SITE INFORMATION AND CORRESPONDENCE_PRE 2019

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Stantec April 30, 2010 Page 2 of 4 Reference: First Quarter 2010 Site Status, Groundwater Monitoring and Remedial Summary Report- Stockton Terminals Technical Committee Facilities Appendix K-Ozone Injection Well Monitoring Program and Revised Contingency Plan be used as an early warning for the Trigger Wells is repeated here from the section entitled Observation Wells on Page 8 of SECOR's June 27, 2003 Response and Addendum. "... well PS/MW-20 will be used as a mid-point observation well to determine the effectiveness of the "B" zone ozone remediation system down-gradient between the trigger wells and the remedial observation wells. Due to the location of the POSDEF COGEN plant, only well PS/MW-20 is situated in a location suitable for a mid-point well. This well will be monitored and sampled quarterly to monitor "B" zone concentrations for an early warning that the trigger wells may be impacted in the future." COMPLIANCE LIMITS The revised compliance limits are outlined the tables below: REMEDIAL OBSERVATION WELL COMPLIANCE LIMITS Ethyl- I Total Well Benzene benzene Toluene Xylenes MTBE TBA Name (Ng/L ) (Ng/L ) (Ng/L ) (Ng/L ) (Ng/L (Ng/L) Remedial Observation Wells-A Zone- Historical Averages PS/MW-18 71.79 0.97 1.69 1.99 492 134# PS/WC-1S 116.46 47.09 6.55 12.47 0.99 5.0 * AR/MW-21A 0.58 0.58 0.58 2.0 280.9 5.0 * Remedial Observation Wells- B Zone- Historical Averages AR/MW-18B 2.35 0.5 0.5 1.54 0.85 6.6 * AR/MW-21 B 1.76 1.7 1.72 3.54 516 5.0 * PS/WC-1M 3,167.8 12.02 57.51 68.03 38.7 14.0# Explanation: pg/L = micrograms per liter MTBE = methyl tertiary butyl ether TBA= tertiary butyl alcohol N/A = not applicable Remedial observation well compliance limits are historical averages based on all data available through fourth quarter 2005. This includes the period prior to ozone injection system start up and the anticipated one-year initial spike in concentrations following the startup of the ozone injection system. The exception is the addition of TBA as a compliance analyte and the TBA compliance limit as indicated above. Per CRWQCB recommendation, TBA compliance limits for indicated limits (*) are based on the median value of all available data through third quarter 2008. For three of these wells, the median was 5.0 pg/L indicating that all results were below the laboratory reporting limits. For indicated limits marked with (#), the values agreed to are based on the method outlined in CRWQCB December 15, 2008 letter.