Active Rail Yard LNAPL Investigation and Remediation
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Project Objective

LNAPL was seeping and discharging into a culvert structure that bisected an approximate 30-arce light non-aqueous phase liquid (LNAPL) body impacting both perched and lower aquifer groundwater due to decades of rail yard operations. The client negotiated a Consent Order & Agreement with the regulating agency that mandates ongoing operation of a LNAPL recovery system as long as downgradient sheening is resulting from LNAPL impacts to the culvert. The overall goal of the project is to eliminate the sheening to the culvert to satisfy consent order requirements.

Geosyntec’s Scope of Services

Geosyntec is responsible for managing operation, maintenance, and optimization of a dual-phase extraction LNAPL recovery network in accordance with the Client’s Consent Order & Agreement. Recovery efforts include operation of 25 active recovery wells configured in eight individual recovery systems for source material removal in targeted areas of the site. Duties include managing weekly operation and maintenance inspections/system maintenance, SPCC/SWPPP required storage tank inspections for LNAPL collection vessels, waste handling and disposal, record keeping, operation and maintenance plan preparation, data analysis, recovery well rehabilitation, monthly reporting to the client on system performance/optimization measures, and quarterly reporting to the regulator.

Geosyntec is also supporting investigation, feasibility study, and remediation design efforts to enhance the existing remediation system and eliminate sheening on the stream surface. Recent investigations used various high-resolution site characterization tools (laser induced fluorescence, optical image profiling, and hydraulic profiling tool). In addition, Geosyntec successfully installed a fiber optic cable in the culvert substrate along the entire length of the culvert to support a year-long distributed temperature sensing (DTS) survey. The DTS survey, in combination with HRSC results and LNAPL physical properties data, identified the location and quantified rates of groundwater/LNAPL seeps into surface water from the lower aquifer. The combined data sets will be used to update the site’s existing 3D conceptual site model, groundwater MODFLOW model, HECRAS model, and LNAPL Distribution and Recovery model to simulate both natural and post-remedy conditions as part of the feasibility study process.

Notable Accomplishments

Through O&M management and recovery system optimization and expansion, approximately 58,000 gallons of LNAPL have been recovered since 2013 while also reducing annual O&M costs. Additionally, Geosyntec was able to negotiate a permit waiver from the state regulator to support DTS cable installation using a vibratory plow. The DTS survey was integral to providing the client with a comprehensive, robust CSM update that considers surface water, groundwater interaction across the entire length and width of the culvert as opposed to previous studies focusing on sections of the culverted stream.