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USGS2023

Updates to the regional groundwater-flow model of the New Jersey Coastal Plain, 1980–2013

A 21-layer three-dimensional transient groundwater-flow model of the New Jersey Coastal Plain was developed and calibrated by the U.S. Geological Survey (USGS) in cooperation with the New Jersey Department of Environmental Protection to simulate groundwater-flow conditions during 1980–2013, incorporating average annual groundwater withdrawals and average annual groundwater recharge. This model is the third version of the New Jersey Coastal Plain regional groundwater-flow model that was initially developed as part of the USGS Regional Aquifer System Analysis (RASA) program. The model simulates groundwater flow in 11 aquifers and 10 intervening confining units of the New Jersey Coastal Plain to provide a regional overview of groundwater conditions. Averaged groundwater withdrawal data for 1980 to 2013 were used in the model. The 11 aquifers in New Jersey are, from shallowest to deepest, the Holly Beach water-bearing zone and the confined Cohansey aquifer in Cape May County; the Rio Grande water-bearing zone; the Atlantic City 800-foot sand; the Piney Point, Vincentown, and Wenonah-Mount Laurel aquifers; the Englishtown aquifer system; and the upper, middle, and lower aquifers of the Potomac-Raritan-Magothy (PRM) aquifer system. The model was developed with the MODFLOW–2005 numerical code and the UCODE parameter estimation technique and calibrated using water-level and base-flow observations. A total of 3,453 water-level observations from 392 wells in New Jersey and 48 wells in Delaware from 1983 to 2013 were used in model calibration, which includes historical water-level trends for 29 wells in New Jersey during 1980–2013 presented in time-series hydrographs. In addition, derived observations also were included by calculating the vertical gradient at 33 pairs of nested observation wells in New Jersey, for a total of 210 observations. Changes in water levels over time were calculated for 134 wells in New Jersey and four wells in Delaware where water levels had varied substantially (approximately 10 ft) over the 30-year span of synoptic water-level measurements, for a total of 767 observations. A total of 1,485 base-flow observations in 47 surface-water basins in New Jersey from 1980 to 2013 were used in model calibration. Updates to the groundwater-flow model include the conversion to a fully three-dimensional model from the previous quasi-three-dimensional model. The new model will allow for potential future uses such as particle tracking or simulation of variable-density groundwater flow that could not be accomplished with earlier versions of the model. Spatially and temporally variable recharge estimated by using a soil-water balance model resulted in a spatially and temporally finer discretization. The Rio Grande water-bearing zone was added to the model as an aquifer layer to refine estimates of simulated flow in Atlantic and Cape May Counties, New Jersey. Hydrogeologic parameters were updated to include the confining units in New Jersey and corresponding hydrogeologic units in Delaware and eastern Maryland. The simulated water levels for the New Jersey Coastal Plain aquifers were compared to water-level measurements made during 1980–2013. The average residual for 4,243 water-level observations for New Jersey (simulated water levels minus measured water levels) is 1.5 feet. The simulated water-level contours for the confined aquifers for 2013 were compared to potentiometric surfaces produced from water levels measured during 2013. Simulated water levels generally matched the 2013 potentiometric surfaces of the confined aquifers in the areas of large withdrawals. Hydrographs of wells in the confined Coastal Plain aquifers of New Jersey show that simulated water levels generally match the magnitude and seasonal variation of the observed water levels. Hydrographs of base flow for the 47 streamgaging stations in New Jersey indicate that most of the simulated and estimated data match reasonably well. Groundwater withdrawals are an important resource for water supply, agricultural, industrial, and commercial needs in the New Jersey Coastal Plain. Groundwater withdrawals from the New Jersey Coastal Plain aquifers have resulted in persistent, regionally extensive cones of depression in the Englishtown aquifer system and Wenonah-Mount Laurel aquifer in Ocean and Monmouth Counties; Wenonah-Mount Laurel and upper, middle, and lower PRM aquifers in Camden County; and Atlantic City 800-foot sand in Atlantic County. Because hydrologic stresses and water-management needs change with time, periodic updates to the groundwater-flow model are required to provide current information about hydrologic conditions in the New Jersey Coastal Plain and to maintain its usefulness as a tool to manage water resources and develop water-resource strategies. The current updates will support the continued application of this model as a tool for evaluating the regional effects of changes in groundwater withdrawals and of current and potential future water-management strategies on groundwater levels in the New Jersey Coastal Plain.

New Jersey Coastal Plain↗
USGS2025

Estimated hydrogeologic, spatial, and temporal distribution of self-supplied domestic groundwater withdrawals for aquifers of the Virginia Coastal Plain

Water use from private-domestic wells accounts for nearly 40 percent of total groundwater withdrawals in the Virginia Coastal Plain Physiographic Province (henceforth called the Virginia Coastal Plain). However, because self-supplied domestic water use generally falls below the Virginia Department of Environmental Quality (VDEQ) reporting and management threshold of 300,000 gallons per month, quantifying these withdrawals is challenging. This report builds upon the foundation of previous U.S. Geological Survey investigations by providing revised techniques to improve estimates of the aquifer source, spatial distribution, and monthly magnitude of these groundwater withdrawals. The aquifer sources of private-domestic wells in the Virginia Coastal Plain were estimated by cross-referencing 8,264 well records from the VDEQ and the Virginia Department of Health to a digital model of the Virginia Coastal Plain hydrogeologic framework. This analysis highlights the regional importance of the Yorktown-Eastover, Potomac, and surficial aquifers. Collectively, these three aquifers account for 80 percent of self-supplied domestic groundwater withdrawals. The population using self-supplied domestic water was estimated using census blocks, well-use ratios, building footprints, and land-use and land-cover data to produce a high-resolution, disaggregated, raster-based dataset. This approach improves upon previous models at the census-block or road-network scale by reducing the low-density spread of the self-supplied domestic population across undeveloped areas and concentrating the population and its corresponding water use in the areas where it is most likely to occur. Results show that an estimated 475,332 people comprise the 2020 self-supplied domestic population of the Virginia Coastal Plain, an increase of 5.7 percent since 2010, and the greatest concentrations of self-supplied domestic population surround large cities. Estimates could be further refined with the addition of current and complete spatial data on public water-system service areas. The quantity of water used by the self-supplied domestic population was estimated by modifying published state per-capita water-use coefficients with the corresponding monthly variability assessed from Virginia Coastal Plain public water-system withdrawal data. This analysis estimates an average increase of 12 percent from June through August and an average decrease of 8 percent from December through March from the baseline annual average of 80 gallons per day per capita, which generally matches similar studies in the eastern United States. The application of these revised methodologies for the estimation of private-domestic wells and the self-supplied domestic population improves understanding of domestic groundwater use in the Virginia Coastal Plain across hydrogeologic, spatial, and temporal scales. These revisions help better inform water-resource managers and decision makers and support higher resolution groundwater modeling. Furthermore, these methods are transferrable to other areas where self-supplied domestic water withdrawals are important to the overall water budget.

Virginia↗
USGS2026

Flood-frequency estimates for Kentucky streamgages based on data through water year 2021 and results of updating the fundamental layers in Kentucky StreamStats

The U.S. Geological Survey, in cooperation with the Kentucky Transportation Cabinet, analyzed flood-frequency statistics for streamgages in Kentucky. Using annual peak-flow data through water year 2021, flood-frequency estimates were computed for 261 streamgages, including unregulated and regulated sites as well as sites with mixed regulation records. Methods followed those outlined in “Guidelines for Determining Flood Flow Frequency—Bulletin 17C” (U.S. Geological Survey Techniques and Methods 4–B5). These estimates included flows corresponding to annual exceedance probabilities of 50, 20, 10, 4, 2, 1, and 0.2 percent. Temporal trend analyses using the Mann-Kendall test indicated that 18 percent of unregulated streamgages with (1) at least 30 years of peak-flow record and (2) peak-flow record at least as recent as water year 2000 showed statistically significant trends, most of which were weak to moderate increases in peak flows. Concurrently, the fundamental geospatial datasets that support the Kentucky StreamStats application were updated by using high-resolution digital elevation models and hydrography datasets to derive flow direction, flow accumulation, and stream definition rasters. Comparisons of regression-based flood-frequency models using the old and new layers demonstrated consistent results, with a statewide root-mean-square error of 0.019, in the base-10 logarithm of cubic feet per second. Furthermore, to assess model performance, flood-frequency estimates made by using the updated layers and previously published regression-based models were compared to flood-frequency estimates newly computed by following Bulletin 17C. This analysis showed the models performed adequately for most Kentucky stream locations. The updated statistics and geospatial layers provide stakeholders with more accurate, current data for flood-risk assessment, infrastructure design, and water-resource management.

Kentucky↗
USGS2000

Use of a ground-penetrating radar system to detect pre- and post-flood scour at selected bridge sites in New Hampshire, 1996-98

Ground-penetrating radar was used to measure the depth and extent of existing and infilled scour holes and previous scour surfaces at seven bridges in New Hampshire from April 1996 to November 1998. Ground-penetrating-radar survey techniques initially were used by the U.S. Geological Survey to study streambed scour at 30 bridges. Sixteen of the 30 bridges were re-surveyed where floods exceeded a 2-year recurrence interval. A 300-megahertz signal was used in the ground-penetrating radar system that penetrated through depths as great as 20 feet of water and as great as 32 feet of streambed materials. Existing scour-hole dimensions, infilled thickness, previous scour surfaces, and streambed materials were detected using ground-penetrating radar. Depths to riprap materials and pier footings were identified and verified with bridge plans. Post data-collection-processing techniques were applied to assist in the interpretation of the data, and the processed data were displayed and printed as line plots. Processing included distance normalization, migration, and filtering but processing was kept to a minimum and some interference from multiple reflections was left in the record. Of the 16 post-flood bridges, 22 ground-penetrating-radar cross sections at 7 bridges were compared and presented in this report. Existing scour holes were detected during 1996 (pre-flood) data collection in nine cross sections where scour depths ranged from 1 to 3 feet. New scour holes were detected during 1998 (post-flood) data collection in four cross sections where scour depths were as great as 4 feet deep. Infilled scour holes were detected in seven cross sections, where depths of infilling ranged from less than 1 to 4 feet. Depth of infilling by means of steel rod and hammer was difficult to verify in the field because of cobble and boulder streambeds or deep water. Previous scour surfaces in streambed materials were identified in 15 cross sections and the depths to these surfaces ranged from 1 to 10 feet below the streambed. Riprap materials or pier footings were identified in all cross sections. Calculated record depths generally agree with bridge plans. Pier footings were exposed at two bridges and steel pile was exposed at one bridge. Exposures were verified by field observations.

New Hampshire↗
USGS2003

Monitoring instream turbidity to estimate continuous suspended-sediment loads and yields and clay-water volumes in the upper North Santiam River Basin, Oregon, 1998-2000

Three real-time, instream water-quality and turbidity-monitoring sites were established in October 1998 in the upper North Santiam River Basin on the North Santiam River, the Breitenbush River, and Blowout Creek, the main tributary inputs to Detroit Lake, a large, controlled reservoir that extends from river mile 61 to 70. Suspended-sediment samples were collected biweekly to monthly at each station. Rating curves provided estimated suspended-sediment concentration in 30-minute increments from log transformations of the instream turbidity monitoring data. Turbidity was found to be a better surrogate than discharge for estimating suspended-sediment concentration. Daily and annual mean suspended-sediment loads were estimated using the estimated suspended-sediment concentrations and corresponding streamflow data. A laboratory method for estimating persistent (residual) turbidity from separate turbidity samples was developed. Turbidity was measured over time for each sample. Turbidity decay curves were derived as the suspended sediment settled. Each curve was used to estimate a turbidity value for a given settling time. Medium to fine clay particle (< 0.002 mm [millimeter] diameter) settling times of 8.5 hours were computed using Stokes Law. An average of 30 persistent turbidity samples was collected from each of the 3 sites. These samples were used to estimate the 0.002-mm-size clay particle persistent turbidity for each site. The monitored instream 30-minute turbidity values were converted to a calculated persistent turbidity value that would have resulted after 8.5 hours of settling in the laboratory. Persistent turbidities of 10 NTU and above were tabulated for each site. (Water of 10 NTU and above can interfere with or damage treatment filters and result in intake closures at drinking-water facilities.) A method was developed that used the persistent turbidity experiments, turbidity decay curves, and stream discharge to estimate the volume of water containing suspended clay that entered Detroit Lake from the three main tributaries. 'Suspended-clay water' was defined as water having a value of at least 10 NTU after settling the required 8.5 hours. The suspended-clay concentrations of 10 NTU or higher were paired with the corresponding stream discharge in the continuous record. These summed discharges represent the annual volume of water containing suspended clay that entered Detroit Lake from the three main tributaries. Higher yields (load per unit area) of suspended sediment and suspended-clay water were observed from the smaller Breitenbush River and Blowout Creek subbasins than from the main-stem North Santiam River for water years 1999 and 2000. The 3-day peak streamflow and turbidity events in 1999 and 2000 carried two-thirds of the annual suspended-sediment load for the three subbasins. Turbidity and suspended-sediment concentration relations within the upper North Santiam River Basin are basin specific and can change annually within a single subbasin. Techniques developed during this study will assist water resource planners in understanding and managing water quality in their watersheds, particularly those in which there are persistent-turbidity problems.

Water-Resources Investigations Report↗
USGS2004

Chemical quality of base flow in 18 selected streams in the upper Susquehanna River basin, New York

The base-flow and runoff components of total streamflow at four selected sites in the upper Susquehanna River Basin in New York were calculated through hydrograph-separation techniques from long-term (1941-93) discharge records. Base flow was found to constitute more than 60 percent of the total annual flow of each stream. Base-flow samples were then collected at 18 stream sites several times during 2001 to define the chemical quality of base flow. The concentrations of selected common ions, nutrients, and pesticides were plotted in relation to the amount of agricultural land and carbonate bedrock in the drainage basin upstream of each site. Sites were selected at locations distant from and unaffected by development and urban areas. Twelve of the sites were again sampled in November 2001 for pesticide analysis. The predominant cations detected in the samples were calcium, magnesium, and sodium; the major anions were chloride, sulfate, and bicarbonate. The predominant nutrient was nitrate. Higher nitrate concentrations in the winter samples than in the summer samples are attributed to the seasonal decrease in plant growth and microbial activity in the streams during the winter, which allows nitrate to persist in the stream water. Lower nitrate concentrations in the summer samples probably result from nitrogen uptake by vegetation and microbial activity in the streams. Base-flow samples from the agricultural, carbonate-rich northern part of the study area had higher concentrations of most inorganic chemical constituents than those from the forested, noncarbonate (shale, siltstone, and sandstone) central and southern parts. The highest nitrate concentrations were in samples from subbasins dominated by agricultural land, and the lowest were in subbasins dominated by forest. The concentrations in samples from subbasins with forested as well as agricultural land were intermediate. Six pesticides were detected in samples from 10 of the 12 sites. All were herbicides. The highest concentrations of pesticides, and the most frequent pesticide detections, were in samples from agricultural subbasins and large main-stem subbasins with mixed land use and mixed bedrock geology. A correlation was indicated between land use and concentrations of atrazine and deethylatrazine. The concentrations of all six compounds were at least an order of magnitude lower than New York State and Federal water-quality standards. Ground water from four production wells in the villages of Afton, Sidney, Unadilla, and Otego was analyzed for chlorofluorocarbons (CFCs) to indicate the approximate age of the water in these wells and the potential for induced infiltration of river water. The water at two of these wells is probably between 26 and 50 years old; the ages of water at the other two wells could not be reliably estimated because of CFC contamination from a nonatmospheric source. The two wells for which CFC analysis gave reliable results (Afton and Otego) probably do not induce infiltration of river water into the aquifer.

New York↗
USGS2005

Borehole-geophysical and hydraulic investigation of the fractured-rock aquifer near the University of Connecticut Landfill, Storrs, Connecticut, 2000 to 2001

An integrated borehole-geophysical and hydraulic investigation was conducted at the former landfill area near the University of Connecticut in Storrs, Connecticut, where solvents and landfill leachate have contaminated a fractured-bedrock aquifer. Borehole-geophysical techniques and hydraulic methods were used to characterize the site bedrock lithology and structure, fractures, and hydraulic properties. The geophysical and hydraulic methods included conventional logs, borehole imaging, borehole radar, flowmeter under ambient- and stressed hydraulic conditions, and discrete-zone hydraulic testing, sampling, and monitoring. The conventional geophysical-logging methods included caliper, deviation, electromagnetic induction, gamma, specific conductance, and fluid temperature. The advanced methods included optical and acoustic imaging of the borehole wall, heat-pulse flowmeter, and directional radar reflection. Borehole-geophysical methods were used to further define conductive features identified with surface-geophysical methods in the first phase of the investigation. The results of the surface- and borehole-geophysical logging were evaluated in an iterative and integrated manner to develop a conceptual model of ground-water flow at the site. The rock type, foliation, and fractures at the site were characterized from high-resolution optical televiewer (OTV) images of rocks penetrated by the boreholes and were compared to drilling logs and conventional geophysical logs. The rocks are interpreted as fine- to mediumgrained quartz-feldspar-biotite-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 electromagnetic-induction and borehole-radar logs. Foliation in the rocks generally strikes to the southwest and northeast, and dips to the northwest and southeast consistent with previous investigations in this area. The orientation of foliation, however, varies locally and with depth in some of the boreholes. These results are consistent with geologic mapping that has identified small-scale folding. The orientations of the transmissive fractures identified in the six boreholes logged for this investigation are similar to the fracture orientations mapped in a previous investigation. Many of these fractures are oriented with a north-northwest strike and have a shallow dip to the west. Other transmissive fractures have a southwest strike and dip at shallow angles to the northwest, and some strike roughly east-west and dip to the north and south. Flowmeter logging was used to identify transmissive fractures and to estimate the hydraulic properties in the boreholes. Ambient down flow was measured in one borehole, and ambient up flow and down flow were measured in another borehole. The other four bedrock boreholes did not have measurable vertical flow. Under low-rate pumping conditions (0.25 to 0.5 gallons per minute), one to three inflow zones were identified in each well. Commonly, fractures that are active under ambient conditions contribute to the well under pumping conditions. The ambient conditions were incorporated into the determination of the relative proportions of transmissivity. Specific capacity and transmissivity were determined for these open-hole low-rate pumping tests. Quasi-steady-state water levels were reached in four of the boreholes, including MW201R, MW204R, MW302R, and W202-NE. When pumped at low-rate conditions for 0.5 to 4 hours, the specific capacity ranged from 0.03 to 0.18 gallons per minute per foot. The open-hole transmissivity estimates ranged from 4.9 to 30 feet squared per day (ft2/d). Open-hole transmissivity was determined for boreholes that did not reach quasi-steady-state conditions under low-rate pumping conditions. Transmissivity was estimated for MW201R, MW202R, and MW203R using non-equilibrium methods, pumping rate, and the transient drawdown data to estimate the open-hole transmissivity. Transmissivity in these boreholes ranged from 0.98 to 3.2 ft 2 /d. The transmissivity and head of individual fractures or zones of fractures were estimated from heat-pulse flowmeter data acquired under ambient and stressed conditions. In the absence of ambient flow, data from two profiles of heat-pulse flowmeter data under two different stressed conditions were used to estimate the transmissivity and head of individual fracture zones. Only two boreholes, MW302R and W202-NE, had sufficient data for these analyses. The estimated transmissivity of individual transmissive zones ranged from 1.2 to 9.2 ft 2 /d. The transmissivity values determined by this numerical simulation method were less than the open-hole estimations, which were 15 and 30 ft 2 /d. Transmissivity also was measured directly over discrete intervals of the borehole using a straddle-packer apparatus and constant-rate pumping tests. Pumping rates were less than or equal to 0.25 gallons per minute. These discretezone single-hole pumping tests were conducted over a short period of time, usually about 30 minutes to 1 hour in duration. Pumping continued until the test zone reached a steady-state water level or until it was determined that the zone could not yield water at the pumped rate. The estimated transmissivity of individual transmissive zones ranged from about 0.21 to 11 ft 2 /d. The zone at a depth of 197 feet in W202-NE was the only zone that had discrete-interval testing with a straddle packer and sufficient heat-pulse flowmeter data for modeling the flow and estimating transmissivity and head. The two methods produced similar results. The straddle-packer method estimated a transmissivity of 4.7 ft 2 /d, and the heat-pulse flowmeter modeling results estimated a transmissivity of 6.9 ft 2 /d. A comparison of the transmissivity estimates indicate estimates typically are within an order of magnitude. The heat-pulse flowmeter methods used in this investigation to determine transmissivity of the boreholes and the individual fractures measure only the upper two or three orders of magnitude of transmissivity. Hence, other fractures in these boreholes permit the movement of water; their transmissivities, however, are lower than the detection limits of the methods that were used for this investigation and very small compared to the transmissive fractures that were studied. The data collected in this investigation were used to design discrete-zone monitoring systems for four of the boreholes used for monitoring. The results of the investigation are useful for refining the conceptual site model of ground-water flow, and for providing critical information for interpreting the results of water-quality sampling.

Connecticut↗
USGS2003

Development and calibration of a ground-water flow model for the Sparta Aquifer of southeastern Arkansas and north-central Louisiana and simulated response to withdrawals, 1998-2027

The Sparta aquifer, which consists of the Sparta Sand, in southeastern Arkansas and north-central Louisiana is a major water resource and provides water for municipal, industrial, and agricultural uses. In recent years, the demand in some areas has resulted in withdrawals from the Sparta aquifer that substantially exceed replenishment of the aquifer. Considerable drawdown has occurred in the potentiometric surface forming regional cones of depression as water is removed from storage by withdrawals. These cones of depression are centered beneath the Grand Prairie area and the cities of Pine Bluff and El Dorado in Arkansas, and Monroe in Louisiana. The rate of decline for hydraulic heads in the aquifer has been greater than 1 foot per year for more than a decade in much of southern Arkansas and northern Louisiana where hydraulic heads are now below the top of the Sparta Sand. Continued hydraulic-head declines have caused water users and managers alike to question the ability of the aquifer to supply water for the long term. Concern over protecting the Sparta aquifer as a sustainable resource has resulted in a continued, cooperative effort by the Arkansas Soil and Water Conservation Commission, U.S. Army Corps of Engineers, and the U.S. Geological Survey to develop, maintain, and utilize numerical ground-water flow models to manage and further analyze the ground-water system. The work presented in this report describes the development and calibration of a ground-water flow model representing the Sparta aquifer to simulate observed hydraulic heads, documents major differences in the current Sparta model compared to the previous Sparta model calibrated in the mid-1980's, and presents the results of three hypothetical future withdrawal scenarios. The current Sparta model-a regional scale, three-dimensional numerical ground-water flow model-was constructed and calibrated using available hydrogeologic, hydraulic, and water-use data from 1898 to 1997. Significant changes from the previous model include grid rediscretization of the aquifer, extension of the active model area northward beyond the Cane River Formation facies change, and representation of model boundaries. The current model was calibrated with the aid of parameter estimation, a nonlinear regression technique, combined with trial and error parameter adjustment using a total of 795 observations from 316 wells over 4 different years-1970, 1985, 1990, and 1997. The calibration data set provides broad spatial and temporal coverage of aquifer conditions. Analysis of the residual statistics, spatial distribution of residuals, simulated compared to observed hydrographs, and simulated compared to observed potentiometric surfaces were used to analyze the ability of the calibrated model to simulate aquifer conditions within acceptable error. The calibrated model has a root mean square error of 18 feet for all observations, an improvement of more than 12 feet from the previous model. The current Sparta model was used to predict the effects of three hypothetical withdrawal scenarios on hydraulic heads over the period 1998-2027 with one of those extended indefinitely until equilibrium conditions were attained, or steady state. In scenario 1a, withdrawals representing the time period from 1990 to 1997 was held constant for 30 years from 1998 to 2027. Hydraulic heads in the middle of the cone of depression centered on El Dorado decreased by 10 feet from the 1997 simulation to 222 feet below NGVD of 1929 in 2027. Hydraulic heads in the Pine Bluff cone of depression showed a greater decline from 61 feet below NGVD of 1929 to 78 feet below NGVD of 1929 in the center of the cone. With these same withdrawals extended to steady state (scenario 1b), hydraulic heads in the Pine Bluff cone of depression center declined an 2 Development and Calibration of a Ground-Water Flow Model for the Sparta Aquifer of Southeastern Arkansas and North-Central Louisiana and Simulated Response to Withdrawa

Water-Resources Investigations Report↗
USGS2003

Use of the Hydrological Simulation Program-FORTRAN and bacterial source tracking for development of the fecal coliform total maximum daily load (TMDL) for Accotink Creek, Fairfax County, Virginia

Impairment of surface waters by fecal coliform bacteria is a water-quality issue of national scope and importance. Section 303(d) of the Clean Water Act requires that each State identify surface waters that do not meet applicable water-quality standards. In Virginia, more than 175 stream segments are on the 1998 Section 303(d) list of impaired waters because of violations of the water-quality standard for fecal coliform bacteria. A total maximum daily load (TMDL) will need to be developed by 2006 for each of these impaired streams and rivers by the Virginia Departments of Environmental Quality and Conservation and Recreation. A TMDL is a quantitative representation of the maximum load of a given water-quality constituent, from all point and nonpoint sources, that a stream can assimilate without violating the designated water-quality standard. Accotink Creek, in Fairfax County, Virginia, is one of the stream segments listed by the State of Virginia as impaired by fecal coliform bacteria. Watershed modeling and bacterial source tracking were used to develop the technical components of the fecal coliform bacteria TMDL for Accotink Creek. The Hydrological Simulation Program-FORTRAN (HSPF) was used to simulate streamflow, fecal coliform concentrations, and source-specific fecal coliform loading in Accotink Creek. Ribotyping, a bacterial source tracking technique, was used to identify the dominant sources of fecal coliform bacteria in the Accotink Creek watershed. Ribotyping also was used to determine the relative contributions of specific sources to the observed fecal coliform load in Accotink Creek. Data from the ribotyping analysis were incorporated into the calibration of the fecal coliform model. Study results provide information regarding the calibration of the streamflow and fecal coliform bacteria models and also identify the reductions in fecal coliform loads required to meet the TMDL for Accotink Creek. The calibrated streamflow model simulated observed streamflow characteristics with respect to total annual runoff, seasonal runoff, average daily streamflow, and hourly stormflow. The calibrated fecal coliform model simulated the patterns and range of observed fecal coliform bacteria concentrations. Observed fecal coliform bacteria concentrations during low-flow periods ranged from 25 to 800 colonies per 100 milliliters, and peak concentrations during storm-flow periods ranged from 19,000 to 340,000 colonies per 100 milliliters. Simulated source-specific contributions of fecal coliform bacteria to instream load were matched to the observed contributions from the dominant sources, which were cats, deer, dogs, ducks, geese, humans, muskrats, and raccoons. According to model results, an 89-percent reduction in the current fecal coliform load delivered from the watershed to Accotink Creek would result in compliance with the designated water-quality goals and associated TMDL.

Virginia↗
USGS2003

Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado

Tracer-injection studies were done in Belcher Gulch in the upper Animas River watershed, southwestern Colorado, to determine whether the alpine stream infiltrates into underground mine workings of the North Star Mine and other nearby mines in the area. The tracer-injection studies were designed to determine if and where along Belcher Gulch the stream infiltrates into the mine. Four separate tracer-injec-tion tests were done using lithium bromide (LiBr), optical brightener dye, and sodium chloride (NaCl) as tracer solu-tions. Two of the tracers (LiBr and dye) were injected con-tinuously for 24 hours, one of the NaCl tracers was injected continuously for 12 hours, and one of the NaCl tracers was injected over a period of 1 hour. Concentration increases of tracer constituents were detected in water discharging from the North Star Mine, substantiating a surface-water and ground-water connection between Belcher Gulch and the North Star Mine. Different timing and magnitude of tracer breakthroughs indicated multiple flow paths with different residence times from the stream to the mine. The Pittsburgh and Sultan Mines were thought to physically connect to the North Star Mine, but tracer breakthroughs were inconclusive in water from these mines. From the tracer-injection tests and synoptic measure-ments of streamflow discharge, a conceptual model was devel-oped for surface-water and ground-water interactions between Belcher Gulch and the North Star Mine. This information, combined with previous surface geophysical surveys indicat-ing the presence of subsurface voids, may assist with decision-making process for preventing infiltration and for the remedia-tion of mine drainage from these mines.

Water-Resources Investigations Report↗
USGS2004

Simulation of regional ground-water flow in the Upper Deschutes Basin, Oregon

This report describes a numerical model that simulates regional ground-water flow in the upper Deschutes Basin of central Oregon. Ground water and surface water are intimately connected in the upper Deschutes Basin and most of the flow of the Deschutes River is supplied by ground water. Because of this connection, ground-water pumping and reduction of artificial recharge by lining leaking irrigation canals can reduce the amount of ground water discharging to streams and, consequently, streamflow. The model described in this report is intended to help water-management agencies and the public evaluate how the regional ground-water system and streamflow will respond to ground-water pumping, canal lining, drought, and other stresses. Ground-water flow is simulated in the model by the finite-difference method using MODFLOW and MODFLOWP. The finite-difference grid consists of 8 layers, 127 rows, and 87 columns. All major streams and most principal tributaries in the upper Deschutes Basin are included. Ground-water recharge from precipitation was estimated using a daily water-balance approach. Artificial recharge from leaking irrigation canals and on-farm losses was estimated from diversion and delivery records, seepage studies, and crop data. Ground-water pumpage for irrigation and public water supplies, and evapotranspiration are also included in the model. The model was calibrated to mean annual (1993-95) steady-state conditions using parameter-estimation techniques employing nonlinear regression. Fourteen hydraulic-conductivity parameters and two vertical conductance parameters were determined using nonlinear regression. Final parameter values are all within expected ranges. The general shape and slope of the simulated water-table surface and overall hydraulic-head distribution match the geometry determined from field measurements. The fitted standard deviation for hydraulic head is about 76 feet. The general magnitude and distribution of ground-water discharge to streams is also well simulated throughout the model. Ground-water discharge to streams in the area of the confluence of the Deschutes, Crooked, and Metolius Rivers is closely matched. The model was also calibrated to transient conditions from 1978 to 1997 using traditional trial-and-error methods. Climatic cycles during this period provided an excellent regional hydrologic signal for calibration. Climate-driven water-level fluctuations are simulated with reasonable accuracy over most of the model area. The timing and magnitude of simulated water-level fluctuations caused by annual pulses of recharge from precipitation match those observed reasonably well, given the limitations of the time discretization in the model. Water-level fluctuations caused by annual canal leakage are simulated very well over most of the area where such fluctuations occur. The transient model also simulates the volumetric distribution and temporal variations in ground-water discharge reasonably well. The match between simulated and measured volume of and variations in ground-water discharge is, however, somewhat dependent on geographic scale. The rates of and variations in ground-water discharge are matched best at regional scales. Example simulations were made to demonstrate the utility of the model for evaluating the effects of ground-water pumping or canal lining. Pumping simulations show that pumped water comes largely from aquifer storage when pumping begins, but as the water table stabilizes, the pumping increasingly diminishes the discharge to streams and, hence, streamflow. The time it takes for pumping to affect streamflow varies spatially depending, in general, on the location of pumping relative to the discharge areas. Canal-lining simulations show similar effects.

Water-Resources Investigations Report↗
USGS2003

Survival, transport, and sources of fecal bacteria in streams and survival in land-applied poultry litter in the upper Shoal Creek basin, southwestern Missouri, 2001–2002

Densities of fecal coliform bacteria along a 5.7-mi (mile) reach of Shoal Creek extending upstream from State Highway 97 (site 3) to State Highway W (site 2) and in two tributaries along this reach exceeded the Missouri Department of Natural Resources (MDNR) standard of 200 col/100 mL (colonies per 100 milliliters) for whole-body contact recreation. A combination of techniques was used in this report to provide information on the source, transport, and survival of fecal bacteria along this reach of Shoal Creek. Results of water-quality samples collected during dye-trace and seepage studies indicated that at summer low base-flow conditions, pastured cattle likely were a substantial source of fecal bacteria in Shoal Creek at the MDNR monitoring site (site 3) at State Highway 97. Using repeat element Polymerase Chain Reaction (rep-PCR), cattle were the presumptive source of about 50 percent of the Escherichia coli ( E. coli ) isolates in water samples from site 3. Cattle, horses, and humans were the most common presumptive source of E. coli isolates at sites further upstream. Poultry was identified by rep-PCR as a major source of E. coli in Pogue Creek, a tributary in the upper part of the study area. Results of the rep-PCR were in general agreement with the detection and distribution of trace concentrations of organic compounds commonly associated with human wastewater, such as caffeine, the antimicrobial agent triclosan, and the pharmaceutical compounds acetaminophen and thiabendazole (a common cattle anthelmintic). Significant inputs of fecal bacteria to Shoal Creek occurred along a 1.6-mi reach of Shoal Creek immediately upstream from site 3. During a 36-hour period in July 2001, average densities of fecal coliform and E. coli bacteria increased from less than or equal to 500 col/100 mL upstream from this stream reach (sample site 2c) to 2,100 and 1,400 col/100 mL, respectively, at the MDNR sampling site. Fecal bacteria densities exhibited diurnal variability at all five sampling sites along the 5.7-mi study reach of Shoal Creek, but the trends at successive downstream sites were out of phase and could not be explained by simple advection and dispersion. At base-flow conditions, the travel time of bacteria in Shoal Creek along the 5.7-mi reach between State Highway W (site 2) and the MDNR sampling site (site 3) was about 26 hours. Substantial dispersion and dilution occurs along the upper 4.1 mi of this reach because of inflows from a number of springs and tributaries and the presence of several long pools and channel meanders. Minimal dispersion and dilution occurs along the 1.6-mi reach immediately upstream from the MDNR sampling site. Measurements of fecal bacteria decay in Shoal Creek during July 2001 indicated that about 8 percent of fecal coliform and E. coli bacteria decay each hour with an average first-order decay constant of 0.084 h -1 (per hour). Results of field test plots indicated that substantial numbers of fecal bacteria present in poul try litter can survive in fields for as much as 8 weeks after the application of the litter to the land surface. Median densities of fecal coliform and E. coli in slurry-water samples collected from fields increased from less than 60 col/100 mL before the application of turkey and broiler litter, to as large as 420,000 and 290,000 col/100 mL after the application of litter. Bacteria densities in the test plots generally decreased in a exponential manner over time with decay rates ranging from 0.085 to 0.185 d -1 (per day) for fecal coliform to between 0.100 and 0.250 d -1 for E. coli . The apparent survival of significant numbers of fecal bacteria on fields where poultry litter has been applied indicates that runoff from these fields is a potential source of fecal bacteria to vicinity streams for many weeks following litter application.

Water-Resources Investigations Report↗
USGS2004

Estimating hydraulic properties of the Floridan Aquifer System by analysis of earth-tide, ocean-tide, and barometric effects, Collier and Hendry Counties, Florida

Aquifers are subjected to mechanical stresses from natural, non-anthropogenic, processes such as pressure loading or mechanical forcing of the aquifer by ocean tides, earth tides, and pressure fluctuations in the atmosphere. The resulting head fluctuations are evident even in deep confined aquifers. The present study was conducted for the purpose of reviewing the research that has been done on the use of these phenomena for estimating the values of aquifer properties, and determining which of the analytical techniques might be useful for estimating hydraulic properties in the dissolved-carbonate hydrologic environment of southern Florida. Fifteen techniques are discussed in this report, of which four were applied. An analytical solution for head oscillations in a well near enough to the ocean to be influenced by ocean tides was applied to data from monitor zones in a well near Naples, Florida. The solution assumes a completely non-leaky confining unit of infinite extent. Resulting values of transmissivity are in general agreement with the results of aquifer performance tests performed by the South Florida Water Management District. There seems to be an inconsistency between results of the amplitude ratio analysis and independent estimates of loading efficiency. A more general analytical solution that takes leakage through the confining layer into account yielded estimates that were lower than those obtained using the non-leaky method, and closer to the South Florida Water Management District estimates. A numerical model with a cross-sectional grid design was applied to explore additional aspects of the problem. A relation between specific storage and the head oscillation observed in a well provided estimates of specific storage that were considered reasonable. Porosity estimates based on the specific storage estimates were consistent with values obtained from measurements on core samples. Methods are described for determining aquifer diffusivity by comparing the time-varying drawdown in an open well with periodic pressure-head oscillations in the aquifer, but the applicability of such methods might be limited in studies of the Floridan aquifer system.

Florida↗
USGS2004

Two-dimensional hydrodynamic simulation of surface-water flow and transport to Florida Bay through the Southern Inland and Coastal Systems (SICS)

Successful restoration of the southern Florida ecosystem requires extensive knowledge of the physical characteristics and hydrologic processes controlling water flow and transport of constituents through extremely low-gradient freshwater marshes, shallow mangrove-fringed coastal creeks and tidal embayments, and near-shore marine waters. A sound, physically based numerical model can provide simulations of the differing hydrologic conditions that might result from various ecosystem restoration scenarios. Because hydrology and ecology are closely linked in southern Florida, hydrologic model results also can be used by ecologists to evaluate the degree of ecosystem restoration that could be achieved for various hydrologic conditions. A robust proven model, SWIFT2D, (Surface-Water Integrated Flow and Transport in Two Dimensions), was modified to simulate Southern Inland and Coastal Systems (SICS) hydrodynamics and transport conditions. Modifications include improvements to evapotranspiration and rainfall calculation and to the algorithms that describe flow through coastal creeks. Techniques used in this model should be applicable to other similar low-gradient marsh settings in southern Florida and elsewhere. Numerous investigations were conducted within the SICS area of southeastern Everglades National Park and northeastern Florida Bay to provide data and parameter values for model development and testing. The U.S. Geological Survey and the National Park Service supported investigations for quantification of evapotranspiration, vegetative resistance to flow, wind-induced flow, land elevations, vegetation classifications, salinity conditions, exchange of ground and surface waters, and flow and transport in coastal creeks and embayments. The good agreement that was achieved between measured and simulated water levels, flows, and salinities through minimal adjustment of empirical coefficients indicates that hydrologic processes within the SICS area are represented properly in the SWIFT2D model, and that the spatial and temporal resolution of these processes in the model is adequate. Sensitivity analyses were conducted to determine the effect of changes in boundary conditions and parameter values on simulation results, which aided in identifying areas of greatest uncertainty in the model. The parameter having the most uncertainty (most in need of further field study) was the flow coefficient for coastal creeks. Smaller uncertainties existed for wetlands frictional resistance and wind. Evapotranspiration and boundary inflows indicated the least uncertainty as determined by varying parameters used in their formulation and definition. Model results indicated that wind was important in reversing coastal creek flows. At Trout Creek (the major tributary connecting Taylor Slough wetlands with Florida Bay), flow in the landward direction was not simulated properly unless wind forcing was included in the simulation. Simulations also provided insight into the major influence that wind has on salinity mixing along the coast, the varying distribution of wetland flows at differing water levels, and the importance of topography in controlling flows to the coast. Slight topographic variations were shown to highly influence the routing of water. A multiple regression analysis was performed to relate inflows at the northern boundary of Taylor Slough bridge to a major pump station (S-332) north of the SICS model area. This analysis allows Taylor Slough bridge boundary conditions to be defined for the model from operating scenarios at S-332, which should facilitate use of the SICS model as an operational tool.

Florida↗
USGS2003

Possible Extent and Depth of Salt Contamination in Ground Water Using Geophysical Techniques, Red River Aluminum Site, Stamps, Arkansas, April 2003

A surface-geophysical investigation of the Red River Aluminum site at Stamps, Arkansas, was conducted in cooperation with the Arkansas Department of Environmental Quality to determine the possible extent and depth of saltwater contamination. Water-level measurements indicate the distance to water level below land surface ranges from about 1.2 to 3.9 feet (0.37 to 1.19 meters) in shallow monitor wells and about 10.5 to 17.1 feet (3.20 to 5.21 meters) in deeper monitoring wells. The two-dimensional, direct-current resistivity method identified resistivities less than 5 ohm-meters which indicated possible areas of salt contamination occurring in near-surface or deep subsurface ground water along four resistivity lines within the site. One line located east of the site yielded data that demonstrated no effect of salt contamination. Sections from two of the five data sets were modeled. The input model grids were created on the basis of the known geology and the results and interpretations of borehole geophysical data. The clay-rich Cook Mountain Formation is modeled as 25 ohm-meters and extends from 21 meters (68.9 feet) below land surface to the bottom of the model (about 52 meters (170.6 feet)). The models were used to refine interpretation of the resistivity data and to determine extent of saltwater contamination and depth to the Cook Mountain Formation. Data from the resistivity lines indicate both near-surface and subsurface saltwater contamination. The near-surface contamination appears as low resistivity (less than 5 ohm-meters) on four of the five resistivity lines, extending up to 775 meters (2,542.8 feet) horizontally in a line that traverses the entire site south to north. Model resistivity data indicate that the total depth of saltwater contamination is about 18 meters (59 feet) below land surface. Data from four resistivity lines identified areas containing low resistivity anomalies interpreted as possible salt contamination. A fifth line located just east of the site showed no saltwater contamination.

Water-Resources Investigations Report↗
USGS2004

Surface-Water, Water-Quality, and Ground-Water Assessment of the Municipio of Mayaguez, Puerto Rico, 1999-2002

The surface-water assessment portion of this study focused on analysis of low-flow characteristics in local streams and rivers, because the supply of safe drinking water was a critical issue during recent dry periods. Low-flow characteristics were evaluated at one continuous-record gaging station based on graphical curve-fitting techniques and log-Pearson Type III frequency curves. Estimates of low-flow characteristics for 20 partial-record stations were generated using graphical-correlation techniques. Flow-duration characteristics for the continuous- and partial-record stations were estimated using the relation curves developed for the low-flow study. Stream low-flow statistics document the general hydrology under current land use, water-use, and climatic conditions. A survey of streams and rivers utilized 37 sampling stations to evaluate the sanitary quality of about 165 miles of stream channels. River and stream samples for fecal coliform and fecal streptococcus analyses were collected on two occasions at base-flow conditions. Bacteriological analyses indicate that a significant portion of the stream reaches within the municipio of Mayaguez may have fecal coliform bacteria concentrations above the water-quality goal (standard) established by the Puerto Rico Environmental Quality Board (Junta de Calidad Ambiental de Puerto Rico) for inland surface waters. Sources of fecal contamination may include: illegal discharge of sewage to storm-water drains, malfunctioning sanitary sewer ejectors, clogged and leaking sewage pipes, septic tank leakage, unfenced livestock, and runoff from livestock pens. Long-term fecal coliform data from five sampling stations located within or in the vicinity of the municipio of Mayaguez have been in compliance with the water-quality goal for fecal coliform concentration established in July 1990. Geologic, topographic, soil, hydrogeologic, and streamflow data were compiled into a database and used to divide the municipio of Mayaguez into five hydrogeologic terranes. This integrated database then was used to evaluate the ground-water potential of each hydrogeologic terrane. Lineament-trace analysis was used to help assess the ground-water development potential in the hydrogeologic terranes containing igneous rocks. Analyses suggest that areas with slopes greater than 15 degrees have relatively low ground-water development potential. The presence of fractures, independent of the topographic slope, may locally enhance the water-bearing properties in the hydrogeologic terranes containing igneous rocks. The results of this study indicate that induced streamflow generally is needed to sustain low to moderate ground-water withdrawal rates in the five hydrogeologic terranes. The ground-water flow systems in the hydrogeologic terranes are only able to sustain small withdrawal rates that rarely exceed 50 gallons per minute. Areas with a high density of fractures, as could be the case at the intersection of lineament traces in the upper parts of the Rio Ca?as and Rio Yaguez watersheds, are worthy of exploratory drilling for ground-water development.

Water-Resources Investigations Report↗
USGS2004

Evaluation of strategies for balancing water use and streamflow reductions in the upper Charles River basin, eastern Massachusetts

The upper Charles River basin, located 30 miles southwest of Boston, Massachusetts, is experiencing water shortages during the summer. Towns in the basin have instituted water-conservation programs and water-use bans to reduce summertime water use. During July through October, streamflow in the Charles River and its tributaries regularly falls below 0.50 cubic foot per second per square mile, the minimum streamflow used by the U.S. Fish and Wildlife Service as its Aquatic Base Flow standard for maintaining healthy freshwater ecosystems. To examine how human water use could be changed to mitigate these water shortages, a numerical ground-water flow model was modified and used in conjunction with response coefficients and optimization techniques. Streamflows at 10 locations on the Charles River and its tributaries were determined under various water-use scenarios and climatic conditions. A variety of engineered solutions to the water shortages were examined for their ability to increase water supplies and summertime streamflows. Results indicate that although human water use contributes to the problem of low summertime streamflows, human water use is not the only, or even the primary, cause of low flows in the basin. The lowest summertime streamflows increase by 12 percent but remain below the Aquatic Base Flow standard when all public water-supply pumpage and wastewater flows in the basin are eliminated in a simulation under average climatic conditions. Under dry climatic conditions, the same measures increase the lowest average monthly streamflow by 95 percent but do not increase it above the Aquatic Base Flow standard. The most promising water-management strategies to increase streamflows and water supplies, based on the study results, include wastewater recharge to the aquifer, altered management of pumping well schedules, regional water-supply sharing, and water conservation. In a scenario that simulated towns sharing water supplies, streamflow in the Charles River as it exits the basin increased by 18 percent during July through September and an excess water-supply capacity of 13.4 cubic feet per second, above and beyond average use, would be available to all towns in the basin. These study results could help water suppliers and regulators evaluate strategies for balancing ground-water development and streamflow reductions in the basin.

Massachusetts↗
USGS1990

Recharge rates and aquifer hydraulic characteristics for selected drainage basins in middle and east Tennessee

Quantitative information concerning aquifer hydrologic and hydraulic characteristics is needed to manage the development of ground-water resources. These characteristics are poorly defined for the bedrock aquifers in Middle and East Tennessee where demand for water is increasing. This report presents estimates of recharge rate, storage coefficient, diffusivity, and transmissivity for representative drainage basins in Middle and East Tennessee, as determined from analyses of stream-aquifer interactions. The drainage basins have been grouped according to the underlying major aquifer, then statistical descriptions applied to each group, in order to define area1 distribution of these characteristics. Aquifer recharge rates are estimated for representative low, average, and high flow years for 63 drainage basins using hydrograph analysis techniques. Net annual recharge during average flow years for all basins ranges from 4.1 to 16.8 in/yr (inches per year), with a mean value of 7.3 in. In general, recharge rates are highest for basins underlain by the Blue Ridge aquifer (mean value11.7 in/yr) and lowest for basins underlain by the Central Basin aquifer (mean value 5.6 in/yr). Mean recharge values for the Cumberland Plateau, Highland Rim, and Valley and Ridge aquifers are 6.5, 7.4, and 6.6 in/yr, respectively. Gravity drainage characterizes ground-water flow in most surficial bedrock aquifer in Tennessee. Accordingly, a gravity yield analysis, which compares concurrent water-level and streamflow hydrographs, was used to estimate aquifer storage coefficient for nine study basins. The basin estimates range from 0.002 to 0.140; however, most estimates are within a narrow range of values, from 0.01 to 0.025. Accordingly, storage coefficient is estimated to be 0.01 for all aquifers in Middle and East Tennessee, with the exception of the aquifer in the inner part of the Central Basin, for which storage coefficient is estimated to be 0.002. Estimates of aquifer hydraulic diffusivity are derived from estimates of the streamflow recession index and drainage density for 75 drainage basins; values range from 3,300 to 130,000 ft^2/d (feet squared per day). Basin-specific and site-specific estimates of transmissivity are computed from estimates of hydraulic diffusivity and specific-capacity test data, respectively. Basin-specific, or areal, estimates of transmissivity range from 22 to 1,300 ft^2/d, with a mean of 240 ft^2/d In general, areal transmissivity is highest for basins underlain by the Cumberland Plateau aquifer (mean value 480 ft^2/d) and lowest for basins underlain by the Central Basin aquifer (mean value 79 ft^2/d). Mean transmissivity values for the Highland Rim, Valley and Ridge, and Blue Ridge aquifer are 320,140, and 120 ft^2/d respectively. Site-specific estimates of transmissivity, computed from specific-capacity data from 118 test wells in Middle and East Tennessee range from 2 to 93,000 ft^2/d with a mean of 2,600 ft^2/d Mean transmissivity values for the Cumberland Plateau, Highland Rim, Central Basin, Valley and Ridge, and Blue Ridge aquifers are 2,800,1,200, 7,800, 390, and 65Oft Id, respectively.

Tennessee↗