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Geological Tecluucslru Page 4 Groundwater Monitoring Report Project No 662 2 August 21,2003 ' • Deep screened well MW-104 contained 62 u /I MTBE This is the fourth ourth consecutive event in which this well has tested positive for MTBE • Figure 4 MTBE vs Groundwater Elevation -- MW-3 illustrates a fairly direct relationship between the concentration of MTBE in groundwater and the elevation of ' groundwater in well MW-3 a Neither BTEX nor TPH-G was present in any of the groundwater samples above the laboratory reporting limits ' • Oxidation-Reduction Potential measurements (Table 3) show that the values for all four wells are positive, suggesting that there is a limited amount of biodegradation of the contaminant plume occurring This is to be expected, since the primary contaminant is ' MTBE, which is resistant to biodegradation GTI makes the following conclusions ' 6 The lateral extent of the groundwater contamination plume is only defined upgradient to the northwest by MW-2 ' + The vertical extent has not been defined since well MW-104 continues to exhibit low concentrations of MTBE However, it is believed to be near the bottom of the contaminant plume GTI makes the following recommendations • Perforin plume definition and evaluate the mass of contaminants present by installing ' additional monitoring wells GTI has submitted to the SJC PHS/EHD a "Soil & Groundwater Investigation Work Plan" dated October S, 2001 The work plan was approved with conditions in the SJC PHS/EHD's October 26, 2001 correspondence ' The first phase of the work, advancing a continuous core boring to determine site lithology, was completed on May 30, 2002 A monitoring well (MW-104) was placed ' in this boring with a five foot screened interval starting at 24 feet below the water table Additional wells will be installed pending concurrence from the SJC PHS/EHD ' 3.0 LIMITATIONS ' This report was prepared in accordance with the generally accepted standard of care and practice in effect at the time Services were rendered It should be recognized that definition and evaluation of environmental conditions is an inexact science and that the state or practice of environmental geology/hydrology is changing and evolving and that standards existing at the present time may change as knowledge increases and the state of the practice continues to improve Further, that differing subsurface soil characteristics can be ' experienced within a small distance and therefore cannot be known in an absolute sense All conclusions and recommendations are based on the available data and intormation. 1 1