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EPA's Region 6 Office

Serving: Arkansas, Louisiana, New Mexico, Oklahoma, Texas, and 66 Tribal Nations

Summaries for the Popile Inc., Arkansas Superfund Site

  • 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 table.
     
  • 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 boundary.
     
  • 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.

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