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<br /> L `. Site Descri tion: Existin Conditions
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<br /> The project locaticn is bounded by an alley to the west, 39`h St to the south, and
<br /> [3urlingtou Northern R.O.W. to the east, near the interscction of 29`h St and Smith Ave in
<br /> North Everett, in the SE % of the S W % of Section 29, T29N, RSE. The area has been
<br /> extensively developed for industrial uses, including much of ihe project site. The project
<br /> _� site is a gravel, heavily overgrown with blackberry bushes, ta the south of an cxis[ing
<br /> warehouse and parking azea. The site was graded and filled in the past, creating a slope
<br /> from west to east, with a steep embanlanent along the easi property line [haY drops dowm
<br /> to the Burlinb*ton Northern R.O.W.. The Snohomish County Soil Survey shows that the
<br /> soil type for the project area is Everett Gravell}' Sandy Loam, which has excelleat
<br /> infiltration characteristics. Howev�r, since the site had fill material placed on it in the
<br /> pas[, a geotechnical report by Earth Consultants Inc. reveals that ti�e soil type undedying
<br /> the project site is actualiy silty sand �nd sandy silt fill ma+erial, which has poor
<br /> �4� ir,filtration characteristics.
<br /> :I. Site Descri tion: Pro osed Develo ment
<br /> The proposed development is to construct a new building with a 6,000 sf footprint and an
<br /> approximately 5,500 sfasphalt ztea. At sometime in the future the property owner
<br /> expects to psve the remaining 0.5R ac of]tis property. Hence, when sizing the
<br /> retention/detention (R'D).acilities, G.84 ac of impervious area was used for the
<br /> calculations. Swrm wa,cer runoff fxom the asphalt azeas v�ill be routed to a catch basin in
<br /> the north east comer of ihe property. Tl:e runoff is then conveyed through a retention
<br /> Pipe, then a wetpond, and ;aa11y to a detention pipe.
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<br /> The minimumstorage volume af the retenlinn-pipe was.calculated as 704 cf, u�ing : rn� ZC.��
<br /> J! Section 3-3.6.1 of the City of E;verett Stc,rr.iwater Management hianual. The retention �
<br /> pipe is 56 ft of four foot diamet:r 14 �;age CMP with 3 x 1 inch corrugations. There is a ��,^
<br /> ' three foot high baffle 1� ft from the inlet side of the vault, dividing the retention pipe ir.to ,.:: 0 �i�
<br /> � two cells �f 2fi%anu 76% of the retained volume. �
<br /> from the retention pipe, storm vrater is convcye�l to a wetpond. The we:tpond has Fieen i� ,�.' .
<br /> �,. sized to retain 15% of the six month storni under developed conditions. The wetpond has
<br /> dimensions of 25 ft x 6 ft x 2 ft, with a storage voiume of 300 cf. Wedand vegetation, �;�,t
<br /> such as cattails and hardstem bulrsh, will be plar.,ed to a density of one plant per 2.2� sf. �
<br /> Runoff from the asplialt areas that exceeds the six month st�rm valume will pass thraugh I � J,
<br /> both the retention pipe ar�d wetpond to a detention pipe. Runoff from the proposed '�
<br /> structure will be routed directly to the detention i ,;. The detention pipe has been sized � ��, �
<br /> to detain runof2'from the en:ire site, 0.84 ac, and ds charge at rates of 50%of the two
<br /> year and 100%of the 10 and l00 year events under pre-developed conditions. The ,
<br /> �. detention pipe is 73 ft of seven foot diameter 14 gage CMP with 3 x I in corrugations. f
<br /> �., Including a safety factor of 50% for a 100% impervious site, the detention pipe exceeds
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