Surface water quality standards for recreational waters were developed by EPA in the mid 1980’s based on epidemiological data gathered and published in August 1984 in an EPA report “Health Effects Criteria for Fresh Recreational Waters”. In this report, the relationship between gastrointestinal illness and levels of E. coli and Enterococcus were observed and risk levels estimated. Subsequent studies by EPA have found relationships between Enterococcus exposure levels and gastrointestinal illness rates.
In Texas, fresh water recreational standards are established in the Texas Surface Water Quality Standards. E. coli is used to evaluate the risk associated with primary contact recreation and the standard established is set to achieve a risk of no more than eight illnesses per 1,000 swimmers, based on the risks established in the EPA report. In urban watersheds in the Houston area, the E. coli water quality standard is not being achieved. The levels of E. coli are quite often up to several magnitudes of order greater than the current standard of 126/100ml. Many of these watersheds are greatly influenced by urban storm water run-off as well as discharges from wastewater treatment plants. These discharges not only provide a continuous source of fecal bacteria, but also nutrients which may provide for continued survival and replication of E. coli.
To set priorities for management practices as well as to judge the success of those practices, the TMDL Bacteria Implementation Plan contains suggested provisions for the monitoring program to look at both E. coli and Enterococcus. Because of the potential for replication of E. coli in the waterways, a supplemental indicator is necessary to validate BMPs and their success. This presentation will look at the relationship of E. coli and Enterococcus in the data presented in the EPA studies, historical data from a non-urban watershed and the urban watersheds in the Houston area.
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