Quantifying Urban Stormwater Pollutant Loads and Management Costs Within the Lower Fox River Basin

Within the Lower Fox River Basin there are approximately 26 municipalities (Cities, Villages, Towns, and Counties) regulated under the State of Wisconsin's stormwater pollution control permit system. The requirements of the program are spelled out in a Wisconsin Pollutant Discharge Elimination System (WPDES) general permit issued under the authority of, and to meet the requirements of ch. 283 Wis. Stats., and chs NR 151 and 216 Wisconsin Administrative Code. In general, the permit lays out the procedures and steps to meet the “six minimum requirements” commonly found in stormwater regulations promulgated to meet the USEPA municipal stormwater management program. Unique to Wisconsin is an additional requirement for all permittees to “the maximum extent practicable”, reduce annual loadings of Total Suspended Solids (TSS) by 20% in 2008 and by 40% in 2013. The focus of this presentation is to describe how two municipalities in the Lower Fox River Basin have conducted the necessary evaluations to determine: 1) the current status of their TSS loadings, 2) the necessary additional management measures to meet the TSS reduction requirements of 2008 and 2013, 3) the estimated capital and non-capital costs to meet those requirements, and 4) how the results will be incorporated into the Lower Fox TMDL.The two largest municipalities in the Lower Fox River Basin are the Cities of Green Bay and Appleton (2000 populations of 102,213 and 70,087, respectively). In the fall of 2006, each community was officially notified of stormwater permit activation. Each community conducted a city-wide pollutant loading analysis using a Windows™ version of a computer simulation model: Source Loading and Management Model™ (WinSLAMM). The model incorporates physical and climate factors to calculate annual pollutant loads in urban stormwater. To meet state regulations the model is run under two scenarios:The regulated urban area as it existed under a “no management” condition as of October 1, 2004. This value sets the baseline TSS annual loading condition for the permittee. This baseline load must be reduced by 20% and 40% by the target dates.The regulated urban area under baseline conditions, incorporating the existing management stormwater pollution measures. The results of this scenario establish the current stormwater TSS control value for the city, and determines if state regulations are being met, or if additional management measures are required.The results of the above analyses for both cities showed that additional management is needed to meet the TSS reduction requirements. At this point a planning level feasibility / optimization analysis is conducted to determine the types, locations, and costs of structural and non-structural measures necessary to meet the permit TSS control requirements. For both cities, substantial capital costs (15 – 25 million) will be required to meet the TSS control requirements.This presentation will detail the processes and results of the WinSLAMM analysis, and the feasibility / optimization analysis for each city. Additionally, the modeling calculated stormwater phosphorus loadings and these values will be incorporated in the Lower Fox River TMDL program.