Updated Industrial Stormwater General Permit Sampling Requirements

The new Industrial Stormwater General Permit (ISGP) sampling requirements for Washington State became effective on January 1, 2020.

The ISGP’s goal is to improve stormwater quality (and reduce pollutants in runoff) through management of stormwater at industrial sites. The ISGP originates from a combination of federal (the Clean Water Act) and Washington state (Water Pollution Control Act) law. Under the ISGP, permittees are required to implement Best Management Practices (BMPs) to reduce stormwater pollution, monitor their stormwater discharges, compare the results with benchmark values, and implement an escalating series of corrective actions depending on the number of times the benchmarks are exceeded.

What Stormwater Provisions Changed? Key Updates

Many of the key provisions didn’t change. Here is a brief summary of the key updates.

  • The five core water quality benchmarks—turbidity, pH, oil sheen, copper and zinc—remain the same, and the requirements and deadlines for implementing corrective actions if those benchmarks are exceeded remain unchanged.
  • The new permit proposes to use 2017 North American Industry Classification System (NAICS) groups to classify the sectors required to apply for permit coverage (the previous permit relied on the 1987 Standard).
  • Industrial Classification (SIC) groups to identify the sectors required to apply for permit coverage. The Clean Water Act remains based on SIC codes, and there is a not a one-to-one relationship between the two codes.
  • The Washington State Department of Ecology has changed the groundwater-related provisions with an intention to increasingly regulate infiltration of stormwater under the ISGP. For sites with a discharge point to groundwater (i.e., infiltration systems), the terms and conditions of this permit will apply. There is an exemption to permit coverage for facilities that discharge only to groundwater.
  • Permittees must sample the stormwater discharge from the first fall storm event each year (the start date for the “first fall storm event” sampling requirement has been moved from October 1 to September 1). First fall storm event means the first time on or after September 1 of each year that precipitation occurs and results in a stormwater discharge from a facility. We’ll likely see more 3rd quarter benchmark exceedances as a result, as there are fewer summer storms to sample to average with the first flush.
  • Permittees claiming “consistent attainment of benchmark” for one or more discharge monitoring parameters will now be required to collect a single annual sample in the 4th quarter.
  • Ecology has retained the provision requiring permittees that discharge to Puget Sound Sediment Cleanup Sites, including the Lower Duwamish Waterway, to conduct line cleaning and storm drain solids characterization sampling once during the permit term.
  • The new permit requires that the stormwater pollution prevention plan (SWPPP) be prepared by qualified personnel. Some additional information and details are also to be presented on figures, such as showing the property size/acreage, areas of existing and potential soil erosion that could result in the discharge of a significant amount of turbidity, sediment, or other pollutants, etc.

For more information, see the Washington State Department of Ecology website’s Industrial Stormwater General Permit page or contact Andrew Kaparos.