Three permit programs under the Clean Water Act are used to regulate discharges of stormwater to receiving waters—one for municipalities, one for industrial facilities, and one for construction sites. Of these, industrial stormwater is particularly challenging to control because of the wide range of industrial sectors that must be accounted for, each of which produces a unique suite of contaminants in stormwater. The industrial stormwater permit program includes a small number of individual facility permits as well as general permits that are issued to groups of industries at the state and federal level. The current Multi-Sector General Permit (MSGP) for industrial stormwater covers over 4,000 facilities nationwide and is used as a framework for dozens of similar state programs.
The National Academies of Sciences, Engineering, and Medicine is conducting a study that will provide input to the Environmental Protection Agency as it revises its Multi-Sector General Permit (MSGP) for industrial stormwater. The National Academies' committee will:
1. Suggest improvements to the current MSGP benchmarking monitoring requirements. Areas to examine could include:
• Monitoring by additional sectors not currently subject to benchmark monitoring;
• Monitoring for additional industrial activity-related pollutants;
• Adjusting the benchmark threshold levels;
• Adjusting the frequency of benchmark monitoring;
• Identifying those parameters that are the most important in indicating whether stormwater control measures are operating at the best-available-technology or best-conventional-technology (BAT/BCT) level of control; and
• New methodologies or technologies for industrial stormwater monitoring.
2. Evaluate the feasibility of numeric retention standards (such as volumetric control standards for a percent storm size or standards based on percentage of imperviousness).
• Are data and appropriate statistical methods available for establishing such standards as both technology-based and water quality-based numeric effluent limitations?
• Could such retention standards provide an effective and scientifically defensible approach for establishing objective and transparent effluent limitations?
• What are the merits and faults of retention versus discharge standards, including any risks of groundwater or surface water contamination from retained stormwater?
3. Identify the highest priority industrial facilities/subsectors for consideration of additional discharge monitoring. By “highest priority” EPA means those facilities/subsectors for which the development of numeric effluent limitations or reasonably standardized stormwater control measures would be most scientifically defensible (based upon sampling data quality, data gaps and the likelihood of filling them, and other data quantity/quality issues that may affect the calculation of numeric limitations).