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USGS1984

Water-table contours, directions of ground-water movement, and measurements of inflow to American Falls Reservoir, southeastern Idaho, April 1984

In 1978 the U.S. Geological Survey began a 5-year study of the High Plains regional aquifer system to provide hydrologic information for evaluating the effects of long-term development of the aquifer and to develop a capability for predicting aquifer response to alternative changes in ground-water management. By use of a digital model, this report presents a quantitative description of the High Plains aquifer in Oklahoma. The High Plains aquifer consists predominantly of the Tertiary Ogallala Formation and overlying Quaternary alluvium and terrace deposits which are hydraulically connected to the High Plains aquifer. Much of the aquifer is underlain by formations of Permian through Cretaceous age, which generally have very small hydraulic conductivities. In some areas parts of underlying Triassic, Jurassic, or Cretaceous rocks are hydraulically connected with the aquifer. The High Plains aquifer is a water-table aquifer in which water moves generally to the east-southeast. Before the beginning of extensive irrigation of the 1960's, the aquifer was essentially in dynamic equilibrium with recharge from precipitation balanced by natural discharge from the aquifer. Ground-water discharge appeared in streams leaving the area or was returned to the atmosphere through evapotranspiration. Accurate records of irrigation pumpage are not available from the High Plains. In order to estimate irrigation pumpage, published records of crop distribution were used and a consumptive use was assigned to each principal irrigated crop. This method gave an estimated irrigation demand. Pumpage was taken as a percentage of the total irrigation demand. Irrigation has decreased ground-water discharge from the High Plains aquifer. Ground-water discharge was estimated as approximately 118 cubic feet per second in 1980. A finite-difference digital model was used to simulate flow in the High Plains aquifer. The recharge was adjusted so that 1980 ground-water discharge was 118 cubic feet per second, the estimated ground-water discharge for 1980. Recharge in the eastern half of the modeled area was 0.45 inch per year; one-half this value was used in the western half of the modeled area. Hydraulic conductivity was divided into three zones: 19.3 feet per day in the eastern zone; 16.2 feet per day in the central zone; and 8.28 feet per day in the western zone. A specific yield of 14.7 percent was used in the model. Using all these parameters, the model was calibrated so that the mean difference between predevelopment modeled and measured head was -0.044 foot. Following the calibration procedure, the model was used to predict the volumes of water in storage and distribution of saturated thickness in 1993 and 2020 using the 1980 pumping rates. The calculated quantity of water in storage in the aquifer in 1941 (predevelopment) was approximately 135.2 million acre-feet; in 1980, approximately 121.9 million acre-feet; in 1993 approximately 112.7 million acre-feet; and in 2020, approximately 96.2 million acre-feet. The High Plains aquifer in Oklahoma will continue to be an important source of water past the year 2000. As withdrawals continue from the aquifer at the present rate, the water table will continue to decline and when the water table drops below the streambed in any part of the area, ground-water discharge to streams will cease in that area. Based on the calculated volumes of water in storage, the volume of water remaining in storage as compared to the predevelopment volume is as follows: 90 percent in 1980, 83 percent in 1993, and 71 percent in 2020.

Idaho↗

USGS1994

Water quality of the Apalachicola-Chattahoochee-Flint and Ocmulgee River Basins related to flooding from Tropical Storm Alberto; pesticides in urban and agricultural watersheds; and nitrate and pesticides in ground water, Georgia, Alabama, and Florida

This report presents preliminary water-quality information from three studies that are part of the National Water-Quality Assessment (NAWQA) Program in the Apalachicola-Chattahoochee-Flint (ACF) River basin and the adjacent Ocmulgee River basin. During the period July 3-7, 1994, heavy rainfall from tropical storm Alberto caused record flooding on the Ocmulgee and Flint Rivers and several of their tributaries. Much of the nitrogen load transported during the flooding was as organic nitrogen generally derived from organic detritus, rather than nitrate derived from other sources, such as fertilizer. More than half the mean annual loads of total phosphorus and organic nitrogen were trans- ported in the Flint and Ocmulgee Rivers during the flood. Fourteen herbicides, five insecticides, and one fungicide were detected in floodwaters of the Ocmulgee, Flint, and Apalachicola Rivers. In a second study, water samples were collected at nearly weekly intervals from March 1993 through April 1994 from one urban and two agricultural watersheds in the ACF River basin, and analyzed for 84 commonly used pesticides. More pesticides were detected and at generally higher concentrations in water from the urban watershed than the agricultural water- sheds, and a greater number of pesticides were persistent throughout much of the year in the urban watershed. Simazine exceeded U.S. Environmental Protection Agency (EPA) drinking-water standards in one of 57 samples from the urban watershed. In a third study, 38 wells were installed in surficial aquifers adjacent to and downgradient of farm fields within agricultural areas in the southern ACF River basin. Even though regional aquifers are generally used for irrigation and domestic- and public-water supplies, degradation of water quality in the surficial aquifers serves as an early warning of potential contamination of regional aquifers. Nitrate concentrations were less than 3 mg/L as N (indicating minimal effect of human activities) in water from about two-thirds of the wells. Water from the remaining wells had elevated nitrate con- centrations, probably the result of human activity. Nitrate concentrations in two of these wells exceeded EPA drinking-water standards. Water samples from eight wells had pesticide concentrations above method detection limits. With the exception of two samples for shallow ground-water wells and one surface-water sample from the urban watershed, concentrations of nitrate nitrogen and detected pesticides were below EPA standards and guidelines for drinking water. However, concentrations of the insecticides chlorpyrifos, carbaryl, and diazinon in the surface-water samples approached or exceeded guidelines for protection of aquatic life.

Alabama, Florida, Georgia↗

USGS1996

Water quality of the lower Columbia River Basin: Analysis of current and historical water-quality data through 1994

The lower Columbia River Basin includes the river basins draining into the Columbia River below Bonneville Dam—the largest of which is the Willamette River. This report presents the results of a study by the U.S. Geological Survey, done in cooperation with the Lower Columbia River Bi-State Water- Quality Program, to describe the water-quality conditions in the lower Columbia River Basin by interpreting historical data collected and data collected in 1994. Historical water-quality data spanning more than 50 years and comprising more than 200 parameters were collated for interpretation in this report. The U.S. Geological Survey, the Oregon Department of Environmental Quality, and the Washington Department of Ecology collected water-quality data at 10 sites in the lower Columbia River Basin from January to December of 1994. Water-quality constituents measured in 1994 were screened against U.S. Environmental Protection Agency (EPA) and State guidelines. Arsenic, a human carcinogen, was detected in 15 of 16 samples in the lower Columbia River, but was not detected in any of the sampled tributaries. All 15 arsenic detections had concentrations that exceeded both the EPA ambient water-quality criteria for the protection of human health and the EPA human-health advisories for drinking water. Chromium was detected at all four Columbia River sites—most frequently in the Columbia River at Hayden Island. None of the chromium concentrations detected, however, exceeded water-quality criteria or guidelines. Measurements of suspended trace-element concentrations (trace-element concentrations associated with the suspended-sediment fraction) showed that the suspended form is the dominant transport phase for aluminum, iron, and manganese, whereas the dissolved form is the dominant transport phase for arsenic, barium, chromium, and copper. On the basis of tributary loads during summer low-flow months, sources of suspended silver, nickel, aluminum, and antimony exist in the lower Columbia River Basin, whereas the sources of suspended zinc and arsenic exist outside of the lower basin. Twenty organic compounds were detected of the 47 compounds analyzed for this study. None of the organic compounds measured exceeded EPA’s ambient water-quality criteria or drinking-water guidelines. The Willamette River at Portland had the largest number of detections, and all 20 compounds were detected at one time or another at that site. The largest concentrations of the agricultural pesticides, atrazine, metolachlor, and simazine were detected in the Willamette River, where they were detected in 93, 86, 93 percent, respectively, of the samples collected. The highest concentrations of atrazine in the Willamette River were associated with the spring application and fall runoff periods. Both historical and current data showed that the highest water temperatures in the lower Columbia River Basin are present during August. For water years 1977–81 in the Columbia River at Bradwood (river mile 38.9), 75 percent of the daily mean water temperatures during August exceeded 20 degrees Celsius, a “special condition” criterion for the State of Washington. The special condition criterion was exceeded at four sites on the lower Columbia River during July and August, 1994—a period coinciding with season-high air temperatures and low streamflow. Trend tests using data from 1974 to 1994 showed significant (r < 0.05) upward trends for water temperature at the Columbia River at Warrendale and the Willamette River at Portland. Concentrations of dissolved oxygen and total dissolved gas were above saturation levels during high stormflows in the lower Columbia River and the Willamette River during 1994. The high concentrations of total dissolved gas in the Columbia River exceeded Oregon and Washington State standards of 110 percent of saturation and were caused by spilling water at the Columbia River dams. Aquatic life in the lower Columbia River Basin was not subjected to low dissolved-oxygen concentrations. Comparison of dissolved-oxygen concentrations in the Willamette River from 1949–58 to 1972–94 showed a significant increase in dissolved-oxygen concentrations during the low-streamflow months of summer. Trend tests showed significant (r < 0.05) downward trends from 1973 to 1994 for three constituents at the Columbia River at Warrendale: phosphorus in unfiltered water, total dissolved solids, and specific conductance. These trends may be a consequence of more conservative agricultural practices in the area upstream from Warrendale.

Oregon↗

USGS1996

Estimates of future water demand for selected water-service areas in the upper Duck River basin, central Tennessee

Estimates of future water demand were determined for selected water-service areas in the upper Duck River basin in central Tennessee through the year 2050. The Duck River is the principal source of publicly-supplied water in the study area providing a total of 15.6 million gallons per day (Mgal/d) in 1993 to the cities of Columbia, Lewisburg, Shelbyville, part of southern Williamson County, and several smaller communities. Municipal water use increased 19 percent from 1980 to 1993 (from 14.5 to 17.2 Mgal/d). Based on certain assumptions about socioeconomic conditions and future development in the basin, water demand should continue to increase through 2050. Projections of municipal water demand for the study area from 1993 to 2015 were made using econometric and single- coefficient (unit-use) requirement models of the per capita type. The models are part of the Institute for Water Resources-Municipal and Industrial Needs System, IWR-MAIN. Socioeconomic data for 1993 were utilized to calibrate the models. Projections of water demand in the study area from 2015 to 2050 were made using a single- coefficient requirement model. A gross per capita use value (unit-requirement) was estimated for each water-service area based on the results generated by IWR-MAIN for year 2015. The gross per capita estimate for 2015 was applied to population projections for year 2050 to calculate water demand. Population was projected using the log-linear form of the Box-Cox regression model. Water demand was simulated for two scenarios. The scenarios were suggested by various planning agencies associated with the study area. The first scenario reflects a steady growth pattern based on present demographic and socioeconomic conditions in the Bedford, Marshall, and Maury/southern Williamson water-service areas. The second scenario considers steady growth in the Bedford and Marshall water-service areas and additional industrial and residential development in the Maury/southern Williamson water-service area beginning in 2000. For the study area, water demand for scenario one shows an increase of 121 percent (from 17.2 to 38 Mgal/d) from 1993 to 2050. In scenario two, simulated water demand increases 150 percent (17.2 to 43 Mgal/d) from 1993 to 2050.

Tennessee↗

USGS1997

Comparison of 1972 and 1996 water levels in the Goleta central ground-water subbasin, Santa Barbara County, California

Ground-water levels for 1996 were compared with 1972 water levels to determine if a "drought buffer" currently exists. The drought buffer was defined previously, in a litigated settlement involving the Goleta Water District, as the 1972 water level in the Central ground-water subbasin. To make this deter mination, a network of 15 well sites was selected, water levels were measured monthly from April through December 1996, and the 1996 water-level data were compared with1972 data. The study was done in cooperation with the Goleta Water District. The 1972-1996 water-level-altitude changes for corresponding months of the comparison years were averaged for each network well. These averaged changes ranged from a rise of 9.4 ft for well 2N2 to a decline of 45.0 ft for well 8K8. The results of the comparison indicate a rise in water level at 1 site (well 2N2) and a decline at 14 sites. The mean of the 14 negative average values was a decline of 24.0 ft. The altitude of the bottom of well 2N2 was higher than the bottom altitudes at the other network sites, and this well is located a few feet from a fault that acts as a hydrologic barrier. The results of the water-level comparison for the Central subbasin were influenced to some unknown degree by the areal distribution of the set of wells selected for the network and the vertical dis tribution of the perforated intervals of the wells. For this reason, the mean water-level change--a decline of 21.8 ft--calculated from the averages of the month-to-month changes for the 15 network sites, should be used with caution. In addition, the number of usable individual monthly comparison measurements available for an individual site ranged from one to nine, and averaged six. Therefore, a weighted mean of the monthly averages was calculated on the basis of the number of comparison measurements available for each site. The weighted mean is a decline of 20.9 ft. All Central subbasin wells that were idle (that is, were not being pumped) when measured in 1972 and that were measureable in 1996 were included in the network. Therefore, the network is the most inclusive possible, given the available data. The objective of the study strictly was to compare 1972 and 1996 water levels in the Central sub basin, and the conclusion is that, overall, 1996 water levels are lower than 1972 levels. In general, hydro graphs for selected network wells indicate stable or rising water levels during 1972-83, declining levels during 1984-92, and rising water levels during 1993-96.

Water-Resources Investigations Report↗

USGS1999

Ground water and surface water in the Haiku area, East Maui, Hawaii

The Haiku study area lies on the gently sloping eastern flank of the East Maui Volcano (Haleakala) between the drainage basins of Maliko Gulch to the west and Kakipi Gulch to the east. The study area lies on the northwest rift zone of East Maui Volcano, a geologic feature 3 to 5 miles wide marked by surface expressions such as cinder, spatter, and pumice cones. The study area contains two geologic units, the main shield-building stage Honomanu Basalt and the Kula Volcanics. The hydraulic conductivity of the Honomanu Basalt was estimated to be between 1,000 and 3,600 feet per day on the basis of aquifer tests and 3,300 feet per day on the basis of the regional recharge rate and observed ground-water heads. The hydraulic conductivity of the Kula Volcanics is expected to be several orders of magnitude lower. An estimated 191 million gallons per day of rainfall and 22 million gallons per day of fog drip reach the study area and about 98 million gallons per day enters the ground-water system as recharge. Nearly all of the ground water currently withdrawn in the study area is from well 5520-01 in Maliko Gulch, where historic withdrawal rates have averaged about 2.8 million gallons per day. An additional 18 million gallons per day of ground-water withdrawal is proposed. Flow in Waiohiwi Gulch, a tributary to Maliko Gulch, is perennial between about 2,000 ft and 4,000 ft altitude. At lower altitudes in Maliko Gulch, flow is perennial at only a few spots downstream of springs and near the coast. The Kuiaha and Kaupakulua Gulch systems are usually dry from sea level to an altitude of 350 feet and gain water from about 350 feet to about 900 feet altitude. The two main branches of the Kaupakulua Gulch system alternately gain and lose water as high as 2,400 feet altitude. Kakipi Gulch has perennial flow over much of its length but is often dry near the coast below 400 feet altitude. Fresh ground water occurs in two main forms: (1) as perched high-level water held up by relatively low-permeability geologic layers, and (2) as a freshwater lens floating on denser, underlying saltwater. The rocks beneath the contact between the Kula Volcanics and the underlying Honomanu Basalt and above the freshwater lens appear to be unsaturated on the basis of several observations: (1) streams are dry or losing water where they are incised into the Honomanu Basalt, (2) the hydraulic conductivity of the Honomanu Basalt is too high to support a thick ground-water lens given the estimated recharge to the study area, and (3) wells that penetrate through the contact have encountered conditions of cascading water from above the contact and dry lava tubes in the Honomanu Basalt. More than 90 percent of the recharge to the study area is estimated to flow downward through the perched high-level water body to reach the freshwater lens. A cross-sectional, steady-state, variably saturated ground-water flow model using the computer code VS2DT was constructed to evaluate whether a two-layer, variably saturated ground-water flow system could exist given the hydrologic and geologic conditions of the Haiku study area. Using 25 inches per year of recharge and hydraulic characteristics representative of the Kula Volcanics and the Honomanu Basalt, the model demonstrates that a 13-foot thick geologic layer with a saturated vertical hydraulic conductivity less than 6.6Y10-2 feet per day can impede vertical ground-water flow enough to produce two separate saturated zones with an unsaturated zone between them. Subsequent lower vertical hydraulic conductivity values for the impeding layer allow even less water to reach the lower layer.

Hawaii↗

USGS1999

Use of environmental tracers to evaluate ground-water age and water-quality trends in a buried-valley aquifer, Dayton area, southwestern Ohio

Chlorofluorocarbons (CFC method) and tritium and helium isotopes (3H-3He method) were used as environmental tracers to estimate ground-water age in conjunction with efforts to develop a regional ground-water flow model of the buried-valley aquifer in the Dayton area, southwestern Ohio. This report describes results of CFC and water-quality sampling, summarizes relevant aspects of previously published work, and describes the use of 3H-3He ages to characterize temporal trends in ground-water quality of the buried-valley aquifer near Dayton, Ohio. Results of CFC sampling indicate that approximately 25 percent of the 137 sampled wells were contaminated with excess CFC's that rendered the ground water unsuitable for age dating. Evaluation of CFC ages obtained for the remaining samples indicated that the CFC compounds used for dating were being affected by microbial degradation. The degradation occurred under anoxic conditions that are found in most parts of the buried-valley aquifer. As a result, ground-water ages derived by the CFC method were too old and were inconsistent with measured tritium concentrations and independently derived 3H-3He ages. Limited data indicate that dissolved methane may play an important role in the degradation of the CFC's. In contrast, the 3H-3He technique was found to yield ground-water ages that were chemically and hydrologically reasonable. Ground-water ages derived by the 3H-3He technique were compared to values for selected water- quality characteristics to evaluate temporal trends in ground-water quality in the buried- valley aquifer. Distinct temporal trends were not identified for pH, alkalinity, or calcium and magnesium because of rapid equilibration of ground-water with calcite and dolomite in aquifer sediments. Temporal trends in which the amount of scatter and the number of outlier concentrations increased as ground-water age decreased were noted for sodium, potassium, boron, bromide, chloride, ammonia, nitrate, phosphate, sulfate, and organic carbon. Elevated concentrations of these constituents in shallow ground water are probably related to human activities. Temporal trends in which concentrations declined as ground-water age increased may reflect natural processes that reduce constituent concentrations to low levels. For example, the absence of nitrate detections in ground water recharged before 1980 may indicate natural removal of nitrate by bacterially mediated denitrification. Temporal trends observed for dissolved oxygen, iron, nitrate and silica indicate that these constituents may help identify recently (post-1990) recharged ground water.

Ohio↗

USGS1955

Geology and ground-water resources of the Douglas basin, Arizona, with a section on chemical quality of the ground water

The Douglas basin is part of a large northwest-trending intermontane valley, known as the Sulphur Spring Valley, which lies in southeastern Arizona, and extends into northeastern Sonora, Mexico. Maturely dissected mountains rise abruptly from long alluvial slopes and culminate in peaks 3,000 to 4,000 feet above the valley floor, Bedrock in the mountain areas confines drainage on the east and west, and an arc of low hills to the north separates the basin from the Willcox basin of the Sulphur Spring Valley. Drainage of the 1,200 square miles in the Douglas basin is southward into Mexico through Whitewater Draw. The mountains include igneous, metamorphic, and sedimentary rocks ranging in age from pre-Cambrian to Tertiary, including Paleozoic and Mesozoic sedimentary rocks that total about 10,000 feet in thickness. The older rocks have been metamorphosed, and all the bedrock has been affected by igneous intrusion, largely in Mesozoic time, and by structural movements, largely in Cenozoic time and extending into the Quaternary period. By the early part of Cenozoic time the major structural features were formed, and mountain ranges had been uplifted above the valley trough along northwest-trending fault zones. Since that time the physiographic features have resulted through erosion of the mountain blocks and the deposition, in places, of more than 2,800 feet of unconsolidated rock debris in the valley. Ground-water supplies of the Douglas basin are developed largely in the saturated zone of the valley-fill sediments. The ground water in the valley fill occurs in thin lenses and strata of sand and gravel, which are interbedded with large thicknesses of silt and day. Scattered gypsum beds and extensive caliche deposits appear at the surface and occur within the valley fill at various depths. Although the valley-fill sediments are as much as 2,800 feet thick, the uppermost 300 feet or so are the most permeable. Ground water originates as precipitation in the mountain areas. The water collects in streams that lose much of their flow into the coarse sediments that fringe the mountains. Part of the water ultimately percolates into the zone of saturation. High evaporation rates, vegetative use, and the presence of caliche and clay at shallow depth in the interstream areas of the valley floor prevent important recharge of the ground-water reservoir from direct rainfall or seepage of water applied for irrigation. The total recharge into the ground-water reservoir of the Douglas basin was about 20,000 acre-feet in 1951. Ground water is discharged from the basin by evapotranspiration, by effluent seepage into Whitewater Draw and underflow out of the basin, and by pumping. In 1951, the total amount of ground water discharged was about 50,000 acre-feet, of which more than 41,000 acre-feet was pumped from wells. Ground water used in excess of recharge is withdrawn from storage, causing a decline in the water table. Maximum declines have occurred in the heavily pumped Elfrida area, where a decline of more than 11 feet occurred in the 5- year period 1947-51, inclusive. Most irrigation wells in the Douglas basin are less than 200 feet in depth and usually produce less than 400 gpm (gallons per minute). The average specific capacity of the wells is about 12 gpm per foot of drawdown. Although water in some parts of the basin is artesian, all irrigation wells must be pumped. Ground water in the basin is generally of excellent to good quality for irrigation use, In small areas along the southern part of Whitewater Draw and east of Douglas the ground water is high in dissolved-solids content. Although most of the water is hard, it is generally satisfactory for domestic use. In many areas the fluoride content is more than 1.5 ppm (parts per million).

Arizona↗

USGS1997

Simulation of the water-table altitude in the Biscayne Aquifer, southern Dade County, Florida, water years 1945-89

A digital model of the flow system in the highly permeable surficial Biscayne aquifer of southern Dade County, Florida, was constructed for the purposes of better understanding processes that influence the flow system and of supporting the construction of a subregional model of the transport of brackish water from a flowing artesian well. Problems that needed resolution in this endeavor included the development of methods to represent the influence of flowing surface water in seasonally inundated wetlands and the influence of a network of controlled canals developed in stages during the simulation time period (water years 1945-89). An additional problem was the general lack of natural aquifer boundaries near the boundaries of the study area. The model construction was based on a conceptual description of the Biscayne aquifer developed from the results of previous U.S. Geological Survey investigations. Modifications were made to an existing three-dimensional finite-difference simulator of ground-water flow to enable an upper layer of the grid to represent seasonally occurring overland sheet flow in a series of transient simulations of water levels from 1945 to 1989. A rewetting procedure was developed for the simulator that permitted re-saturation of cells in this layer when the wet season recurred. An ï¿½equivalent hydraulic conductivityï¿½ coefficient was assigned to the overland flow layer that was analogous, subject to various approximations, to the use of the Manning equation. The surficial semi-confining peat and marl layers, levees, canals, and control structures were also represented as part of the model grid with the appropriate choices of hydraulic coefficient values. For most of the Biscayne aquifer grid cells, the value assigned to hydraulic conductivity for model calibration was 30,000 feet per day and the value assigned to porosity was 20 percent. Boundary conditions were specified near data sites having long-term records of surface-water stages or water-table altitudes, and modifications to the simulator permitted the specification of time-varying pressures at boundary grid cells. Rainfall data from a station in Homestead generally were used as an a really uniform rainfall specification throughout the modeled region. Maximum evapotranspiration rates ranged seasonally from a minimum of 0.08 inch per day in January to a maximum of 0.21 inch per day between June and October. Shallow-root and deep-root zone depths for the evapotranspiration calculation were 3 and 20 feet in the coastal ridge and were 0.10 and 5 feet in the glades regions where peat and marl covers occurred. Results of sensitivity analyses indicated that the simulations of stages and water levels were relatively unresponsive to 50 percent changes in aquifer hydraulic conductivity, porosity, and the equivalent hydraulic conductivity of overland flow. However, 20 percent changes in rainfall and maximum evapotranspiration rates produced significantly different water levels, as did interchange of coastal ridge and glades deep-root zone (extinction) depths. Water levels were simulated very well at most measurement sites. Sensitivity analyses illustrated the significant influence of the uncontrolled agricultural drainage canals on pre-1968 regional water levels and the further influence of Black Creek Canal in draining a region of high water after 1961. Other analyses indicated that the flood-control system of 1968-82 lowered peak water levels in the affected region by as much as 1.5 feet in the wet summers of 1968, 1969, and 1981, and that Levee 67 Extended channeled flows from the S-12 spillway structures and raised overland flow stages in Shark River Slough. Hypothetical scenarios of well-field pumping in the vicinity of Levee 31N indicated that the pumping induced a significant amount of recharge from the adjacent borrow canal, the degree of which depended on the distance between the canal and the well field. The computed ratio of evapotranspiration to rainfall recharge ranged from 88 to 94 percent during water years 1945-82. The ratio increased to about 97.9 percent during water years 1983-89, possibly because of changing water-management practices and deficient rainfall.

Florida↗

USGS2011

Estimating water supply arsenic levels in the New England bladder cancer study

Background: Ingestion of inorganic arsenic in drinking water is recognized as a cause of bladder cancer when levels are relatively high (≥ 150 μg/L). The epidemiologic evidence is less clear at the low-to-moderate concentrations typically observed in the United States. Accurate retrospective exposure assessment over a long time period is a major challenge in conducting epidemiologic studies of environmental factors and diseases with long latency, such as cancer. Objective: We estimated arsenic concentrations in the water supplies of 2,611 participants in a population-based case–control study in northern New England. Methods: Estimates covered the lifetimes of most study participants and were based on a combination of arsenic measurements at the homes of the participants and statistical modeling of arsenic concentrations in the water supply of both past and current homes. We assigned a residential water supply arsenic concentration for 165,138 (95%) of the total 173,361 lifetime exposure years (EYs) and a workplace water supply arsenic level for 85,195 EYs (86% of reported occupational years). Results: Three methods accounted for 93% of the residential estimates of arsenic concentration: direct measurement of water samples (27%; median, 0.3 μg/L; range, 0.1–11.5), statistical models of water utility measurement data (49%; median, 0.4 μg/L; range, 0.3–3.3), and statistical models of arsenic concentrations in wells using aquifers in New England (17%; median, 1.6 μg/L; range, 0.6–22.4). Conclusions: We used a different validation procedure for each of the three methods, and found our estimated levels to be comparable with available measured concentrations. This methodology allowed us to calculate potential drinking water exposure over long periods.

Environmental Health Perspectives↗

USGS1953

Ground-water resources of the Rapid Valley unit, Cheyenne Division, South Dakota, with a section on the surface waters of Rapid Valley

The Rapid Valley unit is in Pennington County, S. Dak., and extends from the east city limits of Rapid City southeastward for 21 miles along Rapid Creek. The bedrock formations that underlie the region are chiefly marine in origin, and they generally dip eastward from the center of the Black Hills uplift. The exposed formations are of Cretaceous age and consist of the Greenhorn limestone, the Carlile shale, the Niobrara formation, and the Pierre shale. The Pierre shale, which underlies the unconsolidated flood plain and terrace deposits in much Of the region is exposed in the erosional slopes along the south side of the valley and in the deeper draws on the north side. The areas in which the other formations are exposed are relatively small and are restricted to the western part of-the region. Four terraces are present on the north side of Rapid Creek. The lowest terrace and the flood plain in the western half of the region are irrigated at the present time, and the two lower terraces and the flood plain in the eastern half have been proposed for irrigation. Abundant supplies of ground water occur in the flood plain and terrace deposits where they are now irrigated. Because the waterbearing materials consist of interfingering layers of differing permeability, the ground water is under water-table conditions in some places whereas it is confined in others. Locally, where there is a confining layer below other water-bearing materials or where a confined layer is itself saturated, the ground water may occur under both water-table and artesian conditions. Seepage from irrigation canals, which is the principal source of recharge, causes high ground-water levels from June to November; as a result, parts of the areas have become waterlogged. In the parts of the region that are not now affected by irrigation, the surface of the ground water is only a few feet above the bedrock surface and 6 ft to 42 ft below land surface; its position is relatively constant throughout the year. Harmful concentrations of salt in the soil are in part due to evaporation of ground water. These are found only locally in the Rapid Valley region and do not present a serious problem at this time. It is thought, however, that the fine-grained materials underlying the Rapid terrace may contain sufficient salt to cause detrimental salt accumulations in the soil if the proposed irrigation causes ground-water levels to rise close to the surface. Lining of the irrigation canals would reduce the amount of seepage and would effect a lowering of ground-water levels, if irrigation practices are extended to other areas, drainage facilities will be necessary both to avoid aggravating the existing conditions of waterlogging and to prevent the waterlogging of other low-lying lands. The flow of Rapid Creek is affected by a variety of conditions. A few miles west of Rapid City, where Rapid Creek flows over the Englewood and Pahasapa limestones and the Minnelusa sandstone, there is a loss of about 8 cfs of water in a distance of a few miles. In the 3-mile reach of Rapid Creek between the Canyon Lake stream-gaging station and the Rapid City stream-gaging station there is a gain of about 20 cfs; much of this gain in flow may be attributed to the inflow from Cleghorn and Jackson springs and to the addition of water from the State-owned cement plant. In the Rapid Valley unit, the flow of the creek during the irrigation season is affected largely by the amount of water diverted for irrigation. The irrigation canals act as bypass channels, much of the water being returned to Rapid Creek by way of spillage into normally dry tributary creek channels and by movement through ground-water bodies that discharge into Rapid Creek.

South Dakota↗

USGS2012

Comparison of 2008-2009 water years and historical water-quality data, upper Gunnison River Basin, Colorado

Population growth and changes in land use have the potential to affect water quality and quantity in the upper Gunnison River Basin. In 1995, the U.S. Geological Survey (USGS), in cooperation with the Bureau of Land Management, City of Gunnison, Colorado River Water Conservation District, Crested Butte South Metropolitan District, Gunnison County, Hinsdale County, Mount Crested Butte Water and Sanitation District, National Park Service, Town of Crested Butte, U.S. Forest Service, Upper Gunnison River Water Conservancy District, and Western State College, established a water-quality monitoring program in the upper Gunnison River Basin to characterize current water-quality conditions and to assess the effects of increased urban development and other land-use changes on water quality. The monitoring network has evolved into two groups of sites: (1) sites that are considered long term and (2) sites that are considered rotational. Data from the long-term sites assist in defining temporal changes in water quality (how conditions may change over time). The rotational sites assist in the spatial definition of water-quality conditions (how conditions differ throughout the basin) and address local and short-term concerns. Biannual summaries of the water-quality data from the monitoring network provide a point of reference for stakeholder discussions regarding the location and purpose of water-quality monitoring sites in the upper Gunnison River Basin. This report compares and summarizes the data collected during water years 2008 and 2009 to the historical data available at these sites. The introduction provides a map of the sampling sites, definitions of terms, and a one-page summary of selected water-quality conditions at the network sites. The remainder of the report is organized around the data collected at individual sites. Data collected during water years 2008 and 2009 are compared to historical data, State water-quality standards, and Federal water-quality guidelines. A seasonal Kendall test for trend analysis is completed when there is sufficient data (typically >5 years) at the station. Data were collected following USGS protocols.

Colorado↗

USGS2014

Continuous water-quality and suspended-sediment transport monitoring in the San Francisco Bay, California, water years 2011–13

The U.S. Geological Survey (USGS) monitors water quality and suspended-sediment transport in the San Francisco Bay. The San Francisco Bay area is home to millions of people, and the bay teems with both resident and migratory wildlife, plants, and fish. Fresh water mixes with salt water in the bay, which is subject both to riverine and marine (tides, waves, influx of salt water) influences. To understand this environment, the USGS, along with its partners, has been monitoring the bay’s waters continuously since 1988. Several water-quality variables are of particular importance to State and Federal resource managers and are monitored at key locations throughout the bay. Salinity, which indicates the relative mixing of fresh and ocean waters in the bay, is derived from specific conductance measurements. Water temperature, along with salinity, affects the density of water, which causes gravity driven circulation patterns and stratification in the water column. Turbidity is measured using light-scattering from suspended solids in water, and is used as a surrogate for suspended-sediment concentration (SSC). Suspended sediment often carries adsorbed contaminants; attenuates sunlight in the water column; deposits on tidal marsh and intertidal mudflats, which can help sustain these habitats as sea level rises; and deposits in ports and shipping channels, which can necessitate dredging. Dissolved oxygen, which is essential to a healthy ecosystem, is a fundamental indicator of water quality, and its concentration is affected by water temperature, salinity, ecosystem metabolism, tidal currents, and wind. Tidal currents in the bay reverse four times a day, and wind direction and intensity typically change on a daily cycle: consequently, salinity, water temperature, suspendedsediment concentration, and dissolvedoxygen concentration vary spatially and temporally throughout the bay, and continuous measurements are needed to observe these changes. The purpose of this fact sheet is to inform the public and resource managers of the availability of these water-quality data.

California↗

USGS2018

Continuous water-quality and suspended-sediment transport monitoring in the San Francisco Bay, California, water years 2014–15

The U.S. Geological Survey (USGS) monitors water quality and suspended-sediment transport in the San Francisco Bay (bay) as part of a multi-agency effort to address management, water supply, and ecological concerns. The San Francisco Bay area is home to millions of people, and the bay teems both with resident and with migratory wildlife, plants, and fish. Freshwater mixes with salt water in the bay, which is subject both to riverine influences (floods, droughts, managed reservoir releases and freshwater diversions) and to marine influences (tides, waves, effects of salt water). To understand this environment, the USGS, along with its partners (see “Acknowledgements”), has been monitoring the bay’s waters continuously since 1988. Several water-quality variables are of particular importance to State and Federal resource managers and are monitored at key locations throughout the bay (fig. 1). Salinity, which indicates the relative mixing of fresh and ocean waters in the bay, is derived from specific conductance measurements. Water temperature, along with salinity, affects the density of water, which controls gravity-driven circulation patterns and stratification in the water column. Turbidity, a measure of light scattered from suspended particles in the water, is used to estimate suspended-sediment concentration (SSC). Suspended sediment affects the bay in multiple ways: attenuation of sunlight in the water column, affecting phytoplankton growth; deposition on tidal marsh and intertidal mudflats, which can help sustain these habitats as sea level rises; deposition in ports and shipping channels, which can necessitate dredging; and often, adsorption of contaminants, affecting their distribution and concentrations in the environment. Dissolved oxygen concentration, essential to a healthy ecosystem and a fundamental indicator of water quality, is affected by water temperature, salinity, ecosystem metabolism, tidal currents, and wind. Tidal currents in the bay reverse four times a day, and wind direction and intensity typically vary on a daily cycle. Consequently, salinity, water temperature, SSC, and dissolved-oxygen concentration vary spatially and temporally throughout the bay. Therefore, continuous measurements are needed to observe these changes. The purpose of this fact sheet is to provide information about these variables, as well as internet links to access these continuous water-quality data collected by the USGS.

California↗

USGS2006

Approach to an assessment of volatile organic compounds in the nation's ground water and drinking-water supply wells

The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) developed an approach for a national assessment of the occurrence, status, and distribution of volatile organic compounds (VOCs) in samples of ground water from aquifer studies and in samples from drinking-water supply wells, specifically domestic and public wells. Data on VOCs in samples from aquifers and from domestic and public wells had three sources: (1) NAWQA sampling of ground water in aquifer studies and of shallow ground water in areas of agricultural or urban land use from 1993-2002, (2) retrospective data from other Federal, State, and local agencies that sampled ground water in aquifer studies from 1985-1997, and (3) sampling of ground water from public wells used as a source of drinking water from 1999-2000 (source-water survey). Data for assessing VOCs in ground water came from the NAWQA sampling of aquifers and from retrospective data (1 and 2). Domestic wells were the most commonly sampled well type in these aquifer studies. Data for assessing VOCs in domestic well samples came from the NAWQA sampling of aquifers and shallow ground water and from retrospective data (1 and 2). Data for assessing VOCs in public well samples came from NAWQA sampling of aquifers and shallow ground water and from the source-water survey (1, 2, and 3). Fifty-five VOCs were included in the national assessment. All ground-water samples were collected using consistent, prescribed field protocols and were analyzed using approved analytical methods. All ground-water collection activities and laboratory procedures included the collection of various quality-control samples in order to ensure the quality of the data. Comparisons of detection frequencies and detected concentrations among individual VOCs, groups of VOCs, aquifer studies, and data sets were performed using two assessment levels: (1) an assessment level of 0.2 microgram per liter (?g/L), and (2) an assessment level of 0.02 ?g/L. Selection of the 0.2-?g/L assessment level was based on historical laboratory reporting levels of VOCs used by the USGS National Water-Quality Laboratory (NWQL) prior to April 1996, and selection of the 0.02-?g/L assessment level was based on a new, low-level analytical method developed by the NWQL and used since April 1996. Relational analyses using multivariate logistic regression were performed on VOC data from aquifers, domestic wells, and public wells to better understand the natural and anthropogenic factors that control or influence the occurrence of VOCs. Ancillary data used in the relational analyses represent a variety of anthropogenic and hydrogeologic controls on the occurrence of VOCs. For aquifers, relational analyses were performed only on NAWQA data analyzed using the new low-level analytical method for 10 frequently detected VOCs. For domestic wells, relational analyses were performed at assessment levels of 0.2 ?g/L and 0.02 ?g/L for 6 and 10 frequently detected VOCs at these levels. For public wells, relational analyses were performed at an assessment level of 0.2 ?g/L for nine frequently detected VOCs.

Open-File Report↗

USGS2006

Water-Surface Elevations, Discharge, and Water-Quality Data for Selected Sites in the Warm Springs Area near Moapa, Nevada

The U.S. Geological Survey, in cooperation with Southern Nevada Water Authority and the Nevada Division of Water Resources, operates and maintains a surface-water monitoring network of 6 continuous-record stream-flow gaging stations and 11 partial-record stations in the Warm Springs area near Moapa, Nevada. Permanent land-surface bench marks were installed within the Warm Springs area by the Las Vegas Valley Water District, the Southern Nevada Water Authority, and the U.S. Geological Survey to determine water-surface elevations at all network monitoring sites. Vertical datum elevation and horizontal coordinates were established for all bench marks through a series of Differential Global Positioning System surveys. Optical theodolite surveys were made to transfer Differential Global Positioning System vertical datums to reference marks installed at each monitoring site. The surveys were completed in June 2004 and water-surface elevations were measured on August 17, 2004. Water-surface elevations ranged from 1,810.33 feet above North American Vertical Datum of 1988 at a stream-gaging station in the Pederson Springs area to 1,706.31 feet at a station on the Muddy River near Moapa. Discharge and water-quality data were compiled for the Warm Springs area and include data provided by the U.S. Geological Survey, Nevada Division of Water Resources, U.S. Fish and Wildlife Service, Moapa Valley Water District, Desert Research Institute, and Converse Consultants. Historical and current hydrologic data-collection networks primarily are related to changes in land- and water-use activities in the Warm Springs area. These changes include declines in ranching and agricultural use, the exportation of water to other areas of Moapa Valley, and the creation of a national wildlife refuge. Water-surface elevations, discharge, and water-quality data compiled for the Warm Springs area will help identify (1) effects of changing vegetation within the former agricultural lands, (2) effects of restoration activities in the wildlife refuge, and (3) potential impacts of ground-water withdrawals.

Open-File Report↗

USGS2016

Quality of surface-water supplies in the Triangle area of North Carolina, water years 2010-11

Surface-water supplies are important sources of drinking water for residents in the Triangle area of North Carolina, which is located within the upper Cape Fear and Neuse River Basins. Since 1988, the U.S. Geological Survey and a consortium of local governments have tracked water-quality conditions and trends in several of the area’s water-supply lakes and streams. This report summarizes data collected through this cooperative effort, known as the Triangle Area Water Supply Monitoring Project, during October 2009 through September 2010 (water year 2010) and October 2010 through September 2011 (water year 2011). Major findings for this data-collection effort include Annual precipitation was approximately 4 percent above the long-term mean (average) annual precipitation in 2010 and approximately 6 percent below the long-term mean in 2011. In water year 2010, streamflow was near the long-term mean for most of the period for the 10 project streamflow gaging stations. Streamflow was near or below the long-term mean at the same streamflow gaging stations during the 2011 water year. More than 13,000 individual measurements of water quality were made at a total of 28 sites—17 in the Neuse River Basin and 11 in the Cape Fear River Basin. Forty-three water-quality properties or constituents were measured; North Carolina water-quality standards exist for 21 of these. All observations met State water-quality standards for water temperature, hardness, chloride, fluoride, sulfate, nitrate plus nitrite, arsenic, cadmium, chromium, lead, nickel, and selenium. State water-quality standards were exceeded one or more times for dissolved oxygen, dissolved oxygen percent saturation, pH, copper, iron, manganese, mercury, silver, and zinc. Exceedances occurred at 27 sites—17 in the Neuse River Basin and 10 in the Cape Fear River Basin. Stream samples collected during storm events contained elevated concentrations of 25 water-quality constituents relative to non-storm events.

North Carolina↗

USGS1995

Simulation of the water-table altitude in the Biscayne Aquifer, southern Dade County, Florida, water years 1945-89

A digital model of the flow system in the highly permeable surficial Biscayne aquifer of southern Dade County, Florida, was constructed for the purposes of better understanding processes that influence the flow system and of supporting the construction of a subregional model of the transport of brackish water from a flowing artesian well. Problems that needed resolution in this endeavor included the development of methods to represent the influence of flowing surface water in seasonally inundated wetlands and the influence of a network of controlled canals developed in stages during the simulation time period (water years 1945-89). An additional problem was the general lack of natural aquifer boundaries near the boundaries of the study area. The model construction was based on a conceptual description of the Biscayne aquifer developed from the results of previous U.S. Geological Survey investigations. Modifications were made to an existing three-dimensional finite-difference simulator of ground-water flow to enable an upper layer of the grid to represent seasonally occurring overland sheetflow in a series of transient simulations of water levels from 1945 to 1989. A rewetting procedure was developed for the simulator that permitted resaturation of cells in this layer when the wet season recurred. An "equivalent hydraulic conductivity" coefficient was assigned to the overland flow layer that was analogous, subject to various approximations, to the use of the Manning equation. The surficial semiconfining peat and marl layers, levees, canals, and control structures were also represented as part of the model grid with the appropriate choices of hydraulic coefficient values. For most of the Biscayne aquifer grid cells, the value assigned to hydraulic conductivity for model calibration was 30,000 feet per day and the value assigned to porosity was 20 percent. Boundary conditions were specified near data sites having long-term records of surface-water stages or water-table altitudes, and modifications to the simulator permitted the specification of time-varying pressures at boundary grid cells. Rainfall data from a station in Homestead generally were used as an areally uniform rainfall specification throughout the modeled region. Maximum evapotranspiration rates ranged seasonally from a minimum of 0.08 inch per day in January to a maximum of 0.21 inch per day between June and October. Shallow-root and deep-root zone depths for the evapotranspiration calculation were 3 and 20 feet in the coastal ridge and were 0.10 and 5 feet in the glades regions where peat and marl covers occurred. Results of sensitivity analyses indicated that the simulations of stages and water levels were relatively unresponsive to 50 percent changes in aquifer hydraulic conductivity, porosity, and the equivalent hydraulic conductivity of overland flow. However, 20 percent changes in rainfall and maximum evapotranspiration rates produced significantly different water levels, as did interchange of coastal ridge and glades deep-root zone (extinction) depths. Water levels were simulated very well at most measurement sites. Sensitivity analyses illustrated the significant influence of the uncontrolled agricultural drainage canals on pre-1968 regional water levels and the further influence of Black Creek Canal in draining a region of high water after 1961. Other analyses indicated that the flood-control system of 1968-82 lowered peak water levels in the affected region by as much as 1.5 feet in the wet summers of 1968, 1969, and 1981, and that Levee 67 Extended channeled flows from the S-12 spillway structures and raised overland flow stages in Shark River Slough. Hypothetical scenarios of well-field pumping in the vicinity of Levee 31N indicated that the pumping induced a significant amount of recharge from the adjacent borrow canal, the degree of which depended on the distance between the canal and the well field. The computed ratio of evapotranspiration to rainfall recharge ranged from 88 to 94 percent during water years 1945-82. The ratio increased to about 97.9 percent during water years 1983-89, possibly because of changing water-management practices and deficient rainfall.

Florida↗