NWT RESEARCH DATABASE

Regions: South Slave Region

Tags: physical sciences, contaminants, hydrology, groundwater

Objective(s): To confirm the presence or absence of contamination, to determine the risk associated with contaminated groundwater infiltration into the lake; and to inspect the fuel storage tanks located on site and collect information required to determine decommissioning requirements.

Project Description: The objective of the groundwater investigation is to confirm the presence or absence of contamination and to determine the risk associated with contaminated groundwater infiltration into the lake (if applicable). This work will include installing five to six monitoring wells at the site in the area adjacent to the Great Slave Lake. A secondary objective is to inspect the fuel storage tanks located on site and collect information required to determine decommissioning requirements. The proposed boreholes will be advanced using a small portable drilling rig (a Geoprobe 420M or equivalent). The boreholes will be advanced to a maximum depth of 3 m below ground surface, until inferred bedrock refusal or permafrost. Field observations and soil sampling information at each borehole location will be recorded in individual logs. Groundwater monitoring wells will be installed to investigate groundwater conditions and to obtain ground water samples for subsequent laboratory analysis. The groundwater monitoring wells will be constructed with polyvinyl chloride (PVC) well screens and solid riser. All monitoring wells will be installed with a screen of 1.5 m and solid riser to grade. A tight fitting slip-on cap will placed at the bottom of the screen and the top of the well will be sealed with compression J-Plug fittings. A clean silica-sand filter pack will be placed in the borehole annulus surrounding the well screen to approximately 30 cm above the top of screen. Bentonite hole plug will be placed in the borehole annulus above the sand pack to approximately 30 cm below grade to prevent infiltration of surface water. Above-grade metal protective casings will be installed around the wells, and concreted in place above the bentonite seal. Following installation, the wells will be surveyed relative to a local geodetic benchmark to obtain elevations relative to mean sea level. The depths to water in each monitoring well will be measured using a Heron Instruments water level meter with an interface probe (or equivalent). Prior to re-use, the interface probe will be thoroughly cleaned using soapy water and rinsed with water to minimize the potential for cross contamination of the wells. All well water samples will be collected using the Waterra system: clear polyethylene tubing with inertial foot valves. Each well will be equipped with its dedicated high density polyethylene (HDPE) tubing with an inertial foot valve attached at its base. The wells will then be prepared for sampling by removing three times the volume of standing water. Upon completion of monitoring well development, each well will be allowed to settle and equilibrate to static conditions. Groundwater samples collected will be submitted for laboratory analysis of F1/BTEX, PHC F2-F4, PAHs and metals. A visual inspection of the fuel tanks present at the site will be conducted, including all associated piping. The presence (or absence) and a volume estimate of residual fuel will also be determined for each of the tanks. A sampling program will include collecting samples of residual petroleum product/ absorbent materials found at the site and also tank paint samples to determine the waste classification of materials prior to decommissioning the tanks. A summary and copy of the final report will be sent to Aurora Research Institute upon completion of the project. The fieldwork for this study will be conducted from August 15, 2014 to September 15, 2014.