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JUL 13 '97 04 55PM CLEARWATER GROUP P 3,'S 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 Ciroundwater Sampling Is Used) 1. The groundwater monitoring well must be screened m an unconfined aquifer UST sates located m 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, tali qualify as leaking UST gasoline sites overlying unconfined aquifers- 2 The top screened area of the groundwater monitoring well must be screened ahave the water table at all times during the monitoring period, the well must be permitted, and well eonstructnon details including 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 tnay 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 concentratiops (TPHG, BTEX, and MTBE) exists and hydrogeologic reports on file contain such analyses, thou the groundwater monitoring wells at the site may not need to be purged prior to sampling for routine groundwater monitoring programs 5 Prior to implementation of the non-purge sampling method at a site, notify the Regional Board, or other appropriate regulatory agency, in writing of the intent to implement the tion-purge sampling method The information listed on the attached Appendix A must be submitted with your notification Purging Is Required Under the following conditions,groundwater manitorng wells must be purged pnor 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 removal of any entrained, fine-grained material romwining 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 sad provided with groundwater monitoring reports 2 The groundwater sainpling and testing program mcludes analysis for chlorinated hydrocarbons, metals, polycyclic aromatic hydrocarbons, and diesel A ,,,'0 peps Cw ffW#40e u 4 PM"*f+"d OMMA60 WiWOW Or 0400 MV Aar 080DOM 4 0*0 V MiYN TM/p0C*ff ftft=V A ME MdieAI 9040muOM