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Mr Harlin Knoll Quarterly Groundwater Monitoring Report, Fourth Quarter 2005 February 8,2006 Page 2 of 2 • sample containers andlaced on ice for p storage prior to transporting to the laboratory The samples were transported, under strict cham-of-c u stody protocols, to KiffAnalytrcal LLC of Davis, California, for analysis for benzene, toluene, ethyl-benzene, total xylenes, total petroleum hydrocarbons in the gasoline range (TPHg), methyl tert butyl ether (MTBE), dusopropyl ether, ethyl tert butyl ether, tert-amyl methyl ether, Cert butanol, 1,2-dichlorethane and 1,2-debromoethane using EPA Method 8260B The analytical data are presented in Table 2 The Groundwater Analytical Map is presented as Figure 5 The laboratory analytical report and chain- of-custody documentation are presented in Appendix C Conclusions Concentrations of TPHg above the laboratory reporting limits were detected in twelve groundwater samples The highest reported concentration of TPHg was 17,000 pg/L in extraction well EX-1 Concentrations of benzene above the laboratory reporting limit were again detected in eight groundwater samples, with the highest reported concentration of 2,900 µg/L in the sample collected at EX-1 Levels of MTBE, above the laboratory reporting limit were detected in groundwater samples at thirteen monitoring wells with the highest reported concentration of 140 µg/L in the sample collected at extraction well EX-1 Significant concentrations of petroleum hydrocarbons were not detected in newly installed down-gradient wells MW-I8 and MW-18D Recommendations Delta recommends continued quarterly groundwater monitoring and sampling The next sampling event is scheduled for March 2006 Delta recommends that the County review and respond to the Corrective Action Plan prepared by ATC Associates Remarks �? The recommendations contained in this report represent Delta's professional opinions based upon the currently available information and are arrived at in accordance with currently acceptable professional standards This report is based upon a specific scope of work requested by the client The Contract between Delta and its client outlines the scope of work, and only those tasks specifically authorized by that contract or outlined in this report were performed This report is intended only for the use of Delta's Client and anyone else specifically listed on this report Delta will not and cannot be liable for unauthorized reliance by any other third party Other than as contained in this paragraph, Delta makes no express or implied warranty as to the contents of this report If you have any questions concerning this project, please contact Jim Brownell at(916) 638-2765 Sincerely, DELTA ENVIRONMENTAL CONSULTANTS, INC Q5� Jason Mata Staff Technician .FDI G4�j fk- James R Brownell, P G California Professional Geologist No 5078 Sa 78 Enclosures oris .tr cc Jack+ Ceccarelli, RPMS of CA 9� Off~I 01: cAlr►� w Vpms ca\lworkmg\project tiles\100966 stockton 2537 waterloo roaftwm\4 q 05\rpms 0966 gwm 41h q05 dot