CHARACTERIZATION OF GROUND WATER FLOW BETWEEN RECHARGE FEATURES AND CARBONATE SPRINGS IN CUMBERLAND COUNTY PENNSYLVANIA WITH FLUORESCENT DYE TRACING

Big Spring Creek is a dominant spring creek of Cumberland County Pennsylvania with two major source springs. Previous fluorescent dye-tracing (FDT) revealed rapid flow along strike from a collapsed stormwater detention basin to the larger west source spring, with weaker connection to the east source spring. The mean effective linear velocity was 1.8 km/day. Objectives of this study were to further define source areas for Big Spring Creek, and to test whether slower recharge to this flow system occurs from a losing stream in the colluvially mantled karst of an adjacent watershed.

We released 4 kg of uranine in Thompson Hollow Creek, 10 km west and south of Big Spring, and 5 kg of sodium naphthionate to a stream swallet in the non-mantled valley center 5.6 km to the west of Big Spring on February 26, 2009. Source springs of Big Spring and six surrounding springs were monitored for dye breakthrough with charcoal receptors and water samples. The latter trace was repeated on October 1, 2009 with 800 g of sulforhodamine B. Big Spring Creek was monitored near its source and 4 km downstream, along with four surrounding springs.

Uranine was strongly detected within 2-3 weeks in the east source of Big Spring Creek. Uranine was more faintly and variably detected in the west spring within 5 to 7 weeks. These results were opposite those of the FDT from the collapsed detention basin, where detection was stronger in the west source spring. Sodium naphthionate and SRB were detected in springs associated with Bullshead Branch of Green Spring Creek however there was also evidence of rapid interbasin flow to Big Spring Creek and a related municipal spring. While these results reinforce the importance of rapid delivery of water and potential surface contaminants to springs from recharge features in the valley center, they also demonstrate relatively rapid (500-700 m/day) effective flow velocities to specific receptors from an exogenous surface basin via the colluvial mantle. Taken together, the FDT results to date suggest conduit-scale porosity from all recharge features to springs, with some fracture flow to other nearby springs.