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In-Well Stripping Installation
at the Second Street Site,
Hastings, Nebraska
Setting |
- Hastings, Nebraska
- One 2-well system near
source area. Plume over 3,000 feet long.
- Coal tar (FGMP) contamination in one unconfined
aquifer
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Hydrogeology |
- Stratified aquifer:
- Hydraulic conductivity:
250 ft/day
- Plume thickness:
60 ft
- Depth to groundwater: 115 ft
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Contamination |
- BTEX and naphthalene
- BTEX concentrations
entering the wells: 1,500 to 2,300 ppb. Naphthalene
concentrations entering the
wells:
60 to 2,100 ppb.
- Primary Objective: Reduce contaminant
concentrations below target levels: benzene 500 mg/L
and Naphthalene
500 mg/L. (Further contaminant reduction downgradient
planned in out years.)
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Inorganic Chemistry |
- Groundwater is in equilibrium with calcite,
indicating potential for calcite scale formation.
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Operation Details |
- One 40 hp positive displacement pressure
blower.
- Closed-loop system. Carbon treatment of air
before return to wells.
- Two piezometers for each well and three
monitoring wells to measure performance.
- Pumping rate: 68 and 96
gpm. Air/water ratio: 27.5:1 and 19.5:1.
- System operation: In service since August
2001, with routine inspection and maintenance of
the mechanical
systems. Plugging of wells experienced: partly silt,
partly calcite, and partly biological. Well efficiency
reduced. Wells re-developed October 2002. Well efficiency
restored.
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Results
- Contaminant removal efficiency in the wells over
95% for all contaminants.
- Monitoring well 200 feet downgradient:
non-detect for all contaminants after eight months of
operation; has remained non-detect since.
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