Geology topics

Margot Truini

Publications and source records attributed to Margot Truini.

25 records · Page 2Linked to original sources

USGS2000

Ground-water, surface-water, and water-chemistry data, Black Mesa area, northeastern Arizona—1999

The N aquifer is the major source of water in the 5,400-square-mile area of Black Mesa in northeastern Arizona. Availability of water is an important issue in this area because of continued industrial and municipal use, a growing population, and a precipitation of only about 6 to 12 inches per year. The monitoring program in Black Mesa has been operating since 1971 and is designed to determine the long-term effects of ground-water withdrawals from the N aquifer for industrial and municipal uses. The monitoring program includes measurements of (1) ground-water pumping, (2) ground-water levels, (3) spring discharge, (4) surface-water discharge, and (5) ground-water chemistry. In 1999, total ground-water withdrawals were 7,110 acre-feet, industrial use was 4,210 acre-feet, and municipal use was 2,900 acre-feet. From 1998 to 1999, total withdrawals increased by 0.7 percent, industrial use increased by 4 percent, and municipal use decreased by 4 percent. From 1998 to 1999, water levels declined in 11 of 15 wells in the unconfined part of the aquifer, and the median decline was 0.7 foot. Water levels declined in 14 of 16 wells in the confined part of the aquifer, and the median decline was 1.2 feet. From the prestress period (prior to 1965) to 1999, the median water-level decline in 31 wells was 10.6 feet. Median water-level changes were 0.0 foot for 15 wells in the unconfined part of the aquifer and a decline of 45.5 feet in 16 wells in the confined part. From 1998 to 1999, discharges were measured annually at four springs. Discharges declined 30 percent and 3 percent at 2 springs, did not change at 1 spring, and increased by 11 percent at 1 spring. For the past 10 years, discharges from the four springs have fluctuated; however, an increasing or decreasing trend was not observed. Continuous records of surface-water discharge have been collected from July 1976 to 1999 at Moenkopi Wash, July 1996 to 1999 at Laguna Creek, June 1993 to 1999 at Dinnebito Wash, and April 1994 to 1999 at Polacca Wash. Median flows for November, December, January, and February of each water year are used as an index of ground-water discharge to those streams. Increasing or decreasing trends are not apparent in these median winter flows for the periods of record. In 1999, water samples were collected from 12 wells and 4 springs and analyzed for selected chemical constituents. Dissolved-solids concentrations ranged from 91 to 630 milligrams per liter. Water samples from 10 of the wells and the 4 springs had less than 350 milligrams per liter of dissolved solids. Water-chemistry data are available for nine wells and four springs from about the mid-1980s. For that time period, the data from those sites have remained fairly stable. From 1987 to 1999, concentrations of dissolved solids, chloride, and sulfate may have increased slightly in samples from Moenkopi School Spring.

Arizona↗

USGS2000

Ground-water, surface-water, and water-chemistry data, Black Mesa area, northeastern Arizona: 1998

The Black Mesa monitoring program is designed to document long-term effects of ground-water pumping from the N aquifer by industrial and municipal users. The N aquifer is the major source of water in the 5,400-square-mile Black Mesa area, and the ground water occurs under confined and unconfined conditions. Monitoring activities include continuous and periodic measurements of (1) ground-water pumpage from the confined and unconfined parts of the aquifer, (2) ground-water levels in the confined and unconfined parts of the aquifer, (3) surface-water discharge, (4) flowmeter tests, and (5) ground-water and surface-water chemistry. In 1998, ground-water withdrawals for industrial and municipal use totaled about 7,060 acre-feet, which is less than a 1 percent decrease from 1997. Pumpage from the confined part of the aquifer decreased by less than 1 percent to 5,470 acre-feet, and pumpage from the unconfined part of the aquifer increased by less than 1 percent to 1,590 acre-feet. Water-level declines in the confined part of the aquifer were recorded in 10 of 14 wells during 1998, and the median change from 1997 was a decline of 3.0 feet as opposed to a rise of 0.2 feet for the change from 1996 to 1997. Water-level declines in the unconfined part of the aquifer were recorded in 9 of 16 wells, and the median change from 1997 was 0.0 feet, which is the same as the median change from 1996 to 1997. Of the 35 pumpage meters on municipal wells that were tested, the difference between metered and tested discharge ranged from +6.3 to -19.6 percent. The average difference was about -3.4 percent. Five of the meters exceeded the allowable difference (10 percent) and should be repaired or replaced. The low-flow discharge at the Moenkopi streamflow-gaging station ranged from 2.6 to 4.7 cubic feet per second in 1998. Streamflow-discharge measurements also were made at Laguna Creek, Dinnebito Wash, and Polacca Wash during 1998. The low-flow discharge ranged from 0.41 to 5.1 cubic feet per second at Laguna Creek, 0.32 to 0.44 cubic feet per second at Dinnebito Wash, and 0.13 to 0.36 cubic feet per second at Polacca Wash. Discharge was measured at four springs. Discharge from Moenkopi School Spring decreased by about 1.1 gallons per minute from the measurement in 1997. Discharge from an unnamed spring near Dennehotso decreased by 4.6 gallons per minute from the measurement made in 1997. Discharge increased slightly at Burro Spring and decreased by about 1 gallon per minute at Pasture Canyon Spring. Regionally, long-term water-chemistry data for wells and springs have remained stable.

Arizona↗

USGS2000

Hydrogeology of the regional aquifer near Flagstaff, Arizona, 1994-97

Sandstones, siltstones, and limestones that are Pennsylvanian to Permian in age underlie the southern part of the Colorado Plateau near Flagstaff, Arizona, and contain a complex regional aquifer that has become increasingly important as a source of water for domestic, municipal, and recreational uses. Ground-water flow in the regional aquifer is poorly understood in this area because (1) depth of the aquifer limits exploratory drilling and testing and (2) the geologic structure increases the complexity of the aquifer characteristics and the ground-water flow system. Four methods were used to improve the understanding of the hydrogeology of the regional aquifer near Flagstaff. • Remote-sensing techniques and geologic mapping provided data to identify many structural features that indicate a more complex structural environment and history than previously realized. • Data from surface-geophysical techniques that included ground-penetrating radar, seismic reflection and seismic refraction, and square-array resistivity, verified that some of the geologic structures expressed at land surface propagate deep into the subsurface and through the principal water-bearing zones of the regional aquifer at near-vertical angles. • A well and spring inventory, borehole-geophysical methods, and well and aquifer tests provided additional information relating aquifer and ground-water flow characteristics to geologic structure. • Water-chemistry data, which included major ion, nutrient, trace-element, and radioactive and stable-isotope analyses, provided an independent means of verifying the hydrogeologic characteristics of the aquifer and were used to determine recharge and discharge areas, groundwater movement, and ground-water age. Ground-water recharge occurs throughout the area but is greatest at higher altitudes where precipitation is greater and in areas where heavily fractured rock units of the aquifer are exposed. The estimated annual average recharge to the regional aquifer in the study area is about 290,000 acre-feet. Ground water flows laterally and vertically through pore spaces in the rock and along faults and other fractures from high-altitude areas in the southern part of the study area to regional drains north of the study area along the Little Colorado and Colorado Rivers, and to drains south of the study area along Oak Creek and the Verde Valley. Ground-water discharge in these areas—about 400,000 acre-feet per year—exceeds the annual recharge to the aquifer in the Flagstaff area, but ground water from areas outside the study area contributes to this discharge as well. The saturated thickness of the regional aquifer averages about 1,200 feet, and the amount of water in storage could be as much as 4,800,000 acrefeet, or about 10 percent of the total volume of the aquifer. The quality of water in the regional aquifer in terms of dissolved-solids concentrations is good for most uses throughout the area. Dissolvedsolids concentrations generally are less than 500 milligrams per liter. Water in the regional aquifer is primarily a calcium magnesium bicarbonate type. In some areas near the Rio de Flag, the water has significant nitrate and chloride components, which indicate direct recharge in these areas from the Rio de Flag. Oxygen and deuterium data indicate a common recharge source for water in the aquifer and that some sites receive recharge from surface waters where evaporation has occurred. Estimated carbon-14 ages and tritium activities indicate ground-water ages from less than 200 years in the Lake Mary area to more than 5,000 years in the Wupatki area. The regional aquifer is heterogeneous and anisotrophic and has a complex ground-water flow system. The most productive water-bearing material tends to be fine- to medium-grained sandstones, and ground-water flow and potential well yields are related to geologic structure. Fracturing associated with structural deformation increases recharge locally and also increases the potential for high well yields. Surface-geophysical techniques provided information on the orientation of high-angle, deep-seated structure in the saturated zone. Borehole-geophysical data identified horizontal to near-horizontal fractures as significant components of the fracture-flow system not apparent in the surface-geophysical data. Structural features that strike northwest appear to be areas that have the greatest potential for high well yields. A north-northeastward-striking structure may be just as promising, but additional data are needed to verify this relation.

Arizona↗

USGS2000

Occurrence and quality of surface water and ground water within the Yavapai-Prescott Indian Reservation, central Arizona, 1994-98

The Yavapai-Prescott Indian Reservation encompasses about 1,395 acres in central Arizona adjacent to the city of Prescott. From October 1994 to September 1997, the annual average rainfall was 14.9 inches and the total annual streamflow leaving the reservation along Granite Creek was about 430 acre-feet more than the amount of streamflow entering the reservation. The channel-fill and valley-fill sediments within the flood plain of Granite Creek make up the principal aquifer. The only ground-water development is from spring discharge that is being contained for livestock and wildlife use. About 29 acre-feet of ground water leaves the reservation each year after discharging into Granite Creek. Water levels in wells throughout the reservation reflect seasonal variations in rainfall and snowmelt. Surface water and ground water on the reservation are calcium bicarbonate types. Specific-conductance field measurements ranged from 187 to 724 microsiemens per centimeter for surface water and 381 to 990 microsiemens per centimeter for ground water. Fecal streptococcal bacteria and fecal coliform bacteria in the surface water make the water unsuitable for domestic use. Some volatile and semivolatile organic compounds were detected in samples of surface water, ground water, and streambed sediment. The potential for contamination exists from point and nonpoint sources on and off the reservation.

Arizona↗

USGS1999

Evaluation of factors that influence estimated zones of transport for six municipal wells in Clark County, Washington

A ground-water flow model was used in conjunction with particle tracking to estimate zones of transport for six municipal well sites in Clark County, Washington. A zone of transport for a well is a three-dimensional volume within a ground-water system that contains all of the ground water that will discharge from that well within a specified time period. All of the zones of transport for a well compose the zone of contribution for the well. Zones of transport and contribution are important considerations in the delineation of wellhead-protection areas. Hydrogeologic factors, such as hydraulic conductivity and porosity, influence the shape and size of the zones of transport, and, therefore, uncertainty in these and other factors can lead to uncertainty in the delineation of the zones of transport. The sensitivity of the zones of transport to uncertainty in selected hydrogeologic factors was evaluated for the six wells. Estimates of the zones of transport were delineated by the U.S. Geological Survey program MODTOOLS from three-dimensional pathlines computed by the U.S. Geological Survey program MODPATH. Input to MODPATH came from steady-state simulations calculated by the U.S. Geological Survey modular three-dimensional finite-difference ground-water flow model, MODFLOW. Three-dimensional modeling is the best method for delineating zones of transport within stratigraphically complex, heterogeneous, anisotropic aquifers that have complex boundary conditions such as streams and multiple, simultaneously discharging wells. In this study, zones of transport were delineated by using simulated particle locations computed from the results of a three-dimensional steady-state regional model for 0-0.5, 0.5-1, 1-5, 5-10, 10-20, and 20-50 year travel times to the selected wells. Zones of transport for a well were delineated by tracking particles along pathlines in the reverse direction of ground-water flow. Sensitivity of the zones of transport to change in the discharge rate of the selected well, porosity, and hydraulic conductivity, as well as to the presence or absence of interfering wells, was evaluated at six well sites to evaluate the effect of uncertainties in these factors on the size and shape of zones of transport. Uncertainty in porosity contributed the most to the uncertainty in delineating the zones of transport. Uncertainty in other factors, such as well discharge rate and horizontal hydraulic conductivity, had measurable effects on the zones of transport, but errors introduced through these factors were less significant. Insight into the causes of the changes in the size and shape of the zones of transport to varying conditions was gained by evaluating the simulated water budget and ground-water levels in the vicinity of the well. Changes in the simulated water budget and ground-water levels provided information to better understand the effects of uncertainties in the data on simulation results.The results of this study suggest that ground-water velocity is the underlying control on the size of the zones of transport. The regional hydraulic gradient is the most significant factor controlling the shape and orientation of the zones of transport. Spatial variation in recharge, discharge, and hydraulic properties can also affect the shape of the zones of transport, however. Underestimation of porosity or overestimation of horizontal hydraulic conductivity leads to overestimation of ground-water velocity and overestimation of the size of zones of transport. Overestimation of porosity or underestimation of horizontal hydraulic conductivity leads to underestimation of ground-water velocity and underestimation of the size of zones of transport. Well discharge rate affects ground-water velocities near the well. Underestimation of discharge (and therefore velocities) will result in underestimation of the size of the zones of transport. The sensitivity of estimated zones of transport to uncertainty in parameters such as porosity and horizontal hydraulic conductivity is a function of the well discharge rate and the proximity of the well to boundaries, such as streams and rivers.

Washington↗

USGS1999

Geohydrology of Pipe Spring National Monument area, northern Arizona

Pipe Spring National Monument is on the Arizona Strip, an area between the Utah border to the north and the north rim of the Grand Canyon to the south. Four springs at the base of Winsor Point on Winsor Mountain (known collectively as Pipe Spring) are a part of the historical significance of the monument. The relation between declining discharges from springs in the monument and ground-water development north of the monument was studied to provide information that could be used for management of the monument resources. Ground-water elevations from wells indicate that ground-water movement is from north to south along the west side of a branch of Sevier Fault. Faulting in the areas has downthrown permeable water-bearing sediments relative to impermeable sediments and is evinced by cliffs along the western and northern edges and flat-lying areas to the east. The Navajo Sandstone and Kayenta Formation are the primary water-bearing units on the west side of the fault. The semipermeable sediments of the Chinle and Moenkopi Formations on the east side of the fault inhibit ground-water movement from the west to the east side of the fault. Ground water south of Moccasin Canyon is higher in total dissolved solids than ground water north of Moccasin Canyon. Wells north of Moccasin Canyon are open primarily in the Navajo Sandstone, and wells south of Moccasin Canyon are open primarily in the upper sandstone facies of the Kayenta Formation. A water-budget estimate for the study area indicates a storage deficit of 780 acre-feet per year. This deficit suggests that some recharge may be occurring outside the study area. Oxygen and hydrogen stable- isotopic data suggest no isotopic variation in recharging waters in the study area and surrounding region. Radiocarbon and tritium activities indicate apparent ground-water ages at wells and springs are between 45 and 9,000 years.

Arizona↗

USGS1997

Ground-water and water-chemistry data for the upper Deschutes Basin, Oregon

This report presents ground-water data collected and compiled as part of a study of the ground-water resources of the upper Deschutes Basin, Oregon. Data in this report include tabulated information and a location map for more than 1,500 field-located water wells, hydrographs showing water-level fluctuations over various time periods for 102 of the wells, and water-chemistry analyses from 26 wells, 7 springs, and 5 surface-water sites.

Oregon↗