Development of a Revised Hydrogeologic Conceptual Model of the Indian Wells Valley Groundwater Basin

Monday, December 3, 2018: 1:20 p.m.
N109 (Las Vegas Convention Center)
Max Halkjaer , Water and Natural Resources, Aarhus, Rambøll, Aarhus, Denmark
Timothy K. Parker, PG, CEG, CHG , Parker Groundwater Management, Sacramento, CA
Don Zdeba , Indian Wells Valley Water District, Ridgecrest, CA

The Indian Wells Valley groundwater basin occupies approximately 600 square miles of high desert and is bounded by the southeast terminus of the Sierra Nevada Mountain range on the west, the Coso Range on the north, the Argus range on the east, and the El Paso mountains on the south. The surrounding watershed encompasses roughly 860 square miles of mountains, hills, and valley floor, occupying the northwestern-most portion of the Mojave Desert, along the western edge of the Basin and Range geologic province.

The geology and structure of the Basin has been well-studied using geophysics, gravity and magnetics, deep boreholes and monitoring wells. Indian Wells Valley is a structural half-graben produced by faulting, primarily along the Sierra Nevada frontal fault and Argus frontal fault, with the basement generally tilted downward to the west. The basin structure is further defined by the Garlock left lateral strike slip fault that bounds the basin along part of it southern boundary. Additional major mapped faults in the basin include the Little Lake and Airport. There are numerous smaller faults making the basin geology and structure complex. The deepest area of the valley (based on drilling data) is in the west-central area with basement encountered at approximately 6,500 feet below land surface.

The basement and highlands of the basin are of late-Cretaceous igneous and metamorphic rocks. Surficial geology in the basin generally consists of alluvium, lacustrine and playa deposits, sand dunes, and consolidated rock. The lower-most alluvial materials are of early Tertiary age, consisting of compact, consolidated alluvium derived from the basement rocks, which include some lacustrine beds containing pyroclastic materials and minor volcanics. Lacustrine and playa lake deposits as much as 800 feet thick underlain by alluvium dominate the north central portion of the basin, and alluvium dominates the western portion of the basin.

Two principal aquifer units have been identified as the shallow and deep (or main regional) aquifers. The shallow aquifer extends from land surface through the sand dune deposits, younger lacustrine and playa deposits, and shallow alluvium to approximately 400 to 500 feet below ground surface. Water quality is generally poor in the shallow aquifer with total dissolved solids (TDS) greater than 1,000 mg/L. The base of the shallow aquifer is not well defined, but has been estimated from 1,950 ft above mean sea level (msl) at its western edge to 1,850 ft above msl near China Lake.

The shallow and deep aquifer are separated by an intermediate hydrogeologic unit consisting mainly of low permeability lacustrine and playa clays, but containing sand stringers that create transmissive water bearing zones that can be highly productive. The unit acts as a confining bed to deeper, productive water bearing zones, but also can be screened by wells and considered part of the deeper aquifer.

The deep aquifer is semiconfined to confined in the eastern portion of the basin by silt and clay from the overlying lacustrine and playa deposits, but otherwise mostly unconfined. The medium-to-coarse grained alluvial and fluvial sands and gravels have an estimated saturated thickness of 1,000 ft and are the main source of water to the Basin producing adequate flow rates and TDS less than 1,000 mg/L.

Groundwater replenishment occurs dominantly from Sierra Nevada Mountain snowmelt and mountain block recharge. Additional smaller sources of recharge include inflows from the adjacent Rose Valley, Coso Valley and El Paso subbasins/subareas. Groundwater flows from the southwestern El Paso subarea to the northeast, the Rose Valley to the southeast, from the Sierra Nevada to the west, towards China Lake and to two pumping centers. Discharge primarily occurs through groundwater pumping and the China, Mirror and Satellite playa lakes located in the east-central portion of the Basin.

The basin is part of the Stanford Groundwater Architecture Project and was surveyed with aerial electromagnetics in late 2017, initially conducted to provide improved information on water quality and lithology to support a brackish groundwater resources feasibility study. An extensive effort to comprehensively assemble all pertinent hydrogeologic data began in late 2017, with all pertinent data stored in the GeoGIS data management system, which was completed in spring 2018. An updated hydrogeologic conceptual model is being developed with GeoGIS and GeoScene3D, to be completed in July 2018, and results will be presented along with the workflow and challenges to complete the project.

Max Halkjaer, Water and Natural Resources, Aarhus, Rambøll, Aarhus, Denmark
Max Halkjaer has a +20 year career as a hydrogeophysicist. He obtained his Master degree in geophysics at Aarhus University, Denmark in 1995. He has contributed to a large number of projects across the world with a focus on protecting groundwater aquifers and groundwater sustainability. With an entrepreneurial mindset he has been involved in the development of GIS based tools used for analyzing water quality, processing geophysical data and interpreting the geometrical extent of aquifers. He is the co-founder of the company SkyTEM Surveys providing airborne geophysics developed specifically for groundwater mapping. He has comprehensive experience with assessing and modeling the interaction of fresh and saline water in arid as well as very humid geographical areas.

Timothy K. Parker, PG, CEG, CHG, Parker Groundwater Management, Sacramento, CA
Tim Parker is Principal Hydrogeologist, Parker Groundwater Management, California, specializing in groundwater resources management. His experience includes water policy analysis, groundwater management and monitoring, recharge & storage, and assessing potential impacts to groundwater from carbon sequestration and hydraulic fracturing. Tim serves GRA as Director and Legislative Chairman, CGC as Director, and National Ground Water Association as Scientist’s and Engineers Division Director. He is principal writer on Sustainability from the Ground Up, Groundwater Management in California, a Framework (ACWA 2011), and co-authored the books Potential Groundwater Quality Impacts Resulting from Geologic Carbon Sequestration (WRF 2009), and California Groundwater Management (GRA 2005).

Don Zdeba, Indian Wells Valley Water District, Ridgecrest, CA
Don Zdeba is currently General Manager of Indian Wells Valley Water District. Don has more than 35 years of management experience including employment as Mine Geologist at a uranium mine in Church Rock, New Mexico and Manager of Mining for a solution mining operation in Trona, California producing borates, soda ash and sodium sulfate.