PROCEDURAL TREATMENT OPTIONS TO ADDRESS INTERMITTENT PENTACHLOROPHENOL EFFLUENT EXCEEDANCES AT A FORMER WOOD-TREATMENT SITE IN BUTTE, MONTANA

The Montana Pole and Treating Plant in Butte, Montana treated wood with preservatives, mainly pentachlorophenol (PCP), which had been dissolved in a carrier fluid. Accidents and careless handling spilled large quantities of the fluid on the site, contaminating the vadose zone and groundwater. This site has been undergoing remediation since it was added to the CERCLA National Priorities List in 1987. Pentachlorophenol and dioxin are the contaminants of concern. Remediation technologies have included soil removal and installation of two water recovery trenches that collect groundwater, which is then pumped through a granular activated carbon (GAC) water treatment system. There were 22 exceedances of the 1 ppb treatment standard from 2003-2014. This thesis assigns a possible cause for each exceedance. Possible causes were determined to be due to normal plant operational procedures (18 exceedances), accidents (three exceedances), and climatic effects (one exceedance). The normal procedure of backwashing both carbon vessel trains on the same day was the possible cause, or one of two causes, for nine of the exceedances. It was recommended that only one of the two GAC vessel trains be backwashed at a time. Events that flushed the vadose zone, which increased PCP concentrations in the influent to the GAC vessels, were implicated in twelve of the exceedances. These events were normal plant operations (shutting down pumps during plant upgrades and rapid onsets of carbon bed exhaustion before the carbon could be replaced), accidents (a power outage and two water main breaks), and infiltration of storm water from off site during a heavy rainfall. Recommendations for counteracting the causes were made that should reduce the number of effluent quality exceedances