From 1944 through 1988, the production of plutonium at Hanford generated about 525 million gallons of radioactive and hazardous waste. Some of the waste was dumped directly into the soil, some was encased in drums or other containers and buried, and some was stored on-site, underground in 149 SSTs and 28 DSTs. This section describes the history of the Hanford tanks, the contents of the tanks, and tank regulations and oversight. The first underground storage tanks at Hanford were SSTs and were built from the 1940s through the mid-1960s. The SSTs consist of an outer concrete wall lined with one layer of carbon steel and were built with a design life of approximately 25 years. While a tank’s design life is not a firm deadline beyond which a tank is no longer viable, site engineers at the time considered design life a reasonable estimate of how long a tank could be expected to effectively contain radioactive and hazardous waste. In the 1940s and 1950s, site contractors did not regard the tanks as a permanent solution to the waste produced at Hanford and viewed tank failures as inevitable. It was assumed that as the tanks failed, new tanks would be constructed to store the waste until a more permanent disposal solution could be developed. Beginning in the 1960s, DOE began reporting that some of the SSTs were leaking waste, and DOE estimates that as many as 61 SSTs may have leaked a total of over 1 million gallons of waste into the ground. After DOE discovered leaks in some of the SSTs, a new tank design using two carbon-steel shells (referred to as DSTs) was adopted. From 1968 through 1986, DOE built 28 DSTs, each with a storage capacity of 1 million gallons or more and each with a design life ranging from 20 to 50 years. (See apps. I - III for design life data for each tank.) The primary design difference between Hanford’s single- and double-shell underground waste storage tanks—a second carbon-steel lining, or shell, within the outer concrete housing to provide secondary containment of the waste—improved DOE’s ability to monitor and assess the tanks’ integrity and contents. As shown in figure 1, the two shells in the DSTs are separated by about 3 feet of space, or annulus, which enables workers to use remote leak detection sensors and remotely operated cameras to see between the inner and outer shells, thereby making it possible to find signs of corrosion or leaks before waste breaches the outer shell and leaches outside the tank structure. Beginning in the 1970s, to minimize the risks of leaking tanks, DOE began transferring much of the liquid waste from the SSTs to the DSTs. This process consisted of removing (1) the liquid (more mobile) waste first and then (2) the rest of the waste from the SSTs, thereby effectively emptying the SSTs. The first part of this process—removing liquid waste from the SSTs and transferring it to DSTs—is referred to as interim stabilization and was largely completed by 2005. The interim stabilization for each tank was considered complete, and DOE could stop pumping liquid waste, when DOE and Ecology agreed that the following criteria were metless than 5,000 gallons of free standing liquid waste remained, less than 50,000 gallons of drainable liquid waste (liquid waste interspersed within the solid waste) remained, and pumping was no longer effective. The second part of the process—removing the remaining waste from the SSTs and transferring it to DSTs—began in 2003 and is still under way. This work is governed by two main compliance agreements: (1) the 1989 Hanford Federal Facility Agreement and Consent Order, or Tri-Party Agreement (TPA), an agreement between DOE, Ecology, and the Environmental Protection Agency and (2) a 2010 consent decree. Under the consent decree, DOE is required to retrieve waste from 19 tanks (transferring the waste to DSTs) and begin operating the WTP and treating waste by 2022. The TPA requires DOE to retrieve the waste from all of the SSTs by no later than 2040 and to have all waste retrieved from all DSTs and treated by 2047. As of July 2014, DOE had completed the retrieval and transfer of waste from 12 of the SSTs into DSTs. In addition to concerns about tank leaks, DOE is also monitoring tanks for water intrusion from rain and melting snow that can enter the underground tanks through the piping connected to them. Water intrusions can increase the consequences of waste leaks and also mask tank leaks, as waste levels in the tanks could remain the same even as waste was leaking into the ground. According to DOE documented reviews of the tanks, DOE has been aware of water intrusions in some SSTs since the 1980s and has detected intrusions into the annulus of some DSTs since the 1990s. The waste stored in the tanks at Hanford generally sits in layers and comes in a variety of forms, depending on its physical and chemical properties. The waste in the tanks takes the following three main forms, which are illustrated in figure 2: Supernate. Above or between the denser layers may be liquids composed of water and dissolved salts that are called supernate. Supernate comprises 21.4 million gallons of the waste in the Hanford tanks and about 24 percent of the radioactivity. Saltcake. Above the sludge may be water-soluble components, such as sodium salts, that crystallize or solidify out of the waste solution to form a moist sandlike material called saltcake. Saltcake comprises 24 million gallons of the waste in the Hanford tanks and about 20 percent of the radioactivity. Sludge. The denser, water-insoluble components of the waste generally settle to the bottom of the tank to form a thick layer known as sludge, which has the consistency of peanut butter. Although sludge makes up the smallest portion of waste in the Hanford tanks (10.7 million gallons), it comprises over half (56 percent) of the total radioactivity in the tank waste. The tanks contain a complex mix of radioactive and hazardous waste in both liquid and solid form. About 46 different radioactive elements—by- products of chemically separating plutonium from uranium for use in nuclear weapons—represent the majority of the radioactivity currently in the tanks. Some of these elements lose most of their radioactivity in a relatively short time, while others will remain radioactive for millions of years. The rate of radioactive decay is measured in half-lives, that is, the time required for half the unstable atoms in a radioactive substance to disintegrate, or decay, and release their radiation. The half-lives of radioactive tank constituents differ widely. The vast majority (98 percent) of the radioactivity of the tank waste comes from two elements, strontium- 90 and cesium-137, which have half-lives of about 29 and 30 years, respectively. The remaining radioactive elements, which account for about 2 percent of the waste’s total radioactivity, have much longer half- lives. For example, the half-life of technetium-99 is 213,000 years, and that of iodine-129 is 15.7 million years. The hazardous wastes in the tanks include various metal hydroxides, oxides, and carbonates. Some of the chemicals—including acids, caustic sodas, solvents, and toxic heavy metals, such as chromium—came from chemically reprocessing spent nuclear fuel to extract weapons-grade plutonium. Altogether, about 240,000 tons of chemicals were added to the tanks from the 1940s to the mid-1980s. A majority of the chemicals were added to neutralize acids in the waste. Other chemicals, such as solvents and several organic compounds, were added during various waste extraction operations to help recover selected radioactive elements (uranium, cesium, and strontium) for reuse. These hazardous chemicals are dangerous to human health, and they can remain dangerous for thousands of years. DOE’s storage of waste at Hanford is governed by federal and Washington State laws and regulations. DOE’s tank waste cleanup program at Hanford is governed by, among other things, the Resource Conservation and Recovery Act of 1976, as amended (RCRA), as implemented by Washington under its Hazardous Waste Management Act, and the Atomic Energy Act of 1954. RCRA governs the treatment, storage, and disposal of hazardous waste and the non-radioactive hazardous waste component of mixed waste. The tank waste at Hanford is considered mixed waste because it contains both chemically hazardous For the chemically hazardous waste in and certain radioactive materials.the tanks, as shown in figure 3, RCRA establishes the following three key requirements (subject to certain limited exceptions): Tank integrity. Under RCRA, tanks must have secondary containment—that is, a second shell—and an integrity assessment must be conducted by a qualified professional engineer to assess whether the tanks are fit for use. Leak detection. RCRA requires a leak detection system to be in place for each tank that will detect the failure of either the primary and secondary containment structure or any release of hazardous waste in the secondary containment system within 24 hours, or at the earliest practicable time. Data gathered from monitoring and leak detection equipment must be inspected at least once each operating day to ensure that the tank system is being operated according to its design. Leak response. Within 24 hours after detection of a leak or, if the owner or operator demonstrates that that is not possible, at the earliest practicable time, RCRA requires the tank owner, among other things, to remove as much of the hazardous waste or accumulated liquid as is necessary to prevent further release of hazardous waste to the environment and allow inspection and repair or closure of the tank system to be performed. If the release was to a secondary containment system, all released materials must be removed within 24 hours or in as timely a manner as is possible to prevent harm to human health and the environment. To address these RCRA requirements, DOE conducts a variety of assessments and monitoring activities. Regarding tank integrity, DOE conducted integrity assessments for the SSTs in 2002 and the DSTs in 2006. To address the leak detection monitoring requirement, for the DSTs, DOE has one waste level monitor installed inside the primary tank space and three waste level monitors in the annulus. These monitors collect waste level data on a daily basis. For the SSTs, because they were built decades before the enactment of RCRA, they do not have secondary containment. As such, DOE has determined that the SSTs cannot readily be made compliant with current regulations and these tanks were determined to be “unfit for use.” Under RCRA, unfit for use tanks are no longer allowed to store waste and must generally be closed. DOE plans to ultimately close the tank farms in accordance with tank farm closure permits to be issued by Ecology. In the meantime, DOE monitors the SSTs under modified operating procedures, including modified leak Under detection and monitoring requirements as agreed with Ecology.these modified procedures and additional DOE operating specifications, the majority of the SSTs are required to be monitored weekly, quarterly, or annually for leaks and intrusions depending on DOE’s knowledge of the condition of the tanks and the type and amount of waste inside them. In 2009, DOE developed an emergency pumping guide outlining procedures for responding to leaks in DSTs, to implement the RCRA requirement that the tank system owner/operator must within 24 hours after detection of the leak or, at the earliest practicable time, remove as much waste as necessary to prevent further releases. DOE’s recent assessments of the SSTs and DSTs determined that they are in worse condition than DOE had assumed when developing its 2011 System Plan schedule for emptying the tanks.series of assessments in 2013 and 2014, DOE concluded that water is intruding into at least 14 SSTs and that at least 1, T-111, is actively leaking. For DSTs, DOE concluded in 2012 that waste was leaking from the primary shell in tank AY-102 and subsequently found that 12 other DSTs have construction flaws similar to those that contributed to the leak in AY-102. According to recent DOE reviews of the tank, water has intruded into the space between the inner and outer shells of tank AY-102 and another tank nearby. In 2013 and 2014, DOE completed assessments of the SSTs and found that they are in worse condition than had been previously believed. As of 2005, DOE and Ecology agreed that the interim stabilization process had reduced the risk of leaks in SSTs, which led DOE, with concurrence from Ecology, to reduce the required frequency of monitoring from daily to quarterly or annually depending on the condition of the tank and the amount of liquid waste inside. However, concerns about historical water intrusions led DOE to reexamine all 149 SSTs in 2011 to determine the extent of the intrusions. This reexamination, which concluded in 2014, confirmed that water was intruding into at least 14 tanks and that the intrusions were adding from less than 10 to more than 2,000 gallons of water annually to each tank. According to a DOE report on intrusions, water intrusion creates additional liquid waste in the tanks as the new water becomes contaminated by the waste in the tanks. Furthermore, water intrusions can affect the level of tank waste, making it difficult to ensure that a tank is not leaking. Officials on an expert panel, convened by DOE in 2009 to assess the condition of the SSTs, concluded in August 2014 that significant amounts of drainable liquid still remain in the SSTs and removing that liquid and preventing future water intrusions should be a high priority. In addition to increasing waste levels in several tanks, DOE found in 2013 that waste levels appeared to be decreasing in several tanks and subsequently confirmed that at least one SST, tank T-111, was actively DOE’s report on the tank leak indicates leaking waste into the ground.that the leak likely began in 2010. According to DOE officials, waste is leaking at a rate of approximately 640 gallons annually, and DOE continues to monitor the leak in tank T-111. DOE has also confirmed that T-111 is one of the SSTs experiencing intrusions. Though the tank is leaking, according to DOE officials, DOE is not required by regulation to remove the liquid waste from T-111 because the amount of liquid waste in the tank does not exceed the interim stabilization criteria and because there are no current requirements to reestablish compliance with interim stabilization criteria if conditions in a tank change. Regarding DSTs, prior to the discovery of the leak in AY-102 in 2012, DOE had assumed that all DSTs were sound for storing waste. In 2006, all 28 DSTs were examined by a qualified professional engineer, as required under RCRA, and deemed fit for use. In a 2010 report on the integrity of the DSTs, DOE reaffirmed their fitness for continuing to store waste. However, after the 2012 leak was discovered, in March 2014, DOE reported the discovery of a second accumulation of waste in a different location in the annulus of tank AY-102. As of August 2014, DOE reported that more than 35 gallons of waste had leaked from the primary shell of AY-102 into the annulus at a rate of about 3 gallons per month. To date, no waste has been detected outside of the secondary tank shell, according to DOE officials. DOE is still investigating the factors that caused the AY-102 leak and the extent to which other DSTs may be susceptible to the same factors. DOE reported in October 2012 that tank construction flaws and corrosion in the bottom of the tank stemming from the type of waste and the sequence in which it was loaded into the tank AY-102 were the likely causes for the According to a 2014 expert panel reviewing the leak, leak in AY-102.corrosion was among the likely causes of the leak. The panelists concluded that the corrosion likely occurred as a result of water collecting under the tank before it was fully enclosed and during a 6-year outage of the ventilation system in the annulus from 1991-1997, rather than as a result of the waste loading sequence. Beginning in 2013, DOE examined the other 27 DSTs to determine the extent to which they had construction flaws similar to AY-102. In a series of reports issued between July 2013 and February 2014, DOE reported that at least 12 of the other 27 DSTs have similar construction flaws. However, DOE has not yet assessed the extent to which the factors that led to corrosion that may have caused the leak in AY-102 are also present in the remaining 27 DSTs. DOE also determined in 2012 that water was likely intruding into the annulus of at least 2 DSTs, including the leaking tank AY-102. This is not the first time DOE has detected intrusions in the DSTs. In 1991, DOE first reported unexplained moisture in DSTs AY-101 and AY-102, the oldest DSTs on the site. Since then, DOE has periodically monitored and reviewed the status of this moisture, concluding in 2001 that water intrusions through corroded tank equipment were the likely cause. After removing some of the suspected connections and further inspecting the two tanks with video cameras, DOE concluded in 2009 that the water intrusions had stopped. However, routine inspections of the tanks in 2012 revealed that water may still be seeping into the annulus of both tanks. According to DOE officials, an investigation into this issue is ongoing. In the 2011 System Plan, DOE stated that the DSTs play an integral role in the tank waste cleanup effort. Following the discovery of the leaks in tanks T-111 and AY-102, and water intrusions in some SSTs, DOE has undertaken or planned several actions. For the SSTs, DOE has, among other things, performed additional inspections and temporarily increased the frequency of monitoring the tank waste levels from annually or quarterly to monthly. For the DSTs, DOE has conducted additional inspections, modified its inspection procedures, convened an expert panel to examine its DST leak detection process, and developed a pumping plan for AY-102. In response to the leak in tank T-111 and intrusions in other SSTs, DOE has taken several actions, including the following: Increased monitoring and conducted additional inspections. In 2012, when the leak was initially discovered in T-111, DOE increased the leak detection monitoring for the tank from annually to weekly. In addition, for 19 other SSTs that were under review for decreasing liquid levels, DOE increased the leak monitoring frequency from annually or quarterly (depending on the tank) to monthly. DOE maintained weekly leak detection monitoring for T-111, but in April 2014 went to monthly monitoring. According to a DOE official, the monthly monitoring was deemed sufficient to understand the relationship between the intrusion and the leak and the monitors are always in place and data are collected more frequently than the monthly requirement. Additionally, monitoring procedures for the other SSTs have since returned to their normal frequency of annual monitoring for intrusions only. For the 14 SSTs with confirmed intrusions and the 5 that do not meet interim stabilization criteria, DOE has placed them on a quarterly monitoring regime. DOE also performed additional inspections of the tanks with decreasing liquid levels but, after further analysis, concluded that none of those tanks were likely leaking. Modified waste analysis procedures. As noted above, as part of its reexamination of SST waste levels, DOE discovered flaws in its methods for reviewing data on SST tank waste levels that it uses to monitor the tanks for leaks and intrusions. DOE officials determined that their method for reviewing tank waste data was flawed and masked increases and decreases in the waste levels in the SSTs that may have been due to water intrusions and leaks. In response, DOE modified its waste level monitoring methodology and procedures for analyzing waste data. For example, in 2013, DOE established a systems engineering group responsible for monitoring waste levels in all tanks. DOE is also developing training based on the modified waste level monitoring methodology, including guidance on tank waste data interpretation, trend analysis, documentation requirements, and review and approval procedures for changes in waste levels. Following the discovery of the leak in AY-102, DOE has taken or planned several actions including the following: Conducted additional inspections and modified inspection procedures. Following the discovery of the leak in AY-102, DOE performed video inspections of the annulus of 6 of the 12 DSTs with construction histories similar to AY-102. The video inspections, which according to a DOE official in the past only examined a portion of the annulus, examined between 95 and 100 percent of the annulus in each of the tanks.continue these full video inspections for the remaining 21 DSTs over the next several years. In addition, in April 2014, DOE formally modified its inspection procedures by shortening the time between inspections from every 5 to 7 years to every 3 years. In addition, in June 2014, DOE began soliciting proposals to award a contract for another independent assessment of the integrity of the DSTs to be completed in 2016. According to DOE officials, DOE plans to Convened expert panel. DOE convened an expert panel to review its DST leak detection procedures and make recommendations for improvement. This panel met three times and developed preliminary findings and suggested program improvements. One of the preliminary findings was that additional DST leaks cannot be ruled out given current DST integrity program limitations and the extended schedule for the construction and operation of the WTP. During the panel’s most recent meeting in August 2014, members of the panel said that more analysis needs to be done to understand the factors that led to the leak in AY-102 and the extent to which the other DSTs are susceptible to similar factors. Developed AY-102 pumping plan. If a leak is detected, RCRA requirements call for the hazardous waste or accumulated liquid to be retrieved from the tank to the extent necessary to prevent further releases within 24 hours or as soon as practicable and to allow inspection and repair. In addition, DOE’s emergency pumping guide outlines steps to “immediately” remove waste from a leaking DST. DOE officials stated that this guide did not anticipate a leak from the bottom of the primary shell of a tank such as the one occurring in AY- 102. Instead, DOE proposed that the waste not be retrieved until at least 2016, maintaining that that was as soon as it could practicably retrieve the waste due to concerns that doing so would cause the temperature of the tank to rise to dangerous levels without liquid waste to act as a cooling agent. In addition, DOE noted in its plan that it needed to procure and install additional equipment in order to pump waste out of the tank. In response to DOE’s submitted plan, Ecology issued an administrative order to compel DOE to begin pumping waste out of AY-102 by September 1, 2014, and retrieve enough waste to allow for an inspection to determine the cause of the leaks no later than December 1, 2016. The two sides reached a settlement agreement in September 2014, under which DOE is to begin pumping the waste out of AY-102 no later than March 2016 and to have the waste removed by March 2017—over 5 years after the leak was first discovered. DOE’s current schedule for retrieving the waste from the tanks (developed in 2011), which includes transferring waste from SSTs to DSTs and treating the waste in the DSTs, does not take into account the worsening conditions of the tanks or the delays in the construction of the WTP. The leak in AY-102 combined with planned waste transfers has reduced the available DST space, and DOE’s plans to create additional space remain uncertain. Future leaks and intrusions, which become more likely as the tanks’ conditions worsen, would place additional demands on the limited available DST space, and it is unclear how DOE would respond. According to DOE, recent efforts to evaporate some of the water from the waste have already freed up 750,000 gallons of DST space. In addition, in March 2014, DOE announced that it plans to indefinitely delay construction of the key WTP facilities needed to retrieve and treat tank waste for disposal until technical issues are resolved. As a result, it is unclear how long waste will remain in the tanks. However, without an analysis of the extent to which the factors which may have led to the leak in AY-102 are present in the other DSTs, DOE cannot be sure how long its DSTs will be able to safely store the waste. The free space available in the DSTs is currently limited, and operational requirements and planned transfers from the SSTs constrain DOE’s ability to respond to future emergencies, such as leaks. As shown in figure 4, SSTs hold a total of about 29 million gallons of waste and, as noted above, have been deemed “unfit for use” under RCRA and therefore cannot be used for storing additional waste. The DSTs currently hold a total of about 27 million gallons of waste, leaving about 5.3 million gallons of available space for waste to be transferred from other tanks. However, DOE policy and planned waste transfers further reduce the amount of space available. As shown in figure 5, about 2.5 million gallons of the 5.3 million gallons of empty space is reserved by DOE for safety purposes, for emergency space if necessary, and to enable DOE to more easily transfer waste among tanks. In addition, planned waste transfers from SSTs (about 1.8 million gallons) and AY-102 (about 800,000 gallons) will further reduce available DST space (see fig. 5). Specifically, DOE plans to first empty an additional 15 SSTs, containing a total of approximately 1.8 million gallons of waste, into DSTs by 2022. Second, DOE plans to pump all of the approximately 800,000 gallons of waste in AY-102 into other DSTs no early than 2016. As a result of these planned transfers and operational requirements, about 200,000 gallons of storage space is actually available in the DSTs. DOE officials said that they plan to restart an evaporator facility at Hanford that could reduce the overall amount of waste in the tanks and result in 3 million gallons of additional DST space. This facility, which began operating in 1973 and was designed to operate for 25 years, has not operated since 2010 and was only recently restarted by DOE. According to DOE officials, since restarting the evaporator in September 2014, DOE has reduced the waste volume by over 750,000 gallons. In addition to these scheduled waste transfers, future leaks and intrusions, which become more likely as the tanks’ condition worsens, would require DOE to pump more waste and place additional demands on the limited remaining DST space. Both DOE and Ecology have reported that leaving waste in the tanks past their design life increases the risk of leaks over time. Similarly, the panel of experts that DOE convened to review the AY-102 leak concluded in May 2014 that, given the extended time frames for the cleanup mission and the growing concerns about the integrity of the tanks, additional leaks cannot be ruled out. Such leaks and intrusions could place further demands on the available space in the DSTs because when leaks occur, DOE is required by RCRA and associated tank monitoring and pumping requirements, as described below, to pump hazardous waste from these tanks into the already limited space available in the nonleaking DSTs. For example, if a leak is detected in a SST that exceeds interim stabilization criteria (i.e., it has more than 5,000 gallons of freestanding liquid or 50,000 gallons of drainable liquid waste), DOE is then required by modified leak detection and monitoring requirements as agreed with Ecology to install emergency pumping equipment and begin pumping the liquid waste out of the tank as soon as practicable. At least five SSTs currently fall into this category because they have exceeded the amount of liquid waste allowed under interim stabilization (likely as a result of water intrusion, according to DOE officials). Similarly, if another DST begins to leak, DOE is required by RCRA to remove the hazardous waste or accumulated liquid from the tank to the extent necessary to prevent further releases within 24 hours or as soon as practicable. The only RCRA compliant alternative currently available for storing this retrieved waste is into the limited space available in the nonleaking DSTs. According to the DOE official responsible for managing Hanford’s tank operations, given the current constraints on available DST space, if another DST was to fail before additional DST space is available, DOE would have nowhere to move the waste. However, according to DOE officials, DOE currently has no plans to build new tanks and estimates that it would take about 8 years before the new tanks would be available to receive waste. In March 2014, DOE reported that unresolved technical issues could prevent the WTP from operating safely as currently designed. Under the existing TPA and consent decree, DOE is required to begin operating the WTP and treating waste in 2022, to have retrieved all waste from the SSTs by 2040, and to have all waste retrieved from all DSTs and treated by 2047. DOE reported in March 2014 that, until the technical uncertainties are resolved, it is not possible to predict when the WTP will be completed. In addition, DOE has proposed building at least two new waste processing facilities to allow waste treatment to begin while it is resolving the WTP’s technical uncertainties. One of the two facilities would, if constructed, treat some of the low-activity waste in the tanks. According to DOE officials, this facility would be operational no later than December 2022 and would make available about 1.3 million gallons of DST space after the first 3 years of operation. DOE has not estimated the impact of the WTP delay on its tank management plans, but delays in the schedule to retrieve waste from the SSTs are already occurring. Before its decision to delay the WTP, in a series of letters to Ecology from November 2011 to September 2014, DOE stated that it would likely miss the scheduled milestones in the consent decree, including milestones for completing the WTP and emptying waste from the SSTs. DOE further reported in March 2014 that delays in the WTP will affect the schedule for retrieving waste from the tanks but that, until the technology it is developing to treat the tank waste in the WTP can be demonstrated to work as intended, it is impossible to estimate what the impact will be on the retrieval of waste from the tanks. DOE cannot reliably update its scheduled deadlines for retrieving waste from tanks without considering the impact of the WTP delay. The technical challenges at WTP and the continued uncertainty about the schedule for retrieving and treating the waste mean that the overall cleanup mission will continue to depend on the integrity of the DSTs. However, the extent to which the DSTs can continue to safely store waste is unknown. In the 2011 System Plan, DOE stated that the DSTs play an integral role in the tank waste cleanup effort. members of DOE’s 2014 expert panel, convened to examine the integrity of the DSTs, have stated that corrosion is a threat to DST integrity, and the expert panel also highlighted deficiencies in DOE’s understanding of corrosion in all of the DSTs. The panel officials concluded in August 2014 that more work needs to be done to better understand the factors that led to the corrosion in AY-102. However, as noted previously, DOE has not examined the other DSTs for the same corrosion factors that may have lead to corrosion in AY-102 and therefore lacks information about the extent to which the other 27 DSTs may also be susceptible to similar corrosion. As a result, DOE lacks assurance that these tanks will be available for use through the end of the cleanup mission, as DOE’s 2011 System Plan contemplates, and cannot reliably update its schedule for emptying the SSTs. In 2001, DOE established a DST Integrity Program to implement controls and inspections to ensure that the DSTs will be available for use through the end of the cleanup mission. All of the SSTs and DSTs will be well beyond their design life before they are emptied. Of the 137 SSTs that are still storing waste, all are currently decades beyond their design life, and all but 13 of them would be at least 40 years beyond their design life before being emptied under DOE’s existing schedule for emptying the tanks. While the design life of the DSTs varies, 4 of the 28 DSTs are already past their design life, and under the current TPA milestones, all DSTs are expected to be well beyond their design life by the time they are scheduled to be emptied. (See app. I and III for design life data for each SST and app. II for design life data for each DST. Figure 6, an interactive figure in appendix I, shows a timeline of all Hanford SSTs. Appendix III, table 1, is the noninteractive, printable version of figure 6.) DOE does not have plans to construct additional storage to address its long-term storage needs and the risks presented by the aging tanks. DOE has looked at options for building new tanks to address the constraints on DST space if the cleanup mission were to take significantly longer than currently planned. DOE has developed a rough estimate of the time and cost that would be required to build additional tanks. Specifically, in 2011, Ecology asked DOE to include the option of building new tanks in an update to its System Plan. In response, DOE developed a rough estimate for how much it would cost to build 8 additional storage tanks, if necessary. DOE estimated that doing so would cost about $800 million and would take about 8 years to complete. According to the System Plan, this was a rough order of magnitude estimate and a more detailed estimate would be required before a decision to build new tanks could be considered. In 2012, DOE issued its final EIS for Hanford, which included discussion of several tank waste cleanup alternatives that would have involved building additional DSTs as part of the response to delayed cleanup schedules. DOE has recently taken and has plans for taking additional steps to improve its tank monitoring and inspection procedures at Hanford and is in the process of reassessing the integrity of the DSTs at the site. However, these steps do not address the longer-term concerns about leaving waste in the aging tanks indefinitely. Specifically, DOE lacks specific information about the condition of the DSTs, including whether the factors that may have led to corrosion contributed to the leak in AY- 102 may affect other tanks which are already many years beyond their design life. Given the current condition of the tanks, it is unclear how long they can safely store the waste. Moreover, following the leak in AY-102, available DST space—which is essential to DOE’s tank management plans—is increasingly limited, constraining DOE’s ability to respond to potential future leaks and protect human health and the environment. It is unclear, however, whether DOE has enough DST space available to address current and future waste transfers. As we mentioned earlier, DOE officials responsible for managing Hanford’s tank operations said that given the current constraints on available DST space, if another DST was to fail, DOE may have nowhere to move the waste. Additional space, either from treating waste or building new tanks, is still at least 8 years away assuming DOE’s schedule estimates for these projects are accurate, although DOE has begun recently to free up some DST space by restarting its evaporator facility. Notably, responding to tank leaks can take many years even when there is available DST space, as the leak in AY-102 illustrates. By developing a more a detailed and up-to-date schedule estimate for emptying the tanks, DOE will be in a better position to consider its waste storage needs and need for new tanks. As the tanks age, there will be a continued and increasing risk of tank failure that can only be permanently addressed by emptying the existing SSTs and DSTs. Given the long-standing technical problems facing the WTP, it is highly uncertain when waste treatment operations could begin to create significant available space in the DSTs. However, creating capacity to move some of this waste to RCRA-compliant tanks would allow DOE to respond to future leaks and ensure it has sufficient space for treatment operations once WTP is completed. To ensure that DOE’s long-term plans for storing waste in the existing SSTs and DSTs at Hanford consider the condition of the tanks and the WTP construction delay, we recommend that the Secretary of Energy take the following three actions: Assess the extent to which the factors that may have led to corrosion in AY-102 are present in any of the other 27 DSTs. Update the schedule for retrieving waste from the tanks, taking into the impact of the delays in the WTP, the risks associated with continuing to store waste in aging tanks, and an analysis of available DST space. Assess the alternatives for creating new RCRA-compliant tank space for the waste from the SSTs, including building new DSTs. We provided DOE with a draft of this report for its review and comment. In its written comments, reproduced in appendix IV, DOE agreed with the report and its recommendations. DOE also provided technical comments that were incorporated, as appropriate. As agreed with your office, unless you publicly announce the contents of this report earlier, we plan no further distribution until 30 days from the report date. At that time, we will send copies of this report to the appropriate congressional committees; the Secretary of Energy; the Director, Office of Management and Budget; and other interested parties. In addition, this report will be available at no charge on the GAO website at http://www.gao.gov. If you or your staff members have any questions about this report, please contact me at (202) 512-3841 or trimbled@gao.gov. Contact points for our Offices of Congressional Relations and Public Affairs may be found on the last page of this report. GAO staff who made major contributions to this report are listed in appendix V. Online, roll your mouse over each year in the figure for additional information. For a printable version, see appendix III, page 30. Figure 7 shows design life data for double-shell tanks. Appendix III: Age and Retrieval Schedule for Hanford Single-Shell Tanks (Corresponds to Fig. 6) Table 1 lists information contained in interactive figure 6. In addition to the individual named above, Dan Feehan, Assistant Director; Mark Braza; John Delicath; Scott Fletcher; Rich Johnson; Jeff Larson; Armetha Liles; and Kyle Stetler made key contributions to this report.

Summary: DOE recently reported that nuclear waste is leaking from two of its underground storage tanks (T-111 and AY-102) at Hanford and that water was intruding into AY-102 and other tanks. Also, DOE has been experiencing delays in the construction of the WTP, a collection of facilities that are to treat the tank waste for disposal. These recently reported leaks and intrusions, combined with construction delays, have raised questions among regulators, the public, and Congress about the risks posed by continuing to store waste in the aging tanks. GAO was asked to report on the tank waste cleanup program. This report examines: (1) the condition of the tanks, (2) actions DOE has taken or planned to respond to the recent tank leaks and water intrusions, and (3) the extent to which DOE's tank management plans consider the condition of the tanks and the delays in completing construction of the WTP. GAO obtained and reviewed relevant reports concerning the leaks, the status of the tanks, and the volumes of waste and available space in the tanks. GAO toured the site and interviewed DOE officials and responsible contractors. From 2012 to 2014, the Department of Energy (DOE) assessed the physical condition of the 177 storage tanks at its Hanford, Washington, site in which it stores about 56 million gallons of nuclear waste and found them to be in worse condition than it assumed in 2011 when developing its schedule for emptying the tanks. For the 149 single-shell tanks (SST), DOE previously pumped nearly all of the liquid waste out of the SSTs into the 28 newer double-shell tanks (DST) to reduce the likelihood of leaks. However, after detecting water intruding into several SSTs, DOE reexamined them all and found that water was intruding into at least 14 SSTs and that 1 of them (T-111) had been actively leaking into the ground since about 2010 at a rate of about 640 gallons annually. Regarding the DSTs, in 2012, DOE discovered a leak from the primary shell in tank AY-102. DOE determined that the leak was likely caused by construction flaws and corrosion in the bottom of the tank. DOE found that 12 DSTs have similar construction flaws but has not determined the extent to which the other 27 DSTs are subject to the same corrosion that likely contributed to the leak in AY-102. In response to the waste leaks and water intrusion, DOE has taken or planned several actions. For SSTs, DOE conducted additional tank inspections and temporarily increased the frequency of monitoring the tank waste levels from annually or quarterly to monthly. In addition, after finding flaws in its methods to monitor for leaks and intrusions, DOE modified its methods, which it believes may lead to more effective monitoring. For DSTs, DOE increased the frequency (from every 5 to 7 years to every 3 years) and scope of its tank inspections and convened a panel of experts to evaluate existing tank monitoring and inspection procedures. DOE also plans an independent assessment of the integrity of the DSTs (scheduled to be completed no later than 2016). DOE's current schedule for managing the tank waste does not consider the worsening conditions of the tanks or the delays in the construction of the Waste Treatment and Immobilization Plant (WTP), a facility being constructed to treat the waste and prepare it for final, long-term disposal. First, the leak in AY-102 combined with planned waste transfers from SSTs has reduced the available DST tank storage capacity. Future leaks and intrusions, which become more likely as the tanks' condition worsens, would place additional demands on the already limited DST storage space, and it is unclear how DOE would respond. According to DOE, recent efforts to evaporate some of the water from the waste have already freed up 750,000 gallons of DST space. Second, in March 2014, DOE announced further delays in the construction of the WTP and that these delays will affect the schedule for removing waste from the tanks. However, DOE has not estimated the impact of the WTP delays on its schedule to remove the waste from the tanks. As a result, DOE cannot estimate how long the waste will remain in the aging tanks. Also, DOE officials and members of a 2014 expert panel convened to examine the integrity of the DSTs have said that corrosion is a threat to DST integrity, and, according to the panel, that there are deficiencies in DOE's understanding of corrosion in all of the DSTs. DOE lacks information about the extent to which the other 27 DSTs may also be susceptible to corrosion similar to AY-102. Without determining the extent to which the factors that contributed to the leak in AY-102 were similar to the other 27 DSTs, DOE cannot be sure how long its DSTs can safely store waste. GAO recommends that DOE assess the extent to which other DSTs have corrosion factors similar to AY-102, update its schedule for removing waste from the tanks, and assess the alternatives for creating additional DST space. DOE agreed with this report and its recommendations.