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4.0 REQUEST FOR SITE CLOSURE <br /> On behalf of the property owner, Ramage Environmental requests that this site be closed as a <br /> low-risk groundwater case This request is substantiated by the following <br /> 1 The leak has been stopped and sources have been removed This includes the removal of <br /> four USTs and the excavation of impacted soil encountered beneath the eastern end of Tank <br /> A Soil beneath the base of the excavation contained up to 12 ppm of TPH-as-gasoline and <br /> undetectable concentrations of benzene As such, any continued leaching to groundwater <br /> has likely been curtailed <br /> 2 The site has been adequately characterized The extent of impacted soil and groundwater <br /> has been determined by three groundwater monitoring wells and 55 sod samples from eight <br /> sod borings in the vicinity of Tank A <br /> 3 The dissolved hydrocarbon plume is not migrating and chemical concentrations do not <br /> increase with time Over five consecutive quarters of groundwater sampling, the <br /> concentration of gasoline hydrocarbons has generally declined from a high of 770 ppb of <br /> TPH-as-gasoline and 3 7 ppb of benzene <br /> 4 No water wells, deeper drinking water aquifers, surface water or other sensitive receptors are <br /> likely to be impacted The nearest water well is approximately 1,000 feet north of the site <br /> Mormon Slough borders the site to the north, cross-gradient from the plume of dissolved <br /> gasoline hydrocarbons The Mormon Slough channel is less than 20 feet bgs and <br /> ` groundwater beneath the site is approximately 31 to 38 feet bgs As such, surface water in <br /> Mormon Slough is likely unaffected by dissolved gasoline hydrocarbons in groundwater <br /> beneath the site <br /> 7 <br />