NPDES permits issued for discharges to impaired water typically include specific requirements so that the new or expanded discharge does not "cause or contribute to" the impairment. General NPDES permits create a special situation in which a portion of permitted discharges may be to impaired waters and the nature of the impairments may be different.
General permits for stormwater discharges are particularly problematic in addressing impaired water and antidegradation requirements. As stormwater discharge permits are revised, States will attempt to address requirements for impaired waters in a manner that would apply to a wide range of discharges. How these requirements are expressed in the permit varies widely from State-to-State.
Some States have opted to incorporate requirements which promote pollution prevention measures. As one example, the State of Texas has detected levels of selected heavy metals in surface waters which are of concern, and has promulgated numeric discharge standards for “hazardous metals” into the industrial stormwater permit. However, the Texas Commission on Environmental Quality (TCEQ) approach is to allow facilities to do a self-assessment for sources of hazardous metals and implement pollution prevention measures to avoid the higher costs of hazardous metal sampling and testing. To be exempted, facilities must certify that:
- Facility does not use a raw material, produce an intermediate product, or produce a final product that contains one of the listed hazardous metals, or
- Any raw materials, intermediate products, or final products which contain a hazardous metal are never exposed to stormwater or runoff, or
- Facility collects and analyses stormwater samples from the facility and the results indicate that hazardous metal(s) are not present in detectable levels.
Waivers may be obtained on a metal-by-metal basis, or on an outfall-by-outfall basis. A waiver from hazardous metals monitoring does not exempt the facility from other benchmark monitoring requirements which may apply.
[Read more about benchmark monitoring]
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