A Review of the Application of in-situ Submerged Oxygen Curtain (iSOC?) Technology for Delivery of Oxygen to Groundwater at Four Sites to Enhance Natural Attenuation of Petroleum Impacts

摘要

The in-situ Submerged Oxygen Curtain (iSOC?) technology was applied at five Flying J, Inc. sites as pilot projects to evaluate its effectiveness at delivering oxygen to the groundwater to enhance the aerobic degradation of dissolved hydrocarbons. The sites are located in Indiana, Michigan, Colorado, and Utah. The impacted groundwater at the sites in Indiana and Michigan is present in near surface sand and silty-sand deposits of glacio-fluvial and glacio-lacustrine origin. The impacted groundwater at the Colorado site is in near surface dense fractured silty-clay. The impacted groundwaters at the Utah sites are in alluvial clayey silt with interbedded fine sand lenses, and imported crushed rock backfill. iSOC? is a microporous mass transfer device manufactured by inVentures Technologies incorporated (iTi) for use in ground water remediation. It is based on iTi's proprietary technology for dissolving gas into liquids without bubbles. At these test sites iSOC? was used to dissolve oxygen into the ground water to promote the aerobic degradation of petroleum products. The iSOC? units are approximately 15 inches long and 1.6 inches in diameter. They were employed in 2-inch diameter wells at the test sites. The units are connected to an oxygen source and used to supersaturate the water columns within the wells being used. The oxygen is then delivered to the groundwater in the surrounding formation primarily by diffusion. The concentration of dissolved oxygen in the water column in the injection wells is dependent on the thickness of the water column in the well. At the Indiana site, Michigan site and one of the Utah sites the injection wells needed to extend below the base of the thin saturated zone in order to create the desired water column thickness of 7 to 10 feet within the wells. With these water column thicknesses a concentration of 20 to 50 mg/L of oxygen could be maintained in the injection wells. At the one Utah and Colorado site, the injection wells are installed to accommodate approximately 15-20 feet of water column thickness and concentrations of between 25 and 35 mg/L of dissolved oxygen have been maintained during the pilot test. At the Indiana site, a pilot test using three injection wells and six monitoring wells was completed over a five month period. At the Michigan site, eight injection wells are being used. Monitoring is being conducted at the injection wells and eight surrounding monitoring wells. The Utah pilot tests were operated for approximately 6 months using one injection well at each site. Monitoring was conducted using geoprobe groundwater sampling techniques and monitoring wells. At both Utah sites, the iSOC? units have been incorporated into the long term Corrective Action Plan. At the Indianan, Utah, and Colorado sites there was a significant increase in dissolved oxygen in the groundwater at the monitoring wells during initial stages of the application. Following the initial increase there was a general decline in dissolved oxygen concentrations. At the Indiana and both Utah sites the decrease in dissolved oxygen was accompanied by a decrease in BOD and BTEX concentrations in a portion of the test area. The decrease in dissolved oxygen following its initial increase is believed to be caused by increased biological activity consuming the oxygen. Monitoring at the Colorado site will include groundwater sampling for BTEX, BOD, and TIC. In conclusion the iSOC? technology was successfully used to deliver oxygen to groundwater under the varying geologic settings tested. The technology is simple to apply with low operation and maintenance costs. The effectiveness of enhancing the aerobic biological degradation of dissolved petroleum impacts should be consistent with other technologies that successfully deliver dissolved oxygen to groundwater.