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i 2.0 PETROLEUM HYDROCARBON RELEASE AND SITE CHARACTERIZATION INFORMATION 2.1 CHEMICALS OF CONCERN I As described in the SECOR September 1994 Report, the historical chemicals of concern discovered I beneath the former tank pit area include the gasoline constituents BTEX, TPH as gasoline, and lead The concentration and distribution of these chemicals is summarized in Section 3 0 of this Addendum Report IThe compounds found in the former septic leach area include a kerosene-range hydrocarbon and the semi-volatile compounds (SVOCs) naphthalene and 2-methylnaphthalene The presence of these compounds is also revisited in Section 3 0 of this Addendum ' Other chemicals of interest found in the Site subsurface include the volatile organic compounds (VOCs) 1,2 d>chloroethane (1,2 DCA) and tetrachloroethylene (PCE) The presence and source of these chemicals are discussed in Section 4 0 of this Addendum i 2.2 SUMMARY OF GROUNDWATER CONDITIONS AT SITE AND VICINITY 2.2.: Site Hydrogeologic Conditions The site is underlain by a laterally competent deposit of clayey silt from the surface to approximately 62 feet bgs This silt deposit appears to be consistent in lithology with a typical composition of approximately 80% silt, 15% clay and 5% fine sand Between 62 and 80 feet bgs, a sandy zone is present At the Site, the sandy zone is an average of 15 feet thick and varies in texture from well I sorted to poorly sorted, typically containing approximately 80% sand and 20% clay and/or silt Underlying this sandy zone are layers of silt and clay to the depths explored in this investigation The exception noted is of a sand deposit logged in the boring for well MW-4 at a depth of 102 feet I bgs Hydrogeologic cross sections depicting the site subsurface conditions based on the information developed in the SECOR and other previous investigations are presented as Figure 2, 3 and 4 A copy of the SECOR, WESTON and Woodward-Clyde field boring logs is found in Appendix B I In Ma /June 1994 first encountered groundwater was found under unconfined conditions at an May/June average depth of approximately 70 feet The zone of saturation for this groundwater is the sandy zone located between approximately 62 and 80 feet bgs Based on the June 1994 and previous investigations, this zone appears to be the highest permeability pathway for groundwater and potential contaminant transport at the Site The groundwater level at the Site has fluctuated SECOR International Inc (SECOR®) CRC Environmental Risk Management,Inc N0026 oo1 01 add 5 November 30 1994