A06_WellSiteReport-WeedHeights_ForReferenceOnly.pdf

Well Site inveStigation

Site Name: Weed Heights Well, Mason Valley Basin (108)—designated basin

Use of water: Stockwater. Permit 49425 / Certificate 12577, 100% BLM ownership. Priority 10/02/1985

Legal Description: T. 14 N., R. 25 E., Section 31, SENW (MDBM) (N14 E25 31DB)

State, County: Nevada, Lyon County

Field Office: Sierra Front Field Office

Date Examined: June 17, 2019 and August 8, 2019

Topographic Map: Mason Butte Quadrangle 7.5 minute series; Carson City 100K

Aerial Photography: n/a

Evaluated by: Niki Cutler, Hydrologist

Accompanied in field by: Dan Erbes, State Lead Hydrogeologist

Altitude of Land Surface (source of elevation data): Approximately 4,430 feet (ft) above mean seal level (amsl) based on United States Geological Survey (USGS) 7.5” topographic map.

Existing Well: The Weed Heights Well (WHW), located in Mason Valley and shown in Figure 1, was completed July 07, 1971 using a cable tool well drilling rig (Well log from BLM files). The well log, included in Appendix A, records layers of clay, sandy clay, gravel and boulders to the completed depth of 110 ft below ground surface (bgs) (e.g., approximately 4,320 ft amsl). First water was encountered at 90 ft bgs. The chief water bearing formation was a gravel layer recorded from 90 – 97 ft bgs. The well was completed in an 8-inch borehole using 6-inch steel casing with perforations (1/8-inch by 2-inch) from 80 – 110 ft bgs. No sand-pack was installed. The standing water level recorded following well completion was 78 ft bgs (e.g., water level elevation approximately 4,352 ft amsl). Appurtenances included a wind water pump (decommissioned in 2015), pipeline and long low half cylinder troughs (44 ft in length). Recent field visits by BLM staff in 2018 and 2019 suggest up to 10 ft of debris in bottom of well and about 1 ft of standing water. A down-hole camera survey conducted in August 2019 recorded 360º every 10 ft and showed perforations have been sealed off due to scaling. A non-use notice of forfeiture was sent to BLM from Nevada Division of Water Resources (NDWR) on August 10, 2017. The State Engineer granted BLM an extension of time until August 10, 2021 to get the water back into use.

Description of Geology: The following geological description is summarized from Morrison and Frye (1965), Proffett (1977), Proffett and Dilles (1984), Parsons (1995) and Reheis (1999).

The WHW site is located within the western Great Basin of the Basin and Range Physiographic Province on the east side of the Sierra Nevada in Lyon County, Nevada. Basin and Range style extension commenced in west-central Nevada during the Miocene (23.0 to 5.3 million-years ago) and continues to present. Two distinct extensional styles are commonly observed: (1) an initial stage of isolated highly extended terranes where mid-crustal rocks are exposed at the surface, exhumed by low-angle normal faults, uplift, and erosion, and (2) a second, later stage of higher-angled block faulting.

The east slope of the Sierra Nevada is complex and irregular and the physiographic and structural break between the Sierra Nevada and the Basin and Range is gradational. The east slope of the range is cut by a number of major normal faults delineating north-trending ranges which are connected to the main mass of the Sierra Nevada on the southern ends but diverge from the range northward creating deep intervening sediment filled basins. The Singatse and Wassuk ranges on either side of Mason Valley are two block ranges bounding a sediment filled basin of this type.

The WHW site is located along the western edge of Mason Valley at the base of the Singatse Range, a primarily west-tilted fault block approximately 25 miles in length. Geologic units exposed near the WHW site in the Singatse Range comprise Oligocene ash-flow tuffs (~28 million years old) primarily quartz latite overlain basal Tertiary deposits of the Yerington batholith (see Figure 2). The Guild Mine Member of the Mickey Pass Tuff are compositionally zoned from 65% SiO2 near the base to 72% SiO2 near the top, while other tuffs are unzoned. All units were tilted steeply to the west as a result of crustal extension in the Miocene and displaced into numerous blocks by easterly-dipping listric normal faults. The eastern front of the Singatse Range is marked by an irregular normal fault scarp (the Montana-Yerington fault) with indicated movements of up to 1,500 ft of down-throw on the east.

During the Pliocene (5.3 to 2.58 million-years ago) and Pleistocene (2.58 to 0.1 million-years ago), Mason Valley received sediments from surrounding highlands. Pleistocene sedimentary rocks included fanglomerates, fluvial deposits (e.g., ancestral Walker River), as well as lacustrine clays and beach deposits formed during two high stands of Pluvial Lake Lahontan (Morrison, 1964), the Eetza high stand rising to an elevation of about 4,380 ft amsl approximately 50,000 years ago, and the Sehoo high stand rising to about 4,370 ft amsl approximately 20,000 years ago. Fanglomerate and fluvial deposition likely continued between lake high stands. Holocene age (0.12 million-years ago to present) deposits included fanglomerate, dune sand, and Walker River floodplain alluvium.

The Walker River flows north through Mason Valley until reaching the valley’s northern end near Wabuska, Nevada. Here the river changes course, turning eastward and ultimately south towards Walker Lake. Sedimentary evidence suggests that the Walker River changed course at least twice in the previous 13,000 years, instead flowing northwest through Adrian Valley (e.g., Churchill Narrows) from a point near present-day Wabuska and into the Carson River. During these course changes the Walker River ceased to flow into Walker Lake, causing it to dry up. During the Pleistocene, the Churchill Narrows also connected Pluvial Lake Lahontan between the Carson Sink and Mason Valley during the Eetza and Sehoo high stands.

Inferred Aquifer (description and depth of producing zone) and Analysis of Data: The following information is referenced from Morrison (1964), NDWR Water Resources Bulletin #38 (Huxel and Harris, 1969), the Geologic Map of the Yerington District, Nevada (Proffett and Dilles , 1984), the Yerington Mine Hazard Ranking System Report (EPA, 2016) and the 2020 Annual Optimized Groundwater Monitoring Report (NDEP, 2020).

Groundwater in Mason Valley generally flows south to north in the direction of the north flowing Walker River. Groundwater flow directions are affected locally by bedrock outcrops along valley margins and drawdown from pumped wells and irrigation activities on cultivated fields in Mason Valley. The alluvial aquifer consists of well-sorted deposits of sand and gravel from ancestral channels of the Walker River and fan deposits from valley floor down-faulting with concurrent up-lifted mountain blocks. Monitoring wells installed throughout the valley are categorized into shallow, intermediate and deep zones based on interbedded clays/fine silts, however these fingers are laterally discontinuous and not indicative of true zones.

The WHW is completed in shallow alluvium near the western valley margin adjacent to the consolidated rock/valley fill boundary and categorized as “less than 60% sand and gravel ratio to all other material” (Huxel and Harris, 1969, pp 11-13, Figure 3). Transmissibility (the capability of water to move through the porous medium) estimates for the area near the WHW site are approximately 25,000 gallons per day per ft (gpd/ft) (Huxel and Harris, 1969, Figure 4).

Transmissibility nearer the center of the valley vary from 50,000-200,000 gpd/ft.

The WHW site resides at a surface elevation of approximately 4,430 ft amsl above and to the west of present-day Walker River. Topographic relief surrounding the WHW site ranges from slight to moderate. Singatse Range, undefined granitic, metamorphic and volcanic rock, rises nearly 700 ft to an elevation of 5,106 ft amsl within eight-tenths of a mile west of the WHW site. The surface slope to the east from the WHW site towards Mason Valley is more gradual, dropping only 70 ft in elevation to 4,355 ft amsl over a distance of one mile.

Bedrock exposed directly west and upslope of the WHW site comprises Yerington batholith quartz latite. The north-south trending Montana-Yerington fault is also directly west at the break in slope, at the bedrock / alluvium interface. This relationship suggests the WHW site likely in the recent alluvium situated east of the Singatse Range and east of the Montana-Yerington fault. The alluvial aquifer thickness in the area surrounding the WHW site is shown in the D-D’ Transect on the the Geologic Map of the Yerington District (Proffett and Dilles , 1984) to have approximately 1000 ft of alluvium thickness, where the listric faults are rotationally pulling valley floor down with increasing alluvium thickness across the valley floor.

Estimated Static Water Level: The standing water level recorded following completion of the WHW in 1961 was 78 ft bgs (e.g., water level elevation approximately 4,352 ft amsl). In 1966, the MPW is cited in NDWR Water Resources Bulletin #38 (Huxel and Harris, Table 25, Well No. 14/25-31db1) as having a water level of 80.2 ft bgs (e.g., approximately 4,349.8 ft amsl). During that period, Anaconda Copper Company operated the Yerington Copper Mine (from 1956 to 1978) with the open pit approximately 3.5 miles southeast of the WHW site. Dewatering associated with open pit mining at the Yerington Copper Mine reportedly did not directly affect the alluvial groundwater west of the open pit (EPA, 2016), and water levels in the alluvial aquifer surrounding the pit have recovered substantially since mining ceased in 1978. Therefore, impacts from nearby open pit mining will not be considered further in this investigation.

Monitoring conducted in 2015 associated with closure of the nearby Yerington Mine Site (EPA, 2016) indicates water levels proximal to the WHW site may have declined over 22 feet to an elevation of 4,327 ft amsl over the last 49 years. There are multiple monitoring wells nearby the WHW site with screens straddling the water table. Water levels recorded from these wells in 2015 and 2020 suggest a constant northwesterly groundwater gradient exists between Mason Valley and the WHW site as shown on Figure 3. This supports with the groundwater gradient observed within Mason Valley which is relatively flat (e.g. suggestive of high permeability/transmissivity). The low gradient proximal to the WHW is likely attributed to the localized thickness of saturated alluvium residing east of the Montana-Yerington fault. Selected well data from wells nearby the WHW site are listed in Table 1.

The groundwater gradient measured in Mason Valley, from monitoring wells close to the WHW site, east of the Montana-Yerington fault appears to be holding true to the potentiometric surface in the shallow alluvial aquifer, which equates to a projected groundwater elevation of 4, 325 – 4,330 ft amsl, or 100 – 105 ft bgs based on the surface elevation of 4,430 ft amsl. Accounting for season fluctuations and seasons with heavy precipitation, the selected well data (B/W-41S, B/W- 33S and B/W-16S) generally do not decline over time, but have a slightly increasing trend.

Table 1. Potentiometric surface, shallow alluvial aquifer (EPA, 2016 & NDEP, 2020) Monitoring well no.

Groundwater elevation, amsl (2015)

Groundwater elevation, amsl (2020)

Screen interval, amsl

Location 11 S

(UTM)

Comment

B/W-27S 4,335.36 4,339-4,319 310801 / 4322746

Near valley floor, background monitoring well

B/W-64S 4,336.5 4,348-4,328 311149 / 4321945

Near valley floor, background monitoring well

B/W-83S 4,336.4 4,326-4,306 311141 / 4322366

Near valley floor, background monitoring well

B/W-16S 4,327.7 4,330.17 4,328-4,308 B/W-33S 4,330.41 B/W-41S 4,327.02 4,330.43 4,324-4,304 1,000 ft east of WHW Weed Heights Well

4,350-4,320 Near western boundary

Anticipated Yield: Weed Heights Well appears to sit in alluvium and nearby monitoring wells have a constant static water level. The depth to water should be a little over 100 ft bgs or 4,330 ft amsl.

Evaluation of Site: It appears that rehabbing the well slots and cleaning out debris from the bottom of the well, would at best result in less than five feet of water.

Drilling and Well Construction Recommendations: A mud-rotary drilling rig would be most appropriate for drilling in loose material anticipated at the WHW site. A pilot hole should be drilled initially to a depth of approximately 150 - 200 ft bgs proximal to the WHW site to identify potential production zones within the shallow alluvium.

The final well design should be based on production zones identified in the pilot hole. A well diameter of 6” will require a borehole of 10” to accommodate for the 2” (minimum) annulus and should allow for sufficient production. The well should be drilled deep enough to accommodate proper efficiency while providing sufficient capacity for the end use. The pump should be set in the cased section of the well within the saturated zone and sufficiently above the lowest screened interval (e.g., for a maximum desired production rate of 20 gpm at a specific capacity of 4 gpm/ft, the pump intake should be set in the cased section of the well at least 5-feet above the lowest screened interval). Acknowledging water levels near the WHW site appear to have declined a half-foot per year over the past 50 years but may be fairly constant within the most recent decade, it would be prudent to include additional saturated capacity within the cased section of the well above the lowest screened interval in the final well design, if possible.

Casing should be set in all unstable or potentially unstable zones, and a well screen installed in the producing zone(s) to prevent sand or silt from entering the well. The annulus will need to be packed properly with filter material, which will prevent (or slow) silt from entering the well. The well screen preferably should be of the continuous slot, wire wound type; louvered or machine cut slots may be used. Perforations made with a cutting torch, hacksaw, or punched in place with a casing perforator should not be used since these perforations allow sand or silt to enter the casing, resulting in damage to the pump. The well should be properly developed by pumping, surging or jetting. An aquifer test for yield must be conducted to verify the quantity of water available, measured in gpm/ft of drawdown. Additionally, a water sample should be collected for majors/miners, isotopes and nutrients as a baseline to compare to later if needed.

The well must be drilled by a Nevada licensed well driller, and in accordance with applicable state regulations.

An access port should be provided at the surface to allow future measurement of water levels. This access port should be at least 1/2 inch in diameter, and should have a screw-on type of cover to allow for ease of removal and inserting a water level tape into the well.

A new pump and power source (e.g., windmill/sucker rod, solar or other appropriate power source) should also be installed. The trough and associated conveyance system should be rebuilt, and a meter should be installed to record production.

References:

Dilles, J. M. and Proffett, J. M., 1984. Mesozoic and Cenozoic geology of the Yerington district, Lyon County, Nevada, Nevada Bureau of Mines and Geology Map 77.

EPA, 2016. Hazard ranking system documentation record (HRS), Anaconda Copper Mine, Yerington, Lyon County, Nevada, EPA ID# NVD083917252, prepared by EPA Region 9 in September 2016.

Huxel, Jr., C. J. and Harris, E. E., 1969. Water Resources Bulletin #38. Water resources and development in Mason Valley, Lyon and Mineral Counties, Nevada, 1948-1965. Prepared in cooperation with United States Department of the Interior Geological Survey. 103 pgs.

Morrison R. B., 1964. Lake Lahontan: Geology of southern Carson Desert, Nevada, a stratigraphic study of the Cenozoic geology of part of the basin of Lake Lahontan, one of the great late Pleistocene lakes of Western Untied States.

Morrison R. B. and Frye J. C., 1965. Correlation of the Middle and Late Quaternary successions of the Lake Lahontan, Lake Bonneville, Rocky Mountain (Wasatch Range), Southern Great Plains, and Eastern Midwest Areas.

Nevada Division of Environmental Protection Anaconda Public Records, 2020. Annual Optimized Groundwater Monitoring Report, 69 pgs.

Proffett, J. M., 1977. Cenozoic geology of the Yerington district, Nevada, and implications for the nature and origin of Basin and Range faulting, Geological Society of America Bulletin, v. 88, p. 247- 266, February 1977.

Parsons, T. E., 1995. The Basin and Range province: Chapter 7, in Continental rifts: evolution, structure, and tectonics, pp. 277-324, K.H. Olsen ed.

Reheis, M., 1999. Extent of Pleistocene lakes in western Great Basin, USGS misc. field studies map

MF-2323.

NDWR, 2019. State of Nevada Division of Water Resources website: http://water.nv.gov/ Permit 49425.

Appendix A Weed Heights Well Log Not attached http://water.nv.gov/