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HomeMy WebLinkAbout961804201 Geotech Assessment ~L'(J©~-- 3~ Project: Regan Residence Location: 92 2"d Ave. Port Hadlock, WA APN: 961 804 201 Legal: SW'/. Section 35, T30N, R1W, WM Design: TTS Date: April 19, 2006 Revised: Geotechnical and Drainage Report Basis of Design Quadra Engineering 240 W. Cedar St. P.O. Box 2356 Sequim, WA. 98382 (360) 683-7019 File #: O j~ t ~O ~CF ~~ F'A~ g ,,23347 p c~,~' ~~oNAI E~ JAN t This report addresses building placement and stormwater management in compliance with Jefferson County Codes. The project will construct a new 1020 sf octagonal two story building with a daylight basement, with driveway access from a private road, septic and storm drainage systems. / P~(~- -,~~o~ Existing Conditions • 0.45-acre parcel north of East Moore Street, between 2~d and 3`d Avenues. - The site slopes toward the southeast with varying grade. - The site is mostly a grassy meadow, with assorted shrubs and evergreen trees along the south property line. - The north side of the property fronts on an existing private gravel road, with a wooded lot to the north. To the east is a single family residence on a wooded lot. To the south is a wooded lot fronting on 3`d Avenue. To the west is a vacant lot with assorted grasses and shrubs. • The site is located in the Urban Growth Area (UGA) and is zoned Urban low density residential (ULDR). The following minimum setbacks apply: - Front; 10-feet from the private road - Side; 5-feet from east and west property lines ' ~ --' ~ ---~-~ - Rear; 5-feet from south property line APB 2 ~ 2006 Soils • The USDA Soils Survey for Jefferson County indicates the project soil type is Cassolary (CfC) with the following properties and characteristics: - The soil consists of stratified sandy loam (0-23"), silt loam and silty clay loam (23-38") and stratified fine sandy loam and medium sand. - the soil is well drained, permeability is moderately slow at a rate of 6.0 to E:1 Jobs10410458 ReganISWM10548 SWM Repo~t.doc Page 1 of 3 ~. Quads Engineering 240 W. Cedar St. P.O. Box 2356 Sequim, WA. 98382 (360) 683-7019 2.0 inches per hour at depths from 0-23", 0.6 to 0.2 inches per hour at depths from 23 to 38" and 6.0 to 2.0 inches per hour at depths from 38 to 60". low shrink-swell potential runoff is slow to medium and the hazard of water erosion is slight to moderate in undisturbed soil. . • The proposed building foundation has been designed by Quadra Engineering with retaining walls and a daylight basement. The foundation is structurally sound and stable and does not have an adverse impact on the stability or erosive potential of the soil Drainage Design - Stormwater management will be by infiltration of roof runoff. - Runoff from the building roof will be directed in buried pipes to the dry wells. - Permanent ground cover is required to be established on all disturbed surfaces. - Limit the infiltration design rate to'/2 the mean SCS permeability rate. - The dry wells are sized to contain stormwater runoff from the building roof fora 100-yr 24-hr event (Q,oo)~ - Site precipitation, as found on the isopluvials in NOAA Atlas 2, Volume IX, fora 100-year recurrence interval, 24-hour duration storm, is 2.7-inches Calculations Calculations were preformed using HydroCAD® by Applied Microcomputer Systems using the following methodologies to address and compensate for limitations of the software: • Infiltration Rate: Dry well dimensions are 3' x 3' to a depth of 5', backfilled with drain rock surrounded with filter fabric. Due to the varying permeability of the soil at different depths, the dry welts were modeled in 3 parts: • Zone 1: infiltration rate of 6.0 to 2.0 inches per hour (depth of 38 - 60") • Zone 2: infiltration rate of 0.6 to 0.2 inches per hour (depth of 23 - 38") • Zone 3: infiltration rate of 6.0 to 2.0 inches per hour (depth of 0 - 23") F:1 Jobs10410458 ReganISWM10548 SWM Report.doc Page 2 of 3 Quadra Engineering 240 W. Cedar St. P.O. Box 2356 Sequim, WA. 98382 (360) 683-7019 Each well is given an assumed elevation of 3' at the base (depth of 5'). Calculate the mean permeability and convert to feet per minute for software compatibility. 1/z x (6.0 + 2.0)'n/1 hr x 1 ft/12in x 1 a`/60min) = 0.0056n/min• '/z x (0.6 + 0.2)'n/1 ~ x 1 ft/12;n x 1 t"/60min) = 0.00056ft1min• Conclusion Roof runoff from the building will be directed through downspouts to pipes leading to 2 dry welts. The dry wells have been sized to infiltrate the 100-yr storm event without flooding. Hydrologic Analysis Summary for Pond 1fi2 2 Dry VMells hflow Area = 0.023 ac, hflow Depth = 2.47" for 100yr-24M event hflow = 0.01 cfs @ 7.88 hrs, Volume= 0.005 of Outflow = 0.01 cfs ~ 8.08 hrs, Volume= 0.005 af, Atten= 24%. Lag= 11.9 min Discarded = 0.01 cfs @ 8.08 hrs, Volume= 0.005 of Routing by Stor-hd method, Time Span= 0.01-24.00 hrs, dt= 0.01 hrs Peak Elev= 6.07' @.8.08 tas Surf.Area= 36 sf Storage= l7 cf Plug-Flow detentiontime= 14.5 min calculated for 0.005 of (100% of inflow) Center-of-Mass del. time=13.8 min (682.7 - 668.8 ) # hvert Avail.Storage Storage Description _ 1 3.00' 10 cf 3.00'YYx 3.00'L x 1.t33'H Prisrrrafoid x 2 33 d Overatl x 30.0°k Voids 2 4.83' 7 cf 3.00'VII x 3-00'L x 1.?SH Prisrrretoid x 2 23 cf Overatl x 30.0% Voids 3 6.08' 10 Cf 3-00'YY x 3.00'L x 1.92'H Prisrrmtoid x 2 35 cf Overatl x 30.0% Voids __ _ 27 d Total Available Storage # Routing hvert Outlet Devices 1 Discarded 0.00' 0.005600 fpm F~d'it#ration over entire YtkUed area 2 Discarded 4.83' 0.000560 fpm f-~d'iMralion over Hor¢ontal area above imrert 3 Discarded 6.08' 0.005600 fpm 6diMration over Har¢orrtal area above invert Discarded Outflow Max=0.01 cfs @ 8.08 hrs HW=6.07' (Free Discharge) 1=6diltratioh (Exfittration ConVols 0.01 cfs) - r-Fxfilfration (Exfiltration ConVols 0.00 cfs) 3=E~diltratioa (ConVols 0.00 cfs) E:1 Jobs10410458 ReganlSWM10548 SWM Report.doc Page 3 of 3