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p ogl gg�gz A M,- M-:- 0-1 t, "M �.. -rho I-i,-1-a-million cancer risk estimates Of 0.19 to 5,6 P I ShOL11d be used as the leisUre of pote.ntial impairment by chloroform of thel�-neficial use of ground water ated that the application of the for domestic supply, Staff of EPA,Region 9 has st, 1-in-a-million cancer risk estimate,instead of the TTHM NICL,as a water quality goal for chloroform in ground water appears to be consistent with the federal Clean Water Act and the Safe Drinking Water Act and that the'nTIM standard is not appropriate for protection of ambient water quality. In fact,virtually all primary MCLs are derived by balancing the technologic and economic concerns that are directly related to the use of water for domestic supply -�fects information developed under the MCL Goalprocess, -1hus wi.th the health ily reliable indicators of protection of beneficial uses of primary MCLs , e riot necessan relied upon as water quality goals in ambientwater,,� .-J should not necessarily be these situations. 'fliere are other instances where water quality criteria mo're stringent than MCLs are applied to protect the beneficial uses of a water resource. For example, it is common practice to require compliancewith a uatic life criteria for heavy metal 1�1 contaminants in suriace waters that are often much ower than MCLs for the same contaminants. e Once it has been decided that some ftradation in water quality will be permitt d(i.e., background water quality is not used for water quality goals),other factors may require water quality oals to be set below water quality standards and criteria. Care s ou taken to consiger other dischargers in the area and the contribution to the degradation of water quality that each imposes. If one discharger is permitted through the disPosal of his waste to degrade the water resource to just below the point where beneficial ..uses are impaired,then no additional capacity exists for further degradation by other Jischarges of waste. In addition,the knowleage of the health and environmental effects of chemicals or combinations of chemicals is constantly evolving. What is considered to be safe at or below 10 lig/1 todav may be found to be harmful at I gg/I tomorrow. A Note About Water Quality Standards Water Quality Standards are a unique application of water quality criteria and are defined in the regulations which implement the Clean Water Act. That definition reads: IlVater quality standards are ions of state or federal law which consist Of a designated use or uses for Keowvia:iters of the United States and water quality criteria for such waters based upon such uses. Water quality standards are to protect the public health or welfare,enhance the quality of water and seA ve the purposes of the Act." —40 CFR 1302(c)and 131.30) In California,the Basin Plans and other water quality control plans,such as the Ocean Plan and the Delta Plan,contain the State's Water Quality Standards b-ecause these plans set forth beneficial uses and water quality objectives. selwiTig wate r QualitV Goals 4