Federal and State agencies have long been concerned with the impact of stormwater discharges from construction sites where soil is washed into adjacent surface waters. The Florida Department of Environmental Protection (“FDEP”) has already established a numeric limit of 29 Nephelometric Turbidity Units (“NTUs”) over natural background for such discharges. However, new EPA regulations, promulgated on December 1, 2009, and effective on February 1, 2010, will both establish limits on the maximum turbidity allowed in a discharge and require that stormwater discharge permits, whether generic or individual, contain specific monitoring requirements.
The regulation requires EPA to phase in numeric limitations over four years. New requirements will be incorporated into all permits issued after February 1, 2010. However, numeric effluent limitations and monitoring requirements will not be applicable until August 2, 2010, if the activity disturbs 20 or more acres of land at one time, and February 2, 2014, if the activity disturbs 10 to 20 acres of land at one time. A construction project’s acreage includes disturbances to any non-contiguous property occurring simultaneously and as part of a common development plan or conveyance.
Individual state permitting authorities will be required to specify monitoring requirements of sufficient sampling frequency to ensure effective monitoring. Recognizing the challenges associated with the inclusion of monitoring requirements in stormwater discharge permits, EPA intends to provide additional monitoring guidance to assist state permitting authorities in the design of monitoring protocols.
The new regulation also limits the average daily turbidity of a discharge to no more than 280 NTUs. However, the regulation exempts discharges if the daily precipitation exceeds the two-year, 24-hour storm.
EPA acknowledges that the compliance and enforcement costs of the regulation are not insignificant. Nevertheless, EPA concluded that the benefits of the regulation outweigh the costs due to the adverse impacts of sediment and turbidity from stormwater discharges at construction sites, such as modified stream flow, reduced or modified organism abundance and species composition, and significant impairment of water quality through the addition of nitrogen and phosphorus.
Although FDEP presently limits the turbidity of discharges to surface waters from construction sites, it does not require any monitoring of these discharges. FDEP is presently considering how it will coordinate the numeric limitations of the new EPA regulation with existing FDEP regulations and determining the specifics of monitoring requirements.