Proposed Limits on Stormwater Discharge

Sept. 1, 2009

The proposal by the US Environmental Protection Agency for a new stormwater runoff rule featuring effluent limitation guidelines should mean more demand for the services of certain qualified professionals-including those registered with EnviroCert International Inc., as a Certified Professional in Erosion and Sediment Control (CPESC), Certified Professional in Storm Water Quality (CPSWQ), or Certified Erosion, Sediment, and Storm Water Inspector (CESSWI). This new rule is part of a court-ordered revision in the Construction General Permit that calls for the use of best available technology to control stormwater discharged from construction sites under the National Pollutant Discharge Elimination System program.

New Performance Criteria
For the first time, the permit would require the use of national performance-based standards to limit the amount of sediment and other pollutants allowed in stormwater runoff from certain construction sites. This is in addition to the continued use of prescriptive standards, which specify various best management practices (BMPs) for controlling construction-site runoff.

Under the proposed guidelines, sites disturbing 10 or more acres at one time would have to install a sediment basin to contain and settle sediment from stormwater runoff. The proposed rule sets minimum standards of design for these basins but also allows for alternatives that provide equivalent control of sediment. What’s more, certain large sites in areas of high rainfall energy and with soils having significant clay content would be required to limit turbidity of stormwater discharges to no more than 13 nephelometric turbidity units (NTUs). This is designed to remove fine-grained particles that settle slowly, if at all. Typically, this would mean the use of an advanced treatment system (ATS) involving the use of chitosan-enhanced sand filtration or other polymers that promote flocculation plus some kind of filter. The EPA is also evaluating the feasibility of a numeric limit that would not rely on the use of ATS for the final rule.

“Assuming the numeric guidelines are adopted, EPA would most likely allow permitting authorities to determine how the turbidity levels would be monitored and how frequently,” says Jesse Pritts, a civil engineer with the EPA’s Office of Water. “This would probably involve the use of grab samples using hand-held turbidity meters. We don’t envision having to send samples to a lab for testing.”

The EPA has until December 1 of this year to publish its final rule in the Federal Register. It would become effective 90 days after publication.

States that have been delegated by the EPA to issue construction general permits would then have up to five years to incorporate the new rules in their permit requirements.

California’s Approach
California is one of a handful of states, including Georgia, Oregon, and Washington, that are revising their construction general permit to include specific limits on the amount of sediment and other pollutants in construction-site runoff. California’s proposed new permit, developed by the State Water Resources Control Board (SWRCB), features numeric effluent limits (NEL). The third and final draft was scheduled to be adopted in early September 2009.

Development of these new rules was a several-year process. It involved a blueribbon panel, which determined that numeric effluent limits could be feasible on larger projects, along with input from the construction community and the public through a series of public workshops with the SWRCB and staff.

“As a result, it’s likely that this permit will be adopted,” says Jeanne Duarte, CPESC. As president of Stormwater Resources, a consulting firm based in Valencia, CA, she has been providing input to the board in developing training to help developers and contractors meet the new permit requirements once the new permit is implemented.

California’s NEL requirements would apply to sites one acre or larger in size, based on the level of environmental risk as determined by such factors as type of soil, proximity to receiving waters, and revised universal soil loss equation (RUSLE) calculations. Only sites assessed as Risk Level 3, the highest, would be required to meet the NEL.

Using the Best Technology
The NEL is based on available technology that would achieve the desired limits, Duarte notes. The new rules propose a pH limit of 6.0 to 9.0 for Risk Level 3 sites. For those sites that require an ATS the turbidity limit would be 10 NTUs. Otherwise, it would be 500 NTUs.

“The pH and NTU parameters were chosen in part because they can be measured in the field with pH meters or turbidity meters, eliminating the expense of a lab analysis,” Duarte explains. “There are still some technical questions about how the SWRCB has linked turbidity measurements to sediment concentrations, but eliminating the need for lab analysis for measurements, such as suspended sediment concentration (SSC), makes the monitoring requirements a bit easier to comply with.”

Under California’s new permit, only a properly credentialed or certificated person would qualify to prepare a stormwater pollution prevention plan as a SWPPP developer or to implement, inspect, or monitor such as plan as a SWPPP practitioner. Depending on the type of service provided, that would include, among others, CPESC, CPSWQ, and CESSWI registrants, she notes.

The proposed permit would become effective 100 days after it is adopted. Assuming adoption in early September, the effective date would fall in the middle of California’s rainy season. “Because of the difficulties in implementing so many major changes when people are trying to keep up with the rain events, there is talk of postponing implementation until the dry weather begins again,” Duarte says.