Integrated Watershed Restoration to Achieve Local and Chesapeake Bay Wasteload Allocations

摘要

In February, 2010, Montgomery County became the first in Maryland to receive the latest generation municipal separate storm sewer system (MS4) national pollutant discharge elimination system (NPDES) permit from the Maryland Department of the Environment. The MS4 permit is one of the most progressive in the nation focusing on comprehensive watershed restoration. For example, it requires the County to restore twenty percent of the untreated impervious surfaces to the maximum extent practicable (MEP). The permit defines restoration as the use of Environmental Site Design (ESD) or other nonstructural techniques, structural stormwater practice retrofitting, and stream channel restoration. The permit also requires the County to make progress towards meeting EPA approved wasteload allocations for Total Maximum Daily Loads (TMDLs) for nitrogen, phosphorus, total suspended sediment, bacteria, and trash within different watersheds of the County. The County must also show progress to meet the commitments for trash reduction associated with the Potomac Trash Treaty and expand public outreach and stewardship opportunities related to MS4 Permit requirements. In 2011, USEPA approved the Chesapeake Bay nutrient TMDLs, and the County is also required to meet its wasteload allocations from that TMDL. To meet the full range of permit requirements and achieve multiple competing objectives, the County utilized the Watershed Treatment Model (WTM) to inventory the baseline status of watershed pollutant loads and forecast the results of implementing countywide watershed restoration to the maximum extent practicable. Treatment strategies were analyzed based on cost effectiveness per unit load removed and other stakeholder identified goals. A countywide strategy was developed to prioritize implementation over a 20- year planning horizon and to understand CIP investment and maintenance cost implications associated with permit and TMDL compliance. The analyses conducted and strategy developed are being used by other Maryland MS4 permittees as an example of the level of effort required to provide an integrated and balanced implementation strategy to meet the MS4 permit requirements for adding runoff management and also meeting wasteload allocations. In addition, several of the lessons learned from the regulatory review process will be shared.