North Boundary Contaminant System. Its initial construction
was started in 1978 and is a 2085 m long slurry wall
of bentonite clay with 35 upgradient dewatering wells
and about 38 downgradient recharge wells. The 38 downgradient
recharge wells have subsequently been replaced
by 15 recharge trenches. The system is operated to maintain
a reverse gradient across the slurry wall.
• Northwest Boundary Contaminant System. Its initial construction
was started in 1984 and is a 427 m long slurry
wall of bentonite clay with 15 upgradient dewatering
wells and 21 downgradient recharge. The slurry wall only
extends along the northeastern half of the barrier system,
making the system partly a physical barrier and
partly a hydraulic barrier.
• Irondale Boundary Contaminant System. In 1981, Shell
Oil Company completed the Irondale Barrier System.
The System, relying on hydraulic gradient control alone,
consists of two rows of 33 dewatering wells and one row
of 14 recharge wells. The original system was later modified
to include additional extraction and recharge wells
and a new absorber.
These barrier systems are containment systems that are
designed to prevent off-site migration of contaminated
groundwater. The Offpost pump and treat systems were designed
and constructed to cleanup the contaminated
groundwater in the alluvial aquifer north of the Rocky Moun-