U.S. EPA Region 8, 61 pp, 2018

Results of groundwater monitoring conducted at the Idaho Pole Company site from January 2017 through December 2017 included performance data from pilot tests conducted at the site during 2015 and 2016. Nutrients injected into groundwater in the bark fill area, along with a surfactant and increased aeration of injection water, were intended to increase microbial activity in groundwater and accelerate degradation of PCP and residual diesel-range petroleum hydrocarbons. At source area wells 5-A and P-2, the PCP concentrations increased soon after each injection and remained elevated after the pilot injections. After the second pilot test, observed PCP concentrations frequently exceeded 1,000 µg/L at 5A and 100 µg/L at P-2. At source area wells EW-1 and P-4, PCP concentrations increased after the second pilot test but then declined. PCP concentrations at EW-1 nearly 1.5 yrs after the second pilot injections were between 50-100 µg/L, similar to the PCP concentrations at EW-1 before the pilot tests. PCP concentrations at P-4 nearly 5 years after the second pilot injections were <50 µg/L, much lower than the PCP concentrations at P-4 before the pilot tests. Results of the two pilot studies show PCP concentrations were neither permanently nor consistently reduced at source area wells by the 2015 and 2016 injections; however, geochemical indicators of natural attenuation suggest that conditions at the site are conducive to the occurrence of biodegradation. https://semspub.epa.gov/src/document/08/100004963 See also the 2016 Phase II Pilot Study Report at https://semspub.epa.gov/src/document/08/1817880.