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SWMU O-1 Interim/Stabilization Measures and Partial Facility Closure Report

Section 2 - Field Investigation

2.1 - Site Interim Measures and Closure Evaluations

As outlined in the Environmental Encyclopedia IM Work Plan (Volume 1-2, SWMU O-1), interim measures for the site included collecting soil samples based on an effort to define the lateral and vertical extent of contamination within SWMU O-1. Upon determining the lateral extent of contamination, a removal action of all contaminated surface soils was conducted to meet RRS1 partial facility closure standards for the unit. All field activities conducted were in accordance with the Field Sampling and Analysis Plan (Volume 1-5, Field Sampling Plan) Quality Assurance Project Plan, and RL74 Addendum).

2.2 - Field Actions

2.2.1   Objectives

The soil gas survey in 1995 detected chlorinated volatile organic compounds (VOCs) at SWMU O-1 that are the same as those which caused the decommissioning of Well 16 as an active water supply source. The objectives of the IM corrective actions are to ensure that interim measures are designed to control or abate threats to human health and/or the environment and to prevent or minimize the further spread of contamination while long-term remedies are pursued at CSSA. Therefore, the project requirements as defined by the SOW and IM Work Plan are:

Target VOCs (PCE, TCE, DCE-isomers, VC, xylenes, and toluene) using U.S. Environmental Protection Agency (USEPA) Solid Waste method SW8260B.

Metals (cadmium and chromium) using USEPA Solid Waste 846 method SW6010A.

During November 1999, an attempt to identify the lateral and vertical extent of contaminants at SWMU O-1 was initiated. Based on former investigations, the constituents of concern (COCs) are VOCs (PCE, TCE, DCE-isomers, VC, xylenes, and toluene) and metals (chromium and cadmium).

2.2.2   Methods

All samples were obtained using either a decontaminated hollow stem auger or hand trowel. All decontamination, sample preparation, and handling followed protocols established in the Field Sampling and Analysis Plan (Volume 1-5, Field Sampling Plan) Quality Assurance Project Plan, and RL74 Addendum).

Environmental sampling also included collection and submittal of quality assurance (QA) and quality control (QC) samples at those frequencies outlined in the AFCEE Quality Assurance Project Plan (QAPP) (Volume 1-4, Quality Assurance Project Plan). All extent investigation samples (including QA/QC) were collected in a collaborative effort from November 1999 through July 2000. Contaminants of concern were identified in previous investigations through boring location identified as O1-SB1 through O1-SB4. Results of the previous investigations are located in the Environmental Encyclopedia (Volume 1-2, SWMU O-1).

2.2.3   Synopsis of the Interim/Stabilization Measures

All samples were collected and submitted to O’Brien & Gere Laboratories (O’B&G) in Syracuse, New York. A total of 25 environmental samples, two field duplicates, two equipment blanks, three trip blanks, and two sets of matrix spike/matrix spike duplicate (MS/MSD) samples were submitted for analyses.

All sampling points were surveyed by Parsons Engineering Science, Inc. (Parsons ES) using a Trimble Asset-grade Global Positioning System (GPS) with 1-meter accuracy. All sample location and analytical data have been incorporated into the CSSA Geographic information system (GIS).

Fifteen shallow subsurface soil borings (identified as O1-SB10 through O1-SB24), generally to a depth of 4 feet or until limestone was encountered, were drilled in locations surrounding the known geophysical anomaly in the SWMU O-1 area. Composite samples from the shallow subsurface soil borings were collected and analyzed to determine the lateral extent of contamination. Five borings (identified as O1-SB5 through O1-SB9 with associated QC samples) were drilled in the center of SWMU O-1 to a depth of approximately 27 feet bgs in an attempt to define the vertical extent of contamination. Grab samples were collected at the soil/rock interface and at total depth. Soil boring logs from the lateral and vertical extent investigations are included in Appendix C.

Analytical results from the initial lateral extent investigation, conducted in November 1999, indicated the lateral extent of contamination at SWMU O-1 was not defined satisfactorily. Additionally, analytical results of the vertical extent investigation indicated that the vertical extent of contamination is below 27 feet bgs and thus not currently defined. No further investigations of the vertical extent of contamination were performed during the remaining IM activities.

An additional six lateral extent borings were drilled in April 2000 (identified as O1‑SB25 through O1-SB29) and July 2000 (identified as O-1-SB30). Upon reviewing results from the samples collected from these borings in combination with previous investigation results, it was determined that the lateral extent of contamination can be accurately defined.

The lateral extent of contamination, and hence extent of removal actions, are shown in Figure SWMU O-1-2. The boundary shown was determined by connecting all boring locations that showed no evidence of contamination that were just beyond borings that showed contamination, progressing outwardly from the points of highest contamination in the center of the former oxidation pond. The boundary encloses all borings that showed some evidence of contamination, while the borings that define the boundary and those outside of the boundary showed no evidence of contamination.

Soils within the lateral extent were characterized for waste disposal in accordance with 30 TAC 335 subchapter R. Ten waste characterization samples were collected within the unit boundaries for establishing proper waste characteristic data. Samples were analyzed by USEPA SW 846 Method 1311 Toxicity Characteristic Leaching Procedure for all constituents of concern. Data results indicated that the soils meet Class 2 Non-hazardous levels specified in 30 TAC 335 subchapter R. The soils were profiled into Waste Management Inc.’s Covel Gardens facility.

Excavation of the subsurface soils from the known extent of contamination within SWMU O-1 began on July 24, 2000. Eagle Construction and Environmental Services, Inc. performed the excavation/disposal effort, including the clay cap installation. The excavation and removal of contaminated soils was completed on July 25, 2000 with approximately 1,515 cubic yards of soil material transported and disposed of in Waste Management Inc.’s, Covel Gardens facility. Figure SWMU O-1-3 shows the approximate extents of the excavation at SWMU O-1.

The area of excavation encompassed approximately 7,000 square feet. Excavation was continued until all soils were removed within and slightly beyond the lateral extent of contamination and to a depth where bedrock was encountered. The resulting excavation was approximately 5 feet deep.

Backfilling of the excavation commenced on July 26, 2000. Backfilling was performed to fill the excavation resulting from removal of contaminated soils and to create a solid foundation for the overlying clay cover. The backfill material was a dense, clay-rich soil, placed in 1-foot lifts and compacted. Specifications for compaction and moisture content of the backfill are presented in Table SWMU O-1-1.

A low-permeability clay liner was constructed over the site. The clay liner is a minimum 2 feet thick at all locations and was constructed in 6-inch lifts to a slope of approximately 4 percent. The construction specifications for the liner are also listed in the Table SWMU O-1-1. Laboratory and field soils testing results are presented Appendix A. Six inches of topsoil were placed on top of the clay liner, and a vegetative surface was established upon the topsoil. As-built construction drawings depicting the completed cover are presented in Appendix B.

Appendix C contains copies of the daily field notes from the IM, soil boring logs, State of Texas Non-hazardous waste manifest for the soil removed, and the photographic data sheets showing the IM work progress.

Table SWMU O-1-1 - Construction Specifications for Soil Components of Liner System

2.3 - Results and Comparisons

As described in section 2.2, no target analytes were detected above background levels or reporting limits (RLs) in any of the environmental samples used in the delineation of the lateral extents of SWMU O-1. Table SWMU O-1-2 presents a summary of the sample results and method detection limits (MDLs) achieved by O’B&G. In terms of closure criteria, CSSA adopted the AFCEE QAPP RLs as the project PQLs. For COCs, the AFCEE RLs are at or below the PQLs stated in SW-846. Therefore, the AFCEE RLs have been accepted by TNRCC for RRS1 closure criteria in correspondence dated October 5, 1999 (Volume 1-1, TNRCC). Results of all IM environmental samples, data validation summaries, and laboratory data packages are included as Appendix D of this report.

2.4 - Operation and Maintenance

The O&M of the cover includes maintaining the grasses on all parts of the cover. Any incidental damage to the cover caused by rainfall shall be repaired.

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