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JUL 13 '97 04 54PM CLEARWATER GROUP P 2/5 RECEIVED MAY t 6 1997 aUEPA PCLC%vamo To Interested Parties April 23, 1997 A/As�gd�a :eglonai Water >"llty Control toard SUBJECT: USE OF NON-PURGE N=OD FOR SAMPLING OF GROUNDWATER ]t CMte PIUA Dave MONITORING WELLS AT GASOLINE U PACTED SrM. Soaieey Pnrk,CA 1734-2136 .i3)2cd.73W Pu ose 4X(213)266-7600 The purpose of this letter is to set forth the mimunum conditions that must be met 1n order to implement the non-purge method of sampling as well as to identify conditions where purging of grouudwate: mowzomg vellr.=requ_med at leaking UST gasoline sites within the Los Angeles Regional Board area i Background A report entitled "The California Groundwater Purging Study for Petroleum Hydrocarbons", prepared by SECOR International Incorporated (October 28, 2996) was commissioned by the Western States Petroleum Association (WSPA) Eleven of the 110 sites included in the WSPA study were selected from the Los Angeles Regional Board geographic area These sites were located in the cities of Whittler, Reseda, Lakewood, Oxnard, Agoura, Redondo Beach, Gardena, Torrance, Los Angeles, and Tarzana This represents a limited, but adequate cross section of ),,,4—e+ c!o- 1Ci rM^:-^.-es i9 =ted LJ lzakm Unud rat nd Storage Tru k `Ua T� kaoline sites to --a��• a a p Y g b aS L J b' evaluate the non-purge method Groundwater monitoring wells at these sites were all reportedly screened across the water table in unconfined aquifers and had been monitored for at least four quarters prior to non-purged sampling The results of the study suggest that the noir purge method of sampling groundwater monitoring wells is a valid alternative to the purge method commonly accepted as standard practice at leaking UST gasoline sites in California Regional Board staff have completed the review of the WSPA report and a report entitled "Groundwater Sampling-A Pilot Study of the Effects of Well Purging" by Ken Williams at al (1996) Staff concluded that for groundwater monitonng wells screened :n unconfined zones at UST gasoline sites, purging is not routinely required under certain conditions The State Water Resources Control Board UST Program Manzger, Mr Allan Patton, issued a guidance letter to Local Oversight Programs and Local Implementing Agencies on March 26, 1997,regarding "The California Groundwater 1?nsrging Study For Petroleum Hydrocarbons." The letter acknowledged the-results of the WSPA report,stated that there were limitations to the non- purge method, and concluded that non-purge methods, where applicable, should be implemented in order to reduce costs whenever possible The discussion which follow describes the conditions udder which purging is and is not necessary Purging Not Necessa ++ I Under the following conditions, groundwater monitoring wells 4o n t need to be purged prior to sampling The minimum reporting requirement for a site using the noel purge method of i I JteCyoyePappr ' Dire mfsvenYWpsiwpwend ewM+K+/f//?i+/NydC/tllearMJwNNMsoWF►74Iq I , ./.m.mrr p.yp.r.Roa.,�w...,a.mwer w.m.w Ivwrnr W p�s�nt.lw Nnar�rwriee+i ,