Basalt flows with overlying sediments of silt and clay. The silt ranges from 20-30 ft. thick. The total thickness of the basalt flows are at least 225 ft. and individual flows are 40-60 ft. thick separated by top flows that are vesicular. Flow interiors tend to be massive and contain fractures caused by jointing and possible faulting.

The water table within the silt is 10-15 ft. bgs. Aquifer zones consist of interflow zones and fractured zones within the basalt separated by sections of basalt flow interiors. There are three aquifer zones which are delineated based on a cobination of geologic characteristics and water production. The highest water production during drilling occurred in the vesicular interflow zones. The interior basalt flows contain vertical jointing and fracturing, which produces hydraulic continuity between the interflow zones.

• Dense Non-aqueous Phase Liquids (DNAPLs)
• Fractured Bedrock

The lateral migration in the shallow ground water is limited to very short distances due to the low hydraulic conductivity and high retardation rates in the silt. Reductive dehalogenation is probably not occurring at appreciable rates due to the lack of natural organic matter.

Lateral migration in the basalt has been limited due to very flat hydraulic gradients

• Trichloroethene (65,000 µg/L)

• Borehole Geophysics
  • Natural Gamma

Comments:
Aeromagnetic survey conducted by USGS in 1993

• Pump and Treat

Restore ground water to protective levels for COCs within a reasonable time frame. If this is not feasible, then provide hydraulic source control to protect unimpacted ground-water resources within the locality for potential future domestic water supply.

Since the system began in August 2000, over 120 million gallons of water were removed which included 2,200 lbs of VOCs.

Capitol costs for the extraction wells were $600,000 and long term maintenance (30 years) is estimated at $2,200,000.