In 1986, water from the Old Oaken Bucket Pond surface water treatment plant was sampled by the MDEP. Two trihalomethanes (THMs), chloroform and bromodichloromethane, were
detected in water obtained from the surface water treatment plant. THMs are a family of chemicals that are formed when drinking water is chlorinated as a method of disinfection. Until recently, the MMCL for total THMs was 100 ppb (total THMs are chloroform, chlorodibromethane, bromodichloromethane, and dibromochloromethane). The federal MCL for total THMs was recently lowered to 80 ppb. Chloroform was detected in treated water from Old Oaken Bucket Pond at a maximum concentration of 130 ppb. Bromodichloromethane was detected at a maximum concentration of 11 ppb. Thus, these results indicate levels of total THMs above the previous and current MCL (100 and 80 ppb, respectively). However, as noted earlier, Scituate’s drinking water is a mixed supply of surface and groundwater sources. Compliance with state drinking water standards for THMs is determined by running annual average sample results from four areas of the distribution system (e.g., tap samples). During these years, the annual average levels of THMs were below 100 ppb and therefore in compliance with state standards (CDM 1988).