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Stantec April 13, 2009 Page 10 of 13 Reference: Response to RWQCB March 11, 2009 Letter r fb Phydrostatic = 1 62.4 3) h(ft)l t Ib2 Phydrostatic= 62.4 3 110 ftt)+144 to =47.6 psi fi jt2 Pminimum Inlectlon Phydrosbtic 47.6 psi Because of the greater pressure than shallow applications and the approximate 2.5 cubic feet of casing volume that needs to be displaced, slightly lower oxygen volumes and weights will be delivered to the aquifer. On the other hand the greater pressure will allow higher concentrations of dissolved oxygen (DO) to be maintained. Overlying, fine- grained, low-permeability strata should minimize potential diffusion of DO to the surface as often occurs in unconfined aquifers. (2) stoichiometrically demonstrate that twice-monthly 13-Ib oxygen injections are sufficient to oxidize the petroleum hydrocarbon mass present in the target zone. As outlined in the January 27, 2009 Pilot Study Work Plan, the objective of the proposed oxygen injection was to facilitate enhanced biodegradation (not oxidation) and mitigate impacts near in the aquifer near well TS/MW-2D. Stoichiometric relationships between the mass of oxygen needed to metabolize petroleum hydrocarbons and the mass of hydrocarbons potentially degraded are available in the literature and typically vary between 3 and 3.5 pounds of oxygen to 1 pound of hydrocarbons. From the April 10, 1998, ASTM E 1943-98 Standard Guide for Remediation of Ground Water by Natural Attenuation at Petroleum Release Sites, Page 22, Appendix Section X5.3.2, A Quantitative Approach to Evaluating Indicators of Biodegradation; The equation that follows was used to determine that 3.1 mg/L of oxygen is necessary to completely metabolize 1 mg/L of toluene. Aerobic Respiration C6H5CH3 + 902 7CO2+ 4H2O As shown in Figure X5.1 of the above reference, the equation is balanced using toluene and would differ slightly for other BTEX constituents, TPH, and fuel oxygenates. The equations balanced for benzene can be found in Wiedemeier et al, 1995, Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater. As is well understood, these are potential relations and depend on many other variables, the spatial distribution of adequate DO concentrations, the appropriate microbial communities, contaminant demands, and other variables. For example, biodegradation of MTBE is generally reduced or delayed until the much of the BTEX constituent mass has been degraded. I:\STTC-Stockton\Reports\Response to Comments\RWQCB Letter 3-11-09\STTC Response to RWQCB 3-11-09 Letter Final.doc