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The Rock River watershed has approximately 130-permitted point discharge sources. In 1996 these dischargers received notification of newly proposed phosphorus limits of one mg/L. To comply with this permit limit would have been a financial burden to each municipality and would still have left questions of the true impact on water quality improvements.
The Wisconsin Department of Natural Resources ruled that the entire river system and its 3,750-square-mile watershed had to be studied before granting relief from the proposed effluent criteria. In 1996, the Rock River Watershed Partnership was formed with the leadership and support of Earth Tech. This partnership grew into a truly representative stakeholder group of private citizens, treatment plant dischargers, agricultural and recreational interests and communities contributing to runoff.
Goals of the partnership included identifying and prioritizing nutrient concerns, identifying water quality objectives and desires, completing an inventory of existing pollutant sources, identifying strategies for achieving objectives and establishing a least-cost mix of control alternatives.
Earth Tech’s activities included the development of a phosphorus control strategy to reduce the negative impact on the Rock River. The large watershed, with diverse land use, soils, topography and water resources presented a challenge for the study. To meet this challenge, Earth Tech modified the SWAT (soil and water assessment tool) model to calculate annual phosphorus loads in 116 sub-basins.
Management alternatives included the potential for the phosphorus reduction goals to be met through “trades" with rural and/or nonpoint sources of pollution. Studying trades shed new light on previously unresearched possibilities. The study revealed how complex trading scenarios can be, the importance of trade ratios, the need to allow sufficient time to consummate a trade and to be flexible and the complexity of regulatory issues.
This study set the course for future phosphorus limits, with an estimated reduction with point/nonpoint source management and the viability of pollutant trading. This innovative approach, along with Earth Tech’s trailblazing techniques to further advance the utilization and implementation of SWAT, may be applied to other watersheds.
