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1 APPENDIX C DEMONSTRATION OF BIODEGRADATION CAPACITY ' This appendix describes ERM's procedures and rationale for determining if biodegradation is occurring and will continue to occur at former tank sites 1 and 2 ' On 22 April 1999 and 29 February 2000, ERM collected ground water samples in monitoring wells at the site to evaluate biodegradation parameters The ground water samples were analyzed for dissolved iron and dissolved manganese by USEPA Method 6010B, nitrate and sulfate by USEPA Method 300 0, and methane by USEPA Method 8015 modified Dissolved oxygen readings were also collected at each monitoring well The ' ground water sampling results are presented in Table C-1 Figures C-1 and C-2 present the monitoring well locations at each former tank site ' if biodegradation is occurring, the concentrations of electron acceptors (sulfate and nitrate) within the hydrocarbon ground water plume should be lower than those outside ' the hydrocarbon plume Similarly, the concentrations of metabolic byproducts (dissolved iron, dissolved manganese, and methane) should be higher in the hydrocarbon ground water plume than outside the hydrocarbon plume Finally, dissolved oxygen concentrations should be sufficient within the ground water at each tank site to allow for biodegradation to occur The results from each sampling event indicate that biodegradation is occurring at the former tank sites At former tank site 1 the concentrations of sulfate and nitrate are lower in samples ' collected from wells within the hydrocarbon plume (MW-1 and MW-4) than the well located upgradient of the plume (MW-3) Similarly, the concentrations of dissolved iron, dissolved manganese, and methane in samples collected from MW-1 and MW-4 are ' greater than in the sample collected from MW-3 Furthermore,a comparison of concentrations observed at MW-1 (located at the downgradient edge of the hydrocarbon plume) and MW-4 (located in the heart of the plume) generally demonstrates a rebound in ' the concentrations of electron acceptors and a decrease in the concentration of metabolic byproducts at MW-1 versus MW-4 This indicates that biodegradation is occurring at a higher rate within the heart of the hydrocarbon plume Finally, readings at wells MW-1, ' MW-3, and MW-4 indicate that dissolved oxygen concentrations range from 147 to 3 22 milligrams per liter (mg/1), which is sufficient for biodegradation to occur Figures C-3 ' through C-7 present the concentrations of electron acceptors and metabolic byproducts observed at each sampling location during the April 1999 and February 2000 sampling events at former tank site 1 ' The sample results also indicate that biodegradation is occurring at former tank site 2 The concentrations of electron acceptors (sulfate and nitrate) are lower in the sample ' C-1