Chemical oxidation of Tetrachloroethene (PCE) contamination in a fractured saprolitic bedrock aquifer

Abstract: This describes the progressive remediation of a PCE contaminant plume using two separate chemical oxidizers in a fractured saprolitic bedrock aquifer in Rockville, Maryland. The geology consists of fine-grained soils overlying weathered-fractured schist and phyllitic bedrock (saprolite). The state of Maryland required that the onsite source be remediated to a risk-based PCE cleanup goal of 253 micrograms per liter (ug/L) and allowed natural attenuation as the offsite remedial action. The source area remediation was initially performed using a Fenton’s Reagent-based chemical oxidation process. A successful bench test and a field scale pilot test were conducted prior to implementing a full-scale program that used ten stainless steel treatment wells. The initial post-treatment results looked promising, but the contaminant concentrations increased (rebounded) significantly following the treatment process. The October 2000 (rebound) PCE contaminant concentrations in the aquifer ranged from 7.8 ug/l to 26 milligrams per liter (mg/L), averaging 8.5 mg/L, as determined from 17 sample points. In response to these rebound concentrations, 11,000 pounds (lbs.) of liquid sodium permanganate were injected into the aquifer at 50 locations in late January 2001. This successful treatment application resulted in an 89.3 percent average PCE reduction in the aquifer with an average concentration of 909 ug/L by late February 2001