ARCHIVED REPORTS_XR0006230 - Laserfiche WebLink

Home Browse Search

7.1 NATURAL ATTENUATION ' The natural attenuation remedial option is not a technology, rather it refers to naturally occurring subsurface processes, such as dilution, volatilization, biodegradation, adsorption, and chemical ' reactions with subsurface materials, which result in reductions in contaminant concentrations Selection of natural attenuation as a remedial option would require groundwater modeling and an evaluation of contaminant degradation rates, verified by long-terra sampling and analysis Natural attenuation is not considered an effective remedial option at former Exxon RS 7-3942, because volatilization and biodegradation processes are inhibited under the submerged source conditions at the site ' 7.2 VERTICAL BARRIER(CONTAINMENT ' The vertical bamer/containment remedial option consists of a trench filled with a slurry grout material The slurry, usually a mixture of bentonite and water, hydraulically shores the trench to prevent collapse and forms a filter cake to reduce groundwater flow There is a potential for slurry wall degradation over time The vertical barrier containment remedial option does not pass the screening, because it will not result in reduction or removal of the submerged hydrocarbon source at former Exxon RS 7-3942 The depth of petroleum hydrocarbons in the ' saturated zone extends to a depth beyond 30 feet bgs, therefore, constructing a 30 foot slurry barrier would require a high capital cost 7.3 AIR SPARGING Air sparging consists of infecting air at high flow rates into the saturated zone, creating an ' underground stripper which removes contaminants in groundwater and soil through volatilization Air sparging has been operating in tandem with soil vapor extraction at former Exxon RS 7-3942 and did not result in any discernible reductions in groundwater hydrocarbon ' concentrations The air sparging remedial option does not pass the screening because the rate of volatilization of dissolved contaminants from groundwater is lower than the rate of dissolution ' into groundwater from the submerged source at the site 7.4 PUMP AND TREAT tPump and treat as a remedial option consists of groundwater extraction and treatment by means of a number of technologies, including air stripping and carbon adsorption The pump and treat ' remedial option does not pass screening at former Exxon RS 7-3942, because it wiII require the discharge or infection of treated water, it will likely result in pulling hydrocarbons from offsite upgradient sources into the site, it has been shown in recent years to be ineffective for source reduction or removal, and it has high capital and O&M costs 7.5 PASSIVE TREATMENT ZONE The passive treatment zone remedial option entails the installation of a permeable zone across the flow path of the contaminant plume, allowing the plume to passively move through the zone The passive treatment zone would consist of closely packed Geoprobe borings grouted with ' WP61 73942 WPI 096 TX 5 13