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S ECOR 7-Eleven Store #14117 Corrective Action Plan-Addendum March 19, 2008 Page 2 outlined in the submitted CAP), SECOR considers an additional injection well located in the UST pit to be counter-productive. • While the USTs would be protected from injection well installation activities by the current conductor casings within the UST pit, the depth of the UST pit in relation to the groundwater elevation and the proposed injection well screen depths should be considered. In order to ensure that the maximum amount of oxygen injected into an injection well completed in the UST pit does not escape into the vadose zone, a proper seal above the well screen is essential. Due to the close proximity of the target sand unit (as outlined above and in the cross sections included in the CAP submitted in October 2007) to the floor of the UST pit, a limited amount of native soil exists between the two that would allow for a proper seal above the injection well screen. This increases the possibility of injected oxygen in the gas-phase migrating directly up the well boring and into the UST pit backfill and increasing the Lower Explosive Limit (LEL) in the vadose zone surrounding the current USTs to potentially dangerous levels. • However, even if a proper seal were to be installed, the close proximity of the target sand unit to the floor of the UST pit is likely to promote the direct migration of the gas-phase oxygen injected directly under the USTs upwards into the UST pit increasing the LEL in the vadose zone surrounding the current USTs to potentially dangerous levels. Based on the comments outlined above, SECOR respectfully requests approval of the previously submitted CAP with the following conditions: • As proposed in the submitted CAP, SECOR will closely monitor the dissolved oxygen (DO) concentrations at the site in monitoring wells MW-2, MW-3 and MW-4 before and after each oxygen injection event to observe the effective ROI of the proposed oxygen injection wells. In addition, DO concentrations will be monitored in more distal groundwater monitoring wells MW-1 and MW-7 before and after each oxygen injection event to assist in evaluation of the ROI. • If it is determined that the ROI of the proposed injection wells is not sufficient (specifically insignificant DO increases in MW-2 after 6 months of injections), SECOR will submit a CAP addendum to the SJCEHD with a proposal for improving the effectiveness of the oxygen injection approach in the area of the UST pit and groundwater monitoring well MW-2. REPORTING As outlined in the submitted CAP, SECOR will include the results of the oxygen injection events as part of the current quarterly groundwater monitoring and sampling reports. Specifically, the reports will include evaluation of the effective ROI of the proposed oxygen injection well array. 14117 CAP Addendum 3-19-08.doc SECOR International, Inc.