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Ground water is a vital resource for the 150,000 people living in 10 separate or contiguous valleys of Bedford, Blair, Centre, Clinton, Fulton, Huntingdon, and Mifflin Counties. These valleys have formed on anticlinal folds in a sequence of Cambrian and Ordovician carbonate strata that exceed 8,000 feet in thickness. Younger clastic strata conformably overlie the carbonate rocks and form ridges along the valley perimeters, which rise 700 to 1,500 feet above the valley floors. About 43 Mgal/d (million gallons per day) of water is withdrawn for use in all the valleys; 90 percent is derived from ground-water sources. Nearly 75 percent of the water is used in the two largest valleys, 49 percent in the Nittany Valley, and another 25 percent in the Morrison Cove and Canoe Valleys. Single wells can produce about 1,000 gal/min (gallons per minute) from the Gatesburg and Nittany Formations; 500 gal/min from the Beliefonte and Axemann Formations; at least 100 gal/min from the undivided Benner through Loysburg, undivided Coburn through Loysburg, undivided Beliefonte and Axemann, undivided Nittany and Larke, Warrior, and Stonehenge Formations; and 50 gallons per minute from the Rockdale Run, Shadygrove, and undivided Coburn through Nealmont Formations. Wells in valleys have the greatest potential yield and wells on hilltops the least. Other topographic positions have intermediate yield potentials. Ideally sited wells, such as those on fracture traces, have greater yields than do randomly sited wells. Local cave-passage orientation correlates with local joint orientation maxima, which correlates with local fracture-trace orientation. These relations can aid in the selection of sites for large production wells. Recharge to the carbonate aquifers is from precipitation directly on the land surface and indirectly from runoff draining mountain slopes. In the latter case, about 80 percent of runoff from mountain slopes infiltrates the colluvium or enters sinkholes in stream channels along the valley perimeters. An estimated 75 percent of the runoff that infiltrates flows through conduits formed in the limestone immediately adjacent to the mountain flanks and discharges as springs a short distance downvalley. Discharges from these springs fluctuate greatly and some springs may be dry during periods of baseflow. Of 42 large perennial springs in the valleys, 26 have flows greater than 1,000 gal/min, and 3 have flows greater than 10,000 gal/min some of the time. Annual precipitation in the Kishacoquillas and Spring Creek basins averages about 38 and 39 inches, respectively. About 21 inches is lost form each basin to evapotranspiration. Another 13 inches leaves the Kishacoquillas basin and 16 inches leaves the Spring Creek basin as ground-water discharge. The remaining water leaves as direct runoff. Water, in amounts equivalent to ground-water discharge, recharge the ground-water system and are available for use. Expressed volumetrically over the basin areas, 0.62 [(Mgal/d)/mi 2 ] (million gallons per day per square mile) is available for use in the Kishacoquillas basin and 0.80 [(Mgal/d)/mi2 ] is available for use in the Spring Creek basin. During drought years, only 0.34 and 0.45 [(Mgal/d)/mi2 ] are available in the Kishacoquillas and Spring Creek basins, respectively. The Sugar, Brush, Penns, and Big Cove Creek Valleys have similar hydrogeologic settings to the Kishacoquillas Creek basin; the Nittany, Morrison Cove, Canoe, and Snake Spring Valleys have similar hydrogeologic settings to the Spring Creek basin. Similar hydrogeologic settings will have similar amounts of ground water available for use. Estimates of transmissivity, based on median specific capacity, range from 15 ft 2 /d (feet squared per day) for the Coburn through Nealmont Formations to 5,200 ft2 /d for the Nittany Formation. Transmissivities determined from pumping test data range from 560 ft2/d for the Benner through Loysburg Formations to 120,000 ft2 /d for the Nittany Formation. The specific yield of the carbonate rocks, based on water table declines during baseflow in the Kishacoquillas and Spring Creek basins, is 0.015. Interference is likely between pumped wells spaced as much as 1,000 feet apart and is greatest parallel to the dominant local fracture systems. Ground-water quality is suitable for drinking and most other uses, but is hard. Iron and manganese concentrations slightly exceed the respective 0.3 and 0.5 milligram per liter, the U.S. Environmental Protection Agency maximum contaminant level (MCL) for potable water in less than 10 percent of the wells sampled. Nitrate concentrations exceed the MCL of 10 milligrams per liter (as nitrogen) in 17 of 146 wells sampled. Median concentrations of nitrate, as nitrogen, range from 3.3 milligrams per liter in the Northern Nittany and Penns, Sugar, and Brush Valleys to 5.9 milligrams per liter in the Kishacoquillas Valley. Herbicides at concentrations less than proposed MCLs, were found in 10 of 20 wells and springs sampled, but only in one sample at a greater concentration of 20 micrograms per liter. Noticeable effects of withdrawals on water levels were noted in the vicinity of State College where an average of 8.1 Mgal/d is pumped from public supply wells and from quarries for purposes of dewatering. Although adequate amounts of potable water are available to meet current demands, monitoring of water levels is needed to manage over droughts. The most widespread and growing water-quality problem is an increase in the amount of nitrate that enters the ground water from agricultural practices. A related potential problem results from the application of herbicides to farmland. At least nine sites that were contaminated by petroleum and other toxic chemical leaks and spills had been discovered, were undergoing cleanup, or were being monitored from 1983-86.

Ground-water resources of Cambrian and Ordovician carbonate rocks in the valley and ridge physiographic province of Pennsylvania