Guest Commentary, submitted by

Mindy Lemoine,
Watershed Programs Manager
Pennsylvania Environmental Council

Implementing a sediment TMDL is a challenge because of the high cost of control measures and the weak legal mechanisms that drive implementation. When the sediment originates in stormwater runoff from numerous land developments and other municipal sources, as in the case of the Wissahickon Creek sediment TMDL, implementation can be particularly complex.

PADEP’s PAG-13 draft permit for MS4 municipalities requires that each MS4 in a TMDL watershed prepare a Stormwater TMDL plan. The draft permit provides some guidance on how to prepare an adequate plan, stating that two of seven recommended control measures should be implemented in the five-year permit period. The draft permit also states that “the Stormwater TMDL Plan shall demonstrate that the required pollutant load reductions will be achieved to the maximum extent practicable, consistent with the TMDL.”  That’s where municipalities get nervous. Neither EPA nor PADEP guidance tell them what is considered maximum extent practicable.

Pennsylvania Environmental Council (PEC) obtained funding from EPA to design a market-based approach to implementing the sediment TMDL in the Wissahickon. PEC believes that employing market mechanisms will support municipalities in achieving the  environmental objectives of the TMDL at the least cost.

PEC’s approach relies on two key assumptions. First, volume is an appropriate surrogate for sediment in urban stormwater. Second, a specific volume of stormwater retention must be established in the MS4 permit as the trigger for trading, and to give municipalities confidence that they can achieve compliance. This volume defines maximum extent practicable in the first five year cycle.

Ideally, a regulatory agency would  establish the level of control required, in this case, PADEP. As PEC’s report was released, PADEP was not prepared to set a number for the required level of control. In the absence of PADEP guidance, PEC examined how aggressively reductions could be obtained.  PEC has estimated the cost of fully implementing the sediment TMDL in the Wissahickon Creek to be between $106 and $230 million.  In the absence of very significant federal or state funding, it is unrealistic to expect municipal taxpayers to shoulder that burden in only one or a few 5-year NPDES permit cycles. Consequently, PEC sought to develop a reduction target that the municipalities and the Pennsylvania Department of Environmental Protection (PADEP) could both embrace. The report recommends that 267,064 cubic feet (also referred to as sediment credits) of new stormwater retention volume be used as the target for the first five-year cycle. PEC envisions that this capacity would create a quantifiable sediment load reduction within the first permit cycle.

The target volume is allocated to municipalities according to their percentage of the total WLA as determined in the TMDL. For example a municipality that contributes 17% of  the total WLA would be responsible for 17% of 267,064 cubic feet, equaling 45,428 cubic feet. That municipality would commit in its stormwater plan to identify a site and to design, construct and maintain 45,428 cubic feet of permanent retention. In each permit cycle, PADEP would assign a new target volume number.

PEC also recognized that stormwater retention is less expensive in some municipalities within the watershed than in others.  By allowing trading contracts between the municipalities, it would be possible for a municipality with high costs to purchase sediment credits from a municipality with low costs i.e. to implement stormwater retention within a neighboring municipality’s boundaries.  This market mechanism approach would reduce the overall cost of sediment reduction, and may encourage municipalities to work more formally.

The Wissahickon Creek Municipal Credit System is an innovative approach to controlling sediment loading carried by stormwater runoff.  PEC will be working with the Wissahickon municipalities to help them implement the system.

PEC’s report on the Wissahickon Creek Municipal Credit System was issued in January.
You can Download it Here or visit PEC’s site for more information.

Mindy Lemoine is one of PEC’s two Watershed Program Managers in the Philadelphia office. Mindy is “on loan” to PEC for about two years from the U.S. Environmental Protection Agency though an Interagency Personnel Agreement. In her work at EPA, Mindy coordinated local government partnerships for the Environmental Assessment and Innovation Division, the Chesapeake Bay Program and the Delaware Estuary Program. Mindy also worked as Regional Environmental Officer for the US Department of Commerce’s Economic Development Administration, and as Natural Resources Specialist and Regional Coordinator for the Louisiana Department of Natural Resources, Coastal Zone Management Program.

Mindy leads PEC’s Wissahickon Roundtable project, which will seek consensus from municipalities, developers and other stakeholders on land use practices that help manage stormwater. She will also manage PEC’s nutrient trading project in the Wissahickon and PEC’s multi-municipal stormwater project in the Pennypack watershed.

Guest Commentary, NPDES / MS4 MS4, PA DEP, sediment control, stormwater legislation, stormwater runoff, stormwater standards, TMDL, volume control, watershed protection