EPA promulgated a final rule at 74 Fed. Reg. 62,996 (December 1, 2009), that requires owners and operators of construction sites disturbing 10 or more acres of land to be subject to monitoring requirements and new numerical limits on stormwater discharges associated with construction activity. The regulation is in response to a court decision filed by the Natural Resource Defense Council in 2004, to set a deadline for the new rules. See NRDC v. EPA, 39 ER 1928 (9th Cir. 9/26/08).

The basic purpose of the rule is to reduce dirty run-off from construction sites, which has caused pollution to rivers and streams. Model technology includes erosion control (e.g., berms) and sediment control (e.g., silt fences), etc. This also includes both advanced and passive treatment systems, such as traps, impoundments, dispersion, dams, and filtration, as well as metering for turbidity (a visual indicator of pollutants in water bodies). Most linear projects (e.g., streets and highways) will not require sedimentation basins. Interstate natural gas pipeline construction projects are also exempt from the new rule.

The rule will take effect on February 1, 2010, but will be phased in over four years. Large construction sites that disturb 20 acres or more at one time will be required to comply beginning 18 months after the effective date of the final rule (August 1, 2011). Smaller construction sites that disturb 10–19 acres will be required to comply 4 years after the effective date of the rule (by February 2, 2014).

The numerical limits in the final rule are 280 nephelometric turbidity units (NTUs) expressed as maximum daily discharge units. Additionally, the rule requires owners and operators of all construction sites disturbing one or more acres to use erosion and sediment control best management practices to ensure that soil disturbed during construction activity does not pollute nearby bodies of water.

The rule-making adopted industry comments on the nephelometric turbidity unit limit. EPA had proposed 13 NTUs, which was very stringent and would have required active filtration treatment systems at construction sites. However, this is not the case under the final rule that was 280 NTUs.

EPA expects to incorporate the rule into EPA and state pollutant elimination discharge system permit programs for water discharges. Louisiana is such a state.