DISCUSSION AND CONCLUSIONS

anchor it in place. On 12 and 13 August, water

HDPE scrim, coated on both sides with black

continued to be pumped into the pit until the

HDPE. A water distribution system of 4-in. (10-

water level was approximately 1 ft (30 cm) above

cm) perforated schedule 40 PVC pipe was placed

on top of the liner and covered with contami-

the surface of the contaminated soil. On 17

nated soil. An air header constructed of 4-in.

August the water level had receded and more

(10-cm) schedule 40 PVC pipe was placed just

water was added. After water had to be added

below the surface of the contaminated soil, with

several times, it was apparent that the liner sys-

25 air diffusers attached to the piping located 4

tem had leaked. Approximately 35,000 gal

in. (10-cm) above the soil surface. Water is added

(132,000 L) of water was pumped into the pit.

to the pit, saturating the contaminated soil, and

This is enough to fill the empty pit. Although the

submerging the air diffusers.

cause of the leak has not been verified, several

Water is circulated through the system using a

possibilities exist: mechanical damage during

1-hp (10-kg cal/min) trash pump to extract water

placement of the contaminated soil with the back-

from the surface of the leach bed. The water is

hoe; tearing of the liner at a seam as it was loaded

pumped to a 1000-gal (3785-L) fertilizer mix tank

with soil; puncturing of the liner by rocks in the

and is allowed to flow by gravity from the bot-

fill material because the liner was not protected

tom of the tank to the water distribution piping

by sand or cushion fabric; or cracks in the thin

in the bottom of the pit. The water then perco-

HDPE coating covering the scrim when the liner

lates up through the soil mass carrying nutrients

was folded into the corners of the pit.

and oxygen to the hydrocarbon degrading bac-

teria. A 9-kW emersion heater is placed in the

Result

tank to elevate the temperature of the circulating

Although we encountered problems with the

water.

recirculating leachbed at the FIA site, a member

Air is supplied to the diffusers by a 2.5-hp (25-

of our research team was involved in designing

kg cal/min) regenerative blower. Aeration was

and operating another recirculating leachbed at

also provided in the mix tank by an air compres-

more northerly location. At this location, TPH

sor, attached to a single air diffuser located in the

levels in a diesel- and waste-oil-contaminated soil

bottom of the tank.

decreased from between 300 and 47,000 mg/kg

to between 240 and 570 mg/kg in 5 weeks at

Construction

Anatuvuk Pass, in northern Alaskan. Correspond-

The leach bed was installed at the location of

ing values for petroleum and hydrocarbon-

the cross-shaped burn pit (Fig. 1c). Contaminated

degrading microorganisms, as determined by the

material in the area was excavated and moved to

sheen screen technique (Brown and Braddock

1990), increased from 1.8 104/g to 4.5 106/g.

the landfarm facility and the area was back-filled

Final diesel-range organics, after 8 weeks of treat-

with mechanically compacted sandy-silt mate-

ment, were less than 200 mg/kg.

rial. The leach bed pit was then excavated and

recompacted. The liner was factory seamed and

arrived at the site as a single 55- 55-ft (16.75-

DISCUSSION AND

16.75-m) sheet. The liner was fitted into the

CONCLUSIONS

excavation and the water distribution manifold

was placed at the bottom of the pit. Approxi-

Landfarm

mately 150 yd3 (115 m3) of contaminated soil that

The results from the landfarm treatment are

was stockpiled in the landfarm was placed in the

promising and significant. A seven-fold variabil-

pit. The air distribution header was buried by

ity in rates suggested that the slower rates could

hand at the surface of the contaminated material

be improved to match or approach the faster

and the skid-mounted mechanical equipment was

rates. Faster degradation rates would reduce the

moved to the site and plumbed to the air and

time and cost required for treatment and conse-

water distribution systems.

quently reduce the chance of leaching or off-site

migration during treatment. At least part of the

Operation

difference in rates may be ascribable to moisture

Beginning on 9 August 1991, water was

and nutrient additions. Evidence of this is seen in

pumped from the infiltration gallery well to fill

the pattern of the degradation variability, which

the leach bed system. Initially, the air manifold

appeared to correspond to the pattern of irriga-

floated to the surface and sandbags were used to

tion and fertilization. Owing to the nature of the