Technology:
Pump and Treat
- Extraction includes interceptor trenches that began operating in 1996 and extraction wells, installed in April 1999 to enhance contaminant recovery in hot spot areas of the plume
- CSFF extraction system - one interceptor trench (170 ft long, 3 ft wide, 12 ft deep) with a geomembrane liner and filled with gravel, and one extraction well (PVC, 6-inch diameter, 15.5 ft deep) located upgradient of the trench; estimated pumping rate of well is 0.5 to 1 gpm
- AS-143 extraction system - one interceptor trench comprised of two legs (85 ft and 70 ft long) joined at a 130 degree angle; two extraction wells - one each located upgradient of each leg of the trench; trench and well construction similar to CSFF
- AS-4151 extraction system - one interceptor trench (185 ft long); one extraction well (28.5 ft deep); trench and well construction similar to CSFF
- Extracted water from trenches at all three sites piped to the CSFF treatment system
- Treatment system includes Stripperator® (combination oil/water separation and air stripping unit); water sent through a bag filter to granular activated carbon (GAC) units; treated effluent discharges to surface drainage; vapors from air stripper discharged to atmosphere; recovered oil stored in drums
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Cleanup Authority:
State of North Carolina UST program
Contact:
Naval Facilities Engineering Command
1100 23rd Avenue
Port Hueneme, CA 93043 |
Contaminants:
BTEX and SVOCs
- Maximum concentrations in groundwater included 2,545 ug/L for benzene; 1,383 ug/L for ethylbenzene; 3,050 ug/L for toluene; and 5,214 ug/L for xylenes |
Waste Source:
Leaks from underground gasoline and fuel storage tanks and from fuel pipelines |
Type/Quantity of Media Treated:
Soil and Groundwater
- Soil at site is sand, silt, and clay, underlain by fine gravel, limey clay, and shell fragments
- Water table is 6-7 ft below ground surface (bgs) |
Purpose/Significance of Application:
Use of pump and treat system to remediate BTEX and SVOC groundwater contamination at three sites |
Regulatory Requirements/Cleanup Goals:
- Groundwater cleanup goals for 12 contaminants of concern including benzene (1 ug/L), ethylbenzene (29 ug/L), toluene (1,000 ug/L), xylenes (400 ug/L), 1,4-dichlorobenzene (1.8 ug/L), ethylene dibromide (0.0004 ug/L), acenaphthene (80 ug/L), acenapthylene (210 ug/L), fluorene (280 ug/L), 1-methylnaphthalene (practical quantification limit), 2-methylnaphthalene (28 ug/L), naphthalene (21 ug/L); required to treat until these goals are met or until asymptotic levels are documented
- Effluent from the CSFF treatment plant must meet the state water quality standards; NPDES permit requirements specified for benzene and toluene |
Results:
- As of May 1999 (2.5 years of operation), the cumulative mass of contaminants removed from the three sites is 3.5 pounds, with less than 0.5 pounds removed since December 1997; installation of extraction wells at each site in April 1999 had not improved mass removal (as of May 1999)
- Influent contaminant concentrations in the CSFF and AS-4151 trenches reached asymptotic levels; during the past 20 months of operation, the mean contaminant concentrations in extracted groundwater have been < 1ug/L in the CSFF trench and not detected in the AS-4151 trench
- For the AS-143 trench, the mean contaminant concentrations in extracted groundwater was 832 ug/L during the initial months of operation, decreasing to 22 ug/L between April 1997 and March 1999; during the last six months of operation, concentrations fluctuated from not detect to 440 ug/L, with the peaks representing hot spots in the plume
- Treatment plant - from July 1996 to March 1999, the effluent has continuously exceeded discharge limits for total metals and total dissolved solids and has exceeded the lead limit 11 times |
Cost Factors:
The capital costs to construct and prove out the system was $507,395; average annual O&M costs are $180,000
- Average cost per pound of contaminant removed is $95,000, based on 3.5 pounds of contaminant removed |
Description:
The Marine Corps Air Station, which is co-located with the Marine Corps Base Camp Lejeune, North Carolina, has three areas where soil and groundwater are contaminated with BTEX and SVOCs - the CSFF site (an active fuel storage facility), Building AS-143 (an active gasoline fueling station ), and Building AS-4151 (a steam generating plant). Leaks from underground gasoline and fuel storage tanks and leaks from fuel pipelines resulted in BTEX and SVOC contamination of soil and groundwater at these sites. Under the State of North Carolina UST program, the corrective action proposed for the sites included soil removal, free product recovery, pump and treat, and long-term monitoring. Contaminated soil has been excavated from each of the sites. A pump and treat system began operating at the sites in 1996.
The extraction system includes interceptor trenches and extraction wells at each site, with the extracted groundwater piped to an above ground treatment plant. The treatment plant includes oil/water separation, air stripping, and filtration. An effectiveness evaluation for the pump and treat system at this site was performed as part of a study by the Remedial Action Operation/Long Term Monitoring working group led by the Naval Facilities Engineering Service Center. The working group concluded that the overall technical performance and cost effectiveness of the system was poor. After 2.5 years of operation, cumulative mass removal for the system was only 3.5 pounds, and two of the trenches (CSFF and AS-4151) have reached asymptotic levels and are no longer removing mass. In April 1999, extraction wells were installed at each site; however, no increase in mass removal has been observed as of May 1999. The average cost per pound of contaminant removed is $95,000. Recommendations for the system include shutting down the CSFF and AS-4151 trenches; continue hot spot removal at the AS-143 site; and collect MNA data to confirm the potential for a passive remedial approach for AS-143 once the remaining hot spots have been removed. |
