Evaluation of Onsite Wastewater System Performance and Nutrient Trading Policy in Support of Falls Lake Nutrient Strategy Development

The Falls Lake Rules consist of a staged and adaptive implementation plan with several regulatory compliance dates. Rule 15A NCAC 02B.0278 (Stormwater Management for Existing Development) requires that stakeholders reduce or offset nutrient contributions from existing development. Stakeholders must start implementing and tracking Stage 1 load reductions from existing development by January 15, 2014 and Stage 2 load reductions by January 15, 2021. The Rule also includes a framework for offsetting nutrient credits. Rule 15A NCAC 02B .0282 outlines the requirements for entities who wish to buy credit for nutrient load-reducing activities (credit buyers) from other entities who are implementing nutrient load reduction activities (credit sellers). The Rule specifies that parties who achieve excess nutrient load reductions under the Falls Nutrient Strategy may recover costs by selling credits and provides opportunity for third parties to produce reductions and sell credits.There is much controversy and disagreement over the fate and effect of nutrients from onsite wastewater treatment systems (OWTS) to surface waters. OWTS have been designated as a nonpoint source contributor to the lake from existing development. The Phase 1 and 2 goals are significant, so the reduction of OWTS in the watershed may provide an opportunity to meet the goals. This paper summarizes the highlights and conclusions of a study commissioned by the City of Raleigh to evaluate the OWTS issue with respect to the Falls Lake Rules. The review included a summary of effluent quality from various OWTS, a discussion on nutrient attenuation in soil, and a discussion of nutrients and groundwater movement to receiving streams. Other objectives included an analysis of various water quality trading policies in other states specific to nitrogen and/or phosphorus.