ARCHIVED REPORTS XR0008941 - Laserfiche WebLink

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Mr Jeffrey Wong C A M B R I A February 23, 2006 block agitation and pump evacuation Blaine's groundwater monitoring and well development report, presenting the laboratory report and supporting field notes, is presented as Attachment C Groundwater Flow Directton Cambria evaluated water-level measurement data from December 29, 2005 and prepared a groundwater elevation contour map (Figure 3) Regional groundwater flow direction is southeasterly with an approximate hydraulic gradient of 0 004 Groundwater flow beneath the site is influenced by pumping from well MW-4 The groundwater elevation in MW-3 is anomalously high and was not contoured Bioparameter Analyses As San Joaquin County Environmental Health Department (SJCEHD) requested, samples from wells MW-4, MW-7, and MW-8 were analyzed for dissolved oxygen (DO), oxidation-reduction potential (ORP), nitrate, sulfate, and methane These wells were chosen because they represent an up-gradient well (MW-8), a source area well (MW-4), and a down-gradient well (MW-7) Cambria presents the results in Table 4 Both nitrate and sulfate concentrations are higher in up-gradient water than in the source area well This indicates that biodegradation may be occurring by denitrification and sulfate reduction processes Methane is not detected in up- or down-gradient wells, but is present in the source . area well (although less than 0 5 ppm), suggesting that methanogenic conditions may also exist in the subsurface With the exception of the third quarter 2005 data, DO concentrations remain consistent throughout the plume, which may indicate that oxygen is available but not being utilized by microorganisms beneath the site The DO and ORP results are inconclusive The declining trend in MTBE concentrations provides the primary line of evidence that this plume is shrinking The nitrate, sulfate, and methane data discussed above provide a Secondary line of evidence supporting the occurrence of biodegradation Since the results from the DO and ORP analyses do not provide conclusive supporting information for bioremediation, no further analyses of these parameters is warranted Further, since the secondary line of evidence provided by the nitrate, sulfate, and methane results has been confirmed for one hydrologic cycle as proposed, Shell will discontinue future analyses for these constituents beginning with the first quarter 2006 sampling event GWE Shell has operated the temporary GWE system since its start-up on September 29, 2005 Initially wells MW-2 and MW-4 were used as extraction wells Because of declining concentrations and because it produces significantly less water than MW4, the pump in well MW-2 was shut off on December 13, 2005 Table 5 summarizes the field data and system aoperation and calculates mass removal Based on the field data, the GWE system averaged a flow rate of 0 54 gallons per minute from September 29, 2005 through December 31, 2005 Through 8