Bannock County Groundwater

Our Water Quality

Based on EPA standards for safe drinking water from public water systems, the municipal water provided by Pocatello and Chubbuck is safe to drink, even though there is known contamination in the groundwater.

By law, public water systems must ensure that the water they provide is safe for human consumption and does not create unacceptable risk to human health. The presence of contaminants does not necessarily indicate that water poses a health risk.

City of Pocatello

In Pocatello, the drinking water that comes out of your faucet is pumped directly out of the ground through seventeen active wells and into the distribution system. In some areas of the city, water is pumped to holding tanks to help improve water pressure. The only water treatment for the Pocatello drinking water system is chlorination, by direct injection into the wells, which takes care of bacteriological contamination only. Chlorination will not reduce or remove any other contaminants in our drinking water.

Best historical water quality summary:

City of Chubbuck

In Chubbuck, the drinking water that comes out of your faucet is pumped from three wells. Water from one well is treated in an air-stripping tower to remove volatile organic contamination, and then put into the distribution system. Water from the other two wells is pumped directly out of the ground and into the distribution system. All three wells are treated with chlorination, which kills any bacteriological contamination.

Best historical water quality summary:

What things affect the quality of our drinking water and our aquifer?

Nitrate from Septic Systems Concerns

Septic Tank Locations

Septic Tank Locations

Areas in the Pocatello/Chubbuck valley that are not served by city sewer have become very large sources of nitrate contamination to our aquifer. Johnny Creek, South 5th Avenue, Mink Creek, and Gibson Jack developments contain a high density of septic systems (see map).

Nitrate enters groundwater through the drainfields of septic systems, even if they are working properly and maintained. Typically, this wastewater is diluted by groundwater flow and nitrate contamination is not a problem. However, problems occur when there are too many septic systems in an area (see map) and the dilution effect is reduced because of the large volume of septic effluent being put into the groundwater system.

How much nitrate is already in our drinking water?

As shown in the adjacent graph, most of the seventeen Pocatello drinking water wells have nitrate levels above 2 parts per million. Nitrate levels above 2 parts per million indicate manmade impacts to groundwater, in this case from septic system waste.

Additionally, many private wells (especially in the South 5th Avenue and Mink Creek areas) have even higher levels, some that far exceed the safe drinking water limit.

Potential Health Effects

High levels of nitrates (above the safe drinking water limit) may cause blue baby syndrome (an oxygen depletion affect seen in fetuses, young infants, and infirm elderly) which may be fatal in some cases. Some research suggests that chronic exposure to nitrate in drinking water, even below the safe drinking water limit, may cause impaired brain and organ development in fetuses and certain cancers.

The Costs of Treating Our Drinking Water

Of Pocatello’s seventeen active drinking water wells, several frequently exceed half of the safe drinking water limit for nitrate. If these wells exceed the limit (10 parts per million), treating the water will be very costly (an estimated $500,000 per well per year – or $31 per customer per well per year).

Nitrate Priority Areas

Nitrate Priority Areas

Some Pocatello municipal drinking water wells and many private wells are located within these defined boundaries. If you are a private well owner and live within one of these areas, it is particularly important to test your well water each year for nitrate and bacteria.

Hazardous Materials Concerns

As in all urban, industrial, and residential areas, hazardous materials threaten our groundwater resource. Sources include leaking underground storage tanks or pipelines; industrial, commercial, or residential chemical uses; spills and leaks on the ground surface; and illegal disposal of chemicals and hazardous waste.

Federal laws govern businesses and industries that use and store large quantities of chemicals or generate large volumes of hazardous waste. Large industry and business must comply with federally mandated health and safety requirements for hazardous materials and generated waste such as reporting spills and leaks, proper storage, inventory listing, spill prevention and containment, inspections, and notification and training of employees.

However, below a certain volume threshold, these federal laws do not apply. It is this population of businesses and industries that are of concern because they are essentially unregulated and can legally conduct a business that involves hazardous materials in quantities that could have significant impacts on our groundwater if there were a release.

In the Lower Portneuf Valley, some areas are known to have hazardous material contamination in groundwater: trichloroethylene (TCE) in the south valley aquifer; perchloroethylene (PCE) and ethylene dibromide (EDB) in the north valley aquifer; and numerous areas affected by spills and leaks from underground storage tanks.

Trichloroethylene (TCE)

Municipal Wells affected by TCE PlumeIn the 1990’s, trichloroethylene (TCE) was discovered in eight Pocatello municipal wells. The source was thought to be barrels of TCE disposed during the 1980’s in the unlined part of the old Bannock County Landfill. After TCE entered the groundwater below the landfill, it merged into the main body of the aquifer and spread rapidly north.

TCE is a chlorinated solvent used commercially as an industrial degreaser, spot remover, and in dry cleaning.

The safe drinking water limit is 5 parts per billion. Chronic TCE exposure can cause damage to the liver, the kidneys and the central nervous system. It may also lead to increased risk of cancer.

Bannock County has installed a remediation system at the base of the landfill that consists of extraction wells and an air stripping unit that removes TCE from groundwater before being reinjected in downgradient clean wells. This system has cost Bannock County, and the tax payers, over 4 million dollars. There will continue to be ongoing costs for several more decades.

When the treatment system became operational in 1979, levels of TCE in some wells exceeded the safe drinking water limit. By 2000, TCE levels in most monitored wells have remained below 2 parts per billion.

Perchloroethylene (PCE)

Chubbuck and Fort Hall Contamination IssuesTwo City of Chubbuck municipal wells are affected by an unknown source of perchloroethylene (PCE or PERC) in groundwater (dark blue area in the adjacent map). PCE is a chlorinated solvent used commercially as an industrial degreaser, spot remover, and in dry cleaning operations.

Chronic PCE exposure can cause damage to the liver, the kidneys and the central nervous system. It may also lead to increased risk of cancer. The maximum contaminant level for PCE is 5.0 ppb (5.0 grams per billion grams of water).

The City of Chubbuck has discontinued use of one of the affected wells. The other well produces water that is treated by means of an air-stripping device that removes or reduces PCE concentrations to safe levels before it enters the municipal water distribution system.

Ethylene dibromide (EDB)

Groundwater sampling activities conducted in the late 1990’s and again in 2004 detected measurable quantities of ethylene dibromide (EDB), some exceeding the safe drinking water limit, in groundwater beneath a sixty-three square mile area on and near the Shoshone Bannock Reservation. The area of contamination, including parts of north Bannock County, is shown in the map above. Though a single source of this contaminant was never identified, it was applied for many years as a pesticide on row crops on the Reservation. EPA banned use of this chemical as a pesticide in 1984. However, it is still manufactured for other purposes.

As a result of this contamination, the city of Fort Hall has placed all of its residents on a municipal water supply system.

Leaking Underground Storage Tanks

Underground Fuel Storage Sites and Leaking TanksMost underground storage tanks are made of steel and will rust over time, sometimes leaking fuel into the ground and our groundwater. Some tanks never leak during their lifespan. Leaking tanks are typically excavated, contaminated soil is removed, and the groundwater is monitored for a period of time. Federal and state regulations require that newly installed underground storage tanks be double lined and have leak detection and monitoring systems.

On this map, the red dots indicate underground storage tanks that have leaked (30% of all known underground storage tanks in the valley). So far, only one is known to have directly affected groundwater.

Stormwater Pollution Concerns

Stormwater run-off threatens our drinking water when pollutants are poured directly into storm drains; or when water that flows over streets, parking lots and yards picks up contaminants such as motor oil, deicing chemicals, lawn care products, and other chemicals. Everything that flows into the storm drain system goes directly into the Portneuf River, ultimately American Falls Reservoir and the Snake River. Polluted stormwater that collects in land swales or depressions percolates into groundwater.

In the southern part of the valley, deicing chemicals have been detected in groundwater from road salting operations.

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