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h- <br /> Na <br /> fluctuations can also affect water quality. When the water table <br /> r <br /> 1 rises, the groundwater wets contaminated soils and dissolves some <br /> of the hydrocarbons adsorbed on the soil. <br /> i4 <br /> i <br /> The quality of groundwater from selected monitoring wells has <br /> F, been monitored regularly since the first observation of <br /> leakage of petroleum underground storage tanks at the site. <br /> Groundwater samples, as well as the influent and effluent to the <br /> a <br /> air stripper, are routinely sampled and analyzed for benzene, <br /> P <br /> toluene '. xylene, and TPH, and occasionally for EDB, 1,2-DCB, <br /> 1 4, <br /> 1,3-DCB, C benzene, and E benzene. In addition, total lead <br /> j` concentrations have been analyzed on occasion. Groundwater <br /> analyses are listed in Appendix C. , <br /> The general .urend of benzene, toluene, and <br /> xylene concentrations <br /> in groundwater has been a decrease in concentration over time. <br /> "� ...' This is a direct effect of the groundwater and free product <br /> rs <br /> recoveryprogram underway at the site. Recent, analyses show that <br /> s <br /> some monitor well (MW-11, MW-12, and WK-22) have no measurable <br /> `T levels of benzene. No free <br /> product has been recovered since ' <br /> . March 1987. <br /> 5 � ; The influence of the cone' of depression pressgenerated by wells RW-1 <br /> and MW-19 contributed- to keeping the majority of contaminated <br /> groundwater lander the site boundaries. <br /> 14 <br /> - <br /> rC.> <br />