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USGS1996

Hydrogeology and ground-water resources of Ngatik Island, Sapwuahfik Atoll, State of Pohnpei, Federated States of Micronesia

The lens of fresh ground water on Ngatik Island contains about 509 million gallons of potable water. Recharge to the freshwater lens is estimated to be 990,000 gallons per day on the basis of an estimated mean annual rainfall of 160 inches. The long-term average sustainable yield is estimated to be about 280,000 gallons per day. The estimated demand for water is about 30,000 gallons per day. Shallow-vertical-tube-wells or horizontal-infiltration wells could be used to develop the freshwater lens. The effect of development on the lens can be determined by monitoring the chloride concentration of water from a network of shallow-water-table wells and deep driven wells. The ground-water resource on Ngatik can be used in conjunction with individual rainwater-catchment systems: rainwater can be used for drinking and cooking and ground water can be used for sanitary purposes. When rainwater- catchment systems fail during extended dry periods, ground water would be available to meet the total demand.

Water-Resources Investigations Report↗

USGS1995

Hydrogeology and ground-water flow of the drift and Platteville aquifer system, St. Louis Park, Minnesota

Three aquifers and two confining units have been delineated within the drift underlying the area near the site of a former coal-tar distillation and wood-preserving plant in St. Louis Park, Minnesota. The hydrogeologic units of the drift, in descending order, are the upper drift aquifer, the upper drift confining unit, the middle drift aquifer, the lower drift confining unit. and the lower drift aquifer. A contamination plume consisting of coal-tar derivatives exists in the drift aquifers and in the Platteville aquifer underlying the southern part of the plant site and areas to the south and east of the plant site. The upper drift aquifer has a maximum saturated thickness of about 25 feet. Horizontal hydraulic conductivities of the upper drift aquifer range from less than 1 to about 25 feet per day in peat areas and from about 50 to 400 feet per day in sand and gravel areas. The upper drift confining unit generally is less than 20 feet thick, with a maximum thickness of 62 feet. The saturated thickness of the middle drift aquifer generally is 20 to 30 feet in areas where the aquifer is both overlain and underlain by a confining unit. The horizontal hydraulic conductivity of the middle drift aquifer ranges from about 50 to 500 feet per day. The lower drift confining unit is as much as 50 feet thick. Model-computed vertical hydraulic conductivities for the upper and lower drift confining units ranged from 0.0002 to 5 feet per day. The lower drift aquifer consists of discontinuous sand and gravel deposits overlying Platteville Formation bedrock and has a maximum thickness of 20 feet where it is overlain by the lower drift confining unit. Water in the drift aquifers and in the Platteville aquifer generally flows from the northwest to the southeast under a hydraulic gradient of about 10 feet per mile. The drift confining units and the Glenwood confining unit. when present, control the vertical movement of water through the aquifers. Discontinuities in these confining units greatly influence patterns of ground-water flow. A numerical cross-sectional ground-water-flow model was used to test concepts of flow of ground water through the drift aquifers and the Platteville aquifer. particularly the effects of confining units and bedrock valleys on vertical flow. The model has eight layers representing, in descending order: ( 1) the upper drift aquifer. (2) the upper drift confining unit, (3) the middle drift aquifer, (4) the upper part of the lower drift confining unit, (5) the lower part of the lower drift confining unit and lower drift aquifer, (6) the Platteville aquifer and bedrock valley deposits, (7) the St. Peter aquifer, and (8) the Prairie du Chien-Jordan aquifer. A sensitivity analysis indicated that model-calculated hydraulic heads in the drift aquifers and in the Platteville aquifer were most sensitive to variations in: (1) the horizontal hydraulic conductivities of the middle drift aquifer, (2) the transmissivities of the Platteville and St. Peter aquifers, (3) the vertical hydraulic conductivities of the lower drift confining unit and the drift material filling the bedrock valley, and (4) the vertical hydraulic conductivity of the basal St. Peter confining unit. The model-calculated water budget indicated that recharge from infiltration of precipitation to the upper and middle drift aquifers and the upper drift confining unit accounts for about 41 percent of the total sources of water. The remaining 59 percent is from subsurface inflow from the west (through specified-head cells). About 70 percent of the outflow from the eastern model boundary was simulated as discharge from the model layers representing the Platteville aquifer and bedrock valley deposits and the St. Peter aquifer. The calibrated simulation indicated that about 99 percent of the total leakage of water from the drift aquifers and from the Platteville aquifer to the underlying St. Peter aquifer occurs through areas where the Glenwood confining unit is absent or discontinuous. Hypothetical changes of the hydraulic properties and the extent of confining units were simulated using the calibrated steady-state model. Increasing the vertical hydraulic conductivity of model layer 4, representing the upper part of the lower drift confining unit, by a factor of 100 in the western part of the cross section resulted in decreased model-calculated leakage to the St. Peter aquifer through the bedrock valley represented in the eastern part of the cross-sectional model. A hypothetical extension of vertical hydraulic conductivities representing the Glenwood confining unit along the entire cross-sectional model resulted in a 98 percent reduction in the model-calculated amount of water leaking from the Platteville aquifer and bedrock valley deposits to the underlying St. Peter aquifer. Model simulations indicate that vertical ground-water flow from the drift aquifers and from the Platteville aquifer to underlying bedrock aquifers is greatest through bedrock valleys. The convergence of flow paths near bedrock valleys and the greater volume of water moving through the valleys would likely result in both increased concentrations and greater vertical movement of contaminants in areas underlain by bedrock valleys as compared to areas not underlain by bedrock valleys. Model results also indicate that field measurements of hydraulic head might not help locate discontinuities in confining units and additional test drilling to locate discontinuities might be necessary.

Minnesota↗

USGS2002

Estimated quantity of water in fractured bedrock units on Mt. Desert Island, and estimated ground-water use, recharge, and dilution of nitrogen in septic waste in the Bar Harbor area, Maine

In 2002, the U.S. Geological Survey, in cooperation with the town of Bar Harbor, Maine, and the National Park Service, conducted a study to assess the quantity of water in the bedrock units underlying Mt. Desert Island, and to estimate water use, recharge, and dilution of nutrients from domestic septic systems overlying the bedrock units in several watersheds in rural Bar Harbor. Water quantity was calculated as the static volume of water in the top 600 feet of saturated thickness of the bedrock units. Volumes of water were estimated on the basis of effective fracture porosities for the five different rock types found on Mt. Desert Island. Values of porosities for the various bedrock units from the literature range more than five orders of magnitude, although the possible range in porosities for most individual rock types is on the order of three orders of magnitude. The static volume of water in the various units may range from a low of 4,000 gallons per acre for intrusive igneous rocks (primarily granites) to 20 million gallons per acre for the Cranberry Island Volcanics, but given the range in porosity estimates, these numbers can vary by orders of magnitude. Water-use data for the municipal water supply in the Town of Bar Harbor (1998-2000) indicate that residential usage averages 225 gallons per household per day. Recharge to the bedrock units in rural Bar Harbor was bracketed using low, medium, and high estimates, which were 3, 9, and 14 inches per year, respectively. Water use in 2001 was about 2.5 percent of the total estimated medium recharge (9 inches per year) in the study area. Dilution of nitrogen in septic effluent discharging to the bedrock aquifer was evaluated for the development density in 2001. On the basis of an assumed concentration of 47 mg/L of nitrogen in septic system discharge, dilution factors in populated rural Bar Harbor watersheds ranged from 4 to 151, for the housing density in 2001. Understanding that ground water in this fractured bedrock system mixes slowly, the fully mixed average nitrate-nitrogen concentrations in ground water estimated for the watersheds ranged from 0.1 to 11 mg/L.

Maine↗

USGS1996

Hydrogeology and ground-water resources of Pingelap Island, Pingelap Atoll, State of Pohnpei, Federated States of Micronesia

The lens of fresh ground water on Pingelap Island, Pingelap Atoll contains about 384 million gallons of potable water. Recharge to the freshwater lens is estimated to be 230,000 gallons per day on the basis of an average annual rainfall of 160 inches. The long-term average sustainable yield is estimated to be about 69,000 gallons per day. The estimated demand for water is about 50,000 gallons per day. Shallow-vertical-tube wells or horizontal-infiltration wells could be used to develop the freshwater lens. The effect of development on the lens can be determined by monitoring the chloride concentration of water from a network of shallow-water-table wells and deep driven wells. The ground-water resource on Pingelap can be used in conjunction with individual rainwater-catchment systems: rainwater can be used for drinking and cooking, and ground water can be used for sanitary uses. When rainwater-catchment systems fail during extended dry periods, ground water would be available to meet the total demand.

State of Pohnpei↗

USGS1974

Mathematical model of San Juan Valley ground-water basin, San Benito County, California

A mathematical model study of the San Juan Valley ground-water basin in San Benito County, Calif., has quantitatively described the ground-water hydrology of the basin under past, present, and future conditions of development. An analysis of conditions in the basin prior to large-scale ground-water development indicates that net recharge equaled 9.23 cubic feet per second and occurred as subsurface flow to the eastern part of the basin and infiltration of rain, direct runoff, and minor streamflows. Net predevelopment discharge equaled 9.23 cubic feet per second and occurred as aquifer discharge to the San Benito River. The 9.23 cubic feet per second of predevelopment recharge is considered to be perennial recharge to the basin. Large-scale ground-water development occurred in the area during the period 1945-68 and caused water levels to decline throughout most of the basin. Progressive depletion of aquifer storage during this period changed the San Benito River from a gaining (perennial) stream to a losing stream along most of its reach in the basin area. Net discharge from the basin during the period 1945-68 averaged 18.10 cubic feet per second. Of this amount 17.82 cubic feet per second occurred as pumpage from wells, and 0.28 cubic foot per second occurred as basin discharge to the San Benito River. Net recharge to the basin during the same period averaged 13.57 cubic feet per second. Of this amount 4.34 cubic feet per second occurred as infiltration from the San Benito River and 9.23 cubic feet per second occurred as perennial recharge. Use of the calibrated mathematical model to simulate quantities of imported water entering the basin from the San Benito River indicates that water levels in San Juan Valley will stabilize or recover when additional recharge equals or exceeds 3,000 acre-feet per year.

California↗

USGS1982

Use of a three-dimensional model for the analysis of the ground-water flow system in Parker Valley, Arizona and California

A three-dimensional, finite-difference model was used to simulate ground-water flow conditions in Parker Valley. The study evaluated present knowledge and concepts of the ground-water system and the ability of the model to represent the system. Modeling assumptions and generalized physical parameters that were used may have transfer value in the construction and calibration of models of other basins along the lower Colorado River. The aquifer was simulated in two layers to represent the three-dimensional system. Ground-water conditions were simulated for 1940-41, the mid-1960's, and 1980. Overall model results generally compared favorably with available field information. The model results showed that for 1940-41 the Colorado River was a losing stream through out Parker Valley. Infiltration of surface water from the river was the major source of recharge. The dominant mechanism of discharge was evapotranspiration by phreatophytes. Agricultural development between 1941 and the mid-1960 's resulted in significant changes to the ground-water system. Model results for conditions in the mid-1960 's showed that the Colorado River had become a gaining stream in the northern part of the valley as a result of higher water levels. The rise in water levels was caused by infiltration of applied irrigation water. Diminished water-level gradients from the river in the rest of the valley reduced the amount of infiltration of surface water from the river. Models results for conditions in 1980 showed that ground-water level rises of several feet caused further reduction in the amount of surface-water infiltration from the river. (USGS)

Open-File Report↗

USGS2001

Ground-water flow and quality in the Atlantic City 800-foot sand, New Jersey

The regional, confined Atlantic City 800-foot sand is the principal source of water supply for coastal communities of southern New Jersey. In response to extensive use of the aquifer--nearly 21 million gallons per day in 1986--water levels have declined to about 100 feet below sea level near Atlantic City and remain below sea level throughout the coastal areas of southern New Jersey, raising concerns about the potential for saltwater intrusion into well fields. Water levels in the Atlantic City 800-foot sand have declined in response to pumping from the aquifer since the 1890's. Water levels in the first wells drilled into the Atlantic City 800-foot sand were above land surface, and water flowed continuously from the wells. By 1986, water levels were below sea level throughout most of the coastal areas. Under current conditions, wells near the coast derive most of their supply from lateral flow contributed from the unconfined part of the aquifer northwest of the updip limit of the confining unit that overlies the Atlantic City 800- foot sand. Ground water also flows laterally from offshore areas and leaks vertically through the overlying and underlying confining units into the Atlantic City 800-foot sand. The decline in water levels upsets the historical equilibrium between freshwater and ancient saltwater in offshore parts of the aquifer and permits the lateral movement of saltwater toward pumping centers. The rate of movement is accelerated as the decline in water levels increases. The chloride concentration of aquifer water 5.3 miles offshore of Atlantic City was measured as 77 mg/L (milligrams per liter) in 1985 at a U.S. Geological Survey observation well. Salty water has also moved toward wells in Cape May County. The confined, regional nature of the Atlantic City 800-foot sand permits water levels in Cape May County to decline in response to pumping in Atlantic County and vice versa. Historically, chloride concentrations as great as 1 ,510 mg/L have been reported for water in a former supply well in southern Cape May County. These data indicate that salty water has moved inland in Cape May County. Analysis of the chloride-concentration data indicates that ground water with a chloride concentration of 250 mg/L is within 4 miles of supply wells in Stone Harbor, Cape May County, and is about 10 miles offshore of supply wells near Atlantic City. Results of numerical simulations of ground-water flow were analyzed to determine the effects of four water-supply alternatives on water levels, the flow budget, and potential saltwater movement toward pumping centers during 1986-2040. In the supply alternatives, pumpage is (1) held constant at 1986 rates of pumpage; (2) increased by 35 percent at 1986 locations; (3) increased by 35 percent, but with relocation of some supply wells further inland; and (4) increased by 35 percent but with some of the increase derived from inland wells tapping the Kirkwood-Cohansey aquifer system rather than the Atlantic City 800-foot sand. Inland relocation of supply wells closer to the updip limit of the overlying confining unit results in the smallest decline in water levels and the smallest rate of ground-water flow between the offshore location of salty water and coastal supply wells. Increased pumpage from coastal supply wells results in the greatest water-level declines and the greatest increase in the rate of ground-water flow from offshore to coastal wells. Flow of undesirable salty ground water from offshore locations remains nearly the same as for current (1986) conditions when pumping rates do not change, and the flow-rate increase is smallest for the relocated pumpage (fourth) alternative. In comparing the two conditions of a 35-percent increase in pumpage, the flow from undesirable salty water positions is lessened and flow from the unconfined aquifer is increased when some of the pumping centers are relocated farther inland. Ground water from the 250-mg/L isochlor position does not reach supply wells during any simulated conditions predicted for 1986-2040. The analysis of the simulation, however, includes only advective freshwater flow from an estimated 250-mg/L isochlor position and does not include density effects. A chloride concentration data-collection network could be designed to monitor for saltwater intrusion and serve as an early warning system for the communities of southern Cape May County and the coastal communities near Atlantic City. Data from existing offshore wells could continue to serve as an early warning system for the Atlantic City area; however, observation wells south of Stone Harbor, in the Wildwood area, would be useful as an early warning system for southern Cape May County.

New Jersey↗

USGS2006

Dichlorobenzene in ground water: Evidence for long-term persistence

Hydrologic and geochemical evidence were used to establish the long-term persistence of dichlorobenzene in ground water that has been contaminated from 50 years of rapid-infiltration sewage disposal. An extensive plume of dichlorobenzene extends more than 3,500 meters downgradient from the disposal beds, with concentrations of the combined isomers ranging from less than 0.01 to over 1.0 ??g/l. Based on estimates of maximum ground-water flow velocities, a minimum age of 20 years was established for the farthest downgradient zone of dichlorobenzene contamination. Branched-chained, alkylbenzenesulfonic acid surfactants, that were introduced into the ground water prior to 1966, occur along with dichlorobenzene in the downgradient part of the plume, further establish residence of the compounds in the aquifer for at least 20 years. Although dichlorobenzene can be biologically degraded under aerobic conditions, its persistence at this field site is attributed to the dynamics of the ground-water system. Denitrifying conditions, resulting from the degradation of organic compounds in the aquifer near the disposal beds, appear to have enhanced the persistence of dichlorobenzene, which is not degraded by anaerobic bacteria. Biological degradation of dichlorobenzene in the aerobic part of the plume downgradient from the source is probably limited by the paucity of a suitable organic-carbon substrate and the low concentrations of dissolved oxygen in the contaminated ground water.

Ground Water↗

USGS1993

Interactions between ground water and wetlands, southern shore of Lake Michigan, USA

Wetlands between, and within, dune-beach complexes along the south shore of Lake Michigan are strongly affected by ground water. The hydrogeology of the glacial drift aquifer system in a 26 km 2 area was investigated to determine the effects of ground water on the hydrology and hydrochemistry of Cowles Bog and its adjacent wetlands. The investigation showed that ground water from intermediate- and regional-scale flow systems discharges to Cowles Bog from confined aquifers that underlie the wetland. These flow systems are recharged in moraines south of the dune-beach complexes. Water from the confined aquifers discharges into the surficial aquifer mainly by upward leakage through a buried till sheet that serves as the confining layer. However, the till sheet is breached below a raised peat mound in Cowles Bog, allowing direct upward discharge from the confinef aquifer into the surficial sand, marl, and peat. The shallow ground and wetland water in the area influenced by this leakage is a calcium magnesium bicarbonate type, with low tritium concentrations consistent with mixing of older ground water and more recent precipitation. Ground water and wetland water from surrounding areas are less mineralized and have higher tritium concentrations characteristic of precipitation in the late 1970s. The results of this study suggest that wetlands in complex hydrogeologic settings may be influenced by multiple ground-water flow systems that are affected by geomorphic features, stratigraphic discontinuities, and changes in sediment types. Discharge and recharge zones may both occur in the same wetland. Multidisciplinary studies incorporating hydrological, hydrochemical, geophysical, and sedimentological data are necessary to identify such complexities in wetland hydrology.

Journal of Hydrology↗

USGS1976

Ground-water quality in the Davie Landfill, Broward County, Florida

Ground-water adjacent to a disposal pond for septic tank sludge, oil, and grease at the Davie landfill, Broward County, Florida was tested for a variety of ground-water contaminants. Three wells adjacent to the disposal pond yielded water rich in nutrients, organic carbon and many other chemical constituents. Total coliform bacteria ranged from less than 100 to 660 colonies per 100 milliliters in samples collected from the shallowest well (depth 20 feet). At well depths of 35 and 45 feet bacterial counts were less than 20 colonies per 100 milliliters or zero. Concentrations of several constituents in water samples collected from the wells downgradient from the landfill, disposal pond, and an incinerator wash pond were greater than in samples collected from wells immediately upgradient of the landfill. A comparison of sodium-chloride ion ratios indicated that downgradient ground-water contamination was related to the incinerator wash water pond rather than the septic tank sludge pond. (Woodard-USGS)

Florida↗

USGS1965

Geology and ground water of the Tualatin Valley, Oregon

The Tualatin Valley proper consists of broad valley plains, ranging in altitude from 100 to 300 feet, and the lower mountain slopes of the drainage basin of the Tualatin River, a tributary of the Willamette River in northwestern Oregon. The valley is almost entirely farmed. Its population is increasing rapidly, partly because of the expansion of metropolitan Portland. Structurally, the bedrock of the basin is a saucer-shaped syncline almost bisected lengthwise by a ridge. The bedrock basin has been partly filled by alluvium, which underlies the valley plains. Ground water occurs in the Columbia River basalt, a lava unit that forms the top several hundred feet of the bedrock, and also in the zones of fine sand in the upper part of the alluvial fill. It occurs under unconfined, confined, and perched conditions. Graphs of the observed water levels in wells show that the ground water is replenished each year by precipitation. The graphs show also that the amount and time of recharge vary in different aquifers and for different modes of ground-water occurrence. The shallower alluvial aquifers are refilled each year to a level where further infiltration recharge is retarded and water drains away as surface runoff. No occurrences of undue depletion of the ground water by pumping are known. The facts indicate that there is a great quantity of additional water available for future development. The ground water is developed for use by some spring works and by thousands of wells, most of which are of small yield. Improvements are now being made in the design of the wells in basalt and in the use of sand or gravel envelopes for wells penetrating the fine-sand aquifers. The ground water in the basalt and the valley fill is in general of good quality, only slightly or moderately hard and of low salinity. Saline and mineralized water is present in the rocks of Tertiary age below the Columbia River basalt. Under certain structural and stratigraphic conditions this water of poor quality contaminates the fresh-water aquifers. Detailed hydrologic and geologic conditions are presented in 5 tables, 7 pictures, and 17 graphic figures and plates.

Water Supply Paper↗

USGS1997

Delineation of ground-water basins and recharge areas for municipal water-supply springs in a karst aquifer system in the Elizabethtown area, northern Kentucky

Ground-water basins and recharge areas for municipal water-supply springs for the Elizabethtown area, northern Kentucky, were delineated using a hydrogeologic-mapping approach, potentiometric map interpretation, anddye-tracing tests. Five distinct ground-water basins drained by major karst springs are present in the Elizabethtown area. These basins are composed of networks of hydraulically interconnected solution conduits and fractures. The boundaries of the basins for Elizabethtown and Dyers Springs-the primary sources of water for the city of Elizabethtown-weredelineated by the positions of inferred ground-water divides on an existing potentiometric contour map. The results of dye-tracing tests, plotted as straight- line flowpaths, were used to confirm the presence and location of inferred ground-water divides and to adjust the position of the basin boundaries. Recharge areas of 4.8 and 2.7 square miles weredelineated for Elizabethtown and Dyers Springs, respectively. Swallets that drain concentrated stormwater runoff from major highways are presentin the recharge areas for both municipal-supply springs. Each spring is therefore potentially vulnerable to stormwater-runoff contaminants oraccidental spills and releases of toxic or hazardous materials into certain highway drainage culverts.

Water-Resources Investigations Report↗

USGS1984

Ground-water conditions and well yields in fractured rocks, southwestern Nevada County, California

This report describes the availability of ground water in the southwestern part of Nevada County, and suggests general guidelines for selecting sites for future ground-water development in the study area. Ground water in this area occurs chiefly in fractures in hard pre-Tertiary metavolcanic and plutonic rocks generally above a depth of 215 feet. Some ground water is found at the contact between alluvium or decomposed granite and the underlying hard rock; little is found in alluvium or colluvium. Mean yield is less than 18 gallons per minute. (USGS)

Water-Resources Investigations Report↗

USGS2003

Diffusion and drive-point sampling to detect ordnance-related compounds in shallow ground water beneath Snake Pond, Cape Cod, Massachusetts, 2001-02

Diffusion samplers and temporary drive points were used to test for ordnance-related compounds in ground water discharging to Snake Pond near Camp Edwards at the Massachusetts Military Reservation, Cape Cod, MA. The contamination resulted from artillery use and weapons testing at various ranges upgradient of the pond.The diffusion samplers were constructed with a high-grade cellulose membrane that allowed diffusion of explosive compounds, such as RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine) and HMX (Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), into deionized water inside the samplers. Laboratory tests confirmed that the cellulose membrane was permeable to RDX and HMX. One transect of 22 diffusion samplers was installed and retrieved in August-September 2001, and 12 transects with a total of 108 samplers were installed and retrieved in September-October 2001. The diffusion samplers were buried about 0.5 feet into the pond-bottom sediments by scuba divers and allowed to equilibrate with the ground water beneath the pond bottom for 13 to 27 days before retrieval. Water samples were collected from temporary well points driven about 2-4 feet into the pond bottom at 21 sites in December 2001 and March 2002 for analysis of explosives and perchlorate to confirm the diffusion-sampling results. The water samples from the diffusion samplers exhibited numerous chromatographic peaks, but evaluation of the photo-diode-array spectra indicated that most of the peaks did not represent the target compounds. The peaks probably are associated with natural organic compounds present in the soft, organically enriched pond-bottom sediments. The presence of four explosive compounds at five widely spaced sites was confirmed by the photo-diode-array analysis, but the compounds are not generally found in contaminated ground water near the ranges. No explosives were detected in water samples obtained from the drive points. Perchlorate was detected at less than 1 microgram per liter in two drive-point samples collected at the same site on two dates about 3 months apart. The source of the perchlorate in the samples could not be related directly to other contamination from Camp Edwards with the available information. The results from the diffusion and drive-point sampling do not indicate an area of ground-water discharge with concentrations of the ordnance-related compounds that are sufficiently elevated to be detected by these sampling methods. The diffusion and drive-point sampling data cannot be interpreted further without additional information concerning the pattern of ground-water flow at Snake Pond and the distributions of RDX, HMX, and perchlorate in ground water in the aquifer near the pond.

Massachusetts↗

USGS2000

Simulation of ground-water flow in an unconfined sand and gravel aquifer at Marathon, Cortland County, New York

The Village of Marathon, in Cortland County, N.Y., has three municipal wells that tap a relatively thin (25 to 40 feet thick) and narrow (less than 0.25 mile wide) unconfined sand and gravel aquifer in the Tioughnioga River valley. Only one of the wells is in use because water from one well has been contaminated by petroleum chemicals from a leaking storage tank, and water from the other well contains high concentrations of manganese. The operating well pumps about 0.1 million gallons per day and supplies about 1,000 people. A three-dimensional, finite-difference ground-water-flow model was used to (1) compute hydraulic heads in the aquifer under steady-state conditions, (2) develop a water budget, and (3) delineate the areas contributing recharge to two simulated wells that represent two of the municipal wells: one 57 feet east of the Tioughnioga River, the other 4,000 feet to the south and 75 feet from a man-made pond. The water budget for simulated long-term average, steady-state conditions with two simulated pumping wells indicates that the principal sources of recharge to the unconfined aquifer are unchanneled runoff and ground-water inflow from the uplands (41 percent of total recharge), precipitation that falls directly on the aquifer (34 percent), and stream leakage (23 percent). Only 2 percent of the recharge to the aquifer is from ground-water underflow into the northern end of the modeled area. Most of the simulated groundwater discharge from the modeled area (78 percent of total discharge) is to the Tioughnioga River; the rest discharges to the two simulated wells (19 percent) and as underflow at the southern end of the modeled area (3 percent). Results of a particle-tracking analysis indicate that the aquifer contributing area of the northern (simulated) well is 0.10 mile wide and 0.15 mile long and encompasses 0.015 square miles; the contributing area of the southern (simulated) well is 0.20 mile wide and 0.11 mile long and encompasses 0.022 square miles. The average traveltime of ground water from the valley wall to either simulated well is about 1.5 years, calculated on the basis of an assumed aquifer porosity of 0.3. The flowpath analysis indicates that both contributing areas contain surface-water sources of recharge; the Tioughnioga River and Hunts Creek contribute water to the northern well, and a pond and a small tributary contribute water to the southern well. Ground-water temperature in an observation well between the Tioughnioga River and the municipal well fluctuated several degrees Fahrenheit in response to pumping of the municipal well. This temperature fluctuation, in conjunction with the pumping well causing a ground-water gradient from the Tioughnioga River to the pumping well (ground-water levels in the pumping well were generally greater than 3 ft lower than that of the Tioughnioga River), indicate that there is a hydraulic connection between the river and aquifer at this site.

Water-Resources Investigations Report↗

USGS1997

Quality of shallow ground water in alluvial aquifers of the Willamette Basin, Oregon, 1993-95

The current (1993?95) quality of shallow ground water (generally, <25 meters below land surface) in Willamette Basin alluvium is described using results from two studies. A Study-Unit Survey, or regional assessment of shallow groundwater quality in alluvium, was done from June through August 1993. During the Study-Unit Survey, data were collected from 70 domestic wells chosen using a random-selection process and located mostly in areas of agricultural land use. An urban Land-Use Study, which was a reconnaissance of shallow urban ground-water quality from 10 monitoring wells installed in areas of residential land use, was done in July 1995. Concentrations of nitrite plus nitrate (henceforth, nitrate, because nitrite concentrations were low) ranged from <0.05 to 26 mg N/L (milligrams nitrogen per liter) in ground water from 70 Study-Unit-Survey wells; concentrations exceeded the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Level (MCL) of 10 mg N/L in 9 percent of Study-Unit-Survey samples. Relationships were observed between nitrate concentrations and dissolved-oxygen concentrations, the amount of clay present within and overlying aquifers, overlying geology, and upgradient land use. Tritium (3H) data indicate that 21 percent of Study-Unit-Survey samples represented water recharged prior to 1953. Nitrogen-fertilizer application rates in the basin have increased greatly over the past several decades. Thus, some observed nitrate concentrations may reflect nitrogen loading rates that were smaller than those presently applied in the basin. Concentrations of phosphorus ranged from <0.01 to 2.2 mg/L in 70 Study-Unit-Survey wells and exceeded 0.10 mg/L in 60 percent of the samples. Phosphorus and nitrate concentrations were inversely correlated. From 1 to 5 pesticides and pesticide degradation products (henceforth, pesticides) were detected in ground water from each of 23 Study-Unit-Survey wells (33 percent of 69 wells sampled for pesticides) for a total of 51 pesticide detections. Thirteen different pesticides were detected; atrazine was the most frequently encountered pesticide. Although detections were widespread, concentrations were low (generally <1,000 ng/L [nanograms per liter]). (One ng/L is equal to 0.001 mg/L [micrograms per liter].) One detection (dinoseb, at 7,900 ng/L) exceeded a USEPA MCL. Relationships were observed between the occurrence of pesticides and the amount of clay present within and overlying aquifers, overlying geology, and land use. Between 1 and 5 volatile organic compounds (VOCs) were detected at each of 7 Study-Unit-Survey sites (11 percent of 65 sites evaluated), for a total of 14 VOC detections. One detection (tetrachloroethylene, at 29 mg/L) exceeded a USEPA MCL. Other detections were at low concentrations (0.2 to 2.0 mg/L). VOC detections generally were from sites associated with urban land use. Concentrations of arsenic ranged from <1 to 13 mg/L in 70 Study-Unit-Survey wells. Concentrations in 16 percent of samples exceeded the USEPA Risk-Specific-Dose Health Advisory of 2 mg/L. Radon concentrations ranged from 200 to 1,200 pCi/L (picocuries per liter) in 51 Study-Unit-Survey wells. All samples exceeded the USEPA Risk-Specific-Dose Health Advisory of 150 pCi/L. All urban Land-Use-Study samples were well oxygenated; thus, nitrate reduction probably did not affect these samples. Urban Land-Use-Study nitrate concentrations were similar to those of the well oxygenated, agricultural subset of Study-Unit-Survey samples. Pesticides were detected in samples from three urban Land-Use-Study sites, but concentrations were low (1 to 5 ng/L). In contrast, VOCs were detected in ground water from 80 percent of urban Land-Use-Study wells; concentrations ranged up to 7.6 mg/L. Trace-element concentrations in the urban Land-Use Study samples were low. Median concentrations consistently were <10 mg/L and frequently were <1 mg/L

Water-Resources Investigations Report↗

USGS2006

Pesticides in ground water - Sublette County, Wyoming, 2004-2005

In 1991, members of local, State, and Federal governments, as well as industry and interest groups, formed the Ground-water and Pesticide Strategy Committee to prepare the State of Wyoming's generic Management Plan for Pesticides in Ground Water. Part of this management plan is to sample and analyze Wyoming's ground water for pesticides. In 1995, the U.S. Geological Survey, in cooperation with the Ground-water and Pesticide Strategy Committee, began statewide implementation of the sampling component of the State of Wyoming's generic Management Plan for Pesticides in Ground Water. During 2004-2005, baseline monitoring was conducted in Sublette County. This fact sheet describes and summarizes results of the baseline monitoring in Sublette County.

Wyoming↗

USGS2006

Pesticides in ground water - Carbon County, Wyoming, 2004-2005

In 1991, members of local, State, and Federal governments, as well as industry and interest groups, formed the Ground-water and Pesticide Strategy Committee to prepare the State of Wyoming's generic Management Plan for Pesticides in Ground Water. Part of this management plan is to sample and analyze Wyoming's ground water for pesticides. In 1995, the U.S. Geological Survey, in cooperation with the Ground-water and Pesticide Strategy Committee, began statewide implementation of the sampling component of the State of Wyoming's generic Management Plan for Pesticides in Ground Water. During 2004-2005, baseline monitoring was conducted in Carbon County. This fact sheet describes and summarizes results of the baseline monitoring in Carbon County.

Wyoming↗