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0 0 <br /> Recently underground tanks were removed from this site and <br /> groundwater infiltrated the tank pit/hole to a depth of six (6) <br /> feet below the surface ( 'bgs) . <br /> In a phone conversation with the geologist from Ground Zero, Greg <br /> Stahl, water samples from the pit showed that high levels of <br /> petroleum constituents were dissolved in the water. (ie; TPH-G = <br /> 1, 800 ppb, and Benzene = 230 ppb. ) <br /> Over excavation of soil around the perimeter of the pit from 71bgs <br /> to 9'bgs removed soil that was odorous and discolored. Soil samples <br /> were taken in the perimeter area to confirm the removal of the <br /> contaminated soil . The results of these samples have not been <br /> submitted to EHD. <br /> Historically the monitoring well closest to the tank pit (MW-#3) <br /> has been non detect or low levels of Benzene and Toluene (5 . 0 ppb <br /> and 2 . 0 ppb resp) . This conflicts with the high levels of water <br /> contamination discovered after the tank pull and EHD suspects that <br /> the water may have been impacted from contaminated soil below the <br /> tanks since lateral data supports that little or no source exists <br /> at least 10 feet from the pit . <br /> The depth to groundwater during monitoring well 3 ' s installation <br /> was at 14 ' bgs in May, 1991 as witnessed by Michael Infurna during <br /> a field inspection. <br /> With this in mind, EHD will require confirmation sampling from the <br /> soil expected to be removed from the tank pit in preparation to <br /> placing the new tanks. As per manufactures' specs, at least 12' bgs <br /> is required to provide adequate clearance for the new tanks . In <br /> order to verify the conditions of the soil beneathe the tanks, EHD <br /> recommends that during this pit deepening, soil samples be <br /> collected and immediately analyzed for TPH-G and D, and BTEX. <br /> If soil results are no detect from this procedure, it will support <br /> conclusions that any contaminated source has been adequately <br /> removed. If analyses verify that soils at 12, 13 , 14, and 15' bgs <br /> are contaminated, further investigation to define the lateral and <br /> vertical extent will be required. <br /> Soil at depth that is not immediately analyzed at this time (to <br /> avoid uncontrolled aeration while sitting in the stockpile) , will <br /> require this investigation in the near future. EHD recommends that <br /> conductor casings be installed between each new tank prior to <br /> gravel back fill placement in order to facilitate later drilling <br /> and not endanger drilling between new fiberglas tanks. <br /> Decisions made now will directely impact future investigations and <br /> EHD will require verification of the soil below the tanks to be <br /> completed prior to issuing site certification. <br /> DRAFT <br /> �dj �� <br />