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,fin �. - x a ,�:;. •, � _ 'Sr �, gl`s^oo��v 1+}�ar h� a - '�f f y:, � - i r _ _ 7 sand and sand with lenses of sandy silt, A 4 foot thick clay unit was observed beneath 1110 11]upperng sen, rillit Below the clay unit lies a light-brown,well graded sand unit,usue,,y at toast 20 feet countered at approximately 48 of wells MW-1o, MW-12, PAW-13, and PAW-14, a second clay unit was en feet below the surface. The second clay unit represents the base of this water bearing zone. 2.2 Site Hydrogeologyfrom 25 to 30 During drilling in October, 1989 groundwater was encountered a,depths ranging feet BGS. Two days after well completion, g roundwater levels had risen to approximately 22 feet BGS. on June 12, 1990, groundwater levels had dropped to approximately 24 feet BGS,within the first clay _ layer. The polentlometric surface map constructed from water table elevations measured on June 12, ic :99C is presented as Figure 5. Over the course at the project,as not ledrtolsigniaca tt�off-sith the SiMis e of r less than 0.001 towards the north. This horizontal gradient h the dissolved petroleum hydrocarbon plume in groundwater. Slug tests were performed in several on-site wells as part of the PAR investigation to determine resents the bearing the flow characteristics of the water bee;is l zone. Theather0cMW-7 of the groundwater r recoverywone ell that requires remediation, and MW-7 is located neard rg agrees with tabulated values for this proposed In this raport. The measured transmissiviry of 500 gp 9 rain material (tor example, Freeze and Cherry 1979), but is lower than that estimated from1 he median gpolf size (d5Q= 0.6-0.8 mm, K = 500-900 gpo1ft2; f3edinger 1961, Masch and puny will be used in design calculations. 2,3 Extent of Hydrocarbon impacted Sol! phase. One is a liquid J Petroleum hydrocarbons exist in two phases in the unsaturatum d0ocarbonszone and dissolved petroleum adsorbed to soil particles,composed e!separate-phase haserwithin the soil pore space. The vapor phase hydrocarbons in pore water;the second is a vvapor p plume is typically greater in extent than the adsorbed phase plume. A soil gas survey was performed from August It to September lata il illustrated ondefine hF'igure 6e The of the vapor phase in the subsurface soil. The results o!this survey shows that hydrocarbon impacted soil vapc,r is limited to the unsaturated zone, and is roughly survey concentric around the former tank with a maximum radiusof a hf drocarbons, as defined by laboratory The lateral extent of soil impacted by adsorbed•p Y tank it. The hydrocarbon impacted soil analyses of soli,Is Less than that determined by the coif gas rvey. This impacted soil in the unsaturated zone extends approximately 5o feet radially around the former - vapor surrounds the adsorbed-phase plume,and the lateral boundaries investigation.oth the dsorbed phase and R the vapor phase plumes in the soil were fully defined during the �X, Gtt Tt:Clt frit'}TEtt t)u - --