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Me establ,.shrnent of R1-1CLs at the highest levels tnat have been snc,.. cause no adv;.rse impact on human h;alth) and proposed a prirnary MCL a;_ _ S ug/l.6 The EPA criteria document for chloroform' mentions the amendment, at ti --- time r -time proposed, to the National Interim Primary Drinking `,Fater which established the MCL for TTHMs of 100pg/I. The criteria docu,r _r states that "(t)his limit was set largely on the basis of technoloalc economic feasibility." When ambient v.,ater contairin ; natural crganic mater, su_-h a': r,um'c "ici-; chlorinated for disinfection, trlhalomethanes (THMs) are produced. There a, -.-- other ,_other methods of disinfection for drinking water, such as ozonation arc radiation, that do not produce THMs. However, the capital cost of convertmc the majority of the nation's water supply systems to these other methods ;= currently prohibitive. If the EPA was to establish an MCL for chlor ofor;-,,- the cancer risk level, the agency would, in essence, be mandating tr..-- conversion r;=conversion of disinfection systems at the local level. Under federal law, th_ federal government would have to provide a significant portion of the fund,nr- for this federally mandated local program. The same analysis applies to state standard setting for drinking water. Therefore, EPA and DHS are unable tr: promulgate a chloroform MCL that is not readily attainable with our current drinking water disinfection technology. The disinfection technology which causes the unintentional formation c° by-products, that is, chloroform and other THMs, in finished drinking wate- serves a valid purpose - the reduction or elimination of the risk of ir.fectior from pathogens contained in raw water supplies. A treatment process i implemented to mitigate a potentially harmful condition. The MCL for TThi,1L- was derived by balancing the benefit of the elimination of pathogens in wat_r against the potential harm caused by the resulting THM contaminants. in tn- balancing, EPA (and later DHS) made the determination that the risk of avers= - health effects from THMs at 100 pg/1 is more acceptable that the risk posec by pathogenic organisms. Thus, a concentration of THMs at the tap of up (;- 100 pg/1 will not result in an enforcement action by EPA or DHS against trr- water supplier. The same balancing of potential harm with benefit cannot be applied to situation in which improper waste discharge practices of an individual pEr chloroform, or any other contaminant, to enter ambient water. in this potentially harmful condition is being caused by the inappropriate action of ar.