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Publications— Scientific Investigations Report

Ground-Water Resources and the Hydrologic Effects of Petroleum Occurrence and Development, Warren County, Northwestern Pennsylvania

U.S. Geological Survey Scientific Investigations Report 2006-5263

By Theodore F. Buckwalter and Michael E. Moore

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Most of the northern half of Warren County is in the Northwestern Glaciated Plateau Section of the Appalachian Plateaus Physiographic Province. The remainder of the county is in the High Plateau Section. The glacial outwash sand and gravel hydrogeologic unit is the most extensively used unconsolidated unit for water supply in Warren County because it is capable of yielding large amounts of water to wells and it is situated in populated valleys. The median well yield for 47 specific- capacity tests was 25 gal/min (gallons per minute); well yields ranged from 2 to 1,600 gal/min. Acceptable well yields for domestic supply also are available from other unconsolidated hydrogeologic units including alluvium, colluvium, glacial drift, ice-contact stratified sand and gravel, and undifferentiated alluvium and glacial lacustrine. The median well yields during specific-capacity tests of wells in these five hydrogeologic units ranged from 8 to 18 gal/min.

A comparison of the median specific capacities for wells in the unconsolidated and bedrock hydrogeologic units indicates that wells completed in the outwash sand and gravel hydrogeologic unit had the highest median specific capacity of 6.0 (gal/min)/ft (gallons per minute per foot); specific capacities for wells completed in the outwash sand and gravel unit ranged from 0.14 to 300 (gal/min)/ft. For wells completed in the bedrock hydrogeologic units, their corresponding median specific capacities are Pottsville Group, 0.5 (gal/min)/ft; Shenango Formation, 0.44 (gal/min)/ft; Cuyahoga Formation, 0.24 (gal/min)/ft; Knapp Formation, 0.45 (gal/min)/ft; Corry Sandstone through Riceville Formation, 0.67 (gal/min)/ft; Riceville Formation, 1.5 (gal/min)/ft; Oswayo Formation, 0.07 (gal/min)/ft; Venango Formation, 1.0 (gal/min)/ft; and Chadakoin Formation, 0.71 (gal/min)/ft.

Annual precipitation at Warren for the years 1984-87 was above the long-term mean. The 4-year average of the annual hydrologic balance for 1984 indicated 40 percent of the precipitation was lost to evapotranspiration. Ground-water discharge, commonly defined as base flow, accounted for about 29 percent of precipitation, and surface runoff made up 31 percent. During 1984-87, ground-water discharge made up from 47 to 50 percent of total runoff or streamflow. In 1990, ground-water withdrawals made up only 1.3 percent [13.8 Mgal/d (million gallons per day)] of the total withdrawals for the county. However, ground water is the predominant source for domestic, municipal, and industrial water supplies in Warren County outside of the larger cities.

Concentrations of dissolved iron exceeded the U.S. Environmental Protection Agency (USEPA) Secondary Maximum Contaminant Level (SMCL) of 300 μg/L (micrograms per liter) in 95 of the 266 wells sampled (36 percent). The Riceville Formation is the only hydrogeologic unit in which ground-water samples did not exceed the SMCL for dissolved iron. Median concentrations of dissolved iron ranged from 50 μg/L in samples from the Shenango and Riceville Formations to 2,350 μg/L in samples from the alluvium and glacial lacustrine, undifferentiated unit. Concentrations of dissolved manganese exceeded the USEPA SMCL in samples from 155 of the 260 wells sampled (60 percent). Samples from at least 40 percent of the wells in each hydrogeologic unit exceeded the SMCL for dissolved manganese, indicating a widespread problem in the county. The median concentrations of dissolved manganese ranged from 25 μg/L in the glacial outwash sand and gravel, the Cuyahoga Formation, and the Riceville Formation to 450 μg/L in the alluvium and glacial lacustrine, undifferentiated.

Concentrations of total dissolved solids exceeded the USEPA SMCL of 500 mg/L in samples from 9 of the 257 wells sampled (3.5 percent). The median concentrations ranged from 66 mg/L in samples from the Pottsville Group to 308 mg/L in samples from the Catskill and Venango Formations. Most samples contained less than 1,000 mg/L total dissolved solids and were classified as fresh water. Samples from only three wells had concentrations classified as slightly saline (2,140, 1,440, and 1,730 mg/L).

Samples collected from 233 water wells were analyzed for arsenic, and 38 samples (16 percent) exceeded the USEPA Maximum Contaminant Level (MCL) of 10 μg/L. Twenty-two of the water wells with arsenic concentrations exceeding the MCL were domestic supply wells. Twenty-five of these 38 wells (66 percent) were completed in the glacial outwash sand and gravel hydrogeologic unit.

In Warren County, ground water moves within and through two general flow systems--a shallow, local aquifer system with active flow, and a deeper, regional aquifer system at flow rates that are slow relative to the circulation of water in the shallow system. In the glaciated area, the upper part of the local flow system is made up of saturated unconsolidated deposits. About 95 percent of the ground-water circulation in the county takes place within the local flow system. The depth of the active local flow system is variable, however, as the bottom of the system parallels the bedrock surface and is about 150 to 175 feet beneath the land surface. The base of the regional aquifer system is unknown. Ground-water flow patterns in the unglaciated area are similar to flow patterns in the glaciated area. In the unglaciated plateau, however, bedrock hillsides and hilltops are covered with colluvium instead of till and other glacial deposits.

Topographic position affects the water levels in wells. Hilltops are areas of aquifer recharge, and valley bottoms are areas of aquifer discharge. Water levels ranged from above land surface in some valley wells to more than 200 feet below land surface in hilltop wells. The average depth to water was 25-30 feet below land surface in a valley wells to about 50 feet below land surface for hilltop wells. Hydrographs from monitor wells in the county illustrated seasonal variation in the water levels. Water levels generally declined during the summer and early fall as a result of evapotranspiration and continuing ground-water discharge from the aquifer.

The development of ground water in Warren County for domestic and municipal use has been difficult because of very shallow petroleum reservoirs in parts of the ground-water system. Analysis of water samples from wells in the Tidioute area indicated poor water quality that would require costly treatment prior to use. Excessive concentrations of iron, manganese, aluminum, chloride, dissolved solids, and methane negated the use of these wells for public supply.

In Pleasant Township, a major subsurface natural gas migration in 1983 resulted in high concentrations of natural gas observed in water wells, a spring, lake, and tributary stream of Chapman State Park. Although natural gas concentrations in ground-water diminished over time in ground water, several wells continued to experience severe natural-gas contamination in 1986. A well containing water that was saturated with natural gas was reported to have exploded, and another well suddenly discharged water from a vent pipe after pumping. Samples from wells in this area had elevated levels of arsenic and barium. Thirty-two of 68 samples collected in this area equalled or exceeded the USEPA MCL of 10 μg/L for arsenic. Barium concentrations ranged from 40 to 1,660 μg/L but were below the USEPA MCL of 2,000 μg/L. It is not know if these elevated concentrations were the result of gas migrations, but the concentrations were higher than those reported for samples collected from other wells in the county that draw water from the same hydrogeologic units.

Table of Contents

     Purpose and Scope
     Previous Investigations
Description of the Study Area
     Hydrologic Setting
          Annual Hydrologic Balance
     Physiography and Geologic Setting
          Geologic Structure
          Stratigraphy and Oil and Gas Geology
     Water Use
     Stratigraphy and Hydrologic Characteristics of Unconsolidated Deposits
          Glacial Drift
          Ice-Contact Stratified Sand and Gravel
          Alluvium and Glacial Lacustrine, Undifferentiated
          Glacial Outwash Sand and Gravel
     Stratigraphy and Hydrologic Characteristics of Bedrock Units
          Pottsville Group
          Shenango Formation
          Cuyahoga Formation
          Knapp Formation
          Corry Sandstone through Riceville Formation
          Riceville Formation
          Oswayo Formation
          Catskill and Venango Formations
          Venango Formation
          Chadakoin Formation
          Upper Devonian, Undifferentiated
          Bradford Group
Ground Water
     Occurrence and Flow System
          Glaciated Area
          Unglaciated Area
     Water Quality
          Major Constituents
               Dissolved Solids
               Sodium and Chloride
          Trace Elements
               Iron and Manganese
               Arsenic and Barium
                    Valley Settings
                    Glacial Terrace Settings
                    Upland Settings
               Additional Trace Elements
          Organic Constituents
               Natural Gas
               Oil and Grease
               Volatile Organic Compounds
               Total Organic Carbon
               Sampling Design and Protocol
               Results of Radionuclide Analysis
Hydrologic Effects of Petroleum Occurrence and Development
     Drilling and Well Completion Practices
     Natural-Gas Migration
     Abandoned Oil and Gas Wells
     Production Fluids
     Case Histories
          Tidioute Borough and Local Area
          Allegheny Reservoir
          Chapman State Park
               Manifestations of Natural-Gas Migration
               Lingering Effects of Natural-Gas Migration
          Anomalies in Ground-Water Levels
          48-Hour Aquifer Test
Guidelines for Developing Ground-Water Supplies
     Site Selection Restricted
     Site Selection Unrestricted
Suggestions for Future Study
References Cited
Appendix 1--Maps showing bedrock geology, surficial geology, and geologic structure contours

Interactive Index of the Geologic Maps Included in this Report

     Explanation for the Surficial Geologic Maps

     Explanation for the Bedrock Geologic Maps

     Explanation for the Geologic Structure Contour Maps

Map of surficial wells in the Hillcrest Housing Development

Download the entire appendix (zipped 1,355 MB)

This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

View the full report in PDF 22.3 MB

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