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USGS2001

Hydrogeologic framework and geochemistry of the intermediate aquifer system in parts of Charlotte, De Soto, and Sarasota counties, Florida

The hydrogeologic framework underlying the 600-square-mile study area in Charlotte, De Soto, and Sarasota Counties, Florida, consists of the surficial aquifer system, the intermediate aquifer system, and the Upper Floridan aquifer. The hydrogeologic framework and the geochemical processes controlling ground-water composition were evaluated for the study area. Particular emphasis was given to the analysis of hydrogeologic and geochemical data for the intermediate aquifer system. Flow regimes are not well understood in the intermediate aquifer system; therefore, hydrogeologic and geochemical information were used to evaluate connections between permeable zones within the intermediate aquifer system and between overlying and underlying aquifer systems. Knowledge of these connections will ultimately help to protect ground-water quality in the intermediate aquifer system. The hydrogeology was interpreted from lithologic and geophysical logs, water levels, hydraulic properties, and water quality from six separate well sites. Water-quality samples were collected from wells located along six ground-water flow paths and finished at different depth intervals. The selection of flow paths was based on current potentiometric-surface maps. Ground-water samples were analyzed for major ions; field parameters (temperature, pH, specific conductance, and alkalinity); stable isotopes (deuterium, oxygen-18, and carbon-13); and radioactive isotopes (tritium and carbon-14). The surficial aquifer system is the uppermost aquifer, is unconfined, relatively thin, and consists of unconsolidated sand, shell, and limestone. The intermediate aquifer system underlies the surficial aquifer system and is composed of clastic sediments interbedded with carbonate rocks. The intermediate aquifer system is divided into three permeable zones, the Tamiami/Peace River zone (PZ1), the Upper Arcadia zone (PZ2), and the Lower Arcadia zone (PZ3). The Tamiami/Peace River zone (PZ1) is the uppermost zone and is the thinnest and generally, the least productive zone in the intermediate aquifer system. The Upper Arcadia zone (PZ2) is the middle zone and productivity is generally higher than the overlying permeable zone. The Lower Arcadia zone (PZ3) is the lowermost permeable zone and is the most productive zone in the intermediate aquifer system. The intermediate aquifer system is underlain by the Upper Floridan aquifer, which consists of a thick, stratified sequence of limestone and dolomite. The Upper Floridan aquifer is the most productive aquifer in the study area; however, its use is generally restricted because of poor water quality. Interbedded clays and fine-grained clastics separate the aquifer systems and permeable zones. The hydraulic properties of the three aquifer systems are spatially variable. Estimated trans-missivity and horizontal hydraulic conductivity varies from 752 to 32,900 feet squared per day and from 33 to 1,490 feet per day, respectively, for the surficial aquifer system; from 47 to 5,420 feet squared per day and from 2 to 102 feet per day, respectively, for the Tamiami/Peace River zone (PZ1); from 258 to 24,633 feet squared per day and from 2 to 14 feet per day, respectively, for the Upper Arcadia zone (PZ2); from 766 to 44,900 feet squared per day and from 10 to 201 feet per day, respectively, for the Lower Arcadia zone (PZ3); and from 2,350 to 7,640 feet squared per day and from 10 to 41 feet per day, respectively, for the Upper Floridan aquifer. Confining units separating the aquifer systems have leakance coefficients estimated to range from 2.3 x 10-5 to 5.6 x 10-3 feet per day per foot. Strata composing the confining unit separating the Upper Floridan aquifer from the intermediate aquifer system are substantially more permeable than confining units separating the permeable zones in the intermediate aquifer system or separating the surficial aquifer and intermediate aquifer systems. In Charlotte, Sarasota, and western De Soto Counties, hydraulic

Water-Resources Investigations Report↗
USGS2001

Use of thematic mapper imagery to assess water quality, trophic state, and macrophyte distributions in Massachusetts lakes

During the spring and summer of 1996, 1997, and 1998, measurements of phytoplankton- chlorophyll concentration, Secchi disk transparency, and color were made at 97 Massachusetts lakes within 24 hours of Landsat Thematic Mapper imaging of the lakes in an effort to assess water quality and trophic state. Spatial distributions of floating, emergent, and submerged macrophytes were mapped in 49 of the lakes at least once during the 3-year period. The maps were digitized and used to assign pixels in the thematic mapper images to one of four vegetation cover classes-open water, 1-50 percent floating-and-emergent-vegetation cover, 51-100 percent floating-and-emergent-vegetation cover, and submerged vegetation at any density. The field data were collected by teams of U.S. Geological Survey and Massachusetts Department of Environmental Management staff and by 76 volunteers. Side-by-side sampling by U.S. Geological Survey and volunteer field teams resulted in statistically similar chlorophyll determinations, Secchi disk readings, and temperature measurements, but concurrent color determinations were not similar, possibly due to contamination of sample bottles issued to the volunteers.Attempts to develop predictive relations between phytoplankton-chlorophyll concentration, Secchi disk transparency, lake color, dissolved organic carbon, and various combinations of thematic mapper bands 1, 2, 3, and 4 digital numbers were unsuccessful, primarily because of the extremely low concentrations of chlorophyll in the lakes studied, and also because of the highly variable dissolved organic carbon concentrations.Predictive relations were developed between Secchi disk transparency and phytoplankton-chlorophyll concentration, and between color and dissolved organic carbon concentration. Phytoplankton-chlorophyll concentration was inversely correlated with Secchi disk transparency during all three sampling periods. The relations were very similar in 1996 and 1997 and indicated that 62 to 67 percent of the variability in Secchi disk transparency could be explained by the chlorophyll concentration. Analysis of color and dissolved organic carbon concentrations in water samples collected by U.S. Geological Survey field teams in 1996-98 indicated that 91 percent of the variance in color in Massachusetts lakes can be explained by variations in dissolved organic carbon.Areas of open-water, submerged vegetation, and two surface-vegetation-cover classes predicted from Thematic Mapper images acquired in the summer of 1996 closely matched the areas observed in a set of field observations. However, the same analysis applied to a set of data acquired in the summer of 1997 resulted in somewhat less reliable predictions, and an attempt to predict 1996 vegetation-cover areas using the relations developed in the 1997 analysis was unsuccessful.

Water-Resources Investigations Report↗
USGS2001

Characteristics of water, sediment, and benthic communities of the Wolf River, Menominee Indian Reservation, Wisconsin, water years 1986-98

Analyses and interpretation of water quality, sediment, and biological data from water years 1986 through 1998 indicated that land use and other human activities have had only minimal effects on water quality in the Wolf River upstream from and within the Menominee Indian Reservation in northeastern Wisconsin. Relatively high concentrations of calcium and magnesium (natural hardness), iron, manganese, and aluminum were measured in Wolf River water samples during water years 1986-98 from the three sampled sites and attributed to presence of highly mineralized geologic materials in the basin. Average calcium and magnesium concentrations varied from 22-26 milligrams per liter (mg/L) and 11-13 mg/L, respectively. Average iron concentrations ranged from 290-380 micrograms per liter ( μ g/L); average manganese concentrations ranged from 53-56 mg/L. Average aluminum concentrations ranged from 63-67 μ g/L. Mercury was present in water samples but concentrations were not at levels of concern. Levels of Kjeldahl nitrogen, ammonia, nitrite plus nitrate, total phosphorus, and orthophosphorus in water samples were often low or below detection limits (0.01- 0.10 mg/L). Trace amounts of atrazine (maximum concentration of 0.031 μ g/L), deethylatrazine (maximum 0.032 μ g/L), and alachlor (maximum of 0.002 μ g/L) were detected. Low concentrations of most trace elements were found in streambed sediment. Tissues of fish and aquatic invertebrates collected once each year from 1995 through 1998 at the Langlade and Keshena sites, near the northern and southern boundaries of the Reservation, respectively, were low in concentrations of most trace elements. Arsenic and silver in fish livers from both sites were less than or equal to 2 μ g/g arsenic and less than 1 μ g/g silver for dry weight analysis, and concentrations of antimony, beryllium, cadmium, cobalt, lead, nickel, and uranium were all below detection limits (less than 1 μ g/g dry weight). Concentrations of most other trace elements in fish were low, with the exceptions of chromium, copper, mercury, and selenium; however, these concentrations are not at levels of concern. Concentrations of all trace elements analyzed in whole caddisfly larvae also were low compared to those reported in the literature. During 1998, a total of 48 species of macroinvertebrates were identified at each of two sampled sites, with similar numbers of genera represented at both: 41 at Keshena and 44 at Langlade. The percentage EPT (Ephemeroptera, Plecoptera, and Trichoptera) was 52 at Keshena and 77 at Langlade; these relatively large percentages suggest very good to excellent water quality at these sites. A total of 52 algal taxa were identified at the Wolf River near Langlade. Diatoms made up 96 percent of the algal biomass. A total of 58 algal taxa were identified at Keshena, including 48 diatom taxa (83 percent). Although diatoms accounted for just 22 percent of the algal relative abundance, in cells per square centimeter, diatoms contributed 91 percent of the total algal biomass. The overall biological integrity of the Keshena and Langlade sites, based on diversity, siltation, and pollution indexes for diatoms is excellent.

Wisconsin↗
USGS2001

Benthic invertebrate communities and their responses to selected environmental factors in the Kanawha River basin, West Virginia, Virginia, and North Carolina

The effects of selected environmental factors on the composition and structure of benthic invertebrate communities in the Kanawha River Basin of West Virginia, Virginia and North Carolina were investigated in 1997 and 1998. Environmental factors investigated include physiography, land-use pattern, streamwater chemistry, streambed- sediment chemistry, and habitat characteristics. Land-use patterns investigated include coal mining, agriculture, and low intensity rural-residential patterns, at four main stem and seven tributary sites throughout the basin. Of the 37 sites sampled, basin size and physiography most strongly affected benthic invertebrate-community structure. Land-use practices also affected invertebrate community structure in these basins. The basins that differed most from the minimally affected reference condition were those basins in which coal mining was the dominant nonforest land use, as determined by comparing invertebrate- community metric values among sites. Basins in which agriculture was important were more similar to the reference condition. The effect of coal mining upon benthic invertebrate communities was further studied at 29 sites and the relations among invertebrate communities and the selected environmental factors of land use, streamwater chemistry, streambed- sediment chemistry, and habitat characteristics analyzed. Division of coal-mining synoptic-survey sites based on invertebrate-community composition resulted in two groups?one with more than an average production of 9,000 tons of coal per square mile per year since 1980, and one with lesser or no recent coal production. The group with significant recent coal production showed higher levels of community impairment than the group with little or no recent coal production. Median particle size of streambed sediment, and specific conductance and sulfate concentration of streamwater were most strongly correlated with effects on invertebrate communities. These characteristics were related to mining intensity, as measured by thousands of tons of coal produced per square mile of drainage area.

North Carolina, Virginia, West Virginia↗
USGS2002

Hydrogeologic and water-quality reconnaissance of the artesian aquifer under the Shoalwater Bay Indian Reservation and Tokeland Peninsula, Pacific County, Washington, 1998-99

The U.S. Geological Survey (USGS) collected and compiled hydrogeologic and water quality data from September 1998 through September 1999 to describe the hydrogeologic setting and to assess the quality of the water in the artesian aquifer under the Shoalwater Bay Indian Reservation and the adjacent Tokeland Peninsula area of Pacific County, Washington. Hydrogeologic data include descriptions of 38 wells, lithologic data for 27 wells, and water-level data for 17 wells and 1 tidal station. Water-quality data include field measurements for temperature, specific conductance, pH, alkalinity, bicarbonate, carbonate, dissolved oxygen, and laboratory analyses for major inorganic ions, metals, nutrients, methylene blue-active substances, and pesticides. None of the 93 field measurements or chemicals analyzed for exceeded the U.S. Environmental Protection Agency (USEPA) primary standards for drinking water and only 2 constituents (iron and manganese) exceeded the USEPA secondary standards. Sixty-six of the constituents (including all 53 pesticides) were at or below the reporting or detection levels established by the USGS National Water Quality Laboratory.

Water-Resources Investigations Report↗
USGS2002

Aquifer geochemistry and effects of pumping on ground-water quality at the Green Belt Parkway Well Field, Holbrook, Long Island, New York

Geochemistry, microbiology, and water quality of the Magothy aquifer at a new supply well in Holbrook were studied to help identify factors that contribute to iron-related biofouling of public-supply wells. The organic carbon content of borehole sediments from the screen zone, and the dominant terminal electron-accepting processes (TEAPs), varied by depth. TEAP assays of core sediments indicated that iron reduction, sulfate reduction, and undetermined (possibly oxic) reactions and microbial activity are correlated with organic carbon (lignite) content. The quality of water from this well, therefore, reflects the wide range of aquifer microenvironments at this site. High concentrations of dissolved iron (3.6 to 6.4 micromoles per liter) in water samples from this well indicate that some water is derived from Fe(III)-reducing sediments within the aquifer, but traces of dissolved oxygen indicate inflow of shallow, oxygenated water from shallow units that overlie the local confining units. Water-quality monitoring before and during a 2-day pumping test indicates that continuous pumping from the Magothy aquifer at this site can induce downward flow of shallow, oxygenated water despite the locally confined conditions. Average concentrations of dissolved oxygen are high (5.2 milligrams per liter, or mg/L) in the overlying upper glacial aquifer and at the top of the Magothy aquifer (4.3 mg/L), and low ( < 0.1 mg/L) in the deeper, anaerobic part of the Magothy; average concentrations of phosphate are high (0.4 mg/L) in the upper glacial aquifer and lower (0.008 mg/L) at the top of the Magothy aquifer and in the deeper part of the Magothy (0.013 mg/L). Concentrations of both constituents increased during the 2 days of pumping. The δ 34 S of sulfate in shallow ground water from observation wells (3.8 to 6.4 per mil) was much heavier than that in the supplywell water (-0.1 per mil) and was used to help identify sources of water entering the supply well. The δ 34 S of sulfate in a deep observation well adjacent to the supply well increased from 2.4 per mil before pumping to 3.3 per mil after pumping; this confirms that the pumping induced downward migration of water. The lighter δ 34 S value in the pumped water than in the adjacent observation well probably indicates FeS 2 oxidation (which releases light δ 34 S in adjacent sediments) by the downward flow of oxygenated water.

New York↗
USGS2001

Historical trends and concentrations of fecal coliform bacteria in the Brandywine Creek basin, Chester County, Pennsylvania

The Brandywine Creek in Chester County is used for recreation and as an important source of drinking water. For this study, 40 sites were established for collection of water samples for analysis of fecal coliform and Escherichia coli bacteria in 1998-99. Samples were collected during base-flow conditions and during five storms in which rainfall exceeded 0.5 inch. During base- flow conditions, the median concentrations of fecal coliform bacteria exceeded 200 col/100 mL at 26 of the 40 sites (65 percent). During stormflow conditions, the median concentration of fecal coliform bacteria exceeded the Pennsylvania Department of Environmental Protection (PaDEP) criterion of 200 col/100 mL at 30 of 33 sites sampled (91 percent). Trends in fecal coliform bacteria concentrations were downward for the period 1973-99 at three long-term water-quality monitor stations, the result of upgrades in wastewater treatment plants, decreases in point-source discharges, and a decrease in agricultural land. A positive relation exists between streamflow and concentrations of fecal coliform bacteria at two of the long-term stations, but concentrations are elevated in base flow and stormflow at all three stations. Factors affecting bacteria concentrations in the Brandywine Creek Basin include nonpoint-source contaminants, reservoirs, seasonality, and stormflow. Nonpoint sources of bacterial contamination in the basin include, but are not limited to, land-surface runoff, urbanization, agricultural processes, groundwater contamination, and wildlife. Bacteria concentrations in streams that flow directly from the reservoirs are much lower than the concentrations in the streams flowing into the reservoirs. During March, April, May, October, and November, the Brandywine Creek tends to have lower water temperatures and bacteria concentrations than during June, July, August, and September. The 10-year median concentrations of bacteria at West Branch Brandywine Creek at Modena and East Branch Brandywine Creek below Downingtown exceed the criterion of 200 col/100 mL established by the PaDEP during the swimming season. The 10-year median concentrations of bacteria at Brandywine Creek at Chadds Ford exceed the criterion of 200 col/100 mL only during June. None of the stations exceed the criterion of 2,000 col/100 mL as established by the PaDEP for the remainder of the year.

Water-Resources Investigations Report↗
USGS2001

Relations among rainstorm runoff, streamflow, pH, and metal concentrations, Summitville Mine area, upper Alamosa River basin, southwest Colorado, 1995-97

The upper Alamosa River Basin contains areas that are geochemically altered and have associated secondary sulfide mineralization. Occurring with this sulfide mineralization are copper, gold, and silver deposits that have been mined since the 1870's. Weathering of areas with sulfide mineralization produces runoff with anomalously low pH and high metal concentrations; mining activities exacerbate the condition. Summer rainstorms in the upper Alamosa River Basin produce a characteristic relation between streamflow and pH; streamflow suddenly increases and pH suddenly decreases (commonly by more than 1 pH unit). This report evaluates changes in pH in the upper Alamosa River Basin during July, August, and September 1995, 1996, and 1997 to examine possible adverse environmental effects due to rainstorm runoff. Ninety-three percent of the rainstorms occurring during 1995?97 produced runoff throughout the entire basin. Out of 54 storms, only 3 storms were isolated to the river reach upstream from the streamflow-gaging station Alamosa River above Wightman Fork, and only 1 storm was isolated to the river reach between the streamflow-gaging stations Alamosa River below Jasper and Alamosa River above Terrace Reservoir. Although most rainstorm runoff events occurred throughout the entire basin, pH changes were highest in parts of the basin that receive runoff from hydrothermally altered areas. The three principal altered areas within the basin are the Jasper, Stunner, and Summitville areas. Only limited mining occurred in the Stunner altered area, and yet significant decreases in pH values occur due to runoff from this area. Even after environmental restoration activities are completed at the Summitville Mine, the main stem of the Alamosa River may continue to be adversely affected by runoff from the Stunner and Jasper altered areas. A comparison of measured pH with Federal and State of Colorado water-quality standards and Toxicological Reference Values indicates pH was too low to support aquatic life in many parts of the basin for extended periods of time. Added stresses from sudden decreases in pH due to rainstorm runoff compound the adverse effects. Discharge of effluent from the Summitville Mine impoundment can significantly decrease pH in the Alamosa River downstream to Terrace Reservoir. A release of only 3 cubic feet per second from the impoundment decreased pH by at least 1 standard unit at all downstream sites. Low-flow years may pose a substantial risk to aquatic organisms within and downstream from Terrace Reservoir. During 1996, the basin had a low-flow year, and water storage and pool size of Terrace Reservoir were significantly reduced. The pH of water discharging from Terrace Reservoir was anomalously low during late August and September 1996, possibly due to geochemical interactions between sediment and the water column within the reservoir. In general, an inverse log-log relation exists between pH and the logarithm of dissolved metal concentrations, but the relations generally are not significant enough to confidently predict metal concentrations based upon measured pH values.

Water-Resources Investigations Report↗
USGS2001

Vertical gradients in water chemistry in the central High Plains aquifer, southwestern Kansas and Oklahoma panhandle, 1999

The central High Plains aquifer is the primary source of water for domestic, industrial, and irrigation uses in parts of Colorado, Kansas, New Mexico, Oklahoma, and Texas. Water-level declines of more than 100 feet in some areas of the aquifer have increased the demand for water deeper in the aquifer. The maximum saturated thickness of the aquifer ranged from 500 to 600 feet in 1999. As the demand for deeper water increases, it becomes increasingly important for resource managers to understand how the quality of water in the aquifer changes with depth. In 1998?99, 18 monitoring wells at nine sites in southwestern Kansas and the Oklahoma Panhandle were completed at various depths in the central High Plains aquifer, and one monitoring well was completed in sediments of Permian age underlying the aquifer. Water samples were collected once from each well in 1999 to measure vertical gradients in water chemistry in the aquifer. Tritium concentrations measured in ground water indicate that water samples collected in the upper 30 feet of the aquifer were generally recharged within the last 50 years, whereas all of the water samples collected at depths more than 30 feet below the water table were recharged more than 50 years ago. Dissolved oxygen was present throughout the aquifer, with concentrations ranging from 1.7 to 8.4 mg/L. Water in the central High Plains aquifer was predominantly a calcium-bicarbonate type that exhibited little variability in concentrations of dissolved solids with depth (290 to 642 mg/L). Exceptions occurred in some areas where there had been upward movement of mineralized water from underlying sediments of Permian age and areas where there had been downward movement of mineralized Arkansas River water to the aquifer. Calcium-sulfate and sodium-chloride waters dominated and concentrations of dissolved solids were elevated (862 to 4,030 mg/L) near the base of the aquifer in the areas of upward leakage. Dissolution of gypsum or anhydrite and halite in sediments of Permian age by ground water was the likely source of calcium, sulfate, sodium, and chloride in those waters. Calcium-sodium-sulfate waters dominated, and concentrations of dissolved solids were as large as 4,916 mg/L near the water table in the area of downward leakage. Dissolution of minerals in sedimentary deposits of marine origin in upstream areas of the Arkansas River drainage were the likely sources of calcium, sodium, and sulfate in those waters. Nitrate was detected throughout the aquifer and the background concentration was estimated to be 2.45 mg/L as N. The largest nitrate concentrations (8.28, 22, and 54.4 mg/L as N) occurred in recently recharged water collected adjacent to irrigated fields. Three pesticides (atrazine, metolachlor, simazine) and five pesticide degradation products (alachlor ethanesulfonic acid, alachlor oxanilic acid, deethylatrazine, metolachlor ethanesulfonic acid, metolachlor oxanilic acid) were detected in recently recharged water from six water-table wells. Five of the six wells were adjacent to irrigated fields. These data indicate that concentrations of nitrate and pesticides increased over time in some areas of the aquifer as a result of agricultural activities. Results from this study indicate that vertical gradients in water chemistry existed in the central High Plains aquifer. The chemical gradients resulted from chemical inputs to the aquifer from underlying sediments of Permian age, from the Arkansas River, and from agricultural activities. In areas where those chemical inputs occurred, water quality in the aquifer was impaired and may not have been suitable for some intended uses.

Water-Resources Investigations Report↗
USGS2002

Borehole-geophysical investigation of the University of Connecticut landfill, Storrs, Connecticut

A borehole-geophysical investigation was conducted to help characterize the hydrogeology of the fractured-rock aquifer and the distribution of unconsolidated glacial deposits near the former landfill and chemical waste-disposal pits at the University of Connecticut in Storrs, Connecticut. Eight bedrock boreholes near the landfill and three abandoned domestic wells located nearby were logged using conventional and advanced borehole-geophysical methods from June to October 1999. The conventional geophysical-logging methods included caliper, gamma, fluid temperature, fluid resistivity, and electromagnetic induction. The advanced methods included deviation, optical and acoustic imaging of the borehole wall, heat-pulse flowmeter, and directional radar reflection. Twenty-one shallow piezometers (less than 50-feet deep) were logged with gamma and electromagnetic induction tools to delineate unconsolidated glacial deposits. Five additional shallow bedrock wells were logged with conventional video camera, caliper, electromagnetic induction, and fluid resistivity and temperature tools. The rock type, foliation, and fracturing of the site were characterized from high-resolution optical-televiewer (OTV) images of rocks penetrated by the boreholes. The rocks are interpreted as fine- to medium-grained quartz-feldsparbiotite-garnet gneiss and schist with local intrusions of quartz diorite and pegmatite and minor concentrations of sulfide mineralization similar to rocks described as the Bigelow Brook Formation on regional geologic maps. Layers containing high concentrations of sulfide minerals appear as high electrical conductivity zones on electromagneticinduction and borehole-radar logs. Foliation in the rocks generally strikes to the northeast-southwest and dips to the west, consistent with local outcrop observations. The orientation of foliation and small-scale gneissic layering in the rocks, however, varies locally and with depth in some of the boreholes. In two of the boreholes, the foliation strikes predominantly to the northwest and dips to the northeast. Although small-scale faults and lithologic discontinuities were observed in the OTV data, no large-scale faults were observed that appear on regional geologic maps. Fractures were located and characterized through the use of conventional geophysical, OTV, acoustic-televiewer (ATV), and borehole-radar logs. The orientation of fractures varies considerably across the site; some fractures are parallel to the foliation, whereas others cross-cut the foliation. Many of the transmissive fractures in the bedrock boreholes strike about N170°E and N320°E with dips of less than 45°. Other transmissive fractures strike about N60°E with dips of more than 60°. Most of the transmissive fractures in the domestic wells strike about N60°E and N22°E with dips of more than 45°. The strike of N60°E is parallel to the trend of a thrust fault that appears on regional geologic maps. Vertical flow in the boreholes was measured with the heat-pulse flowmeter under ambient and (or) pumping conditions. Results of ATV, OTV, and conventional logs were used to locate specific zones for flowmeter testing. Ambient downflow was measured in three boreholes, ambient upflow was measured in two other boreholes, and both ambient downflow and upflow were measured in a sixth borehole. The other five bedrock boreholes and domestic wells did not have measurable vertical flow. The highest rate of ambient flow was measured in the background borehole in which upflow and downflow converged and exited the borehole at a fracture zone near a depth of 62 feet. Ambient flow of about 340 gallons per day was measured. In the other five wells, ambient flow of about 20 to 35 gallons per day was measured. Under low-rate pumping (0.25 to 1 gallon per minute), one to six inflow zones were identified in each well. Usually the fractures that are active under ambient conditions contribute to the well under pumping conditions. To prevent ambient vertical flow and the potential for cross-contamination, temporary borehole liners were installed in five of the boreholes. Specific-capacity and open-hole transmissivity values were determined in eight boreholes completed in bedrock. The specific capacity estimated for these boreholes ranges from 0.14 to 1.6 gallons per minute per foot. The values for open-hole transmissivity range over two orders of magnitude and when proportioned to individual fracture transmissivity, range from 23 to 340 feet squared per day. Two boreholes had been drilled to intersect electrically conductive zones identified by previous surface-geophysical investigations. The borehole-geophysical results indicate that the boreholes penetrate electrically conductive structures consistent with the anomalies interpreted from the surface-geophysical data. Borehole MW121R was located to intersect a dipping electrically conductive anomaly at about 60 feet, interpreted from the two-dimensional direct currentresistivity survey conducted on the western side of the landfill. The electromagnetic-conductivity log in the borehole contains a high electrical conductivity anomaly at a depth of 69 feet. The magnitude of this anomaly is nearly 10,000 millisiemens per meter and is coincident with a layer containing sulfide mineralization, rather than fractures. The other borehole, MW105R, was located to intersect another anomaly south of the landfill. This anomaly was interpreted as a north-south striking, westward dipping feature. In the borehole, two south-striking, westward dipping fractures were identified in the ATV, OTV, and radar logs. The specific conductance of the fluid measured near these fractures was as high as 1,250 microsiemens per centimeter. Water-quality samples collected in October 1999 from an isolated zone from 71.5 to 76.5 feet indicated high specific conductance (810 microsiemens per centimeter), high concentrations of iron and cadmium, negative oxidation-reduction potential, and chlorobenzene. Collectively, these parameters indicate that the high specific conductance in the borehole logs for MW105R was caused by landfill leachate. Therefore, the anomaly identified by boreholeand surface-geophysical surveys is interpreted as a conductive lithologic feature and a permeable fracture zone that contains landfill leachate.

Connecticut↗
USGS2001

Review and analysis of available streamflow and water-quality data for Park County, Colorado, 1962-98

Information on streamflow and surface-water and ground-water quality in Park County, Colorado, was compiled from several Federal, State, and local agencies. The data were reviewed and analyzed to provide a perspective of recent (1962-98) water-resource conditions and to help identify current and future water-quantity and water-quality concerns. Streamflow has been monitored at more than 40 sites in the county, and data for some sites date back to the early 1900's. Existing data indicate a need for increased archival of streamflow data for future use and analysis. In 1998, streamflow was continuously monitored at about 30 sites, but data were stored in a data base for only 10 sites. Water-quality data were compiled for 125 surface-water sites, 398 wells, and 30 springs. The amount of data varied considerably among sites; however, the available information provided a general indication of where water-quality constituent concentrations met or exceeded water-quality standards. Park County is primarily drained by streams in the South Platte River Basin and to a lesser extent by streams in the Arkansas River Basin. In the South Platte River Basin in Park County, more than one-half the annual streamflow occurs in May, June, and July in response to snowmelt in the mountainous headwaters. The annual snowpack is comparatively less in the Arkansas River Basin in Park County, and mean monthly streamflow is more consistent throughout the year. In some streams, the timing and magnitude of streamflow have been altered by main-stem reservoirs or by interbasin water transfers. Most values of surface-water temperature, dissolved oxygen, and pH were within recommended limits set by the Colorado Department of Public Health and Environment. Specific conductance (an indirect measure of the dissolved-solids concentration) generally was lowest in streams of the upper South Platte River Basin and higher in the southern one-half of the county in the Arkansas River Basin and in the South Platte River downstream from Antero Reservoir. Historical nitrogen concentrations in surface water were small. Nitrite was not detected, most un-ionized ammonia concentrations were less than 0.02 milligram per liter, and all nitrate concentrations were less than 1.2 milligrams per liter. Nitrate concentrations were higher in urban and built-up areas than in rangeland and forest areas. Most median concentrations of total phosphorus at individual sites were less than 0.05 milligram per liter, and concentrations were not significantly different among urban and built-up, rangeland, and forest areas. An upward trend in total phosphorus concentration was determined for flow from the East Portal of the Harold D. Roberts Tunnel, but the slope of the trend line was small and the concentrations were equal or nearly equal to the detection limit of 0.01 milligram per liter. Using median phosphorus loads for two South Platte River sites, the annual phosphorus load transported out of Park County in the South Platte River was calculated to be about 10,000 pounds. Median iron and manganese concentrations for most areas of Park County were less than in-stream water-quality standards, even though several individual concentrations were one to two orders of magnitude larger than the standards. The largest concentrations of aluminum, cadmium, chromium, copper, iron, manganese, nickel, and zinc were from the upper North Fork South Platte River Basin or the Mosquito Creek Basin. All ground-water concentrations of chloride and most ground-water concentrations of sulfate were less than the U.S. Environmental Protection Agency (USEPA) drinking-water standard of 250 milligrams per liter. Median dissolved-solids concentrations in ground water ranged from 160 milligrams per liter in the crystalline-rock aquifers to 257 milligrams per liter in the sedimentary-rock aquifers. Dissolved-solids concentrations greater than the USEPA drinking-water standard of 500 milligrams per liter were detected in abo

Water-Resources Investigations Report↗
USGS2001

Hydrogeology, model description, and flow analysis of the Mississippi River alluvial aquifer in northwestern Mississippi

The Mississippi River alluvial aquifer underlies a 7,000-square-mile area of the Mississippi River alluvial plain in northwestern Mississippi, an area locally known as the Delta. The alluvial aquifer is the most heavily pumped aquifer in Mississippi, and wells yielding more than 2,000 gallons per minute are common. About 98 percent of the pumpage from the alluvial aquifer is for agriculture. The sand and gravel that form the alluvial aquifer averages about 110 feet in thickness. The aquifer is confined over most of the Delta, and the upper confining unit averages about 25 feet in thickness. The average depth to water in the alluvial aquifer during fall 1999 was about 25 feet. The alluvial aquifer receives lateral recharge at the western boundary from the Mississippi River and at the eastern boundary from aquifers that directly underlie the Bluff Hills. The alluvial aquifer receives water vertically from precipitation, internal streams and lakes, and locally from the Cockfield and Sparta aquifers where they directly underlie the alluvial aquifer. The alluvial aquifer also discharges water to the underlying aquifers, and during extended periods with no surface runoff, to the Mississippi River and to the internal streams and lakes. The magnitude of recharge from the Mississippi River, precipitation, and internal lakes and streams can vary greatly depending upon hydrologic and climatic conditions. The U.S. Geological Survey modular threedimensional finite-difference ground-water flow model, MODFLOW, was used to simulate the Mississippi River alluvial aquifer flow system in northwestern Mississippi. The model uses one layer with a rectangular-grid and 1-mile square cells to represent the alluvial aquifer. The model was calibrated and verified by using spring and fall water-level measurements from January 1988 through December 1996. The values of selected model calibration-derived parameters for the alluvial aquifer are hydraulic conductivity, 425 feet per day; specific yield, 0.32; and storage coefficient, 0.016. The model showed that the aquifer lost water from storage at an average rate of 404 cubic feet per second during the 9-year simulation period. During this period, the average pumpage rate was 1,270 million gallons per day (1,980 cubic feet per second). Simulated areal recharge from precipitation averaged 2.6 inches per year (1,360 cubic feet per second). Vertical recharge from the internal streams and lakes and lateral recharge from aquifers underlying the Bluff Hills averaged 113 and 108 cubic feet per second, respectively. Model results indicated that net recharge from the Mississippi River and from aquifers directly underlying the alluvial aquifer was small.

Mississippi↗
USGS2001

Simulated response of the Sparta Aquifer to outcrop area recharge augmentation, southeastern Arkansas

Recharge augmentation by construction of infiltration impoundments is a potential means of increasing aquifer water levels and aquifer yield that is under consideration for the Sparta aquifer in southeastern Arkansas. The aquifer is a major water resource for municipal, industrial, and agricultural uses, and approximately 287 million gallons per day was pumped from the aquifer in Arkansas in 1995; this is double the amount pumped in 1975. Historically, the Sparta aquifer has provided abundant water of high quality. In recent years, however, the demand for water in some areas has resulted in withdrawals from the Sparta that significantly exceed recharge to the aquifer, and considerable declines have occurred in the potentiometric surface. To better manage the Sparta aquifer, water users in Arkansas are evaluating and implementing a variety of management practices and assessing alternative, surface-water sources to reduce stress upon the Sparta aquifer. One approach to managing and maximizing use of the Sparta aquifer is augmenting recharge to the aquifer by construction of infiltration lakes or canals within the recharge area. The basic concept of augmented recharge is simply to increase the amount of water being introduced into the aquifer so that more water will be available for use. Ground-water flow model simulations were conducted to assess the effectiveness of constructing lakes or canals to augment recharge. Results show that construction of five new lakes in the Sparta recharge area upgradient from major pumping centers or construction of a series of canals along the length of the recharge area yield notable benefit to aquifer conditions when compared with simulations entailing no augmentation of recharge. Augmentation of recharge in the Sparta aquifer with emplacement of lakes provides slight increase to aquifer water levels. The presence of the lakes increased simulated aquifer water levels 0.5 foot or more across a broad area comprising all or a substantial part of 19 counties after the 30-year simulation period. Substantial increases of 5 feet or greater are limited to a smaller area proximal to the lakes. Increases of 5 feet or more are seen in El Dorado, Pine Bluff, and Stuttgart. The positive effect of the lakes on aquifer water levels is rapidly realized after emplacement of the lakes. For example, in the El Dorado area more than 3 feet of a total of 8 feet of water-level increase is seen in the first 5 years of the simulation; in the Pine Bluff area 9 feet of a total of 16 feet of increase occurs within 5 years. Sustainable yield from the aquifer could be expected to be increased within the zone of influence of the lakes. Augmentation of recharge in the Sparta aquifer with emplacement of canals provides considerable increase of aquifer water levels. The zone of influence in the aquifer with canal-augmented recharge extends from the recharge area eastward to the Mississippi River. Aquifer water levels exhibit an increase of 5 feet or more across a broad area comprising all or a substantial part of 15 counties. Increases of 20 feet or more are seen in El Dorado, Pine Bluff, and Stuttgart. The amount of water moving into the aquifer is substantially increased under this scenario, and the amount of water removed from storage is decreased, thereby, increasing aquifer conditions considerably. Sustainable yield from the aquifer could be expected to be greater within the zone of influence of the canals as compared to either the scenario without recharge augmentation or recharge augmentation with lakes. The effect of the canal on aquifer water levels is rapidly realized after emplacement of the canals. For example, in the El Dorado area, 22 feet of a total of 30 feet of increase is seen in the first 5 years of the simulation; in the Pine Bluff area, 15 feet of a total of 24 feet of increase occurs within 5 years. As constructed, the model simulations imply that any lakes or canals constructed would maintain exce

Arkansas↗
USGS2001

Pond-aquifer interaction at South Pond of Lake Cochituate, Natick, Massachusetts

A U.S. Army facility on a peninsula in South Pond of Lake Cochituate was designated a Superfund site by the U.S. Environmental Protection Agency in 1994 because contaminated ground water was detected at the facility, which is near the Natick Springvale public-supply wellfield. The interaction between South Pond and the underlying aquifer controls ground-water flow patterns near the pond and determines the source of water withdrawn from the wellfield.A map of the bathymetry and the thickness of fine-grained pond-bottom sediments was prepared on the basis of fathometer, ground-penetrating radar, and continuous seismic-reflection surveys. The geophysical data indicate that the bottom sediments are fine grained toward the middle of the pond but are coarse grained in shoreline areas. Natick Springvale wellfield, which consists of three active public-supply wells adjacent to South Pond, is 2,200 feet downgradient from the boundary of the Army facility. That part of South Pond between the Natick Springvale wellfield and the Army facility is 18 feet deep with at least 14 feet of fine-grained sediment beneath the pond-bottom. Water levels from the pond and underlying sediments indicate a downward vertical gradient and the potential for infiltration of pond water near the wellfield. Head differences between the pond and the wellfield ranged from 1.66 to 4.41 feet during this study. The velocity of downward flow from South Pond into the pond-bottom sediments, determined on the basis of temperature profiles measured over a diurnal cycle at two locations near the wellfield, was 0.5 and 1.0 feet per day. These downward velocities resulted in vertical hydraulic conductivities of 1.1 and 2.9 feet per day for the pond-bottom sediments.Naturally occurring stable isotopes of oxygen and hydrogen were used as tracers of pond water and ground water derived from recharge of precipitation, two potential sources of water to a well in a pond-aquifer setting. The isotopic composition of pond water varied seasonally and was distinctly different from the isotopic composition of ground water. The isotopic composition of shallow water beneath and adjacent to South Pond near the wellfield corresponds to the temporal variation of pond water, indicating that nearly all water at shallow depths was derived from pond water. A two-component mixing model based on the average stable isotope values of the source waters indicated that 64 ?15 percent at the 95-percent confidence interval of the water withdrawn at the public-supply wells was derived from the pond; pond water accounted for most of the uncertainty in the result. The rate of infiltration of pond water into the aquifer and discharging to the wellfield was 1.0 million gallons per day at the average pumping rate.

Water-Resources Investigations Report↗
USGS2001

Modeling water quality in the Tualatin River, Oregon, 1991-1997

The calibration of a model of flow, temperature, and water quality in the Tualatin River, Oregon, originally calibrated for the summers of 1991 through 1993, was extended to the summers of 1991 through 1997. The model is now calibrated for a total period of 42 months during the May through October periods of 7 hydrologically distinct years. Based on a modified version of the U.S. Army Corps of Engineers model CE-QUAL-W2, this model provides a good fit to the measured data for streamflow, water temperature, and water quality constituents such as chloride, ammonia, nitrate, total phosphorus, orthophosphate, phytoplankton, and dissolved oxygen. In particular, the model simulates ammonia concentrations and the effects of instream ammonia nitrification very well, which is critical to ongoing efforts to revise ammonia regulations for the Tualatin River. In addition, the model simulates the timing, duration, and relative size of algal blooms with sufficient accuracy to provide important insights for regulators and managers of this river.Efforts to limit the size of algal blooms through phosphorus control measures are apparent in the model simulations, which show this limitation on algal growth. Such measures are largely responsible for avoiding violations of the State of Oregon maximum pH standard of 8.5 in recent years, but they have not yet reduced algal biomass levels below the State of Oregon nuisance phytoplankton growth guideline of 15 ?g/L chlorophyll-a.Most of the dynamics of the instream dissolved oxygen concentrations are captured by the model. About half of the error in the simulated dissolved oxygen concentrations is directly attributable to error in the size of the simulated phytoplankton population. To achieve greater accuracy in simulating dissolved oxygen, therefore, it will be necessary to increase accuracy in the simulation of Tualatin River phytoplankton.Future efforts may include the introduction of multiple algal groups in the model. This model of the Tualatin River continues to be used as a quantitative tool to aid in the management of this important resource.

Oregon↗