Agenda - 12-05-2011 - Information Item 3

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2 nutrients to surface waters. All of these sources can contribute to the total quantity of nutrients carried by surface waters, which is often termed the nutrient "load". In 2004, the state Ecosystem Enhancement Program of NC DENR published the Morgan Creek Local Watershed Plan: Detailed Assessment Report. This publication included estimates of nutrient loading to both University Lake and Jordan Lake from the surrounding watersheds. Nitrogen delivered to Jordan Lake ranged from a low of 1.64- 2.44 pounds/acre/year in the more rural areas of the watershed to 6.31-6.84 pounds/ acre/year in the more developed areas (Chapel Hill and Carrboro). Please note that nutrient loads delivered to Jordan Lake are likely to be slightly lower than the loads exiting the County due to naturally occurring processes including sorption and decay. Estimating Nutrient Loading The simplest method of estimating nutrient loading involves the use of a basic areal loading rate spreadsheet tool. GIS could be used to determine the total area of the county in each of several different categories of land uses, such as medium density residential, etc. Nutrient export rates, such as those included above, could then be assigned to the various land uses and used as input in a spreadsheet, producing nutrient export estimations for each land use type. The estimated values could be summed by watershed, river basin or jurisdiction. This method would be somewhat limited, however, since it does not include naturally occurring processes such as nutrient decay or sorption, for example. • PLOAD (Pollutant Load) is a slightly more involved screening-level GIS-based model, such as that described above, that could be used to determine loading in watersheds.. It is likely that a consultant could use this model to estimate nutrient loading for Orange County for less than $10,000. • Amore complex distributed area model could also be used to estimate County- wide nutrient loading. Such a model would utilize available water quality sampling data as well as stream gage flow information as input. A consultant could use SWAT (Soil and Water Assessment Tool) or a similar model to estimate nutrient loading for Orange County for a fee of approximately $30,000. Another alternative for examining the nutrient load exiting Orange County involves recent activities undertaken by the Upper Neuse River Basin Association (UNRBA). The Falls Lake Nutrient Management Rules (Falls Rules), which became effective in January 2011, include an opportunity for additional information to be provided to the Environmental Management Commission (EMC) by 2024. The UNRBA is currently finalizing the selection of a consultant to begin working on issues that are geared toward modifying Stage II of the Falls Rules. The consultant will be required to compile and review existing water quality data collected in Falls Lake and the surrounding watershed. In addition, the consultant will compare nutrient loading estimates for tributaries and Orange County Department of Environment, Agriculture, Parks & Recreation PO Box 8181, Hillsborough, NC 27278 Phone: (919) 245-2510 Fax: (919) 644-3351