Sunday, March 15, 2009

Use of Aquatic Life Standards As Stormwater Benchmark Values

On July 6, 2009, the Minnesota Pollution Control Agency (MPCA) released the draft of its proposed multi-sector industrial stormwater discharge general permit. This permit, once promulgated, will replace the existing industrial stormwater permit, which expired in October of 2002.

The MPCA draft permit is of interest outside of Minnesota because of the numerous unique requirements that MPCA has included. Many of these go well beyond other current State general permits, and even the most recent US EPA general permit (“MSGP-2008”). Unique features of the MPCA permit include special stormwater antidegradation requirements, design and performance requirements for stormwater infiltration, requirements for mercury minimization, and others.

One unique feature of the draft MPCA general permit is the use of Aquatic Life Standards as Stormwater Benchmarks. Stormwater benchmarks are used to evaluate the effectiveness of stormwater Best Management Practices (BMP). MPCA is currently proposing to use some Final Acute Values (FAV) and “Great Lakes” derived water quality standards as stormwater benchmarks. For other proposed benchmarks, “Best Professional Judgment” is the basis for the values.

MPCA is proposing to use FAV that apply to cold water fisheries or “trout streams” (Class 2A) for a number of benchmark chemicals, including:


For some of these chemicals, MPCA is apparently considering water quality-based adjustments, based on parameters such as hardness, pH, temperature, etc.

These water quality-based benchmarks, as proposed, would not apply to all industrial categories. The industry sectors that would be subject to one or more water quality derived benchmarks include:

Sector A - Timber Products
Sector C - Chemical and Allied Products Manufacturing
Sector E - Glass, Clay, Cement, Concrete, and Gypsum Products
Sector I - Oil and Gas Extraction and Refining
Sector K - Hazardous Waste Treatment, Storage, or Disposal Facilities
Sector L - Landfills, Land Application Sites, and Open Dumps
Sector M - Automobile Salvage Yards
Sector N - Scrap Recycling and Waste Recycling Facilities
Sector Q - Water Transportation
Sector U - Food and Kindred Products
Sector X - Printing and Publishing
Sector Y - Rubber, Miscellaneous Plastic Products, and Miscellaneous Manufacturing
Sector Z - Leather Tanning and Finishing
Sector AA - Fabricated Metal Products
Sector AC - Electronic and Electrical Equipment and Components

Looking for other sector information? Click here for information on proposed stormwater requirements for a specific sector.

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

Caltha LLP Aquatic Toxicology / WQ Standards Services Website