Remediation System Design & Implementation

Former Natural Gas Compressor Station
Adams County, Colorado

Services Provided

Market

Regulatory Agencies Involved
Colorado Oil & Gas Conservation Commission

Remediation_System_Design_Implementation_feature
Trihydro was contracted to design and implement a remediation strategy at a natural gas compressor station site in Colorado. The station was built in the 1970s, and was operating at the outset of the project before being decommissioned for unrelated reasons during the course of remediation. Historical records show that a natural gas condensate spill of about 40 barrels occurred in the 1990s and was addressed by soil excavation to a depth of about six feet at the time. However, hydrocarbon-impacted soil and groundwater were later discovered by the client during an onsite investigation conducted as part of due diligence in connection with their purchase of the station from its previous owner. Five to seven feet of free product (condensate) was identified on the water table at depth of 100 feet in two monitoring wells onsite. In addition, hydrocarbon impacts were observed in the vadose zone and an aqueous-phase benzene plume extended offsite from the station. Trihydro was tasked with developing a remedial strategy to address the hydrocarbon impacts in soil and groundwater and satisfy cleanup goals in compliance with Colorado Oil and Gas Conservation Commission (COGCC) requirements.  

Trihydro recommended and implemented a Laser Induced Florescence (LIF) and Membrane Interface Probe (MIP) investigation to cost-effectively and rapidly delineate the lateral and vertical extent of the hydrocarbon impacts in the vadose zone. The goal of the LIF and MIP investigation was to accurately locate the source material to facilitate removal and expedite groundwater cleanup. The LIF survey was successful in identifying source material in a relatively discrete area split between a shallow zone lying above a clay lense and a somewhat different distribution of hydrocarbons, at depth, below the clay. A small number of soil boring and geotechnical analyses provided the data to quantify soil properties. Compositional analyses of the free product provided information on the relative volatilization potential of the hydrocarbons, which together with soil conditions were favorable for the use of soil vapor extraction (SVE) coupled with product bailing and a skimmer system at one well, both to achieve source reduction in soil and also reduce free product in the site monitoring wells.

A pilot test was performed a few months after the LIF and MIP work to determine the hydrocarbon concentrations in the extracted soil vapor and identify achievable flow rates. This data led to the development of a two-phase SVE system design-implementation plan. Phase I consisted of a high mass-removal internal combustion engine to provide the vacuum for soil vapor recovery and the combustion for off gas control. Advantages of this unit were a high mass recovery rate, relatively high vacuum, and operability without electric power, which is significant because there is no electrical service at the site. The Phase I system was operated for 12 months. 

A blower and catalytic oxidizer (CATOX) SVE system is being implemented for the lower concentration Phase II period, following installation of power to the site. The CATOX system is considerably more efficient at lower soil vapor concentrations. The project’s phased approach should result in the potential shortened remediation time and lowered project costs.
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