Cost and Performance Report: Soil Vapor Extraction at the Hastings Superfund Site, Well Number 3 Subsite Hastings, Nebraska

Table of Contents

• Executive Summary
• Site Information
• Matrix Description
• Treatment System Description
• Treatment System Performance
• Treatment System Cost
• Observations and Lessons Learned
• References
• Appendix A- Treatability Study

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Treatment System Description

Primary Treatment Technology

Soil vapor extraction

Supplemental Treatment Technology

Post-treatment (air) using carbon adsorption

Soil Vapor Extraction System Description and Operation [2, 3, 4]

System Description

The SVE system used at the Hastings Well Number 3 Subsite consisted of 10 extraction wells (5 deep, 3 intermediate, 2 shallow), five monitoring well probes, and associated vacuum and air treatment equipment. The location and depth of these wells are presented in Figure 5 and Table 3, respectively. Extraction wells were installed at different depths to capture the vertical extent of the contamination which ranged from the ground surface to the water table. The extraction wells were constructed with 4-inch diameter, schedule 80 polyvinyl chloride (PVC) pipe, with 0.01-inch PVC screen. The intermediate and deep extraction wells were installed in pairs (three sets of collocated wells) approximately 5 feet apart.

Figure 5. Location of Extraction and Monitoring Wells [2]

Table 3. Status of Extraction and Monitoring Wells [3]

*TS - Treatability Study
FS - Full-Scale Operation

Full-scale system design was based on the results of the pilot-scale treatability study (Appendix A) along with information on the site geology and the results of a pump test. The two deep extraction wells and one of the two shallow extraction wells used in the treatability study were utilized for the full-scale application. One shallow extraction well used in the treatability study was capped and abandoned because the well interfered with placement of the activated carbon canisters. Additional wells added for the full-scale application included one shallow well, three intermediate wells, and three deep wells.

For each well pair, the screened interval of the intermediate well was 50 to 80 feet below ground surface (bgs), and 80 to 110 feet bgs for the deep wells. This configuration allowed selective operation of the wells at higher vacuum/flow conditions than could be achieved through one well.

Each extraction well was installed with a vacuum gauge to monitor well head conditions and a butterfly valve to throttle the well head vacuum and select use of the 30-foot screened well. The extraction wells were hard piped to the extraction and treatment system with heat traced and insulated PVC pipe, as shown in Figure 6.

Figure 6. SVE System Site Layout [2]

The extraction and treatment system consisted of an air/water separator, an air-to-air heat exchanger, a vacuum pump, and vapor phase granular activated carbon (GAC). The extraction system components were mounted on a process skid which included a flow metering piping run where the temperature, pressure, and flow rate of the extracted gas were monitored. The configuration of the equipment on the process skid and the arrangement of the system are shown in Figure 7.

Figure 7. Process Area General Arrangement [2]

The system included six 1,000-pound canisters of GAC, configured in two stages of three canisters each. When spent, carbon canisters were transported to a regeneration facility in Parker, Arizona. The treated vapors were discharged to the air through a 20-foot high steel stack.

System Operation [2, 6]

The SVE system was operated from June 25, 1992 to July 1, 1993 for a total of 6,600 hours. During operation of the SVE system, selective use of the extraction wells occurred, depending on the results of vapor samples collected at the individual wellheads. Additionally, the entire system was temporarily shut down when the overall extraction rate was less than the required cleanup extraction rate, carbon breakthrough occurred, or a sampling event occurred. A chronology of the SVE operations, including a description of activities, is presented in Table 4.

Table 4. SVE System Operations Chronology [6]

Depending on the number of wells being pumped at a given time, the total air flow rate ranged from 519 to 754 standard cubic feet per minute and the extraction well head vacuums ranged from 3.05 to 7.6 inches of mercury.

A detailed description of the SVE operation is presented below [22]:

June-July 1992: The initial operations of the SVE system focused on the "heart" of the contaminated area using extraction wells SVE-1S, -1D, -3S, -5I, and -5D. SVE modeling results indicated that the SVE system at the Well Number 3 Subsite would not generate enough vacuum to effectively remove contaminants if all extraction wells were opened. Initially, the plan was to extract from this area, then to extract from the fringes (extraction wells SVE-4I, -4D, -6I, and -6D), modifying the gas flow pattern as to when wells were opened and closed. This operation plan was unsuccessful because the high vacuum generated by pumping only on the interior wells, drew water into the SVE system, which resulted in a system shutdown. On July 1, 1992, system operation included all extraction wells. The SVE system was operated for 789 hours with vacuum on all wells. The concentration level of CCl₄ in the gas stream collected at the system inlet (S-101), dropped from 140 µg/L to 13 µg/L as measured in the EPA analysis of the 6-L SUMMA^TM canisters. On July 26, 1992, the system was shut down for 9 days to evaluate VOC rebounding effects.

August-September 1992: On August 6, 1992, the system was restarted (all SVE wells) to determine rebounding effects. The analytical results indicated that there was little or no rebounding. The system was operated, pumping on all extraction wells which contained CCl⁴, until September 17, 1992 (1,027 hours) when the system was shut down to replace GAC.

October-January 1993: The system was restarted on October 10, 1992 and operated continuously until January 4, 1993 (an additional 2,036 hours). In November, additional peaks in the sample analyses were noted by the on-site analyst. The on-site analytical system used an electron capture detector which is sensitive to chlorinated solvents. SUMMA^TM canister samples were collected from the wellhead locations from where these extra peaks were noted (S-101 and SVE-5D) on November 23, 1992 and sent to the EPA-Region VII laboratory. Analysis of these samples confirmed the presence of other VOCs in the system.

In December 1992, several operational changes took place. The NDEQ determined that, due to the low levels of VOCs present in the SVE gas stream, the GAC could be removed, and EPA and the NDEQ set an extraction rate remediation goal for CCl₄ at 0.001 pounds/hour. This level would need to be achieved based upon pulsed pumping, and verified with soil-gas sampling using SUMMA^TM canisters. The SVE system was shut down on January 4, 1993 for a two-month resting period.

February 1993: Gas samples were collected on February 6, 1993 for both on-site and EPA analyses. The EPA results indicated that the levels of other VOCs increased in SVE-5D, while the levels of CCl₄ remained low. Gas samples were collected during very cold weather which could have affected the results. SUMMA^TM canister samples were believed to be less affected by the low temperatures than the syringe samples.

March 1993: The system was re-started with pumping from wells SVE-1S, -1D, -3S, -5I, and -5D. Samples were collected with SUMMA^TM canisters on March 4 and 6 to determine rebounding effects. Some inconsistencies between on-site and off-site analysis were noted. There are several reasons why these inconsistencies may have occurred including: (1) sample size (10-mL syringe vs. 6-L SUMMA^TM canisters); (2) temperature effects on collection method; and (3) low contaminant concentrations. On March 24, extraction wells SVE-4I, -4D, -6I, and -6D were added to the system.

April-June 1993: EPA and NDEQ agreed that the system would run continuously until analytical results could be verified, or until July 1, 1993. All extraction wells were being pumped. A final inspection of SVE system operation took place on April 19, 1993. On April 29, 1993, two extraction wells were removed from the system (SVE-3S and -4I) to increase flow to SVE-5D. Collection of verification samples was conducted on May 1, 1993 with the collection of SUMMA^TM canister samples from SVE-5D and S-101 (system inlet). On-site testing results indicated that the CCl₄ levels remained low. Off-site EPA analyses of samples indicated that the on-site, field method has a negative bias of approximately 50%.

Post-June 1993: SVE skid equipment was dismantled and moved to EPA’s storage area in Hastings, Nebraska. EPA abandoned all SVE extraction wells and monitoring probes. The chain-link fence has been reconfigured to accommodate the groundwater treatability study system.

Operating Parameters Affecting Treatment Cost or Performance

The major operating parameters affecting cost or performance for this technology and the values measured for each are presented in Table 5.

Table 5. Operating Parameters [6-19]

Timeline

A timeline for this application is shown in Table 6.

Table 6. Timeline [1, 2, 4, 6]

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References

1. U.S. Environmental Protection Agency. Record of Decision, Hastings Groundwater, NE, September 1989.

2. Morrison-Knudsen Corporation. Preliminary Design Report for a Soil Vapor Extraction System, Well Number 3 Subsite, Revision 1, U.S. EPA ARCS, September 1991.

3. U.S. Environmental Protection Agency. Remedial Action Report for Source Control Operable Unit at the Well #3 Subsite, Hastings, Nebraska, June 17, 1993.

4. Morrison-Knudsen Corporation. Soil Vapor Extraction Treatability Study Report, Well Number 3 Subsite, U.S. EPA ARCS, July 1991.

6. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - May/June 1993 Monthly Status Report," U.S. EPA ARCS, July 7, 1993.

7. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - April 1993 Monthly Status Report," U.S. EPA ARCS, May 3, 1993.

8. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - February/March 1993 Monthly Status Report," U.S. EPA ARCS, April 6, 1993.

9. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - December 1992/January 1993 Monthly Status Report," U.S. EPA ARCS, January 4, 1994.

10. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - November 1992 Monthly Status Report," U.S. EPA ARCS, December 9, 1992.

11. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - October 1992 Monthly Status Report," U.S. EPA ARCS, November 2, 1992.

12. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - September 1992 Monthly Status Report," U.S. EPA ARCS, October 1, 1992.

13. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - August 1992 Monthly Status Report," U.S. EPA ARCS, September 3, 1992.

14. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - July 1992 Monthly Status Report," U.S. EPA ARCS, August 3, 1992.

15. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - May 1992 Monthly Status Report," U.S. EPA ARCS, June 4, 1992.

16. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - April 1992 Monthly Status Report," U.S. EPA ARCS, May 4, 1992.

17. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - March 1992 Monthly Status Report," U.S. EPA ARCS, April 3, 1992.

18. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - February 1992 Monthly Status Report," U.S. EPA ARCS, March 3, 1992.

19. Morrison-Knudsen Corporation. "Well Number 3 Source Control, Remedial Design/Remedial Action - December 1991/January 1992 Monthly Status Report," U.S. EPA ARCS, February 5, 1992.

22. Comments submitted by Diane Easley of EPA Region VII on February 9, 1995.