Exempted and Conditionally Exempted Discharges
All NPDES stormwater permits require municipalities to effectively prohibit the discharge of non-stormwater into storm drains. Certain non-stormwater discharges, such as flows from riparian habitats, wetlands, springs, or unpolluted groundwater, are exempted (i.e., allowed to discharge to storm drains with no control measures). Other non-stormwater discharges, known as conditionally exempted discharges (CEDs), are allowed to discharge to storm drains only if certain measures are taken to control potential pollutants in the discharge.
The Municipal Regional Permit (MRP) includes a list of CEDs that are not prohibited from discharge to storm drains if they are identified as not being sources of pollutants to receiving waters or if appropriate control measures are developed and implemented to prevent or eliminate adverse impacts of such sources. In accordance with the MRP, Co-permittees must implement control measures in accordance with the tasks and implementation levels of each category described in Permit Provision C.15.b if they allow these categories of discharges. The Program developed a program-wide guidance document report entitled Conditionally Exempted Discharges: Classification and Control Measures (February 17, 2011) that describes an approach for each category of discharge. This document supersedes the Conditionally Exempted Discharges Report (dated June 15, 2000).
The Co-permittees are currently implementing the BMPs described in the Conditionally Exempted Discharges: Classification and Control Measures report. They have made the BMPs part of their standard operating procedures for municipal activities. They are requiring businesses and contractors and encouraging residents to comply with these BMPs, and they have included the BMPs in conditions of approval for development projects where applicable.
A separate guidance document was developed for the conditionally exempt discharges related to water utility operation and maintenance (O&M) planned, unplanned and emergency potable water discharges. MRP Provision C.15.b.iii contains specific BMPs, monitoring and reporting requirements that apply to potable water discharges from the Co-permittee water utility O&M activities to the extent a Co-permittee is a water purveyor. The Program finalized the Water Utility Operation and Maintenance Discharge Pollution Prevention Plan (WUDPPP) in early 2011. The objective of the WUDPPP guidance document is to provide water utility personnel and service contractors with the knowledge and tools necessary to minimize adverse environmental impacts, from their operation and maintenance activities. The WUDPPP was updated in August 2012 to reflect a new conditionally exempt category "Low Impact Planned Potable Water Release". The most recent version of the WUDPPP can be found here.