STEADY-STATE BACTERIA DELISTING APPROACH IN GEORGIA
Abstract:Approximately 6,000 miles of streams in Georgia are listed as partially or not supporting water quality standards. This estimate is based upon an assessment of 10,000 of the 70,000 total river and stream miles in Georgia. Most of these listings are due to fecal coliform bacteria levels that exceed water quality standards. Georgia has summertime and winter geometric mean criteria and a “white paper” policy that defines this standard for steady-state (i.e., dry weather) conditions. The majority of the Georgia stream bacteria listings, however, are based upon scheduled data collection, which includes a combination of steady, and non-steady-state wet weather conditions. To remove a stream from the 303(d) list in Georgia for fecal coliform, quarterly geometric means must be calculated from a minimum of four samples taken over a 30-day period. Two of the 30-day geometric mean calculations are required during the winter months (October through April) having a 1,000 colonies per 100ml standard) and two in the summer months (May through September). The winter and summer standards are 1,000 colonies per 100ml, and 200 to 500 colonies per 100ml, respectively.
Major urban streams within Columbus, Georgia and a portion of the Chattahoochee River adjacent to the city center are currently included on the State's 303(d) list of impaired water due to fecal coliform bacteria levels. The Columbus Water Works initiated water quality studies in the early 1990's and invested over 120 million in environmental infrastructure to control its combined sewer overflow (CSO), optimize its wastewater treatment processes, and strengthen the integrity of its network of sanitary sewers. Five years of CSO disinfection testing and regional watershed studies revealed that bacteria exists in concentrated numbers that exceed maximum value criteria from all streams when it rains. Bacteria loads have been successfully quantified, modeled, and separated into wet and dry weather contributions. Urban bacteria, as well as other wet weather pollutants, directly correlate to the percentage of impervious area. Additionally, bacteria loads from urban areas are an order of magnitude above rural watershed contributions.
The Columbus program demonstrates that CSOs can be controlled through cost-effective direct treatment methods and do not cause or contribute to a violation of bacteria standards in the Chattahoochee River. River tributaries can occasionally cause wet weather loads that exceed the river bacteria standards, but are in compliance during steady-state conditions. Dry-weather bacteria monitoring in accordance with state policy shows that most of the urban streams and the Chattahoochee River are in compliance with water quality criteria and is the basis of delisting, with support from the calibrated U.S. Environmental Protection Agency (EPA) BASINS model.
One stream, Weracoba Creek, does not meet the State bacteria standards and sanitary surveys indicate that bacteria sources may be of nonhuman nature. A sizable portion of this stream system is enclosed and is believed to be home to animal populations. Downstream of the enclosed and channelized streams is an open natural creek forming the centerpiece of the oldest and most used park in the city. Water quality objectives are to protect the recreational and aquatic biology of the natural stream reaches through the city.
Study conclusions and recommendations call for a full-scale demonstration to provide embankment stabilization, peak flow attenuation, flushed pollutant removal and disinfection. Stormwater treatment facilities will attenuate wet weather flows in the upstream channelized-reaches; remove pollutants from impervious area flushes and disinfect dry weather as well as a portion of the wet weather flow using ultraviolet light (UV disinfection). The stormwater treatment facility is anticipated to reduce downstream erodible pollutants that impact stream habitat and fish communities. Demonstrations are being implemented through the EPA 319(h) nonpoint source program to define costs and performance and further assess linkage to water quality targets and watershed action strategies.
Document Type: Research Article
Publication date: January 1, 2002
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