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1 y <br /> CWkgl aI7edvaa Inc Page 8 <br /> Groundwater Momtonng Report <br /> Project No 723 2 <br /> October 29, 2004 <br /> ' display a decreasing trend The steep decline in the initial concentrations suggests that <br /> the contaminants detected in the well were uutially a drilling artifact <br /> ❑ Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) measurements (Table <br /> 4) show that all seventeen wells are screened in areas of the groundwater plume that are <br /> affected by the biodegradation reactions occurring within the plume The highly negative <br /> ' ORP values during the May 2004 event indicate that the wells are within the halo of <br /> reaction depleted water caused by biodegradation of the contaminants The low DO <br /> values of the wells also reflected this condition The increase in ORP values for the <br /> ' August event is probably a result of groundwater extraction tests conducted in July 2004 <br /> An influx of fresh water in the plume would alter the chemistry as reflected in the ORP <br /> values' change <br /> ' 3.0 CONCLUSIONS & RECOMMENDATIONS <br /> Conclusions <br /> ' 1 Groundwater flow trends northeast to east The southerly flow direction recorded on <br /> December 4, 2000, appears to be anomalous <br /> 2 High levels of BTEX and TPH-G are present in the groundwater of all sit on site shallow <br /> and intermediate monitoring wells (MW-1 through MW-6) <br /> 3 The main mass of contaminants has migrated to a depth of 45 to 70 ft bgs, indicating that <br /> the contaminants are mobile <br /> ' 4 Cross gradient well set MW-7/107/207 was free of contamination for the second <br /> consecutive event <br /> 5 Down gradient wells MW-8/108/208 contain low levels of TPH-G and BTEX <br /> ' 6 The groundwater contaminant plume is not defined laterally down gradient of MW-108 <br /> 7 Well set MW-9/109/209 defines the lateral extent of the plume in an up gradient <br /> direction <br /> ' 8 Wells MW-7/1071207 define the lateral extent of the plume in a cross gradient direction <br /> 9 The low levels of contaminants in MW-101 and lack of contaminants in well MW-201 <br /> suggests that these wells define the vertical limit of the plume beneath the site <br /> ' 10 The positive change in ORP values reflect the pumping test conducted in July 2004 This <br /> data suggests that the natural attenuation processes are conducive to augmentation by <br /> ' groundwater circulation <br /> Recommendations <br /> ' 1 Continue quarterly groundwater monitoring <br /> 2 The lateral extent of the groundwater plume is undefined down gradient of CMTTm well <br /> MW-8/1081108/308 A limited site investigation should take place to define the down <br /> ' gradient extent of the plume This should consist of direct push probe drilling methods <br /> such as CPTrm to collect discrete groundwater samples rather than installing additional <br /> monitoring wells <br /> 1 <br />