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Scientific Investigations Report 2009–5014

Scientific Investigations Report 2009–5014

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Ground Water in the Upper Humboldt River Basin

Occurrence and Movement

The occurrence and movement of ground water in the upper Humboldt River basin is interpreted using ground-water levels in 161 wells measured by personnel from the USGS, Nevada Division of Water Resources, and Newmont Mining Corporation during the spring and summer 2007. Water levels ranged from at or near land surface in younger basin-fill deposits along stream flood plains to 300–400 ft below land surface in older basin-fill deposits mostly along basin margins. Water-level contours in ft above sea level primarily reflect ground-water levels in older and younger basin-fill deposits, but also may reflect water levels in unconfined carbonate rock aquifers (pl. 1).

Driven by hydraulic gradient, ground water moves through permeable zones from areas of recharge to areas of discharge. Recharge occurs mostly along mountain fronts, but also in mountainous areas underlain by carbonate rocks. Discharge occurs mostly on valley floors by evaporation from open water and moist soils and transpiration by plants called phreatophytes, ground water seepage to stream channels, and pumpage. The main discharge area in the upper Humboldt River basin is the river flood plain, which can be as much as a mile wide.

In Huntington Valley and the South Fork Area, ground-water flow is from the western base of the Ruby Mountains toward Huntington Creek and its confluence with the South Fork Humboldt River. In Huntington Valley, ground-water flow also is from the eastern base of the Diamond Mountains and Pinon Range toward Huntington Creek. Water-level gradients range from 200 ft/mi adjacent to the Ruby Mountains to 10 ft/mi between the Pinon Range and Huntington Creek (pl. 1). This range of gradients either indicates that more recharge originates from the Ruby Mountains than from mountain ranges on the west side of the valley or that basin-fill deposits on the east side of the valley are less permeable than those on the west side. Rush and Everett (1966, p. 26–27) noted that basin-fill deposits on the east side of Huntington Valley are saturated to near land surface and that potential recharge is rejected and leaves the area as streamflow. The sharp, upstream inflections of water-level contours along the axis of Huntington Valley indicate that ground water discharges to the channel of Huntington Creek. However, ground water also flows northward along the axis of the valley along gradients of 5–10 ft/mi.

The high permeability of carbonate rocks likely result in recharge rather than runoff as indicated by the absence of perennial streams in the southern Ruby Mountains (fig. 1 and pl. 1). This, combined with the eastward dip of the rocks, probably results in ground-water flow from the west side of the southern Ruby Mountains to Ruby Valley east of the study area where numerous large springs emanate from the eastern base of the Ruby Mountains (Rush and Everett, 1966, p. 15; Dudley, 1967, p. 88–98). Dudley (1967, p. 97) also determined that the ground-water divide between Huntington and Ruby Valleys may be as much as 2 mi west of the topographic divide between the two valleys suggesting that most of the high-altitude precipitation in the southern Ruby Mountains does not recharge the upper Humboldt River basin.

Ground-water flow from Huntington Valley and the South Fork Area continues northward into the Dixie Creek–Tenmile Creek Area. In addition, ground water flows west and northwest from the recharge area along the mountain front of the Ruby Mountains and north and northeast from the Pinon Range. A low topographic divide separates the Dixie Creek–Tenmile Creek Area from Lamoille Valley to the northeast. A group of unnamed hills separates the Dixie Creek–Tenmile Creek Area from the Humboldt River downstream from Elko. The water-level contours on plate 1 indicate that ground water flows northwest through these hills to the river flood plain.

In Lamoille Valley and Starr Valley Area ground-water flow is from a recharge area along the base of the Ruby Mountains, which are composed entirely of low permeability crystalline rocks. As a result, ground-water recharge is predominantly from infiltration of runoff from the mountains as it crosses the pediment between the mountains and Humboldt River flood plain. A portion of the water leaves the two basins as runoff because aquifers in both valleys are saturated to near land surface and have limited storage available for recharge (Eakin and Lamke, 1966. p. 31). Ground-water flow is to the northwest in Lamoille Valley and to the west in Starr Valley Area. Water-level gradients range from 50–100 ft/mi adjacent to the mountains to 10–30 ft/mi near the Humboldt River flood plain.

Ground-water flow in the Marys River Area generally is southward to the Humboldt River. The lower reaches of Marys River are ephemeral, and water-level contours have no upstream inflection unlike other streams in the study area. Near the Humboldt River flood plain, water-level gradients are about 20 ft/mi.

The North Fork Area consists of upper and lower topographic basins that are connected by streamflow through a canyon in the northern Adobe Range (fig. 1). The upper basin consists of an east sloping pediment of flat-lying to tilted older basin-fill deposits overlain by a thin cover of younger basin-fill deposits (A.R. Wallace, U.S. Geological Survey, oral commun., 2008), as much as 5 mi wide, between the Independence Mountains to the west and Double Mountain and the Adobe Range to the east. Sparse water-level data indicate that ground-water flow is eastward from a recharge area along the eastern base of the Independence Mountains. Water-level data are not sufficient to determine whether the direction of ground-water flow on the east side of the area turns northeastward parallel with the Adobe Range or continues eastward through the range. The first possibility would require a sharp change in the direction of flow from eastward to northeastward. The second does not seem likely because the principle rock types the Adobe Range are 4,000–5,500 ft of poorly permeable shale and sandstone of the Diamond Peak Formation and Chainman Shale (oil wells 8 and 5, pl. 1, table 4).

Ground-water flow in the lower part of the North Fork Area is southeastward from the Adobe Range, and as indicated by the 5,300- and 5,400-ft water-level contours southwestward from the Peko Hills toward the North Fork Humboldt River and then southward along the basin axis toward the Humboldt River (pl. 1). The Peko Hills are underlain by the Diamond Peak Formation, Chainman Shale, and by older and younger carbonate rocks.

Sharp upstream inflections of the water-level contours indicate that the Humboldt River gains flow from ground-water seepage from a few miles west of Wells to the west boundary of the study area. Water-level gradients along the flood plain range from about 7 to 30 ft/mi east of the Elko Hills. Ground-water flow in the Elko Segment (Elko Hills to the west boundary of the study area) is to the southeast from the Adobe Range and northwest from the Dixie Creek–Tenmile Creek Area through the unnamed hills between the Elko Hills and the South Fork Humboldt River. Streamflow gains of the river in the Elko Segment are about 6,600 acre-ft/yr. This ground-water seepage to the river channel primarily moves through a 10-mi wide section of the unnamed hills (pl. 1) under a water-level gradient of 40 ft/mi (0.008 ft/ft).

Transmissivity can be estimated using these values and a form of Darcy’s law:

T = Q/(iw), (1)


T is transmissivity, in feet squared per day;

Q is flow through the section, in cubic feet per day;

i is the water table gradient, in feet per foot; and

w is the width of the flow section, in feet.

The estimated transmissivity of the rocks and deposits in the flow section is about 2,000 ft2/d. However, this is a rough estimate because some subsurface flow resulting in the streamflow gains comes from the Adobe Range.

Water-Level Change

Water levels in the upper Humboldt River basin fluctuate: (1) annually in response to wetter (spring runoff) and drier (lack of summer rain) hydrologic conditions; and (2) to longer term (multiyear) variations in climate. Water-level data from nine wells were used to evaluate these fluctuations. The locations of these wells are shown in figure 4.

Wells 1 and 2 near Deeth and Lamoille, respectively, were measured monthly from 1949 to 1958 (fig. 4, fig. 5 A–B). Well 1 (fig. 5A) is in the flood plain near the confluence of Marys River and the Humboldt River, and water levels at this well probably respond rapidly to changes in stage of either stream. Water levels were about 10 ft below land surface in late winter to early spring, but rapidly rose to within 5 feet of land surface by early to late June. Although no drillers’ log is available for well 1, the log for a nearby well (Nevada log number 76997, table 5) penetrated interbedded sand, gravel, and clay from land surface to depths of 28 ft and blue clay to a depth of 112 ft. The sands and gravels above the blue clay function as a shallow water-table aquifer that is recharged mostly by the spring snowmelt runoff.

Monthly water-level fluctuations at well 2 were similar to those at well 1 (fig. 5B). Well 2 is located about one-half mile from Lamoille Creek in an area dissected by a network of ditches used to irrigate meadows and fields. Depth to water at this well was more than 10 ft in early to late winter, but typically rose abruptly between May and June approaching land surface by late spring or early summer. Annual water-level rises at this well are dependent on the distribution and timing of irrigation and not necessarily on the magnitude of the spring snowmelt runoff. The rapid water-level rise each year indicates a good hydraulic connection through a thin unsaturated zone and limited available storage in the aquifer, which agrees with conclusions from the reconnaissance reports published decades earlier (Eakin and Lamke, 1966, p. 31; Rush and Everett, 1966, p. 26–27).

Well 3 is a stock well at the southwest side of the South Fork Area that has been measured annually by USGS since 1964 (fig. 6A). Depth to water at this well ranged from about 71 ft in 1984 and 1986 to 98 ft in 1995. Annual water levels in the well show multiyear periods of increasing and decreasing levels. Water levels rose 20 ft from 1970 to 1986, declined 27 ft from 1986 to 1995, rose 16 ft from 1995 to 2001, and declined 16 ft by 2003 (fig. 6A). These periods of water-level rise and fall generally correspond to long-term variations in annual precipitation (fig. 6B). The water-level rise from 1970 to 1984 was a 15-year period during which annual precipitation was 8 to 90 percent above average during 8 years and 5 to 50 percent below average during 7 years. However, the total amount of precipitation during above average years was about twice the amount during below average years. Overall, the 15-year period was one of well above average precipitation, and this explains the upward trend of water levels in the well during that period. Similarly, a severe and continuous drought from 1985 through 1994 (fig. 6B) coincides with the abrupt water-level decline from 1986 to 1995 (fig. 6A). The water-level rise from 1995 to 2001 and its decline by 2003 also can be explained by the precipitation record, indicating that water levels in well 3 respond rapidly to variations in climate.

Filling of the South Fork Reservoir has resulted in water-level rises in basin-fill deposits over an area of uncertain extent. The Nevada Division of Water Resources began measuring water levels in wells in the vicinity of the South Fork Reservoir when filling began in December 1987. The time required for filling to a spillway elevation of 5,231 ft is not known and the stage of the reservoir probably fluctuates annually in response to runoff from the South Fork Area and Huntington Valley. Since 1988, water levels have risen 6 ft and 8 ft at two wells about 3,000 ft and 1,000 ft, respectively, from the southwest side of the reservoir (wells 4 and 5 figs. 4 and 7A–B). Both wells are adjacent to the flood plain of the South Fork Humboldt River and penetrate interbedded clay, sand, and gravel to depths of 144–250 ft (table 5). Water levels at a stock well about 1 mi northeast of the reservoir were at about 89 ft through 1992, rose 2 ft in 1993, and fluctuated 1–2 ft through 1997 (well 6, figs. 4 and 7C). Water levels were not measured at the well again until 2005 when the depth to water was about 83 ft. Since then the water level has not changed. Although this well is at a higher altitude than the South Fork Reservoir, the well depth, at 170 ft (5,172 ft altitude), is below the reservoir elevation of 5,231 ft. In addition, this well penetrated interbedded clay and sand (table 5). Water-level rises at the wells 4, 5, and 6 are the result of infiltration of surface water during filling of the reservoir.

Water levels also have risen at two wells on the northwest side of the group of hills that extends from the Elko Hills on the northeast to the north end of the Pinon Range on the southwest (wells 7 and 8, figs. 4 and 8A–B). These hills lie between the Humboldt River flood plain and the Dixie Creek-Tenmile Creek Area. The depth to water at well 7 rose from 225 ft in 1989 to 109 ft in 2008. This well was drilled in 1976 and its log (well 7, table 5) indicates that it penetrated alluvium and gravel to 112 ft, volcanic rocks from 112 to 178 ft, shale from 178 to 255 ft, limestone from 255 to 262 ft, and then faulted shale to a depth of 510 ft. The casing was perforated from 128 to 510 ft. The reason for the continuous water-level rise at this well is not clear because no nearby source of water is evident. One reason could be infiltration from the South Fork Reservoir into carbonate rocks, which are exposed in the canyon where the dam was constructed (pl. 1; Coats, 1987, pl. 1). However, the distance between the dam and well 7 is about 10 mi.

Water levels at well 8 rose from a depth of about 200 ft in 1989 to 145 ft by 2003 (fig. 8B). This well was drilled in 1966 and its log (table 5) indicates that it penetrated gravel, clay, and sandstone to 162 ft and rock and clay from 162 to 200 ft. The casing was perforated from 160 to 180 ft. Center-pivot irrigation and infiltration ponds for disposing of treated sewage, both constructed just west of this well in the early 1990s, are the reason for the water-level rise.

Pumping in the Elko Segment, especially for municipal purposes, probably has resulted in water-level declines. However, water-level monitoring has not been sufficient to identify the areal extent or magnitude of any declines. A secondary effect of municipal pumping can be that of water levels rising because of lawn watering in residential neighborhoods. The graph for well 9 (figs. 4 and 8C) indicates that water levels rose about 43 ft from 1988 through 2008. This well is next to a park and residential neighborhoods on the west side of Elko.

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