Evaluation of water-level decline and aquifer properties in the Virginia City Highlands and Highland Ranches Volcanic Rock aquifer system, Storey County, Nevada

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The Virginia City Highlands and Highland Ranches (VC Highlands) are a rural residential housing area established along the ridge of the Virginia Range in Storey County, Nevada. Approximately 1,400 residents exclusively rely on domestic wells for water supply and domestic well depths range from 75 to 1,175 ft below land surface. NVWSC monitors water levels annually in two domestic wells in the VC Highlands. Recent analysis of water levels indicates a rapid and substantial decline in the water table at these two sites. 

Between 1997 and 2016, water levels declined approximately 50 and 165 ft near the center of development in the VC Highlands. Water levels in the USGS monitoring wells are declining at an average rate of about 5.7 feet per year. Due to the limited measurement frequency and close proximity of the two monitoring well locations, the areal extent of the declining water table is unknown. However, analysis of the State of Nevada Division of Water Resources (NDWR) well log database indicates 103 of 623 domestic wells (17 percent) have been deepened or replaced since the development of the VC Highlands, indicating that water-level declines are widespread and represent a significant cost burden to homeowners in the area. 

USGS hydrologist David Smith measuring a USGS monitoring well in the Virginia City Highlands, Nev.

USGS hydrologist Kyle O'Conner measuring a USGS monitoring well in the Virginia City Highlands, Nev. 

(Public domain.)

Well logs from NDWR indicate recently completed well depths are deepening through time, likely in response to the declining water table. For example, domestic wells completed prior to 1997 had an average depth of 225 ft, and wells completed after 1997 have increased to an average depth of 375 ft. In the most densely developed area of the VC Highlands, approximately 30 percent of domestic wells have been deepened. Housing development in the VC Highlands is currently at one third of the maximum capacity and residents have expressed concern with continued development and use of limited groundwater resources1. Verbal communication with residents has indicated that deepening or replacement of domestic wells for some residents may be financially unrealistic and have opted to contract with private water-services for the delivery of potable water.

Fractured volcanic-rock aquifers, like the one found in the VC Highlands represents the least understood aquifer system in Nevada and the Basin and Range physiographic province2. Communities within the Basin and Range province generally rely on groundwater from basin-fill or carbonate-rock aquifers for domestic supply. Currently, little is known about the volcanic-rock aquifer hydraulic properties, viability, or characteristics as a source of domestic water supply throughout the Basin and Range. 

To increase the understanding of recharge, aquifer properties, and groundwater flow in the VC highlands volcanic-rock aquifer system, NVWSC will

  1. evaluate water-level trends in the VC Highlands,
  2. develop a water-table and water-level change map,
  3. characterize the fractured volcanic-rock aquifer(s) hydraulic properties, and
  4. estimate recharge rates from Lousetown Creek.

Information from this study will benefit Storey County officials and stakeholders by collecting data necessary to improve understanding of recharge, aquifer properties and groundwater flow that will aid in future resource-management decisions in the VC Highlands. Monitoring data will be stored in the USGS National Water Information System (NWIS) Database and will help to improve the overall understanding of volcanic-rock aquifer systems within the Basin and Range Province.

 

USGS Monitoring Wells in the VC Highlands

 

Sources

1 Storey County, 2016, Storey County Master Plan, Chapter 6: Housing.

2 Planert, M., and Williams, J.S., 1995, Ground Water Atlas of the United States: California, Nevada, U.S. Geological Survey, HA-730-B.