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S ECOR <br /> Ms. Lori Duncan <br /> San Joaquin County EHD <br /> May 24, 2005 <br /> Page 4of4 <br /> Natural attenuation parameters will be analyzed in samples collected from all groundwater <br /> monitoring wells as part of the quarterly groundwater sampling event(s). Refer to Table 3 <br /> below for parameters and testing methods. <br /> Table 3: Anal ical Re uirements for Secondary Natural Attenuation Parameters <br /> Anallyte Method <br /> pH EPA Method 150.2 or Field instrument <br /> Dissolved oxygen (DO) EPA Method 360.1 or Down-hole field instrument <br /> Redox Potential (ORP) Field instrument <br /> Ferrous iron Field HACH Kit <br /> The following analysis will be added during the first groundwater monitoring event and <br /> then annually thereafter for seven of the 12 wells: <br /> Sulfate (SO4) EPA Method 300 <br /> Nitrate (NO3) EPA Method 300 <br /> Data from Table 3 analyses will be used to assess the effects of the SVEIAS system on <br /> natural attenuation of groundwater contamination. Data will be compared to previous <br /> available data and will be used to estimate the duration of system operation. Monitoring <br /> of natural attenuation parameters in wells will likely be modified as a better understanding <br /> of plume degradation and site conditions is established. <br /> If you have any questions or comments, please feel free to contact me directly at (925) <br /> 299-9300, extension 222. <br /> Sincerely, <br /> SECOR International Incorporated <br /> pe,- S4-'J <br /> Mario Sternad, PE <br /> Senior Engineer <br /> Figure 1 - Geocon Map, Petroleum Hydrocarbons in Groundwater May 2004 <br /> CC Saiyed Ali, Associate Engineering Geologist, Caltrans <br /> IACALTRAN&Stockton-Shop 101GW MonitoringlLetter to SJ County_Final.doc May 24,2005 <br /> Project No.9407.43148.00 SECOR International Incorporated <br />