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M RECEIVED MAY 1 6 1997 r . Or To Interested Parties Apn1 23, 1997 Governor Axtselts glonW Water )catty conemi lord SUBJECT: USE OF NON-?URGE MMOD FOR SAMPLING OF GROUNDWATER 71 trove Plaza nnVe MONITORING WELLS AT GASOLINE McACTED Sn'ES. Iontcrty Park,CA 1754-7156 -13)266.9300 PRMose ,?X(213)2"44500 The purpose of this letter is to set forth the minimum conditions that must be met rn order to implement the non-purge method of sampling as well as to identify conditions where purging of gmuuf;wate;iz m;mr ng v.ells are raq%r_-s3 at leaking UST gasoline sites within the Los Angeles Regional Board area BacLground 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 area These sites were located in the Cities of Whittier, Reseda, Lakewood, Oxnard, Agoura, Redondo Beach, Gardena, Torrance, Los Angeles, and Taxzana This represents a limited, but adequate cross section of ly.4----�0--�-ic-aic r--;: "es m z--ted by leaki:aB Undz sv—nd Storage Taa (UST) SuialLne stIcs 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 prior 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 monitoring wells screened in unconfined zones at 'c-1:-e UST gasol a sites, purging is not routuiely required under certaut 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 letter acknowledged the-resulls of the WSPA report,stated that there were limitations to the non- purge method, and concluded that non-purge methods, where applicable, should be lmplcmented in order to reduce costs whenever possible The discussion which follow describes the conditions under which purging is and is not necessary Purging Not Necessary Under the following conditions, groundwater monitoring wells do n t need to be purged prior to sampling The minimum reporting requirement for a site using the non-purge method of k7Wa Peyer onrfift"Jan 4 q pwonq cad Mboft"rw view or camw 'I MWMmaom" sow WYA Aw pmpq &Uffa _eM W0~1 rw lw V+P—Oft W P�m Md rwrw ge-embaoi OF