information, the information submitted is, to the best of my knowledge and belief, true, accurate, and complete. I am aware that there are significant penalties for submitting false information, including the possibility of fine and imprisonment for knowing violations." Printed Name / Company (operator/permittee only) Title Signature of Operator/Permittee* Date * Federal regulations require this application is signed by one of the following: A. For a corporation: By a principal executive officer of at least the level of vice president. B. For a partnership or sole proprietorship: By a general partner or the proprietor, respectively. C. For a municipality, state, federal, or other public facility: By either a principal executive officer or ranking elected official. Please sign and return this document to the following address: Washington Department of Ecology - Stormwater P.O. Box 47696 Olympia, WA 98504-7696 ECY 020-85 (Rev. 03/11) DO NO"Y SUBMIT THIS PAGE WITH YOUR APPLICATION If you have questions about this form, contact the following Ecology staff: Location Contact Name Phone E-mail City of Seattle, and Kitsap, Pierce, and Josh Klimek 360-407-7451losh.klimek(a.ecy.wa.gov Thurston counties Island, King, and San Juan counties Clay Keown 360-407-6048 clay.keown@ecy.wa.gov Adams, Asotin, Columbia, Ferry, Franklin, Shawn Hopkins 360-407-6442 shawn.hopkins@ecV.wa.gov Garfield, Grant, Lincoln, Pend Oreille, Skagit, Snohomish, Spokane, Stevens, Walla, Whatcom, and Whitman counties. Benton, Chelan, Clallam, Clark, Cowlitz, Joyce Smith 360-407-6858 ioyce.smith(a)ecy.wa.gov Douglas, Grays Harbor, Jefferson, Kittitas, Klickitat, Lewis, Mason, Okanogan, Pacific, Skamania, Wahkiakum, and Yakima counties. If you have questions about WebDMR, contact the following Ecology staff: Permittees must submit discharge monitoring reports (DMRs) each month using Ecology's secure online system, WebDMR. To have the ability to use the system immediately, you must submit the Electronic Signature Agreement with your application. If you have questions on this process, contact Ecology's WebDMR staff at WebDMR@ecy.wa.gov or 360-407-7097. More information is available at. hyR.#www.ecy.wa.gov/programs/wg/stormwater/construction/. If you need this document in a version for the visually impaired, call the Water Quality Program at 360-407-6401. Persons with hearing loss, call 711 for Washington Relay Service. Persons with a speech disability, call 877-833-6341. ECY 020-85 (Rev. 03111) Walgreens Chapter 9 — Operations and Maintenance Manual Please refer to Appendix C for the Operations and Maintenance Manual. Walgreens A bond quantities worksheet will not be required since no stormwater work will be conducted within the right-of-way. An itemized cost estimate will be provided with a later submittal. Walgreens Figure 1— Existing Conditions N mul 60 N EXISTING OUTF H'7 GRAPHIC 0 30 60 120 i AREA OF DISTURBANCE N81,250SF , EI� EXISTING CB I �I� u NORTH 240 in ( IN FEET ) 1 inch = 60 ft. AAAlEXISTINGI' BY NWS DATE 02.14.12 afghan associates, inc. WALGREENS - EDMONDS WA CHK BY CNH DATE 02.14.12 ENGINEERING JOB No A11182.11 4875 SW Griffith Drive I Suite 300 1 Beaverton, OR 197005 503.620.3030 tel. 1503.620.5539 fax www.aaleng.com FIGURE .q 1 SHEET 1 OF 1 Walgreens f � � \I 60 0 30 60 120 240 AAlafghap associates, inc. ENGINEERING 4575 SW Griffith Drive I Suite 300 1 Beaverton, OR 197005 503.620.3030 tel. 1503.620.5539 fax I www.aaieng.com ( IN FEET ) 1 inch = 60 ft. 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Walgreens O O O� n z II O U 11 3:0 N� O 3:d - O CN N- � II _ D CUA � o N N LC)O O d d- �O@) .off ,o((J3 ,� NLn° �0?� �N00 NaN�D NDN00 NN� NNI_,_ II X00 NII �(-o r --- m 0 ---mN CO IIo m�IIS F0 IIS U AWN U or_," (-o U QWN U �W v - O r Q) Q) U) N N r r N N N N 0 0 Z Z U m m _0 .a (1) a) C �C a) U Ln N C a) t3' a) li C cn Q) 0 C E a) (0 'O Z Z O U CL a) 0 0- o C' r d r LO f� d O 00 O r FLF �� O O o o O O o C) o O rn _ VO 00 et 00 00 LO LO (0 O LO LO r O '3 3 00 "f' O d' 00 eY 00 N m c LL N N co NT N N r N M > LL w rn LO O) O LO LO O tc) O 00 m.� ; LO 00 r LC) 00 I` coLO r U.2 LL U O O r r O N N N a� N (o 00 O 00 00 CO CO 'a c> o v o c O Lin LO f- r Uo' O Lo fn ; r O CI r O O N O O L ' O O O C) 00 O O O O p� c 00 (O 1- r d. CO 1 O O D N J O ; N O O M N r N CO 6 r j r N ei N O O co O O O O O O r N 00 O CO O r r Lr) Lr) Cl? 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O, O" O` O O o O ' o ; LO u) LC) L(i iO tO LO' LO tin u-)tr) tO u) tO Lt) , tc) u) tC) A6 tO°,o tO p� (nLL) :o c cuQ N ; (O 0) O h- 00 O It N 00 M (O LL) M � 00 00 ¢ v U i O r r r r r M N LO N; O O O O O O O O O p N LO CO mco co 't coN O ct U N O r r r r r N W¢ T O O O O O O O o o C) o 0 C) O C) a o C) o 0 0 0 0 M 0 a" 0 ":O) C)o: "(n 0)'o)o C) 0' O" (s� O. o- O m, O m C) m 10 m C) ,""a m" v) a 0) a "o O 0) O o C) rn. O C3 , O. ' O o 0 0 .O _ c N r 00 (O O N r O Q Q V; C) N N `O N T N N O O O O O O O O m CL 0 O E a ¢ m U (o LO a) Q xL CD m m m m = vOj p (D (.D (D __¢ 0 U U U p 0 Of or if tJ i'' J ti '� V ` r 1 1 , f : ` IN ,1 j !f ------------------ pm 9 -. t!f if,Sl I • t t f'f��+JJ�:iif�`tt `�' a � I � o I if`sJ t ( r ® 4, A J fr Jlt :{�I tai I If tli.r Y M r1t+ltrt r (Y 11 tif`, t I l t ffr+t r. f K 1 71 `1f;rG`n. D . fjj LID Jfr'.' i r+J]r' � i AL lfi fjjft �• t1('`ti �hflH 4A M r ' CN 1 it Plili "77 : filalrf�Evt 'flf; trf� _ II `� )TT flfl If f ".` tiff ' LL Mry \ sse rrlJf !r `! Jf t r!, . tq WOO r � ---- --- — F--- 3 ------= o iYl d, 4' g ' 1 Ad, LJ l� W 191 �{ W 99 l • • • (Parcel 11) Subcat Reach Pon Link' All 18 .11 ® Walgreens Edmonds WA (DETENTION) Prepared by AAI Engineering Inc. Printed 2/28/2012 HydroCADO 10.00 s/n 01638 C 2011 HydroCAD Software Solutions LLC Page 2 Area CN Description (acres) (subcatchment-numbers) 1.650 98 Impervious (1S, 2S) 1.650 98 TOTAL AREA All 1 82.11 ® Walgreens Edmonds WA (DETENTION) Type IA 24 -hr 10yr Rainfall=2.20" Prepared by AAI Engineering Inc. Printed 2/28/2012 HydroCAD® 10.00 s/n 01638 © 2011 HydroCAD Software Solutions LLC Page 3 Time span=0.00-24.00 hrs, dt=0.01 hrs, 2401 points Runoff by SBUH method Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: Post Development Runoff Area=21,795 sf 100.00% Impervious Runoff Depth>1.97" Tc=5.0 min CN=98 Runoff=0.25 cfs 0.082 of Subcatchment 2S: Post Development Runoff Area=50,072 sf 100.00% Impervious Runoff Depth>1.97" Tc=5.0 min CN=98 Runoff=0.58 cfs 0.189 of Pond 1P: 36" Pipe Peak Elev=319.95' Storage=1,030 cf Inflow=0.83 cfs 0.271 of Outflow=0.40 cfs 0.271 of Total Runoff Area = 1.650 ac Runoff Volume = 0.271 of Average Runoff Depth =1.97" 0.00% Pervious = 0.000 ac 100.00% Impervious = 1.650 ac ll 182.11 ® Walgreens Edmonds WA (DETENTION) Type IA 24 -hr 10yr Rainfall=2.20" Prepared by AAI Engineering Inc. Printed 2/28/2012 HydroCAD®10.00 s/n 01638 © 2011 HydroCAD Software Solutions LLC Paste 4 Runoff = 0.25 cfs @ 7.88 hrs, Volume= 0.082 af, Depth> 1.97" Runoff by SBUH method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type IA 24 -hr 10yr Rainfall=2.20" Area (sf) CN Description 21,795 98 Impervious 21,795 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, ubcatchment IS: Post Development (Parcel 1) Hydrograph 0. 0. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (hours) All 182.11 ® Walgreens Edmonds WA (DETENTION) Type IA 24 -hr 10yr Rainfall=2.20" Prepared by AAI Engineering Inc. Printed 2/28/2012 HydroCADO 10.00 s/n 01638 © 2011 HydroCAD Software Solutions LLC Page 5 Runoff = 0.58 cfs @ 7.88 hrs, Volume= 0.189 af, Depth> 1.97" Runoff by SBUH method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type IA 24 -hr 10yr Rainfall=2.20" Area (sf) CN Description 50,072 98 Impervious 50,072 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, ubcatchment : Post Development (Parcel 11) Hydrograph Runoff 0.6 0.58 cfs 0.55Y� I ®ter - ------------------ - --- -- -- 1 0.5 Itl ;11 _--------------- N 0.35 ------------ --------------- ---- 0 0.3LL - r 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (hours) All 182.11 ® Walgreens Edmonds WA (DETENTION) Type IA 24 -hr 10yr Rainfall=2.20" Prepared by AAI Engineering Inc. Printed 2/28/2012 HydroCAD®10.00 s/n 01638 @2011 HydroCAD Software Solutions LLC Page 6 Inflow Area = 1.650 ac,100.00% Impervious, Inflow Depth > 1.97" for 10yr event Inflow = 0.83 cfs @ 7.88 hrs, Volume= 0.271 of Outflow = 0.40 cfs @ 8.31 hrs, Volume= 0.271 af, Atten= 52%, Lag= 25.8 min Primary = 0.40 cfs @ 8.31 hrs, Volume= 0.271 of Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 319.95'@ 8.31 hrs Surf.Area= 808 sf Storage= 1,030 cf Plug -Flow detention time= 10.6 min calculated for 0.271 of (100% of inflow) Center -of -Mass det. time= 10.6 min ( 686.2 - 675.6 ) Volume Invert Avail.Storage Storage Description #1 317.70' 1,979 cf 36.0" D x 280.0'L CMP -Round 36" S= 0.0050'P Device Routing Invert Outlet Devices #1 Primary 317.60' 3.2" Vert. 10yr C= 0.600 #2 Primary 319.95' 4.1" Vert. 100yr C=0.600 #3 Primary 320.56' 12.0" Horiz. Emergency Overflow C=0.600 Limited to weir flow at low heads Primary OutFlow Max=0.40 cfs @ 8.31 hrs HW=319.95' (Free Discharge) 1=10yr (Orifice Controls 0.40 cfs @ 7.17 fps) 2=100yr ( Controls 0.00 cfs) 3=Emergency Overflow ( Controls 0.00 cfs) 0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 v 0.5 3 0.45 0 E 0.4 0.35 0.3 0.25 0.2 0.15 0.1 Pond 1 P: 36" Pipe Hydrograph . ...... ...... f f i I P i*E t 1T9 I t�°Y P P PTP'Y # P PS , TR'S®(°Y IT! 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (hours) -=----•---- C Pond 1 P: 36" Pipe Hydrograph . ...... ...... f f i I P i*E t 1T9 I t�°Y P P PTP'Y # P PS , TR'S®(°Y IT! 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (hours) Al 1182.11 - Walgreens Edmonds WA (DETENTION) Type IA 24 -hr 100yr Rainfall=3.00" Prepared by AAI Engineering Inc. Printed 2/28/2012 HydroCAD®10.00 s/n 01638 © 2011 HydroCAD Software Solutions LLC Page 7 Time span=0.00-24.00 hrs, dt=0.01 hrs, 2401 points Runoff by SBUH method Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: Post Development Runoff Area=21,795 sf 100.00% Impervious Runoff Depth>2.76" Tc=5.0 min CN=98 Runoff=0.35 cfs 0.115 of Subcatchment 2S: Post Development Runoff Area=50,072 sf 100.00% Impervious Runoff Depth>2.76" Tc=5.0 min CN=98 Runoff=0.80 cfs 0.265 of Pond 1P: 36" Pipe Peak Elev=320.56' Storage=1,499 cf Inflow=1.15 cfs 0.380 of Outflow=0.74 cfs 0.380 of Total Runoff Area = 1.650 ac Runoff Volume = 0.380 of Average Runoff Depth = 2.76" 0.00% Pervious= 0.000 ac 100.00% Impervious= 1.650 ac 111 82.11 ® Walgreens Edmonds WA (DETENTION) Type IA 24 -hr 100yr Rainfall=3. 00 " Prepared by AN Engineering Inc. Printed 2/28/2012 HydroCAD® 10.00 s/n 01638 © 2011 HydroCAD Software Solutions LLC Page 8 92=22-4 M4 19M, Mi Z 'Jill ll1j'll;!lll!l1F111l iiii1p;Illipill. Runoff = 0.35 cfs @ 7.88 hrs, Volume= 0.115 af, Depth> 2.76" Runoff by SBUH method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type IA 24 -hr 1 00y Rainfall=3.00" Area (sD CN Description 21,795 98 Impervious 21,795 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, All 182.11 - Walgreens Edmonds WA (DETENTION) Type IA 24 -hr 100yr Rainfall=3.00 Prepared by AAI Engineering Inc. Printed 2/28/2012 HydroCAD® 10.00 s/n 01638 0 2011 HydroCAD Software Solutions LLC Page 9 • •111711• •• Runoff = 0.80 cfs @ 7.88 hrs, Volume= 0.265 af, Depth> 2.76" Runoff by SBUH method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type IA 24 -hr 100yr Rainfall=3.00" Area (sf) CN Description 50,072 98 Impervious 50,072 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, ubcatchment 2S: Post Development (Parcel II) Hydrograph Al 1182.11 - Walgreens Edmonds WA (DETENTION) Type IA 24 -hr 100yr Rainfall=3.04x' Prepared by AAI Engineering Inc. Printed 2/28/2012 HydroCADO10.00 s/n 01638 0 2011 HydroCAD Software Solutions LLC Page 10 an =-1 - - • Inflow Area = 1.650 ac,100.00% Impervious, Inflow Depth > 2.76" for 100yr event Inflow = 1.15 cfs @ 7.88 hrs, Volume= 0.380 of Outflow = 0.74 cfs @ 8.15 hrs, Volume= 0.380 af, Atten= 36%, Lag= 16.1 min Primary = 0.74 cfs @ 8.15 hrs, Volume= 0.380 of Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 320.56' @ 8.15 hrs Surf.Area= 708 sf Storage= 1,499 cf Plug -Flow detention time= 14.5 min calculated for 0.380 of (100% of inflow) Center -of -Mass det. time= 14.4 min ( 680.1 - 665.7 ) Volume Invert Avail.Storage Storage Description #1 317.70' 1,979 cf 36.0" D x 280.0'L CMP—Round 36" S= 0.00507' Device Routing Invert Outlet Devices #1 Primary 317.60' 3.2" Vert. 10yr C= 0.600 #2 Primary 319.95' 4.1" Vert. 100yr C= 0.600 #3 Primary 320.56' 12.0" Horiz. Emergency Overflow C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=0.74 cfs @ 8.15 hrs HW=320.56' (Free Discharge) 1=10yr (Orifice Controls 0.45 cfs @ 8.09 fps) 2=100yr (Orifice Controls 0.29 cfs @ 3.18 fps) 3=Emergency Overflow ( Controls 0.00 cfs) , � .. � : � � 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (hours) ry O F— U w Z z O U «9 cn F- ¢ LLJ c=i�n=¢� 0 LLJ w woN�� m Q ( ¢ O O' 00 C) (n z Q O\ J F= 0 Cf) F—wUw Z O m< p S m O w O¢ O Z J J O N 0' U w O>- ¢ — z (n J z Jly Jm� �Q W d Q W ��LQ v� U O m c,4 :E m Lel 7; 0_ Z U \ g 1 «0 k79� j�3_dld�OAd NW F 'NIW „8l w Z — O 11 10 W W cn f— cll Q H W W W J J W n It ' "-tom 7 VV CC�i m ry D U z Q J w w C/) w Q «Z[ o � o z Eli k- =J Uw � O JI QUO Q W c W :2 r- O co U W W cn f— cll Q H W W W J J W n It 0 ry U Ln fle I < ED Ld Ln m 7' 0 wz LLI 0 LLI 0 LLI Q:� < 3: F- LiJ LLj LLJ O J^m < I Uo w (.3 z -j Li n CIOLli M � m LLJ UN a_ �( < ("i m CD M CO — ct:� cl) =) 0 clf C:) Li=D I C-) C) LJ = LLJ < zI < o = = LLJ ;7 Qz U) n 2: — <-J < < I-- < CD Q�� w< L C) ry V) C:) Ld Lli > 0 0 Ln fle I ED Ln Ln fle I munxw°PU-&H@ P -3 -az (SIV)`m3 au-as(su):,gj 1091115-m`m M9I19iS£0S'i°Wd DIN Y3 O)SONYM3 NYS 1IU6 SO V -11 -JUNK 9001 V°°10359001 137!15 AMM3d 89 3d321Ill]31RMSUNINUS39NISAtlB V NIt133N1I�3NID 9 N3 Ol060HS S311N3d0Nd 111H N3fl3S V F— eeH tolle g R ss IR Id N �� E ; � 3€! a eeH Walgreens The facility -specific maintenance standards contained in this section are intended to be conditions for determining if maintenance actions are required as identified through inspection. They are not intended to be measures of the facility's required condition at all times between inspections. In other words, exceedence of these conditions at any time between inspections and/or maintenance does not automatically constitute a violation of these standards. However, based upon inspection observations, the inspection and maintenance schedules shall be adjusted to minimize the length of time that a facility is in a condition that requires a maintenance action. Table 4.5 — Maintenance Standards Maintenance. Defect "= Conditions When'Maintenance Is Results Expec#el When component ., Needed Maintenance is Performed ' ,_. General Trash & Debris Any trash and debris which exceed 5 Trash and debris cleared from site. cubic feet per 1,000 square feet (this is about equal to the amount of trash it would take to fill up one standard size garbage can). In general, there should be no visual evidence of dumping. If less than threshold all trash and debris will be removed as part of next scheduled maintenance. Poisonous Any poisonous or nuisance No danger of poisonous vegetation Vegetation and vegetation which may constitute a where maintenance personnel or the noxious weeds hazard to maintenance personnel or public might normally be. (Coordinate the public. with local health department) Any evidence of noxious weeds as Complete eradication of noxious weeds defined by State or local regulations. may not be possible. Compliance with State or local eradication policies (Apply requirements of adopted IPM required policies for the use of herbicides). Contaminants Any evidence of oil, gasoline, NO and Pollution contaminants or other pollutants eentafainants or-petlxtants (Coordinate removal/cleanup with pry local water quality response agency). Rodent Holes Any evidence of rodent holes if Rodents destroyed and dam or berm facility is acting as a dam or berm, or repaired. (Coordinate with local health any evidence of water piping through department; coordinate with Ecology dam or berm via rodent holes. Dam Safety Office if pond exceeds 10 acre-feet.) f=&tZ_ 2 �Id2�►Cr�� of A)&. 2 tNl��c .9 r/or✓ 4-30 Volume V — Runoff Treatment BMPs February 2005 • 1- • -• 1 • ]111arntenance :.Defect :Conditions When Maintehance 1s ResuifsExpected When Component,; Needed - Maintenance Is Performed Pond Berms Settlements Any part of berm which has settled 4 Dike is built back to the design (Dikes) inches lower than the design elevation. elevation. If settlement is apparent, measure berm to determine amount of settlement. Settling can be an indication of more severe problems with the berm or outlet works. A licensed civil engineer should be consulted to determine the source of the settlement. Piping Discernable water flow through pond Piping eliminated. Erosion potential berm. Ongoing erosion with potential resolved. for erosion to continue. (Recommend a Goethechnical engineer be called in to inspect and evaluate condition and recommend repair of condition. Emergency Tree Growth Tree growth on emergency spillways Trees should be removed. If root Overflow/ creates blockage problems and may system is small (base less than 4 Spillway and cause failure of the berm due to inches) the root system may be left in Berms over 4 uncontrolled overtopping. place. Otherwise the roots should be feet in height. removed and the berm restored. A Tree growth on berms over 4 feet in licensed civil engineer should be height may lead to piping through the consulted for proper berm/spillway berm which could lead to failure of restoration. the berm. Piping Discernable water flow through pond Piping eliminated. Erosion potential berm. Ongoing erosion with potential resolved. for erosion to continue. (Recommend a Goethechnical engineer be called in to inspect and evaluate condition and recommend repair of condition. Emergency Emergency Only one layer of rock exists above Rocks and pad depth are restored to Overflow/ Overflow/ native soil in area five square feet or design standards. Spillway Spillway larger, or any exposure of native soil at the top of out flow path of spillway. (Rip -rap on inside slopes need not be replaced.) Erosion See "Side Slopes of Pond" Q�,C��t2�r'j1Enh'S 0 � N o. 2 � ! N FI �-r 2.�.T► �nJ 4-32 Volume V — Runoff Treatment BMPs February 2005 .::. ....... Maintenance ; Defect Conditions When. Maintenance Is , Results Expected When 6 'Conipooent .' � °Needed. Maintenance 1s . Performed. General Trash & Debris See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Poisonous/Noxious See "Detention Ponds" (No. 1). See "Detention Ponds" Vegetation (No. 1). Contaminants and See "Detention Ponds" (No. 1). See "Detention Ponds" Pollution (No. 1). Rodent Holes See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1) Storage Area Sediment Water ponding in infiltration pond after Sediment is removed rainfall ceases and appropriate time and/or facility is cleaned allowed for infiltration. so that infiltration system works according to A percolation test it or test of facility ( p P Y design. indicates facility is only working at 90% of its designed capabilities. If two inches or more sediment is present, remove). Filter Bags (if Filled with Sediment and debris fill bag more than 1/2 Filter bag is replaced or applicable) Sediment and full. system is redesigned. Debris Rock Filters Sediment and By visual inspection, little or no water flows Gravel in rock filter is Debris through filter during heavy rain storms. replaced. Side Slopes of Erosion See "Detention Ponds" (No. 1). See "Detention Ponds" Pond (No. 1). Emergency Tree Growth See "Detention Ponds" (No. 1). See "Detention Ponds" Overflow Spillway (No. 1). and Berms over 4 feet in height. Piping See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Emergency Rock Missing See "Detention Ponds" (No. 1). See "Detention Ponds" Overflow Spillway (No. 1). Erosion See "Detention Ponds" (No. 1). See "Detention Ponds" (No. 1). Pre -settling Facility or sump 6" or designed sediment trap depth of Sediment is removed. Ponds and Vaults filled with Sediment sediment. and/or debris February 2005 Volume V — Runoff Treatment BMPs 4-33 Maintenance "_ : Compo"nest Defecf Conditions When Maintenance is Needed Results Expected ="When Maintenance is ; �:. " Perfarned �::, Storage Area Plugged Air Vents One-half of the cross section of a vent is blocked at any point or the vent is damaged. Vents open and functioning. Debris and Sediment Accumulated sediment depth exceeds 10% of the diameter of the storage area for 1/2 All sediment and 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 (Will require engineering analysis to are sealed. 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 required by engineer to determine structural replaced to design. 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. Cracks wider than 1/2 -inch at the joint of any No cracks more than inlet/outlet pipe or any evidence of soil 1/4 -inch wide at the particles entering the vault through the walls. joint of the inlet/outlet pipe. 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). 4-34 Volume V — Runoff Treatment BMPs February 2005 iNainfeitance, . ; =Component x. .;. Defect Condifion iNhen Maintenance is wee%6L l ;. . >. Resuifs Expected ; Wien iVlainfenance Isle ormdd=,�., 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 potential of blocking) the overflow pipe. Pipe is free of all obstructions and works as designed. Manhole See "Closed See "Closed Detention Systems" (No. 3). See "Closed Detention Systems" (No. 3). Detention Systems" (No. 3). Catch Basin See "Catch Basins" See "Catch Basins" (No. 5). 1 See "Catch Basins" (No. 5). (No. 5). February 2005 Volume V — Runoff Treatment BMPs 4-35 Maintenance .. , :Deflect 'Conditions When Maintenance is, Needed' ' .Resutts Expected When Component =: Maintenance �s 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 than 10% of the basin opening. No vegetation blocking opening to basin. Vegetation growing in inlettoutlet pipe joints No vegetation or root that is more than six inches tall and less than growth present. six inches apart. 4-36 Volume V — Runoff Treatment BMPs February 2005 No. 6 — Debris Barriers (e.g., Trash Racks) General Contamination See "Detention Ponds" (No. 1). No pollution present. Metal and Pollution Bars are bent out of shape more than 3 inches. Bars in place with no bends more than 3/4 inch. 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 Bars are loose and rust is causing 50% Mechanism maintenance person with proper tools. Bolts proper tools. Not Working into frame have less than 1/2 inch of thread. design standards. nlet/Outlet Fp 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 Grate is in place and Missing. grate. meets design standards. No. 6 — Debris Barriers (e.g., Trash Racks) General Trash and Debris Trash or debris that is plugging more than 20% of the openings in the barrier. Barrier cleared to design flow capacity. Metal Damaged/ Missing Bars are bent out of shape more than 3 inches. Bars in place with no bends more than 3/4 inch. Bars. Bars are missing or entire barrier Bars in place according to design. missing. Bars are loose and rust is causing 50% Barrier replaced or repaired to deterioration to any part of barrier. design standards. nlet/Outlet Fp Debris barrier missing or not attached to Barrier firmly attached to pipe ip e pipe February 2005 Volume V — Runoff Treatment BMPs 4-37 No. Energy Mair►tenance7FC Conditions When Maintenanceis, Results`Ezpected When onents Needed Maintenance isPerformed External: Rock Pad Missing or Only one layer of rock exists above Rock pad replaced to design Moved Rock native soil in area five square feet or standards. larger, or any exposure of native soil. Erosion Soil erosion in or adjacent to rock pad. Rock pad replaced to design standards. Dispersion Trench Pipe Plugged with Sediment Accumulated sediment that exceeds 20% of the design depth. Pipe cleaned/flushed so that it matches design. Not Visual evidence of water discharging at Trench redesigned or rebuilt to Discharging concentrated points along trench (normal standards. Water condition is a "sheet flow" of water along Properly trench). Intent is to prevent erosion damage. Perforations Over 1/2 of perforations in pipe are Perforated pipe cleaned or Plugged. plugged with debris and sediment. replaced. Water Flows Maintenance person observes or Facility rebuilt or redesigned to Out Top of receives credible report of water flowing standards. "Distributor" out during any storm less than the design Catch Basin. storm or its causing or appears likely to cause damage. Receiving Water in receiving area is causing or has No danger of landslides. Area Over- potential of causing landslide problems. Saturated Internal: Manhole/Chamber Worn or Structure dissipating flow deteriorates to Structure replaced to design Damaged 1/2 of original size or any concentrated standards. Post, worn spot exceeding one square foot Baffles, Side which would make structure unsound. of Chamber Other See "Catch Basins" (No. 5). See "Catch Basins" (No. 5). Defects 4-38 Volume V — Runoff Treatment BMPs February 2005 Maintenance Def ct or . Condit on When �� Recommended Maintenan_ ce to Correct Component ; Probtera.. `.Maintenance is Needed 'Pro 16 General Sediment Sediment depth exceeds 2 Remove sediment deposits on grass Accumulation on inches. treatment area of the bio-swale. When Grass finished, swale should be level from side to side and drain freely toward outlet. There should be no areas of standing water once inflow has ceased. Standing Water When water stands in the Any of the following may apply: remove swale between storms and sediment or trash blockages, improve does not drain freely. grade from head to foot of swale, remove clogged check dams, add underdrains or convert to a wet biofiltration Swale. Flow spreader Flow spreader uneven or Level the spreader and clean so that flows clogged so that flows are not are spread evenly over entire swale width. uniformly distributed through entire swale width. Constant When small quantities of Add a low -flow pea -gravel drain the length Baseflow water continually flow through of the swale or by-pass the baseflow the swale, even when it has around the swale. been dry for weeks, and an eroded, muddy channel has formed in the swale bottom. Poor Vegetation When grass is sparse or bare Determine why grass growth is poor and Coverage or eroded patches occur in correct that condition. Re -plant with plugs more than 10% of the swale of grass from the upper slope: plant in the bottom. swale bottom at 8 -inch intervals. Or re- seed into loosened, fertile soil. Vegetation When the grass becomes Mow vegetation or remove nuisance excessively tall (greater than vegetation so that flow not impeded. 10 -inches); when nuisance Grass should be mowed to a height of 3 to weeds and other vegetation 4 inches. Remove grass clippings. starts to take over. Excessive Grass growth is poor because If possible, trim back over -hanging limbs Shading sunlight does not reach and remove brushy vegetation on swale. adjacent slopes. Inlet/Outlet Inlet/outlet areas clogged with Remove material so that there is no sediment and/or debris. clogging or blockage in the inlet and outlet area. Trash and Trash and debris Remove trash and debris from bioswale. Debris accumulated in the bio-swale. Accumulation Erosion/Scouring Eroded or scoured swale For ruts or bare areas less than 12 inches bottom due to flow wide, repair the damaged area by filling channelization, or higher with crushed gravel. If bare areas are flows. large, generally greater than 12 inches wide, the swale should be re -graded and re -seeded. For smaller bare areas, overseed when bare spots are evident, or take plugs of grass from the upper slope and plant in the swale bottom at 8 -inch intervals. February 2005 Volume V — Runoff Treatment BMPs 4-39 • . : • - _I. . • .r 0_ Maintenance , Goniponenf Defect . Condition,When Main#enanct� is Needed Results Expected When Maintenance is Performed General Monitoring Inspection of discharge water for obvious signs of poor water Effluent discharge from vault should be clear with out thick visible sheen. quality. Sediment Sediment depth in bottom of vault No sediment deposits on vault Accumulation exceeds 6 -inches in depth. bottom that would impede flow through the vault and reduce separation efficiency. Trash and Debris Trash and debris accumulation in Trash and debris removed from Accumulation vault, or pipe inlet/outlet, vault, and inlet/outlet piping. floatables and non-floatables. Oil Accumulation Oil accumulations that exceed 1- Extract oil from vault by vactoring. inch, at the surface of the water. Disposal in accordance with state and local rules and regulations. Damaged Pipes Inlet or outlet piping damaged or broken and in need of repair. Pipe repaired or replaced. Access Cover Cover cannot be opened, Cover repaired to proper working Damaged/Not corrosion/deformation of cover. specifications or replaced. Working Vault Structure Vault replaced or repairs made so Damage - Includes Cracks in Walls See "Catch Basins" (No. 5) that vault meets design specifications and is structurally Bottom, Damage to sound. Frame and/or Top Slab Cracks wider than 1/2 -inch at the Vault repaired so that no cracks joint of any inlet/outlet pipe or evidence of soil particles entering exist wider than 1/4 -inch at the joint of the inlet/outlet pipe. 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 person. Access Ladder Ladder is corroded or Ladder replaced or repaired and Damaged deteriorated, not functioning properly, not securely attached to meets specifications, and is safe to use as determined by inspection structure wall, missing rungs, personnel. cracks, and misaligned. 4-48 Volume V — Runoff Treatment BMPs February 2005 Maintenance" Component Defect Conditions Whenntenance'is Needed '= Results Expected When Maintenance is Performed General Sediment Accumulation When sediment forms a cap over the insert media of the insert and/or unit. No sediment cap on the insert media and its unit. Trash and Trash and debris accumulates on insert Trash and debris removed Debris unit creating a blockage/restriction. from insert unit. Runoff freely Accumulation flows into catch basin. Media Insert Not Effluent water from media insert has a Effluent water from media Removing Oil visible sheen. insert is free of oils and has no visible sheen. Media Insert Catch basin insert is saturated with water Remove and replace media Water Saturated and no longer has the capacity to insert absorb. Media Insert -Oil Media oil saturated due to petroleum spill Remove and replace media Saturated that drains into catch basin. insert. Media Insert Use Media has been used beyond the typical Remove and replace media at Beyond Normal Product Life average life of media insert product. regular intervals, depending on insert product. 4-50 Volume V — Runoff Treatment BMPs February 2005 Walgreens February XX, 2012 JN 12034 Seven Hills Properties, LLC 88 Perry Street #800 San Francisco, California 94107 via email. jhill@sevenhillsprop.com Attention: Jonathan Hill Subject: Transmittal Letter — Geotechnical Engineering Study Proposed Walgreens Development 9801 Edmonds Way Edmonds, Washington Dear Mr. Hill: We are pleased to present this geotechnical engineering report for the Walgreens Development project to be constructed at 9801 Edmonds Way in Edmonds, Washington. The scope of our services consisted of exploring site surface and subsurface conditions, and then developing this report to provide recommendations for general earthwork and design criteria for foundations, retaining walls, and shoring. This work was authorized by your acceptance of our proposal, P- 8308, dated January 30, 2012. The attached report contains a discussion of the study and our recommendations. Please contact us if there are any questions regarding this report, or for further assistance during the design and construction phases of this project. Respectfully submitted, GEOTECH CONSULTANTS, INC. D. Robert Ward, P.E. Principal cc: Baysinger Partners Architecture — William M. Ruecker via email. billr@baysingerpartners.com JLH/DRW: jyb GEOTECH CONSULTANTS, INC. Proposed Walgreens 8 p p: Way Edmonds, Washington This report presents the findings and recommendations of our geotechnical engineering study for the site of the proposed Walgreens Development project to be located at 9801 Edmonds Way in Edmonds. We were provided with preliminary plans and a topographic map. Baysinger Partners Architecture developed the plans, the latest of which is dated December 14, 2011. The topographic survey was created by Foster & Maddux Surveying, Inc., and is dated October 31, 2011. Based on the provide information, we understand that the project will consist of removing the existing bowling alley building on the site, and constructing a new, 14,490 square foot Walgreens drugstore building on the northern portion of the site. An access drive is proposed around the east and north sides of the new building, which will require a significant excavation and retaining wall of up to about 35 feet tall along the northern edge of the site and a smaller wall needed on the eastern side. South of the new drugstore, near State Route No. 104 (Edmonds Way) a new, 4,500 square -foot bank building is proposed. Some stormwater infiltration is also proposed in some new rain gardens in an existing parking lot area west of the proposed buildings. Also, there is a possibility of various additional infiltration facilities nearer the proposed Walgreens and bank building. If the scope of the project changes from what we have described above, we should be provided with revised plans in order to determine if modifications to the recommendations and conclusions of this report are warranted. SITE CONDITIONS FJJ:JgA The Vicinity Map, Plate 1, illustrates the general location of the site in Edmonds. The project area includes two parcels located along the northern side of Edmonds Way. The eastern portion of the subject site is mostly developed with a bowling alley and parking lot, while the western side contains a parking lot. The site is bordered to the east and west by commercial properties currently developed with a bank, and grocery and pet store, respectively. The parking lot on the eastern side of the property is used by the grocery and pet store patrons. A residential development is located upslope and north of the property. Most of the site, which includes the bowling alley building and parking lots, is relatively level with just a slight rise to the east/northeast. This flat area has grades ranging from approximately elevation 319 feet to 325 feet. The main (and lowest) level of the bowling alley appears to have a finish floor of approximately 325 feet. The areas directly north and east of the bowling alley building are undeveloped. The northern area is mostly covered with a few large trees and blackberry bushes. The eastern area is mostly covered with grass. A steep slope that rises up to the north at approximately 80 to 90 percent is located north of the building. The height of the slope is approximately 40 to 55 feet. We did not notice any indications of slope instability or seepage along the face of this steep slope at the time of our investigation. The top of the slope appears to be relatively flat; the residential development is located in this flatter area. A stormwater pipe that apparently conveys water from the development and/or upper streets is located on the steep slope GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 2 near the northeastern corner of the site; it discharges water on onto the property at approximately elevation 345 feet. It appears that the water makes its way onto the existing bank property adjacent to the east. The undeveloped area east of the bowling alley is somewhat of a "ridge" that runs north -south between the bowling alley and the adjacent eastern bank parking lot. The ridge declines to the south from approximately elevation 345 feet down to approximately elevation 325 feet. Existing utility lines are located in the southern portion of this undeveloped area. As noted earlier, a new concrete wall is proposed north of the Walgreens building. There is currently already a concrete retaining wall located along the northern edge of the existing western parking lot. This wall is up to approximately 20 feet tall. The new wall will connect to and extend east of this existing wall. WIT-1112-IfI IM![s] The subsurface conditions were explored by drilling five test borings at the approximate locations shown on the Site Exploration Plan, Plate 2. Our exploration program was based on the proposed construction, anticipated subsurface conditions and those encountered during exploration, and the scope of work outlined in our proposal. The test borings were drilled on February 14 and 15, 2012 using a small, track -mounted, hollow - stem auger drill. Samples were taken at 5 -foot intervals with a standard penetration sampler. This split -spoon sampler, which has a 2 -inch outside diameter, is driven into the soil with a 140 -pound hammer falling 30 inches. The number of blows required to advance the sampler a given distance is an indication of the soil density or consistency. A geotechnical engineer from our staff observed the drilling process, logged the test borings, and obtained representative samples of the soil encountered. The Test Boring Logs are attached as Plates 3 through 8. Soil Conditions The test borings generally revealed similar soil conditions beneath the surface of the site; native sand with some gravel was encountered at the surface in the test borings with the exception of the Test Boring 4, drilled in the area of the proposed bank. Up to approximately 7 feet of loose sand, apparently fill soil, was encountered over the sand in this test boring. The test borings revealed that the sand is generally dense near the existing ground surface, and becomes very dense with depth. This sand was glacially consolidated. The deepest boring, Test Boring 1, was drilled to a maximum explored depth approximately 45 feet. Test Boring 1, conducted along the steep northern slope, indicates that dense to very dense native sand comprise the core of the steep slope. No obstructions were revealed by our explorations. However, debris, buried utilities, and old foundation and slab elements are commonly encountered on sites that have had previous development. Groundwater Conditions No groundwater seepage was observed in our test borings. The test borings were left open for only a short time period. Therefore, the seepage levels on the logs represent the location of transient water seepage and may not indicate the static groundwater level. GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 JN 12034 Page 3 Groundwater levels encountered during drilling can be deceptive, because seepage into the boring can be blocked or slowed by the auger itself. It should be noted that groundwater levels vary seasonally with rainfall and other factors. It is possible that groundwater could be found in more permeable soil layers, coarser sand and gravel lenses, and between the near -surface, more weathered soil and the underlying denser soil. The stratification lines on the logs represent the approximate boundaries between soil types at the exploration locations. The actual transition between soil types may be gradual, and subsurface conditions can vary between exploration locations. The logs provide specific subsurface information only at the locations tested. The relative densities and moisture descriptions indicated on the test boring logs are interpretive descriptions based on the conditions observed during drilling. THIS SECTION CONTAINS A SUMMARY OF OUR STUDY AND FINDINGS FOR THE PURPOSES OF A GENERAL OVERVIEW ONLY. MORE SPECIFIC RECOMMENDATIONS AND CONCLUSIONS ARE CONTAINED IN THE REMAINDER OF THIS REPORT. ANY PARTY RELYING ON THIS REPORT SHOULD READ THE ENTIRE DOCUMENT. The test borings conducted for this study generally encountered dense native sand beneath the surface of the site in most locations. The exception being Test Boring 4, conducted in area of the proposed bank building, which encountered approximately 7 feet of loose soil overlying the dense native sand. It appears in the location of the new Walgreens building that dense native sands will likely be exposed at or near the depth of the planned foundation excavations. The possible exception where some overexcavation may be needed to reach the dense sand would be the southern side of the building, although we do expect the overexcavation to be minor. The dense native sand is well suited for the support of the proposed building. Based on our investigation, the proposed new drugstore building may be constructed using conventional foundations supported on the competent, dense native sand. As noted above, in the area of the proposed bank building, loose soil (possibly fill) was encountered to a depth of approximately 7 feet. This loose soil is not suitable for supporting the loads imposed by the new bank building because settlement would occur. The foundation for this building should bear on or into the competent native sand. The entire extent of the loose soil is not known, as only one test boring was done in that areas; however, we anticipate that the loose soil may exist under a majority of the proposed bank foundation. Several options exist for foundation construction that will allow for the loads to be adequately transferred to the competent native sand, including: 1) Remove the loose soil down to the dense sand placing footings on the sand. 2) Remove the loose soil down to the dense sand and replacing it with imported structural fill. The fill could consist of structural fill soil or lean -mix concrete as noted in Conventional Foundations section of this report. 3) Avoid the overexcavation and use a deep foundation system. A very adequate system based on the likely loads of the bank in our opinion would be small diameter steel pipe piles that are driven into the underlying, competent.native soil. GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 4 A significant geotechnical engineering consideration of the project is the large excavation and subsequent retaining wall needed at the northeastern corner. The depth or excavation and subsequent wall will vary from approximately 20 to 35 feet. Due to the depth of excavation, and its location on the steep slope and relatively close to property lines, excavation shoring will be needed for most of the tall wall. One exception could be along the eastern side of the property where a conventional retaining wall could possibly be constructed if temporary excavation easements can be obtained from the neighboring eastern property owner. The shoring should likely be incorporated into the permanent retaining wall system. Based on the soils observed in our test borings, the height and location of the shoring wall, we feel two options are feasible for construction of the shoring wall that is taller than approximately 15 feet; that being a soil nail wall or a tied -back soldier pile wall. More simple, cantilevered soldier piles shoring could be used for shorter excavations. Further recommendations regarding the design and construction of the potential shoring systems can be found in the subsequent sections of this report. We point out two significant items regarding the proposed shoring walls, especially the northern wall: 1) the design of nails or tie -backs must illustrate that these structures will not extend across the property lines; if they do cross property lines, easements will be needed and 2) due to the very step inclination of the northern slope, at least 2 feet of catchment should be included in the final wall design. This is because though the northern slope has a core soil of very dense sand, the outer, weathered surface of the slope is relatively loose (this is typical for any steep slope in the Puget Sound area). Based on The Edmonds Community Development Code (ECDC), Chapter 23 (Geologically Hazardous Areas), the steep northern slope would be classified as a critical area susceptible to two specific types of geological hazards. One is a Landslide Hazard Area due to its steeper than 40 percent slope, and greater than 10 foot vertical relief. The other is an Erosion Hazard Area. The ECDC suggests a minimum development buffer of 50 feet from any landslide area, although this buffer can be minimized to 10 feet. In our professional opinion, this minimum buffer of 10 feet is warranted. However, the ECDC further states that a reduction of the buffer, and alteration or development within Geologically Hazard Areas and their associated buffers, is allowed if supported by a geotechnical report and if certain requirements are followed. We will provide information regarding the requirements below. However, we first want to state that it is our professional opinion from a geotechnical engineering standpoint that the project can be built as planned, whereby development occurs in the Landslide and Erosion Hazard area and the associated buffers, because of two main points: 1) the core soil at the site is dense to very dense, glacially - consolidated, native sand and 2) permanent retaining walls that are designed to modern standards will be placed where steep, unsupported slopes currently exist, and 3) water from a stormwater pipe that currently discharges water onto the northern slope will be repaired so that the water does not discharge onto the slope. Based on ECDC 23.80.060A, an alteration to a Geologically Hazardous Area and associated buffer may occur for activities that: 1. Will not increase the threat of the geologic hazard to adjacent properties beyond predevelopment conditions; 2. Will not adversely affect other critical areas 3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less that predevelopment conditions; and 4. Are certified as safe as designed and under anticipated conditions by a qualified engineer licensed in the State of Washington. The slope on the northern portion of the site is unsupported and extends directly down to the base of an existing building. The project will include the use of a large retaining wall, designed to current GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 5 standards at this slope. This wall will also include catchment. It is our professional opinion that this wall will provide more stability for the slope and area in comparison to the current unsupported slope. In addition, as noted above, water from a stormwater pipe that currently discharges water onto the northern slope will be repaired so that the water does not discharge onto the slope. Lastly, if the recommendations contained in this report are followed, we strongly believe that the project is safe as designed under anticipated conditions. For all these significant reasons, it is our professional opinion that the four points noted in ECDC 23.80.060A are satisfied. In addition, ECDC 23.80.070A2 indicates that alterations of an Erosion or Landslide Hazard Area and buffer may occur for activities for which a hazards analysis is submitted and certifies that: a) The development will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions; b) The development will not decrease slope stability on adjacent properties; and c) Such alterations will not adversely impact other critical areas. This project will decrease, not increase amount of surface water discharge or sedimentation to the adjacent property, so a) is most definitely satisfied. As for b), as noted above, we believe that the construction of new retaining wall will may increase, not decrease slope stability. Lastly, the only other critical area is the steep slope above the proposed retaining wall; this slope will be positively, not adversely affected because of the wall in our opinion. The infiltration of stormwater is being considered for this project. We understand that using rain gardens in the west parking lot area is one consideration. As noted earlier, dense to very dense sand was revealed near the ground surface in the test borings, especially at the northeastern portion of the site. Because of this denseness, it is our professional opinion that infiltration in this area is extremely limited; therefore, stormwater infiltration in that area is not prudent. It is possible that low infiltration rates could be achieved in the areas of the proposed rain gardens. Therefore, the use of the proposed rain gardens appears feasible. Rain gardens have overflow pipes buried within them if and when the infiltration rate of the soil is exceeded. We would expect some water to infiltrate, but not an excessive amount. Storm detention/retention facilities and other utilities are often installed below, or near, structures. The walls of storm vaults must be designed as either cantilever or restrained retaining walls, as appropriate. Wall pressures for the expected soil conditions are presented in the Permanent Foundation and Retaining Walls section of this report. It is important that the portion of the structure above the permanent detained water level be backfilled with free -draining soil, as recommended for retaining walls. Should drainage not be provided, the walls must be designed for hydrostatic forces acting on the outside of the structure. The backfill for all underground structures must be compacted in lifts according to the criteria of this report. Trenches for underground structures and utilities should not cross a line extending downwards from a new or existing footing at an inclination of (1:1) (Horizontal:Vertical), or a line extending downwards from a property line at an inclination of (1:1) (H:V). We should be consulted if these excavation zones will be exceeded for installation of storm facilities or other utilities. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. We anticipate that a silt fence will be needed around the downslope sides of any cleared areas. Rocked construction access roads should be extended into the site to reduce the amount of soil or mud carried off the property by trucks and equipment. Wherever possible, these roads should follow the alignment of planned pavements, and trucks should not be allowed to drive off of the rock -covered areas. Cut slopes and soil stockpiles should GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 6 be covered with plastic during wet weather. Following rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. As with any project that involves demolition of existing site buildings and/or extensive excavation and shoring, there is a potential risk of movement on surrounding properties. This can potentially translate into noticeable damage of surrounding on -grade elements, such as foundations and slabs. However, the demolition, shoring, and/or excavation work could just translate into perceived damage on adjacent properties. Unfortunately, it is becoming more and more common for adjacent property owners to make unsubstantiated damage claims on new projects that occur close to their developed lots. Therefore, we recommend making an extensive photographic and visual survey of the project vicinity, prior to demolition activities, installing shoring, and/or commencing with the excavation. This documents the condition of buildings, pavements, and utilities in the immediate vicinity of the site in order to avoid, and protect the owner from, unsubstantiated damage claims by surrounding property owners. Additionally, any adjacent structures should be monitored during construction to detect soil movements. To monitor their performance, we recommend establishing a series of survey reference points to measure any horizontal deflections of the shoring system. Control points should be established at a distance well away from the walls and slopes, and deflections from the reference points should be measured throughout construction by survey methods. Geotech Consultants, Inc. should be allowed to review the final development plans to verify that the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development, and geotechnical constraints that become more evident during the review process. We recommend including this report, should also be provided to any future recommendations. SEISMIC CONSIDERATIONS in its entirety, in the project contract documents. This report property owners so they will be aware of our findings and In accordance with the International Building Code (IBC), the site soil profile within 100 feet of the ground surface is best represented by Site Class C (Very Dense Soil). The site soils have a low potential for seismic liquefaction because of their dense nature and the absence of near -surface groundwater. This statement regarding liquefaction includes the knowledge of the determined peak ground acceleration noted below. As noted in the USGS website, the mapped spectral acceleration value for a 0.2 second (Ss) and 1.0 second period (S,) equals 1.2g and 0.4g, respectively. The International Building Code (IBC) states that a site-specific seismic study need not be performed provided that the peak ground acceleration be equal to SDs/2.5, where SDS is determined in ASCE 7. It is noted that SDS is equal to 2/3SMs. SMs equals Fa times Ss, where Fa is determined in Table 11.4-1. For our site, Fa = 1.0. Thus, the calculated peak ground acceleration that we utilized for the seismic -related parameters of this report equals 0.328. GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 7 The proposed structures can be supported on conventional continuous and spread footings bearing on undisturbed, medium dense to dense native sand soil, or on structural fill placed above this competent native soil. See the section entitled General Earthwork and Structural Fill for recommendations regarding the placement and compaction of structural fill beneath structures. Adequate compaction of structural fill should be verified with frequent density testing during fill placement. Prior to placing structural fill beneath foundations, the excavation should be observed by the geotechnical engineer to document that adequate bearing soils have been exposed. We recommend that continuous and individual spread footings have minimum widths of 12 and 16 inches, respectively. Exterior footings should also be bottomed at least 18 inches below the lowest adjacent finish ground surface for protection against frost and erosion. The local building codes should be reviewed to determine if different footing widths or embedment depths are required. Footing subgrades must be cleaned of loose or disturbed soil prior to pouring concrete. Depending upon site and equipment constraints, this may require removing the disturbed soil by hand, or re - compaction and moisture conditioning of the bearing surfaces. As discussed in the general section, overexcavation may be required below the footings in some areas to expose competent native soil. Unless lean concrete is used to fill an overexcavated hole, the overexcavation must be at least as wide at the bottom as the sum of the depth of the overexcavation and the footing width. For example, an overexcavation extending 2 feet below the bottom of a 2 -foot -wide footing must be at least 4 feet wide at the base of the excavation. If lean concrete is used, the overexcavation need only extend 6 inches beyond the edges of the footing. If this option is chosen, it may be prudent to conduct the excavation/filling work in short sections to greatly reduce the amount of time the excavations need to remain open. This is because some caving of the loose upper soil is possible. The following allowable bearing pressures are appropriate for footings constructed according to the above recommendations: Placed directly on competent, 5,000 psf native soil or lean -mix concrete placed above the dense native soil Supported on structural fill 2,500 psf placed above the dense native soil Where: (i) psf is pounds per square foot. A one-third increase in these design bearing pressures may be used when considering short-term wind or seismic loads. For the above design criteria, it is anticipated that the total post -construction settlement of footings founded on competent native soil, or on structural fill up to 5 feet in thickness, will be less than one inch, with differential settlements on the order of one-half inch in a distance of 50 feet along a continuous footing with a uniform load. Lateral loads due to wind or seismic forces may be resisted by friction between the foundation and the bearing soil, or by passive earth pressure acting on the vertical, embedded portions of the foundation. For the latter condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level, compact fill. We recommend using the following ultimate values for the foundation's resistance to lateral loading: GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 =.I Coefficient of Friction 0.50 Passive Earth Pressure 300 pcf Where: (i) pcf is pounds per cubic foot, and (ii) passive earth pressure is computed using the equivalent fluid density. JN 12034 Page 8 If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend maintaining a safety factor of at least 1.5 for the foundation's resistance to lateral loading, when using the above ultimate values. PIPE PILES As discussed in the general section, small diameter steel pipe piles could be used to support the portion of the new bank foundation that is underlain by a layer of loose sand soil. Three- or 4 -inch - diameter pipe piles driven with a 650- or 800- or 1,100 -pound hydraulic jackhammer to the following final penetration rates may be assigned the following compressive capacities. Note: The refusal criteria indicated in the above table are valid only for pipe piles that are installed using a hydraulic impact hammer carried on leads that allow the hammer to sit on the top of the pile during driving. If the piles are installed by alternative methods, such as a vibratory hammer or a hammer that is hard -mounted to the installation machine, numerous load tests to 200 percent of the design capacity would be necessary to substantiate the allowable pile load. The appropriate number of load tests would need to be determined at the time the contractor and installation method are chosen. As a minimum, load tests on 20 percent of the piles is typical where alternative pile installation methods are used. As a minimum, Schedule 40 pipe should be used. The site soils should not be highly corrosive. Considering this, it is our opinion that standard "black" pipe can be used, and corrosion protection, such as galvanizing, is not necessary for the pipe piles. Pile caps and grade beams should be used to transmit loads to the piles. Isolated pile caps should include a minimum of two piles to reduce the potential for eccentric loads being applied to the piles. Subsequent sections of pipe can be connected with slip or threaded couplers, or they can be welded together. If slip couplers are used, they should fit snugly into the pipe sections. This may require that shims be used or that beads of welding flux be applied to the outside of the coupler. GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 9 Lateral loads due to wind or seismic forces may be resisted by passive earth pressure acting on the vertical, embedded portions of the foundation. For this condition, the foundation must be either poured directly against relatively level, undisturbed soil or surrounded by level, structural fill. We recommend using a passive earth pressure of 350 pounds per cubic foot (pcf) for this resistance. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend a safety factor of at least 1.5 for the foundation's resistance to lateral loading, when using the above ultimate passive value. Retaining walls backfilled on only one side should be designed to resist the lateral earth pressures imposed by the soil they retain. The following recommended parameters are for walls that restrain level backfill: Active Earth Pressure * 35 pcf Passive Earth Pressure 30 pcf Coefficient of Friction 0.50 Soil Unit Weight 135 pcf Where: (i) pcf is pounds per cubic foot, and (ii) active and passive earth pressures are computed using the equivalent fluid pressures. . For a restrained wall that cannot deflect at least 0.002 times its height, a uniform lateral pressure equal to 10 psf times the height of the wall should be added to the above active equivalent fluid pressure. The values given above are to be used to design only permanent foundation and retaining walls that are to be backfilled, such as conventional walls constructed of reinforced concrete or masonry. It is not appropriate to use the above earth pressures and soil unit weight to back -calculate soil strength parameters for design of other types of retaining walls, such as soldier pile, reinforced earth, modular or soil nail walls. The passive pressure given is appropriate only for a shear key poured directly against undisturbed native soil, or for the depth of level, well -compacted fill placed in front of a retaining or foundation wall. The values for friction and passive resistance are ultimate values and do not include a safety factor. We recommend a safety factor of at least 1.5 for overturning and sliding, when using the above values to design the walls. Restrained wall soil parameters should be utilized for a distance of 1.5 times the wall height from corners or bends in the walls. This is intended to reduce the amount of cracking that can occur where a wall is restrained by a corner. The design values given above do not include the effects of any hydrostatic pressures behind the walls and assume that no surcharges, such as those caused by slopes, vehicles, or adjacent foundations will be exerted on the walls. If these conditions exist, those pressures should be added to the above lateral soil pressures. Where sloping backfill is desired behind the walls, we will need to be given the wall dimensions and the slope of the backfill in order to provide the appropriate design earth pressures. The surcharge due to traffic loads behind a wall can typically be accounted for by adding a uniform pressure equal to 2 feet multiplied by the above active fluid GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 JN 12034 Page 10 density. Heavy construction equipment should not be operated behind retaining and foundation walls within a distance equal to the height of a wall, unless the walls are designed for the additional lateral pressures resulting from the equipment. Wall Pressures Due to Seismic Forces The surcharge wall loads that could be imposed by the design earthquake can be modeled by adding a uniform lateral pressure to the above -recommended active pressure. The recommended surcharge pressure is 8H pounds per square foot (pso, where H is the design retention height of the wall. Using this increased pressure, the safety factor against sliding and overturning can be reduced to 1.2 for the seismic analysis. Retaining Wall Backfill and Waterproofing Backfill placed behind retaining or foundation walls should be coarse, free -draining structural fill containing no organics. This backfill should contain no more than 5 percent silt or clay particles and have no gravel greater than 4 inches in diameter. The percentage of particles passing the No. 4 sieve should be between 25 and 70 percent. If the native sand is used as backfill, (a minimum 12 -inch width of free -draining gravel or a drainage composite similar to Miradrain 6000 should be placed against the backfilled retaining walls. The drainage composites should be hydraulically connected to the foundation drain system. Free -draining backfill or gravel should be used for the entire width of the backfill where seepage is encountered. For increased protection, drainage composites should be placed along cut slope faces, and the walls should be backfilled entirely with free -draining soil. The purpose of these backfill requirements is to ensure that the design criteria for a retaining wall are not exceeded because of a build-up of hydrostatic pressure behind the wall. The top 12 to 18 inches of the backfill should consist of a compacted, relatively impermeable soil or topsoil, or the surface should be paved. The ground surface must also slope away from backfilled walls to reduce the potential for surface water to percolate into the backfill. It is critical that the wall backfill be placed in lifts and be properly compacted, in order for the above -recommended design earth pressures to be appropriate. The wall design criteria assume that the backfill will be well -compacted in lifts no thicker than 12 inches. The compaction of backfill near the walls should be accomplished with hand -operated equipment to prevent the walls from being overloaded by the higher soil forces that occur during compaction. The section entitled General Earthwork and Structural Fill contains additional recommendations regarding the placement and compaction of structural fill behind retaining and foundation walls. ��:C�77P► lei As recommended in the general section, regardless of the type of shoring wall constructed, a catchment wall with a freeboard height of at least 2 feet above the final grade on the uphill side of the wall should be constructed above the northern retaining wall. This catchment freeboard height will need to be maintained to provide adequate protection from any shallow sloughing of near - surface soils upslope of the wall. These recommendations are directed towards protecting the proposed developement and areas downslope from soil only. Trees sometimes accompany even shallow slides as they occur on slopes. Trees can cause significant damage to structures, even GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 11 heavily reinforced concrete walls. Removal of trees from areas above and on steep slopes is a heavily debated issue. While removal of the tree can eliminate the threat of the trunk and branches causing damage to the structure, the healthy root system can provide near -surface soil stabilization benefits. We generally recommend that any unhealthy or undermined trees be removed above the stump. Trees should be evaluated by a professional arborist on a case-by-case basis. The construction of a catchment wall as described above would protect only areas downslope from soil movement, and would not provide protection from trees or other debris. A variety of shoring systems are feasible for use at this site. This section presents design considerations for cantilevered and tied -back soldier -pile walls, and for nailed walls. Since the most suitable choice is primarily dependent on a number of factors under the contractor's control, we suggest that the contractor work closely with the structural engineer during the shoring design. As discussed above, the sensitivity of adjacent buildings and utilities must be considered in the design to reduce the risk of causing settlement of these adjacent elements. Regardless of the system used, all shoring systems will deflect in toward the excavation. Therefore, there is always a risk of noticeable settlement occurring on the ground behind the shoring wall. These risks are reduced, but not entirely eliminated, by using more rigid shoring systems, such as soldier piles. Depending on the required length of tieback anchors, easements may need to be obtained in order to install the anchors onto adjacent properties. The shoring design should be submitted to Geotech Consultants, Inc. for review prior to beginning site excavation. We are available and would be pleased to assist in this design effort. Cantilevered and Tied -Back Soldier Piles Cantilevered and tied -back soldier pile systems have proven to be an efficient and economical method for providing excavation shoring. Tied -back walls are typically more economical than cantilevered walls where the depth of excavation is greater than 15 feet. Soldier -Pile Installation Soldier -pile walls would be constructed after making planned cut slopes, and prior to commencing the mass excavation, by setting steel H -beams in a drilled hole and grouting the space between the beam and the soil with concrete for the entire height of the drilled hole. We anticipate that the holes could be drilled without casing, but the contractor should be prepared to case the holes or use the slurry method if caving soil is encountered. Excessive ground loss in the drilled holes must be avoided to reduce the potential for settlement on adjacent properties. If water is present in a hole at the time the soldier pile is poured, concrete must be tremied to the bottom of the hole. As excavation proceeds downward, the space between the piles should be lagged with timber, and any voids behind the timbers should be filled with pea gravel, or a slurry comprised of sand and fly ash. Treated lagging is usually required for permanent walls, while untreated lagging can often be utilized for temporary shoring walls. Temporary vertical cuts will be necessary between the soldier piles for the lagging placement. The prompt and careful installation of lagging is important, particularly in loose or caving soil, to maintain the integrity of the excavation and provide safer working conditions. Additionally, care must be taken by the excavator GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 JN 12034 Page 12 to remove no more soil between the soldier piles than is necessary to install the lagging. Caving or overexcavation during lagging placement could result in loss of ground on neighboring properties. Timber lagging should be designed for an applied lateral pressure of 30 percent of the design wall pressure, if the pile spacing is less than three pile diameters. For larger pile spacings, the lagging should be designed for 50 percent of the design load. Soldier -Pile Wall Design Permanent soldier -pile shoring that is cantilevered or restrained by one row of tiebacks, and that has a level backslope, should be designed for an active soil pressure equal to that pressure exerted by an equivalent fluid with a unit weight of 30 pounds per cubic foot (pcf). At the northern side of the site where the slope of approximately 40 degrees is located, the active pressure should increase to 60 pcf. To design northern tied -back shoring with more than one row of tiebacks, we recommend assuming that the lateral active soil pressure on the wall, expressed in pounds per square foot (psf), is equal to 41H, where H is the total height of the excavation in feet. Slopes differing from the 40 degree backslope angle above the shoring walls may also exert additional surcharge pressures. These surcharge pressures may vary from the above recommendations, depending on the configuration of the cut slope and shoring wall. We should review recommendations regarding slope and building surcharge pressures when the preliminary shoring design is completed. It is important that the shoring design provides sufficient working room to drill and install the soldier piles, without needing to make unsafe, excessively steep temporary cuts. Cut slopes should be planned to intersect the backside of the drilled holes, not the back of the lagging. Lateral movement of the soldier piles below the excavation level will be resisted by an ultimate passive soil pressure equal to that pressure exerted by a fluid with a density of 600 pcf. A safety factor of 1.5 should be included in a design of This soil pressure is valid only for a level excavation in front of the soldier pile; it acts on two times the grouted pile diameter. Cut slopes made in front of shoring walls significantly decrease the passive resistance. This includes temporary cuts necessary to install internal braces or rakers. The minimum embedment below the floor of the excavation for cantilever soldier piles should be equal to the height of the "stick-up." Tied -back soldier piles should be embedded no less than 12 feet below the lowest point of the excavation, including footing and utility excavations. The vertical capacity of soldier piles to carry the downward component of the tieback forces will be developed by a combination of frictional shaft resistance along the embedded length and pile end -bearing. 7 Pile Shaft Friction 1,500 psf Pile End -Bearing 20,000 psf GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 13 Where: (i) psf is pounds per square foot. The above values assume that the excavation is level in front of the soldier pile and that the bottom of the pile is embedded a minimum of 10 feet below the floor of the excavation. For the pile end -bearing to be appropriate, the bottom of the drilled holes must be cleaned of loosened soil. The shoring contractor should be made aware of this, as it may affect their installation procedures. The concrete surrounding the embedded portion of the pile must have sufficient bond and strength to transfer the vertical load from the steel section through the concrete into the soil. General considerations for the design of tied -back or braced soldier -pile walls are presented on Plate 10. We recommend installing tieback anchors at inclinations between 20 and 30 degrees below horizontal. The tieback will derive its capacity from the soil -grout strength developed in the soil behind the no-load zone. The minimum grouted anchor length should be 10 feet. The no-load zone is the area behind which the entire length of each tieback anchor should be located. To prevent excessive loss -of -ground in a drilled hole, the no-load section of the drilled tieback hole should be backfilled with a sand and fly ash slurry, after protecting the anchor with a bond breaker, such as plastic casing, to prevent loads from being transferred to the soil in the no-load zone. The no-load section could be filled with grout after anchor testing is completed. During the design process, the possible presence of foundations or utilities close to the shoring wall must be evaluated to determine if they will affect the configuration and length of the tiebacks. Based on the results of our analyses and our experience at other construction sites, we suggest using an adhesion value of 2,000 psf in the (very dense sand) to design temporary anchors, if the mid -point of the grouted portion of the anchor is more than 10 feet below the overlying ground surface. This value applies to non -pressure - grouted anchors. Pressure -grouted or post -grouted anchors can often develop adhesion values that are two to three times higher than that for non -pressure - grouted anchors. These higher adhesion values must be verified by load testing. Soil conditions, soil -grout adhesion strengths, and installation techniques typically vary over any site. This sometimes results in adhesion values that are lower than anticipated. Therefore, we recommend substantiating the anchor design values by load -testing all tieback anchors. At least two anchors in each soil type encountered should be performance -tested to 200 percent of the design anchor load to evaluate possible anchor creep. Wherever possible, the no-load section of these tiebacks should not be grouted until the performance tests are completed. Unfavorable results from these performance tests could require increasing the lengths of the tiebacks. The remaining anchors should be proof -tested to at least 135 percent of their design value before being 'locked off." After testing, each anchor should be locked off at a prestress load of 80 to 100 percent of its design load. GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 JN 12034 Page 14 If caving or water -bearing soil is encountered, the installation of tieback anchors will be hampered by caving and soil flowing into the holes. It will be necessary to case the holes, if such conditions are encountered. Alternatively, the use of a hollow stem auger with grout pumped through the stem as the auger is withdrawn would be satisfactory, provided that the injection pressure and grout volumes pumped are carefully monitored. All drilled installations should be grouted and backfilled immediately after drilling. No drilled holes should be left open overnight. Soil Nailin_g Soil nailing is a relatively new shoring system where closely spaced, tieback anchors (nails) are grouted into drilled holes in the cut face as the excavation proceeds, thereby reinforcing the cut face. More anchors are required for this system than for conventional systems, but steel soldier piles and timber lagging are eliminated. The anchored or nailed system essentially operates as a reinforced soil wall or a gravity wall, with the nails tying the soil mass together. We recommend that an allowable adhesion value of 2,000 pounds per square foot (psf) be used for the design of the soil nails. Due to the steep nature of the northern slope, the initial, upper row of anchors should be placed before any cuts into the slope are made. Then, 4- to 6 -foot vertical cuts may be made in the shoring area followed immediately by the placement of anchors. The cut face is then covered with a wire mesh, and shotcrete is placed over the mesh and soil face. Generally, no temporary, unsupported excavations for soil -nail walls should be allowed to stand longer than 12 hours without the acceptance of the geotechnical engineer. Once the shotcrete has hardened, the excavation again proceeds and the nails are placed. A geotextile drainage composite must be placed over the face of the cut prior to shotcreting to prevent buildup of hydrostatic pressures behind the shotcrete facing. As the excavation progresses downward, the drainage composite strips are extended, until reaching the base of the excavation, where weep holes are placed through the shotcrete to be tied into an acceptable conveyance system. Because soil nails are passive elements (they are not pre -stressed as tiebacks are), soil -nail walls will typically deflect more than a soldier -pile wall. This involves more risk of causing damage to adjoining utilities, streets, and other on -grade elements. The shoring designer should provide an estimate of the lateral deflection that is anticipated for the soil nail wall. Caving of loose or granular soils, or in zones of seepage, can require that the shoring contractor modify their installation techniques. This can increase the cost and time necessary to install the nailed wall. We recommend that the shoring contractor be consulted regarding potential difficulties and modifications that can occur during the construction of a soil -nailed wall. This adhesion value should be substantiated by load -testing at least two anchors in each soil type to at least 200 percent of their design capacity, prior to installing production anchors. During shoring construction, at least 5 percent of the production anchors should be proof -tested to 130 percent of the design anchor capacity. GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 JN 12034 Page 15 The shoring designer will likely utilize on of several commercially available computer programs to design the nailed walls. We recommend that the following soil strength parameters be used in the nail wall design: The shoring designer must take into consideration the steepness of the northern slope and the need for 2 feet of catchment. Consideration of the loose condition of the near -surface soils must also considered in the design and construction of the system. Excavation and Shoring Monitorin_g As with any shoring system, there is a potential risk of greater -than -anticipated movement of the shoring and the ground outside of the excavation. This can translate into noticeable damage of surrounding on -grade elements, such as foundations and slabs. Therefore, we recommend making an extensive photographic and visual survey of the project vicinity, prior to demolition activities, installing shoring or commencing excavation. This documents the condition of buildings, pavements, and utilities in the immediate vicinity of the site in order to avoid, and protect the owner from, unsubstantiated damage claims by surrounding property owners. Additionally, the shoring walls should be monitored during construction to detect soil movements. To monitor their performance, we recommend establishing a series of survey reference points to measure any horizontal deflections of the shoring system. Control points should be established at a distance well away from the walls and slopes, and deflections from the reference points should be measured throughout construction by survey methods. At least four points should be established on top of the shoring wall and should be monitored during construction. Additionally, benchmarks installed on any surrounding buildings should be monitored for at least vertical movement. We suggest taking the readings at least once a week, until it is established that no deflections are occurring. The initial readings for this monitoring should be taken before starting any demolition or excavation on the site. WMIX:�#JrEel _►N7 The building floors can be constructed as slabs -on -grade atop the native soils underlying the surface of the site, or on structural fill, or on previously placed fill that has been re -compacted. The subgrade soil must be in a firm, non -yielding condition at the time of slab construction or underslab fill placement. Any soft areas encountered should be excavated and replaced with select, imported structural fill. Even where the exposed soils appear dry, water vapor will tend to naturally migrate upward through the soil to the new constructed space above it. This can affect moisture -sensitive flooring, cause imperfections or damage to the slab, or simply allow excessive water vapor into the space above the slab. All interior slabs -on -grade should be underlain by a capillary break or drainage layer consisting of a minimum 4 -inch thickness of gravel or crushed rock that has a fines content GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 16 (percent passing the No. 200 sieve) of less than 3 percent and a sand content (percent passing the No. 4 sieve) of no more than 10 percent. As noted by the American Concrete Institute (ACI) in the Guides for Concrete Floor and Slab Structures, proper moisture protection is desirable immediately below any on -grade slab that will be covered by tile, wood, carpet, impermeable floor coverings, or any moisture -sensitive equipment or products. ACI also notes that vapor retarders, such as 6 -mil plastic sheeting, have been used in the past, but are now recommending a minimum 10 -mil thickness. A vapor retarder is defined as a material with a permeance of less than 0.3 perms, as determined by ASTM E 96. It is possible that concrete admixtures may meet this specification, although the manufacturers of the admixtures should be consulted. Where vapor retarders are used under slabs, their edges should overlap by at least 6 inches and be sealed with adhesive tape. The sheeting should extend to the foundation walls for maximum vapor protection. If no potential for vapor passage through the slab is desired, a vapor barrier should be used. A vapor barrier, as defined by ACI, is a product with a water transmission rate of 0.01 perms when tested in accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement. In the recent past, ACI (Section 4.1.5) recommended that a minimum of 4 inches of well -graded compactable granular material, such as a 5/8 -inch -minus crushed rock pavement base, be placed over the vapor retarder or barrier for their protection, and as a "blotter" to aid in the curing of the concrete slab. Sand was not recommended by ACI for this purpose. However, the use of material over the vapor retarder is controversial as noted in current ACI literature because of the potential that the protection/blotter material can become wet between the time of its placement and the installation of the slab. If the material is wet prior to slab placement, which is always possible in the Puget Sound area, it could cause vapor transmission to occur up through the slab in the future, essentially destroying the purpose of the vapor barrier/retarder. Therefore, if there is a potential that the protection/blotter material will become wet before the slab is installed, ACI now recommends that no protection/blotter material be used. However, ACI then recommends that, because there is a potential for slab cure due to the loss of the blotter material, joint spacing in the slab be reduced, a low shrinkage concrete mixture be used, and 'other measures" (steel reinforcing, etc.) be used. ASTM E-1643-98 "Standard Practice for Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs" generally agrees with the recent ACI literature. We recommend that the contractor, the project materials engineer, and the owner discuss these issues and review recent ACI literature and ASTM E-1643 for installation guidelines and guidance on the use of the protection/blotter material. We recommend proof -rolling slab areas with a heavy truck or a large piece of construction equipment prior to slab construction. Any soft areas encountered during proof -rolling should be excavated and replaced with select, imported structural fill. Excavation slopes should not exceed the limits specified in local, state, and national government safety regulations. Temporary cuts to a depth of about 4 feet may be attempted vertically in unsaturated soil, if there are no indications of slope instability. However, vertical cuts should not be made near property boundaries, or existing utilities and structures. Based upon Washington Administrative Code (WAC) 296, Part N, the dense to very dense sand soil at the subject site would generally be classified as Type A. Therefore, temporary cut slopes greater than 4 feet in GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 17 height should not be excavated at an inclination steeper than 0.75:1 (Horizontal:Vertical), extending continuously between the top and the bottom of a cut. The above -recommended temporary slope inclination is based on the conditions exposed in our explorations, and on what has been successful at other sites with similar soil conditions. It is possible that variations in soil and groundwater conditions will require modifications to the inclination at which temporary slopes can stand. Temporary cuts are those that will remain unsupported for a relatively short duration to allow for the construction of foundations, retaining walls, or utilities. Temporary cut slopes should be protected with plastic sheeting during wet weather. It is also important that surface water be directed away from temporary slope cuts. The cut slopes should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that sand or loose soil can cave suddenly and without warning. Excavation, foundation, and utility contractors should be made especially aware of this potential danger. These recommendations may need to be modified if the area near the potential cuts has been disturbed in the past by utility installation, or if settlement -sensitive utilities are located nearby. All new permanent cuts into native soil should be inclined no steeper than 1.5:1 (H:V). Fill slopes should not be constructed with an inclination greater than 2:1 (H:V). To reduce the potential for shallow sloughing, fill must be compacted to the face of these slopes. This can be accomplished by overbuilding the compacted fill and then trimming it back to its final inclination. Adequate compaction of the slope face is important for long-term stability and is necessary to prevent excessive settlement of patios, slabs, foundations, or other improvements that may be placed near the edge of the slope. Water should not be allowed to flow uncontrolled over the top of any temporary or permanent slope. All permanently exposed slopes should be seeded with an appropriate species of vegetation to reduce erosion and improve the stability of the surficial layer of soil. Any disturbance to the existing slope outside of the project limits may reduce the stability of the slope. Damage to the existing vegetation and ground should be minimized, and any disturbed areas should be revegetated as soon as possible. Soil from the excavation should not be placed on the slope, and this may require the off-site disposal of any surplus soil. We anticipate that permanent foundation walls will be constructed against the shoring walls. Where this occurs, a plastic -backed drainage composite, such as Miradrain, Battledrain, or similar, should be placed against the entire surface of the shoring prior to pouring the foundation wall. Weep pipes located no more than 6 feet on -center should be connected to the drainage composite and poured into the foundation walls or the perimeter footing. A footing drain installed along the inside of the perimeter footing will be used to collect and carry the water discharged by the weep pipes to the storm system. Isolated zones of moisture or seepage can still reach the permanent wall where groundwater finds leaks or joints in the drainage composite. This is often an acceptable risk in unoccupied below -grade spaces, such as parking garages. However, formal waterproofing is typically necessary in areas where wet conditions at the face of the permanent wall will not be tolerable. If this is a concern, the permanent drainage and waterproofing system should be designed by a specialty consultant familiar with the expected subsurface conditions and proposed construction. GEOTECH CONSULTANTS, INC. Seven Hills Properties JN 12034 February XX, 2012 Page 18 Footing drains placed inside the building or behind backfilled walls should consist of 4 -inch, perforated PVC pipe surrounded by at least 6 inches of 1 -inch -minus, washed rock wrapped in a non -woven, geotextile filter fabric (Mirafi 140N, Supac 4NP, or similar material). At its highest point, a perforated pipe invert should be at least 6 inches below the level of a crawl space or the bottom of a floor slab, and it should be sloped slightly for drainage. Plate 9 presents typical considerations for footing drains. All roof and surface water drains must be kept separate from the foundation drain system. As a minimum, a vapor retarder, as defined in the Slabs -On -Grade section, should be provided in any crawl space area to limit the transmission of water vapor from the underlying soils. Also, an outlet drain is recommended for all crawl spaces to prevent a build up of any water that may bypass the footing drains. No groundwater was observed during our field work. If seepage is encountered in an excavation, it should be drained from the site by directing it through drainage ditches, perforated pipe, or French drains, or by pumping it from sumps interconnected by shallow connector trenches at the bottom of the excavation. The excavation and site should be graded so that surface water is directed off the site and away from the tops of slopes. Water should not be allowed to stand in any area where foundations, slabs, or pavements are to be constructed. Final site grading in areas adjacent to buildings should slope away at least 2 percent, except where the area is paved. Surface drains should be provided where necessary to prevent ponding of water behind foundation or retaining walls. All building and pavement areas should be stripped of surface vegetation, topsoil, organic soil, and other deleterious material. It is important that existing foundations be removed before site development. The stripped or removed materials should not be mixed with any materials to be used as structural fill, but they could be used in non-structural areas, such as landscape beds. Structural fill is defined as any fill, including utility backfill, placed under, or close to, a building, behind permanent retaining or foundation walls, or in other areas where the underlying soil needs to support loads. All structural fill should be placed in horizontal lifts with a moisture content at, or near, the optimum moisture content. The optimum moisture content is that moisture content that results in the greatest compacted dry density. The moisture content of fill is very important and must be closely controlled during the filling and compaction process. The allowable thickness of the fill lift will depend on the material type selected, the compaction equipment used, and the number of passes made to compact the lift. The loose lift thickness should not exceed 12 inches. We recommend testing the fill as it is placed. If the fill is not sufficiently compacted, it can be recompacted before another lift is placed. This eliminates the need to remove the fill to achieve the required compaction. The following table presents recommended relative compactions for structural fill: LOCATION OF FILL MINIMUM RELATIVE' PLACEMENT COMPACTION Beneath footings,slabs or walkways GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 Filled slopes and behind 90% retaining walls 95% for upper 12 inches of Beneath pavements subgrade; 90% below that level Where: Minimum Relative Compaction is the ratio, expressed in percentages, of the compacted dry density to the maximum dry density, as determined in accordance with ASTM Test Designation D 1557-91 (Modified Proctor). JN 12034 Page 19 The sand soil at the site could very likely be used as structural fill provided it does not contain organics and/or is not excessively wet. The sand will need to be compacted using vibratory equipment, preferably large equipment. Structural fill that will be placed in wet weather should consist of a coarse, granular soil with a silt or clay content of no more than 5 percent. The percentage of particles passing the No. 200 sieve should be measured from that portion of soil passing the three -quarter -inch sieve. LIMITATIONS The conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our exploration and assume that the soil and groundwater conditions encountered in the test borings are representative of subsurface conditions on the site. If the subsurface conditions encountered during construction are significantly different from those observed in our explorations, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. Unanticipated soil conditions are commonly encountered on construction sites and cannot be fully anticipated by merely taking soil samples in test borings. Subsurface conditions can also vary between exploration locations. Such unexpected conditions frequently require making additional expenditures to attain a properly constructed project. It is recommended that the owner consider providing a contingency fund to accommodate such potential extra costs and risks. This is a standard recommendation for all projects. The recommendations presented in this report are directed toward the protection of only the proposed development from damage due to slope movement. Predicting the future behavior of steep slopes and the potential effects of development on their stability is an inexact and imperfect science that is currently based mostly on the past behavior of slopes with similar characteristics. Landslides and soil movement can occur on steep slopes before, during, or after the development of property. The use of a catchment wall will deter such movement from reaching the development. This report has been prepared for the exclusive use of Seven Hills Properties, and its representatives, for specific application to this project and site. Our recommendations and conclusions are based on observed site materials, and selective laboratory testing and engineering analyses. Our conclusions and recommendations are professional opinions derived in accordance with current standards of practice within the scope of our services and within budget and time constraints. No warranty is expressed or implied. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 described in our report for consideration in design. minimizing the potential for biological hazards, such the existing or proposed site development. JN 12034 Page 20 Our services also do not include assessing or as mold, bacteria, mildew and fungi in either In addition to reviewing the final plans, Geotech Consultants, Inc. should be retained to provide geotechnical consultation, testing, and observation services during construction. This is to confirm that subsurface conditions are consistent with those indicated by our exploration, to evaluate whether earthwork and foundation construction activities comply with the general intent of the recommendations presented in this report, and to provide suggestions for design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. However, our work would not include the supervision or direction of the actual work of the contractor and its employees or agents. Also, job and site safety, and dimensional measurements, will be the responsibility of the contractor. During the construction phase, we will provide geotechnical observation and testing services when requested by you or your representatives. Please be aware that we can only document site work we actually observe. It is still the responsibility of your contractor or on-site construction team to verify that our recommendations are being followed, whether we are present at the site or not. The following plates are attached to complete this report: Plate 1 Vicinity Map Plate 2 Site Exploration Plan Plates 3 - 8 Test Boring Logs Plate 9 Typical Footing Drain Detail Plate 10 Tied -Back Shoring Detail We appreciate the opportunity to be of service on this project. If you have any questions, or if we may be of further service, please do not hesitate to contact us. Respectfully submitted, GEOTECH CONSULTANTS, INC. Jason L. Hinds Geotechnical Engineer GEOTECH CONSULTANTS, INC. Seven Hills Properties February XX, 2012 JLH/DRW: jyb D. Robert Ward, P.E. Principal GEOTECH CONSULTANTS, INC. 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