AWWA JAW46217

Giardia and Cryptosporidium were monitored monthly for two years to determine their occurrence in the Allegheny and Youghiogheny rivers, their source, and the efficiency of their removal by the Pittsburgh Drinking Water Treatment Plant. Sources investigated included a dairy farm stream, treated effluent from a sewage plant, and several samples from combined sewer overflows, all of which regularly contribute parasites to rivers. Raw, settled, filtered, and filter backwash waters were also sampled. Clarification and filtration generally control passage of protozoa into the drinking water, but small numbers of Cryptosporidium occasionally pass through even in the absence of treatment difficulties. Cysts and oocysts are also reintroduced into the drinking water plant via recycling of backwash water. Includes 15 references, table, figures.