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Mr. Joe Aldridge - 2 - 22 September 2010 <br /> NuStar Terminals Stockton Faci <br /> Table 6 consists of a partial list of monitored natural attenuation (MNA) parameters observed <br /> in B/C zone wells during May 2010 and includes monitoring results for three additional wells <br /> that previously had not been monitored for MNA parameters. Historical MNA results are <br /> tabulated in Appendix G. Central Valley Water Board staff requested that NuStar initiate MNA <br /> monitoring to support recommendations presented in its 5 January 2006 Cleanup Plan <br /> (Cleanup Plan). MNA monitoring commenced in April 2007 and initially was scheduled to last <br /> for about one year. However, NuStar extended the monitoring program to include the <br /> collection of geochemical parameters from newly installed wells. <br /> The Second QMR does not include an interpretation of the C-zone MNA data gathered during <br /> the second quarter. Monitored geochemical parameters were limited to dissolved oxygen <br /> (DO), oxygen reduction potential (ORP), sulfate (SO4), alkalinity, and methane. The monitoring <br /> results appeared to typify the expected distribution of geochemical parameters in a petroleum <br /> hydrocarbon plume. The depleted DO (except at ACA-4C) and increased concentrations of <br /> SO4, alkalinity, and methane at wells with the highest TPH concentrations indicate that <br /> biodegradation processes, including aerobic respiration, sulfate reduction, and <br /> methanogenesis, have been active in the plume interior. This trend is not consistent with the <br /> observed ORP data, however, which is expected to be lowest at the center of the plume. The <br /> monitoring data show that the ORP data is actually lowest at plume fringe. <br /> While the geochemical data indicate that MNA is occurring at the Site, additional lines of <br /> evidence, including evaluation of contaminant mass loss and the presence of BTEX <br /> breakdown products, are necessary to demonstrate that there is sufficient assimilative <br /> capacity to degrade the remaining pollutants. Central Valley Water Board staff did not concur <br /> that NuStar's previous projections, presented in the 29 February 2008 Monitored Natural <br /> Attenuation Evaluation Report, indicated that water quality objectives would be achieved in a <br /> reasonable time and requested additional vertical delineation, which is underway. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4811 or <br /> beta ylor wate rboa rd s.ca.gov. <br /> BRIAN TAYLOR. P.G. <br /> Engineering Geologist <br /> cc: Ms. Adrienne Ellsaesser, San Joaquin County Environmental Health Dept., Stockton <br /> Ms. Jeffery Wingfield, Port of Stockton, Stockton <br /> Mr. Paul Supple, Atlantic Richfield Company, San Ramon, CA <br /> Ms. Amanda Spencer, Ash Creek Associates, Inc., Portland, OR <br /> Mr. Jeremy Hughes, LFR, Roseville <br /> Mr. Rusty Benkosky, Stantec Consulting Corporation, Rancho Cordova <br />