GEOTHERMAL SURVEYS USED TO MAP KARST FEEDER CHANNELS

U.S. Safe Drinking Water Act requires springs used by the public must be free of surface water influences. Springs that do not pass surface water protocol tests (SWIPP) must be filtered or abandoned within a specific period. Even if a spring's groundwater basin is shown to be free of surface water influences, it may fail SWIPP if its orifice(s) is inadequately protected. Springs must be covered to eliminate sunlight, exposure to dust, debris, birds and animals, and otherwise protected.

Two shallow temperature surveys are described that identified possible inflow points to springs within central PA. A shallow soil temperature survey was conducted within the pool of Big Spring, Bellefonte, PA. These data were used to select four groundwater inflow points for SWIPP testing. Groundwater (14-16 mg pd) was shown to be free of surface water influences following 8 months of testing despite the spring's urbanized location and exposed pool. Soil-temperature surveys were conducted around the pool to locate channels that might nourish Big Spring. A similar survey was conducted for Graysville Spring. These data were used to design hydraulic barriers to protect both springs from surface and near surface influences and to evaluate the effectiveness of engineered barriers following construction. Multiple barriers for Big Spring include: a jet-grout curtain, concrete capping wall, floating cover, sloping concrete deck and drainage swale to divert surface water and French drain to reverse hydraulic gradients from the spring pool. The drain skims pollutants that might enter shallow groundwater. Confirmation temperature surveys revealed where grout columns were partially completed. Jet grouting had to be terminated periodically to protect drinking water during construction. A stainless steel tank was used to protect the Graysville Spring when temperature data revealed that groundwater was migrating upward along deep vertical fractures rather than along shallow lateral fractures.