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USGS2000

Water-resources-related information for the St. Croix Reservation and vicinity, Wisconsin

The St. Croix Chippewa Tribe is interested in documenting water-quality conditions in lakes and streams adjacent to their Reservation lands in northwestern Wisconsin and developing management plans to protect these water resources. This report provides the Tribe with a retrospective summary and analysis of available water-resources-related information for their Reservation and vicinity. The study area is divided into four main watersheds: Big Round Lake, Clam River at Clam Lake Outlet, Yellow River at Danbury, and Loon Creek at Danbury. The Clam River Watershed includes the subwatersheds of Bashaw and Sand Lakes. The Yellow River Watershed includes the subwatersheds of Big Sand and Gaslyn Lakes. In all, 41 surface-water studies or reports that include information relevant to the study area were identified. Most of the surface-water studies were regional or statewide summaries. Fifteen of these studies include lake information and 36 include stream information. Twenty-eight of the studies include water-quality data and 16 include information describing aquatic biology. Water- and sediment-quality data were obtained for 80 lakes and 23 streams in the study area. Lake information includes data for 101 water-quality characteristics from nearly 4,300 water and sediment analyses of samples collected between 1972 and 1998. Stream information summarized in this report includes data for 135 water-quality characteristics and nearly 4,500 water and sediment analyses of samples collected at 23 sites between 1964 and 1999. A total of 41 ground-water studies or reports that include information relevant to the study area were identified. Most of the ground-water studies were regional or statewide summaries. Of the 41 studies, 33 include water-quality information, 9 include information regarding water use, and 23 provide descriptions of geology and aquifer characteristics relevant to the study area. Water-quality information for 773 wells was compiled. Most of the sampled wells were used for drinking water, and most of the drinking-water wells represent domestic supplies. Water-quality data summarized in this report represent 270 characteristics and more than 10,300 analyses of samples collected from drinking-water wells between 1911 and 1999; however, most of the water-quality data were collected after about 1990.

Wisconsin↗
USGS2000

Design of a shallow ground-water network to monitor agricultural chemicals, Lake Wales Ridge, central Florida

Extensive agricultural land use and dynamic hydraulic connections between the land surface and ground-water resources render many of Florida's aquifers vulnerable to chemical contamination. In these areas, there is a need to monitor shallow ground water for agricultural chemicals to evaluate potential migration of the chemicals to the subsurface and to deeper aquifers, and to assess the effects of agricultural practices on ground-water quality. Historically, efforts to monitor water-table aquifers have been minimal compared with monitoring deeper aquifers used for municipal drinking-water supply. The Florida Department of Agriculture and Consumer Services has proposed the establishment of long-term, water-quality networks to monitor shallow ground water in agricultural areas of Florida. These networks will bridge the current information gap between local-scale short-duration field studies, which are required for pesticide licensing, and statewide monitoring of deeper ground-water resources. Laboratory (experimental) and short-term field evaluations of the transport of agricultural chemicals to the subsurface contain some degree of uncertainty due to widespread variations in environmental conditions. The proposed regional-scale shallow ground-water networks will serve as "early warning" networks to avoid contamination of ground-water resources. The objectives of these shallow ground-water networks are to provide information for early detection of pesticides and nitrate in the subsurface, and for evaluating temporal trends in concentrations in relation to changes in land use and agricultural practices. Information on trends is important to the U.S. Environmental Protection Agency, State agencies, and agricultural managers, and is an integral part of Florida's Pesticide Management Plan, which evaluates the effectiveness of implementing "best management practices" to minimize environmental impacts. Lake Wales Ridge in Polk and Highlands Counties has been identified by the Florida Department of Agriculture and Consumer Services as a pilot study area for implementing a regional shallow ground-water network. Information gained from designing the Lake Wales Ridge Network will be used to develop plans as similar networks are considered for other areas of Florida. Lake Wales Ridge is heavily utilized for citrus production, but the well-drained, clean sands underlying the region, coupled with a hydraulic connection with deeper karst formations, render the area extremely vulnerable to the transport and migration of agricultural chemicals within the subsurface. The network design for Lake Wales Ridge was developed on the basis of the objectives of monitoring, factors affecting aquifer vulnerability, probability (statistical) sampling theory, and specifications regarding well construction, sampling, and laboratory analysis. The network will provide estimates of regional pesticide and nitrate concentrations in targeted ground water, monitor for trends over time, and will provide baseline, regional-scale information. The areas targeted for sampling were citrus groves located on soils classified as vulnerable to leaching of agricultural chemicals, and ground water in close proximity to the water table. The duration of monitoring is planned to be long term. Chemicals targeted for monitoring include selected nutrients, trace elements, and pesticides used for citrus management. Standardization of field sampling and laboratory methods, and construction of a computerized data-base repository will be important for long-term utility of the data. The proposed network design consists of existing and newly drilled wells. Existing wells were evaluated as candidates for the network based on location and well-construction specifications for water-quality monitoring. Using probability selection techniques, new well locations were selected in areas that lacked adequate existing wells. Implementation of the network will occur in phases. Quarterly sampling of 13 Phase I wells commenced in April 1999. An additional 11 Phase II wells were added to the network in April 2000. Proposed locations have been identified for 8 Phase III wells. Future topics for study include a regional water-quality analysis, a network design evaluation, and consideration of local-scale studies needed to support regional monitoring efforts. An analysis of historical water-quality data for Lake Wales Ridge, including Phase I wells, is needed for the purpose of examining trends, providing a preliminary description of spatial and short-term variability in water quality, and evaluating the proposed network design for cost effectively meeting program objectives. Local-scale, process-oriented studies are needed to provide important information for evaluating regional water-quality data. Coordination between individuals conducting such local-scale studies and those interpreting regional sampling results will be considered as a component of the network design, and will require coordination between multiple agencies.

Florida↗
USGS2000

Methods for estimating low-flow statistics for Massachusetts streams

Methods and computer software are described in this report for determining flow duration, low-flow frequency statistics, and August median flows. These low-flow statistics can be estimated for unregulated streams in Massachusetts using different methods depending on whether the location of interest is at a streamgaging station, a low-flow partial-record station, or an ungaged site where no data are available. Low-flow statistics for streamgaging stations can be estimated using standard U.S. Geological Survey methods described in the report. The MOVE.1 mathematical method and a graphical correlation method can be used to estimate low-flow statistics for low-flow partial-record stations. The MOVE.1 method is recommended when the relation between measured flows at a partial-record station and daily mean flows at a nearby, hydrologically similar streamgaging station is linear, and the graphical method is recommended when the relation is curved. Equations are presented for computing the variance and equivalent years of record for estimates of low-flow statistics for low-flow partial-record stations when either a single or multiple index stations are used to determine the estimates. The drainage-area ratio method or regression equations can be used to estimate low-flow statistics for ungaged sites where no data are available. The drainage-area ratio method is generally as accurate as or more accurate than regression estimates when the drainage-area ratio for an ungaged site is between 0.3 and 1.5 times the drainage area of the index data-collection site. Regression equations were developed to estimate the natural, long-term 99-, 98-, 95-, 90-, 85-, 80-, 75-, 70-, 60-, and 50-percent duration flows; the 7-day, 2-year and the 7-day, 10-year low flows; and the August median flow for ungaged sites in Massachusetts. Streamflow statistics and basin characteristics for 87 to 133 streamgaging stations and low-flow partial-record stations were used to develop the equations. The streamgaging stations had from 2 to 81 years of record, with a mean record length of 37 years. The low-flow partial-record stations had from 8 to 36 streamflow measurements, with a median of 14 measurements. All basin characteristics were determined from digital map data. The basin characteristics that were statistically significant in most of the final regression equations were drainage area, the area of stratified-drift deposits per unit of stream length plus 0.1, mean basin slope, and an indicator variable that was 0 in the eastern region and 1 in the western region of Massachusetts. The equations were developed by use of weighted-least-squares regression analyses, with weights assigned proportional to the years of record and inversely proportional to the variances of the streamflow statistics for the stations. Standard errors of prediction ranged from 70.7 to 17.5 percent for the equations to predict the 7-day, 10-year low flow and 50-percent duration flow, respectively. The equations are not applicable for use in the Southeast Coastal region of the State, or where basin characteristics for the selected ungaged site are outside the ranges of those for the stations used in the regression analyses. A World Wide Web application was developed that provides streamflow statistics for data collection stations from a data base and for ungaged sites by measuring the necessary basin characteristics for the site and solving the regression equations. Output provided by the Web application for ungaged sites includes a map of the drainage-basin boundary determined for the site, the measured basin characteristics, the estimated streamflow statistics, and 90-percent prediction intervals for the estimates. An equation is provided for combining regression and correlation estimates to obtain improved estimates of the streamflow statistics for low-flow partial-record stations. An equation is also provided for combining regression and drainage-area ratio estimates to obtain improved e

Massachusetts↗
USGS2000

Simulation of the shallow hydrologic system in the vicinity of Middle Genesee Lake, Wisconsin, using analytic elements and parameter estimation

Middle Genesee Lake is a ground-water flow-through lake located in a developing area in southeastern Wisconsin. Because the lake is in good connection with the shallow ground-water system, hydrologic stresses to the shallow ground-water system could adversely affect the lake system. In order to assess the effects of potential stresses on the lake, a study was completed by the U.S. Geological Survey, in cooperation with the Middle Genesee Lake Management District. The objective of the study was to identify areas that contribute ground water to the lake and estimate the hydrologic budget of the lake and hydraulic parameters affecting ground-water flow. A two-dimensional, steady-state analytic element model of the lake and surrounding area was developed using the computer code GFLOW. A parameter estimation model, UCODE, was used to optimize the calibration to measured water levels and streamflow. The calibrated model was used to evaluate the effect of three hypothetical stress scenarios on the stage of Middle Genesee Lake; the simulations were linked to UCODE, which formally incorporated parameter uncertainty into 95-percent confidence intervals around the simulated value. The scenarios included: (1) pumping from upgradient irrigation wells, (2) pumping from Lower Genesee Lake to lower lake levels, and (3) reduction in recharge resulting from development. The results of the simulations demonstrated that lake levels could be affected by hydrologic stresses in the shallow hydrologic system, with effects ranging from a 2.7 feet decline in lake stage resulting from pumping in Lower Genesee Lake to a 0.1 feet decline in lake stage from development in part of the upgradient recharge area. The range of lake stage decline increased when parameter uncertainty was included, from a decline of 3.1 feet for pumping from Lower Genesee Lake to no reduction in lake stage for the development in the recharge area. Whereas these simulated effects are within the natural variation in lake stage, they represent a systematic reduction of ground-water flow to the lake. Therefore, these hypothetical stresses are expected to establish a new, lower, baseline lake stage over which the natural variation due to climatic effects are added and subtracted.

Wisconsin↗
USGS2000

Nitrate source indicators in ground water of the Scimitar Subdivision, Peters Creek area, Anchorage, Alaska

A combination of aqueous chemistry, isotopic measurement, and in situ tracers were used to study the possible nitrate sources, the factors contributing to the spatial distribution of nitrate, and possible septic system influence in the ground water in the Scimitar Subdivision, Municipality of Anchorage, Alaska. Two water types were distinguished on the basis of the major ion chemistry: (1) a calcium sodium carbonate water, which was associated with isotopically heavier boron and with chlorofluorocarbons (CFC's) that were in the range expected from equilibration with the atmosphere (group A water) and (2) a calcium magnesium carbonate water, which was associated with elevated nitrate, chloride, and magnesium concentrations, generally isotopically lighter boron, and CFC's concentrations that were generally in excess of that expected from equilibration with the atmosphere (group B water). Water from wells in group B had nitrate concentrations that were greater than 3 milligrams per liter, whereas those in group A had nitrate concentrations of 0.2 milligram per liter or less. Nitrate does not appear to be undergoing extensive transformation in the ground-water system and behaves as a conservative ion. The major ion chemistry trends and the presence of CFC's in excess of an atmospheric source for group B wells are consistent with waste-water influences. The spatial distribution of the nitrate among wells is likely due to the magnitude of this influence on any given well. Using an expanded data set composed of 16 wells sampled only for nitrate concentration, a significant difference in the static water level relative to bedrock was found. Well water samples with less than 1 milligram per liter nitrate had static water levels within the bedrock, whereas those samples with greater than 1 milligram per liter nitrate had static water levels near or above the top of the bedrock. This observation would be consistent with a conceptual model of a low-nitrate fractured bedrock aquifer that receives slow recharge from an overlying nitrate-enriched surficial aquifer.

Water-Resources Investigations Report↗
USGS2000

A hydrologic primer for New Jersey watershed management

The U.S. Geological Survey (USGS) and the N.J. Department of Environmental Protection (NJDEP), and many other agencies and organizations are striving to educate the public about New Jersey’s water resources. In 1996, the NJDEP began implementing a “watershed management approach” to maintain the physical, chemical, and biological integrity of New Jersey’s waters. This approach concentrates on managing individual watershed areas by (1) defining the physical geographic boundaries of the watersheds, (2) basing water policy on sound scientific principles, and (3) developing partnerships with the public--the people most affected by watershed-management policies. New Jersey can be divided into five water regions as defined by the NJDEP: the Northeast, Raritan, Northwest, Lower Delaware, and Atlantic Coastal water regions (fig. 1). Each water region has been divided into three to five “watershed-management areas,” each of which encompasses a particular group of major rivers (fig. 2a-e). Each watershed management area consists of many smaller watersheds. Hydrologic data collected by Federal and State government agencies are invaluable as resources to policymakers who make decisions that affect the use of water in a particular watershed. The purpose of this report is to educate water-resource managers, policymakers, government officials, and the public about hydrologic concepts and the water-resource data needed to make informed decisions about water-management issues. (“Hydrologic” means relating to the occurrence, distribution, movement, and chemistry of all waters of the Earth (Fetter, 1980)). The first part of the report describes basic hydrologic concepts and includes explanations of the hydrologic cycle, the water budget, the surfacewater and ground-water flow systems, water-quality concepts and standards, and water use. The second part of the report summarizes the types of waterresource data that are available from Federal and State government agencies. Instructions on how to obtain the data and contact the appropriate Federal and State agencies, as well as suggestions for additional reading, also are included.

New Jersey↗
USGS2000

Occurrence and quality of surface water and ground water within the Yavapai-Prescott Indian Reservation, central Arizona, 1994-98

The Yavapai-Prescott Indian Reservation encompasses about 1,395 acres in central Arizona adjacent to the city of Prescott. From October 1994 to September 1997, the annual average rainfall was 14.9 inches and the total annual streamflow leaving the reservation along Granite Creek was about 430 acre-feet more than the amount of streamflow entering the reservation. The channel-fill and valley-fill sediments within the flood plain of Granite Creek make up the principal aquifer. The only ground-water development is from spring discharge that is being contained for livestock and wildlife use. About 29 acre-feet of ground water leaves the reservation each year after discharging into Granite Creek. Water levels in wells throughout the reservation reflect seasonal variations in rainfall and snowmelt. Surface water and ground water on the reservation are calcium bicarbonate types. Specific-conductance field measurements ranged from 187 to 724 microsiemens per centimeter for surface water and 381 to 990 microsiemens per centimeter for ground water. Fecal streptococcal bacteria and fecal coliform bacteria in the surface water make the water unsuitable for domestic use. Some volatile and semivolatile organic compounds were detected in samples of surface water, ground water, and streambed sediment. The potential for contamination exists from point and nonpoint sources on and off the reservation.

Arizona↗
USGS2001

Cross-hole radar scanning of two vertical, permeable, reactive-iron walls at the Massachusetts Military Reservation, Cape Cod, Massachusetts

A pilot-scale study was conducted by the U.S. Army National Guard (USANG) at the Massachusetts Military Reservation (MMR) on Cape Cod, Massachusetts, to assess the use of a hydraulic-fracturing method to create vertical, permeable walls of zero-valent iron to passively remediate ground water contaminated with chlorinated solvents. The study was conducted near the source area of the Chemical Spill-10 (CS-10) plume, a plume containing chlorinated solvents that underlies the MMR. Ground-water contamination near the source area extends from about 24 m (meters) to 35 m below land surface. The USANG designed two reactive-iron walls to be 12 m long and positioned 24 to 37 m below land surface to intersect and remediate part of the CS-10 plume.Because iron, as an electrical conductor, absorbs electromagnetic energy, the US Geological Survey used a cross-hole common-depth, radar scanning method to assess the continuity and to estimate the lateral and vertical extent of the two reactive-iron walls. The cross-hole radar surveys were conducted in boreholes on opposite sides of the iron injection zones using electric-dipole antennas with dominant center frequencies of 100 and 250 MHz. Significant decreases in the radar-pulse amplitudes observed in scans that traversed the injection zones were interpreted by comparing field data to results of two-dimensional finite-difference time-domain numerical models and laboratory-scale physical models.The numerical and physical models simulate a wall of perfectly conducting material embedded in saturated sand. Results from the numerical and physical models show that the amplitude of the radar pulse transmitted across the edge of a conductive wall is about 43 percent of the amplitude of a radar pulse transmitted across background material. The amplitude of a radar pulse transmitted through a hole in a conductive wall increases as the aperture of the hole increases. The modeling results indicate that holes with an aperture of less than 40 percent of the dominant wavelength of the radar pulse are not likely to be detected.Based on the results of the numerical and physical modeling, the decreases in radar-pulse amplitudes observed in scans traversing the injection zones are interpreted as electrically conductive zones that outline the distribution of iron. The area interpreted as iron in the northern A-wall contains two zones -- an upper zone about 10 m wide, extending from about 25 to 31 m below land surface, and a lower zone about 8 m wide, extending from 31.5 to 34.5 m below land surface. The area interpreted as iron in the southern B-wall is about 9 m wide, extending from about 27 to 34.5 m below land surface. No discrete holes were interpreted in either the A- or B-wall zones.The interpretation of the field data suggests that (1) the hydraulic-fracturing method introduced iron into the subsurface, but not in the dimensions originally proposed; (2) the iron within the treatment zones is distributed in a generally continuous manner; and (3) excluding the discontinuity in the A-wall, holes within the iron treatment zone, if any, exist at scales smaller than about 10 cm, the resolution limit of the radar antennas and acquisition geometry used for this study. The cross-hole radar method appears to have been an effective method for delineating the distribution of iron in the two walls; however, the veracity of the results cannot be ascertained without excavation or drilling into the treatment zone.

Massachusetts↗
USGS2000

Ground-water quality and vulnerability to contamination in selected agricultural areas of southeastern Michigan, northwestern Ohio, and northeastern Indiana

Ground-water quality was assessed in the northeastern part of the Corn Belt, where tile-drained row crops are underlain by fractured glacial till. Data were collected from 30 shallow monitor wells and 18 co-located domestic wells as part of the U.S. Geological Survey’s National Water- Quality Assessment in the Lake Erie-Lake St. Clair Basin. Pesticides or pesticide degradates were detected in 41 percent of the monitor wells and 6 percent of the domestic wells. The pesticides detected closely correspond to those most heavily applied—herbicides used on corn and soybeans. Pesticide degradates were detected three times more frequently, and at higher concentrations, than were parent compounds. No pesticide concentration exceeded a USEPA Maximum Contaminant Level (MCL), but MCL’s have not been established for 9 of the 11 compounds detected. Thirty-seven percent of monitor-well samples had nitrate concentrations indicative of human influences such as fertilizer, manure or septic systems. Nitrate was the only chemical constituent detected at a concentration greater than an MCL. The MCL was exceeded in 7 percent of samples from monitor wells which were too shallow to be used as a source of drinking water. Pesticide and nitrate concentrations in the study area are low relative to other agricultural areas of the Nation. Several authors have suggested that ground water in parts of the Upper Midwest is minimally contaminated because it is protected by the surficial glacial till or tile drains. These ideas are examined in light of the relations between concentration, well depth, and groundwater age in the study area. Most of the shallow ground water is hydraulically connected to the land surface, based on the observations that 83 percent of waters from monitor wells were recharged after 1953, and 57 percent contained a pesticide or an elevated nitrate concentration. Fractures or sand-and-gravel stringers within the till are the probable pathways. In some areas, deeper parts of the groundwater- flow system are also hydraulically connected to the land surface. Almost half the waters from wells 50 to 100 feet deep were recharged after 1953. Anthropogenic constituents were detected in samples from three domestic wells 60 to 121 feet deep, in areas where the till is relatively coarse-grained. The hydrogeologic system has several geochemical characteristics conducive to transformations or sorption of nitrate or pesticides: (1) the till is clay-rich, has a high organic-carbon content, and contains an abundance of pyrite-rich shale fragments, (2) the ground water has low dissolved- oxygen concentrations, and (3) iron and manganese oxides and oxyhyroxides line the faces of fractures in the unsaturated zone. Although the aquifer system appears be protected from contamination in some areas, the fact that the surficial till is heterogeneous and of variable thickness suggests that the protection is not uniform. The protection can be breached by fractures or sand-and-gravel stringers, which are apparent in core samples but not noted on domestic-well logs.

Indiana, Michigan, Ohio↗
USGS2000

Detection of conduit-controlled ground-water flow in northwestern Puerto Rico using aerial photograph interpretation and geophysical methods

The development potential of ground-water resources in the karst limestone of northwestern Puerto Rico, in an area extending from the Río Camuy to Aguadilla, is uncertain as a result of limited knowledge of the location of areas where a high density of cavities (interconnected fractures, conduits, and other dissolution features) might suggest the occurrence of high water yields. The presence in northwestern Puerto Rico of numerous coastal submarine springs, cavernous porosity in some of the wells, and rivers with entrenched and underground paths, indicate that it is probable that water-bearing, subterranean interconnected cavities occur in the area between the Río Camuy and Aguadilla. The number of exploratory wells needed to determine the location of these conduits or zones of enhanced secondary porosity could be substantially reduced if more information were available about the location of these subterranean features, greatly reducing the drilling costs associated with a trial-and-error exploratory process. A 3-year study was conducted by the U.S. Geological Survey, in cooperation with the Puerto Rico Aqueduct and Sewer Authority, to detect the presence of cavities that might suggest the occurrence of conduit-controlled groundwater flow. Aerial photographs, geologic and topographic maps, and field reconnaissance were used to identify such linear terrain features as ridges, entrenched canyons, and fracture traces. Natural potential and gravity geophysical methods were also used. The following sites were selected for the aerial photograph interpretation and geophysical testing: Caimital Bajo uplands and former Ramey Air Force Base in Aguadilla; Quebrada de los Cedros between Aguadilla and Isabela; the University of Puerto Rico Agricultural Experiment Station, Otilio dairy farm, and Pozo Brujo in Isabela; the Monte Encantado area in Moca and Isabela; and the Rio Camuy cave system in Hatillo and Camuy. In general, the degree of success varied with site and the geophysical method used. At some sites such as Pozo Brujo, the University of Puerto Rico Agricultural Experiment Station, and Monte Encantado area, natural potential anomalies strongly suggest the existence of conduits with flowing water. At most sites, however, the results obtained did not clearly reveal the presence of subsurface cavities that might be associated with the occurrence of conduit-controlled ground-water flow. Sites such as the University of Puerto Rico Agricultural Experiment Station, Pozo Brujo, and Quebrada de los Cedros warrant a more detailed analysis, including a test well drilling phase to confirm the presence of suspected high-yield water-bearing zones.

Water-Resources Investigations Report↗
USGS2000

Hydrogeology, hydrologic budget, and water chemistry of the Medina Lake area, Texas

A three-phase study of the Medina Lake area in Texas was done to assess the hydrogeology and hydrology of Medina and Diversion Lakes combined (the lake system) and to determine what fraction of seepage losses from the lake system might enter the regional ground-water-flow system of the Edwards and (or) Trinity aquifers. Phase 1 consisted of revising the geologic framework for the Medina Lake area. Results of field mapping show that the upper member of the Glen Rose Limestone underlies Medina Lake and the intervening stream channel from the outflow of Medina Lake to the midpoint of Diversion Lake, where the Diversion Lake fault intersects Diversion Lake. A thin sequence of strata consisting primarily of the basal nodular and dolomitic members of the Kainer Formation of the Edwards Group, is present in the southern part of the study area. On the southern side of Medina Lake, the contact between the upper member of the Glen Rose Limestone and the basal nodular member is approximately 1,000 feet above mean sea level, and the contact between the basal nodular member and the dolomitic member is approximately 1,050 feet above mean sea level. The most porous and permeable part of the basal nodular member is about 1,045 feet above mean sea level. At these altitudes, Medina Lake is in hydrologic connection with rocks in the Edwards aquifer recharge zone, and Medina Lake appears to lose more water to the ground-water system along this bedding plane contact. Hydrologic budgets calculated during phase 2 for Medina Lake, Diversion Lake, and Medina/Diversion Lakes combined indicate that: (1) losses from Medina and Diversion Lakes can be quantified; (2) a portion of those losses are entering the Edwards aquifer; and (3) losses to the Trinity aquifer in the Medina Lake area are minimal and within the error of the hydrologic budgets. Hydrologic budgets based on streamflow, precipitation, evaporation, and change in lake storage were used to quantify losses (recharge) to the ground-water system from Medina Lake, Diversion Lake, and Medina/Diversion Lakes combined during October 1995–September 1996. Water losses from Medina Lake to the Edwards/Trinity aquifers ranged from -14.0 to 135 acre-feet per day; Diversion Lake ranged from -1.2 to 93.1 acre-feet per day; and Medina/Diversion Lakes combined ranged from 36.1 to 119 acre-feet per day. Monthly average recharge during December 1995–July 1996 was estimated using an alternative method developed during this study (current study method) and compared to monthly average recharge during December 1995–July 1996 estimated using the existing USGS method and the Trans-Texas method. Recharge to the Edwards aquifer estimated using the current study method was about 69 and 73 percent of the recharge estimated using the USGS and Trans-Texas methods, respectively. The USGS and Trans-Texas methods overestimated recharge from Medina Lake compared to the recharge estimated with the current study method when Medina Lake stage was between about 1,027 and 1,032 feet above mean sea level and underestimated recharge from Medina Lake when lake stage was between about 1,036 and 1,045 feet above mean sea level. The USGS and Trans-Texas methods underestimated recharge from Diversion Lake compared to the recharge estimated with the current study method when Diversion Lake stage was greater than 913 feet above mean sea level and overestimated recharge from Diversion Lake when lake stage was less than 913 feet above mean sea level. The water quality of Medina Lake and Medina River and in selected wells and springs in the Edwards and Trinity aquifers was characterized during phase 3 of the study. Environmental isotope analyses and geochemical modeling also were used to determine where water losses from the lake system might be entering the ground-water-flow system. Isotopic ratios of deuterium, oxygen, and strontium were analyzed in selected surface-water, lake-water, and ground-water samples to trace the isotopic “signature” of the lake water as it mixes with the ground water and to determine the fraction of lake water and ground water in selected Edwards aquifer wells. Isotopic data and geochemical modeling were used to show that lake water is moving into the Edwards aquifer in two fault blocks in the eastern Medina storage unit. One fault block is bounded on the north by the Vandenburg School fault and on the south by the Haby Crossing fault, and the second fault block is bounded on the north by the Diversion Lake fault and on the south by the Haby Crossing fault. In selected Edwards aquifer wells located southwest of Medina Lake and west of Diversion Lake, the proportion of lake water ranged from about 10 to 45 percent. Geochemical modeling using NETPATH confirms the degree of mixing between lake water and aquifer water shown by the isotopes.

Texas↗
USGS2000

Vulnerability of ground water to contamination, Edwards Aquifer recharge zone, Bexar County, Texas, 1998

The Edwards aquifer, one of the most productive carbonate-rock aquifers in the Nation, is composed of the Kainer and Person Formations of the Edwards Group plus the overlying Georgetown Formation. Most recharge to the Edwards aquifer results from the percolation of streamflow loss and the infiltration of precipitation through porous parts of the recharge zone. Residential and commercial development is increasing, particularly in Bexar County in south-central Texas, atop the densely fractured and steeply faulted recharge zone. The increasing development has increased the vulnerability of ground water to contamination by spillage or leakage of waste materials, particularly fluids associated with urban runoff and (or) septic-tank leachate. This report describes a method of assessing the vulnerability of ground water to contamination in the Edwards aquifer recharge zone. The method is based on ratings of five natural features of the area: (1) hydraulic properties of outcropping hydrogeologic units; (2) presence or absence of faults; (3) presence or absence of caves and (or) sinkholes; (4) slope of land surface; and (5) permeability of soil. The sum of the ratings for the five natural features was used to develop a map showing the recharge zone's vulnerability to ground-water contamination.

Water-Resources Investigations Report↗
USGS2001

Hydrogeology and water quality of five principal aquifers in the Lower Platte South Natural Resources District, eastern Nebraska, 1994

The U.S. Geological Survey, in cooperation with the Lower Platte South Natural Resources District, conducted a hydrogeologic and water-quality reconnaissance study of the five principal aquifers in deposits of Quaternary age in the Natural Resources District. The purpose of the study was to delineate the approximate extent of the aquifers, to estimate volumes of drainable water in three aquifers, to provide information that could be useful in designing future ground-water-quality monitoring, and to determine baseline water-quality conditions in the aquifers, focusing on nitrate concentrations. The approximate lateral boundaries of the Dwight-Valparaiso, Crete-Princeton-Adams, and Waverly aquifers were defined as areas in which the thickness of continuous sand and gravel deposits was less than 40 feet. The three aquifers were determined to contain about 1,340,000; 1,540,000; and 172,000 acre-feet of drainable water, respectively, assuming a specific yield of 0.20. During the summer of 1994, ground-water samples were collected from 46 wells in the five aquifers and analyzed for nitrate and screened for triazine herbicides. Additionally, water samples from 39 of these wells were analyzed for major ions, iron, and manganese, and 35 were analyzed for radon. Water-quality analyses revealed that the water in the five aquifers had specific conductances that ranged from 399 to 2,040 micro-siemens per centimeter and was a calcium-carbonate to calcium-magnesium-sodium carbonate type. The most mineralized water samples were from the Crete-Princeton-Adams aquifer, which contained a median concentration of dissolved solids of 520 milligrams per liter. Concentrations of nitrate in water samples from the aquifers ranged from less than 0.05 to 23 milligrams per liter as nitrogen, and only six water samples exceeded the Maximum Contaminant Level established by the U.S. Environmental Protection Agency of 10 milligrams per liter. The median concentration of radon for water samples from the five aquifers was 300 picocuries per liter, which is the proposed Maximum Contaminant Level. Water samples from the Crete-Princeton-Adams and Waverly aquifers had the largest concentrations of radon among the five aquifers. The Crete-Princeton-Adams aquifer had a median concentration of 440 picocuries per liter, and the Waverly aquifer had a median concentration of 390 picocuries per liter. Herbicides were detected in water from only six wells, which were in four of the five aquifers. Atrazine, metabolites of atrazine, metolachlor, and metribuzin were detected in concentrations generally less than 1.00 microgram per liter.

Water-Resources Investigations Report↗
USGS2000

Results of well-bore flow logging for six water-production wells completed in the Santa Fe Group aquifer system, Albuquerque, New Mexico, 1996-98

Over the last several years, an improved conceptual understanding of the aquifer system in the Albuquerque area, New Mexico, has lead to better knowledge about the location and extent of the aquifer system. This information will aid with the refinement of ground-water simulation and with the location of sites for future water-production wells. With an impeller-type flowmeter, well-bore flow was logged under pumping conditions along the screened interval of the well bore in six City of Albuquerque water-production wells: the Ponderosa 3, Love 6, Volcano Cliffs 1, Gonzales 2, Zamora 2, and Gonzales 3 wells. From each of these six wells, a well-bore flow log was collected that represents the cumulative upward well-bore flow. Evaluation of the well-bore flow log for each well allowed delineation of the more productive zones supplying water to the well along the logged interval. Yields from the more productive zones in the six wells ranged from about 70 to 880 gallons per minute. The lithology of these zones is predominantly gravel and sand with varying amounts of sandy clay.

Water-Resources Investigations Report↗