AWWA ACE95240

When the Surface Water Treatment Rule was passed in 1989, most utilities found there would be little impact from the Giardia and virus treatment requirements on their facility. Between the removal and disinfection credit given for Giardia, most utilities knew they would be able to comply with the regulation at all times. However, work published by Ongerth and Stibbs in 1987 and LeChevallier et. al. in 1991 introduced another dimension to the ability to treat surface water against parasites. They showed that not only Giardia, but also Cryptosporidium were likely present in many, if not all, surface waters. Because of the resistance of Cryptosporidium to chlorination and the small size of the organism, some utilities began programs designed to determine if the parasite was present in their source water and, if so, in what densities. Also, how effective were the various treatment processes of our surface plan in removing parasites? These were the questions that we in Cincinnati started out to answer. They are simple questions that every utility will want to have answered. We now have almost four years of data. What have we learned about Cryptosporidium with the data we have at hand? We did not truly realize the importance that this program was to us until rumors of the proposed Enhanced Surface Water Treatment Rule (ESWTR) began to circulate. Our data then took on added significance because the concept of treatment based on percent efficiency or log removal for Cryptosporidium did not look very promising at our facility when compared to the proposed worst case requirements of 99.9999 percent or 6 log removal based on raw water parasite concentrations greater than 100 organisms/100 liters. This paper will briefly describe data that we collected at our fairly conventional surface water treatment plant and discuss some of the other activities that we believe are necessary to cope with the problems posed by the mounting interest in Cryptosporidium.