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f <br /> fSouthland/Stockton 7 <br /> March 1991 <br /> f <br /> f <br /> 8968, 9140, 9158 and NYM (9172) A review of the laboratory analyses results from water samples <br /> fcollected from the seven regularly sampled domestic wells shows that drinking water standards for BTEX <br /> compounds have not been exceeded since December 1968 Summary tables showing laboratory results <br /> ffor TPH-as-gasoline from the domestic wells over the life of the project are provided in Appendix D <br /> SOIL SAMPLING AND RESULTS OVERVIEW <br /> I <br /> Field observations, photo-ionization detector readings and analytical laboratory results confirmed <br /> fthe presence of petroleum-impacted soil at the site at the time that the initial monitoring and pumping <br /> wells were installed A cross section location map and cross section profile is provided for graphical <br /> f representation of the TPH-as-gasoline impacts detected during the drilling for monitoring wells 1 through <br /> 6 and 12 during 1986 and 1987 (Figures 4 and 5) The impact to sods In the vicinity of the tanks was <br /> f due primarily to the downward migration of product from the point of loss to the water table <br /> Subsequently, hydrocarbons were able to adsorb onto soil particles across the site as the water levels <br /> declined, leaving a newly exposed hydrocarbon-impacted vadose zone <br /> f <br /> The lowering of the water table has been advantageous from a remediation view point, as <br /> fhydrocarbons were transferred from the dissolved phase within the groundwater to the adsorbed phase <br /> on sods in an unsaturated environment The soil-vent system extracted hydrocarbons which would have <br /> fotherwise required removal using the pump-and-treat program, and it has been proven that where <br /> applicable, hydrocarbon removal rates are higher with in situ soil venting than by pump-and-treat <br /> fmethods <br /> Reductions in hydrocarbon concentrations in the vapor extraction air-stream indicate that the <br /> fsod-vent system has reduced petroleum hydrocarbon concentrations in the soils within the system's <br /> radius of influence In addition, analyses of soil samples collected during the drilling of well 17A <br /> freported non-detectable petroleum hydrocarbon concentrations in two samples from about 35 and 45 <br /> I <br /> I <br /> GROUNDWATER <br /> TECHNOLOGY, INC <br />