Abstract

To support the remediation design for a diesel-oil pipeline break near a remote railway river crossing near the British Columbia and Alaska border, a treatability test was designed to assess the in situ bioremediation potential under four conditions of soil amendments at 5 °C. The four conditions were:

  1. intrinsic bioremediation, where the soil received only water;

  2. biostimulation with one application of slow release fertilizer;

  3. bioaugmentation with one application of both fertilizer and a psychrotrophic (cold-adapted), hydrocarbon-degrading bacterial culture; and

  4. surfactant enhanced bioavailability, where the soil received one application of fertilizer and treatment with a biodegradable surfactant solution.

Tests were monitored by soil respiration and bacterial enumeration and total extractable hydrocarbon (TEH) content by GC/FID.

After 40 days incubation under aerobic conditions, all tests showed significant reduction in diesel range (C-C30) TEH-contamination. The intrinsic control was least effective, but still showed 66% TEH reduction at 5 °C. The biostimulated soil performed the best, allowing 86% TEH reduction. The bioaugmented soil and surfactant treated soil both allowed about 75% TEH reduction. The study concluded that simple biostimulation with slow-release fertilizers would be the most appropriate bioremediation approach for this site.

Introduction

A four-inch diameter petroleum pipeline, located adjacent to the rail tracks of the White Pass and Yukon Route Railroad, was broken by heavy equipment working in the area in October 1994. A significant quantity of Arctic diesel fuel was leaked and immediate efforts were made to recover most of the product through the Summer of 1995. Following site investigation in November 1995, a plume of diesel contamination was delineated in the gravely cobbles and boulder fill supporting the railway bridge over the East Fork Skagway River. This plume has migrated downward through the fill to bedrock surface and liquid product at the toe of the slope can discharge with shallow groundwater flow over ground surface into the river. The 500 m3 of residual hydrocarbon-contaminated fill supporting the railway bed needs remediation to prevent continued contamination of the water passing through the contaminated area.

Initial soil chemical and biological data indicated that active natural biodegradation of petroleum hydrocarbons may be occurring at the site, but appears limited by natural nutrient level and the indigenous bacterial population at the site. The gravely soil near the toe of the slope contains between 1000 and 5000 mg/kg of total extractable hydrocarbons (TEH) and has an indigenous heterotrophic bacteria population of between 104 and 106 bacteria/g of soil.

Excavation of the slope and structural fill supporting the operating railway was not feasible; therefore, in situ remediation options were considered. Because of the generally low volatility of some components of Arctic diesel and the lack of electrical power at the remote site, in situ bioremediation was considered the most feasible option.

To determine the optimal conditions for in situ bioremediation of the hydrocarbon-contaminated soil, a laboratory-scale treatability study was carried out. Because of the cold climate near the Alaska-British Columbia border, it was imperative that the testing be performed at the expected ambient soil temperature of about 5 to 8 °C.

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