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The population of Island County has grown from 6,700 in 1940 to about 22,000 in 1964, causing a corresponding increase in the demand for water. Ground water is the only significant source of water within the county. Average annual precipitation ranges from less than 20 to more than 40 inches, and is the only recharge to the ground-water body.
Systematic ground-water development began in Utah shortly after settlement by Mormon pioneers in 1847. By 1939, about 230,000 acrefeet per year of ground water was being withdrawn from wells for irrigation, public supply, industrial use, and rural-domestic and stock supply. Withdrawals increased from about 600,000 to 700,000 acre-feet per year during 1963-67 to about 800,000 to 900,000 acre-feet per year during 1989-93, with a peak of 940,000 acre-feet in 1990. Most ground-water withdrawals from wells have been from unconsolidated basin-fill deposits in 13 areas along or near the eastern edge of the Basin and Range Province, which extends from the northern edge of Utah to its southwestern part. The proportions of withdrawals for various uses have changed; in 1964, 72 percent of withdrawals was for irrigation and II percent for public supply, whereas in 1993,64 percent was for irrigation and 21 percent for public supply. Long-term withdrawals from wells have caused declines in water levels in parts of western Utah from the 1940's and 1950's to 1994; the withdrawals apparently have caused local increases in dissolved-solids concentrations in ground water. Water levels have declined as much as 67 feet owing to withdrawals for public supply and industrial use in northwestern Utah, and as much as 88 feet owing to withdrawals for irrigation in southwestern Utah. Declines of this magnitude, however, are confined to local areas of large withdrawals. Withdrawals for irrigation apparently have caused increases in dissolved-solids concentrations in ground water in at least six irrigated areas of western Utah. Minor land subsidence related to compaction of basin-fill deposits caused by water-level declines has been observed locally in southwestern Utah.
A numerical three-dimensional (3D) transient ground-water flow model of the Death Valley region was developed by the U.S. Geological Survey for the U.S. Department of Energy programs at the Nevada Test Site and at Yucca Mountain, Nevada. Decades of study of aspects of the ground-water flow system and previous less extensive ground-water flow models were incorporated and reevaluated together with new data to provide greater detail for the complex, digital model. A 3D digital hydrogeologic framework model (HFM) was developed from digital elevation models, geologic maps, borehole information, geologic and hydrogeologic cross sections, and other 3D models to represent the geometry of the hydrogeologic units (HGUs). Structural features, such as faults and fractures, that affect ground-water flow also were added. The HFM represents Precambrian and Paleozoic crystalline and sedimentary rocks, Mesozoic sedimentary rocks, Mesozoic to Cenozoic intrusive rocks, Cenozoic volcanic tuffs and lavas, and late Cenozoic sedimentary deposits of the Death Valley Regional Ground-Water Flow System (DVRFS) region in 27 HGUs. Information from a series of investigations was compiled to conceptualize and quantify hydrologic components of the ground-water flow system within the DVRFS model domain and to provide hydraulic-property and head-observation data used in the calibration of the transient-flow model. These studies reevaluated natural ground-water discharge occurring through evapotranspiration and spring flow; the history of ground-water pumping from 1913 through 1998; ground-water recharge simulated as net infiltration; model boundary inflows and outflows based on regional hydraulic gradients and water budgets of surrounding areas; hydraulic conductivity and its relation to depth; and water levels appropriate for regional simulation of prepumped and pumped conditions within the DVRFS model domain. Simulation results appropriate for the regional extent and scale of the model were provided by acquiring additional data, by reevaluating existing data using current technology and concepts, and by refining earlier interpretations to reflect the current understanding of the regional ground-water flow system. Ground-water flow in the Death Valley region is composed of several interconnected, complex ground-water flow systems. Ground-water flow occurs in three subregions in relatively shallow and localized flow paths that are superimposed on deeper, regional flow paths. Regional ground-water flow is predominantly through a thick Paleozoic carbonate rock sequence affected by complex geologic structures from regional faulting and fracturing that can enhance or impede flow. Spring flow and evapotranspiration (ET) are the dominant natural ground-water discharge processes. Ground water also is withdrawn for agricultural, commercial, and domestic uses. Ground-water flow in the DVRFS was simulated using MODFLOW-2000, a 3D finite-difference modular ground-water flow modeling code that incorporates a nonlinear least-squares regression technique to estimate aquifer parameters. The DVRFS model has 16 layers of defined thickness, a finite-difference grid consisting of 194 rows and 160 columns, and uniform cells 1,500 m on each side. Prepumping conditions (before 1913) were used as the initial conditions for the transient-state calibration. The model uses annual stress periods with discrete recharge and discharge components. Recharge occurs mostly from infiltration of precipitation and runoff on high mountain ranges and from a small amount of underflow from adjacent basins. Discharge occurs primarily through ET and spring discharge (both simulated as drains) and water withdrawal by pumping and, to a lesser amount, by underflow to adjacent basins, also simulated by drains. All parameter values estimated by the regression are reasonable and within the range of expected values. The simulated hydraulic heads of the final calibrated transient model gener
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A landfill in Falmouth, Massachusetts, is upgradient of a pond used for municipal water supply, but analysis of groundwater flow directions and groundwater quality indicates that leachate from the landfill does not threaten the municipal water supply. A network of water table observation wells was established, and water table altitudes were measured in these wells on several dates in 1981. Water quality analyses and specific conductance measurements were made on water samples from several wells in the vicinity of the landfill between October 1980 and April 1983. A water table altitude contour map of the area between the landfill and Long Pond for April 16-17, 1981, indicates that the direction of groundwater flow is primarily southwest from the landfill to Buzzards Bay. A similar map for September 2, 1981--a time at which the water table was unusually low--indicates the possibility of groundwater discharge to Long Pond from the landfill site. Groundwater quality beneath the landfill exceeded U.S. EPA water quality criteria for domestic water supply for manganese and total dissolved solids. Concentrations as high as 52 mg/L of nitrogen as ammonia and 4,500 micrograms/L (ug/L) of manganese were found. Concentrations of ammonia, manganese, calcium, potassium, and alkalinity exceeded local background levels by more than a factor of 100; specific-conductance levels and concentrations of hardness, barium, chloride, sodium, magnesium, iron, and strontium exceeded local background levels by more than a factor of 10; and cadmium concentrations exceeded local background levels by more than a factor of 5. Water quality analyses and field specific conductance measurements indicate the presence of a volume of leachate extending south-southwest from the landfill. Average chloride concentrations of landfill leachate, precipitation on the surface of Long Pond, and recharge from the remainder of the recharge area were 180, 3, and 9 mg/L, respectively. No significant degradation of the quality of water in Long Pond is expected as a result of leachate from this landfill. (Author 's abstract)
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Ground-water withdrawal estimates from 1913 through 2003 for the Death Valley regional ground-water flow system are compiled in an electronic database to support a regional, three-dimensional, transient ground-water flow model. This database updates a previously published database that compiled estimates of ground-water withdrawals for 1913-1998. The same methodology is used to construct each database. Primary differences between the 2 databases are an additional 5 years of ground-water withdrawal data, well locations in the updated database are restricted to Death Valley regional ground-water flow system model boundary, and application rates are from 0 to 1.5 feet per year lower than original estimates. The lower application rates result from revised estimates of crop consumptive use, which are based on updated estimates of potential evapotranspiration. In 2003, about 55,700 acre-feet of ground water was pumped in the DVRFS, of which 69 percent was used for irrigation, 13 percent for domestic, and 18 percent for public supply, commercial, and mining activities.
MODOPTIM is a non-linear ground-water model calibration and management tool that simulates flow with MODFLOW-96 as a subroutine. A weighted sum-of-squares objective function defines optimal solutions for calibration and management problems. Water levels, discharges, water quality, subsidence, and pumping-lift costs are the five direct observation types that can be compared in MODOPTIM. Differences between direct observations of the same type can be compared to fit temporal changes and spatial gradients. Water levels in pumping wells, wellbore storage in the observation wells, and rotational translation of observation wells also can be compared. Negative and positive residuals can be weighted unequally so inequality constraints such as maximum chloride concentrations or minimum water levels can be incorporated in the objective function. Optimization parameters are defined with zones and parameter-weight matrices. Parameter change is estimated iteratively with a quasi-Newton algorithm and is constrained to a user-defined maximum parameter change per iteration. Parameters that are less sensitive than a user-defined threshold are not estimated. MODOPTIM facilitates testing more conceptual models by expediting calibration of each conceptual model. Examples of applying MODOPTIM to aquifer-test analysis, ground-water management, and parameter estimation problems are presented.
The U.S. Geological Survey, in cooperations with the U.S. Army Corps of Engineers, conducted a study during October 1993-April 1994 to improve an understanding of the hydrology of the Lost River watershed near Orleans, Ind. Elements of the study included: (1) constructing a map of the composite ground-water potentiometric-surface of the study area, (2) injecting and recovering fluorescent dyes at karst features in the study area to help locate ground-water-flow paths and drainage divides, (3) compiling a bibliography of references describing the study area, and (4) constructing a map of karst features. The composite ground- water-potentiometric surface map and the eight dye traces done as part of this study indicate the approximate locations of the subsurface drainage divides near Orleans. Subsurface drainage near Orleans flows primarily southwest to a reemergence at Orangeville Rise, Orangeville, Ind. Dye clouds injected north of the Orangeville Rise drainage basin reemerged in the Hamer Cave outlet stream, Spring Mill State Park, Ind. The drainage divide that separates subsurface flow to Orangeville Rise from flow to Hamer Cave does not coincide with the surface-water drainage divide. Several factors may contribute to the flooding in Orleans, including: (1) an overtaxed storm sewer system, (2) location of the town in a karst valley, (3) a high runoff- rainfall relation for a 1oess- and residuum-covered area that drains into an occluded sinkhole near the center of Orleans, and (4) an overtaxed subsurface drainage system during periods of intense rainfall.