Phase 2 study of the area contributing groundwater to the spring supplying the A.M. Powell State Fish Hatchery, Washington County, Maryland
2009, Duigon, M.T.
Open-File Report 08-02-18
Geologic inference and dye tracing of groundwater flow were used to investigate the boundary of the area contributing groundwater to the flow of the spring supplying the Albert M. Powell State Fish Hatchery in Washington County, Maryland. The contributing area extends about 5 miles northeast from the hatchery spring, broadening to the west from about 1 mile in width at the southwestern end to about 2.5 miles at the northeastern end, and has an area of approximately 8.2 square miles. It is bounded on the east by the Beaver Creek Fault, an old, mylonitized thrust fault presumed to be a barrier to groundwater flow. The Eakles Mills Fault on the west is a younger, high-angle fault along which the rock reacted in a brittle fashion, thereby likely becoming a linear zone of enhanced permeability. The Eakles Mills Fault may act as a linear sink draining toward the southwest, intercepting any groundwater flow coming from the west. During periods of high groundwater levels, some of the water draining along the Eakles Mills Fault may be diverted by a cross fault located on the hatchery property to Beaver Creek and, during periods of highest groundwater levels, to the hatchery spring.
Dye injected into Beaver Creek approximately 1.2 miles north-northeast of the hatchery spring was detected at the spring about one day after injection, confirming the hypothesis that a portion of springflow consists of water that has leaked through the streambed of Beaver Creek (at least under similar flow conditions when the stream is losing water along this reach). Dye injected into a sinkhole located about 2.8 miles north-northeast of the spring took about two and a half days to arrive. Dyes injected into a well located about 400 feet northwest of the spring and into a sinkhole located about 2.9 miles north of the spring were not detected at the spring. The latter sinkhole was located to the west of the Eakles Mills Fault.
Physical properties and major-ion concentrations measured in the hatchery spring water were typical of groundwater from the Elbrook Formation in Washington County—very hard with total-dissolved solids concentration just over 300 milligrams per liter. Nitrate concentration in two samples taken from the spring were 5.36 and 6.08 milligrams per liter (as N), suggesting there may be some nutrient input from the basin (which is in largely agricultural and residential use). Fifteen of 28 trace elements for which the samples were analyzed were detected. All of the pesticides and wastewater compounds for which the samples collected in 2008 were analyzed were below detection limits except for CIAT (also known as deethylatrazine, a degradation product of the herbicide atrazine) and tetrachloroethylene (a solvent, degreaser, and dewormer), and those concentrations were close to detection limits.