THE CEDAR RIVER BASIN PATHOGEN TOTAL MAXIMUM DAILY LOAD – A CASE STUDY FOR WATERSHED-SCALE TOTAL MAXIMUM DAILY LOADS

摘要

A recent analysis of the Total Maximum Daily Load (TMDL) program by theEnvironmental Protection Agency (EPA) concluded that states are confronted with asignificant increase in the number of TMDLs that need to be developed in the nextdecade. The majority of these TMDLS will be more complex than those developed todate and the level of resources and funding are not anticipated to increase. Toexacerbate the problem, many states are behind the curve and others have to complywith Consent Decrees that establish an accelerated pace of TMDL completion. EPAconcluded that one strategy to address the maximum number of impairments in themost expeditious and cost-effective manner was developing TMDLs using a holisticapproach on hydrologically connected impaired segments; i.e., a watershed-scaleapproach to TMDL development and implementation.This paper presents a case study of the watershed approach applied to Cedar RiverBasin located in Iowa. The watershed is approximately 8,000 square miles in size,has nine waterbodies impaired for bacteria, and is under a Consent Decree thatrequires an aggressive schedule for TMDL development. The source allocation wascomplicated by the fact that there are 11 Municipal Separate Storm Sewer Systems(MS4s) within the watershed, over 100 National Pollutant Discharge EliminationSystem (NPDES) facilities, and over 80 percent of the watershed is used for raisingcrops and a large population of livestock.This paper will present a framework that was developed to perform the allocationanalysis and estimate the impact reductions to loads from these stressors had on instreamconcentrations throughout the watershed. The framework uses the BacterialIndicator Tool (BIT), Hydrologic Simulation Program-Fortran (HSPF), the Load DurationCurve (LDC) model, and MATLAB to analyze the data and perform postprocessing onmodel results. The framework ensures that water-quality impacts from sourcereductions upstream to downstream adequately account for the impacts of pollutantfate and transport mechanisms. This ensures the TMDLs and implementation planswithin the watershed are linked.