Orange County NC Website
Browse       Search
=12 <br /> worked closely with researchers,third-party model reviewers, and DWR modeling staff to review and <br /> vet the watershed and lake models. Key findings from the UNRBA monitoring and modeling efforts <br /> are listed here and further described in the sections below as well as the UNRBA modeling reports: <br /> • Efforts to reduce loading from the watershed since the baseline year of the Rules and DWR <br /> modeling(2006) have significantly reduced nutrient loading to Falls Lake. <br /> — Major wastewater treatment plants have reduced total nitrogen loads by 57 percent and <br /> total phosphorus loads by 73 percent(based on four-year average of loads discharged from <br /> 2015 to 2018). <br /> — Over 350 stormwater control measures and best management practices have been <br /> implemented to mitigate loading from existing development. <br /> — Requirements to limit nutrient export from development occurring since 2012 (i.e., new <br /> development) have been implemented by every local government in the watershed. <br /> — Atmospheric deposition of total nitrogen has decreased by approximately 20 percent since <br /> baseline. <br /> — Best management practices implemented on agriculture including nutrient management <br /> plans, livestock exclusion, and stream buffer restoration have reduced loading from this <br /> source. The acreage of agriculture has declined 44 percent since baseline due to economic <br /> and other pressures. <br /> • 75 percent of the watershed is unmanaged, and opportunities for further nutrient reductions are <br /> limited. <br /> • Precipitation is the key driver of increases in nutrient loading to the lake and an important driver <br /> of increase/decrease in lake residence time which is a controlling factor for algal growth. <br /> • The watershed soils and lake sediments adsorb nutrients that can be released slowly over <br /> decades, extending the time that changes in the watershed will result in water quality changes in <br /> the lake. <br /> • Reductions to the nutrients applied or deposited in the watershed do not have an equivalent <br /> reduction in delivered loading to Falls Lake. Only 20 percent of the loads applied to the <br /> watershed reach the lake, so reducing a pound applied or released will only result in <br /> approximately 0.2 pounds reduction to the lake. <br /> • Levels of algae indicated by chlorophyll-a are not well correlated to nutrient loading. The <br /> hydrology, morphology, retention time, depth, and characteristics of the different areas of the <br /> lake are just as important as nutrient loading. <br /> • Nutrient concentrations in Falls Lake are relatively low. Chlorophyll-a can reach high <br /> concentrations even when nutrient concentrations remain low. <br /> • Falls Lake is meeting its designated uses: <br /> — Algal toxin levels are below U.S. Environmental Protection Agency(EPA) guidelines for <br /> drinking water and recreation (DWR 2021).Nutrient-related fish kills have not occurred in <br /> nearly 40 years since the lake was filled (NCDEQ annual fish kill reports). <br /> — Recreation is not limited by water quality(USACE 2013). <br /> — The City of Raleigh provides safe drinking water to over 500,000 customers and indicates <br /> that Falls Lake is an excellent source of raw water (DWR 2021) <br /> — In 2023, the American Water Works Association ranked the City of Raleigh 3rd in its <br /> international ""Best of the Best" Water Taste Test" <br /> iii <br />