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�_tablishniert of Pt1CL5 at the Npect I�� Is trat have Deen ShOti'✓n to ia:i5e no ao'der_, impact on human health) and nropo«o a primary MCL also at 5 aci/If' The EPA criteria document for chloroform mentions the amendment, at trat time proposed, to the National Interim Primary Drinking ';later P,eoulations which established the MCL for TTHiIS of 100pg/l. The criteria document states that 1t)his limit was set largely on the basis of technologic and economic feasibility." When ambient water containing natural organic matter, such as humic acids, is chlorinated for disinfection, trihalomethanes (THMs) are produced. There are other methods of disinfection for drinking water, such as ozonation and radiation, that do not produce THMs. However, the capital cost of converting the majority of the nation's water supply systems to these other methods is currently prohibitive. If the EPA was to establish an MCL for chloroform at the cancer risk level, the agency would, in essence, be mandating the conversion of disinfection systems at the local level. Under federal law, the federal government would have to provide a significant portion of the funding for this federally mandated local program. The same analysis applies to state standard setting for drinking water. Therefore, EPA and DHS are unable to promulgate a chloroform MCL that is not readily attainable with our current drinking water disinfection technology. The disinfection technology which causes the unintentional formation of by-products, that is, chloroform and other THMs, in finished drinking water serves a valid purpose— the reduction or elimination of the risk of infection from pathogens contained in raw water supplies. A treatment process is implemented to mitigate a potentially harmful condition. The MCL for TTHMs was derived by balancing the benefit of the elimination of pathogens in water against the potential harm caused by the resulting THM contaminants. In this balancing, EPA (and later DHS) made the determination that the risk of adverse health effects from THMs at 100 pg/l is more acceptable that the risk posed by pathogenic organisms. Thus, a concentration of THMs at the tap of up to 100 ug/1 will not result in an enforcement action by EPA or DHS against the water supplier. The same balancing of potential harm with benefit cannot be applied to a situation in which improper waste discharge practices of an individual permit chloroform, or any other contaminant, to enter ambient water. In this case, a potentially harmful condition is being caused by the inappropriate action of an