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JUL 13 '97 04 55PM CLEARWATER GROUP P.3f5 07 Interested Parties Use Of Non Purge Sampling Method April 23, 1997 Page 2 groundwater sampling is contained in the attached Appendix A (Items To Be Submitted For Sites Where Non-purge Method Of Groundwater Sampling Is Used) 1 The groundwater monitoring well must be screened is an unconfined aquifer UST sites located in the San Fernando Valley, San Gabriel Valley, Los Angeles Coastal Plain, Oxnard Coastal Plain, and other groundwater basins with documentanon cited in site assessment reports, can qualify as leaking UST gasoline sites overlying uncoafmcd aquifers 2 The top screened area of the groundwater mronitormg well must be screened at+ove the water table at all times dunng the monitoring period, the well must be permitted, and well construction details including boring logs signed by a registered engineerlgeologM are contained to 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 On a case by case basis, should the results of pre-purge/non-purge study indicate that no significant variance in petroleum hydrocarbon concentrattops !TPHG, B'r£X_, grid Iv!TBE) 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 implementation of the non-purge sampling method at a site, notify the Regional Board, or other appropriate regulatory agency, in wasting of the intent to implement the non-purge sampling method The information listed on the attached Appendix A must be submitted with your notification Puratn I ,Required Under the following conditions, groundwater monitoring wells l=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 se oval of any entrained, fine-grained material remaining 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 rate must still be recorded cad provided with groundwater monitoring reports 2 The groundwater sampling and testing program weludes analysis for chlorinated hydrocarbons. metals,polycyclic aromatic hydrocarbons, and diesel RN1�Iad iepw 'l ow nwabe u!o OmNM @Ad 6"f�i t w C+rsanw's cocoa.tisaMeea,.col I 1 1 ®r Nrw+�9NM pAp�� -,:-No Intl~V111 va"fI V*aeMA1 d pr Went end hnm F&AN MMM I ' I 1 f k ! I r l I ill i �i --