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Memorandum 3T,-TEO C_'LFr;r4,A REGIONAL WATER QUALITY CONTROL BOARD 4 CENTRAL VALLEY REGION 3201 "S" S,ree 03'' .~iento, �3hlou-m3 9` 6' , DO Phone 9 i 6/-15 ,�� 6- r 1 -0270 TO: Tom Pinkos, Chief Ground Water Protection & Investigations Section FROM: Jon Marshack Environmental Support Unit DATE: 24 July 1586 SIGNATURE: SUBJECT: CLEANUP CRITERIA FOR CHLOROFORM (CHCY Problem: There is an inconsistency in the application of water quality standards and criteria for cleanup of sites contaminated with chlorinated volatile organic contaminants. For most potentially carcinogenic VOCs, the 10-6 cancer risk level is used as the upper limit, above which contaminants in ground water are assumed to impair its use for domestic supply. A common example is the S pg/1 value for TCE. For chloroform, another potentially carcinogenic VOC, some staff and dischargers are applying the MCL for total trihalomethanes (TTHMs) of 100 pg/1, a value that is over 500 -times greater than the 10-6 cancer risk level for chloroform. Chloroform is one of the four chemicals covered by the term "trihalomethanes". DHS is also advocating the use of the TTHM standard as a cleanup criterion for chloroform in ground water. Proposed Solution.- EPA olution: EPA has stated that the MCL for TTHMs was based mainly on technology and economics. I Therefore, this standard does not clearly protect the beneficial use for domestic supply of waters of the state. The MCL for TTHMs was derived for application to water as it is delivered to consumers after disinfection by chlorination, and not to the protection of the ambient quality of domestic water supply sources. In site cleanup situations the 10-6 cancer risk level of 0.19 pg/1 should be used as the measure of potential impairment by chloroform of the beneficial use of groundwater for domestic supply. In fact, virtually all primary MCLs are derived by balancing technologic and economic concerns directly related to the use of water for domestic supply