Pennsylvania

Mahantango Creek studies.   For a number of years BRASS has been working in the East Mahantango Creek Watershed, Pennsylvania Valley and Ridge, in cooperation with the USGS Water Resources Discipline, the USDA Agricultural Research Service (ARS), and the USGS Chesapeake Bay Program, to understand the influence of fracture orientation on ground water flow and the rate of dissemination of dissolved nitrogen into the Bay.  This watershed is developed on an anticline of sandstone and siltstone that has a very regular fracture pattern. Most of the PA work has taken place in the WE-38 subwatershed, at the south end of which are located two piezometer transects.  Age-dating of environmental tracers by Niel Plummer and Eurybiades Busenberg of the USGS Reston CFC lab has determined a distinctive age pattern for ground water, suggesting that ground-water flow pathways are controlled by the bedrock fracture pattern.  Dissolved nitrate concentrations measured by Bruce Lindsey of the USGS PA District in the same transect shows a pattern parallel to the age pattern.  This has significant consequences for modeling nitrate flux into the Chesapeake Bay watershed over time.  Results are published in a paper in Ground Water and a USGS Water Resources Investigation Report.

In order to understand further the controlling effects of bedrock fractures on ground-water flow, ARS and BRASS have developed a research well array at the western edge of the WE-38 subwatershed.  This well array will be used for geophysical experiments and single-hole and cross-hole pump tests that investigate the effect of anisotropic fracture patterns on ground water flow.

Publications:

Burton, W.C., Plummer, L.N., Busenberg, E., Lindsey, B.D., Gburek, W.J., 2002, Influence of fracture anisotropy on ground water ages and chemistry, Valley and Ridge province, Pennsylvania, Fractured-Rock Aquifers 2002 conference, March 13-15, 2002, Proceedings: Denver, CO, National Ground Water Association, p. 200-204.

Burton, W.C., Plummer, L.N., Busenberg, E., Lindsey, B.D., Gburek, W.J., 2002, Influence of fracture anisotropy on ground water ages and chemistry, Valley and Ridge province, Pennsylvania, Ground Water, v. 40, no. 3, p. 242-257.
 
Related links:
USDA Agricultural Research Service
USGS Pennsylvania District
USGS Reston CFC Lab
USGS Chesapeake Bay Program