Case Study of a SCAT Survey and Successful Remediation Strategy by Mechanical Mixing of a Fuel Oil Spill into a Mountain Stream

Abstract

The cargo of a double-tank truck carrying diesel and gasoline was released directly into a fast-flowing upland stream following an accident on a mountainous section of road in British Columbia (BC), Canada. High concentrations of the product were trapped in the interstitial spaces of coarse (cobble-boulder) sediments during a period of rising water levels. Almost the entire river backshore in the affected area was characterized by steep wooded slopes so that access everywhere was very difficult. These constraints for the SCAT program largely were overcome where direct backshore access was not possible using river rafts, boats (on the reservoir above the dam) and small Unmanned Aerial System (sUASs). Based on the survey results, a 4x4 Spider Walking Excavator equipped with a Universal grab on the hydraulic arm was deployed over a 2.5 km section of river immediately downstream of the accident site over a 9-day period. The grab rotated to mix the sediment or lifted and moved cobbles and boulders along the channel margin and in river bed sediments to release the oil. Swift Water Rescue personnel and river rescue response equipment were positioned with the Spider operations and the SCAT river bank surveys throughout the project, and used to scout river conditions ahead of SCAT rafting operations. Air monitoring was maintained throughout the response during all operations both along river banks as well as in the cab of the Spider while working in the river. A small UAS quadcopter was deployed to monitor the mixing activity in real time where the excavator could operate but ground access was unsafe or physically not possible. Standard SCAT practices were followed to provide the Unified Command (UC) with Shoreline Treatment Recommendation (STR) forms to guide the operations activities and once the treatment criteria were achieved STR Inspection Reports (SIRs) were submitted for approval by the UC. A downstream daily water sampling program monitored for PHs, VOCs and PAHs in the river waters during the mixing operations downstream of the operations area. At no time during the mechanical mixing activities (April 3 – 12) did the results of the analyses exceed Canadian and BC Water Quality Guidelines standards downstream past the confluence with the Salmo River and standards only were exceeded for the first few days of mechanical mixing (April 3 – April 5) during the period that the Spider was working on the upper reaches of the South Salmo.