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.

The purpose of this study was to map the thickness and the configuration of the base of the unconfined aquifer in southeastern Sussex County, Delaware (figure 1). The unconfined aquifer provides much of the water used in this part of the State and is the first unit to be affected by pollution or waste disposal problems. Contour maps and geologic sections were prepared from available geologic, geophysical, and drillers' logs and previously published reports and maps. Six test holes (figure 1) were drilled to supplement available data.

Numerical indicators, or indices, are widely used to measure the status of complex relationships. As such, indices have become accepted by researchers and the public in such disparate fields as economics, air quality, and weather. In this paper we explore the formulation of an indicator of water conditions in northern Delaware, propose formulas that may be applicable, and test those proposals against long-term records of basic data. The need for a simple indicator of water supply conditions in Delaware, and especially in New Castle County, has become increasingly apparent.

Examination of continuous water-level hydrographs from two artesian observation wells in the Piedmont near Newark, Delaware reveals water-level fluctuations caused by earthquakes and by earth tides. The effects of 14 distant earthquakes with MS (surface wave) magnitudes between 6.7 and 8.0 and MB (body wave) magnitudes between 5.9 and 7.0 (National Earthquake Information Service, 1975-1977) have been recorded over a two-year and ten-month period.

In the period between January 27 and February 6, 1998, the Mid-Atlantic region experienced two significant northeasters that affected the coast of Delaware and Maryland. These storms produced heavy rains and high winds, waves, and tides that created dune washovers, flooding, wind damage, and beach erosion and migration. Coastal communities were impacted by flooding that closed roads, by beach erosion that affected structures, streets and boardwalks, and by high winds that damaged structures and trees.

On January 4, 1992 an intense storm moved from the east across the Delmarva Peninsula and the Chesapeake Bay. Its track was the result of the low pressure being pulled westward by a strong cold-cored upper low moving across Georgia and South Carolina. The storm exhibited tropical/subtropical characteristics on radar. Satellite photos indicate that an "eye" to the storm formed just prior to landfall. Landfall occurred over the southern Delmarva Peninsula just prior to the time of high tide (0648 at Ocean City, Md).

Heavy precipitation associated with intense thunderstorm activity occurred in northern New Castle County, Delaware, from 0500 to 1300 hours on July 5, 1989. The most intense rainfall, which fell between 0600 and 1100 hours, is classified as a 100 year event in New Castle County. Record high stream discharges occurred at five gaged sites and three miscellaneous sites. One hundred-year floods were recorded at four sites.

A quasi three-dimensional model was constructed to simulate the response of the Piney Point and Cheswold aquifers underlying Kent County, Delaware to ground-water withdrawals. The model included the Magothy, Piney Point, Cheswold, and unconfined aquifers, and was calibrated using historical pumpage and water-level data. Model calibration was accomplished through the use of both steady-state and transient-state simulations.

Southern New Castle County has a land area of 190 square miles in north-central Delaware. It is predominantly a rural area with a population of about 9,000 people who are engaged chiefly in agriculture. By and large, the residents are dependent upon ground water as a source of potable water. This investigation was made to provide knowledge of the availability and quality of the ground-water supply to aid future development. The climate, surface features, and geology of the area are favorable for the occurrence of ground water.