Summary of hydrogeologic and ground-water-quality data and hydrogeologic framework at selected well sites, Adams County, Pennsylvania

Water-Resources Investigations Report 99-4108




Rapid population growth in Adams County has increased the demand for ground water and led Adams County planning officials to undertake an effort to evaluate the capabilities of existing community water systems to meet future, projected growth and to begin wellhead-protection programs for public-supply wells. As part of this effort, this report summarizes ground-water data on a countywide scale and provides hydrogeologic information needed to delineate wellheadprotection areas in three hydrogeologic units (Gettysburg Lowland, Blue Ridge, and Piedmont Lowland). Reported yields, specific capacities, well depths, and reported overburden thickness can vary by hydrogeologic unit, geologic formation, water use (domestic and nondomestic), and topographic setting. The reported yields of domestic wells drilled in the Gettysburg Lowland (median reported yield of 10 gallons per minute) are significantly greater than the reported yields from the Blue Ridge, Piedmont Lowland, and Piedmont Upland (median reported yields of 7.0, 8.0, and 7.0 gallons per minute, respectively). Reported yields of domestic wells completed in the diabase and the New Oxford Formation of the Gettysburg Lowland, and in the metarhyolite and metabasalt of the Blue Ridge, are significantly lower than reported yields of wells completed in the Gettysburg Formation. For nondomestic wells, reported yields from the Conestoga Formation of the Piedmont Lowland are significantly greater than in the diabase. Reported yields of nondomestic wells drilled in the Gettysburg, New Oxford, and Conestoga Formations, and the metarhyolite are significantly greater than those for domestic wells drilled in the respective geologic formations. Specific capacities of nondomestic wells in the Conestoga and Gettysburg Formations are significantly greater than their domestic counterparts. Specific capacities of nondomestic wells in the Conestoga Formation are significantly greater than the specific capacities of nondomestic wells in the metarhyolite, diabase, and Gettysburg and New Oxford Formations.Well depths do not vary considerably by hydrogeologic unit; instead, the greatest variability is by water use. Nondomestic wells drilled in the metarhyolite, Kinzers, Conestoga, Gettysburg, and New Oxford Formations are completed at significantly greater depths than their domestic counterparts. The reported thickness of overburden varies significantly by geologic formation and water use, but not by topographic setting. The median overburden thickness of the Blue Ridge (35 feet) is greater than in any other hydrologic unit. Except where adversely affected by human activities, ground water in Adams County is suitable for most purposes. Calcium and magnesium are the dominant cations, and bicarbonate is the dominant anion. In general, the pH and hardness of ground water is lower in areas that are underlain by crystalline rocks (Blue Ridge and Piedmont Upland) than in areas underlain by sedimentary rocks, especially where limestone or dolomite is dominant (Piedmont Lowland). Dissolved nitrate (as N) and dissolved nitrite (as N) concentrations in the water from 9 of 69 wells and 3 of 80 wells sampled exceeded the U.S. Environmental Protection Agency (USEPA) maximum contaminant levels (MCL) of 10 and 1.0 mg/L (milligrams per liter), respectively. Sulfate concentrations greater than the proposed USEPA MCL of 500 mg/L were reported from the water in 3 of 110 wells sampled. Iron concentrations in the water from 13 of 67 wells sampled and manganese in the water from 9 of 64 wells sampled exceeded the USEPA secondary maximum contaminant level (SMCL) of 300 and 50 mg/L (micrograms per liter), respectively. Aluminum concentrations in the water from 16 of 22 wells sampled exceeded the lower USEPA SMCL threshold of 50 mg/L. Pesticides were detected in the water from seven wells but at concentrations that did not exceed USEPA MCL?s. Most volatile organic compounds detected in the ground water were confined to USEPA S

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Publication type:
Publication Subtype:
USGS Numbered Series
Summary of hydrogeologic and ground-water-quality data and hydrogeologic framework at selected well sites, Adams County, Pennsylvania
Series title:
Water-Resources Investigations Report
Series number:
Year Published:
U.S. Geological Survey
Contributing office(s):
Pennsylvania Water Science Center
viii, 86 p. :ill. (some col.), maps (some col.) ;28 cm.