Service: Environmental Engineering and Consulting
Project: Former Tank Farm Groundwater Monitoring and Treatment System Optimization
Client: U.S. Army Corps of Engineers, New England District
Site Location: Former Quonset Point Naval Air Station, North Kingstown, RI
Period of Performance: 2006

H&S conducted groundwater monitoring and remediation system optimization for this Formerly Used Defense Site (FUDS) at the former Quonset Point Naval Air Station.  An existing trench and recovery well-based LNAPL recovery system was collecting petroleum hydrocarbons present in the groundwater at this former aviation and jet fuel tank farm site which is an estaurine emergent wetland. Our geologists collected and evaluated groundwater samples from monitoring wells to determine the extent and changes of contaminant plume over time. This site remediation is being conducted in compliance with CERCLA guidelines under authority of the State of Rhode Island DEM.

H&S was contracted to operate and maintain the LNAPL and dissolved phase collection and recovery system.  During routine maintenance we determined that the LNAPL recovery system was not effectively recovering contaminants. We performed a value engineering analysis including a detailed review and evaluation of past site assessments and system construction data to evaluate the effectiveness of the existing recovery system under current hydrogeologic and contaminant conditions. This review of site conditions, and treatment system and groundwater well recovery data indicated that the monitoring well screens were no longer intercepting the current water table, and the well screen packing contained sediment, limiting recovery efficiency. Our evaluation concluded that the previously collected monitoring data likely overstated the volume of recoverable oil at the site.

H&S then collected 24 rounds of periodic groundwater monitoring data and evaluated this data against historic site data to determine effectiveness of LNAPL recovery system. Our evaluation concluded that active passive natural attenuation processes were removing the remnant fuel contaminants due to decreasing concentrations of dissolved VOCs in outer monitoring wells to levels below MCLs.

H&S developed a revised operating plan which included a series of low-cost enhancements that increased contaminant recovery by 20% while lowering the remediation system lifecycle costs by $75,000. We negotiated a revised remediation strategy (shut down of system and reduced monitoring requirements to test natural attenuation) with State and local regulators resulting in a 33% cost reduction in monitoring costs and expedited closure of this FUDS site.