The results of this investigation of the Columbia aquifer in coastal Sussex County, Delaware, provide some of the data necessary to evaluate the condition of the area's primary source of fresh water. Chemical analyses of water samples from domestic, agricultural, public, and monitoring wells document the effects of past and present land use practices. Groundwater flow paths and flow systems are inferred from flow-net analysis, ground-water chemistry, and isotopic composition.
Borehole Oh25-02, located about 3 miles southwest of Lewes, Delaware, ends at a total depth of 1,337 ft in a mid-Oligocene glauconitic silt unit. It penetrated 317 ft of glauconitic sands and silts between the base of the Calvert Formation at a depth of 1,020 ft and total depth. A hiatus at 1,218 ft separates an outer neritic lower Miocene interval (Globorotalia kugleri Zone) above it from a deep upper bathyal mid-Oligocene (G. opima opima Zone) section below; the lower section is characterized by abundant large uvigerinid benthic foraminiferal species representing the transition from Uvigerina tumeyensis to Tiptonina nodifera. Similar uvigerinid assemblages identify the mid-Oligocene unit in boreholes near Bridgeville and Milford, Delaware; Cape May, New Jersey; and Ocean City, Maryland. Updip from these boreholes, the Calvert Formation, of latest Oligocene-middle Miocene age in Delaware, unconformably overlies middle Eocene glauconitic sands of the Piney Point Formation. The juxtaposition of the downdip mid-Oligocene rocks against the updip middle Eocene rocks can best be explained by a fault between the two regions.
Subsurface temperatures were measured in instrumented boreholes for about one and one-half years at depths down to 10 feet below land surface at four locations in the State. In New Castle County, temperatures were measured periodically in the field about twice a month at three sites, and, in Sussex County, they were automatically recorded every 15 minutes at one site. The depths of interest are generally in the unsaturated zone and are subject to both daily temperature fluctuations and longer seasonal changes.
RI45 Effects of Agricultural Practices and Septic-System Effluent on the Quality of Water in the Unconfined Aquifer in Parts of Eastern Sussex County, Delaware
The unconfined aquifer is a major source of water supply in eastern Sussex County, Delaware. It also is an important source of water for surface-water bodies and deeper, confined aquifers. The aquifer consists mainly of permeable sand and gravel; its shallow water table is susceptible to contamination by nitrate and other chemical constituents associated with agricultural practices and effluent from septic systems.
Water-level records from 19 observation wells in Delaware for the period January 1978 - December 1987 provide the bases for analyses of water-level fluctuations. Water levels in shallow water-table wells generally rise from November to March when recharge exceeds discharge and decline during the warm growing season from May through September. Although water levels in individual water-table wells fluctuated by as much as 11.72 feet during the 10-year period studied, the water-table system remained in a state of dynamic equilibrium and exhibited no significant changes in aquifer storage.
Onshore and offshore geological and geophysical data were used to investigate the lithostratigraphy, seismic stratigraphy, and depositional history of the late Tertiary age post-Choptank Chesapeake Group rocks in Sussex County, Delaware and adjacent counties in Maryland. The results of this investigation suggest that the St. Marys (?) Formation and the sandy interval of which the Manokin aquifer is a part, are distinct lithostratigraphic units. The Manokin formation is proposed as an informal lithostratigraphic unit that refers to the sandy interval of which the Manokin aquifer is a part. On a regional scale, the section containing the Ocean City and Pocomoke aquifers and adjacent and intervening confining beds is best treated as a single undifferentiated lithostratigraphic unit. The Bethany formation is proposed as an informal lithostratigraphic unit that refers to this section.
A multiple linear regression method was used to estimate water-table elevations under dry, normal, and wet conditions for the Coastal Plain of Delaware. The variables used in the regression are elevation of an initial water table and depth to the initial water table from land surface. The initial water table is computed from a local polynomial regression of elevations of surface-water features. Correlation coefficients from the multiple linear regression estimation account for more than 90 percent of the variability observed in ground-water level data. The estimated water table is presented in raster format as GIS-ready grids with 30-m horizontal (~98 ft) and 0.305-m (1 ft) vertical resolutions. Water-table elevation and depth are key facets in many engineering, hydrogeologic, and environmental management and regulatory decisions. Depth to water is an important factor in risk assessments, site assessments, evaluation of permit compliance data, registration of pesticides, and determining acceptable pesticide application rates. Water-table elevations are used to compute ground-water flow directions and, along with information about aquifer properties (e.g., hydraulic conductivity and porosity), are used to compute ground-water flow velocities. Therefore, obtaining an accurate representation of the water table is also crucial to the success of many hydrologic modeling efforts. Water-table elevations can also be estimated from simple linear regression on elevations of either land surface or initial water table. The goodness-of-fits of elevations estimated from these surfaces are similar to that of multiple linear regression. Visual analysis of the distributions of the differences between observed and estimated water elevations (residuals) shows that the multiple linear regression-derived surfaces better fit observations than do surfaces estimated by simple linear regression.
In view of the possible need for disposal of low-level radioactive waste in Delaware under the Nuclear Waste Policy Act of 1982, the Delaware Geological Survey has prepared this report to assist the citizens of our State in understanding this complex subject. Emphasis here is on geologic and hydrologic aspects of disposal. Health, social, and economic factors are outside the scope of this report and are not discussed. However, they are very important integral parts of the safe disposal of low-level radioactive waste, and must be considered when selecting suitable disposal sites.
To conduct an elevation survey, a surveyor needs a starting point for which the exact elevation above mean sea level is known. These starting points are called benchmarks. State and federal agencies install benchmarks throughout every State, creating a network of elevation points which covers the entire continental United States. These benchmarks are considered to be permanent, and usually consist of a brass, bronze, or aluminum disc about 4 inches in diameter mounted in a cement post or in a drill hole in a permanent foundation. Each benchmark also has the installing agency's name and an identification number stamped into it. In December of 1980 the Federal Emergency Management Agency (FEMA) allotted the State of Delaware funds to determine the number and condition of federal benchmarks and other elevation reference control points. The National Flood Insurance Program (NFIP), contained within FEMA, requires accurate flood surveys of property in flood-prone areas. An extensive and accurate benchmark network throughout the State is needed to help meet these needs.
In the United States more than 3.5 billion tons of solid waste are generated annually. Of this, more than 2 billion tons are agricultural waste, such as manure and crop waste. Almost 300 million tons are generated by commercial and industrial activities and municipalities, and another 1.1 billion tons are attributed to various mining operations (Vaughan, 1969). Increasing amounts of solid waste have had detrimental effects on environmental quality. It has become necessary to reprocess and reuse some, and to provide safe and environmentally acceptable ways of disposing of the remaining waste in properly constructed landfills. Pollution brought about by improperly constructed landfills may be very severe. For example, the contaminants generated by the waste at the old, abandoned Army Creek Landfill, New Castle County, Delaware, were so widespread that the situation received national attention. General and sincere concern expressed by many citizens of our State has prompted the Delaware Geological Survey to prepare this report. The report explains the functioning of a landfill, problems improperly constructed landfills may cause, and the geologic and hydrologic aspects that have to be considered in selecting a suitable disposal site for solid waste. The report does not contain discussions of other important factors, such as social impact, transportation, and specific health hazards, that must also be considered.
This report was prepared to provide a simple but comprehensive overview of programs and concepts of highly radioactive waste disposal. This report is not based on original research, but was prepared from data and information reported in voluminous publications of the U.S. Department of Energy, the Nuclear Regulatory Commission, the U.S. Environmental Protection Agency, and the U.S. Geological Survey.
The purpose of this report is to provide information on the mining industry of Delaware as an essential component of a growing economy. The industry, particularly in sand and gravel mining, must deal with uneven regulation, land use competition, and environmental pressures. It is hoped that the information gathered here will assist planning and regulatory agencies as well as an interested general public in evaluating the role of the extractive mineral industry.