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P. T. Harte

Publications and source records attributed to P. T. Harte.

16 recordsLinked to original sources
USGS2010

Mapping of road-salt-contaminated groundwater discharge and estimation of chloride load to a small stream in southern New Hampshire, USA

Concentrations of chloride in excess of State of New Hampshire water-quality standards (230 mg/l) have been measured in watersheds adjacent to an interstate highway (I-93) in southern New Hampshire. A proposed widening plan for I-93 has raised concerns over further increases in chloride. As part of this effort, road-salt-contaminated groundwater discharge was mapped with terrain electrical conductivity (EC) electromagnetic (EM) methods in the fall of 2006 to identify potential sources of chloride during base-flow conditions to a small stream, Policy Brook. Three different EM meters were used to measure different depths below the streambed (ranging from 0 to 3 m). Results from the three meters showed similar patterns and identified several reaches where high EC groundwater may have been discharging. Based on the delineation of high (up to 350 mmhos/m) apparent terrain EC, seven-streambed piezometers were installed to sample shallow groundwater. Locations with high specific conductance in shallow groundwater (up to 2630 mmhos/m) generally matched locations with high streambed (shallow subsurface) terrain EC. A regression equation was used to convert the terrain EC of the streambed to an equivalent chloride concentration in shallow groundwater unique for this site. Utilizing the regression equation and estimates of onedimensional Darcian flow through the streambed, a maximum potential groundwater chloride load was estimated at 188 Mg of chloride per year. Changes in chloride concentration in stream water during streamflow recessions showed a linear response that indicates the dominant process affecting chloride is advective flow of chloride-enriched groundwater discharge. Published in 2010 by John Wiley & Sons, Ltd.

Hydrological Processes↗
USGS2007

The effect of terrace geology on ground-water movement and on the interaction of ground water and surface water on a mountainside near Mirror Lake, New Hampshire, USA

The west watershed of Mirror Lake in the White Mountains of New Hampshire contains several terraces that are at different altitudes and have different geologic compositions. The lowest terrace (FSE) has 5 m of sand overlying 9 m of till. The two next successively higher terraces (FS2 and FS1) consist entirely of sand and have maximum thicknesses of about 7 m. A fourth, and highest, terrace (FS3) lies in the north-west watershed directly adjacent to the west watershed. This highest terrace has 2 m of sand overlying 8 m of till. All terraces overlie fractured crystalline bedrock. Numerical models of hypothetical settings simulating ground-water flow in a mountainside indicated that the presence of a terrace can cause local ground-water flow cells to develop, and that the flow patterns differ based on the geologic composition of the terrace. For example, more ground water moves from the bedrock to the glacial deposits beneath terraces consisting completely of sand than beneath terraces that have sand underlain by till. Field data from Mirror Lake watersheds corroborate the numerical experiments. The geology of the terraces also affects how the stream draining the west watershed interacts with ground water. The stream turns part way down the mountainside and passes between the two sand terraces, essentially transecting the movement of ground water down the valley side. Transects of water-table wells were installed across the stream's riparian zone above, between, and below the sand terraces. Head data from these wells indicated that the stream gains ground water on both sides above and below the sand terraces. However, where it flows between the sand terraces the stream gains ground water on its uphill side and loses water on its downhill side. Biogeochemical processes in the riparian zone of the flow-through reach have resulted in anoxic ground water beneath the lower sand terrace. Results of this study indicate that it is useful to understand patterns of ground-water flow in order to fully understand the flow and chemical characteristics of both ground water and surface water in mountainous terrain.

Hydrological Processes↗
USGS2006

Simulation of solute transport across low-permeability barrier walls

Low-permeability, non-reactive barrier walls are often used to contain contaminants in an aquifer. Rates of solute transport through such barriers are typically many orders of magnitude slower than rates through the aquifer. Nevertheless, the success of remedial actions may be sensitive to these low rates of transport. Two numerical simulation methods for representing low-permeability barriers in a finite-difference groundwater-flow and transport model were tested. In the first method, the hydraulic properties of the barrier were represented directly on grid cells and in the second method, the intercell hydraulic-conductance values were adjusted to approximate the reduction in horizontal flow, allowing use of a coarser and computationally efficient grid. The alternative methods were tested and evaluated on the basis of hypothetical test problems and a field case involving tetrachloroethylene (PCE) contamination at a Superfund site in New Hampshire. For all cases, advective transport across the barrier was negligible, but preexisting numerical approaches to calculate dispersion yielded dispersive fluxes that were greater than expected. A transport model (MODFLOW-GWT) was modified to (1) allow different dispersive and diffusive properties to be assigned to the barrier than the adjacent aquifer and (2) more accurately calculate dispersion from concentration gradients and solute fluxes near barriers. The new approach yields reasonable and accurate concentrations for the test cases.

Journal of Contaminant Hydrology↗
USGS1995

Geohydrology and water quality of stratified-drift aquifers in the Contoocook River basin, south-central New Hampshire

Stratified-drift aquifers discontinuously underlie 121 mi2 (square miles) of the Contoocook River Basin, which has a total drainage area of 776 mi2. Maps of these aquifers, showing water-table configurations, saturated thicknesses, and transmissivities were prepared from well and test-hole data and seismic-refraction profiles. The distribution of stratified-drift aquifers is largely controlled by the Pleistocene glaciation process and the formation of multiple glacial lakes along the main stem of the Contoocook River. Locally, saturated thickness of stratified drift within these aquifers are as great as 200 feet. Estimated transmissivities exceed 8,000 ft2/d (squared feet per day) at three locations and is as high as 22,800 ft2/d at one location. Stratified-drift aquifers that have the greatest potential to supply additional amounts of water include the aquifers at Greenfield-Otter Brook and Hancock-Norway Pond. Potential yields to hypothetical supply wells were estimated for the Greenfield-Otter Brook, Hillsborough-Contoocook River, and Andover- Blackwater River aquifers by use of a analytical ground-water-flow model. The model results predict that the potential yields are greatest from the Greenfield-Otter Brook aquifer, yielding up to 1.85 gallons per day during half-year periods of no recharge. The effective ground-water recharge to the entire basin, which includes recharge to the till, bedrock, and stratified drift, is 13.9 in./yr (inches per year) (521 million gallons per day) on the basis of hydrograph separation of streamflow. The quality of water obtained from 11 observation wells and 10 municipal supply wells is generally suitable for drinking and most other domestic purposes. Ground water in the region has low alkalinity, is slightly acidic, and has low concentrations of dissolved solids. Concentrations of dissolved constituents in ground-water samples were generally less than the U.S. Environmental Protection Agency's primary and secondary maximum contaminant levels except for elevated iron concentrations (in water from six wells) and manganese concentrations in water from seven wells.

Water-Resources Investigations Report↗
USGS1992

Geohydrology of, and simulation of ground-water flow in, the Milford-Souhegan glacial-drift aquifer, Milford, New Hampshire

Hydrogeologic data collected since 1990 were assessed and a ground-water-flow model was refined in this study of the Milford-Souhegan glacial-drift aquifer in Milford, New Hampshire. The hydrogeologic data collected were used to refine estimates of hydraulic conductivity and saturated thickness of the aquifer, which were previously calculated during 1988-90. In October 1990, water levels were measured at 124 wells and piezometers, and at 45 stream-seepage sites on the main stem of the Souhegan River, and on small tributary streams overlying the aquifer to improve an understanding of ground-water-flow patterns and stream-seepage gains and losses. Refinement of the ground-water-flow model included a reduction in the number of active cells in layer 2 in the central part of the aquifer, a revision of simulated hydraulic conductivity in model layers 2 and representing the aquifer, incorporation of a new block-centered finite-difference ground-water-flow model, and incorporation of a new solution algorithm and solver (a preconditioned conjugate-gradient algorithm). Refinements to the model resulted in decreases in the difference between calculated and measured heads at 22 wells. The distribution of gains and losses of stream seepage calculated in simulation with the refined model is similar to that calculated in the previous model simulation. The contributing area to the Savage well, under average pumping conditions, decreased by 0.021 square miles from the area calculated in the previous model simulation. The small difference in the contrib- uting recharge area indicates that the additional data did not enhance model simulation and that the conceptual framework for the previous model is accurate.

Water-Resources Investigations Report↗
USGS1986

Ground-water-quality data for Picatinny Arsenal, New Jersey, 1958-85

The water resources of Picatinny Arsenal in northern New Jersey are described using the results of 1,129 analyses of groundwater , including 522 determinations of inorganic constituents and 607 determinations of organic constituents. Water samples were collected from 56 wells on the site from 1958 through 1985. Of these wells, 50 are screened in stratified drift aquifers and 6 are in bedrock. Samples were collected and analyzed by a total of four agencies: one State, one Federal, and two private. Of the 1,129 samples, 51 were collected and analyzed by the U.S. Geological Survey. The data on inorganic constituents exhibit much variability. Specific conductance ranges from 40 to 2,150 microsiemens per centimeter at 25 degrees C, pH ranges from 2.9 units to 10 units, and dissolved solids ranges from 51 to 1,210 milligrams per liter. Trace elements that display wide variations in concentration ranges are iron (<2 to 540,000 micrograms/L), manganese (<1 to 55,000 micrograms/L), and zinc (<3 to 1,900 micrograms/L). The organic compounds with the widest variations in concentration are: 1 ,2-transdichloroethylene (<1 to 542 micrograms/L), tetrachloroethylene (<1 to 386 micrograms/L), 1,1 ,1-trichloroethane (<1 to 1,780 micrograms/L), and trichloroethylene (<1 to 25,000 micrograms/L).

New Jersey↗