Groundwater Quality

Groundwater quality in Utah is good in most places. Exceptions occur where groundwater travels slowly through an aquifer that consists of chemically reactive minerals such as halite (salt) or gypsum, which may dissolve into the groundwater. Mineral dissolution increases the total dissolved solids (TDS) concentration and may add constituents that limit or preclude its use (for example, high salinity, sulfate, or arsenic). The type of geologic materials in a groundwater basin and the length of time groundwater is in contact with those materials are fundamental controls on water chemistry.

Dissolved Solids

Groundwater in the basin- and valley-fill aquifers is typically fresh, dominated by calcium, magnesium, and bicarbonate (HCO3) ions, and generally has dissolved-solids concentrations less than 1,000 milligrams per liter (mg/L). Groundwater having less than 250 mg/L TDS concentration is typically located in recharge areas along valley or basin margins and in high mountainous areas. Lower parts of valleys/basins typically contain more saline (salty) water.

Clay and Expansive Soil, Arapien Shale, White Hills North of Salina, Utah

  • Groundwater with high TDS concentrations, especially calcium and sulfate, exists in some areas having rocks abundant in gypsum or salt, such as in wells downgradient from the salt-rich Arapien Shale in Sanpete Valley.
  • Groundwater with high TDS concentrations, especially sodium and chloride, exists near playa areas and saline lakes, such as in wells located near the shore of Great Salt Lake.

Water quality often declines over time in areas where groundwater pumping for irrigation lowers the water table and recharge comes from water recycled through the soil, such as the Sevier Desert, Pahvant Valley, and the Beryl-Enterprise area. Sandstone aquifers generally have TDS concentrations less than 1,000 mg/L.

Groundwater Chemistry and Environmental Tracers

The water chemistry from wells, springs, and streams in different locations and at different well depths, when viewed with other physical data, can help scientists infer flow paths and residence time of groundwater and interactions with surface water.

The proportion and amount of dissolved ions in groundwater, often visualized using Piper diagrams, can reveal clues about how much mixing occurs between aquifers and which rocks have the most influence on groundwater chemistry.

Environmental tracers are naturally occurring constituents, man-made chemicals, or isotopes that can indicate water sources and flow processes such as recharge, flow rate, geologic subsurface interactions, residence times, and mixing between sources. Data from environmental tracers coupled with solute chemistry can help identify groundwater provenance (origin) and surface water/groundwater interaction. Ideal tracers have well defined input sources and input histories, are inert (no reactions) or geochemically conservative (limited reactions), have transport mechanisms identical to water, and are detected precisely and economically. Tracers commonly used by UGS scientists include stable isotopes of water (oxygen-18 [δ18O] and deuterium [δ2H]), tritium (3H), noble gases (helium, neon, argon, krypton, and xenon), and radiocarbon (carbon-14 [14C] and carbon-13 [δ13C]).

FIGURE: Piper diagram of water chemistry in bedrock wells in Ogden Valley, Weber County, Utah. The location of symbols in the triangles shows the relative proportion of cations and anions in samples, whereas the size of the symbols is proportional to the amount of total dissolved solids (TDS) in the samples. The maps below the Piper diagram show where each of the samples are located, allowing the viewer to see where groundwater may be influenced by rock type. For example, limestone likely influences wells located at red squares (calcium-bicarbonate dominant water) and halite may be impacting green square wells (sodium-chloride dominant water). Comparing this Piper diagram of bedrock groundwater chemistry to similar diagrams of streams or the valley-fill aquifer wells can show the location of bedrock aquifer discharge to the valley fill or streams.

Groundwater Quality Classification

Many communities in Utah are experiencing population growth. Many rural areas in Utah depend on groundwater as their primary source of water within valley-fill aquifers, and with increasing population growth, some communities are opting to classify their local aquifer. The UGS has been involved with 10 hydrogeologic studies in Utah to help communities gather the necessary hydrogeologic data required to formally classify aquifers, and thereby provide a measure of protection to their groundwater resources.

Under Utah’s Administrative Rules for Ground Water Quality Protection, groundwater quality classes are based on total-dissolved-solids (TDS) concentrations as shown in the table below. Two other classes, IB and IC, are not based on groundwater chemistry.

Groundwater quality classes under the Utah Water Quality Board’s total-dissolved-solids- (TDS) based classification system
(modified from Utah Division of Water Quality, 1998)
Groundwater Quality Class
TDS Concentration
Beneficial Use
Class IA/IB1/IC2 Less than 500 mg/L3 Pristine/Irreplaceable/Ecologically Important
Class II 500 to less than 3000 mg/L Drinking Water4
Class III 3000 to less than 10,000 mg/L Limited Use5
Class IV 10,000 mg/L and greater Saline6

1Irreplaceable groundwater (Class IB) is a source of water for a community public drinking-water system for which no other reliable supply of comparable quality and quantity is available due to economic or institutional constraints; it is a groundwater quality class that is not based on TDS.

2Ecologically Important groundwater (Class IC) is a source of ground-water discharge important to the continued existence of wildlife habitat; it is a groundwater quality class that is not based on TDS.

3For concentrations less than 7000 mg/L, mg/L is about equal to parts per million (ppm).

4Water having TDS concentrations in the upper range of this class must generally undergo some treatment before being used as drinking water.

5Generally used for industrial purposes.

6May have economic value as brine.

Highlighted Scientific Publications

Report of Investigation 282

Time Series Analyses of a Great Basin Groundwater-Fed Wetland Complex, Juab County, Utah: Climate Effects on Groundwater-Dependent Wetlands

Special Study 165

Characterization of the Groundwater System in Ogden Valley, Weber County, Utah, with Emphasis on Groundwater–Surface-Water Interaction and the Groundwater Budget

Public Interest Articles

An In-depth Look at Ogden Valley's Groundwater Groundwater 2020
Monroe’s “Sweet” Groundwater Points to Contamination Source Water 2018
Monitoring Groundwater Response to Large-Scale Juniper Treatments Water 2018
Crystal Geyser, Grand County Water 2018
Does Utah really use more water than any other state? Water 2018
UGS’s Role in Contributing Water-Quality Data to the National Ground-Water Monitoring Network Groundwater 2017
Deep Nitrate in an Alluvial Valley: Potential Mechanisms for Transport Groundwater 2015
UGS Groundwater & Spring Flow Monitoring in Snake Valley Groundwater 2014
Roosevelt Hot Springs Geothermal Area, Beaver County Water 2014
Using Aquifers for Water Storage in Cache Valley Water 2013
Establishing Baseline Water Quality in the Southeastern Uinta Basin Water 2013
Gandy Warm Springs, Millard County Water 2013
What do environmental tracers tell us about groundwater in Snake Valley? Groundwater 2011
Modeling Ground-Water Flow in Cedar Valley Groundwater 2010
Utah Geological Survey’s West Desert Ground-Water Monitoring Network: Progress Report Groundwater 2010
Unusually High Nitrate Concentrations in Southern Sanpete County’s Ground Water Groundwater 2009
Geothermal Energy Development in Utah Geothermal Energy 2008
Cascade Springs, Wasatch County Water 2008
Ground-Water Monitoring in Utah’s West Desert Groundwater 2007
Groundwater Water 2006
Proposed Ground-water Withdrawal in Snake Valley Groundwater 2006
Pilot Project Shows Promise for Aquifer Storage and Recovery Groundwater 2005
The Midway hot pots – natural hot springs, Wasatch County Water 2004
New Aquifer Storage and Recovery Project, Ogden Area Groundwater 2003
Cache Valley sensitivity and vulnerability to pesticides Groundwater 2002
Hydrologic Cycle Specific to Utah Water 1999
Do I have to travel all the way to Yellowstone, or can I see beautiful hot springs here in Utah? Water 1998
Thermal Springs in Utah Water 1995

Topic Articles: 28