In-Well Stripping Pilot Study:
10th Street Site
Columbus, Nebraska
Setting |
- Columbus, Nebraska
- One -well pilot installation
- TCE and PCE in one unconfined
aquifer
|
Hydrogeology |
- Unconfined aquifer: 64 feet to 73 feet
of unconsolidated sand
and gravel underlain by
13 feet to 18 feet of silty clay.
- Hydraulic conductivity:
271 ft/day to 295ft/day
- Plume thickness: ~50 ft
- Depth to groundwater: 14 ft
|
Contamination |
- TCE peak concentration: 620 mg/L
- PCE peak concentration:
164 mg/L
- Primary Objective: Reduce TCE and PCE concentrations
below MCLs downgradient of treatment well
|
Inorganic Chemistry |
- Groundwater is in equilibrium with calcite,
indicating the potential for calcite scale formation.
An automated acid addition was installed and operated
to reduce calcium carbonate precipitation in the
DDC well.
|
Operation Details |
- One 10 hp positive displacement pressure
blower with a variable frequency control (VFD)
to regulate air flow.
- Closed loop system. No emission
control required. Carbon treatment of air prior to
recycling to well.
- pH control: batch hydrochloric
acid addition to well
- Eight monitoring wells and two
piezometers to measure performance/treatment zone
- Pumping
rate: 55 gpm; air/water ratio: 13.6:1
|
Results
- Stripping efficiencies, the percent reduction
in a single pass through the well, were 75% for TCE and
85%
for PCE. Monitoring of upgradient/downgradient concentrations
indicates 90.1 % removal of TCE and 98.2% removal of
PCE in three passes through the treatment zone.
- System operation:
in-service for 239 days with limited inspection and no
maintenance other than maintaining the acid level
in the supply drum.
The pilot system was started in June 12, 2001. A transducer
study was performed to determine the capture width of the
DDC well. Transducers were installed in all eight
monitoring wells. The result of the study was that
the capture width of the DDC well was 216 feet when pumping
at 55 gpm. Single-pass stripping efficiency in the
well was 75% for TCE and 85% for PCE in two separate tests. Overall
removal efficiency of the well, defined as the concentration
of contaminant in the groundwater upgradient of the well
versus the concentration of he contaminant in the groundwater
downgradient of the well, was 90% for TCE and 98% for PCE.
Figure 1 - Overall Removal
Efficiency - Click to
enlarge
The 216-foot capture width achieved by the system and measured
by a transducer study can be seen below.
Figure 2 - Particle Tracking
Model Result - Click to enlarge
|
