USGS

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2004-5124

Determining Sources of Water and Contaminants to Wells in a Carbonate Aquifer Near Martinsburg, Blair County, Pennsylvania, By Use of Geochemical Indicators, Analysis of Anthropogenic Contaminants, and Simulation of Ground-Water Flow

By Bruce D. Lindsey and Michele L. Koch

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ABSTRACT

Water supply for the Borough of Martinsburg, Pa., is from two well fields (Wineland and Hershberger) completed in carbonate-bedrock aquifers in the Morrison Cove Valley. Water supply is plentiful; however, waters with high concentrations of nitrate are a concern. This report describes the sources of water and contaminants to the supply wells. A review of previous investigations was used to establish the aquifer framework and estimate aquifer hydraulic properties. Aquifer framework and simulation of ground-water flow in a 25-square-mile area using the MODFLOW model helped to further constrain aquifer hydraulic properties and identify water-source areas in the zone of contribution of ground water to the well fields. Flow simulation identified potential contaminant-source areas. Data on contaminants and geochemical characteristics of ground water at the well fields were compared to the results of flow simulation.

The Woodbury Anticline controls the aquifer framework near the well fields and four carbonate-bedrock formations contain the primary aquifers. Three carbonate-bedrock aquifers of Ordovician age overlie the Gatesburg aquifer of Cambrian age on the flanks of the anticline. Fracture, not conduit, permeability was determined to be the dominant water-bearing characteristic of the bedrock. The horizontal hydraulic conductivity of the Gatesburg aquifer is about 36 feet per day. The other carbonate aquifers (Nittany/Stonehenge, Bellefonte/Axemann, and Coburn through Loysburg aquifers) overlying and flanking the Gatesburg aquifer have horizontal hydraulic conductivities of about 1 foot per day. Regional directions of ground-water flow are toward the major streams with Clover Creek as the major discharge point for ground water in the east. Ground-water flow to the well fields is anisotropic with a 5:1 preferential horizontal direction along strike of the axial fold of the anticline. Thus, the zone of contribution of ground water to the well fields is elongate in a north-south direction along the anticline axis, with the majority of the flow to the well fields originating from the south.

Human activity in the areal extent of the zone of contribution to the well fields was the source of contaminants. The areal extent of the zone of contribution included both urban areas in the Borough and a large amount of agricultural land. By relating results of flow simulation, natural geochemistry, and analyses of anthropogenic (human-made) contaminants, the source areas for water and contaminants were determined with more confidence than by using only flow simulation. Analysis of natural geochemistry identified water sources from both limestone and dolomite aquifers. Geochemistry results also indicated fractures, not conduits, were the dominant source of water from aquifers; however, quantitative source identification was not possible. Chemical ratios of chloride and bromide were useful to show that all samples of ground water had sources with chemical contributions from land surface. Nitrogen isotope ratio analysis indicated animal manure as the possible primary source of nitrate in most ground water. Some of the nitrate in ground water had chemical fertilizer as a source. At the Wineland well field, chemical fertilizer was likely the source of nitrate. The nitrate in water from the Hershberger well field was from a mixture of fertilizer and animal-manure sources. Human sewage was ruled out as a major source of nitrate in water from the municipal wells by results showing 1) wastewater compounds in sewage were rarely detected and 2) a mass-balance calculation indicating the small contribution of nitrogen that could be attributed to septic systems.

Table of Contents

Abstract
Introduction
     Purpose and Scope
     Acknowledgments
     Description of Study Area
          Geologic Setting
          Hydrogeology and Aquifer Characteristics
          Well-Field Characteristics
     Land Use and Sources of Nitrogen
Study Methods
     Field Data Collection and Analytical Methods
     Methods to Determine Sources of Contaminants to Ground-Water Wells
          Natural Geochemistry of Water
          Anthropogenic Contaminants
          Microbial Source Tracking
          Simulation of Ground-Water Flow
Sources of Water and Contaminants to Martinsburg Municipal Wells
     Geochemical Indicators
          Source of Water
          Type of Permeability
     Sources Based on Analysis of Anthropogenic Contaminants
          Nitrate-Nitrogen
          Nitrogen Isotopes
          Chloride/Bromide Ratio
          Boron
          Wastewater Compounds
          Microbial Source Tracking
     Sources Based on Simulation of Ground-Water Flow
          Conceptual Model
          Model Design
          Model Calibration
          Simulation Results and Sensitivity
          Zone of Contribution to Municipal Wells
     Relating Simulation Results, Natural Geochemistry, and Anthropogenic Contaminants to Determine Source Areas
     Limitations of Data and Findings
Summary and Conclusions
References Cited

Figures

1-3. Maps showing:
     1. Location of the Ridge and Valley Physiographic Province, carbonate bedrock in Pennsylvania, and the Borough of Martinsburg, Pennsylvania
     2. Location of the Morrison Cove Valley, Martinsburg, Pennsylvania, boundary of ground-water model area, and land use
     3. Geologic formations, structure, and geologic section in the study area near Martinsburg, Pennsylvania
4. Shaded-relief map of the Martinsburg, Pennsylvania Quadrangle showing topography, lithology, and stream drainage near Martinsburg, Pennsylvania
5. Conceptual model of ground-water-flow system near Martinsburg, Pennsylvania
6. Map showing basic soil types and their relation to bedrock lithology near Martinsburg, Pennsylvania
7. Conceptual model of hypothetical orientation of major fracture sets in study area near Martinsburg, Pennsylvania
8-12. Maps showing:
     8. Karst features within ground-water model boundary near Martinsburg, Pennsylvania
     9. Water levels near Martinsburg, Pennsylvania
     10. Generalized land use in the area of Martinsburg, Pennsylvania
     11. Types of nitrogen applied to fields and areas served by public sewer lines near Martinsburg, Pennsylvania
     12. Location of wells, springs, and streams sampled or measured in and near Martinsburg, Pennsylvania
13. Graph showing d15N relative to organic carbon: total nitrogen for (A) nitrogen-source materials; and (B) suspended particulates in water, Susquehanna River Basin, Pennsylvania
14. Piper diagram showing concentrations of major ions in water from wells near Martinsburg, Pennsylvania
15. Graph showing binary mixing curves for chloride to bromide ratios for water from wells and streams near Martinsburg, Pennsylvania
16. Map showing location of model grid, boundaries, streams, drain nodes, and wells near Martinsburg, Pennsylvania
17. Hypothetical cross section of model layers used for simulation of ground-water flow
18-19. Graphs showing:
     18. Composite scaled sensitivities for parameters used in model calibration
     19. Calibration results showing simulated and measured water levels near Martinsburg, Pennsylvania
20. Diagram showing simulated water-budget summary for layers 1 and 2 of hydrologic model
21-22. Maps showing:
     21. Simulated water table and zone of contribution to wells near Martinsburg, Pennsylvania
     22. Areal extent of zone of contribution to wells, pathlines, and source areas near Martinsburg, Pennsylvania, under normal and low recharge conditions
23-24. Model sections showing:
     23. Simulated water table and pathlines to municipal wells from south to north along model column 33
     24. Simulated water table from west to east along model row 20
25-28. Maps showing:
     25. Areal extent of zone of contribution to wells near Martinsburg, Pennsylvania, illustrating simulation with horizontal anisotropy and without horizontal anisotropy
     26. Geology and karst features in the areal extent of the zone of contribution to well BA 332 and well BA 545 near Martinsburg, Pennsylvania
     27. Land use in the areal extent of the zone of contribution to well BA 332 and BA 545 near Martinsburg, Pennsylvania
     28. Sources of nitrogen, nitrate concentration, and d15N in municipal wells near Martinsburg, Pennsylvania

Tables

1. Geologic-stratigraphic and hydrologic units column near Martinsburg, Blair County, Pennsylvania
2. Hydrogeologic properties of aquifers in the study area
3. Land covers included in the land-use groupings in the study area near Martinsburg, Pennsylvania
4. Wells sampled and/or used for model calibration near Martinsburg, Pennsylvania
5. Sampling requirements and analytical methods for water analyses from wells and streams near Martinsburg, Pennsylvania
6. Data from previous studies of water from Ridge and Valley carbonate aquifers in Pennsylvania showing geochemical indicators of source of water
7. Data on geochemical indicators of type of permeability from previous studies of Ridge and Valley carbonate aquifers in Pennsylvania
8. Geochemical composition of water from wells sampled near Martinsburg, Pennsylvania
9. Selected chemical analyses from wells, springs, and a spring sampled near Martinsburg, Pennsylvania
10. Optimum values of aquifer properties estimated near Martinsburg, Pennsylvania
11. Water budget for steady-state simulation near Martinsburg, Pennsylvania


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 3.92 MB

For more information about USGS activities in Pennsylvania contact:
District Chief
U.S. Geological Survey
Water Resources Discipline
215 Limekiln Road
New Cumberland, Pennsylvania 17070
Telephone: (717) 730-6960
Fax: (717) 730-6997
or access the USGS Water Resources of Pennsylvania home page at:
http://pa.water.usgs.gov/.




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