Engineering Case Studies
Remediation Using Soil Vapor Extraction and Air Sparging
Superior was retained by a southern Michigan trucking company to oversee the removal of gasoline, diesel fuel, and used motor oil underground storage tank (UST) systems. The USTs were being removed to facilitate the sale of the site. A release was discovered during the removal of the gasoline and diesel fuel USTs. During the removal, an unregistered UST was discovered and removed. A second release was discovered during the removal of the used oil UST.
Sixty cubic yards of impacted soil were excavated from the used oil tank area. Soil verification samples and groundwater sampling confirmed that all contamination was removed from the used oil area.
Superior excavated approximately 1,300 cubic yards of impacted soil and pumped approximately 30,500 gallons of impacted groundwater from the gasoline and diesel fuel UST area. Excavation was discontinued due to the presence of a shallow groundwater unit with a high recharge rate.
Superior conducted investigation activities to delineate the extent of soil and groundwater impact from each release. Superior advanced 27 soil borings and installed 7 monitoring wells to evaluate the extent of soil and groundwater impact from the gasoline and diesel fuel releases. Borings were advanced using a Geoprobe®, and monitoring wells were installed using hollow-stem augers. The results of the investigation activities indicated the presence of contaminants exceeding indoor air, direct contact, drinking water, and groundwater/surface water interface (GSI) criteria. The site was adjacent to the River Raisin, a sensitive receptor.
Superior conducted a Feasibility Study (FS) to evaluate the most cost-effective and technically feasible approach to remediation of contaminants in soil and groundwater. The GSI criteria were selected as the target cleanup criteria due to the presence of the river. The results of the FS indicated that soil vapor extraction (SVE) and air sparging (AS) were both suitable remediation alternatives based on the distribution of contaminants and soil types. A combination SVE/AS system was selected as the remediation technologies.
Superior conducted a 2-day pilot test to evaluate the radius of influence for the SVE/AS system. SVE and AS wells were installed in the impacted area. The radius of influence was found to be approximately 20 feet for the SVE wells and approximately 15 feet for the AS wells. The results of investigation activities, the FS, and pilot study were documented in an Initial Assessment Report (IAR) and a Final Assessment Report (FAR) that were submitted to the Michigan Department of Environmental Quality (MDEQ).
The data from the pilot test was used to develop full specifications for the SVE/AS remediation system. Superior installed four SVE points and eight AS wells. A catalytic oxidizer was used to treat vapors prior to atmospheric discharge. A trailer was moved to the site to house the remediation equipment, and a fence was installed around the trailer to prevent unauthorized access. The remediation system operated for approximately 3 months, at which time the catalytic oxidizer was shut down due to low vapor recovery. The system operated for an additional 3 months, at which time groundwater monitoring results indicated contaminant concentrations below target cleanup goals. The SVE/AS system was shut down for 3 months, and then groundwater samples were collected from the monitoring wells. The analytical results indicated the contaminant concentrations were below target cleanup goals. Soil verification samples were collected from the remediation area using a Geoprobe®. Soil analytical results indicated that contaminants were reduced to levels below target cleanup goals and the SVE/AS system was removed from the site.
Superior conducted two additional quarterly groundwater monitoring events to evaluate groundwater quality. The analytical results confirmed the contaminants were reduced to levels below target cleanup goals. A Tier I unrestricted closure report was prepared and submitted to the MDEQ. The project was completed on time and within budget, resulting in an unrestricted closure of the releases.
At the beginning of the project, the owner of the site was in negotiation with a prospective buyer to sell the site. The prospective buyer was concerned about the due care obligations associated with contamination from the leaking USTs. Superior openly communicated the results of its investigation activities and shared long-term plans for remediating the site with the prospective purchaser. This gave the purchaser confidence that the client would meet their cleanup obligations and helped to facilitate the real estate transaction.
Ozone-Augmented Air Sparging
Due to our experience and success with ozone-augmented air sparging, Superior was retained as a contractor by another environmental consultant to aid in a remediation project. The consultant’s client was an owner and operator of a gasoline station with an adjacent small bulk fuel storage facility. Subsurface investigations revealed that soil and groundwater were impacted by gasoline constituents benzene, toluene, ethylbenzene, xylenes (BTEX) and methyl-tert-butyl ether (MTBE). The dissolved plume extended approximately 1 mile and was impacting a school’s water supply. Because MTBE is resistant to bioremediation and granulated activated carbon (GAC) filtration, ozone was specified as the most effective way to address MTBE in the source area and mitigate further off-site migration.
After designing and conducting an ozone sparging pilot test, Superior designed a full-scale ozone sparging system. The design consisted of the location and construction details of the injection wells, as well as layout and materials specifications for the underground piping distribution system. Superior was then asked to proceed with the installation of the sparging well array and subsurface piping. A major component of the project was the design and construction of two enclosed treatment trailers. Each custom trailer housed an air compressor, on-board oxygen concentration system, ozone generator, and sparging distribution system capable of producing and delivering 6.4 pounds of ozone per day. Comprehensive control, monitoring, and safety systems were included in both trailers.
With construction completed, Superior initiated startup and provided 6 months of operation and maintenance services as well as detailed training for the consultant. After several years of operation, Superior continues an ongoing relationship with the consultant and provides assistance upon request.
Groundwater Collection with Innovative Treatment
Superior submitted a bid to the State of Michigan to conduct economic and technical analyses of existing remediation activities at a former 300-acre refinery in central Michigan. Due to a high level of contaminants, approximately $15,000 of granulated activated carbon (GAC) was being used monthly for groundwater treatment, and the state was looking for alternative approaches to reduce this cost. Numerous product spills were reported during historical operations, and it was estimated that up to 5,000 gallons of recoverable free product were present at the site. Free product and impacted groundwater had been migrating into nearby wetlands and ultimately entered a nearby waterway.
Superior was successful in winning the bid and was selected for our technical approach to an alternative treatment system. Superior provided the engineering design, construction, and operation of a free-product recovery and groundwater remediation system. Our approach included the redesign and modification of the existing treatment system and long-term monitoring operations.
The project was conducted in three phases. The first phase involved the design of a fixed-film biological remediation system to treat approximately 100 gallons per minute of groundwater impacted with hydrocarbons. This treatment system was determined to be more cost-effective than conventional groundwater treatment technologies such as granular carbon adsorption or air stripping.
The second phase involved the construction of the fixed-film biological treatment system. This included an analysis of the performance of the groundwater recovery system. Groundwater was being extracted from a series of existing recovery trenches to prevent migration of the contaminants into the wetlands. Superior modified the trenches, as well as installed new pumps, flow meters, and other appurtenances. During the construction of the system, the State of Michigan found additional areas of contamination. Superior also redesigned the system to encompass the treatment of the additional areas of contamination and the system designs were subsequently constructed. Once construction of the fixed-film biological system was completed, it was tested for one month to correct any operational problems and ensure the system was running within the defined operational parameters. The treated water was discharged via a National Pollutant Discharge Elimination System (NPDES) permit.
The third phase involved the operation and maintenance of the system for 5 years. The water extracted from the recovery trench wells was pumped into a fixed-film biological system. The treatment system uses bacteria attached to plastic media to breakdown the contaminants. Superior is responsible for ensuring that the system is operating smoothly and within the specified parameters, obtaining and analyzing system samples, and obtaining groundwater samples to determine the effectiveness of the system.
Indoor Excavation and In-Situ Chemical Oxidation Remediation Services Sodium Permanganate Injection
Commercial Dry Cleaning Facility
Superior was contracted by a commercial dry-cleaning business in Illinois to remediate perchloroethylene (PCE) contamination in the soil to a site-specific soil component to groundwater ingestion remediation objective of 45 milligrams per kilogram (mg/kg), which was approved by the Illinois Environmental Protection Agency (IEPA).
Approximately 85 tons of PCE impacted soils were discovered at depths ranging from 1 to 10 feet below ground surface (bgs) inside the building beneath the rear portion of the dry-cleaning facility. At approximately 6 feet bgs, PCE concentrations measured 2,700 mg/kg, which is more than 10 times the soil saturation limit.
The shallow soils were remediated by removing a portion of the concrete floor and excavating the soils with a mini excavator. Structural concerns with the building foundation did not allow the excavation deeper than 4 feet bgs. Per the request of the property owner, Superior completed the excavation without widening the back entrance of the facility. Approximately 30 tons of excavated soils were carefully loaded into two roll-off boxes and transported to a licensed hazardous waste landfill in Michigan.
Deeper impacted soils were treated using In-Situ Chemical Oxidation (ISCO). After the excavation, Superior constructed a scaffolding platform over the remediation area. The platform allowed Superior to safely inject the oxidation chemicals and provided a temporary barrier over the remediation area. Approximately 1,100 gallons of sodium permanganate at a 15 percent solution were injected into the impacted soils that could not be excavated. The sodium permanganate was injected into 41 injection points at a pressure of 5,000 pounds per square inch (psi).
Approximately 12 weeks following the injection, 10 confirmation soil samples were collected from 5 soil borings drilled into the remediation area. The soil sampling results showed reductions in the contaminant concentrations up to 99.99 percent. PCE concentrations in the confirmation soil samples ranged from non-detection up to 0.85 mg/kg in soils previously measuring up to 2,700 mg/kg. The ISCO reactions resulted in destruction of PCE to below the IEPA approved remediation objectives with no generation of daughter products such as trichloroethylene, cis-1,2 dichloroethene, or vinyl chloride.