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9tantec • April 13, 2009 Page 9 of 13 Reference: Response to RWQCB March 11, 2009 Letter utilized three injection wells (IS-1, IS-2, and IS-3) and evaluation monitoring well AR/MW-5A, all located on the far west side of the BP 40T terminal approximately 600 feet from the subsequently installed ozone injection arrays. Stantec is currently searching through the archives to determine if an appropriately located MNA study has been performed that would allow quantitative calculation of biodegradation rates downgradient of the arrays. Analytical data from wells downgradient of the arrays indicate significant reductions in groundwater impacts have occurred as a result of installation of the arrays in late 2004. Therefore, these data indicate that the MNA study would need to be performed somewhat contemporaneously with a potential failure of the arrays for it to be relevant. Alternatively, the MNA study should at least be conducted subsequent to the reduction of groundwater impacts downgradient from the arrays. 8 For the proposed TS/MW-2D oxygen-injection pilot study, we are concerned that there may be significant limitations to using bottled oxygen to deliver the oxygen to groundwater. This proposed methodology was employed at a nearby site last year where bi-weekly injections of 13-pound oxygen bottles were used to attempt to attain a DO concentration of 10 milligrams per liter (mg/L) to promote biodegradation. Results were mixed, even after equipping the injection wells with diffuser tips designed to deliver the oxygen directly to water bearing units considerably shallower than the D zone units that will be targeted at.STTC. The STTC must supplement the description of the oxygen-injection pilot study to show (1) how they calculated that the oxygen will be delivered with sufficient pressure to overcome the 110-foot groundwater column overlying the TS/MW-2D well screen and (2) stoichiometrically demonstrate that twice-monthly 13-lb oxygen injections are sufficient to oxidize the petroleum hydrocarbon mass present in the target zone. Typical large bottled oxygen cylinders deliver approximately 150 cubic feet of oxygen with a weight of approximately 13.3 pounds and are pressurized to approximately 2,015 pounds per square inch (psi). Hydrostatic pressure increases at the rate of approximately 4.3 psi for every ten feet of water depth. The hydrostatic pressure of a 110-foot water column is calculated to be slightly less than 50 psi. The following formula is used to calculate the Minimum Injection Pressure, which is the hydrostatic pressure or the pressure on the water column due only to the water column height above the sparge point. Phydrostatic = (y H2O)*(hhydrostatic) Where: '1120 = Specific weight of water @ 0 degrees Celsius = 62.4 /b Ib t hhydrostaoc Depth to top of well screen (DTTWS) - Depth to water(DTW) = h(ft) I.\STTC-Stockton\Reports\Response to Comments\RWCCB Letter 3-11-09\STTC Response to RWQCB 3-11-09 Letter Final.doc