|Hydrogeology & Hydrology Program|
Wicomico River and
Rockawalking Creek basins
David Andreasen (firstname.lastname@example.org)
T. Brandon Fewster (email@example.com)
Contributing areas of existing and hypothetical public-supply wells screened in the unconfined Salisbury aquifer in the Upper Wicomico River Basin and the Metro Core Area west of that basin (Rockawalking Creek study area) were determined using two separate finite-difference, ground-water-flow models (MODFLOW) and a particle-tracking routine (MODPATH). The contributing area of a pumping well is the area supplying recharge to the well from precipitation. The Salisbury aquifer, which is a shallow, water-table aquifer with relatively high transmissivity, is vulnerable to contamination. The mapped contributing areas can be used in the development of a well-head protection plan to protect supply wells from contamination. The wells selected for analysis include City of Salisbury Park wells 17 and 18, other public-supply wells serving 25 people or more such as mobile-home parks and some commercial wells, and hypothetical production wells. Contributing areas of all other public-supply wells operated by the City of Salisbury were determined in an earlier study. The key results of the study include:
UPPER WICOMICO RIVER BASIN
The 50-year contributing area of City of Salisbury Park wells 17 and 18, pumping at a simulated rate of 0.36 million gallons per day, form an elongated pattern that extends approximately 4 miles from the wells in an east-northeast direction. Minimum travel time was 242 and 425 days for wells 17 and 18, respectively.
The 50-year contributing area of 14 public-supply wells or well fields range in length from 0.25 to 3.2 miles and width from 0.1 to 0.5 miles and are either contiguous with the wells or occur at distances up to 1.8 miles from the wells.
The 50-year contributing area of three hypothetical wells pumped simultaneously at 2 million gallons per day and located in the paleochannel range in length from 1.3 to 4 miles and width from 0.3 to 1 miles. The 50-year contributing area of a hypothetical well pumped at 0.36 million gallons per day and located in the Park well field was 3.5 miles long and less than 0.2 miles wide.
ROCKAWALKING CREEK STUDY AREA
Currently there are no public-supply wells pumping from the Salisbury aquifer in the Rockawalking Creek study area. The 50-year contributing area of three hypothetical wells pumped independently at 0.25 million gallons per day range in length from 0.7 to 1.6 miles and width from 0.5 to 0.65 miles. Minimum particle travel time ranged from 62 to 95 days. When the pumping rate is increased two-fold (0.5 million gallons per day) the 50-year contributing area expands down-gradient (southward) an additional 0.28 miles.
Water for potable use in the Salisbury aquifer is currently limited to domestic supply from individual wells. The 20-year contributing area for clustered domestic wells within subdivisions are generally localized, occurring within 500 to 2,500 feet from withdrawal sites determined by particles backtracked from the mid-point of the aquifer. The average particle travel time was 6.8 years.