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Iw � • Interested Parties-Use Of Non-Purge Sampling Method April 23, 1997 Page 2 r groundwater sampling is contained in the attached Appendix A (Items To Be Submitted For Sites Whwe Non purge Method Of Groundwater Sampling 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 Plain, Oxnard Coastal Plain, and other groundwater basins with documentation cited in site assessment reports, can qualify as leaking UST gasoline sites overlying ureonfined aquifers. 2 The top screened area of the groundwater monitoring well must be screened 8hovP the water table at all times during the momttorimg period, the well must be permitted, and well construction details including bong logs signed by a registered engineer/gealogtst 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 size specific pre-purged and non-purged groundwater inonitormg study may be used to evaluate sites not,meeting the above mimimum entena. On a case by case basis, should the results of pre-purge/non-purge study indicate that no significant variance in petroleum Hydrocarbon concen"poQs (TPFIO, BTET-, and IN=) exists and hydrogeologic reports on fele contain such analyses, thert the groundwater monitoring wells at the site may not need to be purged prior to sampling for routine groundwater monitoring programs. S Prior to unplcmentauon of the non purge sampling method at a site, notify the Regional Board, or other appropriate regulatory agency, m writing of the imtent to implement the non-purge sampling method The information listed on the attached Appendix A must be submitted with your notification. Purging Is Required red Under the following conditions, groundwater monitonng wells aL t be purged prior to sampling 1 All newly installed groundwater monitoring wells must be rigorously developed and purged for the izanal two sampling events This practice is to ensure ie oval of any entrained, fine-grained material rcnaaiming 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 ante 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 I I r r AaycYd� � r CIM ffw~a$4 W060~NO aaAa"w OlfAWft ce COMWOr7.0".map-me**ad r 00"M VMM PVPW aM7"aw 0"1ftawM aM AW Weemom Of praaaf*ad hlwa vffi l www. r I 1 I r 4 II r ,