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Fort Hall Mine Landfill Groundwater Remediation

Bannock County is actively cleaning up chemicals in groundwater coming from an old, now closed, part of Fort Hall Mine Landfill. The chemicals, including trichloroethene (TCE), tetrachloroethene (PCE), and other volatile organic compounds (VOCs), pose very limited risk to nearby residents. We are directly communicating with the residents whose wells the chemicals impact.

Click through the tabs below to learn more about the clean-up effort. Hover over words in blue to see definitions.

The Fort Hall Mine Landfill, located south of Pocatello, Idaho, has operated since 1943. From 1943 to 1993, Bannock County residents and businesses threw away waste (including hazardous chemicals) in the part of the landfill called Cell 1. Cell 1 is unlined, meaning it does not have the barrier between the waste and nearby environment now required at landfills.

In 1973, the City of Pocatello bought the landfill and transferred operations to the City’s Sanitation Department. The Idaho Legislature passed a law in 1976 that placed all solid waste disposal facilities under county-level control. Thus, in 1976, Bannock County bought the landfill.

Watch how the clean-up is going and hear from our experts.

Bannock County contracted landfill operations to the Snake River Sanitation Company from 1976 to 1979. Then, Bannock County took over landfill operations. In 1991, Bannock County found chemicals, including trichloroethene (TCE), tetrachloroethene (PCE), and other volatile organic compounds (VOCs), discharging from Cell 1 into the groundwater, which is the source of drinking water in Bannock County. Bannock County studied release and remedy options while working to close Cell 1.

In 1993, Bannock County closed Cell 1. At the same time, the Idaho Department of Environmental Quality (IDEQ) issued a consent order to assess and reduce the impacts of TCE, PCE, and other VOCs coming from Cell 1. In 2002, Bannock County installed and began operating a groundwater remediation system to remove and treat the groundwater. By 2015, IDEQ determined that the remediation system had only partially stopped the chemicals from leaving the landfill. IDEQ directed Bannock County to re-evaluate the remediation system and study the nearby environment to improve the clean-up approach.

In 2016, Bannock County and IDEQ began a revised consent order that outlined a thorough approach to understanding and cleaning up remaining groundwater contamination. Groundwater near Cell 1 is in an aquifer that impacts the Lower Portneuf Valley Aquifer and supplies drinking water to Bannock County residents. The consent order dictates that to protect public health, TCE and PCE need to be cleaned up below the United States Environmental Protection Agency (EPA) standards, known as maximum contaminant levels (MCLs), and IDEQ primary standards.

In October 2018, the Bannock County Solid Waste Division partnered with CDM Smith, an engineering and construction firm, to reevaluate the sources of groundwater contamination from Cell 1 and groundwater remediation system effectiveness. The team is exploring different technologies to clean up the contaminated groundwater.

Since 2018, Bannock County has committed $10 million to clean up the groundwater. In 2019, Bannock County began a new strategy to learn how chemicals are moving underground, improve the remediation system, and explore different technologies to clean up contaminated groundwater. See the Site Status tab to learn more.

 

 

 

 

 

 

Site Status

Bannock County is still remediating chemicals leaching from the closed Cell 1 area, but other areas of the landfill are still active. For example, Cell 4 is currently in use and lined to prevent chemicals from waste placed on top of the liner from discharging into the environment.

Bannock County has committed $10 million to clean up the groundwater since 2018. In 2019, Bannock County changed their approach to learn how trichloroethene (TCE), tetrachloroethene (PCE), and other volatile organic compounds (VOCs) are moving underground. The new strategy looks to improve the remediation system and explore different technologies to clean up groundwater.

The chemicals from within or beneath the landfill continue to leach into the Lower Portneuf Valley Aquifer. Bannock County found TCE, the chemical of greatest concern, in some domestic wells at levels above the United States Environmental Protection Agency (EPA) and Idaho Department of Environmental Quality (IDEQ) drinking water standards, known as maximum contaminant levels (MCLs). The MCL for TCE is 5 micrograms per liter (µg/L) of water.

What is the risk?

Sampling helps Bannock County learn about changes in chemical levels and how the chemicals move. Crews sample groundwater wells twice a year at the landfill and once a year at nearby properties. The results of these efforts are available in the monitoring reports on the Documents tab.

According to CDM Smith’s 2023 screening level risk assessment, water from some domestic wells may be unsafe to drink. We update the risk assessment after crews sample select domestic wells each summer. The results are available to the public in offsite monitoring reports on the Documents tab. None of the unsafe wells are used for drinking water supply, but we inform affected property owners in case they are used for drinking in the future. Private well water is safe to drink from most private wells in the area. City water is also safe to drink.

Learn more about health risks and the County’s efforts to protect residents’ drinking water by clicking on the other tabs above.

What is Bannock County doing to clean up the chemicals?

Bannock County currently uses a groundwater remediation system to remove TCE and PCE. We are also studying why the system does not capture all the contaminated groundwater coming from Cell 1 of the landfill.

The existing remediation system targets high chemical concentrations, like TCE greater than 100 µg/L in groundwater flowing from the Cell 1 area. The system uses extraction wells to pump contaminated groundwater to an above-ground treatment building. The system removes the chemicals from the extracted groundwater and then re-injects clean water into the groundwater.

Groundwater moves in complex underground pathways from the Cell 1 area to the Lower Portneuf Valley Aquifer. Because of this, some of the contaminated groundwater is moving past the remediation system without being treated.

Bannock County began a new strategy in 2019 to improve the system, which includes an updated groundwater monitoring program, geophysical measurements, and modeling to better understand the movement of the contaminants in groundwater. Our goal is for the system to treat contamination before it moves downgradient and off-site. In 2022, Bannock County improved the remediation system, repairing and upgrading equipment like pumps and valves. Now, Bannock County and CDM Smith maintain and operate the remediation system. Permit requirements for the system ensure re-injected water is treated below MCLs and IDEQ primary standards.

Pilot Study

In April 2023, Bannock County performed two different tests during a pilot study to help inform the groundwater treatment strategy. One of the tests evaluated a technology to destroy the contaminants in the groundwater without having to pump them to the ground surface. This technology uses microbes and injects amendments, which create conditions supporting the TCE and PCE degradation. Bannock County will make future cleanup decisions based on the test results, which we will add to the Pilot Study tab when available.

Bannock County Tests Groundwater Flow and Groundwater Cleanup Technology

In April 2023, Bannock County performed two tests during a pilot study to help inform the groundwater treatment strategy at Fort Hall Mine Landfill. Bannock County will make future cleanup decisions based on the test results.

Test #1—Groundwater Flow Tracer Study

Tracers are substances added to water to track its speed and flow direction throughout the groundwater. Groundwater movement helps explain contaminant movement in an area and can help with assessing other treatment technologies. Bannock County injected a sodium bromide tracer into a groundwater well. We sampled groundwater to track the injected tracer in wells near and downgradient of its injection location to learn the speed and direction of groundwater flow from the landfill to the Lower Portneuf Valley Aquifer.

Sodium bromide is a safe, naturally occurring substance commonly used as a tracer to study groundwater movement. Learn more about sodium bromide tracers studies here: tracers summaries.

Test #2—Groundwater Cleanup Study

The team completed a small-scale test study to learn if an amendment slurry injected into groundwater could break down contaminants in a small (approximately 40-foot) area using two injection points. The amendment slurry is a liquid mixture of substances that stimulate microbes and break down groundwater contaminants

In April 2023, a Bannock County subcontractor injected about 50,000 gallons of amendment slurry into two wells in a contaminated area near the landfill office over 2 weeks. We are sampling nearby wells to check for changes to the groundwater after the injection.

If the slurry successfully degrades contaminants in the injection area, then Bannock County may use this cleanup technology on a larger scale to treat the groundwater. Although the pilot study is ongoing, preliminary results suggest that the amendment slurry is helping degrade trichloroethene (TCE). We expect final results by 2025.

Tetrachloroethene (PCE) is a chemical that dissolves oils and grease. Industry uses it for dry cleaning and metals degreasing. PCE is found in common consumer products. Visit the Agency for Toxic Substances and Disease Registry’s PCE summary to learn more about PCE.

Trichloroethene (TCE) is a chemical that dissolves oils and grease. It is used in dry cleaning, metals degreasing, and making adhesives and refrigerant chemicals. To learn more about TCE, Visit the Agency for Toxic Substances and Disease Registry’s TCE summary.

The United States Environmental Protection Agency (EPA) sets maximum contaminant levels (MCLs) for each chemical. An MCL is the maximum amount of a pollutant that is allowed in drinking water to protect public health. The MCLs for PCE and TCE are 5 micrograms per liter (µg/L) each.

The Idaho Department of Environmental Quality water quality standards for PCE and TCE are 5 micrograms per liter (µg/L) each. These are the same as the United States Environmental Protection Agency’s maximum contaminant levels (MCLs).

Sampling activities look at how chemicals, like PCE and TCE, are distributed in groundwater. The Portneuf Valley Aquifer is a drinking water source for people living in and around Pocatello in Bannock County. The pilot studies’ findings will help Bannock County improve the groundwater remedy to remove TCE and PCE from the groundwater in the Portneuf Valley Aquifer.

We regularly sample wells to keep track of water quality conditions and learn about changes over time due to the season or ongoing cleanup efforts. Our team samples wells within the Portneuf Valley Aquifer and around areas of known or possible groundwater contamination.

To collect samples that represent groundwater within the aquifer, we must pump about 200 gallons of water from most domestic supply wells. We can safely dispose of extracted water in vegetative and pasture areas.

Most domestic wells we sample do not have water contaminated with the chemicals that Bannock County is studying. It is safe to dump that pumped water on the ground. Water at the few properties with wells contaminated with PCE and TCE is also safe to dispose of on the property. TCE and PCE are volatile, which means that when groundwater with TCE and PCE at the relatively low concentrations observed at these properties is poured onto the ground, they transfer from the water to the air. So, dumping that water on the ground is safe.

We send letters to residents and property owners with sampling results after each annual summer sampling. CDM Smith, Bannock County’s environmental contractor, will call to make sure you received your letter.

We know where TCE and PCE concentrations are above regulatory standards, but the contaminants can move through the groundwater over time. We look at wells within or near areas of the known contamination to understand how it is moving. If TCE and PCE were not in your well before, it is still possible they will be in your well the next time we sample.

Residents with contaminated private wells may be exposed to chemicals through the following:

* Drinking, breathing, or touching well water.

* Breathing vapors that move upward through soil and into homes by a process called vapor intrusion.

* Eating fruits and vegetables watered with well water.

* Livestock and other animals drinking well water.

We evaluate the sampling results to determine if you may be at risk from any of these exposures.

Our risk assessment examined how humans and the environment could be exposed specifically to PCE and TCE, known as exposure routes. Exposure routes of concern for TCE and PCE are:

* Drinking, washing, or bathing with groundwater from a well.

* Breathing indoor air containing TCE or PCE through a process called vapor intrusion.

We compared groundwater results to United States Environmental Protection Agency’s (EPA’s) risk-based concentrations for each exposure route. The results are available in the annual offsite reports on the Documents tab.

Accordion Sample DescriptionYes. Children are often more at risk from chemicals in the environment than adults. Our risk assessment considers this and the United States Environmental Protection Agency’s (EPA’s) 5 micrograms per liter (µg/L) maximum contaminant level (MCL) protects children.

Possibly, depending on your well. The risk from drinking well water, and using it for other household purposes, like showering and cooking, may be above the “safe” level in some of the domestic wells sampled. The offsite monitoring reports on the Documents tab include the most recent results for domestic wells. The “safe” level for PCE and TCE is less than 5 micrograms per liter (µg/L). Drinking well water from these wells above the “safe” level and using it for household purposes may be a health risk. We informed property owners and tenants if their well posed a risk.

Possibly, depending on your well. The risk from breathing vapors from contaminated groundwater may be above the “safe” exposure level in some of the domestic wells sampled. The offsite monitoring reports on the Documents tab include the most recent results for domestic wells. At wells above the “safe” exposure level, there is a possibility for negative effects, especially in sensitive populations like the elderly, children, and immunocompromised. We inform property owners and tenants if a risk of vapor intrusion exists.

No. Using well water as drinking water for pets, livestock, and fish is unlikely to pose a risk even at the highest PCE and TCE concentrations found in domestic well water from the aquifer. During the risk assessment, we looked at ecological risk screening levels for multiple mammals and fish. We determined that using domestic well water for pets, livestock, and fish is considered safe because the highest TCE and PCE concentrations were less than ecological risk screening levels.

No. Vegetables irrigated with well water are safe to eat. PCE and TCE are volatile chemicals, meaning very little will be left in the water during irrigation. The TCE and PCE left does not absorb well into the vegetables. If the vegetables do absorb TCE and PCE, the chemicals will move through the leaves into the air. Consuming vegetables irrigated with well water is considered safe.

Bannock County saves all well sampling results and notifications. If you did not receive your results or cannot find them, please email remediation@bannockcounty.gov to request sampling results for your address and the timeframe you are looking for.

No. We do not recommend acting if PCE and TCE concentrations are below standards. Regulatory standards represent the maximum allowable levels of TCE and PCE deemed safe in drinking water.

Possibly, depending on your well. We sample wells each year around areas impacted by PCE and TCE in groundwater within the Portneuf Valley Aquifer. Multiple sampling events help identify any changes in concentrations and verify risk assessment findings. Bannock County will continue to select sample wells yearly during ongoing cleanup efforts.

Bannock County will continue to tell property owners and tenants if PCE and TCE concentrations in their wells are above regulatory standards. You should not use well water with TCE or PCE above regulatory standards for drinking water. The City of Pocatello gives those properties the option to connect to City water.

No. Neither Bannock County nor the Idaho Department of Environmental Quality have the authority to shut down private wells. The County will continue to sample for PCE and TCE with the property owner’s permission. The sampling results tell property owners about water quality conditions, but the law does not require any action.

Please email remediation@bannockcounty.gov to request sampling or ask for us to stop sampling your well.

Yes. The City of Pocatello provides hookups to City water for drinking water use. Any property owner within the impacted area can connect to City water at any time.

No. A property owner will not be required to hook up to City water. Private wells with groundwater PCE and TCE concentrations above regulatory standards should use a different drinking water source or treat the water.

No reimbursement for City water hookup fees is currently available. The County will tell property owners and tenants about any changes.

You can install granular activated carbon or reverse osmosis treatment options for PCE and TCE at the top of your well. Granular activated carbon absorbs and removes TCE and PCE. Reverse osmosis is a filter- based system that removes TCE and PCE.

You are not required to install wellhead treatment. Using contaminated well water for irrigation and gardening poses a low risk.

Installing well treatment is voluntary. The property owner/tenant would be responsible for installing and paying for well treatment. No reimbursement options are currently available from Bannock County.

Property owners should give a potential buyers or renters their private well sampling results and tell them about sampling activities. Property owners should inform renters of restricted uses.

Amendment Slurry

A liquid mixture of substances that break down groundwater contaminants. Slurries can be injected into the ground to improve breakdown processes for many years.

Contamination

The presence of chemicals in the ground in high enough amounts to pose a risk to human health or the environment.

Consent Order

A legally binding agreement between parties to take action.

Downgradient

The direction of groundwater flow. An area downgradient will receive the groundwater, along with contamination, from an area upgradient. Wells downgradient of the Cell 1 area are at the greatest risk from the groundwater contamination.

Exposure Route

A pathway for a human or animal to come into contact with a chemical. Exposure routes can include breathing, eating, drinking, or skin contact. The most likely exposure routes for humans and TCE or PCE in Bannock County are through breathing or drinking.

Extraction Wells

Wells with pumps under the ground that pull contaminated groundwater above the surface and into the treatment system.

Granular Activated Carbon

A commonly used material in remediation that can remove contaminants from water and vapor. Water or air flows through and the chemicals stick to the surface of the granules. Clean water or air then leaves the system, and the granules are disposed of once there is no more space on their surface for chemicals.

Groundwater

Groundwater is water that exists underground beneath the land surface. Groundwater flowing below the Fort Hall Mine Landfill enters the Lower Portneuf Valley Aquifer, the source of drinking water in Bannock County.

Maximum Contaminant Levels (MCLs)

The U.S. Environmental Protection Agency’s standards for the highest amount of a contaminant allowed in drinking water.

Micrograms per Liter (µg/L)

A unit of measurement for chemicals in water. One µg/L is about one drop of water in a 10,000-gallon swimming pool.

Pilot Study

A pilot study is a small-scale test to assess how a technology or strategy performs at a site. If the pilot study is successful, the technology or strategy may be applied to more areas of the site.

Remediation

Cleaning up environmental contamination. At Bannock County, remediation includes addressing the chemical plume from the landfill. Activities that support remediation include the groundwater remediation system, pilot study, and well monitoring.

Reverse Osmosis

A filtering process that removes contaminants based on size. The filters allow water to pass through the barrier and keeps contaminants on the other side of the barrier.

Risk Assessment

A process that looks at hazards, exposure pathways, and exposure amounts to understand the level of risk to a community.

Sodium Bromide

A safe, naturally occurring substance commonly used as a tracer to study groundwater movement. Learn more about sodium bromide tracer studies here: tracers summaries.

Tracers

Substances commonly used in remediation to explain the direction and speed of groundwater flow. Tracers can be measured at different points in time and locations to understand how contaminants may be moving in the aquifer.

Tetrachloroethene (PCE)

A chemical that dissolves oils and grease, used for dry cleaning and metals degreasing. PCE is found in common consumer products. Visit the Agency for Toxic Substances and Disease Registry’s PCE summary to learn more about PCE.

Trichloroethene (TCE)

A chemical that dissolves oils and grease, used for dry cleaning and metals degreasing. TCE is also used to make adhesives and refrigerant chemicals. Visit the Agency for Toxic Substances and Disease Registry’s TCE summary to learn more about TCE.

Vapor Intrusion

The process of contaminants moving upward from the soil into the air, sometimes entering buildings.

Vinyl chloride

A breakdown product of PCE and TCE. When PCE and TCE degrade, the chemicals may become Vinyl Chloride, which poses a human health risk in drinking water.

Volatile

The ability of a liquid molecule to turn into a gas or vapor. PCE and TCE are volatile compounds, meaning they may be found in the air through vapor intrusion.

2023
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2023

Pilot study to test new clean-up method begins

2019-Present
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2019-Present

Bannock County team studies how to improve clean up

2019
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2019

Bannock County submits new site characterization plan to IDEQ

2018
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2018

Bannock County hires new environmental contractor, CDM Smith

2016
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2016

IDEQ issues new consent order to Bannock County

2014
L
2014

IDEQ determines treatment is ineffective and additional actions are required

2002-Present
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2002-Present

Bannock County constructs and operates groundwater remediation system

1993
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1993

Idaho Department of Environmental Quality (IDEQ) issues consent order to Bannock County

1993
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1993

Bannock County closes Cell #1

1991
L
1991

Groundwater contamination discovered

1979-Present
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1979-Present

Bannock County operates the landfill

1976-1979
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1976-1979

Landfill operation contracted to Snake River Sanitation Company

1976
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1976

Idaho legislation requires solid waste facilities to come under county-level control

1973-1976
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1973-1976

City of Pocatello Sanitation Department operates landfill

1973
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1973

City of Pocatello purchases landfill

1943-1973
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1943-1973

Landfill privately owned and operated

Contact Us

To learn more about the work to clean up Fort Hall Mine Landfill, please email remediation@bannockcounty.gov or you can leave comments through the form below:

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More Information

Contact Information:

Dillon Evans
Bannock County Landfill Manager
208-236-7408
dillone@bannockcounty.us

Tamzen Macbeth
CDM Smith (Environmental Contractor)
Remediation Practice Leader
208-569-5147 macbethtw@cdmsmith.com

Dustyn Walker Idaho Dept. of Environmental Quality
Project Manager
208-236-6160
Dustyn.Walker@deq.idaho.gov

Chris Cathcart Idaho Dept. of Environmental Quality
Senior Hydrogeologist
208-236-6160 Chris.Cathcart@deq.idaho.gov

 

About CDM Smith:

In October 2018, the Bannock County Solid Waste Division partnered with CDM Smith to reevaluate the sources of groundwater contamination from Cell 1 and groundwater remediation system effectiveness. CDM Smith is a privately owned engineering and construction firm with over 40 years of experience cleaning up hazardous waste. They focus on creating solutions to characterize and treat the source of contamination while protecting human health and the environment. CDM Smith’s work identifies where contaminants are and how they move, then designs and implements site-specific strategies to clean them up.  

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