Potential IGP implications from the National Academy of Sciences MSGP Report
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The National Academies of Sciences, Engineering, and Medicine reviewed the existing Environmental Protection Agency (EPA) Multi-Sector General Permit for Industrial Stormwater Discharges (MSGP) to identify improvements to be considered during the next MSGP revisions planned in 2020 (NAS Report).

California's industrial general permit (IGP) was informed by many of the MSGP's components including IGP numeric action levels (NALs) based on the MSGP benchmarks, and therefore the findings of this report may have implications for the future of the IGP. The presenters, including a NAS committee member and NAS Report technical reviewer, will first provide an overview of the NAS recommendations and then focus the remaining time discussing the recommended improvements to benchmark thresholds, which may more directly impact the IGP NALs.

The NAS Report general findings include recommendations on benchmark thresholds, improvements to how control measure effectiveness is measured, monitoring methods and frequency, tiered-based monitoring, and encouraging infiltration and capture and use where feasible. A brief overview of these findings along with potential IGP implications will be discussed at the outset. Following this discussion, the presenters, along with audience participation, will focus on the NAS Report's recommendation that EPA suspend or remove magnesium and iron benchmarks until acute aquatic life criteria are established or benchmarks are developed based on chronic effects from intermittent exposure. Meeting the iron and magnesium NALs has consistently been a challenge for many IGP dischargers due to the low magnesium NAL (originally established based on the highest method detection limit multiplied by 3.18) and the prevalence of iron in background soils and other site materials. A brief overview of IGP discharger stormwater compliance monitoring data will be summarized from the Stormwater Multiple Application and Report Tracking System (SMARTS) to present the distribution of stormwater discharge concentrations compared to the NALs for a variety of industry types based on their standard industrial classification (SIC) code. The discussion will also include other IGP-monitored parameters that are a consistent concern due to non-industrial sources (e.g., Aluminum) or other parameters recommended for evaluation in the NAS Report (selenium, arsenic). Finally, the discussion will conclude with a summary of additional research needs to fill data gaps including an interactive question and answer components with audience members to better understand the state of the science and how these recommendations may lessen or increase future burdens on IGP dischargers.

This presentation will include multiple opportunities for audience engagement and is directly related to the conference's theme of "Stormwater… Why We Do What We do: Looking back and Looking forward" as the presentation provides a review of past regulations and how suggested improvements, if implemented, may impact the future of industrial stormwater regulations in California.

Publication Summary

  • Geosyntec Authors: Brandon Steets
  • All Authors: Brandon Steets, Geosyntec Consultants; Michael Stenstrom, UCLA
  • Title: 2019 CASQA Annual Conference
  • Event or Publication: Event
  • Practice Areas: Urban Stormwater Management Planning and Design
  • Citation: Geosyntec will make substantial technical contributions at the California Stormwater Quality Association (CASQA) Annual Conference at the Monterey Conference Center in Monterey, California on October 7-9, 2019.
  • Date: October 7-9, 2019
  • Location: Monterey, California
  • Publication Type: Platform Presentation