Evaluation of Nutrient Trading Policy to Support Nutrient Strategy Development in Falls Lake


  • Mary E. Sadler, Damann Anderson, Joe Sowinski - Hazen and Sawyer

The City of Raleigh commissioned Hazen and Sawyer to investigate the potential impacts of onsite sewer disposal systems (OSDS) in the nutrient-impaired Falls Lake Watershed. The study objectives were to provide a literature review perspective on the OSDS issue, an evaluation of approaches to assess nutrient load contribution, and an analysis of various water quality trading and credit policies in other states specific to nitrogen and/or phosphorus. The overall objective of the analysis was to provide a balanced perspective on the OSDS issue coupled with an analysis of nutrient point to nonpoint source trading strategies to help facilitate the development of a trading policy framework for the Falls Lake watershed. This paper will summarize the findings of this study with respect to nutrient trading policy.

There are multiple factors that influence OSDS nutrient contribution to water quality impairment. It was clear that the cause and effect link to eutrophication impairment is not straightforward. While there is agreement that onsite systems contribute to nutrient enrichment, there is disagreement regarding the extent and magnitude of impairment from these systems coupled with the long-term effects of small continuous nutrient inputs to the environment. Studies provide conflicting evidence regarding effluent quality from onsite systems or the fate and effect of nutrients via soil attenuation relative to groundwater movement. This issue is reflected in estimates of the percentage of nitrogen contribution in receiving waters as ammonia or nitrate. Other factors may include the atmospheric deposition relative to OSDS.

The water quality trading strategies that were selected for review included an overall framework for point to nonpoint source trading or had specific guidelines for trading between point sources and septic systems. Fact Sheets were developed for the Chesapeake Bay, Connecticut, Idaho, Maryland, Massachusetts, Minnesota, Ohio, Pennsylvania, Virginia, and Wisconsin trading programs. Each Fact Sheet included a detailed description of the trading program, the type of nutrient credit and credit price, who can buy or sell credits, the availability of septic system credits, specific trading examples, and relevance to the Falls Lake Nutrient Strategy.

For more information, please contact the author at msadler@hazenandsawyer.com.

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