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8 Stormwater - Provide structural calculations for the detention vault. Structural Calculations will be a deferred KJH <br /> Technical These may be a deferred submittal. submittal. <br /> Memorandum <br /> • Vaults shall be designed to meet the structural <br /> requirements for overburden, vactor truck loads, and Specifications for the vault do <br /> where appropriate traffic loadings. See the attached require the AASHTO LRFD Bridge <br /> structural design vehicle loading for the detention Design and HL-93 live load <br /> vaults. Our policy is to have the capability to bring requirements along with overburden. <br /> COE trucks onsite to vactor the vault if the owner is <br /> not maintaining it. [DCSS 4-4.4(3)3]. <br /> • Vaults within a traveled way which exceed 20 feet in <br /> length along the direction of travel shall be designed to <br /> meet bridge structural standards in accordance with <br /> the current version of AASHTO LRFD Bridge Design <br /> Specifications. Vaults meeting these criteria shall be <br /> designed by a structural engineer licensed in the State <br /> of Washington. [DCSS 4-4.4(3)3] <br /> 9 Stormwater - For the detention vault, demonstrate that buoyancy will not Buoyancy calculations will be part of the KJH <br /> Technical be an issue or provide calculations to demonstrate stability vault structural calculations in the deferred <br /> Memorandum where seasonal groundwater may induce flotation. Or the submittal. <br /> geotech can verify this during construction and provide a The provided Geotech report shows <br /> report. groundwater elevation in the vicinity as 27ft <br /> below grade which is 15 ft below the bottom <br /> elevation of the vault. <br /> 10 Stormwater 5 We do not see information in the Manual indicating that Section V-4.1 states "Roof downspout BMPs KJH <br /> Technical BMP T5.10A is only for residential roofs. Please cite can be applied to individual commercial lot <br /> Memorandum specific infeasibility criteria from Volume V in the Manual. developments when the percent impervious <br /> area and pollutant characteristics are <br /> comparable to those from residential lots." <br /> This is an industrial site which is <br /> approximately 95-percent impervious on the <br /> buildable area. The roof is part of a large <br /> warehouse style building used for bus <br /> maintenance. The site does not have similar <br /> percent impervious or pollutant <br /> characteristics of a residential lot. <br /> Page 5 of 12 <br />