Studies Related to Corrective Action Goals
Above-ground Tank Failure, Oil Field in Colorado:
A 4,000-gallon spill from an oil field tank battery had been thoroughly investigated for three years by another consultant via numerous nested monitoring wells. However, the release’s migration pathway was not well understood, so LWS was requested to develop a 3D visual model of site conditions. LWS developed the 3D model using data from boring logs (lithology and organic vapor readings on soil), synoptic benzene concentrations in ground water, and water level measurements in nested wells. LWS developed a 3D model within 2 weeks for about the same cost as evaluations using standard 2D methods. Using the 3D model tools allowed LWS to slice the model in any direction and understand how the slug release migrated downward through soils and then spread along the claystone bedrock/seasonal water table surface until it passed down into the unsaturated bedrock, at which point the plume migration direction changed to follow a preferential pathway in sandstone lenses.
LWS constructed a fate and transport model to evaluate a DNAPL release. The fate and transport model depends on numerous factors: the contaminant properties (solubility, density, volatility, etc.), hydrogeologic conditions, preferential pathways, receptor locations, and mitigation measures taken at the primary release source. The 3D hydrogeologic model allowed us to determine the most appropriate course of action based on an evaluate of multiple scenarios: (a) Natural attenuation with no active remediation to evaluate when, and if, the plume may reach a sensitive receptor; (b) Remediation wells in the affected aquifer near the release source area to capture the most-impacted ground water, while allowing the plume further downgradient to attenuate naturally; and (c) Include Scenario (b) plus the addition of deeper remediation wells to capture downward vertical contaminant migration.
LNAPL Interceptor Trench for Gas Station Release in Colorado:
An adjacent daycare building was at risk for exposure to volatile organic compounds from a shallow LNAPL plume of gasoline. LWS personnel acted quickly to obtain the necessary right-of-way permits and coordinate with the local fire department to install a 15-foot deep, 100-foot long interceptor trench below the sidewalk. Fire-suppression foam was used to control vapors during excavation of the trench. Multi-phase extraction wells installed in the trench, backfilled with gravel, recovered approximately 1,000 gallons of gasoline and then continued to operate to mitigate vapors from the subsurface. Recovered fluids and vapors from the extraction system were processed through a treatment train, including a product skimmer, knock-out tank to separate vapors from liquid, and air-stripper to remove volatiles from water discharged via a permit to the sanitary sewer system. Numerous continuous fluid-level and vapor-monitor sensors were utilized to automatically operate the system and provide fail-safe shutdown of the system at pre-determined safeguard levels.
Soil Vapor Extraction and Air-Sparging Remediation System in Denver:
LWS personnel managed the pilot testing and design of an air-sparge/soil vapor extraction system in suburban Denver. The system was operated intermittently to introduce pressurized air to oxygenate the ground water and liberate volatile organics to the vapor phase so they could be removed via soil vapor extraction wells. Vapors discharged to the atmosphere were periodically monitored to ensure that the system was operated within allowable air discharge limits.