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State & Municipal Government


City of Lincoln, Nebraska
Salt Creek, Nebraska

The City of Lincoln has two municipal wastewater treatment facilities that discharge to a naturally saline segment of Salt Creek. Compliance with proposed NPDES permit limits for ammonia would have required the City to spend an estimated $30 million in treatment facility improvements to meet the proposed discharge limits.  As part of the City's project study team, EA conducted 6 years of seasonal biological assessments (fish and macrobenthic invertebrates) in addition to extensive chemical water quality sampling to develop definitive baseline surveys for Salt Creek. The project team then used these data to address Nebraska Department of Environmental Quality’s stream standards classification, and to calculate and negotiate site-specific ammonia limits using Salt Creek-segment specific biological data.

The study involved chemical characterization; physical characterization; habitat evaluation; biological studies of the stream using Rapid Bioassessment Protocols (developed by EA); in situ and laboratory toxicity testing; and extensive review, evaluation, and discussions with Nebraska Department of Environmental Quality and U.S. Environmental Protection Agency Regional staff. Site-specific data included 5 years of intensive summer and winter bioassessments on adult and larval fish, benthic macroinvertebrates, and habitat attributes; and 30-day chronic in situ toxicity tests using two test species (larval fathead minnows and juvenile channel catfish. During this period, six summer and five winter bioassessments were conducted to characterize the condition of the biological community in the Creek and to identify the major limiting factors to the community—channelization, high ambient chloride, and effluent ammonia. Pseudoreplicate sampling (to assess precision, accuracy, representativeness, completeness, and comparability of the biological data) was performed in conjunction with standard bio-assessments during the March 1997 and August 1999 sampling events to strengthen statistical evaluations.

The in situ chronic toxicity testing program was performed by EA to calculate a 30-day IC20 value using fathead minnows and channel catfish, and to use those data in combination with the other studies to determine a weight-of-evidence-based site-specific water quality criterion for ammonia. The in situ toxicity tests used caged fish continuously exposed for 30 days at nine instream locations to characterize the complex interactions of ammonia in Salt Creek waters. The in situ study evaluated two toxicological endpoints (mortality and growth), which are combined into a “biomass” determination.

Six summer and five winter bioassessments, using the U.S. Environmental Protection Agency’s rapid bioassessment procedures, were used to develop site-specific chronic water quality criteria for ammonia in Salt Creek. The effects of ammonia to the biological community in Salt Creek were measured by observing decreases in the numbers of fish and minnow species, benthic macroinvertebrates, and fly taxa at sampling sites located downstream from the two wastewater treatment plants. The response of the Rapid Bioassessment Protocol metrics to degradation was demonstrated with data from channelized and ammonia-impacted streams from eastern Nebraska. Impairment to the biological communities in Salt Creek was assessed by evaluating the Relative Difference between upstream and downstream biological metric values.

A continuous simulation model of total ammonia concentrations in Salt Creek was used to estimate the highest 30-day average ammonia concentrations for 30, 60, 90, or 180 days prior to each bio-assessment.

The taxa richness biometrics selected for Salt Creek were determined to be a reliable indicator of pollution stress to aquatic organisms in this system. The metrics incorporate the response of a large number of taxa: 17 fish species, 7 native cyprinid species, 135 macroinvertebrate genera, and 21 chironomid genera.

Based on this large dataset, the maximum safe total ammonia concentrations predicted for the Theresa Street and Northeast wastewater treatment plants were calculated.  The project also involved a formal peer review of the entire study and program by a Peer Review Panel from the Water Environment Research Foundation to enhance regulatory acceptance of these innovative studies.