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Mr. Jack Badey - 2 - 7 February 2014 <br /> carbon, alkalinity, and degradation products are still elevated in MW-5A, and alkalinity in MW-5B <br /> is still above background concentrations. <br /> In the third water-bearing zone, the concentration of PCE in MW-5C declined from 150 mg/L to <br /> 37 mg/L and degradation products are present. However, the alkalinity and dissolved organic <br /> carbon concentrations have not increased commensurate with the increases observed in the <br /> upper water bearing zones. Therefore, Central Valley Water Board staff recommend another <br /> year of monitoring to assess if degradation will continue at the site of injections. <br /> Another year of monitoring may also reveal whether the recent increase of PCE in MW-5A is an <br /> anomaly or indicates an ongoing influx of dry cleaning solvents. <br /> Monitored Natural Attenuation <br /> In the Pilot Test Report, AMEC proposes monitored natural attenuation to complete the <br /> subsurface remedial actions. Contrary to AMEC's assertions in the reports, Central Valley <br /> Water Board staff have not concurred with monitored natural attenuation. However Central <br /> Valley Water Board staff concur that it is appropriate to revise the monitoring and reporting <br /> program to remove constituents that have not been indicative of geochemical changes at this <br /> site. Central Valley Water Board staff will provide a draft revised monitoring and reporting <br /> program for UniFirsts' review under separate cover. <br /> Background Geochemistry Concentrations <br /> UniFirst proposed background concentrations for the geochemical parameters of dissolved iron <br /> and manganese, total dissolved solids and electrical conductivity as required by the monitoring <br /> and reporting program. AMEC presented these values, which were obtained from upgradient <br /> monitoring wells MW-1 and MW-6, and the supporting rationale in the First Semiannual 2013 <br /> Groundwater Monitoring Report. Central Valley Water Board concur with the proposed <br /> background concentrations. <br /> Summary <br /> UniFirst shall conduct at least two more consecutive semi-annual monitoring events to <br /> determine if the HRC remediation has been exhausted. Central Valley Water Board staff will <br /> provide a draft revised monitoring and reporting program under separate cover. <br /> If you have any questions, you may contact me by telephone at (916) 464-4680 or by email at <br /> Amy.Terrell@W terboards.ca.gov. <br /> eRRELL <br /> AMY T , P.E. <br /> Federal and Private Sites Cleanup Unit <br /> cc: Mr. Nuel Henderson, San Joaquin County Environmental Health Dept., Stockton <br /> Mr. Tom Cosgrave, UniFirst Corporation, Willmington, MA <br /> Mr. Monte Schlittenhard, UniFirst Corporation, Stockton <br /> Mr. William Aravanis, AMEC Environment and Infrastructure, Fresno <br />