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* CAM B R I A <br /> FEASIBILITY STUDY <br /> Cambria reviewed groundwater analytical data for the subject site to determine whether there is <br /> evidence that biodegradation/natural attenuation is occurring beneath the subject site The <br /> historical trends of the groundwater analytical data show that concentrations are declining, <br /> suggesting biodegradation is occurring <br /> Cambria proposes implementing quarterly bio-parameter monitoring and dissolved oxygen (DO) <br /> sampling to further assess the extent of bioremediation at the site This assessment will aid in <br /> determining whether monitored natural attenuation is a viable remedial alternative for this site, or <br /> if perhaps enhanced bioremediation is more appropriate <br /> Bioparameter Monitoring <br /> The following is a summary of bioparameters that will be evaluated to determine if <br /> bioremediation is occurring <br /> • Dissolved Oxygen During aerobic biodegradation, DO levels are reduced as aerobic <br /> respiration occurs DO is the most thermodynamically favored electron acceptor used in <br /> aerobic biodegradation of petroleum hydrocarbons Active aerobic biodegradation of BTEX <br /> compounds requires at least 2 ppm DO in groundwater DO concentrations can naturally be <br /> as high as 8 to 10 ppm in oxygen-saturated groundwater Therefore, DO concentrations that <br /> vary inversely to hydrocarbon concentrations indicate the occurrence of aerobic degradation, <br /> provided that at least 2 ppm of DO is present <br /> • Oxidation-Reduction Potential. The ORP of groundwater is a measure of electron activity <br /> and is an indicator of the relative tendency of a solute species to gain or lose electrons The <br /> ORP of groundwater generally ranges from -400 millivolts (mV) to +500 mV Under <br /> oxidizing conditions the ORP of groundwater is positive, while under reducing conditions <br /> the ORP is usually negative Reducing conditions (negative ORP) suggests that anaerobic <br /> biodegradation is occurring Generally, the ORP of groundwater inside a BTEX plume <br /> should be somewhat less than that measured outside the plume <br /> 1399 4 <br />