Arsenic in the Upper Republican Natural Resources District’s Groundwater

Arsenic in the Upper Republican Natural Resources District’s Groundwater

In the summer of 2020, Upper Republican Natural Resources District (URNRD) staff collected water samples from 144 irrigation wells throughout the URNRD and sent the samples to a certified laboratory to determine the arsenic concentration in the water. The figure titled Arsenic Concentration in the URNRD in 2020 shows the results of this testing and the location of the sampled wells. Most of the groundwater in Dundy County appears to exceed the US Environmental Protection Agency’s (EPA) drinking water standard for arsenic. Also, a portion of southern Chase County, northwestern Chase County, and southwestern Perkins County exceeded the arsenic drinking water standard. In general, the arsenic concentration in the groundwater decreases from south to north in the URNRD. The City of Benkelman recently drilled new municipal wells and installed a water-delivery pipeline from the wells to the city, because of the high arsenic and uranium levels in their previous water supply.

Source of Arsenic in Ground Water

Arsenic is the 20th most abundant element in the earth’s crust, occurring naturally in rocks and soil. When water passes through and over soil and rock, it dissolves many compounds and minerals, which may include arsenic and cause soluble arsenic in ground and surface water. While arsenic in drinking water may also result from human activities, it is believed that the arsenic in the URNRD’s ground water is from natural sources and comes from the aquifer from which the water is pumped.

Indications of Arsenic in Water

Because arsenic cannot be detected in drinking water by taste, sight, or smell, sampling and testing is the only way to determine the concentration of arsenic in water.

Potential Health Effects

Arsenic exposure can cause a variety of adverse health effects. The severity of the effect depends on how much arsenic is in the water, how much water is consumed, how long a person has been exposed to the water, and a person’s general health. Arsenic poisoning can be acute (brief and severe) or chronic (occurring over a long time). Acute poisoning can occur when a high concentration (over 60 mg/L) of arsenic is ingested over a short period of time. This is more likely to occur in situations where industrial processes or unregulated waste disposal sites have concentrated arsenic, which probably has not occurred in the URNRD.

Chronic poisoning can occur when moderate or small amounts of arsenic are ingested over long periods, such as where groundwater containing arsenic is consumed daily for extended periods. Some Nebraska groundwater supplies contain arsenic in high enough concentrations to present an increased risk of chronic poisoning.

There is still uncertainty in the exact connection between level of arsenic, duration of exposure, and health effects; however, studies summarized in a report by the National Research Council indicate that long-term ingestion of arsenic can increase the risk of skin, bladder, lung, kidney, liver, and prostate cancer. Non-cancer effects of ingesting arsenic may include cardiovascular, pulmonary, immunological, neurological effects, and endocrine problems such as diabetes.

Symptoms of chronic arsenic poisoning usually are delayed, with years of exposure required to initiate the disease process. Factors such as genetics, age, metabolism, diet, and overall health also may impact health risks associated with arsenic exposure, because they potentially affect one’s ability to remove arsenic from the body. Individuals with chronic Hepatitis B infection, protein deficiency or malnutrition may be more sensitive to the effects of arsenic. Children and older adults may be other groups at special risk.

EPA Drinking Water Standard for Arsenic

In regulating a contaminant, the EPA first sets a maximum contaminant level goal (MCLG), which establishes the contaminant level at which no known or anticipated adverse health effects occur. MCLGs are non-enforceable health goals. For arsenic, EPA set the MCLG at zero. The EPA then set an enforceable maximum contaminant level (MCL) as close as technologically possible to the MCLG. In addition, the EPA used its discretion in setting the MCL by choosing an MCL that is protective of public health while also ensuring that the quantified and non-quantified costs are justified by the quantified and non-quantified benefits of the drinking water standard. For arsenic, EPA has set an MCL of 0.01 mg/L (0.01 ppm). The EPA evaluated the following five factors to determine the MCL for arsenic:

• The analytical capability and laboratory capacity,

• The likelihood of water systems choosing various compliance technologies for several sizes of systems based on source water properties,

• The national occurrence of arsenic in water supplies,

• Quantified and non-quantified costs and health risk reduction benefits likely to occur at the MCLs considered, and

• The effects on sensitive subpopulations.

Water Treatment Methods

Options for Public Water Supplies

Of the 94 public water systems in Nebraska affected by the arsenic rule, some communities addressed this MCL by shutting down or replacing one or two wells. Other communities have used other approaches for lowering the arsenic concentration in the drinking water. These alternatives may range from finding new wells that yield water with a lower arsenic concentration, treating the water, or becoming part of a larger rural or community water district (which benefits from economies of scale in treating water or obtaining water from a high-quality source). Management and disposal of the waste stream generated from treatment (arsenic removed) must also be taken into consideration. Community-based water users wishing to reduce arsenic levels prior to a community achieving compliance can treat water as described in the Options for Private Water Supplies section.

Options for Private Water Supplies

It may be possible to obtain a satisfactory alternate water supply by drilling a new well in a different location. However, drilling a new well does not guarantee a satisfactory water supply will be found. Another alternative source of water is bottled water that can be purchased in stores or direct from bottling companies.

In addition, research is being conducted to find new technologies for arsenic removal from private drinking water supplies. The treatment system or combination of systems that will be best for a private well user depends on several factors including the level of arsenic in the water, desired level of arsenic removal from the water, the quantity of water to be treated, and the chemistry of the water.

Treatment systems that can be used for arsenic reduction include reverse osmosis, distillation, adsorption, and (anion) ion exchange. Reverse osmosis utilizes a pressure driven membrane. Pretreatment may be required to remove sediment and/or hardness. Distillation is achieved by heating water and collecting the steam as treated water. For more information on these treatment options see University of Nebraska-Lincoln NebGuides Drinking Water Treatment: Reverse Osmosis (G1490) and Drinking Water Treatment: Distillation (G1493). Adsorption utilizes porous granular media with adsorptive properties that adsorb arsenic from the water as it passes through the treatment system. Media shown to be effective in arsenic adsorption include activated alumina, granular ferric hydroxide, and titanium dioxide. Anion exchange is an adsorption treatment process. The process is similar to water softening, but contaminant-specific adsorption media is used. The chemistry of arsenic complicates arsenic removal.

Arsenic treatment systems for private water supplies come in Point-of-Entry (POE) and Point-of-Use (POU) systems. POE systems treat water before it enters the home, so all the home’s water will be treated. POU systems treat water where it is used. For instance, a POU system could be hooked up under the kitchen sink and only treat the water that comes out of that faucet.

Residential point-of-entry (POE) treatment methods are:

• Iron oxide/hydroxides (adsorption),

• Activated alumina (adsorption),

• Anion exchange in a fixed bed (requires regeneration),

• Manganese greensand (requires regeneration) (Ion exchange),

• Titanium oxyhydroxide (adsorption), and

• Iron-doped anion resin and activated alumina (adsorption).

Residential point-of-use (POU) treatment methods are:

• Iron oxide/hydroxides (adsorption),

• Activated alumina with or without iron oxide coating (adsorption),

• Anion exchange,

• Distillation,

• Titanium oxyhydroxide (adsorption), and

• Reverse osmosis (RO).

The treatment methods listed above are recognized to be effective in reducing the arsenic contaminants sufficiently to meet or exceed the relevant MCL. However, this list does not reflect the fact that point-of-

use/point-of-entry (POU/POE) devices and systems currently on the market may differ widely in their effectiveness in treating specific contaminants and performance may vary from application to application. Also, interfering reductants and competitive adsorbates reduces the effectiveness of many of these treatment technologies. Always conduct a complete water analysis prior to any treatment application. It is recommended that devices and systems that are independently certified to appropriate NSF/ANSI standards should be preferably used. Whenever possible, assistance from a water professional or expert should be sought in the selection, installation, and operation of a chosen technique. Visit to locate water professionals in your area. Note that Certified Water Specialists have passed the water treatment education program with the Water Quality Association and continue their education with recertification every 3 years.