Evolving stormwater regulations

August 2011 » Features » PROGRESSIVE ENGINEERING
EPA continues to evaluate numeric effluent limitations that will impact the design of construction site sediment and erosion controls.
Wendell A. Burkart
The numeric effluent limitation applies to all discharges from a site except on days when total precipitation exceeds the local two-year, 24-hour storm event.

On Dec. 1, 2009, the U.S. Environmental Protection Agency (EPA) published effluent limitations guidelines (ELGs) and new source performance standards (NSPS) to control the discharge of pollutants – particularly sediment – from construction and development sites (74 Federal Register 62996). The regulation was incorporated into the National Pollutant Discharge Elimination System (NPDES) and became effective on Feb. 1, 2010. After this date, all permits issued by the EPA or delegated states must incorporate the final rule requirements, which include numeric and non-numeric effluent limitations.

Non-numeric effluent limitations
The non-numeric effluent limitations are listed in 40 CFR 450.22(c) – 450.22(h) and include requirements for the use of sediment and erosion controls for all construction and development sites requiring a NPDES permit (land disturbance is greater than one acre, or less than one acre but part of a larger common plan of development or sale). Specifically addressed in the rule are types of erosion and sediment controls, soil stabilization requirements, dewatering requirements, pollution prevention measures, prohibited discharges, and surface outlets requirements.

Permittees are required to design, install, and maintain effective erosion controls and sediment controls to minimize the discharge of pollutants. The design, installation, and maintenance of erosion and sediment controls must address factors such as the amount, frequency, intensity, and duration of precipitation; the nature of resulting stormwater runoff; and soil characteristics, including the range of soil particle sizes expected to be present on the site.

Numeric effluent limitations
The numeric effluent limit is listed in 40 CFR 450.22(a). Beginning on Aug. 2, 2011, sites that disturb 20 or more acres of land at one time are required to comply with the limit. On Feb. 2, 2014, the limitation will apply to all construction and development sites disturbing 10 or more acres of land at one time. The numeric limitation is 280 Nephalometric Turbidity Units (NTUs), expressed as a maximum daily discharge limitation. Daily discharge is defined as the "‘discharge of a pollutant' measured during a calendar day or any 24-hour period that reasonably represents the calendar day for purposes of sampling." This means the permittee may sample the turbidity of their discharges once or multiple times during the course of a day and average the results. Stormwater discharges leaving the site cannot exceed 280 NTUs. Compliance with this numeric standard will require a greater level of inspection, monitoring, and possibly chemical treatment.

To allow states with regulating authority for NPDES permits to incorporate the limits into their General Permits, the effective date of the numeric effluent limitation and associated monitoring requirements is Aug. 2, 2011, or the date of the new state General Permit, whichever occurs first for sites disturbing 20 acres or more at one time. For states where the EPA is the permitting authority, the new requirements will be incorporated into a reissued EPA Construction General Permit (CGP), which was set to expire on June 30, 2011. These delayed effective dates do not affect the compliance requirements for the non-numeric effluent limitations.

Sampling methods and frequency requirements will be determined by delegated state or the EPA in the new General Permits. Monitoring frequency is expected to be at a regular, pre-determined interval, at a minimum of three samples per day at discharge points while a discharge is occurring. It is the EPA's view that any stormwater event or snowmelt that generates a discharge from a construction site should be monitored.

Monitoring equipment and test methods also will be at the discretion of the permitting authority and are expected to include the use of automated samplers and/or turbidity meters with data loggers (see "Advances in stormwater monitoring," CE News, June 2011, page 44). It also is expected that the use of a properly calibrated field turbidi-meter will be sufficient.

The EPA recommends the use of representative sampling points as being acceptable for linear construction projects because of their potential unique nature (refer to page 213 of the final rule for additional details).

The numeric limitation applies to all discharges from the site except on days when total precipitation during that day exceeds the local two-year, 24-hour storm event. Non-numeric limitations will still apply and permittees will still be required to monitor their discharges that day, unless weather conditions are too dangerous for the sampler.

Challenge to rule causes uncertainty
Petitions for reconsideration of the rule received since it was published identified potential deficiencies with the data that the EPA used to develop the 280 NTU limit. The EPA stated that it improperly interpreted the data and the calculations are no longer valid.

The design, installation, and maintenance of erosion and sediment controls must address factors such as the amount, frequency, intensity, and duration of precipitation; the nature of resulting stormwater runoff; and soil characteristics.

The EPA requested the 7th District Court to set aside the numerical limit while it re-evaluated the data, and to remand that part of the rule back to the EPA and to hold the case in abeyance for 18 months. The court granted the EPA's request to remand the rule and to hold the suit in abeyance, but denied the request to set aside the numerical limit. Even though the EPA has acknowledged that the numeric limit is invalid, according to the court, it remains an enforceable component of the rule.

EPA issues general permit for comment
With the expiration date of the EPA's General Permit approaching, the EPA issued the new General Permit for a 30-day comment period. Inside the new EPA General Permit the EPA incorporated the requirements that went into effect in February 2010, and the numeric effluent limitations that were to go into effect in August 2011. However, they have not stated what the numeric effluent limitation will be.

With the issuance of the General Permit for comment, the EPA extended the 2008 General Permit expiration date from June 30, 2011, until January 31, 2012. By extending the date of the 2008 General Permit, this gives the EPA enough time to incorporate the changes into the new permit.

While the EPA takes another look at the data, many states' Construction Stormwater Permits are due to expire. The Clean Water Act does not require states whose construction General Permit expires prior to the promulgation of the new corrected numeric limit to include the 280 NTU numeric limit into their new permit. For states needing to finalize their General Permits before the effective date of the corrected numeric limit, the EPA advises them to issue their permit without the numeric limit. The EPA encourages these states to consider a shorter permit term in order to incorporate the corrected limit sooner than five years.

Wendell A. Burkart works for Terracon Consultants Inc.'s Wichita, Kan., office. Erin C. Brady, CHMM, CPESC-IT, works for Bombardier Aircraft Services in Wichita.

Find more information about the new stormwater rule at http://water.epa.gov/scitech/wastetech/guide/construction/index.cfm.
Information about the EPA's CGP is available at http://cfpub.epa.gov/npdes/stormwater/cgp.cfm
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