DBP occurrence survey
Results of a disinfection by-product (DBP) survey and two years of distribution system DBP monitoring are presented for more than 100 treatment plants of the American Water System (AWS), the largest investor-owned water utility in the United States. Monitoring of total organic carbon (TOC) indicated that 83 percent of the AWS surface water treatment plants that exceed a raw water TOC concentration of 2 mg/L will not receive predisinfection credit for the use of chlorine. With existing treatment practices, approximately 20 and 66 percent of the AWS water treatment plants studied will exceed the proposed Stage I and Stage II trihalomethane (THM) maximum contaminant levels (MCLs) of 80 and 40 μg/L, respectively. Similarly, approximately 16 and 52 percent of the AWS systems studied will exceed the proposed Stage I and II haloacetic acids (HAA5) MCLs of 60 and 30 μg/L, respectively. Based on these estimates, it is believed that Stage II requirements may significantly affect future water treatment practices and costs.