Abstract
In situ chemical oxidation (ISCO) of petroleum hydrocarbons (PHCs) within groundwater is considered a proven approach to addressing PHC-impacted groundwater in nonsaline environments. One of the most common oxidants used for oxidation of PHCs in groundwater is hydrogen peroxide (H2O2). Due to its highly reactive nature, H2O2 is often stabilized to aid in increasing its reactivity lifespan. Limited research and application of ISCO has been completed in warm, saline groundwater environments. Furthermore, even fewer studies have been completed in these environments for ISCOusing stabilized H2O2. In this research, stabilizedH(2)O(2) was examined to determine its effectiveness in the treatment of PHCs and the additive methyl tert-butyl ether (MTBE). Three stabilizers (citrate, phytate, silica [SiO2]) were tested to determine if the stabilizers could enhance and extend the treatment life of H2O2 within saline groundwater. To determine the effect of salinity on the three stabilizers, groundwater and aquifer samples were collected from two saline locations that had different salinity (total dissolved solids of about 7,000 mg/L and 18,000 mg/L). Specific target chemicals for treatment were water soluble, mobile components of gasoline including benzene, toluene, ethylbenzene, xylenes, (BTEX) and MTBE. Previous studies using unactivated persulfate indicated that the PHCs within the groundwater could be oxidized, however, only limited oxidation of the MTBE could be affected. The results of the laboratory tests indicated that greater than 95 percent of the target hydrocarbons were removed within 7 days of treatment. Microcosms with citrate-stabilized H2O2 demonstrated a significantly faster and greater decline with most hydrocarbon concentrations reaching < 5 mu g/L. The exceptions were ethylbenzene andm-xylene, which were slightly decreased to about 30 and 20 mu g/L, respectively. Initial mean concentrations of the BTEX compounds within the citrate-stabilized microcosms were 10,554 mu g/L, 9,318 mu g/L, 6,859 mu g/L, and 14,435 mu g/L, respectively. The silicate-stabilized H2O2 microcosms showed no significant benefit over the unstabilized control microcosms. The better performance of citrate-stabilized microcosms was confirmed by increasing delta 13C values of remaining hydrocarbons. MTBE declined from > 400 mg/L to < 100 mg/L in allmicrocosms, again with the best removal (> 90 percent) being measured in the citrate-stabilized microcosms. Unfortunately, H2O2 oxidation in the microcosms also resulted in production of up to 40 mg/L TBA or approximately 10 percent of the MTBE oxidized.