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Large springs in the United States

What are the largest springs in the United States, how much water do they discharge, and what geologic conditions produce them are questions of much popular interest and considerable scientific and economic importance. Yet the information in regard to large springs has been so widely scattered and so difficult to interpret that most people have only very vague notions on the subject. The present paper is in a sense a by-product of a more comprehensive investigation of the origin, discharge, and quantity of ground water in the United States. It has, however, required, extensive search for data and critical analysis of the data that were obtained. The task would have been virtually impossible except for the hearty cooperation of the district engineers and other members of the water- resources branch of the Geological Survey, who are really coauthors of this paper. I wish to acknowledge especially the help of Kirk Bryan, G. C. Stevens, W. E. Hall, W. E. King, E. L. Williams, H. C. Beckman, C. E. Ellsworth, C. E. McCashin, C. G. Paulsen, W. G. Hoyt, H. T. Stearns, H. D. McGlashan, R. C. Briggs, F. F. Henshaw, W. A. Lamb, G. M. Hall, E. C. LaRue, and A. B. Purton

Water Supply Paper↗

Water levels in observation wells in Santa Barbara County, California, in 1962

Investigation of the ground-water resources of Santa Barbara County was continued during 1962 by the U. S. Geological Survey in cooperation with the Santa Barbara County Water Agency. Monthly water-level measurements were made in 201 wells, in 9 of which automatic water-level recorders were operated. Earlier measurements, covering the period 1941 through 1955, have been published in U.S. Geological Survey Water-Supply Papers (19)43-1957); those for 1:56 through 1961 have been released locally in duplicated form (Muir and Merritt, 1957; Evenson 1950; Miller, 1959; Muir, Merritt, and Miller, 1960; Merritt, 1961; and Muir, 1962). LaRocque, Jr., and others (1950) contains tabulated descriptions of 2,246 wells in existence in 1942 in the several ground-water basins of the county. The same publication also contains many water-level measurements made prior to 1942 by the city of Santa Barbara, Santa Maria Valley Water Conservation District, San Joaquin Power Division of the Pacific Gas and Electric Co., Union Sugar Co., Union Oil Co., and other organizations and individuals. Comprehensive reports on the geology and and ground-water resources of the Santa. Ynez River basin (Upson and Thomasson, 1951, and Wilson, 1959), the south-coast basin (Upson, 1951), the Santa Maria Valley area (Worts, 1951), and the Cuyvma Valley (Upson and Worts, 1951) have been published as Water-Supply Papers 1107, 1467, 1108, 1000, and 1110-B, respectively. A similar report on the San Antonio Creek Valley is in preparation. A report on stream runoff and ground-water storage capacity of the Santa Ynez River Valley (Troxell and Wilson, 1952) was released to the open file in October 1952. In addition to the water-level measurements made by the Geological Survey in 1962, measurements made by the Santa Maria Valley Water Conservation District are included in this report. Not included in this report are miscellaneous measurements made by the U.S. Bureau of Reclamation in wells along the middle reach of the Santa Ynez River between Cachuma Dam and Rucker Crossing.

California↗

Yellowstone grizzly bear investigations: Annual report of the Interagency Grizzly Bear Study Team, 2006

The contents of this Annual Report summarize results of monitoring and research from the 2006 field season. The report also contains a summary of nuisance grizzly bear ( Ursus arctos horribilis ) management actions. The Interagency Grizzly Bear Study Team (IGBST) continues to work on issues associated with counts of unduplicated females with cubs-of- the-year (COY). These counts are used to establish a minimum population size, which is then used to establish mortality thresholds for the Recovery Plan (U.S. Fish and Wildlife Service [USFWS] 1993). After considerable delays due to programming issues, a computer program that defines the rule set used by Knight et al. (1995) to differentiate unique family groups was development and tested in 2005 and 2006. Simulations using observations of collared females with COY were randomly sampled to generate datasets of observations of random females with COY. These datasets were then run though the simulations program to test the accuracy of the rules. Data are currently being summarized. This project has been completed and a manuscript was submitted to the Journal of Wildlife Management. The grizzly bear recovery plan (USFWS 1993) established human-caused mortality quotas. We used the latest information on reproduction and survival to estimate population trajectory in the same simulation model originally used by Harris (1984). A Wildlife Monographs was published in 2006. Additionally, the study team, in cooperation with several quantitative experts, reassessed how population size is indexed and how sustainable mortality rates are established. A draft report was presented to the Yellowstone Ecosystem Subcommittee in spring 2005. It was published as part of the USFWS Delisting Rule (Federal Register Vol. 70, No. 221, Nov. 17, 2005, 69853–69884) and subjected to public comment. This workshop document can be found at http://www.fws.gov/mountain-prairie/species/mammals/grizzly/yellowstone.htm. During the summer of 2006, a second workshop was held to address public comment and professional peer review. The result of this workshop was a supplement to the 2005 workshop document. This supplement can be found at http://www.fws.gov/mountain-prairie/species/mammals/grizzly/yellowstone.htm under the link Revised Methods to Estimate Population Size and Sustainable Mortality Limits. Results of those estimates are provided in Appendix A. Our project addressing the potential application of stable isotopes and trace elements to quantify consumption rates of whitebark pine ( Pinus albicaulis ) and cutthroat trout ( Oncorhynchus clarki ) by grizzly bears was completed. Our manuscript on consumption rates of whitebark pine was published in the Canadian Journal of Zoology 81:763-770. Results of the mercury studies were also published in the Canadian Journal of Zoology 82:493–501. Copies can be found on the IGBST website http://www.nrmsc.usgs.gov/research/igbst-home.htm. Based upon this work, we submitted a proposal to analyze all historic tissue samples from grizzly bears in the ecosystem. That proposal was funded and samples have been sent to a lab for isotopic analysis. We hope to have those results in early 2008. Results of DNA hair snaring work conducted on Yellowstone Lake were submitted and published in the Journal Ursus (Haroldson et al. 2005). Results of this study conducted from 1997–2000 showed a decline in fish use by grizzly bears when compared to earlier work conducted by Reinhart (1990) in 1985–1987. As a consequence, the IGBST submitted a proposal to the National Park Service and received 3 years funding to repeat that work. This project began in 2007. There are 2 graduate students and several field technicians working on the program. We completed the final field season in Grand Teton National Park evaluating habitat use both temporally and spatially between grizzly and black bears ( Ursus americanus ). We continue to use GPS technology that incorporates a spread spectrum communication system. Spread spectrum allows for transfer of stored GPS locations from the collar to a remote receiving station. Results of the 2006 field season are reported here. We plan to complete the final report in late 2007. We continued to monitor the health of whitebark pine in the Greater Yellowstone Ecosystem (GYE) in cooperation with the Greater Yellowstone Whitebark Pine Monitoring Working Group. A summary of the 2006 monitoring is also presented (Appendix B). The IGBST uses counts of winter-killed ungulates to index spring carcass abundance for grizzly bears. Likewise, we use wier counts and stream surveys to index cutthroat trout abundance. We ask Dr. Steve Cherry, Department of Mathematical Sciences, Montana State University-Bozeman, to review the protocols and make recommendations for improving them. That review and recommendations are presented in Appendix C. Finally, the state of Wyoming, following recommendations from the Yellowstone Ecosystem Subcommittee and the IGBST, launched the Bear Wise Community Effort. The focus is to minimize human/bear conflicts, minimize human-caused bear mortalities associated with conflicts, and safeguard the human community. Results of these efforts are detailed in Appendix D. The annual reports of the IGBST summarize annual data collection. Because additional information can be obtained after publication, data summaries are subject to change. For that reason, data analyses and summaries presented in this report supersede all previously published data. The study area and sampling techniques are reported by Blanchard (1985), Mattson et al. (1991 a), and Haroldson et al. (1998).

Idaho, Montana, Wyoming↗

Flood of May 2006 in New Hampshire

From May 13-17, 2006, central and southern New Hampshire experienced severe flooding caused by as much as 14 inches of rainfall in the region. As a result of the flood damage, a presidential disaster declaration was made on May 25, 2006, for seven counties-Rockingham, Hillsborough, Strafford, Merrimack, Belknap, Carroll, and Grafton. Following the flooding, the U.S. Geological Survey, in a cooperative investigation with the Federal Emergency Management Agency, determined the peak stages, peak discharges, and recurrence-interval estimates of the May 2006 flood at 65 streamgages in the counties where the disaster declaration was made. Data from flood-insurance studies published by the Federal Emergency Management Agency also were compiled for each streamgage location for comparison purposes. The peak discharges during the May 2006 flood were the largest ever recorded at 14 long-term (more than 10 years of record) streamgages in New Hampshire. In addition, peak discharges equaled or exceeded a 100-year recurrence interval at 14 streamgages and equaled or exceeded a 50-year recurrence interval at 22 streamgages. The most severe flooding occurred in Rockingham, Strafford, Merrimack, and eastern and northern Hillsborough Counties.

Open-File Report↗

1976 water-quality data in Bear Creek basin, Medford, Oregon

The U.S. Geological Survey, in cooperation with the Rogue Valley Council of Governments, is studying surface-water-quality problems and their causes in the Bear Creek basin of southwestern Oregon. Two specific areas of investigation include: measurements of the quality and quantity of water in the irrigation canals and drainage system and the diel (during a 24-hour period) variation of water-quality parameters in the main stem of Bear Creek. The irrigation and drainage study involves 25 sites in canals and natural drainageways. One hundred thirty-three samples were collected for analysis, and discharge was determined at the time of collection. The diel study includes six sites on Bear Creek. On August 23-24, four parameters were monitored at all six sites during a 24-hour period.

Oregon↗

Potentiometric surface, 2013, and water-level differences, 1991-2013, of the Carrizo-Wilcox aquifer in northwest Louisiana

The Carrizo-Wilcox aquifer is the primary source of fresh groundwater for public supply as well as industrial, agricultural, and domestic uses in several parishes in northwestern Louisiana, including Bienville, Bossier, Caddo, De Soto, Natchitoches, Red River, Sabine, and Webster. In 2010, about 19 million gallons per day (Mgal/d) were withdrawn from the Carrizo-Wilcox aquifer in Louisiana. This is an increase of over 6 Mgal/d from 1990 withdrawal amounts. The largest increase in withdrawals occurred in Caddo (3.79 Mgal/d) and De Soto Parishes (2.32 Mgal/d), whereas the largest decrease in withdrawals occurred in Natchitoches Parish (1.17 Mgal/d). Groundwater withdrawals from the Carrizo-Wilcox aquifer have caused water-level declines throughout much of the aquifer in the study area. Additional knowledge about the effects of withdrawals on water levels and flow directions in the Carrizo-Wilcox aquifer are needed to assess current conditions in the aquifer. In 2012, the U.S. Geological Survey (USGS) in cooperation with the Louisiana Department of Natural Resources began a study to document current water levels and water-level changes in selected aquifers. This report presents data and maps that illustrate the potentiometric surface of the Carrizo-Wilcox aquifer during March–May 2013 and water-level differences from 1991 to 2013. The potentiometric surface map can be used for determining the direction of groundwater flow, hydraulic gradients, and effects of withdrawals on the groundwater resource. The rate of groundwater movement also can be estimated from the gradient when the hydraulic conductivity is applied. Water-level data collected for this study are stored in the USGS National Water Information System (NWIS) ( http://waterdata.usgs.gov/nwis ) and are on file at the USGS office in Baton Rouge, La.

Louisiana↗

Methods for peak-flow frequency analysis for streamgages in or near Montana, North Dakota, South Dakota, and Wyoming

The U.S. Geological Survey, in cooperation with the Montana Department of Natural Resources and Conservation, North Dakota Department of Water Resources, South Dakota Department of Transportation, and the Wyoming Water Development Office, has developed standard methods of peak-flow frequency analysis for studies in Montana, North Dakota, South Dakota, and Wyoming. These methods describe the implementation of national flood frequency guidelines described in Bulletin 17C ( https://doi.org/10.3133/tm4B5 ) for the four States and deviations from Bulletin 17C standard procedures to accommodate unusual hydrologic conditions. A U.S. Geological Survey data release accompanying this report ( https://doi.org/10.5066/P1WHRK8H ) provides example peak-flow frequency analyses for selected streamgages in the study area. The methods described in this report can be used to publish similar data releases for other streamgages in the study area.

Montana, North Dakota, South Dakota, Wyoming↗

Report on the operations of the coal-testing plant of the United States Geological Survey at the Louisiana Purchase Exposition, Saint Louis, Missouri, 1904: Part I.--Field work, classification of coals, chemical work

The authority for conducting at the Louisiana Purchase Exposition an investigation of the coals and lignites of the United States is contained in the act of Congress providing for the urgent deficiencies in the appropriations for the fiscal year 1905, and approved February 18, 1904, as follows: For analyzing and testing. at the Louisiana Purchase Exposition the coals and lignites of the United States, in order to determine their fuel values mid the most economical method for their utilization for different purposes, under the supervision of the Director of the United States Geological Survey, thirty thousand dollars, to be available until expended: Provided, That all testing machinery and all coals and lignites to be tested shall be contributed without charge to the Government. In the general deficiency bill approved April 27, 1904, an additional appropriation of $30,000 was provided, making the total sum appropriated for this work $60,000. For carrying out the provisions of these acts the Director of the Geological Survey appointed a committee, consisting of Edward W. Parker, Joseph A. Holmes, and Marius R. Campbell, to direct the construction and operation of the plant. It will be observed that under the law authorizing this work all of the testing machinery and all of the coals to be tested had to be furnished to the Government free of charge. Under these conditions it was not possible to equip an ideal testing plant, and the assembling and construction of such equipment as conld be obtained under these provisions entailed some annoying delays in the completion of the plant. In addition to this, the delivery of a considerable quantity of operating and conveying apparatus purchased from the Link Belt Machinery Company, of Chicago, was delayed by a strike in the works of that company. As a result of these combined influences the plant was not put in operation until the 1st of September. Notwithstanding these delays, the committee feels that through the hearty and patriotic cooperation of a large number of manufacturers of apparatus and machinery it was able to collect and install, within a notably short time, a testing plant that was well suited for such pioneer work.

Missouri↗

Alkylphenols, other endocrine-active chemicals, and fish responses in three streams in Minnesota — Study design and data, February-September 2007

This report presents the study design and environmental data for an integrated chemical and biological study of three streams (South Fork Crow River, Redwood River, and Grindstone River) that receive wastewater in Minnesota. The objective of the study was to identify distribution patterns of endocrine-active chemicals and other organic chemicals indicative of wastewater, and to identify fish responses in the same streams. Endocrine-active chemicals are a class of chemicals that interfere with the natural regulation of endocrine systems, and an understanding of their distribution in aquatic systems is important so that aquatic organism exposure can be evaluated. This study was a cooperative effort of the U.S. Geological Survey (USGS), the Minnesota Pollution Control Agency, and St. Cloud State University (St. Cloud, Minn.). The USGS collected and analyzed water and quality-assurance samples and measured streamflow during six sampling events in each of three streams. Water samples were collected upstream from and at two successive points downstream from wastewater-treatment plant (WWTP) effluent discharge and from treated effluent from February through September 2007. Bed-sediment samples were collected during one sampling period at each of the stream locations. Water and bed-sediment samples were analyzed for endocrine-active chemicals including alkylphenols, alkylphenol polyethoxylates, and nonylphenol ethoxycarboxlylates (NPECs). Water samples also were analyzed for major ions, nutrients, and organic carbon. In addition, as part of an intensive time-series investigation, the USGS staff collected daily water samples for 8 weeks from the Redwood River near Marshall, Minn., for analyses of total alkylphenols and atrazine. St. Cloud State University staff collected and analyzed fish to determine male fish responses at all water sampling sites and at an additional site near the discharge of wastewater-treatment plant effluent to these streams. Male fish responses included the presence and concentration of vitellogenin in plasma, gonadosomatic indices, and histological characterizations of liver and testes tissue. Hydrologic, chemical and biological characteristics were different among sites. The percentage of streamflow contributed by WWTP effluent (ranging from less than 1 to 79 percent) was greatest at the South Fork Crow River and least at the Grindstone River. WWTP effluent generally contributed the greatest percentage of streamflow during winter and late summer when streamflows were low. A wide variety of chemicals were detected. More chemicals were detected in WWTP effluent samples than in stream samples during most time periods. The most commonly detected chemicals in samples collected monthly and analyzed at the USGS National Research Program Laboratory were 2,6-di- tert -butyl-1,4-benzoquinone, 2,6-di- tert -butyl-4-methylphenol, 3- beta -coprostanol, 4-methylphenol, 4-nonylphenol (NP), 4- tert -octylphenol, bisphenol A, cholesterol, ethylenediaminetetraacetic acid, and triclosan. The chemicals 4-nonylphenolmonoethoxycarboxylate (NP1EC), 4-nonylphenoldiethoxycarboxylate (NP2EC), and 4-nonylphenoltriethoxycarboxylate (NP3EC) also were detected. Excluding nondetections, the sum of NP1EC through NP3EC concentrations ranged from 5.1 to 260 µg/L among all samples. NP was detected in upstream, effluent, and downstream samples in each stream during at least one time period. NP was detected in 49 percent of environmental samples. Excluding nondetections, concentrations of NP ranged from 100 to 880 nanograms per liter among all samples. NP was also detected in more than one-half of the bed-sediment samples. The most commonly detected wastewater indicator chemicals in samples analyzed by schedule 4433 at the USGS National Water Quality Laboratory were 3,4-dichlorophenyl isocyanate, acetyl-hexamethyl-tetrahydronaphthalene, benzophenone, cholesterol, hexahydrohexamethyl-cyclopenta-benzopyran, N,N-diethyl- meta -toluamide, and tri(dichloroisopropyl) phosphate. Male fish responses were the focus of the fish analyses, and 508 male fish were collected among all sampling sites. Vitellogenin was detected in 57 percent of the 415 male fish analyzed; concentrations ranged from an estimated value of 0.1 to 330 micrograms per milliliter (µg/mL) (average of 17.1 µg/mL). Intersex (the presence of oocytes in testes tissue) was observed in only one fathead minnow from an upstream site on the Grindstone River.

Minnesota↗

Water quality, discharge, and groundwater levels in the Palomas, Mesilla, and Hueco Basins in New Mexico and Texas from below Caballo Reservoir, New Mexico, to Fort Quitman, Texas, 1889-2013

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department, compiled data from various sources to develop a dataset that can be used to conduct an assessment of the total dissolved solids in surface water and groundwater of the Palomas, Mesilla, and Hueco Basins in New Mexico and Texas, from below Caballo Reservoir, N. Mex., to Fort Quitman, Tex. Data include continuous surface-water discharge records at various locations on the Rio Grande; surface-water-quality data for the Rio Grande collected at selected locations in the Palomas, Mesilla, and Hueco Basins; groundwater levels and groundwater-quality data collected from selected wells in the Palomas and Mesilla Basins; and data from several seepage investigations conducted on the Rio Grande and selected drains in the Mesilla Basin.

New Mexico, Texas↗

Evaluation of sample preservation methods for analysis of selected volatile organic compounds in groundwater at the Idaho National Laboratory, Idaho

During 2020, water samples were collected from 25 wells completed in the eastern Snake River Plain aquifer and from 1 well completed in perched groundwater above the aquifer at the Idaho National Laboratory to determine the effect of different sample-preservation methods on the laboratory determinations of concentrations of volatile organic compounds. Paired-sample sets were collected at each well. One sample in each set was preserved with hydrochloric acid, and one sample without. Both samples were chilled after collection and during shipping to the laboratory for analysis. The samples were analyzed for 61 volatile organic compounds at the U.S. Geological Survey National Water Quality Laboratory in cooperation with the U.S. Department of Energy. A comparison of the reproducibility of the analyses of co-located unpreserved and preserved samples by a relative percent difference method determined that all sample pairs were statistically equivalent. Using a normalized absolute difference method, 81 percent of the analyses were found to be statistically equivalent. This study confirms that the results of analyses of historical collected samples, which were preserved by chilling only, are statistically comparable to the analyses of samples being currently collected and preserved by both hydrochloric acid and chilling, and thus are valid for use in future geochemical evaluations.

Idaho↗

Base-flow studies Nueces River, Texas quantity and quality, November 23-25, 1964

An investigation was made by the U.S. Geological Survey, under a cooperative agreement with the Texas Water Development Board, to determine the changes in quantity and chemical quality of the base flow of the Nueces River in a 52.2-mile reach beginning at U.S. Highway 90 and extending to the crossing of Farm Road 1025 north of Crystal City. Knowledge of the changes in quantity and chemical quality of base flow is necessary for any evaluation of the effectiveness of the river channel in conveying water released from potential upstream reservoirs. The investigation was made November 23-25, 1964, during a period when evaporation and transpiration were small and the discharge past the stream-gaging station, Nueces River below Uvalde, was constant. Floods of September 1964 contributed considerably to the recharge of the alluvium in the reach investigated, resulting in a higher than average base flow.

Texas↗

Man against volcano: The eruption on Heimaey, Vestmann Islands, Iceland

The U.S. Geological Survey carries out scientific studies in the geological, hydrological, and cartographic sciences generally within the 50 states, but also in cooperation with scientific organizations in many foreign countries for the investigation of unusual earth science phenomena throughout the world. The following material discusses the impact of the 1973 volcanic eruption of Eldfell on the fishing port of Vestmannaeyjar on the island of Heimaey, Iceland. Before the eruption was over, approximately one-third of the town of Vestmannaeyjar had been obliterated but, more importantly, the potential damage had been reduced markedly by the spraying of seawater onto the advancing lava flows, causing them to be slowed, stopped, or diverted from the undamaged portion of the town. The Survey's interest and involvement in the Heimaey eruption in Iceland was occasioned by the possibility that the procedures used to control the course of the flowing lava and to reduce the damage in a modern town may some day be needed in Hawaii and possibly even in the continental United States. This publication is based on the observations of two USGS geologists, Richard S. Williams, Jr. and James G. Moore, as well as on information from the Icelandic Ministry for Foreign Affairs, Icelandic scientists' reports through the Center for Short-Lived Phenomena, and other published scientific reports. A number of Icelandic scientists studied the scientific aspects of the eruption and the engineering aspects of the control of lava flows, in particular, Professors Thorbjb'rn Sigurgeirsson and Sigurdur Thorarinsson of the University of Iceland Science Institute. Also, Icelandic governmental officials provided logistical and other support, in particular, Mr. Steingnmur Hermannsson, Director, Icelandic National Research Council and Professor Magnus Magnusson, Director, University of Iceland Science Institute.

Vestmannaeyjar↗

Water table in Long Island, New York, March 1971

The geologic framework and the hydrologic situation in Long Island are periodically reviewed by the U.S. Geological Survey as new knowledge is obtained from current investigations. This work is done through cooperative programs with Nassau and Suffolk County agencies and the New York State Department of Environmental Conservation. A unique opportunity to update many of the hydrogeologic maps occurred when the Geological Survey's Mineola, N.Y., office participated in the New England River Basins Commission's "Long Island Sound Study." This map, one of a series of open-file maps showing the updated information, was compiled from data obtained from G. E. Kimmel (written commun., July 1972) and Jensen and Soren (in press). Comparison of the March 1971 data with similar data for March 1970 (Kimmel, 1970) shows virtually no change in water levels on Long Island during the 12 month period, except for a slight decline in levels in central Suffolk County.

New York↗

Investigations into near-real-time surveying for geophysical data collection using an autonomous ground vehicle

The U.S. Geological Survey and the National Aeronautics and Space Administration are cooperatively investigating the utility of unmanned vehicles for near-real-time autonomous surveys of geophysical data collection. Initially focused on unmanned ground vehicle collection of magnetic data, this cooperative effort has brought unmanned surveying, precision guidance, near-real-time communication, on-the-fly data processing, and near-real-time data interpretation into the realm of ground geophysical surveying, all of which offer advantages over current methods of manned collection of ground magnetic data. An unmanned ground vehicle mission has demonstrated that these vehicles can successfully complete missions to collect geophysical data, and add advantages in data collection, processing, and interpretation. We view the current experiment as an initial phase in further unmanned vehicle data-collection missions, including aerial surveying.

California↗

Earth Mapping Resources Initiative protocols—Sampling hard-rock mine waste and perpetual mine water sources

Supporting the overarching goal to evaluate critical minerals nationwide, the mine waste characterization effort in the U.S. Geological Survey (USGS) Earth Mapping Resources Initiative has created a series of protocols to standardize sampling carried out under this effort by the participating State geological surveys and their cooperators. The protocols are based on published, reviewed methods that can be deployed in the field. The protocols include (1) collecting and processing composite samples of mine and mill waste, including tailings, waste rock, gangue, heap leach piles, ore stockpiles, slag, or other mineralized and processed materials and (2) collecting and preserving water samples from perpetual or long-term mine water sources. The protocols also specify information to document on field sheets and detail the collection of geospatial data. The analytical methods used by the USGS and USGS contract laboratories are described in this report, including the data delivery pathway for USGS-derived data.

Scientific Investigations Report↗

Potentiometric surface of the Cockfield aquifer in southeastern Arkansas and the Wilcox aquifers in southern and northeastern Arkansas, October 1996-July 1997

The Cockfield and Wilcox aquifers are secondary sources of water for local use in southern and northeastern Arkansas, where in 1995 more than 51 million gallons per day of water was withdrawn. During October 1996 to July 1997, water levels in the Cockfield and Wilcox aquifers were measured in 104 wells in Arkansas. The potentiometric surface data reveal spatial trends in both aquifers across the study areas. The regional direction of ground-water flow of the Cockfield aquifer is generally southeastward, away from the outcrop area, except where affected by intense ground-water withdrawals. The potentiometric surface indicates that heavy pumpage has altered or reversed the natural direction of flow in some areas. Flow in these areas is toward centers of pumping within cones of depression. A cone of depression caused by the pumpage near Greenville, Mississippi, extends into Chicot, Desha, and Drew Counties. This cone of depression has altered flow patternArkansas. Long-term hydrographs of six wells, during the period 1971-1996, showed water levels declined at an average rate between 0.5 and 1.0 foot per year at these locations. The regional direction of ground-water flow in the Wilcox aquifers is generally toward the east and south, away from the outcrop except where water levels are affected by intense ground-water withdrawals. The potentiometric surface indicates that heavy pumpage has altered or reversed the natural direction of ground-water flow in some areas. Flow in these areas is toward centers of pumping within cones of depression. Two cones of depression are centered in the vicinity of Paragould and West Memphis, Arkansas, where ground-water withdrawals have altered the natural direction of flow. Long-term hydrographs of seven wells, during the period 1971- 1996, show water-level declines in the Wilcox aquifer in northeastern Arkansas generally were between 0.5 and 1.0 foot per year but were more than 1.0 foot per year in two wells. The U.S. Geological Survey in cooperation with the Arkansas Soil and Water Conservation Commission and the Arkansas Geological Commission has monitored water levels in the Cockfield and Wilcox aquifers since the 1960's. During October 1996 to July 1997, 53 water-level measurements were made in wells completed in the Cockfield aquifer, 13 water-level measurements were made in wells completed in the Wilcox aquifer in southern Arkansas, and 38 water-level measurements were made in wells com- pleted in the Wilcox aquifer in northeastern Arkansas. The purpose of these measurements was to provide information to describe the recent potentiometric surfaces and long-term water-level trends in the Cockfield and Wilcox aquifers. This report presents the results as potentiometric surface maps and as long-term water-level hydrographs.

Arkansas↗

Historical Ground-Water Development in the Salinas Alluvial Fan Area, Salinas, Puerto Rico, 1900-2005

The Salinas alluvial fan area has historically been one of the most intensively used agricultural areas in the South Coastal Plain of Puerto Rico. Changes in agricultural practices and land use in the Salinas alluvial fan have also caused changes in the geographic distribution of ground-water withdrawals from the alluvial aquifer. As a result, the ground-water balance and ground-water flow pattern have changed throughout the years and may explain the presence of saline ground water along parts of the coast at present. By providing a reconstruction of historical ground-water development in the Salinas alluvial fan area, from the initial years of aquifer development at about 1900 to the most recent conditions existing in 2005, water resources managers and planners can use the results of the analysis for a more complete understanding of aquifer conditions especially pertaining to water quality. This study effort was conducted by the U.S. Geological Survey in cooperation with the Puerto Rico Department of Natural and Environmental Resources as a contribution in the management of the Jobos Bay National Estuarine Research Reserve. The study area encompasses about 20 mi2 (square miles) of the extensive South Coastal Plain alluvial aquifer system (fig. 1). The study area is bounded to the north by foothills of the Cordillera Central mountain chain, to the south by the Caribbean Sea, and to the east and west by the Rio Nigua de Salinas and the Quebrada Aguas Verdes, respectively. Fan-delta and alluvial deposits contain the principal aquifers in the study area.

Scientific Investigations Map↗