Wednesday, December 5, 2007 : 10:40 a.m.

Ground-Water Piracy in a Central Pennsylvania Watershed

Todd Giddings, Todd Giddings and Associates Inc.

Stream piracy is when one stream, through headward erosion, intercepts and ‘pirates’ the flow of an adjacent stream.  Extending the piracy concept from surface water into ground-water hydrology provides the ground-water piracy label for a watershed that intercepts and ‘pirates’ ground-water flow from an adjacent watershed.  The Spring Creek Watershed is located in the westernmost valley of the Valley and Ridge physiographic province in central Pennsylvania, and through ground-water piracy, has a ground-water watershed area that is 20% larger than its surface-water watershed area.  Large solution conduits, which developed at depth along the regional Birmingham Thrust Fault, drain ground water from the adjacent Spruce Creek Watershed and convey it 15 miles to where it discharges from Big Spring, the second largest spring in Pennsylvania.  Local folklore attributes the 19.5 million gallons per day flow of Big Spring to Lake Erie as the source, in spite of Lake Erie being 135 miles away and 174 feet lower than Big Spring.

 

Water-table elevations were measured in drilled residential and farm wells located in the southwestern area of the Spring Creek Watershed.  Contouring of these water-table elevations indicated that the ground-water boundary of the watershed was as much as 6 miles beyond the surface-water boundary.  Successive rounds of water-level measurements during all four seasons confirmed the location.  Geochemical studies and area-discharge ratio analyses also have confirmed that the ground-water watershed area is 20 percent larger than the surface-water watershed area.  More than 16 million gallons per day of ground water are pumped from the carbonate aquifers within the Spring Creek Watershed to meet the needs of one of the fastest growing areas in Pennsylvania.  The successful future development, management, and source-water protection of these aquifers will depend upon the accurate definition of the ground-water watershed area.

Todd Giddings, Todd Giddings and Associates Inc. Todd Giddings, Ph.D., P.G., is a registered professional geologist, and the principal hydrogeologist and president of Todd Giddings and Associates, Inc. He has more than 40 years of experience in ground-water resources development, management, and remediation. His areas of professional interest are karst hydrogeology, water-resources education, and Web-based communication. He is a Director and Treasurer of the Pennsylvania Ground Water Association, and is Webmaster of their Web site at www.pgwa.org . Both his home and his office building are heated and cooled by open-loop geothermal heat pump systems.


2007 NGWA Ground Water Expo and Annual Meeting