 |
|
|
||||
| Scientific Investigations Report 2005-5232 |
By Donald H. Schaefer, Susan A. Thiros, and Michael R. Rosen
Version 1.0
The carbonate-rock aquifer of the Great Basin is named for the thick sequence of Paleozoic limestone and dolomite with lesser amounts of shale, sandstone, and quartzite. It lies primarily in the eastern half of the Great Basin and includes areas of eastern Nevada and western Utah as well as the Death Valley area of California and small parts of Arizona and Idaho. The carbonate-rock aquifer is contained within the Basin and Range Principal Aquifer, one of 16 principal aquifers selected for study by the U.S. Geological Survey’s National Water Quality Assessment Program.
Water samples from 30 ground-water sites (20 in Nevada and 10 in Utah) were collected in the summer of 2003 and analyzed for major anions and cations, nutrients, trace elements, dissolved organic carbon, volatile organic compounds (VOCs), pesticides, radon, and microbiology. Water samples from selected sites also were analyzed for the isotopes oxygen-18, deuterium, and tritium to determine recharge sources and the occurrence of water recharged since the early 1950s.
Primary drinking-water standards were exceeded for several inorganic constituents in 30 water samples from the carbonate-rock aquifer. The maximum contaminant level was exceeded for concentrations of dissolved antimony (6 µg/L) in one sample, arsenic (10 µg/L) in eleven samples, and thallium (2 µg/L) in one sample. Secondary drinking-water regulations were exceeded for several inorganic constituents in water samples: chloride (250 mg/L) in five samples, fluoride (2 mg/L) in two samples, iron (0.3 mg/L) in four samples, manganese (0.05 mg/L) in one sample, sulfate (250 mg/L) in three samples, and total dissolved solids (500 mg/L) in seven samples.
Nine different pesticides or metabolites were detected at very low concentrations in the 30 water samples. The lack of volatile organic compound detections in water sampled from most of the sites is evidence that volatile organic compounds are not common in the carbonate-rock aquifer. Arsenic values for water range from 0.7 to 45.7 µg/L, with a median value of 9.6 µg/L. Factors affecting arsenic concentration in the carbonate-rock aquifer in addition to geothermal heating are its natural occurrence in the aquifer material and time of travel along the flow path.
Most of the chemical analyses, especially for volatile organic compounds and nutrients, indicate little, if any, effect of overlying land-use patterns on ground-water quality. The water quality in recharge areas for the aquifer where human activities are more intense may be affected by urban and/or agricultural land uses as evidenced by pesticide detections. The proximity of the carbonate-rock aquifer at these sites to the land surface and the potential for local recharge to occur through the fractured rock likely results in the occurrence of these and other land-surface related contaminants in the ground water. Water from sites sampled near outcrops of carbonate-rock aquifer likely has a much shorter residence time resulting in a potential for detection of anthropogenic or land-surface related compounds. Sites located in discharge areas of the flow systems or wells that are completed at a great depth below the land surface generally show no effects of land-use activities on water quality. Flow times within the carbonate-rock aquifer, away from recharge areas, are on the order of thousands of years, so any contaminants introduced at the land surface that will not degrade along the flow path have not reached the sampled sites in these areas.
Abstract
Introduction
Purpose and Scope
Acknowledgments
Description of Study Area
Hydrogeology
Ground-Water Recharge, Flow, and Discharge
Study Design and Methods
Site Selection
Sample Collection
Sample Analysis
Quality Assurance
Ground-Water Quality
Occurrence of Inorganic and Organic Chemicals
Effects of Hydrogeologic Factors on Water Quality
Effects of Environmental Factors on Water Quality
Historical Changes in Water Quality
Summary
References Cited
Figure 1. Selected features of the Great Basin and extent of the carbonate-rock aquifer
Figure 2. Paleozoic-rock section as exposed in the Sheep Range, Nevada
Figure 3. Generalized cross section through the carbonate-rock aquifer in southern
Nevada
Figure 4. Generalized hydrogeologic section through the carbonate-rock aquifer and
overlying basin-fill deposits
Figure 5. Carbonate-rock aquifer, evapotranspiration areas, and sample sites
Figure 6. Major-ion composition of water sampled from the carbonate-rock aquifer
Figure 7. Major-ion composition of water sampled from the Colorado flow system
Figure 8. Major-ion composition of water sampled from the Great Salt Lake Desert
flow system
Figure 9. Relation of water temperature to A, arsenic, B, boron, C, lithium, and D, silica
concentrations in water sampled from the carbonate-rock aquifer
Figure 10. Arsenic concentrations in water sampled from the Colorado flow system
Figure 11. Ratio of chloride to bromide compared to chloride concentration compared to
chloride for water sampled from the carbonate-rock aquifer
Figure 12. Relation between delta deuterium and delta oxygen-18 for water sampled from
the carbonate-rock aquifer
Figure 13. Land-use patterns, evapotranspiration areas, and sample sites, in the
carbonate-rock aquifer
Table 1. Selected characteristics of sites sampled in the carbonate-rock aquifer system
Table 2. Isotope data, estimated ages, and potential indicators of land-use effects for
water sampled from the carbonate-rock aquifer system
Table 3. Historical water quality data for selected constituents at Army Well #1
Appendix 1. Water-quality constituents analyzed in ground-water samples from wells and
springs in the carbonate-rock aquifer, Nevada and Utah
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 load.
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 | |
| U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/sir20055232 Page Contact Information: Publishing Service Center Last modified: Tuesday, February 21 2006, 04:16:05 PM |
  |