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Y Work Plan for Additional Site Assessment and Interim Remediation/Feasibility Testing ARCO Facility No.5469 Stockton,California Page 5 overlain by,low permeability clayey silts, could potentially;result in ineffective capture of injected air. Air sparging under these geologic settings could also potentially result in uneven migration of contaminants and a'greater area of impact. Therefore, Delta does not propose to evaluate air sparging at this time. Review of published literature and discussions with the California Regional Water Quality Control Board (CRWQCB) indicate that'the time involved in remediation using C-SpargerTM is approximately 3 to 18 "months (S,ee Appendix B). However, -ozone injection at similar sites has indicated that'oxidation'of high concentrations occurs within a short period (3 to 6 months), but oxidation of low concentrations occurs over a longer time period. The proposed C-SpargerTm well locations were strategically selected to affect the dissolved extent of the MTBE plume onsite. The design depth of 55 feet for the sparge wells was selected based on known`impacvto the upper sandy unit. The C-SpargerTM introduces ozone into groundwater through a 2" by;30" micro-porous tubing, assembled at the base of the sparge well, that "is designed to generate very small bubbles (approximately SO micrometers). Based o'n manufacturer's recommendation, installation . of the sparge wells to approximately 55 feet"bgs should allow for an adequate radius of influence around each sparge point. Figure 4 presents the location of the sparge points and their estimated radius of influence. The C-SpargerT"' well-to-well spacing of 25 to 30 feet provides overlap in treatment areas between the C-SpargerT wells. See Appendix B for additional information on the C-SpargerTM technology. Delta proposes to evaluate the results of ozone injection for a period of six months. During this period, Delta will monitor.;;changes :in the concentration of petroleum hydrocarbons and other parameters such as dissolved oxygen, ferrous iron, pH, temperature, and turbidity. The extended testing period (6 months) is required to-evaluate long term results of ozone injection to groundwater. Delta will prepare and submit periodic status reports documenting the progress of the interim remediation/feasibility study. At the end'.of 6 months of ozone injection, other possible remedial alternatives will be evaluated if ozone injection is not a viable remedial solution. Delta will prepare and submit a report incorporating the results o .the interim remediation/feasibility study with recommendations for final remediation,'; or propose additional feasibility testing,. if warranted. P:IARCOU4691Work Plan15469 wrkpin 03-2002.doc