Known: SWMU B-3 is a former landfill area that consists of two trench areas of unknown depth. The trenches were reportedly created by taking advantage of the natural slope to the west, and by cutting into the weathered limestone to provide greater disposal volume. It was generally thought these trenches were used for garbage disposal and burning trash. The trench areas were filled in 1990-1991.

Chlorinated hydrocarbons were detected in Well 16 in 1991 at concentrations above drinking water standards, prompting several investigations aimed at identifying possible source areas that could have contributed to the contamination. Well 16 is located less than 1/8-mile north of SWMU B-3. Source characterization began in the vicinity of Well 16 with surface geophysical surveys performed in 1995 at seven potential source areas. Two large anomalous areas were detected at SWMU B-3 during these surveys. A subsequent soil gas survey of SWMU B-3 identified TCE and PCE associated with geophysical anomalies, with occasional detection of 1,2-DCE. The presence of these chlorinated compounds implicated SWMU B-3 as a likely source area for the contamination detected in Well 16.

Previous Investigations: The following summary and associated SWMU B-3 maps can be found in Volume 4 behind the Soil Vapor Extraction tab. Under Order 67, available records at CSSA were reviewed for an evaluation of groundwater contamination. Three geophysical anomalies were observed during an EM geophysical survey (1 February 1995); however, one anomaly was attributed to underground piping to the north of the two B-3 trench anomalies. A GPR survey was completed on 15 March 1995.

Also under Order 67, seven soil borings were completed between 7 and 16 March 1995. Soil/rock samples were collected during drilling activities, and one groundwater sample was collected from SB1 on 9 March 1995. PCE, TCE, vinyl chloride, chromium, lead and nickel were all detected in the soil/rock samples above comparison criteria. PCE, cis-1,2-DCE, TCE and vinyl chloride were detected in the SB1 borehole perched groundwater sample. Chemron analyzed samples collected during this phase of the investigation.

Two phases of soil gas surveys were completed during June and November/December 1995. PCE and TCE were observed at high concentrations in the immediate vicinity of the anomalies, and cis-1,2-DCE was detected in association with the PCE and TCE. Parsons ES used a field gas chromatograph to test soil gas samples directly in the field.

A limited SVE pilot test was performed under Order 67 in February and March 1996 to collect site characterization data from the trench soil, and to evaluate SVE as a possible removal mechanism for remediation of VOC contamination in the trench. Six VEWs and six multi-depth vapor monitoring points (VMPs) were installed in and around the main trench area (west trench) at SWMU B-3. A blower was manifolded to five of the six VEWs with the system piping constructed aboveground. Each VEW was constructed with a pressure monitoring port, a flow measurement port, and an individual flow control valve.

Fifteen soil samples were collected during the pilot test system installation and analyzed for VOCs, while ten of the samples were tested for metals and geotechnical parameters, such as grain size, total organic carbon, porosity, pH, and biological nutrient content (nitrogen and phosphates). Chemron performed the analysis of the samples for metals and VOCs, and Core Laboratories performed the geotechnical testing. The highest VOC concentrations were detected in the soil samples collected from VEW-1, VEW-2, MPA, and MPD, which were all located in within the limits of the main landfill trench at SWMU B-3. The analytical results also indicated that the greatest contaminant concentrations were encountered in samples collected from 13 to 15 feet BGL. The contaminant levels of TCE detected in soil samples exceeded the TNRCC risk reduction standard 2 (RRS2) groundwater protection criteria for residential use in eight of the fifteen samples tested. Three samples exceeded the criteria for cis-1,2-DCE, and one sample exceeded the criteria for PCE. Except for the PCE detection in monitoring point MPE, all of the exceedences occurred in samples collected within the limits of the main landfill trench.

The two week pilot test completed in March 1996 consisted of initial soil gas testing, air permeability testing, pressure influence evaluation, and SVE exhaust emission testing. The results of this testing demonstrated that an SVE system operated at the site could significantly reduce the VOC concentrations present in the trench area. The results also indicated that the subsurface soil and limestone at the site are very complex, and that it would be difficult to extrapolate the pilot test results across the entire site without the collection of additional data. Based on the emission data collected during the pilot test, the TNRCC approved a standard exemption request to allow off-gas to be directly emitted from the SVE system to the atmosphere.

A three-month treatability study was performed to provide additional data concerning the effectiveness of SVE at removing VOCs at SWMU B-3. During the 3-month study, an estimated 18 pounds of TCE and 9.7 pounds of DCE were removed from the trench areas. The total contaminant mass in the existing treatment area (above the fractured limestone) was estimated to be less than 100 pounds. Twelve additional VEWs were installed in the main trench area, and expanded treatability testing was performed under delivery order RL17 from December 1996 through April 1997. A soil boring was drilled near MPA, MPD, VEW-1 and VEW-2 for collection of confirmation soil samples, and twelve additional soil borings were advanced for installation of VEWs in the expanded 18-VEW SVE system. One soil sample was collected from each of the VEW borings. The confirmation samples were tested for VOCs and compared to initial pilot test VOC concentrations, while the samples collected from the VEWs were analyzed for VOCs, metals, and miscellaneous physical parameters. The samples collected under this delivery order were analyzed by ITS Laboratory. Because of issues concerning the quality of any data generated from the ITS laboratory, the data were determined to be questionable, and only usable as screening or qualified data. The ITS qualified data compliments the existing screening data collected in the field using direct read instruments and meters (air flow rate, total volatile hydrocarbons, oxygen, carbon dioxide, and pressure).

Several treatability study tasks were performed on the expanded SVE system. The primary tasks included a hydrocarbon recovery test performed after shutting down the pilot test system to determine recovery rates of VOCs in soil gas and the approximate time required for soil gas to return to near static conditions, and periodic testing of three different extraction configurations to determine the effective radius of influence of each VEW extraction configuration. The multiple configuration tests (MCTs) enabled the estimation of VOC removal rates from three different six-VEW configurations, and the contribution to the removal rate of each VEW in each particular configuration. The MCTs also allowed for monitoring of pressure and soil gas changes within the main trench.

Most of the treatability testing was performed with direct read field instruments, but a few soil gas samples were collected from specific VEWs for laboratory testing prior to the initial system shut down for the hydrocarbon recovery test. These samples were intended to provide a general relationship between specific contaminant concentrations as measured using EPA protocols in an off-site lab with the TVH readings measured with the field instruments. Additional laboratory testing was performed on samples collected from VEW-01 over a 30-day period to evaluate the occurrence of biological degradation from within the trench. Emission samples were also collected for laboratory testing from the system exhaust prior to the shutting down the initial pilot test configuration, and during all three MCTs. All soil gas samples were tested by ITS.

Results from the treatability testing activities further demonstrated that SVE can be a valuable mechanism for removal of VOC contamination at SWMU B-3. VEW-04 and VEW-05, which are located outside the trench limits in native limestone, were the extraction wells that contributed most to VOC mass removal, suggesting that VEWs outside the main trench may be capable of exerting the greatest influence (and VOC removal) on the largest portions of the treatment area. The results indicated that two of the VEWs (VEW-10 and VEW-12) located in the middle of the main trench showed the next greatest VOC removal rates during their respective MCTs. These conclusions were drawn primarily from data generated in the field with direct read instruments, and were not adversely affected by the data quality problems associated with the ITS data.

The results also indicated that the portion of the trench represented by VEW-3, VEW-17, and VEW-18 may be difficult to treat due to poor removal rates. ITS results from samples collected from these borings indicated that TCE was above the cleanup criteria.

Planned Rework: The data collected during the initial pilot test under Order 67 indicates that several VOCs are present in the trench area. TCE and cis-1,2-DCE exceeded TNRCC’s RRS2 residential criteria for groundwater protection from samples collected inside the main trench area. TCE was detected in each of the twelve samples collected from VEW borings and tested by ITS, but only above RRS2 criteria in three locations (VEW-13, VEW-17, and VEW-18). Due the questionable nature of the ITS data, each soil boring location and depth interval corresponding to the twelve VEWs installed for the 1997 treatability study should be resampled and tested for VOCs by method SW-8260B. This data is critical, since it may impact the determination of the extent of future treatment areas in SWMU B-3.

The analytical results from the four confirmation samples showed a significant reduction in contaminant concentrations in the vicinity of the pilot test VEWs with the exception of the sample collected from VEW-01 from 9-11 feet bgs. This sample was the only one collected from a depth less than 13 feet bgs. These results imply that the SVE system is very effective at removing VOCs from the deeper soil in the trench, which is meaningful because the majority of contamination has been identified in the deeper portions of the trench. Although the ITS data is qualified, the sharp reductions observed in the deeper samples collected at each location are more than one order of magnitude less than concentrations reported for the pilot test data. No resampling is warranted for these samples because the existing data clearly illustrates VOC reductions in the deeper soils near the VEWs. The confirmation soil data were also intended to be "time-sensitive" to quantify VOC reductions due to the prior six months of continuous extraction for the five-VEW pilot SVE system. It is not possible to replicate this data because the soils in question have undergone four months of treatability testing, and approximately two years of semi-continuous (periodic operation) extraction.

The metals data from ITS are also questionable, but appear to correlate reasonably well with data generated by Chemron during the initial pilot test. Of the twelve samples analyzed for metals, only one sample, VEW-08(8-10), had metals detected at concentrations significantly greater than background. It is important to note that VEW-08 is located less than 15 feet from MPD, which was the only sample location inside the main trench area that had high levels of metals from the pilot test sampling. Based on the valid data from the pilot test, and the qualified data from ITS, it appears that the only portion of the SWMU B-3 trench with significant metals contamination is located in the northern portion trench near MPD. However, samples should be collected for metal analysis from every location except VEW-08(8-10) to verify that metal contamination is not present in the fill material located in the main trench south and west of MPD. Re-analysis of a sample from VEW-08(8-10) will not provide any new information about this portion of the trench exhibiting high metal levels. This portion of the trench is already represented by the valid data reported at MPD.

Ten soil samples were collected during drilling of the additional VEWs for geotechnical analyses. The testing results from these samples were similar to the test results for the geotechnical analyses performed by Core Laboratories on samples collected during the pilot test, with the exception of porosity and clay content. The porosities reported by ITS appear more realistic than the porosities reported by Core Laboratories (pilot test results) given the types of soil that were encountered in the trench area. The ITS data also indicated slightly higher clay contents than the pilot test data. The grain sizes were determined by sieve analysis and by using the hydrometer method. There is little opportunity for laboratory reporting errors that would result in significant differences in actual grain size. The geotechnical data from ITS should still be considered usable for defining soil characteristics in the trench, and should be averaged with the geotechnical data from the pilot test to provide working numbers for determining soil mass and for eventual use in contaminant fate and transport models. Resampling for geotechnical data would not result in significant changes in the physical characteristics of the soil, so no resampling for these parameters is proposed.

ITS data did not affect the findings of the treatability testing relating to SVE effectiveness, VOC removal, and influence testing. Soil gas samples analyzed by ITS consisted primarily of emission samples collected from the system during a specific test at a specific time. It would be impossible to replicate the conditions that existed at the time of each test, so no resampling of these tests are planned. The objectives of each test were clearly reached using the field data, and the qualified ITS data provides some insight into the composition of the VEW air flows that contained the greatest levels of VOCs. Emission data from the initial pilot study was used to obtain the modification to the existing standard exemption (approved by TNRCC in Spring 1999) for emitting exhaust from the SVE system directly into the atmosphere. No additional data is warranted.

Rationale for Analytical Program: Based on previous analytical results and historic usage as a landfill, chemicals of potential concern include VOCs, and metals. In addition, volatiles were detected at SWMU B-3 during soil gas surveys in 1995 (TCE and PCE).

Resampling Activities: The following activities constitute an additional investigation at SWMU B-3 to resample some of the soil samples from the treatability study that were collected to characterize the nature and extent of soil contamination within the SWMU B-3 area. This re-work will be completed as part of the requirements under the RCRA 3008(h) Order:

1. The boring logs from the installation of the VEWs will be copied and reviewed by the supervising geologist prior to beginning any rework at SWMU B-3. In particular, the geologist will review the PID readings and recovery volumes obtained from the existing VEW borehole.

2. Drill twelve soil borings within three to five feet of the existing VEWs completed when the SVE system was expanded in December 1997. The rework soil samples will be collected from each boring from the same depth intervals as the first set of subsurface soil samples, unless field instruments indicate that VOCs are present in the boring from a different depth. If PID readings indicate that VOCs are present, then the subsurface soil sample from that interval will be submitted to the laboratory for analysis. The total depth of each boring will be at approximately the same depth as the first set of soil borings. Each rework sample will be analyzed for the appropriate VOC and metallic constituents as indicated in the table below. QA/QC samples will be collected as described in Section 2.4 of the FSP.

3. Boring logs for the rework will not be completed. Instead, the original boring logs created from the boring completed in December 1997 will be available onsite during rework activities (See activity 1). Changes to the boring log will be made if field geologist observes a major difference in the rework boring from the original soil boring.

4. Investigation derived waste will be handled as specified in the FSP. To minimize waste, solid flight augers may be used to drill to the approximate resample depth, and then a split spoon or shelby tube sampler will be used to collect the sample at the appropriate depth. If borehole stability does not allow the use of solid flight augers, hollow stem augers will need to be used.

5. Water is not expected to be encountered in the borings at the site. If water is discovered in any of the soil borings, it will be reported to AFCEE and CSSA immediately. Completion of wells is beyond the scope of this rework as no monitoring wells were previously installed at the site.

6. Handle IDW as specified in the FSP.

7. Analytical results for the data quality rework samples will be reported in the Rework ITIR.

8. If the results of the above work indicate that the site can be closed under RRS1 without any further investigation and/or remediation, a technical/closure report will be prepared under the RL17 SOW and submitted in accordance with TNRCC closure requirements. If the site does not meet RRS1 closure requirements, a technical report describing the results of the investigation and recommended additional investigation and/or remediation will be prepared under the RL17 SOW.

ITS Sampling Summary - SWMU B-3

Rework Sampling and Analysis Plan - SWMU B-3