Surfactant Flushing Remediation
Citgo Petroleum Remediation Project

ENERCON was contacted by Citgo Corporation in 2001 regarding their desire to remediate and close an ongoing regulatory case on one of their closed marketing facilities. The leak case history included a catastrophic tank failure loss of greater than 3,000 gallons of gasoline in one event, along with lesser historic losses. The marketing facility was closed and the tanks had been removed from the ground by 2001.

Delineation drilling and groundwater monitoring wells installed by the initial contractor had identified free-product NAPL (gasoline) 2 feet thick. The contractor had also installed and operated a multi-well free-product removal system consisting of hydrophobic skimmers and pneumatically-driven pumps.

ENERCON utilized hollow-stem auger drilling to install additional groundwater monitoring wells in key locations, such as adjacent to residential properties. ENERCON also used direct-push soil borings and temporary wells to delineate the non-aqueous phase liquid (NAPL) and dissolved phase plumes for remediation design.

ENERCON prepared and submitted multiple delineation drilling and contaminant mapping reports to the regulatory agency. Delineation work found that the NAPL plume was up to 2 feet thick over an area of 60,000 square feet. The estimated cleanup volume was 10,600 cubic yards. ENERCON updated the risk assessment report, revised and clarified the cleanup goals, and prepared a Remedial Action Plan with Cost Proposal.

ENERCON proposed an aquifer flush remediation method. Feasibility testing included aquifer drawdown and sustained injection tests. Bench-scale laboratory testing was performed to determine appropriate aquifer-flush chemistry.

Key components of the Remediation Approach were achieving the cleanup standard of 1/8 inch or less of free-product, and ensuring that the injection/recovery processes would not spread contamination to previously non-impacted areas.

The remediation system included 75 remediation wells that were configured for use as injectors or extractors. The site also included 23 groundwater monitoring wells that were used to monitor remediation processes. The remediation area was totally enclosed by 8 foot tall chain-link fence.

The remediation equipment system consisted of two high-vacuum pumps, four above-ground storage tanks, one 60 gallon-per-minute air stripper, one petroleum-vapor discharge box, and associated pumps, manifolds, lines, and valves.

The aquifer flushing process required coordinated injection of a solution of surfactant-enhanced water and other chemicals. As the solution moved through the aquifer it was removed along with the NAPL by extraction wells. Contaminated groundwater and treatment solution were phase separated and treated through the air-stripper. Recovered and treated groundwater was used to mix additional treatment solution, then re-injected into the aquifer. There was no water discharged to sanitary or storm sewers, or to the surface from the remediation system.

ENERCON staff operated the system on a daily basis. Portions of the flush were operated on a 24-hour basis. System optimization efforts included chemical formulation, aquifer monitoring, and adjusting injection and extraction rates. Daily gauging and monitoring data were compiled and mapped to provide data for system adjustments. Over the full scope of the remediation work, the system was optimized by moving the injection/extraction pattern across the aquifer in the appropriate manner to sweep areas of restricted permeability. Residual NAPL traps were observed and interpreted based upon the aquifer characteristics. After reaching the appropriate conditions using the surfactant-enhanced flushing fluid, aquifer flushing continued using modified groundwater without surfactants. Petroleum vapor discharged from the air stripper was routed through a bio-filter box to reduce air emissions.

Clean up was achieved in 90 days.

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