 |
|
|
||||
| Scientific Investigations Report 2006-5127 |
Version 1.0
In 1999, the U.S. Environmental Protection Agency introduced a rule to protect the quality of ground water in areas other than source-water protection areas. These other sensitive ground-water areas (OSGWA) are areas that are not currently but could eventually be used as a source of drinking water. To help determine whether a well is in an OSGWA, the Nevada Division of Environmental Protection needs statewide information on the susceptibility and vulnerability of Nevada's aquifer systems to contamination. This report presents an evaluation of the quality of ground water and susceptibility of Nevada's aquifer systems to anthropogenic contamination.
Chemical tracers and statistical methods were used to assess the susceptibility of aquifer systems in Nevada. Chemical tracers included nitrate, pesticides, volatile organic compounds (VOCs), chlorofluorocarbons (CFCs), dissolved gases, and isotopes of hydrogen and oxygen. Ground-water samples were collected from 133 wells during August 2002 through October 2003. Logistic regression was done to estimate the probability of detecting nitrate above concentrations typically found in undeveloped areas. Nitrate is one of the most common anthropogenic contaminants that degrades ground-water quality, is commonly measured and is persistent, except in reducing conditions. These characteristics make nitrate a good indicator of aquifer susceptibility. Water-quality data for 5,528 wells were compiled into a database. The area around each well was characterized using information on explanatory variables that could be related to nitrate concentrations. Data also were used to characterize the quality of ground water in Nevada, including dissolved solids, nitrate, pesticide, and VOC concentrations.
Executive Summary
Introduction
Purpose and Scope
Acknowledgments
Previous Studies of Ground-Water Quality
Nitrate and Synthetic Organic Compounds in the Environment
Aquifer Susceptibility and Vulnerability
Aquifer Systems in Nevada
Precipitation
Recharge
Unsaturated Zone
Hydrogeologic Units
Ground-Water-Flow Paths and Velocities
Methods
Chemical Techniques
Chlorofluorocarbons
Dissolved Gases
Isotopes of Hydrogen and Oxygen
Well Selection
Sampling Procedures
Quality Assurance
Statistical Techniques
Correlations and Comparisons
Logistic Regression
Water-Quality Data Compilation
Geographic Information System Datasets
Ground-Water Quality
Dissolved Solids
Nitrate 26
Concentrations in Undeveloped Areas
Relations Between Nitrate and Explanatory Variables
Synthetic Organic Compounds
Co-Occurrence of Nitrate and Synthetic Organic Compounds
Aquifer Susceptibility
Chemical Results
Chlorofluorocarbons
Dissolved Gases
Stable Isotopes of Hydrogen and Oxygen
Logistic Regression
Summary
References
| Figure 1. | Nevada and locations of wells sampled for this study. |
|---|---|
| Figure 2. | Deviation from mean annual precipitation for selected stations in Nevada. |
| Figure 3. | Typical ground-water flow and recharge patterns perpendicular to the long axis of valleys in Nevada for mountain blocks with different permeability and annual precipitation. |
| Figure 4. | Concentrations of soil organic material. |
| Figure 5. | Ranges in the horizontal hydraulic conductivity of aquifers in Nevada. |
| Figure 6. | Atmospheric mixing ratios of CFC-11, CFC-12, and CFC-113 for the northern hemisphere. |
| Figure 7. | Locations of wells in Nevada with water-quality data. |
| Figure 8. | Dissolved-solids concentrations in ground water, playas, and ground-water discharge areas in Nevada. |
| Figure 9. | Nitrate concentrations for domestic monitoring, and production wells in undeveloped areas. |
| Figure 10. | Concentrations of nitrate in ground water. |
| Figure 11. | Nitrate concentrations versus well category. |
| Figure 12. | Nitrate concentrations versus A, depth to water and B, well depth. |
| Figure 13. | Nitrate concentrations versus well category in Eagle Valley. |
| Figure 14. | Number of A, pesticides and B, volatile organic compounds detected versus well depth. |
| Figure 15. | Apparent recharge date versus A, water level above the top of the screen and B, well depth. |
| Figure 16. | Nitrate concentration versus apparent recharge date. |
| Figure 17. | Apparent recharge dates versus aquifer type. |
| Figure 18. | Apparent recharge dates versus hydrologic setting. |
| Figure 19. | Recharge temperature estimated from dissolved gases versus estimated mean annual air temperature. |
| Figure 20. | Locations of wells and springs where isotopes have been sampled. |
| Figure 21. | Deuterium versus 18O measured in ground water and springs in Nevada. |
| Figure 22. | Deuterium in ground water and springs versus A, latitude; B, well depth; and C, altitude. |
| Table 1. | Range in soil permeability for descriptive categories of unconsolidated sediments and corresponding geomorphic features (from Maurer and others, 2004) |
|---|---|
| Table 2. | Summary statistics of soil organic material in selected western states and the United States. Values are in percent by weight. |
| Table 3. | Number of wells sampled in hydrologic landscape regions of Nevada |
| Table 4. | Summary of water-quality data compilation |
| Table 5. | Explanatory variables used in logistic regression |
| Table 6. | Dissolved-solids concentrations in unconsolidated sediment and ground-water discharge areas |
| Table 7. | Spearman rank correlations between nitrate, clay, and depth to water in selected areas |
| Table 8. | Pearson correlations between binary nitrate data using a background concentration of 2 milligrams per liter and explanatory variables. Only statistically significant correlations (p<0.05) are shown |
Worksheet 1. Station information
Worksheet 2. Chlorofluorocarbon data
Worksheet 3. Dissolved gas data
Worksheet 4. Isotope Data
This report is contained in the following files:
|
For viewing and printing upon download. |
To view files in PDF format, download free copy of Adobe Reader.
Downloading Suggestion It is best to download and save a large PDF file to your hard drive rather than to open it inside your browser.
A standard click may automatically open the PDF file inside the browser but doing so will result in a very slow download.
Downloading the PDF file may take several moments but will be worth the wait.
Once it is downloaded, open the PDF from your hard drive using Adobe Acrobat—it will open in a fraction of the time it would take to open the PDF over the
Internet.
1. Right-click the link to a file, and then choose 'Save (Link) Target As' from the pop-up menu.
2. In the Save As dialog box, select a location on your hard drive, and then click Save.
1. Right-click (or Control-click) the link to a file, and then choose 'Download Link to Disk' from the pop-up menu.
2. In the Save dialog box, select a location on your hard drive, and then click Save.
| AccessibilityFOIAPrivacyPolicies and Notices | |
  |
|