The Lakes TMDL Study and Implementation Plan
a groundbreaking approach integrating TMDLs and MS4s
This study was initiated in 2003 for lakes located within the Minnehaha Creek Watershed District (MCWD) that were listed on Minnesota's 303(d) list of impaired waters due to excessive nutrients. Thirty-three regulated MS4s are within the study area, and, during the course of the project, it became apparent that an MPCA-led effort to address the integration of MS4 stormwater permitting and TMDLs was necessary.
The project was selected as a case study by EPA Region V, and MPCA has since then developed guidance for MS4 and TMDL integration. The Lakes TMDL project was re-initiated in 2007, and the scope was re-defined to incorporate the newly defined MPCA approach to completing TMDLs that have a stormwater permitting component.
Study tasks:
- collaborate with MPCA staff, watershed district staff, and MS4 stakeholders to develop a technical approach that satisfies their respective needs
- evaluate in-lake water quality goals to determine applicability of site-specific standards
- complete watershed phosphorus load model (P-load) and in-lake nutrient response models (Bathtub)
- complete TMDL calculations, including wasteload allocations for all permitted stormwater sources, load allocations, and margins of safety
- develop implementation strategy for the lakes to achieve water quality standards
- complete TMDL report to satisfy state and federal requirements
- develop method for accounting for existing and planned BMPs and adjusting required load reductions for all phosphorus sources
- develop an implementation plan that integrates the watershed district’s watershed management plan, local surface water management plans for each affected community, and TMDL goals
EOR has worked closely with MPCA and MCWD staff to ensure that the local, state, and federal needs are all met in this TMDL. MPCA guidance regarding MS4 integration into TMDLs is being developed concurrent with this project, and EOR staff have provided input to and have been intimately involved with MPCA TMDL and stormwater staff in the decision-making process.