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JUL 13 '97 04 54PM CL.EARWATER GROUP P 3/5 RECEIVED MAQY Z 6 1997 oUEPA PCIC wasm NW To Interested Fames April 23, 1997 Go-erna, .00 AAPI&S teglonal Water lmdity Control ioWd SUBJECT: USE OF NON-PURGE METHOD FOR SAMPLING OF GROUNDWATER 31 centre Pfau A7ve MONITORING WELLS AT GASOLINE EWPACTED SrM. low"sy Parr CA 1754.2136 -13)266-7500 Pu ose 4X(213)265-7600 —�—�- The purpose of this letter is to set forth the minimum conditions that must be met in order to implement the non-purge method of sampling as well as to identify conditions where purging of grouuawata. mon:.orng :re reqs:.-ed at leaking UST gasoline sites within the Los Angeles Regional Board area Bac_ 1 A report entitled "The California Groundwater Purging Study for Petroleum Hydrocarbons", prepared by SECOR International Incorporated (October 28, 1996) was commissioned by the Western States Petroleum Association (WSPA) Eleven of the I10 sites included in the WSPA study were selected from the Los Angeles Regional Board geographic area These sites were located in the cities of Whittier, Reseda, Lakewood, Oxnard, Agoura, Redondo Beach, Gardena, Torrance, Los Angeles, and Tarzana This represents a limited, but adequate cross section of arcne~lCaic r_a_mes :mp -ted by loakmg Unde:ero— d Storage Taak (UST) gubohne sites to 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 pnor to non-purged sampling The results of the study suggest that the non-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 et al (1996) Staff concluded that for groundwater monrtonng wells screened in unconfined zones at !cWt,:ab UST gaseln+e sites, purging is not routinely required under certain conditions The State Water Resources Control Board UST Program Manager, Mr Allan Patton, issued a guidance letter to Local Oversight Programs and Local Implementing Agencies on March 26, 1997,regarding "The California Groundwater Purging Study For Petroleum Hydrocarbons " The lever 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 under which purging is and is not necessary Purging Nqt Necessary Under the following conditions, groundwater monitoring wells 4orf t need to be purged prior to sampling The minimum reporting requirement for a site using the non-purge method of 0R_)tw POP- ow"Au 1.10 pW4@iw*acomb"Maw NW vuya&or combs w8w nsowsar sew ev W Us l7+wr ppp�w aftc x r.a op.prwt w mr goo W prWnj MO FUWM 96-0—Kj