Karst springs of Cumberl and County, Pennsylvania, are important water resources, but their sources and flow paths are unknown. We traced flow in a mantled-karst ground water system in the Great Valley section of the Valley and Ridge Physiographic Province using fluorescent dyes, with focuson Big Spring Creek. Upper Big Spring Creek is assigned High Quality/Exceptional Valuestat us by Pennsylvania Base don its high water quality and value as a multi-use resource with exceptional Recreational or ecological ignificance. Subsurface flow followed the geologic strike after Sulpho Rhoda mine B(Acid Red 52) dye was release don exposed carbonates. Subsurface Flow had a maximum effective line arvelo city of 2.5 km d21, which is 8 times greater than Sodium fluoresce in (AcidYellow73) dye released separately in toalosing stream over Colluvium(0.3kmd21). Sulpho Rhoda mine was detected strongly 8.9 km away at Big Spring Creek’s largest source spring (,250 ppt water; 50 pp beluate),but weak lyinan East source(2.5ppbeluate). Sodium fluoresce in was detectedafterfourweeksat0.07to 0.15 pp bineluate at springs at Hunts dale Hatchery, 9.5km from release at îp the colluvial mantle. Slow flow derived from losing stream sonthe colluvial mantle likely maintains water quality of Big Spring Creek and similar systems. However, this recharge Is distant, and the flow passes below karst recharge features in the valley center, creating many opportunities for contamination. Future studies of contaminant and sediment loading stosub terrane an basin sand of source-water protection strategies that recognize These pattern sare necessary to protect these streams.