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Final Report
Remediation of Anaerobic Digesters
Winston-Thomas Waste Water Treatment Plant
Sept 21, 1998
PSARA Technologies for CBS Corp.
1.0 INTRODUCTION
This document constitutes the final report for the 1998 sampling and remediation of the anaerobic digesters at the Winston Thomas site in Bloomington, Indiana. Figure 1 illustrates the location of the digesters at the Winston Thomas site.
This report includes a descriptive narrative of work performed, along with associated figures and tables. Additional records associated with this project, including air monitoring results, weekly progress reports, laboratory certificates of analysis, and chainof-custody records, etc., were maintained under the Trickling Filter Remediation Project and will be included in that report.
2.0 SUMMARY OF PROJECT ACTIVITIES
The anaerobic digesters at the Winston Thomas site were remediated during the fall of 1997. The scope ofwork for this remediation project is described in the Work Plan for the remediation of the digesters and drying beds. A final report describing this remediation effort was previously submitted to the Consent Decree parties.
2.1 DIGESTER WALLS AND FLOOR
Following the removal of sludge from the digesters, the remediation contractor, OHM Remediation Services Corporation (OHM) thoroughly cleaned the interior surfaces of the four digesters by pressure washing. CBS collected eight post-cleaning wipe samples (two in each digester) from the concrete wall and floor surfaces. The sample results were all below the PCB cleanup standard presented in the approved Work Plan. These results were reported to the Consent Decree parties. In addition to the CBS samples, the U.S. Environmental Protection Agency (USEPA) chose to collect an additional 32 surfacewipe samples (eight samples were collected from each of the four digesters). Sampling in each digester included five wipe samples from the wall surfaces and three from the floor. The analytical results of the USEPA sampling effort are presented in Table 1.
Three of the 32 samples collected by the USEPA showed analytical results above the PCB cleanup criterion of 100 ug/100 cm . Digesters 1, 3, and 4 were represented by these three samples. Two of the three samples were from side walls, whereas the third was a floor sample. The results of these three samples did not suggest any trend or identify specific areas of ineffective decontamination. The USEPA requested that CBS inspect these three areas for any evidence of inadequate cleaning and then to resample each of these three locations.
PSARA Technologies was contracted by CBS to perform the digester inspections and additional sampling. PSARA performed this assignment on June 10, 1998. Two of the three areas inspected did not exhibit any noticeable differences relative to the adjacent concrete floor and wall surface areas. The wall surface area in Digester 4 corresponding to sample S21(NE 4-5), however, showed some discoloration relative to the other decontaminated areas. The discoloration encompassed a section of the west wall of the digester from the floor to a height of about 8 feet. All three locations were sampled by PSARA on June 10, 1998.The sampling was observed and documented by the City of Bloomington.
The results of this resampling effort are presented in Figure 2. As the figure illustrates, the locations in Digesters 1 and 3 did not exhibit elevated surface PCB levels, whereas the discolored area in Digester 4 showed a PCB level of 130 ug/100 cm .
On July 21, 1998, PSARA recleaned the west wall of Digester 4 by pressure washing the affected area. Following the recleaning, a verification wipe sample was collected near the location of the previous samples. As shown in Figure 3, the result showed a PCB level of 12 ug/100 cm2. Based on this post-cleaning result, no additional surface decontamination was required.
2.2 SOILS ADJACENT TO THE DIGESTERS
Following the removal of sludge from the digesters, CBS excavated a limited amount of soil from the load-out areas between the digesters. The purpose of this excavation was to remove any incidental spillage thatmay have occurred during sludge removal.
A total of six verification soil samples were then collected from the excavated areas between the digesters. Figure 4 illustrates these sampling locations and presents the results of this sampling effort.As shown in Figure 4, PCBs were identified at a concentration of 2900 ppm from the location adjacent to Digester 4. CBS's contractor subsequently removed approximately 1 ft of additional soil from this location.
Following the removal of affected soils from around Digester 4, a second verification sample was collected from the excavation area. As illustrated in Figure 5, PCBs were identified in this sample at a concentration of 31 ppm. Unfortuneately this sample was collected just prior to the demobilization of the excavation equipment, and the resources were not available at the site to perform additional excavation at that time. On May 22, 1998, in conjunction with the excavation around the perimeter of the sludge dryingbeds,
CBS's contractor removed approximately 5 additional cubic yards of soil adjacent to Digester 4. A final verification soil sample was collected on May 22, 1998. The results of this sample were below the PCB detection limit of 1 ppm. Figure 6 shows the approximate area of excavation and the post-excavation soil sample result.
Following completion of this remediation and sampling effort, CBS backfilled the excavated areas with clean crushed stone to original grade.
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