3.4.4 Soil Remediation
3.4.4.1 Safety
The excavation activities discussed in this section can be conducted only if proper procedures and practices are instituted to ensure the health and safety of personnel from both radiological exposure and physical and/or mechanical hazards. A site specific HASP (Appendix A) has been developed in accordance with the OSHA's Safety and Health Standards 29 CFR 1910.120, 29 CFR 1926, and the Hazard Communication Standard 29 CFR 1910.1200. The purpose of the Health and Safety Plan is to establish safe procedures and practices for the personnel engaged in field activities associated with the Remedial Action.
3.4.4.2 Soil Excavation and Segregation
The scope of work for the remediation of soils includes the excavation and loading into transportation containers approximately 8,062 cubic yards of soil and concrete with plutonium contamination less than 2000 pCi/g and 160 cubic yards of soils greater than 2000 pCi/g. These soils and concrete extend from the missile shelter area to the drainage ditch. A localized area located across Route 539 and along the drainage ditch will also require excavating down to four feet. The contaminated soils in front of Shelter 204 will be addressed first during the excavation phase of the project. After completion, the contaminated soil along the drainage ditch will be removed followed by the removal of the contaminated soils across Route 539.
3.4.4.3 Shelter 202 and 206 Demolition
Due to the anticipated depth of the excavation near shelters 202 and 206, selective demolition will be accomplished. Because these shelters are no longer in use, the front bay (20 feet) of each shelter will be removed in order to gain access to the load bearing soils adjacent to each shelter. This phase of the demolition work will be completed concurrently with the decontamination of Shelter 204.
3.4.4.4 Main Excavation
The main excavation for the removal of the contaminated soils is located adjacent to Shelter 202, 204, and 206. Based on the Site Characterization Report, contaminated soils above the 8 pCi/g release level is present up to a depth of 24 feet below existing land surface. The approximate volume of contaminated soils near Shelter 204 including the concrete apron is 6,700 cubic yards. However, to gain access to deeper contamination or for the purposes of sloping the excavation walls, approximately 4,500 cubic yards of clean soils will also be removed.
Based on historical investigation, the depth to groundwater at the Shelter 204 area is approximately 50 feet. Therefore, groundwater should not be encountered during excavation activities.
3.4.4.4.1 General Excavation Procedures
Excavation of radiologically contaminated soil will commence after the area of excavation has been delineated on the existing ground surface and Shelter 204 has been dismantled. The current delineated area of >8 pCi/g Pu-239/240 soils is presented on Drawing 799147-C1 and C2.
To gain access to the contaminated soils in front of Shelter 204, the concrete cover will be demolished using a hydraulic hammer mounted on an excavator. Concrete debris will be screened and transferred to the appropriate stockpile. After the entire concrete section has been removed, excavation of the soils will commence.
The delination of the perimeter of the exavation limits will be based on a 5-meter grid system. After the delineation of the perimeter, a hydraulic excavator will excavate the >8 pCi/g soils in two-foot vertical lifts.
The excavator will load the >8 pCi/g soils into a front-end loader, the side of the excavation, or directly into a collapsible intermodal container (CIC). The loader will transport the >8 pCi/g soils to the staging area depicted in Drawing 799147-C1. If a CIC was loaded directly, the container will be transported to the staging area using a forklift. The front-end loader will utilize the same path to and from the stockpile to minimize the spreading of any contamination.
If necessary, a front-end loader will then load the >8 pCi/g soils into 12 ton collapsible intermodal containers at the staging area. The containers will be cleaned, secured, inspected, surveyed, and then transported to the rail loading facility located in Lakehurst, New Jersey for transportation to the disposal site, see Drawing 799147-B3, Transportation Route (Appendix F). The containers will be loaded onto transportation trucks using a crane or a forklift.
After a 2-foot lift of the excavation has been removed, another survey will be conducted at the perimeter of the excavation for the delineation of the next 2-foot lift. Along with surveying, perimeter soil samples will be collected for analysis by the on-site laboratory. The excavation work, surveying, and sampling will continue until sample results indicate that no further excavating is required.
Excavation of clean soils in order to access contaminated soils or to maintain appropriate excavation slopes will proceed in the same manner as excavation of >8 pCi/g soils. Clean soils will be excavated with a dedicated "clean" excavator in two-foot lifts and transferred by a dedicated "clean" loader to the clean stockpile area. The path used for transportation of clean soils through the excavation area will be located within <8 pCi/g soil areas. The loader will dump the clean soils at the stockpile area, where they will be held until needed for back filling operations.
Dust nuisance will be reduced primarily through the use of controlled spraying and watering. Water used for dust control will include decontamination water and stormwater run-off for the >8 pCi/g soil areas, and potable water for the <8 pCi/g soil areas. Appropriate measures to control stormwater and sediment will be implemented throughout the time that soils are stockpiled. These measures will consist of the installation and maintenance of silt fence and other erosion control devices around the entire perimeter, as required.
Final status surveying will be performed during the excavation activities when an area is clean based on the delineation sampling and when no further excavating is required.
3.4.4.4.2 Shelter 204 Bunker Removal
The Utility bunkers in front of Shelter 204 will be removed during the main excavation activities. After exposing all sides, the bunkers will be broken in place into sections using a hydraulic hammer on the excavator. After sectioning, the pieces will be removed from the excavation and placed on plastic sheeting next to the excavation area. The concrete pieces will then be surveyed and decontaminated similar to Shelter 204. A temporary plastic cover may be erected around the decontamination area and will be placed under negative vacuum with HEPA filtration. After decontamination efforts, the concrete pieces will be re-surveyed and relocated to the appropriate stockpile (contaminated or clean). The temporary decontamination area will be located far enough from the excavation for excavation activities to resume.
3.4.4.5 Drainage Ditch Excavation
After the completion of the main excavation, the drainage ditch contamination will be addressed. This portion of the site is down slope of the main excavation area, is less contaminated, and requires a shallower excavation, which is why it will be excavated after the main excavation. By excavating this section last, any contamination that might have spread downslope of the main excavation will now be removed during the removal effort at the ditch area.
The excavation will proceed from the north to the south. Perimeter surveying, sampling, and excavating will be conducted similar to the main excavation. However, the excavation will be approximately two to four feet in depth. Contaminated soils will be transferred to the stockpile area for off-site transportation. Due to the configuration and depth of the contamination in this area, the quantity of clean soils removed will be minimal.
Surface runoff during storm events will diverted from the excavated areas through the use of swales and berms. The location of the swales are depicted in Figure 799147-C2. The excavation area will be lined with plastic sheeting in the event that a storm event is forecasted. Surface water within the excavated area will be pumped to a temporary storage tank near the decontamination pad.
Immediately following the excavation at the drainage ditch, a Final Status Survey (FSS) will be conducted as per the Sampling and Analysis Plan.
3.4.4.6 Route 539 Soil Excavation
One soil sample collected across Route 539 along the drainage swale contained Pu 239/240 concentrations above the release limit. The estimated depth of contamination is 4 feet and the volume of contaminated soil is approximately 100 cubic yards.
Perimeter surveying and soil sampling will be collected from this area based on 5-meter grid system and the area requiring excavation will be accurately delineated.
The excavation will be conducted using a small backhoe to reduce the amount of vegetation and trees requiring clearing to gain access to the excavation area.
A limited botanical survey of the area and the access path will be conducted to verify the absence of endangered plants prior to clearing the area. The surveyor will also document the types of plants and trees present for replanting after the excavation. The path to the excavation will be determined based on the least amount of disturbance to the vegetation. All cleared trees and bushes will be stockpiled to the side in a nearby area. The area will then be cordoned off using ropes and signs indicating that the area is a radiological control area.
A backhoe will excavate the delineated area after the completion of the survey and sampling. Excavated soils will be removed and loaded directly into an intermodal container that is placed on a small flat bed truck with a load capacity of 12 tons. Additionally, a 10-mil plastic will be placed under the truck around the bed to capture loose soils dropped during the loading.
After the container is full, the container will be sealed, cleaned and surveyed for contamination at the excavation area. A limited survey of the truck will also be conducted to insure that contamination is not present on the truck.
The truck will then transfer the container to the loading station at the BOMARC facility using the same on-site path used by main transport contractor. A crane or forklift will remove the container and stage it on-site until it is picked up by the transport contractor for off-site disposal.
The truck will be loaded with an empty container and return to the excavation for another load-out. This process will continue until sampling indicates a clean excavation.
The duration of work for this stage is anticipated to be 1-2 days. Because of the location of the excavation (within the swale), the excavation will be conducted during clear weather to avoid having to control run-off water entering the swale.
Immediately following the excavation activities, a Final Status Survey (FSS) will be conducted along the drainage area across Route 539. The excavation will be lined as described in Section 3.4.4.7.
After review and approval of the FSS results, the excavation will be immediately backfilled with borrow material, and the area re-graded to original conditions based on the topographic survey of the area conducted at the start of the project. Tree seedlings, plants and bushes will be planted within the disturbed areas based on the initial botanical survey.
3.4.4.7 Excavation Storm Water Control
As described in Section 3.3.3, swales and berms will be constructed and maintained during the excavation activities to divert surface runoff from entering the excavation pit.
In addition, the excavation will be covered with plastic sheeting at the end of each day to prevent precipitation from entering the excavation. The plastic sheeting will be draped over the excavation sidewalls and placed over the floor of the excavation. The liner will be secured with sandbags at the outer limits of the liner and set in place either manually or with the excavator at regular intervals within the excavation. The liner will be disposed with other remedial waste at the end of the project.
3.4.4.8 Excavation Soil Management
The stockpile areas are also dedicated to the materials they are storing. As a result of the surveying and sampling effort, only soils and debris identified as contaminated will be transported for off-site disposal. As a result of the segregating efforts, the site will contain five separate dedicated stockpiles including:
· Contaminated soils for off-site disposal,
· Contaminated debris for off-site disposal,
· Contaminated debris from shelter 204 with potential for lead contamination,
· Clean soil stockpile,
· Clean debris stockpile
As an extra precaution, all stockpiles will be staged on 10-mil plastic and will be covered with sheeting and sandbags. Sampling and surveying of the stockpiles will be conducted periodically at the discretion of the on-site CHP or as required by the disposal facility. Additionally, the clean soils will be sampled to confirm soil quality prior to backfilling.
The size of the stockpiles will be maintained at 500 cubic yards to reduce the difficulties in covering and uncovering stockpiles. As soil stockpiles (clean and contaminated) reach the 500 cubic yard limit, a composite soil sample will be collected for analyzed by the on-site laboratory. Composite samples will be collected in accordance with the Sampling and Analysis Plan, Appendix C.
3.4.4.9 Equipment
Several pieces of equipment will be required to conduct excavation activities. A brief description of each of these pieces of equipment and their intended use is provided below;
Hydraulic Excavator- A hydraulic excavator operates using the same principles as a backhoe, except at a larger scale. The hydraulic excavator will be of a track-mounted variety. The bucket to be used in excavation will be either an excavation bucket or a utility bucket. The standard bucket capacity is approximately 0.5 cubic yards for a 24-inch wide bucket and 0.75 cubic yard for a 36-inch wide bucket. Hydraulic excavators have a boom and stick assembly that can typically reach soil at ground level 25 to 35 feet away and can excavate to a depth of 20 feet. However, as depth increases, reach decreases and as reach increases, depth decreases. Depth and reach can be maximized by utilizing a high horsepower excavator (typically, higher horsepower equates to greater reach and depth) or by specifying a longer boom and stick assembly. Excavator attachments (hammer and shears) will also be utilized during demolition activities near Shelter 204.
Front -End Loader - A front-end loader is utilized in situations where a large volume of soil may need to be moved in one bucket. The front-end loader will be of the wheel-mounted variety. A wheel mounted front-end loader can travel quickly between the stockpile soils and the location containers are loaded. The bucket to be used for loading is called a general-purpose bucket. The standard bucket capacity is approximately 5.0 cubic yards for a 9 feet wide bucket and 7.5 cubic yards for a 12 feet wide bucket. The width of the machine varies from 8 feet to 11 feet.
Dozer - A Dozer will be used during the backfilling operations for the spreading and compacting of the soils in the excavation. Once the soils within the excavation are 4 feet below the surface, the dozer can enter the excavation, and spread and compact the soils evenly throughout the excavation area.
Water Truck - A water truck will be required on-site to assist in the control of dust during remedial action. The truck will be required to control dust on the access road between the excavation and the load out area, within the excavation area during excavation and within the excavation during backfill operations. The water to be used for dust control will be obtained from stormwater collection devices or from potable water sources, depending upon the area to be sprayed. Potable water will be used for all clean haul roads.
Crane - A 20-ton crane could be used at the load-out area to load filled intermodal containers onto the flat bed trucks for transport to the rail facility. A crane will also be located at the rail facility and will be operated by the transportation contractor for loading intermodals onto the rail cars.
Forklift - A heavy duty forklift could be used to move the filled intermodal containers from the excavation area to the load-out area. The forklift can also be used for loading the containers onto transport trucks and rail cars.
Flat Bed Truck - A flat bed truck will be used in moving intermodal containers to and from the loading pad and the rail facility. The trucks will be on-road straight trucks and each truck will be carrying two filled intermodal containers.
3.4.4.10 Personnel
Experienced personnel will be required to implement excavation and dismantlement activities as discussed herein. Equipment operators will be utilized for hydraulic excavators, front-end loaders, forklifts, and cranes. The number of operators required would be dependent on the quantity of equipment and the task being completed. Operators will be required to comply with the PPE and radiological procedures established in the HASP.
Experienced personnel will also be required to oversee activities in a non-operator capacity. Spotters will be required to assist in the excavation and loading activities. After excavation is completed, they will spot loads for location and placement of backfill materials. Maintenance personnel will also be required to clean up spills of contaminated soils resulting from spilled soils in transport to the load-out area. Finally, an excavation coordinator will be required to supervise all activities and to coordinate equipment and labor between several work areas.
During dismantlement of Shelter 204, experienced personnel familiar with decontamination procedures and equipment will be utilized.
Decontamination, surveying, and sampling activities will be supported by a team of HP technicians under the direct supervision of the on-site CHP.
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