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At least 1,099 records · Page 61Linked to original sources
USGS1990

Volcanic and seismic hazards on the Island of Hawaii

The eruptions of volcanoes often have direct, dramatic effects on the lives of people and on their property. People who live on or near active volcanoes can benefit greatly from clear, scientific information about the volcanic and seismic hazards of the area. This booklet provides such information for the residents of Hawaii so they may effectively deal with the special geologic hazards of the island. Identifying and evaluating possible geologic hazards is one of the principal roles of the U.S. Geological Survey (USGS) and its Hawaiian Volcano Observatory. When USGS scientists recognize a potential hazard, such as an impending eruption, they notify the appropriate government officials, who in turn are responsible for advising the public to evacuate certain areas or to take other actions to insure their safety. This booklet was prepared in cooperation with the Hawaii County Civil Defense Agency.

General Interest Publication↗
USGS2011

The Haleakala Argentine ant project: A synthesis of past research and prospects for the future

1. The Haleakala Argentine Ant Project is an ongoing effort to study the ecology of the invasive Argentine ant in the park, and if possible to develop a strategy to control this destructive species. 2. Past research has demonstrated that the Argentine ant causes very significant impacts on native arthropods where it invades, threatening a large portion of the park’s biodiversity in subalpine shrubland and alpine aeolian ecosystems. 3. Patterns of spread over the past 30+ years indicate that the invasion process is influenced to a substantial degree by abiotic factors such as elevation, rainfall and temperature, and that the ant has not reached its potential range. Predictions of total range in the park suggest that it has only invaded a small fraction of available suitable habitat, confirming that this species is one of most serious threats to the park’s natural resources. 4. Numerous experiments have been conducted since 1994 in an attempt to develop a method for eradicating the Argentine ant at Haleakala using pesticidal ant baits. Thirty baits have been screened for attractiveness to ants in the park, and ten of these were tested for effectiveness of control in field plots. While some of these baits have been very effective in reducing numbers of ants, none has been able to eliminate all nests in experimental plots. 5. Research into a secondary management goal of ant population containment was initiated in 1996. By treating only expanding margins of the park’s two ant populations with an ant pesticide, rates of outward spread were substantially reduced in some areas. While this strategy was implemented from 1997 to 2004, it was ultimately discontinued after 2004 because of the difficulty and insufficient effectiveness of the technique. 6. In order to achieve the types of results necessary for eradication, the project would probably need to explore the possibility of developing a specialized bait, rather than relying on a commercially produced bait. An alternative would be to pursue approval to use Xstinguish bait, a commercial bait manufactured in New Zealand and not registered for use in the US, which has yielded good results against Argentine ants. Either route would involve significant regulatory hurdles. Because the baits ultimately used would likely be liquid or paste in form, there would also be major logistical challenges in devising methods to successfully apply the baits across the two large ant populations at Haleakala.

Technical Report↗
USGS1972

Map showing length of freeze-free season in the Salina quadrangle, Utah

In general, long freeze-free periods occur at low elevations, and short freeze-free periods occur at high elevations. But some valley floors have shorter freeze-free seasons than the glancing foothills because air cooled at high elevations flows downward and is trapped in the valleys. This temperature pattern occurs in the western part of the quadrangle in Rabbit Valley, Grass Valley, and the Sevier River Valley near Salina. Because year-round weather stations are sparse in Utah, a special technique for estimating length of freeze-free season was developed by Dr. Gaylen L. Ashcroft, Assistant Professor of Climatology, Utah State University, and E. Arlo Richardson, State Climatologist, U.S. Weather Bureau, based on average annual temperature, average annual temperature range, average daily temperature range, and average july maximum temperature. This technique was used in preparation of the map showing “Length of 32°F freeze-free season for Utah,” figure 23 in Hydrologic Atlas of Utah (Utah State University and Utah Division of Water Resources, 1968), from which the data for this map were taken.

Utah↗
USGS1951

Flood of August 4-5, 1943, in central West Virginia, with a summary of flood stages and discharges in West Virginia

During the night of August 4-5, 1943, a violent, thunderstorm of unusual intensity occurred in parts of Braxton, Calhoun, Gilmer, Ritchie, and Wirt Counties in the Little Kanawha River Basin in central West Virginia. Precipitation amounted to as much as 15 inches in 2 hours in some sections. As a result, many small streams and a reach of the Little Kanawha River in the vicinity of Burnsville and Gilmer reached the highest stages known. Computations based on special surveys made at suitable sites on representative small streams in the areas of intense flooding indicate that peak discharges closely approach 50 percent of the Jarvis scale. Twenty-three lives were lost on the small tributaries as numerous homes were swept away by the flood, which developed with incredible rapidity during the early morning hours. Damage estimated at $ 1,300,000 resulted to farm buildings, crops, land, livestock, railroads, highways, and gas- and oil-producing facilities. Considerable permanent land damage resulted from erosion and deposition of sand and gravel.

West Virginia↗
USGS1987

Quality of ground water in Idaho

The major aquifers in Idaho are categorized under two rock types, sedimentary and volcanic, and are grouped into six hydrologic basins. Areas with adequate, minimally adequate, or deficient data available for groundwater-quality evaluations are described. Wide variations in chemical concentrations in the water occur within individual aquifers, as well as among the aquifers. The existing data base is not sufficient to describe fully the ground-water quality throughout the State; however, it does indicate that the water is generally suitable for most uses. In some aquifers, concentrations of fluoride, cadmium, and iron in the water exceed the U.S. Environmental Protection Agency's drinking-water standards. Dissolved solids, chloride, and sulfate may cause problems in some local areas. Water-quality data are sparse in many areas, and only general statements can be made regarding the areal distribution of chemical constituents. Few data are available to describe temporal variations of water quality in the aquifers. Primary concerns related to special problem areas in Idaho include (1) protection of water quality in the Rathdrum Prairie aquifer, (2) potential degradation of water quality in the Boise-Nampa area, (3) effects of widespread use of drain wells overlying the eastern Snake River Plain basalt aquifer, and (4) disposal of low-level radioactive wastes at the Idaho National Engineering Laboratory. Shortcomings in the ground-water-quality data base are categorized as (1) multiaquifer sample inadequacy, (2) constituent coverage limitations, (3) baseline-data deficiencies, and (4) data-base nonuniformity.

Water Supply Paper↗
USGS1944

Surface water resources of Iowa for the period October 1, 1940 to September 30, 1942

The State and Federal cooperative program for the systematic collection of stream-flow records in Iowa was initiated in L914, although a few records were obtained by special arrangements during an earlier period. Since the beginning of the cooperative program measurements of stage or discharge have been obtained at about 100 stations on Iowa streams and lakes for periods of various lengths. The longest records are those for the Mississippi River at Le Claire and Keokuk where authenticated data have been used to extend the record back to 1873 with decreasing accuracy for the earlier years. In addition to the records of daily stages or discharges, hundreds of measurements of a miscellaneous character also have been made at other points.

Iowa↗
USGS2007

Remotely Sensed Data Collections: Offerings from EROS

The U.S. Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) maintains a wide variety of remotely sensed data collections that contain a wealth of information about the Earth’s land surfaces. Acquired by special sensors carried aboard civilian satellites and aircraft, the images and other data in these collections provide a unique perspective of the terrestrial environment. They represent invaluable resources for scientists, resource managers, policy makers, and educators to use in studying such things as natural hazards, conservation issues, land use and economic development, and environmental change at local, regional, and global levels. Different types of sensors record different types of information, resulting in diverse data products, each with its own particular strengths. Highlighted here are eight remotely sensed data collections that are currently available from EROS.

Fact Sheet↗
USGS1949

Ground-water in the Austin area, Lander County, Nevada

The U.S. Geological Survey, in cooperation with the State Engineer of Nevada, made a preliminary survey of ground-water conditions in the Austin area, Nev., during the period July 25 to 28, 1949. The purpose was to evaluate ground-water conditions with special reference to the quantity of ground water that might be available in the area--an adequate water supply has been a constant problem throughout the history of the Austin area. The investigation was made by the writer under the supervision of Thomas W. Robinson, district engineer, Ground Water Branch, U.S. Geological Survey. Material assistance was given in the field by local residents. Frank Bertrand, water commissioner, Thomas Peacock, county assessor, and George McGinnis, county commissioner, guided the writer to springs new utilized by the town of Austin and rendered other valuable field assistance.

Nevada↗
USGS1989

Stream temperature investigations: field and analytic methods

This document provides guidance to the user of the U.S. Fish and Wildlife Service’s Stream Network Temperature Model (SNTEMP). Planning a temperature study is discussed in terms of understanding the management objectives and ensuring that the questions will be accurately answered with the modeling approach being used. A sensitivity analysis of SNTEMP is presented to illustrate which input variables are most important in predicting stream temperatures. This information helps prioritize data collection activities, highlights the need for quality control, focuses on which parameters can be estimated rather than measured, and offers a broader perspective on management options in terms of knowing where the biggest temperature response will be felt. All of the major input variables for stream geometry, meteorology, and hydrology are discussed in detail. Each variable is defined, with guidance given on how to measure it, what kind of equipment to use, where to obtain it from another agency, and how to calculate it if the data are in a form other than that required by SNTEMP. Examples are presented for the various forms in which water temperature, discharge, and meteorological data are commonly found. Ranges of values for certain input variables that are difficult to measure of estimate are given. Particular attention is given to those variables not commonly understood by field biologists likely to be involved in a stream temperature study. Pertinent literature is cited for each variable, with emphasis on how other people have treated particular problems and on results they have found. Model calibration, verification, and validation steps are defined and outlines, with measures of "goodness-of-fit" given for comparing simulated stream temperatures with observed values. The question of how good is good enough is explored, and attention is given to the kinds of simulation and data reduction errors that one should be alert for. Some special cases dealing with ice and reservoir temperature are mentioned. Special attention is given to understanding micro-thermal habitats that act as important thermal refugia under low flow conditions; their causes, extent, and management implications are discussed. Alternative public domain stream and reservoir temperature models are contrasted with SNTEMP. A distinction is made between steady-flow and dynamic-flow models and their respective capabilities. Regression models are offered as an alternative approach for some situations, with appropriate mathematical formulas suggested. Appendices provide information on State and Federal agencies that are good data sources, vendors for field instrumentation, and small computer programs useful in data reduction.

Report↗
USGS2014

Brine contamination to aquatic resources from oil and gas development in the Williston Basin, United States

The Williston Basin, which includes parts of Montana, North Dakota, and South Dakota in the United States and the provinces of Manitoba and Saskatchewan in Canada, has been a leading domestic oil and gas producing region for more than one-half a century. Currently, there are renewed efforts to develop oil and gas resources from deep geologic formations, spurred by advances in recovery technologies and economic incentives associated with the price of oil. Domestic oil and gas production has many economic benefits and provides a means for the United States to fulfill a part of domestic energy demands; however, environmental hazards can be associated with this type of energy production in the Williston Basin, particularly to aquatic resources (surface water and shallow groundwater) by extremely saline water, or brine, which is produced with oil and gas. The primary source of concern is the migration of brine from buried reserve pits that were used to store produced water during recovery operations; however, there also are considerable risks of brine release from pipeline failures, poor infrastructure construction, and flow-back water from hydraulic fracturing associated with modern oilfield operations. During 2008, a multidisciplinary (biology, geology, water) team of U.S. Geological Survey researchers was assembled to investigate potential energy production effects in the Williston Basin. Researchers from the U.S. Geological Survey participated in field tours and met with representatives from county, State, tribal, and Federal agencies to identify information needs and focus research objectives. Common questions from agency personnel, especially those from the U.S. Fish and Wildlife Service, were “are the brine plumes (plumes of brine-contaminated groundwater) from abandoned oil wells affecting wetlands on Waterfowl Production Areas and National Wildlife Refuges?” and “are newer wells related to Bakken and Three Forks development different than the older, abandoned wells (in terms of potential for affecting aquatic resources)?” Of special concern were the wetland habitats of the ecologically important Prairie Pothole Region, which overlays a part of the Williston Basin and is recognized for the production of a majority of North America’s migratory waterfowl. On the basis of the concerns raised by on-the-ground land managers, as well as findings from previous research, a comprehensive study was developed with the following goals: summarize existing information pertaining to oil and gas production and aquatic resources in the Williston Basin; assess brine plume migration from new and previously studied sites in the Prairie Pothole Region; perform a regional, spatial evaluation of oil and gas production activities and aquatic resources; assess the potential for brine contamination to wetlands and streams; and hold a decision analysis workshop with key stakeholders to discuss issues pertaining to oil and gas production and environmental effects and to identify information gaps and research needs. This report represents an initial, multidisciplinary evaluation of measured and potential environmental effects associated with oil and gas production in the Williston Basin and Prairie Pothole Region. Throughout this report there are reviews of current knowledge, and discussions relating to data gaps and research needs. On the basis of the information presented, future research needs include: regional geophysical and water-quality assessments to establish baselines for current conditions and estimate the extent of previous brine contamination, investigations into the direct effects of brine to biotic communities, and evaluations to identify the most effective techniques to mitigate brine contamination.

Montana, North Dakota↗
USGS1950

A comparative study of mean-section and mid-section methods for computation of discharge measurements

In February, 1949, Mr. J. V. B. Wells, Chief of the Surface Water Branch, appointed a committee of three hydraulic engineers assigned to the Washington office to make a comparative study of the relative merits of the mean-section and mid-section methods of computing discharge measurements. this was done in order that there might be a basis for either adhering to the present "official" method, or adopting another method as the "official" one. This study is based on a collection of field data consisting of discharge measurements made with approximately four times the usual number of observations. There was a total of 213 of these special measurements made by all the district offices. The two methods of computation were examined as to accuracy and time savings. This was done by selecting observation stations from the special measurements to arrive at a synthetic measurement with the usual number of observations. This normal measurement was then computed by both the mean-section and mid-section method of computation for a comparison of results in discharge. A record was kept of the time consumed for computing and checking measurements so that any time savings in either method could be found. Much of the computation work was done in four of the district offices, with a variety in personnel as to grade and to experience in the use of the two methods.

Open-File Report↗
USGS1980

Map data catalog

The National Cartographic Information Center (NCIC) is the information branch of the National Mapping Program, U.S. Geological Survey. NCIC's mission is to help users gain better, faster, low-cost access to the cartographic holdings of Federal, State, and private agencies. This catalog tells how to order a wide range of mapping byproducts that may help to fill one or more of your special needs. For each such product, the catalog: - Describes and illustrates the product offered. - Explains the scope of geographic coverage available. - Lists typical uses of the product. - Explains how to order the products you need. Only a few of the products listed in this catalog are stocked. Most of them must be custom-produced to meet your particular requirement. Prices for the variety of products, formats and sizes are contained in a separate and periodically updated list. The price list is available free upon request from any NCIC office.

Report↗
USGS1906

Geology and underground waters of the Arkansas Valley in eastern Colorado

In the valley of Arkansas River in southeastern Colorado there is an area of considerable extent in which artesian flows are available. During the last ten years numerous wells have been sunk to develop this important resource and, in most cases in the lower lands, abundant water supplies have been obtained. The principal water-bearing bed is the "Dakota" formation, which consists of two sheets of porous sandstone separated by a small body of clay and overlain in the greater portion of the area by a mass of impervious shales. The sandstones receive their waters from, rainfall and from the sinking of streams along the foothills of the Rocky Mountains and on some of the higher slopes south of the Arkansas Valley. In the passage of this sandstone underground, the waters which it contains are held down by the overlying shales, but, as some of the sandstone outcrops are at relatively low levels to the east only a moderate head or pressure is sustained. On account of this low head, artesian flows are available only in the lower lands, and one of the principal objects of this investigation has been the determination of the area in which flows are to be expected. The "Dakota" sandstone and associated formations do not lie level, or even slope regularly to the east, but are flexed into low arches and shallow troughs of considerable complexity of configuration. Accordingly, in investigating this source of water supply, it has been necessary to ascertain the structure and distribution of the various formations in order to indicate the variations in depth to the water-bearing stratum. The principal results of these investigations are set forth: (1) In the geologic map (Pl. VI), which shows the distribution of the formations on the surface; (2) in the map, Pl. XXV, which shows the depth to the water-bearing horizon, the area in which flows are expected, the head of the underground waters, and other features, and (3) in the cross sections (Pls. VII and XXIII), which show the principal underground features. The investigation has been in progress for several years and is an extension of the preliminary examination of the region by G. K. Gilbert in 1894 and 1895. For the western portion of the area the maps and texts of the Pueblo, Elmoro, Walsenburg, Spanish Peaks, and Pikes Peak folios have been utilized as far as practicable. For the central and eastern portions the larger features of the geology have been specially mapped, and considerable detailed mapping has been done in the region south and southeast of Canyon and Colorado Springs. In the field work I have been assisted by Mr. C. A. Fisher, who has examined in detail the Nepesta quadrangle and contributed numerous other data. Dr. W. S. Tangier Smith and Messrs. C. E. Sicbenthal and W. T. Lee have made observations in certain areas. Much valuable information respecting wells has been furnished by Mr. William Archer, of the Atchison, Topeka and Santa Fe Railway Company, and Mr. C. H. McVay, well driller at Rocky Ford.

Colorado↗
USGS1982

Guidelines for determining flood flow frequency: Bulletin #17B of the Hydrology Subcommittee

In December 1967, Bulletin No. 15, "A Uniform Technique for Determining Flood Flow Frequencies," was issued by the Hydrology Committee of the Water Resources Council. The report recommended use of the Pearson Type III distribution with log transformation of the data (log-Pearson Type III distribution) as a base method for flood flow frequency studies. As pointed out in that report, further studies were needed covering various aspects of flow frequency determinations. In March 1976, Bulletin 17, "Guidelines for Determining Flood Flow Frequency" was issued by the Water Resources Council. The guide was an extension and update of Bulletin No. 15. It provided a more complete guide for flood flow frequency analysis incorporating currently accepted technical methods with sufficient detail to promote uniform application. It was limited to defining flood potentials in terms of peak discharge and exceedance probability at locations where a systematic record of peak flood flows is available. The recommended set of procedures was selected from those used or described in the literature prior to 1976, based on studies conducted for this purpose at the Center for Research in Water Resources of the University of Texas at Austin (summarized in Appendix 14) and on studies by the Work Group on Flood Flow Frequency. The "Guidelines" were revised and reissued in June 1977 as Bulletin 17A. Bulletin 17B is the latest effort to improve and expand upon the earlier publications. Bulletin 17B provides revised procedures for weighting a station skew value with the results from a generalized skew study, detecting and treating outliers, making two station comparisons, and computing confidence limits about a frequency curve. The Work Group that prepared this revision did not address the suitability of the original distribution or the generalized skew map. Major problems are encountered when developing guides for flood flow frequency determinations. There is no procedure or set of procedures that can be adopted which, when rigidly applied to the available data, will accurately define the flood potential of any given watershed. Statistical analysis alone will not resolve all flood frequency problems. As discussed in subsequent sections of this guide, elements of risk and uncertainty are inherent in any flood frequency analysis. User decisions must be based on properly applied procedures and proper interpretation of results considering risk and uncertainty. Therefore, the judgment of a professional experienced in hydrologic analysis will enhance the usefulness of a flood frequency analysis and promote appropriate application. It is possible to standarize many elements of flood frequency analysis. This guide describes each major element of the process of defining the flood potential at a specific location in terms of peak discharge and exceedance probability. Use is confined to stations where available records are adequate to warrant statistical analysis of the data. Special situations may require other approaches. In those cases where the procedures of this guide are not followed, deviations must be supported by appropriate study and accompanied by a comparison of results using the recommended procedures. As a further means of achieving consistency and improving results, the Work Group recommends that studies be coordinated when more than one analyst is working currently on data for the same location. This recommendation holds particularly when defining exceedance probabilities for rare events, where this guide allows more latitude. Flood records are limited. As more years of record become available at each location, the determination of flood potential may change. Thus, an estimate may be outdated a few years after it is made. Additional flood data alone may be sufficient reason for a fresh assessment of the flood potential. When making a new assessment, the analyst should incorporate in his study a review of earlier estimates. Where differences appear, they should be acknowledged and explained.

Bulletin↗
USGS1998

Ecology of Siberian Taimen Hucho taimen in the Lake Baikal Basin

Taimen Hucho taimen historically inhabited most tributaries and littoral areas of Lake Baikal, in south central Siberia, where they supported subsistence and commercial fisheries. Logging, pollution, and overfishing have caused dramatic population declines or local extinction of most stocks. Most of what is known about this species has been published in eastern journals and therefore is not readily available to western scientists. New data collected during the 1980s and 1990s have been combined with other reports to provide an overview of the biology and life history of this species. Taimen are long-lived fish and can reach ages of 29 years and sizes up to 60 kg. Populations can either be strictly riverine or anadromous. Adults from both life histories ascend rivers in spring to spawn and feed, and less extensive migrations occur in fall to prey on spawning omul ( Coregonus autumnalis migratorius ). Principal food items for age 1 and 2 taimen are macroinvertebrates, but young taimen quickly become piscivorous at age 2 when they consume mainly black Baikal grayling ( Thymallus arcticus baicalensis ), and sculpins ( Taracottus kneri, Cottus kesslerij ). Males reach sexual maturity at ages 7 to 8 and later for females at ages 8 to 9. Average egg production per female was about 22,000 eggs. Parasite burdens are heavy but composed of few species and mediated by prey items consumed. This fish is a highly-specialized predator and plays an indispensable role in the structure of fish communities in mountains and foothills. Taimen conservation in the Baikal region is impossible without adoption and implementation of a dedicated rehabilitation program that includes the protection of remaining populations and habitat, and possibly introduction of hatchery-reared fish in selected areas where habitat remains, but parental stocks are low.

Journal of Great Lakes Research↗
USGS1989

Cartography at the U.S. Geological Survey: the National Mapping Division's cartographic programs, products, design, and technology

The U.S. Geological Survey (USGS) is the prime source of many kinds of topographic and special-purpose maps of the United States and its outlying areas. It is also a prime source of digital map data. One main goal of the USGS is to provide large-scale topographic map coverage of the entire United States. Most of the Nation is already covered. We expect that initial coverage will be completed by 1991. For many purposes, many public agencies, private organizations, and individuals need reliable cartographic and geographic knowledge about our Nation. To serve such needs, all USGS maps are compiled to exacting standards of accuracy and content.

General Information Product↗
USGS1946

Section of Morgan formation, Pennsylvanian, at Split Mountain in Dinosaur National Monument, Uintah County, Utah

Extension of the oil pool in the Weber sandstone (Pennsylvanian), in the Rangely oil field, Rio Blanco County, Colorado, subsequent to the completion of the filed work on which Preliminary Chart 16 is based, has stimulated special interest in the beds beneath that sandstone as potential oil reservoirs. In compliance with the demand for additional information concerning these beds, a detailed description of the sequence immediately underlying the Weber sandstone at Split Mountain, Utah, is here given. That part of Split Mountain where the section was measured is approximately 35 airline miles northwest of the town of Rangely. The section itself is shown graphically and somewhat generalized in column 8, sheet 2, Preliminary Chart 16. A more detailed graphic section is presented in the accompanying column section.

Utah↗
USGS2009

Groundwater-quality data in the South Coast Interior Basins study unit, 2008: Results from the California GAMA Program

Groundwater quality in the approximately 653-square-mile South Coast Interior Basins (SCI) study unit was investigated from August to December 2008, as part of the Priority Basins Project of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The GAMA Priority Basins Project was developed in response to Legislative mandates (Supplemental Report of the 1999 Budget Act 1999-00 Fiscal Year; and, the Groundwater-Quality Monitoring Act of 2001 [Sections 10780-10782.3 of the California Water Code, Assembly Bill 599]) to assess and monitor the quality of groundwater used as public supply for municipalities in California, and is being conducted by the U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board (SWRCB). SCI was the 27th study unit to be sampled as part of the GAMA Priority Basins Project. This study was designed to provide a spatially unbiased assessment of the quality of untreated groundwater used for public water supplies within SCI, and to facilitate statistically consistent comparisons of groundwater quality throughout California. Samples were collected from 54 wells within the three study areas [Livermore, Gilroy, and Cuyama] of SCI in Alameda, Santa Clara, San Benito, Santa Barbara, Ventura, and Kern Counties. Thirty-five of the wells were selected using a spatially distributed, randomized grid-based method to provide statistical representation of the study unit (grid wells), and 19 were selected to aid in evaluation of specific water-quality issues (understanding wells). The groundwater samples were analyzed for organic constituents [volatile organic compounds (VOCs), pesticides and pesticide degradates, polar pesticides and metabolites, and pharmaceutical compounds], constituents of special interest [perchlorate and N-nitrosodimethylamine (NDMA)], naturally occurring inorganic constituents [trace elements, nutrients, major and minor ions, silica, total dissolved solids (TDS), and alkalinity], and radioactive constituents [gross alpha and gross beta radioactivity and radon-222]. Naturally occurring isotopes [stable isotopes of hydrogen, oxygen, and carbon, and activities of tritium and carbon-14] and dissolved noble gases also were measured to help identify the sources and ages of the sampled groundwater. In total, 288 constituents and water-quality indicators (field parameters) were investigated. Three types of quality-control samples (blanks, replicates, and matrix spikes) each were collected at approximately 4–11 percent of the wells, and the results for these samples were used to evaluate the quality of the data for the groundwater samples. Field blanks rarely contained detectable concentrations of any constituent, suggesting that contamination was not a significant source of bias in the data obtained from the groundwater samples. Differences between replicate samples generally were less than 10 percent relative standard deviation, indicating acceptable analytical reproducibility. Matrix spike recoveries were within the acceptable range (70 to 130 percent) for most compounds. This study did not attempt to evaluate the quality of water delivered to consumers; after withdrawal from the ground, untreated groundwater typically is treated, disinfected, and/or blended with other waters to maintain water quality. Regulatory thresholds apply to water that is served to the consumer, not to untreated groundwater. However, to provide some context for the results, concentrations of constituents measured in the untreated groundwater were compared with regulatory and nonregulatory health-based thresholds established by the U.S. Environmental Protection Agency (USEPA) and California Department of Public Health (CDPH), and to nonregulatory thresholds established for aesthetic and technical concerns by CDPH. Comparisons between data collected for this study and thresholds for drinking water are for illustrative purposes only, and are not indicative of compliance or noncompliance with those thresholds. Most inorganic constituents that were detected in groundwater samples from the 35 grid wells in the SCI study unit were found at concentrations below drinking-water thresholds; additionally, all detections of organic constituents in SCI grid well samples were below health-based thresholds.

California↗