United States Department of Transportation
i
Volume balance and toxicity analysis of highway storm water discharge from Cross Lake Bridge : technical summary report.
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2009-09-01
[PDF-25.04 KB]
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Edition:Technical summary report.
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Abstract:The Cross Lake Bridge is approximately 10,000 feet long and spans Cross Lake. It is part of
Interstate 220 that bypasses Shreveport, Louisiana from Interstate 20, the longest interstate
highway in the country and heavily traveled by both car and truck traffic. Cross Lake, however,
serves as the potable water supply for the city of Shreveport. During construction of the bridge,
concern was expressed over the possibility of an accident on the bridge that might result in
contamination of the city’s water supply. As a result, the Louisiana Department of
Transportation and Development (LADOTD) agreed to modify the bridge to include a “closed”
drainage system and to construct a concrete-lined holding pond on the east bank of the lake to
collect and hold runoff from precipitation prior to testing and discharge.
Previous research results found that only about 50 percent of the rainfall onto the bridge was
reaching the pond due to leakage of the collection system on the bridge. As a result, LADOTD
carried out repairs to the collection system, creating the need to determine the degree to which
the repairs were successful.
Earlier research also identified substantial levels of conventional pollutants as well as heavy
metals in runoff from the bridge. Much of this material was sediment bound and settled to the
bottom of the pond. Toxicity testing has become a popular means of assessing effluent quality
in a variety of discharges, and a need was identified for an easy-to-use, rapid means of
determining the toxicity of the pond discharge to downstream life forms.
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