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Interested Parties-Use Of Non-Purge Sampling Method April 23, 1997 Page 2 groundwater sampling is contained m the attached Appendix A (items To Be Submitted For Sites Where Non-purge Method Of Groundwater Samp1mg. Is Used) 1. The groundwater monitoring well must be screened in an unconfined aquifer UST sites located in the San Fernando Valley, San Gabriel Valley, Los Angeles Coastal Phun, Oxnard Coastal Plain, and other groundwater basins with documentation cited in site assessment reports, can qualify as leaking UST gasoline sites overlying unconfined aquifers- 2 The top screened area of the groundwater monitoring well must be, acreeaed at+ovP the water table at all times during the monitoring period, the well ;oust be permitted, and well construction details mcludmg boring logs signed by a registered engineer/geologist are contained in the UST case file for review 3 Monitoring wells are completed in moderate to high recovery aquifers and formations consisting predominantly of coarse grained sediments (sands and gravels) 4 A site specific pre-purged and non-purged groundwater monitoring study may be used to evaluate sites not meeting the above minimum criteria Ona case by case basis, should the results of pre-purge/non-purge study indicate that no significant variance in petroleum hydrocarbon concentrat's (TPHG, B77y-, "d -M-TRE) exists and hydrogeologic reports on file contain such analyses, then the groundwater monitoring wells at the site may not need to be purged prior to sampling for routine groundwater monitoring programs S Prior to uuplezaamtation of the non-purge samplmg method at a site, notify the Regional Board, or other appropriate regulatory agency, in wnting of the intent to implement the non-purge sampling method The information listed on the attached Appendix A must be submitted with your notification ,P„umine Is Required Under the following conditions, groundwater monitoring wells mu5t be purged prior to sampling 1 All newly installed groundwater monitoring wells must be rigorously developed and purged for the initial two sampling events This practice is to ensure reuaoval of any entrained, fuse-grained material mviatning from well construction and development procedures, as well as to provide data for comparison to non-purge testing Data on turbidity, pH, specific conductance, temperature, and recharge sate must still be recorded and provided with groundwater monitoring reports. 2 The groundwater sampling and testing program includes analysis for chlorinated hydrocarbons, metals,polycyclic aromatic hydrocarbons, and diesel ow cur~n so p.wa.ow*MWAM wVmaw of cam"we.."-w.or.c WA a" 0149 .o w veo«:M=ien&"oft2iom ow im40"DOM 0 P.efid 0"hfi n #"*M ont