RI79 Simulation of Groundwater Flow and Contaminant Transport in Eastern Sussex County, Delaware With Emphasis on Impacts of Spray Irrigation of Treated Wastewater
This report presents a conceptual model of groundwater flow and the effects of nitrate (NO3-) loading and transport on shallow groundwater quality in a portion of the Indian River watershed, eastern Sussex County, Delaware. Three-dimensional, numerical simulations of groundwater flow, particle tracking, and contaminant transport were constructed and tested against data collected in previous hydrogeological and water-quality studies.
The simulations show a bimodal distribution of groundwater residence time in the study area, with the largest grouping at less than 10 years, the second largest grouping at more than 100 years, and a median of approximately 29 years.
Historically, the principal source of nitrate to the shallow groundwater in the study area has been from the chemical- and manure-based fertilizers used in agriculture. A total mass of NO3- -nitrogen (N) of about 169 kg/day is currently simulated to discharge to surface water. As the result of improved N-management practices, after 45 years a 20 percent decrease in the mass of NO3- -N reaching the water table would result in an approximately 4 percent decrease in the mass of simulated N discharge to streams. The disproportionally smaller decrease in N discharge reflects the large mass of N in the aquifer coupled with long groundwater residence times.
Currently, there are two large wastewater spray irrigation facilities located in the study domain: the Mountaire Wastewater Treatment Facility and Inland Bays Wastewater Facility. The effects of wastewater application through spray irrigation were simulated with a two-step process. First, under different operations and soil conditions, evaporation and water flux, NO3- -N uptake by plants, and NO3- -N leaching were simulated using an unsaturated flow model, Hydrus-1D. Next, the range of simulated NO3- -N loads were input into the flow and transport model to study the impacts on groundwater elevation and NO3- -N conditions.
Over the long term, the spray irrigation of wastewater may increase water-table elevations up to 2.5m and impact large volumes of groundwater with NO3-. Reducing the concentration of NO3- in effluent and increasing the irrigation rate may reduce the volumes of water impacted by high concentrations of NO3-, but may facilitate the lateral and vertical migration of NO3-. Simulations indicate that NO3- will eventually impact deeper aquifers. An optimal practice of wastewater irrigation can be achieved by adjusting irrigation rate and effluent concentration. Further work is needed to determine these optimum application rates and concentrations.
The Determination of Total Nutrient Loads from the Nanticoke Watershed above the USGS Nanticoke at Bridgeville Gauging Site (USGS 01487000) from Data Provided by an Automated Nutrient Analyzer (Greenspan, Aqualab)
The US Geological Survey in cooperation with the Delaware Geological Survey through a State-Federal partnership program operates and maintains stream and tide gages throughout Delaware. The streamgage network is a component of the National Streamflow Information Program (NSIP), a program that provides real-time and long-term current and historical streamflow information that is not only accurate and unbiased, but also meets the needs of many users.
USGS 01484525 MILLSBORO POND OUTLET AT MILLSBORO, DE
USGS 01484100 BEAVERDAM BRANCH AT HOUSTON, DE
USGS 01483200 BLACKBIRD CREEK AT BLACKBIRD, DE
The DGS is, by statute, the state agency responsible for entering into agreements with its counterpart federal agencies, including the U.S. Geological Survey, the USGS Office of Minerals Information (formerly the U.S. Bureau of Mines), and the Bureau of Ocean Energy Management, Regulation and Enforcement (formerly the U. S. Minerals Management Service), and for administering all cooperative programs of the State with these agencies. The DGS also works with many in-state and out-of-state partner agencies and organizations.
USGS 01477800 SHELLPOT CREEK AT WILMINGTON, DE
USGS 01488500 MARSHYHOPE CREEK NEAR ADAMSVILLE, DE
Water Conditions Index for Northern New Castle County
Water Conditions Summary Streamflow Graphs