Agenda 11-02-23; 4-a - Resolution Endorsing Consensus Principles II for Revised Falls Lake Rules

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=33 New development is already managed by every jurisdiction in the watershed under the current Falls Lake New Development Rule. An example of installation of SCMs in an urban environment is in the City of Durham where the City installed over 350 nutrient and flow reduction measures by the end of 2015 on developed sites to improve water quality(Figure 7). Other local governments in the watershed have also installed retrofits to treat existing development. These projects were accounted for during calibration of the watershed model and were used for support of the IAIA concept. Installation of these projects illustrates the commitment of the jurisdictions in this watershed to mitigate water quality impacts of existing land use in the watershed. More focused research on the question of applying retrofits was done through NC State University (Hunt et al. (2012), funded by the North Carolina Urban Water Consortium Stormwater Group, through the Water Resources Research Institute of The University of North Carolina). This study assessed opportunities and costs for the installation of SCM retrofits in several developed watersheds including Ellerbe Creek in the City of Durham. The findings indicated that if every potential existing development retrofit identified in the Ellerbe Creek watershed were implemented (at a cost of$16 million capital and $7 million annual maintenance costs), it would only reduce nitrogen loads by approximately 10 percent and total phosphorus loads by 25 percent. These reductions are much lower than the Stage II reduction requirements prescribed in the Falls Lake Rules (40 percent for total nitrogen and 77 percent for total phosphorus). Development in the watershed occurring after 2011 is subject to the new development rules in the Falls Lake Nutrient Management Strategy. These rules have been implemented by the local governments and require installation of stormwater control measures to limit the amount of nutrients leaving the development to 2.2 pounds per acre of total nitrogen 0.33 pounds per acre of total phosphorus; 50 percent of these reductions must occur on site and 50 percent can be obtained through offsite credits acquired from the State. These amounts were set so that as lands in the watershed were developed,the load delivered to Falls Lake would not increase. The City of Durham began implementing new development requirements before the rules were passed and the loading targets were established. These interim development controls were adopted to reduce the amount of development requiring retrofits once the rules were passed. State law no longer allows for this type of proactive approach. Soil Properties, Hydrologic, and Nutrient Application Data Soils data and precipitation data are key drivers of hydrologic response and determine actual loading to streams from nutrients "applied" or deposited in the watershed. These inputs not only determine stream flows and nutrient loads delivered to Falls Lake but also the ability of nutrients to be stored and cycled in the system. Soil hydrologic and chemistry data were obtained from the US Department of Agriculture Natural Resources Conservation Service and the US Geologic Survey. Radar precipitation data for 78 locations in the watershed were provided by the NC State Climate Office (with support from NC Department of Transportation). Human inputs of nutrients to the land surface are also an important part of the nutrient balance. The model accounts for monthly nutrient application to land surfaces on urban and agricultural lands. Atmospheric deposition of nitrogen and phosphorus is also applied to water surfaces and all land within the watershed, including unmanaged lands. The passage of the Falls Lake Nutrient Management Strategy resulted in the formation of the Watershed Oversight Committee (WOC)for the Falls Lake Basin. Under the Rules, the WOC is charged with compiling, analyzing, and reporting data related to agricultural production, nutrient reductions, and compliance with the Falls Lake Nutrient Management Strategy. The WOC includes staff from the NCDA&CS Division of Soil and Water Conservation (DSWC),the USDA Natural 14