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Stormwater discharge screening.

The terms "illicit connection" and "illicit discharge" were made synonymous in the 1991 proposed EPA stormwater rules. Illicit connections were defined as point-source discharges that are not composed entirely of stormwater and are not covered by an existing National Pollution Elimination System permit and that discharge through a municipal storm sewer system. Despite EPA's emphasis on illicit connections, investigations in Houston, Texas, revealed that most of the city's stormwater problems came from broken wastewater collection system lines discharging to the system or directly to a body of water. In March 1991, the Houston Public Utilities Department began to assess the EPA's field screening program. Because the department had been conducting a remediation program to locate and eliminate problem discharges to the main wasteway--Buffalo Bayou--since March 1989, the city wanted to determine if additional information required by the EPA regulation would enhance Houston's program. Houston's remediation program for locating nonstormwater discharges uses a step-by-step approach. Existing data generated from stream monitoring of the city's major bayous are used as baseline information. Monthly samples are taken from each bayou at selected bridge crossings. Parameters used are carbonaceous BOD, ammonia nitrogen, nitrate nitrogen, pH, total suspended solids, dissolved oxygen, temperature, fecal coliform, and chlorine residual. If significant contamination is found, the city then undertakes a comprehensive weekly sampling program for fecal coliform, dissolved oxygen, and temperature. This additional sampling, approached by boat, identifies the sediment of the bayou with the problem. Once a specific section of the storm sewer is identified, a land-based search begins. The first step is to collect a benchmark sample, as near to the outfall as possible. This sample is analyzed for carbonaceous BOD, ammonia nitrogen, nitrate nitrogen, total Kjeldahl nitrogen, pH, fecal coliform, and metals. The problem discharge is evaluated by analyzing dry-weather ammonia, calculating flow, and identifying indicator aquatic flora and fauna at the outfall. Indicator species include red-eared turtles and mullet and a gray-colored filamentous bacteria, Sphaerotilus. If a concentration of an indicator species is observed without high levels of nutrients, then an intermittent water quality problem is suspected. The results of the EPA field screening were similar to the findings of Houston's ongoing remediation program. Detergent and ammonia values were positive at least 90 percent of the time. Because an estimated 85 percent of the problems in Buffalo Bayou was caused by wastewater collection system failures, it was expected that these values were comparable city-wide. Because Houston is able to find and remediate contaminated sites based on low-flow water quality ammonia data, there have been significant improvements in the bayou water quality. Based on the analyses taken from a benchmark sampling point the Buffalo Bayou fecal coliform log-mean concentration was reduced from 20,000 to 2,000 colonies per 100 ml eight months after remediation was initiated. The concentration fluctuates monthly because of the dynamic nature of the system, but on an annual basis, the fecal coliform results show a steady decline. Undertaking a comprehensive management plan to reduce the discharge of pollutants is the next challenge. Given the lack of sensitivity of the EPA field screening test kits, and the high probability that most problems result from failure of the infrastructure, Houston recommends: 1) testing should be included among the EPA required parameters for screening; 2) given the extensive land area of a large city storm sewer system and the limited resources available to most municipalities, it is not practical to locate discharge problems through random sampling; a more practical approach is to view water quality in the receiving stream, determine the affected areas, and in these areas perform comprehensive sampling to identify problem discharges; and 3) field screening tests should be confined to locate pollutant discharges in the field. The process of reclaiming water body is a never-ending project in densely populated urban areas. Because Houston's approach has quantified trends in fecal coliform concentrations, contamination is easier to monitor and remediation is implemented more efficiently.

"The Illicit Connection--Is It the Problem?" By Theo Glanton, M. T. Garrett, Jr., and Bill Goloby, engineer, manager, and biologist, respectively, Wastewater Operations Division, Houston Public Utilities Department, Houston, Texas. Water Environment & Technology, September 1992.
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Title Annotation:Environmental Wastes Control Digest
Author:Billings, Clayton H.
Publication:Public Works
Date:Jan 1, 1993
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