EPA's Region 6 Office
Serving: Arkansas, Louisiana, New Mexico, Oklahoma, Texas, and 66 Tribal Nations
- Contaminants are present at the site in several forms: NAPL, dissolved
phase, and matrix phase. Free products of creosote and PCP penetrated
through the unsaturated zone beneath the source areas and into the groundwater
- Owing to the RA source removal, further downward migration of the
free products is limited as the main driving force has been eliminated
and the remaining NAPL has reached residual saturation. Resistance exists
for the gravity driven downward movement, as the pressure head in the
sand aquifer is upward.
- Low solubilities of the COCs inhibit their rates of dissolution into
the groundwater. The very slow mass transfer process for PCP and PAHs
diffusing from the interior of the free product globules to the groundwater
interface is critical in controlling the dissolution across the phase
- Sorption capacity is high due to the disseminated and layered carbonaceous
materials within the Cockfield formation sands.
- Vertical penetration of NAPL and dissolved phase contaminants through
the Cook Mountain formation is virtually impossible.
- Lateral spreading of dissolved PCP and PAHs occurs within the sand
aquifer under semi-confined conditions. Lateral migration in the upper
fine-grained unit and the lower carbonaceous layer is insignificant.
- Contaminants are available for microbial degradation when released
to the groundwater. However, the rate of degradation is controlled by
the rate of dissolution from NAPL to the groundwater.
- Organic contaminants are biodegrading in aerobic and anaerobic forms
within the groundwater. The dominant degradation mechanism is an aerobic
process. Anaerobic degradation occurs only in zones where dissolved
oxygen level is very low.
- At Popile, the rate of biodegradation equals the rate of release of contaminants, resulting in a stable plume for the last 30 years. Existing contamination will not spread.