The Murky Future of Stormwater Numeric Standards

EPA recently withdrew a proposed rule that sought to impose a numeric turbidity standard and ongoing monitoring obligations on construction sites 10 or more acres in size. This move follows an industry challenge to the rule and suggests that the agency’s efforts to transition stormwater regulations away from Best Management Practices and towards numeric standards and analytical monitoring may be faltering.

The backstory: In December, 2009, EPA issued a rule as part of 40 C.F.R. Part 450, regulating stormwater discharges from construction sites of one acre of more. Construction sites 10 or more acres in size were required for the first time to meet a numeric standard for turbidity (280 nepholometric turbidity units or NTUs) and conduct analytical sampling of their discharges to confirm compliance with the standard. The rule resulted from a lawsuit filed by environmental groups in 2004, which lead to a court order mandating EPA to establish a numeric turbidity standard for construction stormwater discharges by December, 2009.

The new rule applied to all construction sites - residential, commercial, and infrastructure - over 10 acres in size. EPA estimated that the rule would affect over 82,000 construction and development companies, result in the removal of 4 billion pounds of year of sediment and pollutants from construction site stormwater discharges, and cost $953 million annually to comply with.

Trade groups took a different view, contending that the numeric standard would be exceedingly difficult to meet and estimating that annual compliance costs would exceed $10 billion. These groups sued for judicial review of the rule. Last August, EPA acknowledged that they had mis-interpreted data when they set the 280 NTU standard, which led to a court remand of the rulemaking back to EPA. EPA then forwarded a revised rule to the Office of Management and Budget last December for review, but is not known what numeric turbidity standard EPA was proposing in the revised rule.

Apparently as a result of OMB’s review, EPA is now withdrawing the revised rule and going back to the drawing board. The agency will gather additional data on stormwater treatment options at construction site, presumably to better understand the costs and effectiveness of various treatment technologies.

Why is all of this administrative process of interest? First, it confirms that trade group participation in the rulemaking process is critical. In this case, but for the intervention of groups like the National Association of Home Builders, EPA was prepared to enforce a numeric effluent limitation that was based on flawed science.

More importantly, this regulatory stumble may presage how stormwater discharges will be regulated in the future. Because of the high degree of variability in stormwater discharges, regulatory controls have focused on the use of Best Management Practices (e.g., swales, detention basins, good housekeeping measures) over numeric effluent standards and monitoring. But EPA recently stated in a memo that it intends to increase the use of numeric effluent standards for discharges at small construction sites and municipal separate storm sewer systems (MS4s). While that memo drew considerable criticism from regulated stakeholders, it did signal an intention to move away the stormwater program away from a more flexible BMP program and towards a more rigid system involving discharge standards confirmed through regular monitoring - as found the NPDES permitting program for wastewater discharges. However, by withdrawing its proposed turbidity effluent standard for large construction sites, EPA appears to be acknowledging the complexity of regulating stormwater discharges through numeric effluent standards and monitoring, due to the variability in precipitation, pollutant sources and pollutant transport in stormwater discharges, as opposed to wastewater discharges.  

The next step: EPA will issue a notice in the Federal Register soliciting data to assist its further rulemaking “in the near future.”