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have been installed in fine-grained "non-aquifer formations" <br /> (Gass 1989 ) , such as the silty clay in the subsurface at 909 West <br /> Hammer Lane. This is due to the small size of clay soil parti- <br /> cles from the "non-aquifer" formation, which may not be held back <br /> by the filter pack, and to the low-energy, relatively ineffective <br /> flushing action which characterizes the development of a well <br /> that does not recharge quickly. Excessive turbidity of the sam- <br /> R ples can be reduced through the use of the gentlest possible <br /> purging methods and low purge rates. <br /> The December 1989 and February 1990 samples collected from the <br /> wells were collected using hand bailing methods (Appendix B), <br /> b which can be gentle if proper care is taken. Every effort will <br /> i <br /> be made in the future to collect samples with low turbidity <br /> through these purging and sample-collection strategies. <br /> � <br /> EAIs 'standard water sampling protocols involve purging three to <br /> five casing volumes of well water before sampling. While the <br /> t purge 'water is removed, the.chemical parameters (temperature, <br /> .` <br /> conductivity, pH) of the purge watr are monitored. The well is <br /> sampled only after these paramet*rs have stabilized, thereby <br /> indicating, that water being removed from the well is. groundwater <br /> from the aquifer formation.. not water which has been inside :the <br /> well casing " <br /> `r 4. RWQCB contends that "significant concentrations <br /> ,of hydro + <br /> carbons are present in soils in the unsaturated zone, " _. <br /> based on results of vapor samples taken from the mon - s <br /> toring wells in .1987. <br /> S <br /> 9 <br /> Il' <br /> T- In"'November 1987EA:measured:.the concentrations of- petroleum <br /> hydrocarbons <br /> in the headspace of monitoring wells MW1 to. MW5 T <br /> 4 <br /> :during an an SVCA. These analyses.measured detectable Concentra <br /> , <br /> tions .of .petrole'um hydrocarbons` in the well "headspace samples " <br /> I Y <br /> (Table 3) . ` Ver . levels of petroleum. hydrocarbons. were . <br /> j detected in :vapors collected from the. soil column (Tables "3,..4 ). <br /> e35/71.050/2-90/tx .10 <br /> i <br /> r <br /> � � f <br />