SECTION THREE
Construction Activities
The AS/SVE system was constructed between October 19 and December 29, 1994. Details of
the system's construction are discussed below. Appendix A presents matrix characteristics and
operating parameters.
PILOT SYSTEM
The pilot system used in this application consisted of one AS well, three SVE wells, ten vadose
zone piezometer (VZP) wells, two groundwater monitoring wells, and three dissolved oxygen
sensor (DOS) wells, as well as an impermeable plastic cover for the ground surface and well
monitoring equipment. The AS and SVE wells were located near monitoring well LF5-MW8A,
from which groundwater samples with the highest recorded TCE concentrations in the project
area had been collected.
The AS well was used to inject clean air into the aquifer, using an above-ground blower, to strip
volatile contaminants from the aquifer into the soil in the subsurface at the site. Dissolved
oxygen (DO) concentrations in the aquifer were measured during AS using DOS wells. The DO
results were used to estimate the radius of influence of the AS well during the pilot test. The
SVE wells were used to extract volatile contaminants from the subsurface soil, and the VZP
wells were used to measure the radius of influence of the SVE wells.
The impermeable plastic cover was used to enhance the radius of influence for the SVE wells by
moving the air recharge boundary a greater distance from the SVE wells. The cover was
constructed of a 20-millimeter (mil) thick layer of very low density polyethylene (VLDPE) and
laid down over a cleared area. The cover had a radius of approximately 200 feet, and was
covered with 4 to 6-inches of gravel to assure tight contact with the ground surface, and to allow
for light vehicular traffic (pickup trucks) over the cover. All wells were drilled using a 4-inch
inner diameter (ID) hollow stem auger.
Operation of the pilot system consisted of a SVE pilot test and a combined AS/SVE pilot test.
FULL-SCALE SYSTEM
The full-scale system used in this application consisted of five AS wells, six SVE wells, ten VZP
wells, three groundwater monitoring wells, three DOS wells, four passive injection wells, and
associated well-monitoring equipment. The passive injection wells were positioned where
modeling results showed significant stagnation zones when two adjacent SVE wells were
operated at the same time. The full-scale system also used the same impermeable plastic cover
for the ground surface that was used in the pilot system. Two parallel systems of vapor-phase
granular activated carbon (GAC) were used in the full-scale system.
Extracted vapors were first treated using a moisture (water/vapor) separator to remove entrained
water, and then treated using activated carbon filter canisters (GAC), prior to discharge to the
atmosphere.
The AS system consisted of an inlet particulate filter, compressor, moisture separator, and flow
control valve.
3-1
Ft. Griffey Landfill 5 OU Interim RA Report
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