Remediation Status: In active remediation

Why the technology was selected:
The UVB wells were installed as an interim remedial measure to capture and treat contaminated groundwater and prevent it from migrating to the lake located downgradient of the facility.

Date implemented:
December 10, 1997

Final remediation design:
Two UVB (Unterdruck Verdampster Brunnen) or "vacuum vaporizing wells" were installed 300 ft downgradient of the facility, approximately 85 ft apart. The design capture zone for the system was 200 ft wide and 45 ft deep. The wells were constructed of 10-inch diameter schedule 80 PVC with two stainless stell screens (0.01-inch slots). Contaminated groundwater was extracted through the upper screen (3.5-12.5 ft bgs - upper surficial aquifer) utilizing a 1 H.P. Grundfos submersible variable-speed stainless stell pump. The water was treated in an in-well stripping unit (vacuum stripping canister) installed on the top of the wellhead. Treated water was injected through the lower screen interval (39-45 ft bgs - lower surficial aquifer) using a 1/3 H.P. Grundfos KP 250 sump pump. The design flow rate for each submersible pump was 40 gpm. A 5 H.P. Elekror centrifugal blower located at the surface was utilized to generate negative pressure inside the well. Design vacuum was 20 inches of water with a 530 cfm air flow. VOC emissions from the system were estimated to be approximately 2.0 lbs/day and therefore, no emissions treatment system was installed.

Results to date:
Results achieved to date:: The startup pumping rate for the UVB wells was 10 gpm. The sump pumps were almost immediately upgraded to 3/4 H.P. Goulds Submersible pumps (discharge head 60 ft (26 p.s.i.) at 10 gpm. Other early maintenance and operational problems included failed packers, iron precipitation and sand/silt entering the well casings. The effluent injection rate could not be balanced with the influent influent pumping rate (influent pumping rate >effluent injection rate). A holding tank (3 ft x 4 ft) was installed at the surface to receive and hold influent water, until it was injected. However, design pumping rates could not be achieved. In the second year of system operation, a biocide injection system was installed. Groundwater extraction rates were 4-6 gpm and were limited by influent injection rates. The submersible pumps were therefore cycled to operate for 20 minutes of pumping followed by 30 minutes of down time to allow for influent injection (rate ~ 2 gpm). By the fourth quarter of 1999, influent pumping rates were limited to 2 - 2.5 gpm and effective injection rates were approximately 1.5 gpm. Biologic and geochemical fouling was occurring. By May of 2000, injection tests of the lower surficial aquifer revealed that a rate of only 0.46 - 1.0 gpm could be achieved. In the fall of 2000, the UVB wells were shut down and were later converted to a pump & treat system with effluent treated using a shallow tray air stripper. Treated water was discharged to the City of Orlando sewer system.