Tesoro Alaska Petroleum Company has an oil refinery in Kenai, Alaska, on a bluff approximately 100-feet above the shores of the Cook Inlet. Historic practices at the site contributed to the presence of refined petroleum products in groundwater migrating toward the shoreline bluff. Tesoro retained Geosyntec to design and build a system to collect impacted groundwater and redirect it to a treatment facility.
Geosyntec's Scope of Services
The Geosyntec system collected impacted groundwater along a 250-ft long section of the bluff and directed it to a central sump via a collection system. The collection system consisted of a barrier system and a collection gallery. The barrier consisted of a sheet pile wall that is keyed into the underlying clay aquitard. The interlocks of the sheet piles are sealed with a hydrophilic material to form an effective barrier. The collection gallery was installed on top of the clay aquitard on the inside of the wall and drained to a central sump area. From the central sump area, the contaminated groundwater was pumped into a 2,000-gallon capacity oil-water separator for preliminary treatment. The separated groundwater and petroleum product are pumped back to the refinery for final treatment and recovery, respectively.
The sheet pile wall was designed to withstand and constructed in extreme weather conditions. These weather conditions include the 30-ft tidal range of Cook Inlet, wave loading from storms, temperatures as low as minus 50 degrees Fahrenheit, and large magnitude earthquakes.
Geosyntec provided Tesoro with an innovative application of existing technology to accomplish their project objectives. Our approach consisted of sheet pile interlocks with a hydrophilic seal that replaced a two foot clay vertical barrier. Geosyntec also used a smaller sheet pile wall that was tied-back to a "deadman" as opposed to the larger, more commonly proposed "clamshell" style of sheet pile wall. As a result, Geosyntec's approach reduced Tesoro's implementation costs by several hundreds of thousands of dollars.