Site investigations

OVM

DEPTH READING

20'

Figure 2. Zone of contaminated soil following tanker spill (OVM is organic vapor meter; 1 ft = 0.3048 m).

burn pit areas and at the site of the truck tanker

Site investigations

body. Benzene detected in the groundwater was

Organic vapors in the soils at various depths

below federal maximum contaminant levels

were analyzed using a hand-held photo-ionization

(MCL), and hydrocarbon contamination was pri-

meter to delineate the plume that resulted from

marily confined to the surface soils.

the railroad tank car release (Fig. 2). The primary

spill covered an area approximately 25 ft (8 m) in

Subsoil and

diameter and 7.5 ft (2 m) deep. Soils at the ground-

groundwater characteristics

water level were contaminated and groundwater

The area that had been used for the fire train-

was affected by the spill. The fuel oil migrated

ing activities was generally underlain by gravel

along the surface of a silt layer located beneath

that was 2 to 3 ft (0.5 to 1 m) thick. Other portions

the 2- to 3-ft-thick (0.5- to 1-m-thick) gravel work

of the area were underlain by silt, sandy silt,

pad covering the area, resulting in a secondary

sand, and silty sand. Soil borings and excava-

plume.

tions at some locations indicated lenses of sandy

During the summer of 1989, a preliminary site

gravel. The water table fluctuates 5 to 7 ft (1.5 to 2

investigation (Shannon & Wilson, Inc. 1989) indi-

m), depending on the stages of the Tanana and

cated that hydrocarbon contamination was

Chena Rivers, and has been measured as high as

present at the old and new burn pit areas, near

2 to 3 ft (0.5 to 1 m) from the surface at some

the truck tanker body, at the burning prop simu-

locations within the site. July 1989 measurements

lator area, near the railroad tanker body, and at

showed a gradient of approximately 0.25 m per

the old drum storage areas (Fig. 1c). The highest

1000 m toward the northwest (Shannon & Wilson,

concentrations were found in the old and new

4