TMDLs and PRPs

The Environmental Protection Agency (EPA) and/or the Pennsylvania Department of Environmental Protection (DEP) identify stream segments and other waterbodies that are not meeting their designated use(s) as being impaired. As of 2018, Pennsylvania had over 29,000 miles of impaired streams and over 78,000 acres of impaired lakes. DEP’s Integrated Water Quality Report, which is updated every two years, defines the designated uses and attainment status.

Total Maximum Daily Loads (TMDLs)

 A Total Maximum Daily Load (TMDL) establishes the maximum amount of a pollutant allowed in a waterbody and serves as the starting point and planning tool for restoring water quality. TMDL reports are approved by the Environmental Protection Agency (EPA). These reports detail the characteristics of the waterbody; causes and sources of impairment; the actual calculations of maximum daily amounts of pollutant allowed in the water body by source; and recommendations for meeting the TMDL. Completed TMDLs can be found through DEP’s TMDL Search Tool. Also see SPC’s TMDL maps by county.

If a community is an MS4 permit-holder, consult DEP’s MS4 Requirements Table to see if you have a TMDL in your municipality. MS4 municipalities with a TMDL for sediment and/or nutrients (nitrogen or phosphorus) must develop a plan to meet the TMDL. These plans need to be submitted with your MS4 permit. Find more information on DEP’s TMDL page.

Pollution Reduction Plans (PRPs)

Pollution Reduction Plans (PRPs) function separately from TMDL plans and both can be part of the MS4 permit. Beginning with the 2018 MS4 permit cycle, communities with a National Pollutant Discharge Elimination System (NPDES) General Permit (PAG-13) that have streams impaired for sediment or nutrients, or discharge into the Chesapeake Bay watershed are required to have a Pollutant Reduction Plan (PRP). In Southwestern Pennsylvania, there are no MS4 communities in the Chesapeake Bay watershed. PRPs function separately from Total Maximum Daily Loads (TMDLs); therefore some MS4 communities may have to submit a TMDL plan and a PRP.

PRPs include many requirements, which can be found in the permit instructions. PRPs must reduce sediment pollutant loads by 10% and nutrient (total phosphorus) pollutant loads by 5% for impaired waters not in the Chesapeake Bay watershed. Note: the 10% sediment reduction can also accomplish the 5% phosphorus reduction as well. PRPs are made up of a municipal storm sewershed (MS3) map, existing load and waste load allocations for each pollutant, and best management practices (BMPs) to reduce the pollutant load. BMPs are required to be implemented within five years of the PAG-013 General Permit issuance.

Find more information on DEP’s PRP page or browse our resources.

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