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USGS1982

Occurrences of copper minerals in Alaska

The following references give data, as of June 1, 1982, on localities where copper minerals have been found in Alaska. References are keyed by number to locations shown on the accompanying map. An asterisk (*) preceding a locality name indicates recorded production. In most instances the report(s) cited for each occurrence is a summary of data in older reports and was compiled since 1975. Most of the summary reports contain lists of the reports used in their compilation. Citations are in standard bibliographic format with the exception that each includes, in parentheses, an abbreviation for the report or map series and the number of the report or map. Abbreviations used are: AOF, State of Alaska Division of Geological and Geophysical Surveys Open-File Report; B, U.S. Geological Survey Bulletin; BMOF, U.S. Bureau of Mines Open-File Report; C, U.S. Geological Survey Circular; MF, U.S. Geological Survey Miscellaneous Field Studies Map; OF, U.S. Geological Survey Open-File Report; P, U.S. Geological Survey Professional Paper.

Alaska↗

USGS1982

South Atlantic summary report 2: A revision of Outer Continental Shelf oil and gas activities in the South Atlantic (U.S.) and their onshore impacts, a summary report, July 1980

The search for oil and gas on the Outer Continental Shelf (OCS) in the South Atlantic Region began in 1960, when geophysical surveys of the area were initiated. In 1977, a Continental Offshore Stratigraphic Test (COST) well was drilled in the Southeast Georgia Embayment. In March 1978, the first lease sale, Sale 43, was held, resulting in the leasing of 43 tracts. Approximately a year later, in May 1979, the first exploratory drilling began, and by February 1980, six exploratory wells had been drilled by four companies. Hydrocarbons were not found in any of these wells. Lease Sale 56, the second lease sale in the South Atlantic Region, was held in August 1981. The sale resulted in the leasing of 47 tracts. Most of the leased tracts are in deep water along the Continental Slope off North Carolina. To date, no drilling has occurred on these tracts, but it is likely that two wells will be drilled or will be in the process of being drilled by the end of 1982. Reoffering Sale RS-2 is scheduled for July 1982, and it will include tracts offered in Lease Sale 56 that were not awarded leases. Lease Sale 78 is scheduled to be held in July 1983. The most recent (March 1982) estimates of risked resources for leased lands in the South Atlantic OCS are 27 million barrels of oil and 120 billion cubic feet of gas. To date, onshore impacts resulting from OCS exploration have been minimal, and they were associated with Lease Sale 43 exploratory activities. Tenneco, using existing facilities, established a support base in Savannah, Georgia; Getty, Transco, and Exxon used a support base established for them by the city of Brunswick, Georgia. The port at Morehead City, North Carolina, is expected to provide the onshore facilities for exploration in the near future on Lease Sale 56 tracts. Arrangements for the use of these facilities are currently being negotiated. In June 1981, the South Atlantic Regional Technical Working Group prepared a Regional Transportation Management Plan for the South Atlantic OCS. The plan is principally an integration of regulatory frameworks, policies, and plans that are applicable to pipeline siting from each of the South Atlantic coastal States and Federal agencies with jurisdiction in the area.

Outer Continental Shelf, South Atlantic↗

USGS1982

A summary of geologic hazards for proposed OCS oil and gas lease sale 68, southern California

A geophysical survey, consisting of about 6,880 line-km of multisensor, high-resolution, seismic reflection data, was run in 161 of the 221 tracts tentatively selected by the U.S. Department of the Interior for inclusion in the southern California Outer Continental Shelf Oil and Gas Lease Sale 68. Geologic hazards identified in the study area for which stipulations are recommended are active faults, mass transport, steep slopes (>10?), and steep-walled submarine canyons. Geologic hazards whose effects can be mitigated through existing technology and design and are not considered cause for stipulation are shallow faults, buried and filled channels, shallow gas, gas-charged sediments, hydrocarbon seeps, and unstable fan deposits. The Minerals Management Service has recommended that a stipulation be applied to 83 tracts where there is evidence of existing or potential sea-floor instability over a significant portion of the tract. Further data acquisition and analysis on a more detail-ed grid will be required of lessees or operators before drilling will be permitted on leases issued as a result of the sale.

Open-File Report↗

USGS1985

Preliminary report on gold deposits at Meshaheed, Kingdom of Saudi Arabia

A fault-controlled, hydrothermal system deposited gold, stibnite, and quartz in metasediments, intrusive basalt, and diorite in an area approximately 3 by 5 km in the Meshaheed area of the northeastern Arabian Shield. Veins in metasediments appear to be lenticular and average less than 1 m thick. A related, quartz-pyrite stockwork in fractured, hydrothermally altered basalt is approximately 1 km long and at least 100 m wide. Poorly defined veins and veinlets bear gold, stibnite, and quartz, A few areas of ancient goldmining activity are in metasediments at the perimeter of a large diorite pluton. The arrangement of the pits also indicates that unexposed veinlet systems may be as much as 40 m wide. Small areas of diorite have also been hydrothermally altered where gold-stibnite-quartz veins were emplaced. A molybdenite-quartz stockwork and other quartz stockworks bearing traces of molybdenum, bismuth, and silver are in small diorite plutons. Large areas of moderately hydrothermally altered metasediments bearing trace molybdenum are also present. These mineralized zones are not cogenetic with the gold-stibnite-quartz deposits. A separate stream-sediment sampling program has shown the area southeast of Meshaheed to be anomalous in lead, copper, boron, tin, iron, and molybdenum, and a preliminary geophysical survey found resistivity anomalies coincident with the altered, intrusive basalt.

Open-File Report↗

USGS1999

Alaska resource data file: McGrath quadrangle

The unnamed occurrence was investigated by the reporter in 1978 during a 1:63,360 scale geologic mapping effort for the Alaska Division of Geological and Geophysical Surveys in the McGrath quadrangle (Bundtzen and Laird, 1983). Two grab samples from the mineralized zone contained up to 222 ppm copper, 0.6 grams/tonne silver, and 100 ppm lead.

Alaska↗

USGS1977

Studies related to the Charleston, South Carolina, earthquake of 1886: A preliminary report

PART A: The seismic history of the southeastern United States is dominated by the 1886 earthquake near Charleston, S.C. An understanding of the specific source and the uniqueness of the neotectonic setting of this large earthquake is essential in order to properly assess seismic hazards in the southeastern United States. Such knowledge will also contribute to the fundamental understanding of intraplate earthquakes and will aid indirectly in deciphering the evolution of Atlantic-type continental margins. The 15 chapters in this volume report on the first stage of an ongoing multidisciplinary study of the Charleston earthquake of 1886. The Modified Mercalli intensity for the 1886 earthquake was X in the meizoseismal area, an elliptical area 35 by 50 km, the center of which was Middleton Place. Seismic activity is continuing today in the Middleton Place-Summerville area at a higher level than prior to 1886. The present seismicity is originating at depths of 1 to 8 km, mostly in the crystalline basement beneath sedimentary rocks of the Coastal Plain. The crystalline basement beneath the Charleston-Summerville area is not simply a seaward extension of crystalline rocks of the Appalachian orogen that are exposed in the Piedmont to the northwest, but has a distinctive magnetic signature that does not reflect Appalachian orogenic trends. The area underlain by this distinctive geophysical basement, the Charleston block, may represent a broad zone of Triassic and (or) Jurassic crustal extension formed during the early stages of the opening of the Atlantic Ocean. The Charleston block is characterized in part by prominent, roughly circular magnetic and gravity highs that are thought to reflect maflc or ultramafic plutons. A continuously cored borehole put down over the shallowest (about 1.5 km deep) of these magnetic anomalies on the edge of the meizoseismal area bottomed at 792 m in amygdaloidal basalt. Although the K-Ar ages of about 100 m.y. for the basalt are consistent with the Late Cretaceous (Cenomanian) age of the overlying Cape Fear Formation, this must be a minimum age as a result of chemical alteration. The interpreted magmatic composition of the basalt most closely resembles the high-Ti quartz-normative tholeiites of Late Triassic and Early Jurassic age from eastern North America; age of the basalt is probably similar. Various geophysical surveys suggest that Coastal Plain sedimentary rocks do not simply dip homoclinally to the southeast on a gently dipping basement surface but are disturbed by structures not yet clearly deciphered. The present stress regime of the Charleston-Summerville area appears to be one of NE-SW. compression rather than of extension as it presumably was in the Mesozoic. The present stress regime seems similar to that of much of the eastern United States. Comparison of several seismic source areas in eastern North America shows that epicenters are typically near the periphery of positive gravity features interpreted to represent mafic or ultramafic bodies. Earthquakes may be caused by the concentration of regional stress around the peripheries of these inhomogeneities in an otherwise more homogeneous plate. Whether the inhomogeneities are more or less rigid than the. surrounding material is uncertain. PART B: In 1889, C. E. Dutton published all his basic intensity data for the 1886 Charleston, S.C., shock but did not list what intensity values he assigned to each report, nor did he show the distribution of the locations of these data reports on his isoseismal map. The writer and two other seismologists have each independently evaluated Dutton's 1,300 intensity reports (at least two of the. three interpreters agreed on intensity values for 90 percent of the reports), and the consensus values were plotted and contoured. One map was prepared on which contours emphasized the broad regional pattern of effects (with results similar to Dutton's) ; another map was contoured to depict the more

South Carolina↗

USGS2023

Ambient seismic noise tomography of the Kingdom of Saudi Arabia

Harrat Rahat is a Cenozoic volcanic field in the west-central part of the Kingdom of Saudi Arabia, 150 kilometers east of the Red Sea, and is the site of the most recent eruption in the country (1256 C.E.; 654 in the year of the Hijra). The city of Al Madīnah lies at the north end of Harrat Rahat, and its volcanic and seismic risks are frequently reassessed. In 2009 C.E. an earthquake swarm at Harrat Lunayyir, 200 km west-northwest of Al Madīnah, produced significant shaking and some building damage in nearby communities, which prompted a revision of seismic hazard models for the region. A network of seismic stations on this volcanically active western side of the Arabia Plate was installed, and stations were also added in the tectonically active northern part of the country. Although regional earthquakes may be used to determine the crustal structure of the western Arabia Plate, such crustal models are hindered by insufficient numbers of earthquakes in the stable plate interior. Tomography studies can be used to infer material properties of the subsurface, such as presence of partial melt, and are beneficial for volcanic hazard assessments. We use ambient seismic noise to compute Rayleigh and Love surface-wave dispersion maps between 5 and 12 second periods for a subset of seismic stations within and near northern Harrat Rahat. The surface-wave maps are inverted to produce shear-wave velocities using a neighborhood algorithm and interpolated into a pseudo three-dimensional model. The distributions of surface-wave and shear-wave velocities are heterogenous, varying from ±3–8 percent. However, low velocities are not restricted to Harrat Rahat. We observed a difference between Rayleigh- and Love-wave velocities that extends north of the site of the 1256 C.E. eruption and coincides with a low gravity anomaly. We obtain a shear-wave velocity increase of 10–15 percent between 15- and 25-kilometers depth, which is consistent with the presence of a transition between the felsic upper crust and the mafic lower crust of the Arabian Shield. The average shear-wave velocities of the upper and lower crust are estimated to be 3.64 and 3.95 kilometers per second using Rayleigh waves and 3.53 and 4.16 kilometers per second using Love waves, which are in good agreement with the results of other geophysical surveys in this area. The modest magnitude of the low-velocity anomalies within the crust and their locations extending well beyond the limits of Harrat Rahat indicate that they are not caused by a crustal magma chamber. If magma chambers exist, they are smaller than can be imaged with our seismological method (resolution corresponds to a 15-kilometer wavelength), deeper than 30 kilometers, or shallower than 5 kilometers with a small velocity contrast. The last possibility is discounted by weak-to-absent surface geothermal activity and by a lack of shallow seismicity that characterizes other areas with known shallow magmas, such as Hawaiʻi. We then expanded our work to the entire Arabian Shield with principally the same methodology to look at large-scale regional patterns. We found modest shear-wave velocity deviations on the order of only ±3 percent, which are within expected ranges for lithological variation.

Professional Paper↗

USGS2005

Geologic map of the Ikpikpuk River quadrangle, Alaska

This map is a product of the USGS Digital Geologic Maps of Northern Alaska project, which captures in digital format quadrangles across the entire width of northern Alaska. Sources include geologic maps previously published in hardcopy format and recent updates and revisions based on field mapping by the Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys and Division of Oil and Gas, and the U.S. Geological Survey. Individual quadrangles are digitized at either 1:125,000 or 1:250,000 depending on the resolution of source maps. The project objective is to produce a set of digital geologic maps with uniform stratigraphic nomenclature and structural annotation, and publish those maps electronically. The paper version of this map is available for purchase from the USGS Store.

Alaska↗

USGS2006

Geologic map of the Lookout Ridge quadrangle, Alaska

Alaska↗

USGS2006

Geologic map of the Utukok River quadrangle, Alaska

Alaska↗

USGS2008

Geologic map of the Point Lay quadrangle, Alaska

Alaska↗

USGS2006

Hydrogeology and ground-water quality, Chippewa Township, Isabella County, Michigan, 2002-05

The ground-water resource potential of Chippewa Township, Isabella County, Mich. was characterized on the basis of existing hydrogeologic data, water-level records, analyses of water samples, and interpretation of geophysical survey data. Eight ground-water samples were collected and analyzed for major ions, nutrients, and trace-metal composition. In addition, 10 direct current-resistivity soundings were collected throughout Chippewa and Coe Townships to identify potential freshwater in the aquifer system. The aquifer system includes complexly interbedded glaciofluvial, glaciolacustrine, and basal-lodgment tills, which overlie Jurassic or Pennsylvanian sedimentary rocks. In parts of the township, freshwater is present in all geologic units, but in most areas saline water is encountered near the base of Pleistocene glacial deposits and in the Jurassic or Pennsylvanian bedrock. A near-surface sheet of relatively dense basal-lodgment till likely prevents, or substantially retards, significant direct recharge of ground water to glacial and bedrock aquifers in Chippewa and adjacent townships. Glacial sands and gravels form the principal aquifer for domestic wells (97.5 percent of wells in the township). The single community water supply in the township has wells screened in glacial deposits near the base of the glacial drift. Increased withdrawals of ground water in response to increasing demand has led to a slight decline in water quality from this supply. This water-quality decline is related primarily to an increase of dissolved sulfate, which is probably a function of well depth and dissolution of gypsum, a common mineral constituent in the Jurassic “red beds” , which form the uppermost bedrock unit throughout most of the township. One explanation for the increase in sulfate is upconing of saline water from bedrock sources, which may contain saline water.

Michigan↗

USGS2011

Geology, Hydrology, and Water Quality of the Little Blackwater River Watershed, Dorchester County, Maryland, 2006-09

The Little Blackwater River watershed is a low-lying tidal watershed in Dorchester County, Maryland. The potential exists for increased residential development in a mostly agricultural watershed that drains into the Blackwater National Wildlife Refuge. Groundwater and surface-water levels were collected along with water-quality samples to document hydrologic and geochemical conditions within the watershed prior to potential land-use changes. Lithologic logs were collected in the Little Blackwater River watershed and interpreted with existing geophysical logs to conceptualize the shallow groundwater-flow system. A shallow water table exists in much of the watershed as shown by sediment cores and surface geophysical surveys. Water-table wells have seasonal variations of 6 feet, with the lowest water levels occurring in September and October. Seasonally low water-table levels are lower than the stage of the Little Blackwater River, creating the potential for surface-water infiltration into the water table. Two stream gages, each equipped with stage, velocity, specific conductance, and temperature sensors, were installed at the approximate mid-point of the watershed and near the mouth of the Little Blackwater River. The gages recorded data continuously and also were equipped with telemetry. Discharge calculated at the mouth of the Little Blackwater River showed a seasonal pattern, with net positive discharge in the winter and spring months and net negative discharge (flow into the watershed from Blackwater National Wildlife Refuge and Fishing Bay) in the summer and fall months. Continuous water-quality records showed an increase in specific conductance during the summer and fall months. Discrete water-quality samples were collected during 2007--08 from 13 of 15 monitoring wells and during 2006--09 from 9 surface-water sites to characterize pre-development conditions and the seasonal variability of inorganic constituents and nutrients. The highest mean values of nitrogen are found in the deep groundwater system, with relatively low values in the water table. Surface-water-quality samples in the lower half of the basin show a significant increase in inorganic seawater constituents, especially in summer, corresponding with net negative discharge from the Little Blackwater River. Samples also were collected from nine wells and four surface-water sites for pesticides in June 2008. The herbicides atrazine, metolachlor, and simazine, and the insecticide fipronil were detected at each of the four surface-water sites, with concentrations less than 2 micrograms per liter. Concentrations of pesticides found in groundwater were typically one to two orders of magnitude lower than pesticide concentrations found in surface water of the Little Blackwater River. Seasonal hydraulic-gradient reversals between the shallow groundwater system and the Little Blackwater River, coincident with the inflow of brackish water from Fishing Bay and Blackwater National Wildlife Refuge, indicate a potential for saltwater intrusion into the water table. The likelihood of saltwater intrusion into the water table is further supported by high chloride concentrations observed in water-table wells near the Little Blackwater River.

Scientific Investigations Report↗

USGS2013

Hydrogeologic framework and estimates of groundwater storage for the Hualapai Valley, Detrital Valley, and Sacramento Valley basins, Mohave County, Arizona

We have investigated the hydrogeology of the Hualapai Valley, Detrital Valley, and Sacramento Valley basins of Mohave County in northwestern Arizona to develop a better understanding of groundwater storage within the basin fill aquifers. In our investigation we used geologic maps, well-log data, and geophysical surveys to delineate the sedimentary textures and lithology of the basin fill. We used gravity data to construct a basin geometry model that defines smaller subbasins within the larger basins, and airborne transient-electromagnetic modeled results along with well-log lithology data to infer the subsurface distribution of basin fill within the subbasins. Hydrogeologic units (HGUs) are delineated within the subbasins on the basis of the inferred lithology of saturated basin fill. We used the extent and size of HGUs to estimate groundwater storage to depths of 400 meters (m) below land surface (bls). The basin geometry model for the Hualapai Valley basin consists of three subbasins: the Kingman, Hualapai, and southern Gregg subbasins. In the Kingman subbasin, which is estimated to be 1,200 m deep, saturated basin fill consists of a mixture of fine- to coarse-grained sedimentary deposits. The Hualapai subbasin, which is the largest of the subbasins, contains a thick halite body from about 400 m to about 4,300 m bls. Saturated basin fill overlying the salt body consists predominately of fine-grained older playa deposits. In the southern Gregg subbasin, which is estimated to be 1,400 m deep, saturated basin fill is interpreted to consist primarily of fine- to coarse-grained sedimentary deposits. Groundwater storage to 400 m bls in the Hualapai Valley basin is estimated to be 14.1 cubic kilometers (km 3 ). The basin geometry model for the Detrital Valley basin consists of three subbasins: northern Detrital, central Detrital, and southern Detrital subbasins. The northern and central Detrital subbasins are characterized by a predominance of playa evaporite and fine-grained clastic deposits; evaporite deposits in the northern Detrital subbasin include halite. The northern Detrital subbasin is estimated to be 600 m deep and the middle Detrital subbasin is estimated to be 700 m deep. The southern Detrital subbasin, which is estimated to be 1,500 m deep, is characterized by a mixture of fine- to coarse-grained basin fill deposits. Groundwater storage to 400 m bls in the Detrital Valley basin is estimated to be 9.8 km 3 . The basin geometry model for the Sacramento Valley basin consists of three subbasins: the Chloride, Golden Valley, and Dutch Flat subbasins. The Chloride subbasin, which is estimated to be 900 m deep, is characterized by fine- to coarse-grained basin fill deposits. In the Golden Valley subbasin, which is elongated north-south, and is estimated to be 1,300 m deep, basin fill includes fine-grained sedimentary deposits overlain by coarse-grained sedimentary deposits in much of the subbasin. The Dutch Flat subbasin is estimated to be 2,600 m deep, and well-log lithologic data suggest that the basin fill consists of interlayers of gravel, sand, and clay. Groundwater storage to 400 m bls in the Sacramento Valley basin is estimated to be 35.1 km 3 .

Arizona↗

USGS2017

Hydrogeologic and geochemical characterization and evaluation of two arroyos for managed aquifer recharge by surface infiltration in the Pojoaque River Basin, Santa Fe County, New Mexico, 2014–15

In order to provide long-term storage of diverted surface water from the Rio Grande as part of the Aamodt water rights settlement, managed aquifer recharge by surface infiltration in Pojoaque River Basin arroyos was proposed as an option. The initial hydrogeologic and geochemical characterization of two arroyos located within the Pojoaque River Basin was performed in 2014 and 2015 in cooperation with the Bureau of Reclamation to evaluate the potential suitability of these two arroyos as sites for managed aquifer recharge through surface infiltration. The selected reaches were high-gradient (average 3.0–3.5 percent) braided channels filled with unconsolidated sand and gravel-sized deposits that were generally 30–50 feet thick. Saturation was not observed in the unconsolidated channel sands in four subsurface borings but was found at 7–60 feet below the contact between the unconsolidated channel sands and the bedrock. The poorly to well-cemented alluvial deposits that make up the bedrock underlying the unconsolidated channel material is the Tesuque Formation. The individual beds of the Tesuque Formation are reported to be highly heterogeneous and anisotropic, and the bedrock at the site was observed to have variable moisture and large changes in lithology. Surface electrical-resistivity geophysical survey methods showed a sharp contrast between the electrically resistive unconsolidated channel sands and the highly conductive bedrock; however, because of the high conductivity, the resistivity methods were not able to image the water table or preferential flow paths (if they existed) in the bedrock. Infiltration rates measured by double-ring and bulk infiltration tests on a variety of channel morphologies in the study reaches were extremely large (9.7–94.5 feet per day), indicating that the channels could potentially accommodate as much as 6.6 cubic feet per second of applied water without generating surface runoff out of the reach; however, the small volume available for storage in the unconsolidated channel sands (about 410 acre-feet in the east arroyo and about 190 acre-feet in the west arroyo) and the potential for the infiltrating water to preferentially flow over the bedrock contact and out of the reach present a challenge for storing water. Although a detailed assessment of the infiltration rate of the Tesuque Formation is beyond the scope of this investigation, one double-ring infiltrometer test was conducted on an outcrop, resulting in an estimated infiltration rate of about 4 feet per day. The shallow groundwater observed in this investigation was determined to be recharged locally on the basis of groundwater elevations and geochemical and isotopic signatures. The channel sands and shallow bedrock were observed to be weathered, indicating contact with oxic groundwater following deposition. This observation was supported by whole-rock elemental analysis and mineralogy of several core samples. The downward groundwater gradient between the shallow wells and those wells screened at greater depths suggests that the shallow groundwater is recharged by local precipitation and has the potential to migrate to the deeper aquifer units. The two age-dating tracers measured in this investigation, however, demonstrate that the shallow groundwater flow paths are very slow and that the deeper flow paths are likely part of a larger regional system. The composition of the shallow, native groundwater suggests that storing water diverted from the Rio Grande is not likely to leach constituents of concern that would cause the stored water to exceed health-based U.S. Environmental Protection Agency Maximum Contaminant Levels.

New Mexico↗

USGS1974

Application of surface geophysics to ground-water investigations

This manual reviews the standard methods of surface geophysics applicable to ground-water investigations. It covers electrical methods, seismic and gravity methods, and magnetic methods. The general physical principles underlying each method and its capabilities and limitations are described. Possibilities for non-uniqueness of interpretation of geophysical results are noted. Examples of actual use of the methods are given to illustrate applications and interpretation in selected geohydrologic environments. The objective of the manual is to provide the hydrogeologist with a sufficient understanding of the capabilities, imitations, and relative cost of geophysical methods to make sound decisions as to when to use of these methods is desirable. The manual also provides enough information for the hydrogeologist to work with a geophysicist in designing geophysical surveys that differentiate significant hydrogeologic changes.

Techniques of Water-Resources Investigations↗

USGS2000

Hydrogeology, water quality, and stormwater-sediment chemistry of the Grande Wash area, Fort McDowell Indian Reservation, Maricopa County, Arizona

Grande Wash is a tributary of the Verde River and drains an area of 13 square miles within the McDowell Mountains and the Town of Fountain Hills in Central Arizona. The wash enters the Fort McDowell Indian Reservation at the eastern boundary of Fountain Hills and is incised in coarse-grained alluvium that is contiguous with the alluvial aquifer along the Verde River. The aquifer is used by the Fort McDowell Indian Community and the City of Phoenix for municipal water supplies. Episodic flows in Grande Wash, in response to storms, carry potentially hazardous runoff from Fountain Hills onto the reservation. Additional potential hazards to ground water include contamination from a wastewater-treatment plant located less than 1 mile upstream from the reservation boundary, and from a landfill and a cement-processing plant immediately adjacent to the main channel of the wash. Coarse-grained deposits in Grande Wash also include recent stream-channel deposits, soil backfill, landfill material, and the upper coarse-grained layer of basin-fill sediments. Surface-geophysical surveys and drilling indicated that the coarse-grained deposits are less than 60-feet thick along the wash and in adjacent areas within the reservation, and are underlain by a thick clay and silt unit, the base of which is below the bottom of the deepest monitor well (317 feet below land surface). The coarse-grained deposits form the alluvial aquifer beneath Grande Wash. Ground water in the alluvial aquifer beneath the wash is shallow and mounded above a less permeable clay and silt unit. Depth to water in the aquifer ranges from 1 to 22 feet below land surface. Saturation of the coarse-grained deposits does not extend laterally for more than about 1,000 feet from the main channel of Grande Wash; the extent varies in response to recharge amounts. Flux of ground water through the alluvial aquifer beneath the wash is toward the Verde River and is estimated to be about 8,000 cubic feet per day (about 0.2 acre-feet per day). The flow rate is four orders of magnitude less than the flow rate in the Verde River. Vertical flux of ground water through the underlying clay and silt unit is estimated to be 7,000 cubic feet per day (0.17 acre-feet per day). The volume of ground water in storage in the alluvial aquifer beneath Grande Wash is estimated to be about 5.6 million cubic feet (129 acre-feet). Concentrations of dissolved inorganic constituents in ground water and surface water are high relative to concentrations found in the regional aquifer in surrounding areas and are indicative of salts that can be expected to be mobilized by runoff in the drainage area. Concentrations of nitrate, chloride, and sulfate are near U.S. Environmental Protection Agency Primary or Secondary Drinking-Water Regulations. Concentrations of arsenic, antimony, and strontium are below drinking-water standards but can be attributed to geologic deposits in and near the study area. Low concentrations of anthropogenic compounds, including chloroform and dichlorobromomethane, were detected. These compounds are disinfection by-products of chlorinated water. Eight pesticide compounds were detected in the surface water, and two pesticide compounds were detected in the ground water. Pesticide concentrations were below U.S. Environmental Protection Agency Maximum Contaminant Levels. Several other organic anthropogenic compounds that probably originated from commercial activities in the area were detected but at concentrations below laboratory calibration standards. Concentrations of trace metals in the stormwater sediment collected from the sediment retention basin in the lowest part of the wash were low and several were below the laboratory’s detection limits. Concentrations of most organic compounds in the stormwater sediment were below detection limits. Organic compounds present at concentrations above detection limits were p-cresol and two phthalate esters—bis (2-ethylhexyl) phthalate and dibutyl phthalate. P-cresol is used in pesticides or in disinfectants and deodorizers, and phthalate esters are commonly used in plastics, hydraulic fluid, and electric capacitors.

Arizona↗

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↗