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9 Monitoring, Remediation, and Risk Technical Elements As noted in Chapter 3, detailed science and technology (S&T) plans for the Remediation, Monitoring, and Risk Technical Elements were being developed during the committee's information gathering for this report. S&T plans for the Remediation and Monitoring Technical Elements will not be issued until fiscal years 2002 and 2003,4 respectively, and the S&T plan for the Risk Technical Element exists only in draft form (DOE, 2000d).2 Consequently, the committee was unable to obtain detailed descriptions of the projects under these technical elements, and it is therefore able to provide only a general overview and assessment of the planned work. The main sources of information used in this assessment are the Integration Project Roadmap (DOE, 2000a) for the Remediation and Monitoring Technical Elements and that roadmap and subsequently issued risk S&T plan (DOE, 2000cl) for the Risk Technical Element. A summary of the S&T activities and projected budgets are given in Table 9.1 . MONITORING AND REMEDIATION TECHNICAL ELEMENTS The Monitoring Technical Element and the Remediation Technical Element have only one planned S&T activity each, and they are scheduled for completion in 2003. The S&T activity for the Remediation Technical Element, identification, development, and deployment of improved groundwater Remediation strategies, includes two projects to develop an improved technical basis for remediation of contaminant plumes at the Hanford Site. In the first project (Rem-13), the distribution of carbon tetrachloride plumes in the 200 West Area (see Chapter 2) will be investigated, and the results will be used to assist in the development of a strategy for corrective actions. The planned work is to include geophysical, geochemical, and modeling studies to assist with the selection and deployment of remediation technologies. These plans were originally scheduled to be issued in fiscal years 2001 and 2002, respectively, but were delayed because of funding cutbacks. The committee received a copy of this draft in October 2000. 3As noted in previous chapters, the projects under each of the six activities are given these identification numbers in DOE (2000a, Table 4-1~. 125

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126 Science and Technology for Environmental Cleanup TABLE 9.1 Summary of S&T Activities and Planned S&T Projects Under the Monitoring Remediation, and Risk Technical Elements S&T Activity S&T Project Objectives Project Hanford EMSP Projects duration Funding Funding Planned (fiscal (thousand (thousand years) dollars) dollars) Monitoring Identification, development, and deployment of improved environmental monitoring Remediation Idenfflcation, development, and deployment of improved groundwater remediabon strategies Risk 1 2 Investigate and develop strategies and technologies for environmental monitoring of multiple media Investigate the distribution of DNAPLs in the 200 Area and contaminant plumes in the 100 Area, and assist in the development of corrective strategies 2001-2003 0 2,600 2001-2003 0 5,300 2001 150 0 General risk 1 Develop methods to assessment identify, involve, and build consensus among stakeholders on desired foci for the risk technical element Ecological risk 11 Develop methods to 2001-2003 9,900a 0 assessment predict the impacts of exposures to contaminants from the Hanford Site on selected species Economic risk 5 Develop methods and 2001-2003 3,300& 0 assessment data for predicting how human populations and economies will respond from potential exposures of environmental contamination at the Hanford Site Human health 9 Develop methods to 2001-2003 8,900a 0 risk predict the impacts on assessment humans of exposures to contaminants from the Hanford Site Sociocultural 1 Develop a risk 2002 600a 0 risk assessment perception model for groups affected by Hanford Site contaminants NOTE: DNAPL = dense nonaqueous phase liquid; EMSP = Environmental Management Science Program 'The Integration Project intends to seek funding from national S&T programs (e.g., from DOE Headquarters) for some of this work. SOURCE: DOE, 2000a, Figure 4-1, Table ~1.

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Monitoring, Remediation, and Risk Technical Elements In the second project (Rem-2), contaminant plumes (particularly chromium, strontium, and tritium plumes) in the 100 Area will be investigated, and the results will assist in the development of a strategy for corrective actions. The planned work will include geophysical and geochemical studies to help select and deploy remediation technologies. The S&T activity for the Monitoring Technical Element, identification, development, and deployment of improved environmental monitoring, involves one project (M-1 ) to develop technologies and strategies to monitor air, vadose zone, groundwater, river, and selected biota, especially after the active phase of site cleanup is completed. Evaluation of Work Planned Under the Monitoring and Remediation Technical Elements 127 The monitoring and remediation projects were begun before S&T plans were developed, so it is difficult for the committee to judge the appropriateness or effectiveness of current work. The total planned funding for these technical elements is $2.6 million and $5.3 million, respectively (last column of Table 9.1), all of which is being provided to principal investigators through the Environmental Management Science Program (EMSP, see Chapter 3~. The Integration Project has no plans at present to provide Hanford Site funding to these efforts. Detailed S&T plans for these technical elements are still not complete, and detailed objectives and S&T projects are not yet defined. If the planned projects are executed appropriately, however, the broad objectives defined for the Remediation Technical Element may be attainable. Knowledge of the distribution of contaminant plumes obtained from the planned S&T work will feed other Department of Energy (DOE) programs in the Office of Science and Technology that deal with remediation technology selection and deployment. There is a clear opportunity to develop and evaluate new geophysical and geochemical methods for plume detection and treatment under these technical elements. The current field testing of in situ treatment of chromium in 100 Area groundwater is noteworthy in this regard.4 Additionally, there exists much prior knowledge on remediating 4The In Situ Redox Manipulation Treatability Test is occurring near the 100-D Area. It involves the installation of a line of injection wells into the groundwater to intercept a plume of chromium(\/l) just east of the Columbia River. A solution of sodium bichromate is being injected into the groundwater through these wells to form a chromium barrier. The solution reduces irontl11) in the sediments to irontil), which in turn undergoes a redox reaction with chromium(VI) and reduces it to insoluble chromium~l11) that precipitates onto the sediment grains. The test was

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128 Science and Technology for Environmental Cleanup carbon tetrachloride and other dense nonaqueous phase liquids (DNAPLs) at other sites that should be applicable to Hanford. New treatment methods and better technologies for locating and defining plumes should have broad application throughout the site (see Figure 2.8, for example) and to other DOE sites as well. Knowledge of the quantities and distributions of contaminants in the subsurface is essential so that decisions can be made to contain, actively treat, or rely on natural attenuation processes. Not only will monitoring methods have to be developed to meet site needs for unprecedented time periods after the active phase of cleanup is completed, but monitoring results will be critical in decisions resulting in transitions from "watchful waiting" (surveillance) to active containment or remediation. However, there is insufficient information provided in the Integration Project Roadmap (DOE, 2000a) to determine whether the S&T work planned under the Monitoring Technical Element addresses Hanford's most critical needs in this area. Discussion In the committee's view, there is disproportionately small emphasis in the S&T program on remediation~nly two projects are planned (Table 9.1), and both focus on determination of contaminant distributions in groundwater plumes. Little is being done within the S&T program on remediation technologies per se and their potential applications to waste pits, cribs, and other disposal areas. Further, there is no Integration Project S&T work planned on barriers to isolate, contain, and treat contaminants that will remain in the subsurface after the active cleanup program is completed. The committee views the development of effective long-term barriers as one of the most important S&T needs at the Hanford Site, and an earlier National Research Committee (NRC) also identified this need as significant for DOE's national cleanup program (DOE, 2000a). In fact, S&T to develop and deploy effective barriers at Hanford has been under way for the better part of the last decade. Field research on surface barriers in the 200 Area was initiated in the early 1 990s with construction of the Field Lysimeter Test Facility (Fayer et al., 1999), followed by construction of the Hanford Surface Barrier over an actual waste site in 1994 (DOE, 1 999d). These two initiated in 1997 with the installation of a 50-meter-long segment of wells, and initial tests look promising. Recently, however, some breakthrough of chromium(VI) has been detected, likely due to oxygenation of groundwater near the test wells. The cause of this oxygenation is under investigation.

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Monitoring, Remediation, and Risk Technical Elements 129 facilities are unique, with the Iysimeter providing site-specific information on fluid infiltration rates and amounts through different surface soil and vegetative covers and the surface barrier providing site-specific data on the effectiveness of a specially designed cover system (the Hanford Surface Barrier) in preventing fluid infiltration into a waste crib (Figure 9.1~. In 1996, a feasibility study (BHI, 1996) examined possible designs for capillary-evapotranspiration barriers. These included (1 ) the Hanford Surface Barrier, a thick, multilayer, long-term barrier intended for use on the most contaminated sites (e.g., cribs and trenches; see Figure 9.1 ); (2) a standard Resource Conservation and Recovery Act (RCRA) C (hazardous waste) barrier; (3) a modified RCRA C barrier, to be used for ,~ ~ - ~ ~ ~ ~ ~ .. ~ .. ~.~ ~ .. ~ ~ ~ ~..~:~ - Figure 9.1 Cross-sectional view of the Hanford Barrier. SOURCE: DOE, 1998d, Figures 1.2,1.3, 1.4.

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130 Science and Technology for Environmental Cleanup low-level and mixed (radioactive and chemical) waste sites; and (4) a modified RCRA D (municipal waste) barrier for municipal and low-level waste sites without hazardous chemicals. Some additional work on surface barriers is planned by DOE and Hanford, as noted below:5 . The Office of Science and Technology is initiating a three- year project in fiscal year 2001 on the Hanford Surface Barrier to (1 ) compare geophysical techniques, including ground-penetrating radar, for monitoring seasonal changes in moisture storage in the top two meters at scales larger than can be detected using neutron probe methods;6 (2) determine the as-built water storage capacity of the barrier; and (3) validate the performance of the asphalt layer at the base of the barrier using chemical tracers. A study of the RCRA C barrier is also planned to begin in fiscal year 2001, with identification of local soil materials for use in its construction, followed by construction of a prototype barrier in the 200 Area in 2002 and performance monitoring thereafter. One of the Hanford Site's core projects, the 200 Area Remedial Action Project (see Chapter 3), is carrying out this work. Funding for the construction and monitoring phases is to be provided by Hanford and possibly by the Office of Science and Technology. Detailed monitoring of properly constructed RCRA C (hazardous- toxic waste) and RCRA D (municipal waste) barriers has shown cover and liner systems to be very effective in preventing infiltration of water and escape of leachate. Some areas of the Hanford Site will remain too contaminated for any use other than waste disposal and containment for a very long time for example, the 200 Area tank farms and disposal facilities like the Environmental Restoration Disposal Facility (see Chapter 2~. Concentration and containment of waste using barriers with careful monitoring over time are environmentally defensible strategies. Continued infiltration of wastes into the vadose zone in the 200 Area from tanks, cribs, waste ditches, and ponds may exacerbate the site remediation problems, as may the continued migration of contaminants away from these locations. Characterization data on the vadose zone (Chapter 5), combined with a fully functioning System Assessment 5This information was provided in a teleconference call with Integration Project and Pacific Northwest National Laboratory staff on October 3, 2000. 6Horizontal tubes were built into the Hanford Surface Barrier so that neutron probes could be inserted to measure moisture storage in the barrier materials (see Figure 9.1~. Such methods provide only near-field moisture values that is, values in the vicinity of the probe tubes.

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Monitoring, Remediation, and Risk Technical Elements Capability (SAC; see Chapter 4), can be used to illustrate how barriers over some or all of the source areas could reduce contaminant migration and plume development. Furthermore, use of surface and in-ground barrier systems can serve the additional purpose of containment, both temporary and long term. As new waste treatment technologies become available in the future, they could be used to treat and mitigate the hazards from wastes contained within them. Interim barriers could find wide application across the site, for 131 example, as barriers to reduce water infiltration in and around tank farms that have leaked waste,7 or as subsurface barriers to reduce contaminant leakage into the vadose zone during single-shell tank waste retrieval operations. Access restrictions to and additional loading on the 200 Area tank farms have been cited to the committee as reasons for not placing interim barriers over them to reduce infiltration. However, there are options to avoid these problems; for example, tent-type structures that could easily be constructed over the tank farms, with grading to intercept surface runoff. S&T can play an important role in investigating and testing the feasibility of such strategies. Perhaps the past and planned studies cited above account for the lack of a major S&T program on barriers as part of the Integration Project. Nonetheless, the committee believes that more research is needed on the development, deployment, and evaluation of interim, long-term, and reactive barrier systems. Recent research on new technologies for site remediation using chemically reactive barriers shows great promise. The development of reactive barrier systems for the unique site and waste conditions at Hanford could be an especially fruitful area of research. The committee makes the following recommendations with respect to barrier S&T: S&T research on the feasibility, effectiveness, and long- term performance of surface barriers should be expanded to include other barrier types and materials for prevention of surface water infiltration into tank farms and other regions containing high concentrations of buried and spilled waste. S&T should be undertaken to assess the potential for using vertical and inclined cutoff barriers and reactive barriers as part of "interim" waste containment systems, which can provide containment for one to a few decades, as well as "permanent" waste 7At the request of DOE, a TechCon Forum was held in Richland, Washington, on May 4-6, 1999 to discuss approaches for reducing water infiltration around the Hanford tanks. The forum concluded that many technologies were already available or could be developed and deployed at the site (TechCon, 1 999a, 1 999b).

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132 Science and Technology for Environmenta/ Cleanup containment systems that are designed to last for much longer periods. S&T should also be undertaken to develop reactive barriers that can be used to treat or immobilize radionuclide and chemical contaminants of concern in Hanford Site groundwater. Since the development of new and improved barriers would likely find wide application across the DOE complex, much of the needed S&T work might be done in cooperation with other DOE programs. The focus of S&T at Hanford might be to adapt technologies developed elsewhere to the needs and environmental conditions at the site and perform pilot demonstrations. The need for more and better methods for site characterization and monitoring has been cited throughout this report (see especially Chapters 5, 6, and 8~. Monitoring is now being used at the site to detect contaminant transport in the environment, especially the groundwater and river (PNNL, 1999), and monitoring will no doubt find widespread use to assess the efficacy of future containment and cleanup actions. Monitoring utilizes many of the same strategies and tools as characterization and, in fact, is often piggybacked on,8 or iterated with, characterization efforts. Thus, as characterization capabilities are improved through Integration Project S&T efforts (see Chapter 5), there will be parallel opportunities to improve monitoring capabilities, especially through the use of minimally invasive or noninvasive approaches based on new detection, data collection (including improved statistical strategies for sampling), data transmission, data processing, and information display technologies. Such improvements are especially needed for monitoring the vadose zone, which will contain most of the waste and contamination to be left in place at the site when DOE's cleanup program is completed, and where contamination is especially difficult to detect because of subsurface heterogeneity and transient hydrologic conditions. The development of new and improved monitoring strategies and capabilities is a difficult technical challenge, and it will likely take many years of effort to make useful progress. Consequently, S&T on monitoring strategies and tools must begin now so that useful results will be available before the initiation of large-scale remediation and containment activities at the site. Therefore, the committee recommends that Integration Project S&T on new and improved strategies and technologies for monitoring the vadose zone be expanded. As part of this work, the Integration Project should assess what monitoring capabilities will be needed in the future at the site, based on cleanup decisions to be For example, boreholes drilled to obtain data on subsurface characteristics may subsequently be used for groundwater monitoring.

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Monifonng, Remediation, and Risk Technical Elements made and likely end-state scenarios, so that the SOT work can be properly planned and prioritized. Since the development of new and improved monitoring capabilities would likely find wide application across the DOE complex, much of the needed S&T work might be done in cooperation with other DOE programs. The focus of S&T at Hanford might be to adapt technologies developed elsewhere to the needs and environmental conditions at the site and perform pilot demonstrations. RISK TECHNICAL ELEMENT 133 The Risk Technical Element has one general S&T activity on stakeholder involvement and four S&T activities focused on ecological, human health, economic, and sociocultural issues (Table 9.1~. In general, the objective of the planned S&T work is to reduce uncertainties associated with risk assessments so that less conservative assumptions and models can be used. The approach taken is described in Appendix B and Table 4-1 in the Integration Project Roadmap (DOE, 2000a) and also in DOE (2000d). 1. General risk assessment This activity includes one project (R-1) to develop methods to identify, develop, and build consensus among Hanford stakeholclers on areas of focus for the Risk Technical Element. 2. Ecological risk assessment. This activity includes 11 projects (R-2 through R-12) to address technical gaps in ecological risk issues relevant to the Hanford Site. One project, described as contributing to better understanding of problem formulations, is designed to explore the relationship between impacts on individual entities and effects considered on a community level. Three exposure-related projects are described; these include the effects of multiple exposure pathways on uptake, uptake factors for plants and benthic species, and bioavailability. Six projects are defined that address ecological effects. These include a study of continuous (in contrast to acute) toxicological response, extrapolations across end points (such as population-level and individual-level responses) and taxa, toxicity by mode of action, and adaptive response. Finally, a risk characterization project is proposed in which a "weight-of- evidence" approach, as used for human health risk assessment, would be applied to the integration of data on ecological effects. 3. Economic ask assessment. This activity includes five projects (R-13 through R-17) to assess recreational use patterns for the Columbia River that can be used to define human exposure scenarios, assessment

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134 Science and Technology for Environmental Cleanup of how people might respond to risk information of various types, preferences regarding ecological scenarios, and study of population mobility and benefits transfer. 4. Human health risk assessment. This activity includes nine projects (R-18 through R-26) that address bioavailability, food-chain transfer factors, biomarkers, exposure pathways-factors, variability in exposures, toxicokinetics, treatment of uncertainties in cancer slope factors, and characterization of multiple health end points. Several of these projects (food-chain transfer factors and exposure pathways) would address risk assessment issues relevant to more accurate characterization of exposures of Native Americans. 5. Sociocultural risk assessment. This activity consists of one project (R-27) to model risk knowledge, in which cultural experts would attempt to convert information on concentrations of contaminants in environmental media into impacts on cultural values. Evaluation of Work Planned Under the Risk Technical Element As shown in Table 9.1, work on some of these projects is under way and will be completed in fiscal year 2003. The total planned funding for this technical element is about $22.8 million (second-to-last column of Table 9.1~. These budget estimates are taken from the Integration Project Roadmap (DOE, 2000a), which was published before the more detailed draft Risk Assessment Science and Technology Plan (DOE, 2000d) was issued. DOE (2000d) does not include budget information, so it is not clear to the committee whether the budget has evolved along with the technical project plans. In comparison to DOE (2000a), the project descriptions in DOE (2000d) indicate that substantial progress has been made in defining risk- related projects concerning issues at the Hanford Site. A majority of the projects in the human health risk area apply to generic (rather than site- specific) risk assessment issues (e.g., R1 8-R20, R22, Ram. These generic risk assessment issues have been recognized as important by many organizations and agencies, and technical advances in these areas would lead to reductions of uncertainty in risk estimates. However, these technical issues can have a strong influence on how environmental health risks are regulated and, for this reason, are of active interest to the Environmental Protection Agency (EPA) and other agencies. Additional comments on this point are offered later in this analysis. Despite improvements in the planned risk project descriptions in DOE (2000d), many are still general and vague, such that detailed review

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Monitoring, Remediation, and Risk Technical Elements 135 comments cannot be provided. For example, the description of the biomarkers-of-exposure project does not identify specific chemicals or technical approaches, nor does it provide any comparison with the current capabilities (e.g., sensitivity of measures of chromosome aberrations to ionizing radiation) relative to exposures of interest at the Hanford Site. Can the objectives of this work be achieved? The human health risk projects that involve factors specific to the Hanford Site are achievable. These projects (bioavailability, food-chain transfer factors, exposure pathways, and spatiotemporal variation in exposure) involve measurements and analyses that have been performed successfully in other contexts. Other aspects of the risk element are more ambitious and seem unlikely to be achieved except over extended periods of time. The determination of health and ecosystem risks from complex mixtures is an example of such an issue; this has been studied by various government and research agencies for many years. Some of the scientific issues listed for the human health risk component are issues in which there is substantial regulatory involvement (determination of cancer slope factors, for example). In general, regulators require the use of published guidance such as that found in EPA's Integrated Risk Information System (IRIS) for cancer slope factors. Although EPA periodically updates the IRIS values and will consider submitted information when it does so, this is not an area in which the Integration Project should expect large changes from the status quo. The only exception may be for rarely encountered substances for which the toxicological information base is poor. The ecosystem risk analysis is similarly hampered by a dependence on exposure-concentration-effect concentration pairs that are unknown or poorly defined for multiple stressors. In the committee's judgment, these more ambitious proposed health science and ecosystem impact analysis activities would make more sense as components of long-term research supported by DOE Headquarters or other agencies such as EPA than as S&T under the Hanford Integration Project. To be useful at Hanford, any scientific advances in human health risk assessment would first have to be accepted by national and international scientific bodies, and then adopted by EPA. The committee notes that although a number of these ambitious projects appear in the S&T plan (DOE, 2000a, Table 4-1 ), they have not yet been funded under the Integration Project.

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136 Science and Technology for Environmental Cleanup Does the planned work represent new science? The achievable aspects of the work, such as a refined characterization of Native American diets and other exposure factors, would improve the quality and applicability of site risk assessments. Some of the more ambitious human health and ecosystem studies would represent new science if successful, but as noted above, the committee's view is that such work would be a better fit elsewhere in DOE or other agencies. The planned ecosystem risk analysis approach does not represent new science, and the planned studies to begin defining dose- response relationships for Columbia River flora and fauna are necessary, but studies of this type are standard toxicological testing elements of risk assessment. Can the planned work have an impact on cleanup decisions at the Hanford site? To the extent that Hanford cleanup decisions will be based on avoiding unacceptable risks to human health and the environment, the committee judges that this work can be helpful in several respects. The ecological work to refine the understanding of food webs could allow for more robust assessments of the effect of contaminant seepage into the Columbia River, and there is a critical need to build ecosystem risk foundations based on a comprehensive understanding of ecosystem structure and function in the Columbia River. However, the committee's view is that, taken as a whole, the Risk Technical Element is less likely to impact site decisions than is S&T to better characterize the locations concentration, and speciation of existing contaminants (see Chapter 5~. Does the planned work address important issues? The committee believes that the planned work does address important issues. The primary objective of most Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) activities is the protection of human health and the environment in the future. The CERCLA process also identifies community concerns as important to site decisions. The risk element directly addresses these Issues.

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Monitoring, Remediation, and Risk Technical Elements Are there other concerns, comments, or suggestions that should be considered by the Integration Project in executing the planned work? 137 The committee's main concern with the planned work, as noted in the previous discussion, is that it addresses issues that have been studied by various government and research agencies for many years and have substantial regulatory involvement. The work planned under the auspices of the Integration Project's S&T program is modest in comparison to the scope and magnitude of work on these issues by other agencies and is therefore unlikely to make major contributions to resolving these issues. Consequently, these issues are more appropriate targets for long-term research programs funded by DOE Headquarters and other federal agencies. The Integration Project's main focus should be to maintain awareness of this work and to use new results as they become available. Most of these projects of questionable value have not yet been funded by the Integration Project and probably should not be funded in the future for the reasons given above. Discussion The Risk Technical Element includes some potentially important work to identify ecological impacts that may result from contaminant seepage into the Columbia River. In particular, the identification of locations where contaminant concentration and characteristics of exposure can have substantial effects on Columbia River flora and fauna is likely to be very useful in future versions of the SAC. The committee's review of the Risk Technical Element revealed two important issues that are not being addressed by the S&T program at present: (1 ) the impacts of extreme events on the risk assessment and (2) the appropriateness of the time period selected for risk assessment. The committee comments on these in the following paragraphs. Rare but high-magnitude (also known as "extreme") events such as fires, floods, and earthquakes are considered routinely in risk assessments. A large range fire, such as occurred at the Hanford Site in the summer of 2000, could have a substantial effect on contaminant releases by removing protective ground cover, which could lead to increased infiltration and surface runoff and erosion (see Figure 9.2~. Other episodic events also could affect the movement of subsurface contaminants, such as climate changes that result in drought or increased precipitation. Floods have been an important erosional agent at the Hanford Site, as evidenced by the geological record of extreme flooding during the past 100,000 years (Sidebar 9.1~.

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?38 Sconce and ~chno~ far amend bags .... ague 9.2 July 12, 2000, SPOT image of we Hangs Site showing the extent of the June 2000 range fee. Dark regions on the photo ar burned areas. Copyright CNES~000.

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Monitoring, Remediafion, and Risk Technical Elements Sl DE BAR 9.1 Extreme ~ Ever~ ~at H a nfo~ ~ ~ - 139 e d ew i=D m d d hg- oI wnt2 ~ ~drs nto the ew mnm~~nt A though ~e ;: S~, W:~ 'over the ti'.me' s~l'es. (1 03.- ~.O5-- ' i ~ ' ~ - il'l ' i ~ '' ' hazardous.- _ ~_ ~_: asev~acnceaDy _ ~ r =: burr~er ore hen ,) _ _ ~ ~ ~ ~ H~ '~Site.The unb 27- uy 2000 b u ~ r andriestro er~1 imi ar a aa y structures near the== he si e Such f res probah ~have~a ~ ;~ : rQ~nnn: neri.od- ~ ~ I I :i :~ & i ~ ~ ~ ~ ~. ~ , .... ~. 1 .-..~-~. :.,.- -~ .~ ~.~ 1 . ~ -~' ~ .... ...... : contaminant Innspor ~ ~e ~ te ~ing inkastructum-atHa ~i i ~ i ~ ~ s~ -b Far~ (An~on~ t o~ni ntastrophhr~lekks; are t j` ~i i liff ~1t E~dejtntheaprdO;nstruOfjgrdatior' the o es ~n bu eakane ~ines mayd - to be a pn~ the in~a~ru~ure ages. ~ ~ ~;~ ~ ~ ~ - ; ~ ~ ~ ~ ~ ~.... ~ ~ ~, ~.~ ~. ...~ ....,..~. ~ ..,..~ .~ ~ ~.~,~,~.,~ ~.~.,~.~.~..~ ... . ~ ~ ~ . ~ .... ~ ~ ~ . ... ~ ~ . ~ . ~ ... ~ .. ~ . . ~ . . ~. ~ ~ . ~ ~ ~ ~ ~ ~, ..... ~ ~ ~ ~ ~ ... - ~ ....... ~ ~ ~ ~.: . .. . ~ ~ ~ ~ . ~ . ~ ~ ~ . ~ ~ ~ ~ ~ ~ - ~ ~ ~ ~ ~ . . - ~ ~ ~ ionger-~time seal ~ t ~ r - ite i 1 bi - ~- ~ ~ . ~ 1 catast~phic-Pooding-.-~e~g I i ~ ~ I~ (1 ~ ~- p t d~-~ ~ ~-~-~ I inundations during glacial periods i h ~ ~ ar e ~Sidebar2.1~.During~is-time fl oodwaters-fro I ial e i I re~peat~ly-s=ured the Han~rdSl~ i t ~ O i ~-k ~- of times the volume pre rivers o its ice ~ became buovarit and~brok~periods ~. :~: ~ j~ j~ ~ ~:~ ~ ~ ~ ~: ~ ~ ...-. The: most reGent scooring evei~ti-occurred~about 15 000 years

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140 Science and Technology for Environmental Cleanup ~.. ~ ~ ~ ~ ~ .. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ :: ~ ~ ~... ~ . ~ .. ... ~ . ~ ~ ~ ~ ~ ~ . . ~. .. . . . . . . . ~ ~ ..The:S=...~.fo.cusespr~mar~ly n~th--;s~anda~s bs ~- -~- ue~us . ~ ~ a . n s p o ~ . p . a t t ~ ~ a y . . f o r - : . ~ e ~ ~ a s e - . o f . . c a n ~ a m ~ n a . n ~ s . . f ~ o ~ n t b e . s ~ t ~ ~ , - . . w ~ t h : .~ ... ..... ~ , ~. , , , . ~ ~ ~ . emohas-'s on --th.e :'s.~lat'an canab.'l't~es .of a: th.~ck ~drv.`'adose~ zone. .... ~ , .. ~ . . . . ..... .~. ~ , ~ ~ .~ . ~ . ........ ....... . ...... ~ ., ~ . - ~ .~:(Chap~te.r.A;.~see~es.pe~.al.lY F-~.~re.4-~.~ ~ Ho~weV e-r..e~enunder~rent~ l . ~ ~ ~ ~ . ~ ~ . ~ ~ ~ ~ ~ ~ 1 . , . . ~ . . . . ~ . ~ ~ - ~ . .. ... . ~ . ~ . ~ .... Inl.e~ acl-a J c lmallG..~ 1llons.,..1n ense ra~.ln~ - ~cas~ona y sa um ~s ~e. land su~ce ;ana generates ~ ~ e s i e ~ ~ . . ~ .~ ~ ~ ~ ~ . ~ ~ ~ ~ ~ ~ ~. ~ transpod. Momover, !f one se~Q~sIv:~onsid-e a lo g r-time~--katme:~ -- ..... - ~ ~ ~ - ~ .... ~ - ~ .... ~1.00,.0.0.0 vearsl1 Qther.~exno.sure .~hwa~s.a.r-e l~kel.v to~become~ ~ ~ : . I~pU~..~.R ~pan~.cu.~ar.,. ~ne..er.os~Qn~ ~spo~...ano.r aepo~sltI~n or..~ ~--~. . :~ ::: ~:: ~:~ ~ .: ~ .. : :, .~ ~ ~. . ~ ,~:~ . : ~ .. .. . ~ ..~... .. contam.~n.ated.~sed.~men~ and e.mplaced w.aste .m.ater~als ~ ~ ~ ~-.~ ~- . : : :;, ~ : ,, ,, ,,,,,-' '': ' :":'" ' ':' ': ':":::':.'::' ~ Documents and presentations to the committee indicate that risk assessments to be made using the SAC are to be carried out for of 1,000 years following site closure, from 2050 to 3050 (see Chapter 4~. The committee has two recommendations with respect to this period of analysis. First, the committee recommends that the results of such calculations be reviewed to ensure that the analytical period includes the time of peak dose or risk. Such a review could be undertaken under the auspices of the Risk Technical Element. For some toxic materials, the rate of transport through the subsurface may be so slow that peak concentrations at locations of concern, especially the Columbia River, could occur more than 1,000 years in the future. If peak risks occur beyond 1,000 years, then other assumptions in the SAC may also need to be reexamined, particularly the assumption of no climate change (see Table 4.1~. The second recommendation concerns the "status quo" assumption made in the SAC with respect to the continuing existence of dams along the Columbia River. As discussed in Chapter 4 (see especially Table 4.1), the SAC contains the assumption that Columbia River dams will continue to operate for 1,000 years following the assumed closure of the Hanford Site in 2050. No justification for this assumption is given in any of the documents that the committee has reviewed, and it seems on its face to be unrealistic. The committee recommends that an evaluation be made of the sensitivity of SAC risk assessments to the assumed continuing existence of these dams. Again, such a review could be undertaken under the auspices of the Risk Technical Element. The committee is not recommending that analyses be made of a broad array of alternative future states with respect to the dams, only that the potential effect on analytical results of changes to the dams be considered.