The Next Stage for the Numeric Limit

Nov. 1, 2010

For everyone who will be affected by the EPA’s effluent limitation guidelines (ELG) for construction sites, there is a new chapter opening in what has already been a several-year saga.

EPA first issued a draft of the ELG in December 2008, with a proposed turbidity limit of 13 nephelometric turbidity units (NTUs) for stormwater discharges from certain construction sites of 30 acres or more. During the public comment period that followed, there were many objections to that number–some people believed it would be prohibitively expensive to achieve, some said it was unachievable at any cost at many of the sites in question, and some even thought that such a low number, at least in places where the background turbidity is typically higher, wasn’t even a desirable thing to achieve in the first place.

In late 2009, EPA issued its final rule, with a significantly higher numeric limit of 280 NTU. (The limit, however, applied to smaller sites than before.) The plan was that the rule would take effect in stages: By August 2011, construction sites disturbing 20 or more acres at one time would have to meet the limit, and by February 2014, the limit would apply to sites disturbing at least 10 acres.

Legal challenges have now derailed, or at least delayed, implementation of the numeric limit. EPA estimated, in its various drafts of the ELG, the cost to the construction industry to comply with the new rule, and it was primarily on that cost model that the challenge was based. The National Association of Home Builders (NAHB), among others, maintained that EPA’s cost estimates were based on the use of passive stormwater treatment; that the 280-NTU limit is not reachable with passive treatment, but in most cases requires active or advanced treatment systems; and finally that EPA relied too extensively on data from vendors in developing its cost model. You can find more details and links to the court documents on NAHB’s Web site at

The upshot is that in August 2010, EPA “vacated” the numeric standard and will issue a revised rule. It’s been suggested by some of the organizations that challenged the rule that a more reasonable limit, to be achieved with passive treatment, would be 800 NTU.

While there will undoubtedly be some big changes–perhaps EPA will set a higher numeric limit, or perhaps it will abandon the goal of having a single limit for all construction sites that fall under the rule–there’s little doubt that some sort of numeric limit will still be in place, and that testing will be necessary to ensure compliance.

Just as cities and counties did in the months before Phase II of the National Pollutant Discharge Elimination System took place, developers and contractors are anticipating how they’ll deal with the final rule–even though they don’t know yet exactly what it will look like. That preparation includes figuring out just how they’ll handle the testing process itself, as well as anticipating the additional training onsite employees will need.

What do you think–Is the 280-NTU limit too strict? Would setting the bar at 800 NTU be too lenient? Let us know your thoughts by commenting on

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