Friday, April 3, 2009

CT DEP Stormwater Target Values, Action Levels and Benchmarks

The Connecticut Department of Environmental Protection (“DEP”) has proposed to revise and renew its General Permit for the Discharge of Stormwater Associated with Industrial Activity. The previous General Permit was adopted in 2002, modified in 2003, and expired on September 30, 2007. It was extended on October 1, 2007 and October 1, 2008 through March 31, 2008 without change by DEP to provide ongoing coverage to approximately 1,500 registrants.

The 2002 permit required annual monitoring of stormwater discharges from qualifying storm events for an expansive list of chemical and physical parameters, including whole effluent toxicity, and a set of Target Values for the parameters based on the 80th percentile of the monitoring data collected in previous years.

In 2008, DEP announced that it would be revising the permit. It proposed to update its 80th percentile Target Values to reflect the monitoring data acquired since the prior permit was adopted in 2002. DER also proposed Action Levels at the 95th percentile of prior monitoring results which would require follow-up action by registrants to investigate the source of the exceedances and modify their BMPs and SWPPP.

On February 4, 2009, DEP issued a new proposed draft which adopts ten sectors modeled on the EPA “MSGP-2008” Multisector permit, with semi-annual monitoring. The previously proposed “Action Levels” have become “Benchmarks” to track the federal language. DEP’s proposal retains the broad spectrum of parameters to be included in the monitoring program, including toxicity, but makes some sector specific adjustments. The toxicity monitoring requirement carries with it no Benchmark. The draft also adds annual monitoring for parameters for which receiving waters have been designated impaired or subject to Total Maximum Daily Load restrictions.

The Benchmark values for copper, lead and zinc are based on Connecticut’s State Water Quality Standards. The Benchmarks for remaining parameters (pH, O&G, COD, TSS, TP, TKN, and NO3), are based on the 50th percentile of the previously acquired monitoring data.

DEP expects to go to notice on a new proposal in April 2009. In the meantime, the DEP has published notice that it intends to extend the 2002 General Permit once again until September 30, 2010.

[Read more about Water Quality Standards, Aquatic Toxicology and NPDES Permit Limits]

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address Stormwater Permitting & Regulatory Support, Stormwater Pollution Prevention Plans (SWPPP), Stormwater Monitoring and Stormwater Training.

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