Request for Approval of Design Modification

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Eunice Foster
5 years ago
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1 March 7, 2017 Piper Peterson U. S. Environmental Protection Agency 1200 Sixth Avenue, ECL-122, Suite 900 Seattle, Washington Subject: Request for Approval of Design Modification T-117 Early Action Area, Phase 2: Adjacent Streets and Residential Yards Study Area, Part 2: Adjacent Streets and Stormwater Dear Ms. Peterson: As requested in your March 2, 2017, letter, this memorandum includes drawings for the pending revisions to the non-motorized path and vegetated depression in the vicinity of the Dallas Avenue S. and S. Donovan Street intersection that were included in the revised Removal Action Construction and Completion Report (RACR; Figures 2-5 through 2-7). The City would like to proceed with contractor negotiations and construction in the near term. Therefore, we are providing the drawings under a separate cover to expedite approval of these drainage revisions. Please let us know if the City is authorized to proceed. The project objective concerning this non-motorized intersection is that stormwater runoff will be directed to Bioretention Cell H2 and/or the vegetated depression. As currently constructed, there is a low spot between the two stormwater management features. In addition, a second low spot is present south of the seat wall area. Observations of the stormwater runoff patterns near the Dallas/Donovan intersection indicate that some localized rework is needed to minimize the potential for ponding on the path and improve the function of drainage elements. The rework will consist of the following elements: Demolition, regrading, and repaving of a portion of the non-motorized path Placement of thickened-edge asphalt and/or extruded curb Reshaping of the streambed cobble area adjacent to bioretention cell H2 Placement of streambed cobbles near the southern end of the seatwall area Grading of a portion of the landscaping between the vegetated depression and seatwall area Installation of a second overflow structure. Corrective measures will be performed later this year. Documentation of the work performed will be provided in a subsequent submittal. If you have any questions about this request, please contact me at (206)

2 Sincerely, Mary Mitchener T-117 Project Coordinator Seattle City Light Attachments cc: Jeff Massie, SPU Beth Schmoyer, SPU Linda Baker, Integral Kristen Kerns, USCOE Roy Kurowia, Port of Seattle PAGE 2 OF 2

3 SAWCUT AT EDGE CONC PANEL. APPROX LOC SHOWN 0.60% DALLAS AVE S SCALE IN FEET 1.12% LEGEND: ASPH THICKENED EDGE RESHAPE EDGE OF H2 AND STREAMBED AGG TYPE 1 TO PROVIDE FLOW PATH TO BIORETENTION CELL H2. SALVAGE STREAMBED AGG TYPE 1 FOR USE IN DRYWELL 1.46% PAV 401D, 3" HMA CL 1/2" OVER MNRL AGG TYPE 2, 6" COMPACTED DEPTH WITH ASPHALT THICKENED EDGE MNRL AGG TYPE 2 REMOVAL TAPER PAVEMENT TO FORM TRANSITION TO ASPHALT THICKENED EDGE " EXTRUDED CURB ON PAVEMENT PER STANDARD PLAN 412 TRANSITION PAVEMENT TO ASPHALT THICKENED EDGE OVER 6' (MIN) MNRL AGG TYPE 2 6" GRAVEL SHOULDER GRADING EXTENTS\ REPLACE DISTURBED MULCH % 2.00% % CROWN ELEV ADJUST RIM AS NECESSARY NOTES: 1. RESTORE VEGETATION, SOIL AMENDMENTS, MULCH AND SEEDING IN DISTURBED AREAS PER SHEET 3 2. RESHAPE AREAS ADJACENT TO NEW PAVING WITH PLANTING SOIL AND MULCH UNLESS OTHERWISE NOTED 3. EXISTING CONDITIONS BASED ON CONTRACTOR-PROVIDED RECORD SURVEY DATED AUG 31, 2016 SDMH RIM=19.15' 12"DI NW IE=15.6' 0+00 SAWCUT REMOVE ASPHALT, REGRADE AND REPAVE. PAV 401D, 3" HMA CL 1/2" OVER MNRL AGG TYPE 2, 6" COMPACTED DEPTH WITH ASPHALT THICKENED EDGE % POINT TABLE S DONOVAN ST 1.15% 2.00% CB241 RIM=19.10' 8"DI E IE=16.9' SD % SAWCUT 19.5 NO DESC ELEV NORTHING 195, , , , , , , , EASTING 1,275, ,275, ,275, ,275, ,275, ,275, ,275, ,275, FILEPATH: P:\Clients\Seattle\Dallas Ave\DWG\EXHIBITS\Donovan Dallas\Donovan Dallas.dwg REMOVE TRAIL ROOT BARRIER ALONG NEW PAVING. DO NOT REPLACE T-117 ADJACENT STREETS CLEANUP & STORMWATER INFRASTRUCTURE FIELD MEMO #107 FEBRUARY 3, 2017 SHEET 1 OF 3 2' SHOULDER WITH 2.00% MAX CROSS SLOPE (TYP) REMOVE RECYCLED PLASTIC EDGING AND SEEDED VEGETATION FROM STA ON DONOVAN TO STATION ON DALLAS AVE Bothell Way NE Suite 600 Lake Forest Park, WA P: F: " IE " INL CONN % INL TYPE 250A WITH NO RISER STA , 19.69' RT RIM " IE (N) EXCAVATE TO SUBGRADE NECESSARY FOR PLANTING SOIL, MULCH AND AMENDMENTS PER LANDSCAPE DRAWING (SHEET 3) AND SPECIFICATIONS. EXCAVATED SOIL MAY BE STOCKPILED AND REUSED. SCARIFY COMPACTED AREAS AS DIRECTED BY ENGINEER. REMOVE BERM. REMOVE PLANTS, STOCKPILE (HEEL IN), AND REPLANT PER LANDSCAPE PLAN. PROTECT PLANTS NOT FLAGGED FOR REMOVAL 18.5 TRIM EXISTING LOG INSTALL 2'x4'x2' DRY WELL INSTALL 6" EXTRUDED CONC CURB ON EX PAVEMENT PER STANDARD PLAN 412. DOWELS PER STANDARD PLAN 411

STREAMBED AGG TYPE 1 4" PERF OR SLOTTED PIPE WITH WELL CAP 2" EX PAVEMENT EX MULCH & PLANTING SOIL 15" 9" 6" 18" PAV401D 6" 8" 3" 3/4" TO 1-1/2" WASHED GRAVEL NON-WOVEN GEOTEXTILE FOR SEPARATION MNRL

4 STREAMBED AGG TYPE 1 4" PERF OR SLOTTED PIPE WITH WELL CAP 2" EX PAVEMENT EX MULCH & PLANTING SOIL 15" 9" 6" 18" PAV401D 6" 8" 3" 3/4" TO 1-1/2" WASHED GRAVEL NON-WOVEN GEOTEXTILE FOR SEPARATION MNRL AGG TYPE 2 COMPACTED SUBGRADE EXISTING GRADE 22 FILEPATH: P:\Clients\Seattle\Dallas Ave\DWG\EXHIBITS\Donovan Dallas\Donovan Dallas.dwg T-117 ADJACENT STREETS CLEANUP & STORMWATER INFRASTRUCTURE FIELD MEMO #107 FEBRUARY 3, 2017 SHEET 2 OF % -3.38% -3.00% Bothell Way NE Suite 600 Lake Forest Park, WA P: F: FINISHED GRADE 1.40% SCALE IN FEET SCALE IN FEET

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