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5.1 GEOLOGY AND SOIL

This section describes the potential impacts of the TWRS EIS alternatives on the geologic resources and soils of the Hanford Site. For both geology and soil, the potential impacts of each alternative, except the No Action alternative, would be small and similar both in nature and magnitude. The No Action alternative would not have any additional impacts on geologic resources or soils. For both geology and soil issues, the level of impacts would be linked directly to the amount of land disturbance. Generally, the more land disturbed, the higher the level of impacts to geologic resources and soils.

5.1.1 Mineral Resources

Mineral resources (i.e., silt, sand, gravel, and rip rap) would be required in varying degrees for each alternative ranging from none for the No Action alternative to 5 .1E+06 cubic meters (m³) ( 6.7 E+06 cubic yards [yd³]) for the Ex Situ No Separations (Vitrification) alternative. Table 5.1.1 shows the mineral resources that would be required for remediation activities and those that would be required for the total alternative activities (remediation activities plus the tank closure scenario included for comparative analysis [closure as a landfill]). During remediation, the earthen materials primarily would be used to make concrete during construction of facilities. For the In Situ Fill and Cap alternative, earthen materials would be used to fill the tanks, and for the In Situ Vitrification alternative, the earthen material would be used as a glass former during vitrification. All other earthen borrow material would be used for the construction of the Hanford Barrier over the tank farms and low-activity waste (LAW) vaults during closure activities (Volume Two, Appendix B). All of the material would be obtained from the Hanford Site as described in Section 3.6.

Because sand, gravel, and rip rap all are readily available on the Hanford Site in quantities greatly exceeding the TWRS requirements, there would be small impacts on local availability and the cost of the resources.

5.1.2 Topography

No changes in topography would result from the implementation of the No Action alternative. For the Long-Term Management alternative, only small, localized changes in topography would result during construction of replacement double-shell tanks (DSTs). The current topography at these areas is flat, and the areas around the replacement tanks would be regraded to conform with the natural terrain. Under the In Situ Fill and Cap alternative and the In Situ Vitrification alternative, the only substantive impacts during remediation would occur at the earthen borrow sites where material would be obtained to fill the tanks and for use as glass formers, respectively. Under all of the ex situ alternatives, there would be small changes to the topography where the remediation facilities would be constructed. The current topography in these areas is flat, and the area around all facilities would be regraded to conform with the natural terrain.

Only small, localized changes in topography would result from constructing Hanford Barriers over the tank farms during closure activities for all in situ and ex situ alternatives, and for constructing the LAW disposal facility associated with the Ex Situ Intermediate Separations, Ex Situ Extensive Separations, and Ex Situ/In Situ Combination 1 and 2 alternatives. The Hanford Barriers over the tank farms would cover a total of approximately 25 hectares (ha) (62 acres [ac]) with an average height of 4.5 meters (m) (15 feet [ft]). The Hanford Barrier over the LAW disposal facility would cover up to approximately 7 ha ( 17 ac). The Hanford Barrier would be a flat-topped, slightly abovegrade, engineered soil structure whose function would be to isolate the waste site from the environment (Volume Two, Appendix B). The Hanford Barrier would be composed of 10 layers with a combined thickness of 4.5 m (15 ft), which would be placed over the top of the stabilized tanks and the LAW disposal facility. The Hanford Barriers would cover groups of tanks (tank farms), not individual tanks. Each Hanford Barrier would extend an additional 9 m (30 ft) beyond the perimeters of the tanks and vaults. All disturbed areas would be graded to conform to the surrounding topography and drainage systems.

Table 5.1.1 Key Geology and Soil Impact Parameters

Use of borrow sites for silt, sand and gravel, and quarry operations for rip rap would cause topographic changes at borrow sites. For purpose of analysis, three potential borrow sites were chosen as the basis for calculations: Pit 30 (located between the 200 East and West Areas); Vernita Quarry (located north and west of the 200 Areas); and the McGee Ranch (located north and west of the 200 Areas). Removing borrow materials would result in topographic depressions at the borrow sites. An excavation depth of 3 m (10 ft) was assumed for purposes of calculating the disturbed area. These sites would be recontoured to be made compatible with the surrounding terrain and drainage systems and would be revegetated, although some permanent terrain depressions would remain.

5.1.3 Soil

Soil at the tank farms, and at most of the area near the waste treatment facilities site in the 200 East Area for the Ex Situ Intermediate Separations, Ex Situ No Separations, Ex Situ Extensive Separations, Ex Situ/In Situ Combination 1 and 2 , and the Phased Implementation alternatives, previously has been disturbed so there would be only a small amount of additional soil disturbance during remediation. Each of the alternatives (except No Action) would temporarily disturb soil outside the facility footprint, primarily in the trample zone around work areas, heavy equipment traffic areas, and material laydown areas. Temporary impacts would include soil compaction and increased potential for soil erosion (Table 5.1.1).

Soil would be disturbed during closure activities at the potential locations where borrow materials would be obtained from the Pit 30, Vernita Quarry, and the McGee Ranch sites. The potential Pit 30 borrow site is an existing gravel pit and is a partly disturbed area. The potential Vernita Quarry borrow site is also an existing borrow site for basalt materials, and it is partly disturbed. The potential McGee Ranch borrow site is largely undisturbed. None of the areas that would be disturbed under any of the alternatives have prime or unique farmlands. There would be permanent loss of soil cover at the tank farms for all alternatives except for the No Action alternative. The treatment facilities proposed in the 200 East Area for the Ex Situ Intermediate Separations, Ex Situ No Separations, Ex Situ Extensive Separations, the Ex Situ/In Situ Combination 1 and 2 alternatives, and the Phased Implementation alternative also would result in long-term soil losses because the ground surface would be covered with buildings and paved areas at the facility sites (Table 5.1.1).