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Final TO42 Site Survey Report
Survey of Potential Settling Basin Locations
Location and Purpose � As a possible waste management alternative for drilling fluids, containment areas are being considered as catchment basins for potentially-contaminated groundwater and sediment generated during drilling activities. Several options being considered include one centralized large containment point, or multiple smaller satellite containment areas. Implementation of settling basins will require regulatory concurrence and approval.
A reconnaissance visit to select potential sites was made by a Parsons geologist and civil engineer on November 20, 2001. The two prime locations for consideration are shown in Figure 2. The main concern after the initial visit was whether a sufficient soil profile exists that would be conducive to constructing a lined basin. A follow-up visit was made on December 13, 2001 by two Parsons geologists. With the assistance of a CSSA equipment operator, eight to ten shallow boreholes (less than 3 feet) were drilled using a small-diameter (9-inch) auger mounted on a Bobcat loader. The purpose of the boreholes was to determine the nature, as well as the lateral and vertical extent of the soil profile.
The Basin �A� site is located 450 feet west of the H&I section and 350 northwest of the proposed CS-MW12 cluster, along the south D-24 roadside. A half-acre clearing between oak trees is fairly level, and has excellent roadway access. This location is being considered because of its proximity to multiple wells being drilled in the vicinity of the Well 16 groundwater plume. Ten soil borings to depths of nearly 3 feet were drilled at locations shown in Figure 3. The soils are calcareous clays with some limestone gravel. The ground surface and near-surface soils are relatively free of limestone aggregate in contrast to much of CSSA. Some rock outcrop was noted near the southern edge of the area. At least 0.4 acres of acceptable soil conditions are available at this site.
A second location, Basin �B,� was selected as a potential alternative because of its proximity to the Building 90 (AOC-65) investigation. A settling basin in this locality would add convenience and reduce overall waste transport time during the drilling phase. The selected location is less than 100 feet east of Building 96, in the southeast corner at the nearby intersection of two unnamed roads. The available area is approximately 0.7 acres in size, and slopes to the east. The past use of this area is unknown, but the location appears to be re-worked and may consist of backfilled or imported fill material. Both roadways and a leveled equipment staging area form a berm around three sides of the surveyed area. A significant ridgeline is present along the eastern margin of the site. Eight soil borings were drilled at this site as shown in Figure 4. At least 3 feet of good, clayey soil was encountered in the five westernmost borings (B-1, B-2, B-3, B-4, and B-8). The soil profile thins significantly toward the east at locations B-5, B-6, and B-7 and becomes more fill-like with large gravel and cobbles. At least 0.4 acres of acceptable soil conditions are available at this site. Other sites may need to be identified, such as re-use of PIMS basin area after PIMS soil is gone, or where cost effectiveness/efficiency is gained. Construction of Basins A, B, or other locations will require CSSA approval prior to construction.
Accessibility � Both sites have very good access for equipment needed. Improved and semi-improved roads are available at both areas. There is plenty of access for equipment during the construction phase. Generated drilling fluids may be off-loaded easily from the roadside with a vacuum truck. IDW fluids from CS-MW12 drilling can be pumped directly to Basin A. Fluids from CS-MW11 and -16 could conceivably be pumped directly to Basin B. At the discretion of the design engineer, an all-weather road at the perimeter of the basins may be necessary. A security fence may be required to restrict personnel and wildlife entry.
Personnel requiring access to the site are Parsons field teams and vehicles, construction company with heavy equipment, and the drilling subcontractor with vacuum truck.
Utilities � No utilities are in the immediate vicinity of Basin A. Underground utilities will be an issue at Basin B. One underground wastewater line and overhead utility lines are trending east/west at the northern edge of the site. There is also an underground water line and possible electrical (or telephone) line trending north/south at the western margin of the site. If needed, a fire hydrant is located 75 feet to the northwest of the site.
Other Site Issues � There are no extenuating site issues at the Basin A location at this time. At the Basin B site, sensitivity issues include buried and overhead utilities, removal of dead trees, and public visibility of site activities from Leon Springs Villa and Hidden Springs Estates to the south.