Detecting a leak is difficult
Determining whether a single-shell tank is actively leaking is a complex process because the tanks are buried and because the leaks are relatively small and travel very slowly through the soil.
Workers removed a majority of the liquids in Hanford’s 149 single-shell tanks in the mid-1980s through the early 2000s as part of Hanford’s interim stabilization program. The liquid waste was moved to the site’s 28 double-shell tanks.
Any remaining liquids in the single-shell tanks are mostly entrained within the tanks’ sludge waste, which has a consistency similar to pudding. Over time, some liquid seeped out of both sludge and saltcake in the tanks. Rainwater and snowmelt can also intrude into the tank, adding to the volume of liquid waste that could then leak.
When Energy detects a change in the waste levels in a tank, they use several methods to determine if that tank is leaking waste including:
- A device called an ENRAF – a weight on a cable used to measure the height of the waste in a tank
- Liquid Observation Wells
- Liquid level measurements under the surface of the solid waste
- Drywell monitoring
Energy uses information from all these sources to determine if a leak is actually occurring, or if there is some other explanation for what is happening. For example, decreases in waste levels could result from tank waste releasing gases, or as a result of an instrument malfunction.
In addition, the surface of the waste in a tank can consist of many valleys and hills which might change as waste shifts under monitoring equipment. Energy’s experts evaluate these shifts and other potential causes during the leak assessment process to determine if there is an actual active leak
B-109 leak assessment began July 2020
When monitoring data indicates that a tank might be leaking, Energy is obligated to begin a formal leak assessment process and notify us. Energy notified us in July 2020 that it was beginning a leak assessment for Tank B-109. A leak assessment is a complex process that can take more than a year to complete. We monitor the process and await the results to review what Energy finds.
Notified of B-109 leak in April 2021
Since Energy’s assessment concluded Tank B-109 was leaking, Energy was required by law to notify us that dangerous waste was leaking into the environment. Energy notified us that it had confirmed that B-109 was leaking in April 2021.
Proposed response to the B-109 leak by Energy
Under state and federal law, Energy must take action to stop a tank leak and clean up the contamination caused by the leak. If Energy does not take timely and appropriate action to mitigate an active leak, Ecology can and will take enforcement actions as necessary.
Energy proposed a few minor actions for Tank B-109 in April 2021 that would mitigate some risk, but not address the leak itself. For example, they proposed installing a barrier above the B tank farm to slow down the movement of contamination to the groundwater.
Regulatory authority to protect the environment
The Tri-Party Agreement sets forth the process we and Energy must go through when a tank is determined to be leaking.
Our agency and Energy must first try to agree on how to respond to a leak. If no agreement is reached, we have the authority to issue an Administrative Order dictating the actions Energy must take to stop the tank leak and when those actions must happen.
In this case, we negotiated an Agreed Order with Energy that defines how Energy will respond to the active and future leaks. However, if Energy doesn't comply with the order, we have the authority to enforce the agreement's requirements and deadlines, and to issue civil penalties for noncompliance.
Tank B-109 and Tank T-111 are part of separate tank farms that were constructed between 1943 and 1944.
Both tanks are used to store mixed radioactive and chemically hazardous waste generated from decades of plutonium production.
Energy announced that Tank B-109 was actively leaking on April 29, 2021, following a formal leak assessment process that began in July 2020.
Tank B-109 received reprocessing waste from 1944 until 1976. Most of the tank's drainable liquid wastes were retrieved in 1985 and moved to a double-shell tank as part of Hanford's interim stabilization program.
Today, Tank B-109 holds about 123,000 gallons of waste, most of which is saltcake and sludge, with about 13,000 gallons of liquid. Energy estimates about 560 gallons of waste are leaking per year into the surrounding soil.
Single-shell Tank T-111 was most recently declared leaking in 2013, after earlier leak concerns in the 1970s. Energy chose to install an active ventilation system as a mitigation measure, which operated from July 2015 to April 2019.
In 2019, Energy determined that this system directly connected to Tank T-112, causing inadvertent evaporation from that tank.
Energy halted active ventilation of T-111 because the existing air permit didn't authorize ventilation of Tank T-112. Current liquid level decreases in Tank T-111 are at least as large as they were before and during the active ventilation, indicating that a different leak response action is needed for this tank.
Tank T-111 began receiving reprocessing waste in 1945.
Energy first suspected the tank was leaking in 1974. Between 1974 and 1976, workers transferred 63,000 gallons of waste to other tanks as part of a tank stabilization effort. Most of the tank’s drainable liquid wastes were retrieved and moved to a double-shell tank in 1995 as part of Hanford’s interim stabilization program.
In 1995, T-111 also underwent interim stabilization.
In 2013, Energy found T-111 had one of the highest decreases in liquid levels, among the single-shell tanks.