Case Histories Main Page
VACUUM EXTRACTION SYSTEM DESIGN
Confidential Major Chemical Manufacturer, Texas
A major chemical company, closed two process drainage ditches as part of ongoing plant upgrade projects. The ditches were 800 and 1,200 feet long and carried waste water with high levels of chlorinated solvents. The soils in the ditches were highly plastic, saturated clays.
Analysis of soil samples indicated the presence of TCE and PCE at levels that required cleanup.
A soil vapor survey was conducted in the ditches to delineate the lateral distribution of VOCs and to evaluate the pneumatic permeability of the soils. The results of the field studies showed that vapor flow could be induced through the clay at distances adequate to capture the TCE and PCE by way of single horizontal extraction lines running the length of the impacted portions of the ditches. A remediation system including synthetic liners to prevent the inflow of either rainfall or ground water and vacuum units capable of remediating the trenches in a two year period was designed. Due to the considerable mass of TCE and PCE to be removed, the design included a granular activated carbon (GAC) vapor treatment unit with on-site regeneration.
TWO-PHASE VACUUM EXTRACTION PILOT STUDY AND REMEDIAL DESIGN
Confidential Major Aerospace Corporation, New Jersey
A major corporate acquisition had triggered the New Jersey Environmental Cleanup Responsibility Act (ECRA) process. An extensive environmental investigation was completed at the subject site in accordance with an approved ECRA sampling plan and a site cleanup plan was prepared. The cleanup plan included the application of Two-Phase Vacuum Extraction (TPVE) at areas of the site in which soil and groundwater had been impacted by volatile organic compounds (VOCs), primarily chlorinated solvents. The state accepted the cleanup plan contingent upon the results of a pilot study and required that the results of the study be available within 90 days. Plans for the pilot study were completed, the necessary permits and permit waivers were obtained, the site was prepared, a diesel generator was provided, a newly fabricated trailer mounted TPVE unit was mobilized, the pilot study was conducted during the month of January 1992, and the results were reported to the state on time. The results included greatly accelerated rates of ground water removal (compared to conventional pumping) and the removal of as much as 200 pounds per day of VOCs from the subsurface. These results were incorporated in the final remedial action plan for the site.
The detailed design of the various components of the remedy included:
The final remedial action for this site is currently under construction.
TWO-PHASE VACUUM EXTRACTION PILOT STUDY
Confidential Consumer Products Manufacturer, North Brunswick, New Jersey
In 1988, a leaking 4,000-gallon unleaded gasoline underground storage tank (UST) was removed from beneath an asphalt parking lot and the excavation was backfilled. Based on the results of a soil gas survey , another consultant installed a vapor extraction system. After approximately two years of operations, the consultant recommended that the single-phase system be expanded.
At that point, the site owner asked a third party to evaluate the proposed expansion. The third party collected soil samples to delineate the extent of residual soil contamination. It was determined that the parking lot was underlain by approximately 20 feet of fill material (sand and gravel) and at least 4 feet of clay and there was a two-foot thick perched water table at the sand-clay interface. The water contained benzene, toluene, ethylbenzene, and xylene (BTEX).
No water had been found during the original site investigation which had been conducted during a drought. Seven monitoring wells were installed to delineate the extent of the BTEX in the groundwater. The average dissolved concentration in the area was 18,000 micrograms per liter (ug/L). Although the formation was fairly permeable, the average initial yield of the monitoring wells was less than 0.5 gallons per minute (gpm) due to the low head available in the thin perched aquifer. BTEX concentrations in soil just above the water table exceeded the most stringent New Jersey standards over an area of approximately 6000 square feet. This zone had not been thoroughly cleaned by the previous soil vapor extraction.
New Jersey regulations applicable to the site require that residual hydrocarbons in both soil and groundwater be remediated. In June and July 1993, a Two-Phase Vacuum Extraction (TPVE) pilot study was conducted to demonstrate the ability of the TPVE process to accelerate removal of hydrocarbons from both media at the site. The TPVE system was operated for 30 days with an initial yield from the extraction well of 2.5 gpm. Significant dewatering was accomplished. After several days, the sustainable yield stabilized at the site hydraulic recharge rate of approximately 0.75 gpm. During the TPVE pilot study, 25,000 gallons of groundwater (approximately 1/3 of the total volume of water present in the area), and approximately 2.5 pounds of BTEX (approximately 1/3 of the total BTEX present in the groundwater before the pilot study) were removed from the site. In one month, 9.2 million cubic feet of air were moved through the soil column, removing approximately 125 pounds of non-methane hydrocarbons from the soil.
Measurements of induced vacuum and water table drawdown showed that the TPVE capture zones encompassed the entire known extent of hydrocarbon impact in the soil and groundwater.
A technology evaluation report is being prepared for this site. In addition to TPVE, other candidates for remediation at the site include natural attenuation, groundwater pumping supplemented by vapor extraction, bioremediation, and TPVE augmented by biological techniques.
VACUUM EXTRACTION AND BIOVENTING
Confidential Printing Industry Client, Central Pennsylvania
A printing company removed a fuel oil underground storage tank (UST) in preparation for the construction of a new warehouse and required an investigation of the soils in the location of the former UST. The client was interested in expediting the investigation and remediation processes so that the new warehouse could be constructed above the location of the former tank without entering into a time consuming or costly remediation program.
The environmental investigation revealed that the soils in the area of the former UST had been impacted by fuel oil contamination. The constituents of primary concern were benzene, toluene, ethylbenzene, and xylene. A remedy was designed that could be implemented without delaying construction of the new warehouse. The Pennsylvania Department of Environmental Resources (PADER) approved the remediation plan.
The plan included the use of five vapor extraction wells in the oil impacted area. The wells were completed and vacuum piping was installed prior to construction of the floor slab for the new warehouse. The warehouse was then constructed and the vacuum extraction system installed on the first floor.
Throughout the remediation program the systems carbon dioxide concentrations in the extracted soil gas were monitored as in indication of biological activity. Based on the high CO2 concentrations it was calculated that the rate at which petroleum hydrocarbons were being biodegraded was as much as 10 times the rate of physical removal by the applied vacuum.
Vapor sampling confirmed that the remediation objectives had been met after just six weeks of operations. On the basis of the results, PADER issued a notice that no further action was required.
TWO-PHASE VACUUM EXTRACTION SYSTEM FOR GROUNDWATER REMEDIATION AT A GASOLINE SERVICE STATION
Mobil Oil Corporation Blackwood, New Jersey
During the rebuilding of one of Mobil's gasoline service stations, it was discovered that the underground gasoline storage tanks had leaked. The tanks were removed and contaminated soil was excavated and transported offsite; however, investigations revealed that volatile organic compounds (VOCs) had impacted the groundwater. Two Phase Vacuum Extraction (TPVE) was applied to remediate residual soil contamination and capture and remediate the groundwater plume at the site. The project required obtaining local and state permits for construction of the system and for discharge of treated air and water streams. A catalytic oxidation unit was provided to treat extracted soil gases. A trailer mounted TPVE system was mobilized to the site. Application of TPVE by way of a single well resulted in the capture of the entire known ground water plume at the site (approximately 1 acre in extent) and the removal and destruction of as much as 300 pounds per day of hydrocarbons.
SOIL AND GROUNDWATER REMEDIATION GASOLINE STATION AND CONVENIENCE STORE
Munro Petroleum & Terminal Corporation Biloxi, Mississippi
A gasoline leak from aging USTs had impacted soil and groundwater at he Central Beach gasoline station and convenience store site in Biloxi, Mississippi. Although the Mississippi Department of Environmental Quality had allocated funds for one year of TPVE operations, the remediation of the site was completed in just four months.
An environmental assessment at this very active convenience store determined the concentration and location of contaminants in both the soil and groundwater . While most of contamination was limited to the immediate vicinity of the dispenser islands, some gasoline had migrated underneath the adjacent state highway. Since heavy highway traffic prohibited soil cleanup by excavation, the use of TPVE was recommended to cleanup both soil and groundwater.
The TPVE system was installed and started up in early August, 1993. The system extracted in excess of 7,000 gallons of groundwater per day. Mathematical modeling techniques showed that the zone of influence of the TPVE extended across the adjacent state highway. Approximately 2,500 pounds of hydrocarbons were removed from the site in four months.
The cleanup progressed much faster than anticipated. The rate of extraction of hydrocarbons dropped off significantly by early December of 1993 and the analysis of groundwater samples collected then showed that the state mandated ground water cleanup objectives had been surpassed by a factor of more than ten. MDEQ therefore required no further remediation. The project, initially budgeted at about $138,000 was completed for a total cost of less than $71,000 with no interruption of station operations.
EMERGENCY CLEANUP OF WATER SUPPLY
City of Rayville Physical Plant Rayville, Louisiana
Routine sampling by the Louisiana Department of Environmental Quality (DEQ) detected benzene in a city water supply well. An underground gasoline tank system that had been formerly located just 70 feet from the well was the suspected source. A hydrogeological characterization of the site confirmed that gasoline from the UST had migrated towards the well. DEQ required an emergency cleanup of the source area.
With the concurrence of the DEQ, a Two-Phase Vacuum Extraction system was deployed to the site to extract contaminated groundwater and soil vapors. The removal of ground water was facilitated by the introduction of atmospheric air using the priming method invented by TSI employee Steven Morrow and described in U. S. Patent Number 5,076,360. More than 450,000 gallons of contaminated water and 1,000 pounds of hydrocarbons were removed in one month. Four subsequent rounds of sampling over a two year period have shown no recurrence of benzene in the well water.
The innovative use of the priming method and the successful restoration of the quality of the city water supply for very low cost (the remediation was completed for less than $30,000) led the Pennsylvania Consulting Engineers Council to recognize this project with an Honor Award for Engineering Excellence in 1994.
FREE PRODUCT GASOLINE RECOVERY
Cloyd's Corner Exxon Service Station Monroe, Louisiana
Inventory records and tank and line tightness tests indicated that the UST system at the Cloyd's Corner site had leaked at several locations between March, 1985 and April, 1990. In May 1990, an investigation was conducted to determine the horizontal and vertical extent of petroleum hydrocarbon migration in soil and groundwater. Subsurface conditions were found to be as follows:
The areal extent of soil contamination is approximately 40,000 square feet, with concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX) above 10 parts per million (ppm) predominately in the upper six feet of soil.
Three to five inches of free phase hydrocarbons were observed in two of the monitoring wells and discharging into an adjacent creek. It was estimated that the free phase plume extended over 4,275 square feet.
Dissolved hydrocarbons were present in groundwater over an approximate 31,000 square foot area.
As an interim measure, an interceptor trench was installed between the source of the release and the creek to provide a hydraulic barrier and to create a continuous zone of influence and capture zone for removal of free and dissolved phase hydrocarbons. The trench was approximately 125 feet long, 3 feet wide, 8 feet deep, and was filled with pea gravel. A pumping test conducted on a recovery well installed in the trench indicated that the sustainable pumping rate (from the trench) would be less than 3 gallons per minute (gpm). Using this pumping rate, cleanup costs and duration were estimated using results of a batch-flushing analysis (EPA/541/6-88/003: "Guidance on Remedial Actions of Contaminated Groundwater at Superfund Sites", Interim Final, December, 1988). Based on the significant costs and cleanup duration indicated by this model, installation of a two-phase vacuum extraction (TPVE) system was proposed to accelerate the remediation at the site.
LDEQ accepted the plan to conduct a TPVE pilot study at Cloyd's Corner. The results of the TPVE operation were as follows:
The application of TPVE resulted in the removal of all the free product from the subsurface at the site in less than 5 weeks. Free product has not been detected in any of the monitoring wells at the site since the system was shut down in June, 1993.
More than 3,100 pounds (1,600 pounds liquid plus 1,500 pounds vapor) of gasoline were removed from the subsurface.
The rate of groundwater withdrawal from the recovery trench and from the monitoring wells by TPVE was significantly greater than could be achieved by conventional pumping.
The entire known contaminant plume in groundwater was captured using TPVE applied to the interceptor trench.
While the ability of the process to remove free product and contaminated groundwater have been well demonstrated, it has not been demonstrated whether TPVE will or will not effectively cleanup soil at Cloyd's Corner.
LDEQ is conducting a risk assessment at the Cloyd's Corner Exxon Convenience Store. The removal of more than 3,000 pounds of gasoline during the TPVE pilot study has helped to reduce any risk to human health and the environment. If, nevertheless, the results of LDEQ's assessment indicate that there is an unacceptable risk due to residual gasoline components in the groundwater and that some additional active cleanup is necessary, TPVE applied to the interceptor trench should be considered based on its proven effectiveness.
If the results of the risk assessment indicate that there is an unacceptable risk due to residual gasoline components in the soil, TPVE applied to horizontal trenches constructed in the smear zone (the zone about 6 feet below the surface where hydrocarbons have been transported by fluctuations in water table elevation) is recommended based on the demonstrated ability of the process to dewater that zone and to remove hydrocarbons in the vapor phase.
BIOVENTING, BIOREMEDIATION AND STABILIZATION TREATABILITY STUDIES
Confidential Pharmaceutical Manufacturer, Pennsylvania
Wastewater treatment sludge and laboratory wastes had been disposed of by onsite landfilling at this major pharmaceutical research and manufacturing facility. Recent plans for significant new construction called for expansion into the disposal areas.
The owner sought alternatives to excavation and offsite disposal for the waste material still in place after the first phase of building footprint excavations. The goals of an alternative treatment would be to remove the RCRA characteristic volatile and semi-volatile compounds, to eliminate the extremely noxious odors that made the first excavation work less than pleasant, and to convert the semifluid sludge into a soil like material that would be more easily removable or could support future surface loads.
A three part treatability study was designed including: sludge stabilization, bioremediation, and bioventing. The bioventing study included field work to determine whether air flow could be induced through the fine grained material in-situ and bench work conducted over a period of 8 weeks.
Application of vacuum to the in-place waste by way of specially constructed wells showed that flow could be induced and that volatile compounds could be removed in measurable (using a photo-ionization detector) quantities. The bench work showed that significant biological activity was stimulated by drawing air through the samples. The biological activity was indicated by the measured increase in CO2 concentrations across the tested soil columns and the visually evident growth of microbial colonies. The CO2 measured entering the columns was at the atmospheric concentration of about 300 ppm while it was in excess of 6000 ppm exiting the columns during the early stages of treatment. The decline in the exiting concentrations over time showed that the aerobic bioactivity decreased as the microbes consumed the available nutrients.
The objectives of the treatability studies were to determine, for each technology, whether it could reduce the toxicity of the waste material, convert the viscous waste into a soil like material, eliminate odors, and be implementable at reasonable cost. Representative samples of the waste material were collected at the site and analyzed. Bench scale application of the treatment technologies showed that:
TPVE IN CLAYEY SOIL AND FRACTURED BEDROCK
Confidential Client, New Jersey
Two tank farms that had been in service since the 1940's were the sources of releases of volatile organic compounds to the soil, fractured bedrock and groundwater at this major manufacturing facility. The site is underlain by the Brunswick formation, which is composed of red shales and siltstones and is characterized by dipping bedding planes and vertical jointing. The hydrologic characteristics of the upper part of the formation include low groundwater yield and unpredictable flow patterns. These characteristics pose difficulties for remediation. The subsurface included a shallow, poor-yielding zone with elevated VOC levels, and a deeper, higher yielding fracture system with somewhat lower VOC concentrations. For the deeper zone, a groundwater extraction was designed with treatment by air stripping and carbon polishing. The treated water was used as non-contact cooling water prior to discharge to the local sewer authority, resulting in decreased use of the public water supply. This approach made it possible for the authority to accept the discharge despite a regulatory climate in which treatment of contaminated groundwater was discouraged. The groundwater plume was completely controlled by pumping 15 gpm from 120 feet, however, less than 100 pounds total VOCs were removed in a year of pumping. In 1992, a pilot test of two-phase vacuum extraction (TPVE) was conducted in soil and shallow (10 to 70 feet below grade) bedrock groundwater. The results of the test included:
Based on these results, a remedial action plan that included continued control of the deeper plume by pumping and treating and cleanup of the source areas in the soil and shallow fractured bedrock by the application of TPVE was approved by the New Jersey Department of Environmental Protection. Final design work is underway.
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