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RECEIVED MAy 1 6 JW itlW PA Peet wasoo To Inter+csted Parties April 23, 1997 �Angeles real Water ty t:ontml toad SUBJECT: USE OF NON PURGE METHOD FOR SAMPLING OF GROUNDWATER 71 Cenzm Pisa Dnve MONITORING WELLS AT GASOLINE Il"ACIED STYES. lanwmy Paris,CA 1734.2156 _ _13)766.7300 Pumose 1X(I13)266-7600 The purpose of this letter is to set forth the minimum conditions that must be met m order to implement the non-purge method of sampling as well as to identify conditions where purgmg of grougidwau.mon..arng wells :re requ:.-e3 at leaking UST gasoline sites within the Los Angeles Regional Board area Background 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 110 sites included in the WSPA study were selected from the Los Angeles Regional Board geographic arra These sites were located in the cities of Whitner, Reseda, Lakewood, Oxnard,Agoura, Redondo Beach, Gardena, Torrance, Los Angeles, and Tarzana This represents a Limited, but adequate cross section of i�t..irnns�InniC r';;-_—as :SQ .'..".ted b' 1—caking Un.3z :—.% a � Te••.•. .--a--•-e a F f $ s'- d torsge Tz..,t t a i l gb.,oiuie sites to evaluate the non-purge method Groundwater monitoring wells at these sites were all reportedl) screened across the water table in unconfined aquifers and had been monitored for at least four quarters prior to non-purged saaripling. The results of the study suggest that the non-purge method of sampling groundwater monitoring wells is a valid alternative to the pargc 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 monitoring wells screened in unconfined zones at :c:-t•:wb UST gaselMe sites, Purging is not routinely required under certain conditions The State Water Resources Control Board USS 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 letter acknowledged the-insults of the WSPA report,stated that there were limitations to the non- purge method, and concluded that note-purge methods, where applicable, should be implemented is order to reduce costs whenever possible. The discussion which follow describes the conditions under which purging is and is not necessary Pur¢ing Not Neccssmx Under the following conditions, groundwater monitoring wells do n t need to be purged prior to sampling The i munum reporting requirement for a site using the non-purge method of �Arrypro PrPrr Owenwmn Ie m Pwwa.•PC#.emir OIr QVIW QCiMl M* WWWO roriwf 4r0 i rrerhr Air pi"pr�.rep.ae....e ariOr.�rM b sr!+-r�r M p".rM eM wRrw�rnrew� I ji i I i