George (Bud) Ivey, B.Sc., CES, CESA, P.Chem, EP, President and Senior Remediation Specialist, Ivey International Inc.
Co-Authors: Daniel Hirth and Desirée Craig, BlueSphere Environmental
The former Bacchus Marsh Gasworks (1889-1973) was located within a wide alluvial plain of the Werribee River, near Melbourne, Australia. In this region, shallow groundwater is highly utilised for irrigation and rationed through the auctioning of water shares. The presence of coal tar NAPL (and associated dissolved phase groundwater impacts) emanating from a former gasholder and tar disposal wells into the upper aquifer presents risks to local groundwater irrigation users and freshwater ecosystems. This presentation focuses on remediation of two coal tar NAPL plumes that was conducted in-situ attempting to meet regulatory and client sustainability goals. While statutory goals include the removal of NAPL to the extent practical and restoration of all relevant uses, the project remediation objectives included the reduction of NAPL mass and the elimination of measurable NAPL in any wells.
After extensive review of possible sustainable remediation options, surfactant enhanced aquifer remediation (SEAR) was selected to address the coal tar NAPL in the aquifer at the site. The surfactant selected was a non-ionic surfactant engineered to dissolve long-chain petroleum hydrocarbons. The surfactant was used in a variety of push-pull and recirculation methods to enhance coal tar recovery. Most of the coal tar NAPL observed in wells was slightly denser than water (1.03 SG), had moderate viscosity (114 cP at 20°C) and rested within the poorly sorted clayey, sandy gravel lenses of the alluvial aquifer. After initial push-pull applications of SEAR, recirculation was established between a switched array of 4 injection wells and 4 to 6 extraction wells that were changed daily. Approximately 12 different injection wells were utilized in each of the coal tar NAPL plumes.
The mobilised NAPL and a small proportion of emulsified hydrocarbons were removed using a multiphase extraction (MPE) technology. Wastewater was treated on-site and re-used to prepare surfactant solutions (x̅=3% v/v) or reinjected under permit from the regulatory agency to the extent that was practicable. Reinjection was conducted in a manner to optimize the surfactant plume behavior while it was being extracted. However, the presence of ammonia limited the capacity to re-inject the treated groundwater and the majority of wastewater disposal occurred through sewer disposal. The accounting of contaminant mass removal was complex and included a summation of NAPL, dissolved hydrocarbons, and vapours. Recovery of the emulsified NAPL was observed to separate from solution after approximately 30 minutes. The rapid emulsion breakdown was beneficial to the water treatment plant efficiency, as a very small amount of hydrocarbon was adsorbed to the plant’s activated carbon. However, the coating of coal tar NAPL on to the interiors of tanks and pipes was unforeseen and created challenges in the quantification of NAPL recovery rates. SEAR remediation was conducted for six months and resulted in the extraction of approximately 18% of the estimated coal tar NAPL mass. Due to the behaviour of the non-ionic surfactant with coal tar, most of the coal tar recovered was through the mobilisation of NAPL globules, and not the emulsification, dissolution or volatilisation of hydrocarbons. In conclusion, SEAR has proven to be a viable method of groundwater remediation to reduce recalcitrant hydrocarbon mass and decrease overall plume lifespan in a poorly sorted unconsolidated aquifer at a relatively small manufactured gas plant.
George (Bud) Ivey is the President and Senior Remediation Specialist with Ivey International Inc. with global headquarters in Vancouver, Canada. He has over twenty-five years of international environmental site assessment and remediation experience. He has worked on more than 2500 major environmental projects, taking him to over 50 countries globally. His multi-disciplinary education includes: Synthetic Organic Chemistry, Geological Engineering, and a Master’s Certification in Project Management.