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5.20 MITIGATION MEASURES

This section describes measures to mitigate potential impacts of the alternatives in two areas. Section 5.20.1 summarizes measures that currently are included in the alternatives to prevent or mitigate environmental impacts. Section 5.20.2 summarizes additional measures that could be included in the alternatives to further reduce or mitigate potential environmental impacts described previously in other portions of Section 5.0 if deemed necessary. The section focuses on measures to mitigate potential impacts during remediation. Future NEPA documentation will specifically address in detail impacts and mitigation of post-remediation tank closure where, for example, most of the impacts of borrow site activities would occur.

5.20.1 Measures Included in the Alternatives

A large number of measures have been incorporated into all of the alternatives to ensure safe implementation, reduce environmental impacts, and meet all regulatory requirements (except as described in Section 6.0). The following measures apply to all of the alternatives for the tank waste and capsules except as indicated.

• All nuclear facilities would be designed, constructed, and operated in compliance with the comprehensive set of DOE or commercial requirements that have been established to protect public and worker health and the environment. These requirements encompass a wide variety of topics, including radiation protection, design criteria for nuclear facilities, fire protection, emergency preparedness and response, seismic events, and operations safety requirements.
• Measures would be taken to protect construction and operations personnel from occupational hazards. These measures include the following:
• Emphasis on safety awareness;
• Radiation and hazardous waste training;
• Use of appropriate personal protective equipment (e.g., gloves, eye protection, and respirators);
• Personal and environmental radiation monitoring and the application of administrative limits to restrict exposures to within regulatory limits and as low as reasonably achievable;
• Administrative controls for potentially hazardous areas;
• Use of hearing protection and monitoring exposure to occupational noise;
• Good housekeeping of work areas; and
• Preparing and implementing safety plans for all field work activities.
• Emergency response plans would be developed to rapidly respond to potentially dangerous unplanned events.
• Water and surfactants would be used to control dust emissions especially at borrow sites, gravel or dirt haul roads, and during construction earthwork.
• Areas for new facilities would be selected to minimize environmental impacts to the extent practicable, such as avoidance of undisturbed shrub-steppe habitat.
• Pollution control or treatment would be used to reduce or eliminate releases of contaminants to the environment and to meet regulatory standards. Among the measures included are the following:
  • Treating liquid through a variety of processes, including evaporation, prior to discharging the water into the subsurface;
  • Treating air emissions through the use of high-efficiency particulate air filters and scrubbers to reduce levels of air emissions to within regulatory standards;
  • Incorporating appropriate metal and concrete shielding to control exposures to workers from gamma radiation; and
  • Use of double liners, double-wall piping, and other double containment and backup systems to control leaks that might occur. Double containment is not included for the existing SSTs.
• Extensive environmental monitoring systems would be implemented to continually monitor potential releases to the environment including the following:
  • Air monitoring within buildings, certain tanks, and the ambient atmosphere;
  • Groundwater and vadose zone monitoring around the tank farms;
  • Comprehensive radiation monitoring during all construction and operation; and
  • Post-remediation monitoring and maintenance for up to 100 years for any radioactive and hazardous materials that remain onsite.
• All newly disturbed areas would be recontoured to conform with the surrounding terrain and would be revegetated with locally derived native plant species consistent with Sitewide biological mitigation plans.
• All shipments of radioactive or hazardous materials on public roads would be performed in compliance with all regulatory requirements including requirements for the following:
  • Maintaining manifests;
  • Using appropriate shipping containers;
  • Using trained and licensed transporters;
  • Using appropriate signs on vehicles;
  • Providing appropriate notices to potentially involved organizations; and
  • Using specially designed containers for shipment of HLW to reduce the possibility of public exposure in the extremely unlikely event of a release.
• Although much of the area proposed for the remedial activities is in areas currently disturbed, activities in some areas have the potential to impact historic, prehistoric, or cultural sites. These areas have not been fully surveyed because they are potential borrow sites subject to change during final design. The final selection of borrow sites would be made through future NEPA analysis . Historic, prehistoric, and cultural resource surveys would be performed for any undisturbed areas to be impacted and the following measures could be implemented.
• Prior to any ground disturbance activities, consultations would be conducted with the DOE Richland Operations Office Historic Preservation Officer, the Hanford Cultural Resource Laboratory, Washington State Historic Preservation Officer, and concerned Native American Tribal groups and governments.
• Avoidance of prehistoric and historic site areas identified would be the primary form of mitigation whenever practicable.
• An archaeological monitor would be onsite during ground disturbing activities of highly sensitive areas to ensure that construction impacts were limited to the remediation area only whenever practicable.
• If prehistoric or historic materials sites were encountered, construction activities would be stopped or diverted to other areas until the site was evaluated and appropriate consultations were conducted.

Consultation with Tribal Nations groups and governments would be performed early in the planning process to determine areas or topics of importance to these groups such as religious areas and potential resources of medicinal plants.

5.20.2 Potential Mitigation Measures

The following mitigation measures could be incorporated into one or more of the alternatives as indicated. A decision on which, if any, of these measures to incorporate would be made by DOE and the Washington State Department of Ecology (Ecology). The decisions would follow the public comment period and would be incorporated into the Mitigation Action Plan and the Record of Decision. The TWRS Mitigation Action Plan, which will be published with the Record of Decision, will describe the plan for implementing mitigation commitments made in the Record of Decision for the alternative selected for implementation.

Tank Waste

Under all tank waste alternatives except In Situ Vitrification, contaminant levels in the groundwater potentially would exceed safe levels . Potential health effects (incidences of cancer) could occur to anyone routinely consuming this water. This impact could be mitigated by placing restrictions on the use of the groundwater such as prohibiting the installation of wells for drinking water or irrigating crops. Potential impacts would last for more than 10,000 years, and the effectiveness of administrative controls in preventing or limiting the installation of wells over this length of time is uncertain. However, it should be noted that the area that would require administrative controls due to TWRS remediation contains groundwater that currently is contaminated at levels far above safe levels . Therefore, unless this existing contamination is remediated in the future, administrative controls would be necessary with or without the additional TWRS impacts to groundwater.

All of the tank waste alternatives, except the No Action and Long-Term Management alternatives, would include the placement of a Hanford Barrier over the tanks and the LAW vaults (when applicable) to reduce the amount of precipitation that would infiltrate the waste and leach contaminants into the groundwater. For the analysis performed in this EIS, a Hanford Barrier was used to bound impacts. A Hanford Barrier would be a 4.5-m (15-ft)-thick, earthen cap constructed primarily of 10 layers of soil, rock, and synthetic materials. It would be designed to inhibit the infiltration of precipitation, limit intrusion by plant roots and burrowing animals that could penetrate the Hanford Barrier, and inhibit inadvertent human intrusion into the waste. The Hanford Barrier would be expensive to construct and would require using a large volume of earthen materials from borrow sites. Using borrow sites would require disturbing shrub-steppe habitat. These impacts could be partially mitigated by substituting a different type of surface barrier for the Hanford Barrier, such as the type of barrier required for hazardous waste sites under RCRA. These barriers may be somewhat less effective than the Hanford Barrier but they may be adequate for some or all of the alternatives to protect the groundwater. Selection of a specific barrier design is a decision that will be made in the future when final decisions are made on closure of the tank farms. At that time, alternate barrier designs that may be less consumptive of resources could be examined. This mitigation measure could be especially applicable to the In Situ Vitrification alternative because the barrier would be needed to prevent human and wildlife intrusion and would not be needed to protect the groundwater from contamination .

All of the tank waste alternatives except No Action and Long-Term Management would include filling the tank void spaces with soil or rock. This would require the extensive use of earthen borrow sites, which would potentially disturb areas of shrub-steppe habitat. The tanks could be filled with contaminated soils excavated during closure activities or during the implementation of other Hanford Site remediation projects, which would reduce the amount of shrub-steppe habitat disturbed. Because a Hanford Barrier would be constructed over the tanks during closure (if closure as a landfill was selected), additional landfills would not need to be constructed for closure or the other soil remediation projects. Contaminated soil could also be used as the glass former for the In Situ Vitrification alternative, which would provide greater protection of the groundwater because the contaminants in the soil would be immobilized in the vitrified tank waste.

Subsurface barriers could be used with any of the alternatives to contain leakage and minimize the migration of waste away from the tank in the event of a leak. Subsurface barriers are impermeable layers that would be installed in the soil surrounding a tank to contain any leakage that might occur. Subsurface barriers could be used with any of the tank waste alternatives but would be most suitable for SSTs that would be retrieved under the ex situ alternatives. The SST waste retrieval primarily would be performed using hydraulic sluicing, which has a high potential for leakage. The possibility of using subsurface barriers resulted from the concern about the potential for leaks from the tanks during hydraulic sluicing for retrieval. Subsurface barriers would not prevent tank leakage but they would function to prevent leakage from migrating beyond the barrier and into the vadose zone. This would minimize the volume of soil contaminated by a leak, and result in easier cleanup of contaminated soils.

A number of subsurface barrier technologies exist that could be used during waste retrieval operations to minimize the potential for release of contaminants to the vadose zone (see Volume Two, Section B.9). Close-coupled subsurface barriers could be installed directly adjacent to the outer tank sides and bottom or offset from the tank. The close-coupled barriers would minimize the contamination of soils if a leak were to occur, and the offset barriers could be used to contain existing soil contamination and could have features to collect and recover tank leaks. Subsurface barrier technologies that have been investigated for use at the Hanford Site include: close-coupled injected chemical barriers, box-shaped chemical walls, v-shaped chemical barriers, freeze walls, and circulating air barriers (Treat et al. 1995). Some technologies such as freeze walls are active and would require continuous equipment operation to maintain the barrier integrity. Other technologies such as chemical barriers are passive and once installed would only require monitoring. The functional requirements potentially could be satisfied by any of the subsurface barrier technologies evaluated. Mitigation of waste leakage during retrieval would be evaluated as information is developed in support of tank closure and retrieval-based leakage criteria.

All of the alternatives that would retrieve tank waste assumed that a heel of waste equal to 1 percent of the tank contents would be left in the tank. This heel would not be immobilized and over a period of time would be dissolved by infiltrating water and transported to the groundwater. Mitigating the impacts from the tank residuals would involve immobilizing the residual waste to slow the release of contaminants from the residual waste. Broadcasting a dry grout mixture on the tank floor following retrieval would combine with any liquids remaining in the tanks and partially immobilize the contaminants. The grout would maintain the remaining solids at a high pH to further inhibit solid dissolution and would recrystallize over time to further stabilize the solids.

In situ vitrification is another technology that could be used as a mitigative measure to immobilize tank residuals and contaminated soils. In situ vitrification of residual waste and contaminated soil would immobilize contaminants in a waste form that would substantially reduce the long-term release of contaminants to the vadose zone.

Under the In Situ Fill and Cap alternative and the fill and cap portion of the Ex Situ/In Situ Combination 1 and 2 alternatives, there would be the potential for flammable gases (primarily hydrogen) to collect within the top of the tank and possibly under the asphalt layer of the Hanford Barrier. If this buildup occurred, and an ignition source such as sparks or heat from friction during an earthquake occurred, there would be a possibility that the gases could ignite or explode. This event could be mitigated by providing a mechanism for the gases to vent to the atmosphere. One way to accomplish this would be to include risers that extended from the tanks through the Hanford Barrier to the surface. These risers would allow the gases to vent to the surface. Because the generation of hydrogen gas and other flammable gases is decreasing over time, these risers could be plugged at the end of the administrative control period. In addition, when the tank was filled a hole could be cut in the top of the tank dome to provide adequate venting into the Hanford Barrier and a hole would be left in the asphalt layer of the Hanford Barrier, which would allow gas to vent to the surface. On reaching the surface, hydrogen would diffuse upward (it is less dense than air) and be dispersed into the atmosphere. Should an ignition source occur at the surface such as lightning, the ignition would not propagate downward through the soil into the tank. Flames would not propagate through small pore spaces such as those that would be in the soil at the top of the earthen barriers. Extensive tank waste characterization and engineering would be necessary to implement this mitigation measure.

An additional mitigative measure could be the engineered placement of catalytic recombiners in and near the tanks. The catalytic recombiners would promote the low-temperature reaction of hydrogen and oxygen to form water. The continual reaction of the hydrogen as it was formed could prevent its concentration from reaching flammable or explosive limits. The rate of generation of flammable gas has been decreasing over time and may be decreasing by one-half every 15 years as the heat-producing radionuclides decay and volatile organics are depleted.

A pressurized spray release resulting from a mispositioned jumper during a tank waste transfer is an accident that would be common to all tank waste alternatives. The LCF point estimate risk ranged from 2.0E+00 to 5.6E+00 among the alternatives for the bounding scenario and from 9.3E-02 to 2.6E-01 for the nominal scenario. A mitigative measure that could reduce the risk of a spray release would be to ensure that cover blocks were in place at all times when the jumper was in service during tank waste transfers. Ensuring that the cover blocks were in place would not prevent the accident from occurring, but it could mitigate the consequences of the accident by over five orders of magnitude.

A hydrogen deflagration in a DST or SST prior to or during remediation is an accident that would be common to all tank waste alternatives. The LCF point estimate risk ranged from 1.9E+00 to 1.6E+01 among the alternatives for the bounding scenario and from 3.2E-02 to 2.7E-01 for the nominal scenario. A mitigative measure that could reduce the risk of a hydrogen deflagration would be to install active ventilation systems and mixer pumps in those tanks that pose the risk. This mitigative measure could reduce the probability of the accident occurring and reduce the potential energy of the deflagration if the accident did occur, resulting in a direct reduction of the consequences.

For the In Situ Vitrification alternative, it was postulated that a double-ended break would occur in the off-gas line between the off-gas hood and the off-gas facility as a result of an earthquake. The LCF point estimate risk was 8.3E-01 for the bounding scenario and 3.3E-03 for the nominal scenario. Mitigative measures that could reduce the risk of this accident would be to install a seismic qualified off-gas duct system and seismic shut-off switches that could remove the power to the electrodes and to the off-gas exhaust system and reduce the consequences.

The retrieval accident in which a ventilation heater failed due to an electrical fault resulting from humid air plugging the HEPA filter and filter blow-out would be common to all the ex situ alternatives and the ex situ component of the Ex Situ/In Situ Combination 1 and 2 alternatives. The LCF point estimate risk was approximately 2.3E-03 for the bounding scenario and 8.8E-05 for the nominal scenario. A mitigative measure that could reduce the risk of this accident would be to install a pressure differential shut-off switch that would measure the pressure differential over the HEPA filters. This action could reduce the probability of the accident occurring.

For the In Situ Fill and Cap alternative and the fill and cap remediation portion of the Ex Situ/In Situ Combination 1 and 2 alternatives, it was postulated that a deflagration could occur while the tank was filled with gravel using a rock slinger. A spark from the gravel could ignite a hydrogen gas plume, subsequently overpressurizing the tank. The LCF point estimate risk for a hydrogen deflagration during the fill and cap operation was approximately 2.3E-03 for the bounding scenario and 1.2E-04 for the nominal scenario. A mitigative measure that could reduce the risk of this accident would be to use wet sand or grout as fill. This action could reduce the probability of the hydrogen ignition and therefore reduce the probability of the accident occurring.

These accidents will be evaluated in more detail in Final Safety Analysis Reports, which will provide the basis for safe operations.

With the exception of the No Action, Long-Term Management, and In Situ Fill and Cap alternatives, the schedule of activities for the tank waste alternatives would cause one or more boom-bust cycles in the local economy. These cycles would place a strain on the availability of housing and cause large upward and downward swings in housing prices. These cycles also could cause strains on local school districts. The careful scheduling of activities, primarily construction, could reduce the severity of the boom-bust cycle. It would be possible to build certain facilities in sequence rather than concurrently although this could cause small delays in the initiation or completion of the project and increases in project cost.

The calculation of impacts in this EIS is based on a representative location for process facilities. The representative location was chosen from three similar locations that were considered in a preliminary site selection process. However, this EIS does not support a decision on the final selection of a site for any facilities that would be constructed during remediation. The selection of the precise location of remediation facilities would be the subject of future NEPA analyses when more detailed information is available on the number, size, and configuration of the required facilities. The potential impacts to sensitive habitats would be one of the evaluation criteria used to select sites for required facilities.

All of the alternatives except the No Action alternative would disrupt shrub-steppe habitat. These impacts would be mitigated to the extent appropriate by implementing the following hierarchy of measures.

• Avoid shrub-steppe areas to the extent feasible by choosing alternative locations or configurations for project elements such as new power lines.
• Minimize impacts to the extent feasible, possibly by modifying facility layouts, design elements, altering construction timing, or by salvaging (transplanting) some resources.
• Restore temporarily disturbed areas, possibly by replanting indigenous species taken from other disturbed areas.

Mitigation of impacts to habitats of special importance to the ecological health of the region is most effective when planned and implemented on a Sitewide basis. Recognizing this, DOE is preparing a Sitewide biological management plan to protect these resources. Under this Sitewide approach, the potential impacts of all projects would be evaluated and appropriate mitigation would be developed based on the cumulative impacts to the ecosystem. Mitigation to reduce the ecological impacts from TWRS remediation would be performed in compliance with the Sitewide biological management plan. Mitigation would focus on disturbance of contiguous, mature sagebrush-dominated shrub-steppe habitat. Compensation (habitat replacement) would occur where deemed appropriate. Specific mitigation ratios, sites, and planting strategies (e.g., plant size, number, and density) would be defined in the Mitigation Action Plan, which would be prepared for specific facility siting decisions. The Mitigation Action Plan would be prepared in consultation with the Washington State Department of Fish and Wildlife and the U.S. Fish and Wildlife Service, with input from the Hanford Site's Natural Resources Trustees Council.

All facilities could be constructed using colors that conformed with surrounding visual resources. This would involve using earth tones such as sandstone and sage colors on all facilities practicable. This would reduce the background visual impacts from the air emission stacks, middle ground impacts from the large facilities, and all impacts from all facilities from elevated locations such as Gable Mountain.

All of the alternatives currently assume 16-m³ (20-yd³) trucks would be used to haul earthen material from the borrow sites to the TWRS sites. This would involve increased traffic congestion and high haulage cost. If a dedicated haul road was constructed, 30- to 60-m³ (35- to 70-yd³) trucks could be used to reduce these impacts.

Under all of the tank waste alternatives, except No Action, Long-Term Management, and In Situ Fill and Cap, there would be extremely heavy traffic congestion on the State Route 240 Bypass Highway near the intersection with Stevens Road on Route 4 west of the Wye Barricade and on Stevens Road north of Richland. The congestion would last for several years. These impacts could be partially mitigated by providing bus service to the 200 Areas, providing incentives to vanpool and carpool, or by staggering work start times to the extent practicable. Other mitigation measures could include modifications to Stevens Road such as adding turn lanes, sequencing traffic signals to improve traffic flow, modifying access approaches to certain facilities, or by widening Route 4 west of the Wye Barricade.

Two areas of potentially disproportionate, significant, and adverse impacts on minority populations or low-income populations were identified. These impacts include 1) increases in housing prices that could adversely impact access to affordable housing by low-income populations; and 2) continued restrictions on access to portions of the 200 Areas that could impede the ability Yakama Indian Nation and the Confederated Tribes of the Umatilla Indian Reservation to exercise access, certain land-use treaty rights, and interest in future land ownership.

To mitigate the increased housing prices to low-income populations, the Federal or State government could provide grants for constructing additional low-income housing. Having additional low-income housing available would affect market conditions and tend to keep prices at lower levels. The Federal or State government could also provide grants for constructing low-income housing with guaranteed purchase and rental rates, which could issue low-interest rate home loans with qualifying requirements to low-income applicants.

To mitigate the impacts that continued access restrictions could have on the ability of Native Americans to exercise certain treaty rights, DOE could provide increased protection from disturbance for areas of special importance to the Native Americans, and allow and encourage Native American participation in the planning and mitigation phases of the project. DOE also could purchase and transfer title to lands outside of the 200 Area as compensation for continued access restrictions in the 200 Area.

All of the alternatives would involve traffic accidents and fatalities (six or more fatalities ) because of the large number of employees and the long distance traveled by employees to reach the 200 Areas each work day. Although the accident and fatality rates would not be higher than the State-wide averages, the number of fatalities could be reduced by widening Route 4 west of the Wye Barricade, or by reducing the speed limits on Route 4.

All of the mitigative measures would have cost associated with them, and DOE and Ecology would consider the benefits of performing these measures against this cost, and the effect this additional cost might have on the availability of funding for other projects.

Cesium and Strontium Capsules

None of the capsule alternatives, except the Onsite Disposal alternative, would involve substantial environmental impacts so no mitigative measures specific to these alternatives were developed. The Onsite Disposal alternative would involve the disruption of shrub-steppe habitat and the same potential mitigation measures described for the tank waste alternatives could also be used to mitigate impacts on the shrub-steppe habitat for the Onsite Disposal alternative.