Wastewater antidegradation analysis and NPDES permit renewal

About this project

Confidential chemical manufacturer
Midwestern U.S.
$190,000 (Barr's fees)
completion date

Barr performed a wastewater antidegradation analysis for a large chemical producer and prepared an application for renewal of the facility’s NPDES permit.

Antidegradation analysis: Because our client was anticipating an increase in its rate of organic pesticide production, an antidegradation analysis was needed to discover if that would negatively affect the receiving water body or require changes to the facility’s discharge permit.

Barr began by determining the facility assimilative capacity (FAC), conducting a pollutant-by-pollutant evaluation of the amount of each substance that could be discharged to the receiving water without exceeding the water quality standard. We then calculated how much of the FAC would be consumed by the increase in production. In accordance with the state’s antidegradation implementation procedure, we evaluated the parameters—including those imposed by federal effluent limitation guidelines (ELGs) the facility was subject to—which were:

  • Total suspended solids

  • Chemical oxygen demand

  • Biochemical oxygen demand

  • Total organic pesticides

  • Organic pesticide subject to the planned production increase

We determined the FAC for each pollutant according to state water quality criteria; however, where numeric criteria were not available, we used other methods of establishing comparison values. For biochemical oxygen demand, we employed a previous Streeter-Phelps model to derive the dissolved-oxygen impact and compared the result to the state criteria, which showed that the proposed condition would not cause a dissolved-oxygen excursion. For total suspended solids, Barr used existing data on the receiving water body to propose a site-specific comparison value for the FAC, which indicated that the proposed rise in production would not significantly increase suspended solids in the receiving water.

Overall, the antidegradation analysis found that the planned production increase would be minimally degrading to the receiving water body: for each pollutant, the change in water quality was well below 10 percent of the FAC.

NPDES permit renewal application: Before starting to prepare the application for renewal of the facility’s NPDES permit, Barr and the facility met with staff from the state regulatory agency to establish goals and timelines for the application and to document any recent changes in permit procedures. The meeting helped establish open communications with the agency staff, which later helped prevent delays and reduce uncertainty in the permitting process.

Barr performed a mixing-zone study for the facility’s primary receiving water body by aggregating flow data from a nearby U.S. Geologic Survey stream gage and calculating 1Q10, 7Q10, and 30Q10 low-flow values at the discharge point (the lowest 1-, 7-, and 30-day average flows that occur (on average) once every 10 years. With those data and bathymetric cross-section information, we generated CORMIX model scenarios to determine the effluent mixing at each flow scenario for the primary outfall. The revised model indicated that there was enough mixing that the discharge would not cause violations of water quality criteria.

Next we generated a parameter table for each outfall, which showed what analytical data would be needed to complete the application. After reviewing existing data from the facility’s discharge monitoring reports and internal monitoring, we identified gaps in the data and recommended additional sampling. Once all necessary information had been collected, we completed the application forms and worked with our client to submit them before the deadline.

In addition to the permit application, Barr developed a background-information document to help state regulators understand the complexities of the facility in relation to its wastewater discharge. The document included detailed information about: 

  • The characteristics and designated uses of, and criteria for, the receiving water body

  • Applicable ELGs and calculation of ELG-based effluent limits

  • Calculation of water-quality-based effluent limits

  • Analysis of the reasonable potential to exceed water quality criteria

  • Special considerations for emerging pollutants

  • Industrial stormwater

The permit is currently under review by the regulatory agency.

Key team members

Rob Morrison

Vice President
Senior Water Resources Engineer

Ed Galbraith

Senior Environmental Engineer

Logan Cole

Senior Environmental Scientist

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