A recently concluded NAHB study on stormwater discharges from construction sites indicates that builders and developers will face challenges in complying with a pending numeric effluent limit from the Environmental Protection Agency.

In the study, NAHB gathered field data on current levels of turbidity — or solid particles — in the stormwater coming off construction sites to be able to assess whether the EPA’s new limit can be consistently achieved using passive control systems.

Under Effluent Limitation Guidelines that were finalized on Dec. 1, 2009, the EPA had established a numeric effluent limit of 280 NTUs (Nephelometric Turbidity Units) for construction sites larger than 10 acres.

However, after the rule was challenged by NAHB, the agency admitted that it had “improperly interpreted the data” and could no longer support that effluent limit. It is currently in the process of determining a new limit.

Findings from the NAHB research make it difficult to make definitive determinations on what the effluent limit should be.

Turbidity values — provided by association members and builders of commercial properties and roads from the Associated General Contractors of America (AGC) — varied widely, from 5 NTU to 735 NTU.

But it is clear from the study that taking turbidity measurements and monitoring sites will be difficult.

Participants in the study mailed water samples to NAHB, where readings were taken using a turbidimeter. Volunteers also provided information on the overall conditions of the site and the size of the rainfall that occurred prior to or during the collection of the discharge.

Participants were required to collect three samples from a single point of discharge over 24 hours, but the EPA guidelines will require sampling from all discharge points, which will be even more burdensome.

The limited number of personnel who may be on the site immediately after storms will raise logistical problems for taking discharge samples.

Also, in many cases the same person will have to take samples from multiple sites, which may not be feasible depending upon the distances between those sites.

In any event, the study indicates that there will be a learning curve associated with monitoring construction site turbidity.

The results of the study will be used by NAHB in providing feedback to the EPA during the public comment period on the new rule and will also be used to inform legal decisions.

Those who have sampling vials can still take samples and return them to NAHB.

For more information, email Larissa Mark at NAHB, or call her at 800-368-5242 x8157.

Are You Ready for a Visit From the EPA? 

“Storm Water Permitting: A Guide for Builders and Developers,” available through BuilderBooks.com, provides a starting point for builders and developers to use in locating and understanding storm water permitting requirements.

The publication has been prepared to help builders comply with the U.S. Environmental Protection Agency's stormwater requirements, and includes information on state permitting programs and more than 50 of the most commonly used Best Management Practices.

Also included are tips on compliance, including how to handle visits from inspectors.

To view or purchase this guide online, click here, or call 800-223-2665.