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Geological reCknfrs&C. Page 6 <br /> Groundwater Monitoring Report <br /> Project No. 1030.2 <br /> November 18,2004 <br /> 0 The domestic well was non-detect above laboratory reporting limits for all analyzed <br /> constituents and has been non-detect since testing began on January 28, 1997. <br /> 2.4 Groundwater Parameters <br /> Field measurements from the October 14, 2004 sampling event indicate the following: <br /> 0 The average pH recorded during this event was 7.94. This pH is conducive to <br /> maintaining aerobic biodegradation activity. <br /> • The average EC recorded during this event was 2339 (Dmhos/cm. <br /> • The average temperature recorded during this event was 70.6°F. This temperature is <br /> conducive to maintaining aerobic biodegradation activity. <br /> • Oxidation-reduction potential (ORP) was negative in the six monitoring wells. <br /> • Measured dissolved oxygen (DO) levels in the water table wells ranged from 0.22 ppm in <br /> MW4 (edge of plume) to 1.20 ppm in MW-3 (background conditions). Most of the <br /> water table and deep wells had DO measurements <1 ppm. DO levels below 1 ppm are <br /> not conducive to aerobic degradation. <br /> A summary of groundwater parameters is included as Table 4. <br /> 3.0 CONCLUSIONS AND RECOMMENDATIONS <br /> Petroleum Hydrocarbons <br /> • MW-1,MW-4 and MW-101 show the presence of BTEX and/or TPH-G constituents. <br /> • MW-2, MW-3, MW-5 and the domestic well were non-detect above laboratory reporting <br /> ' limits for all analyzed constituents. <br /> Site Characteristics <br /> • The plume is defined laterally by MW-2 to the southeast, MW-3 to the southwest and <br /> MW-5 to the north (all screened from 5 to 20-feet bgs). <br /> ' • MW-4 appears to be located near the leading edge of the plume. <br /> • Groundwater slope is gradual, averaging 0.0037 ft/ft, and likely slows down the migration <br /> of the plume. <br /> • The plume is defined vertically by MW-101 (screened from 29.5 to 34.5-feet bgs). MW- <br /> 101 contained trace levels of BTEX for the first time. <br /> • The clay layer at 19 feet bgs provides a significant barrier to vertical plume migration. <br /> • Vertical groundwater gradient is historically positive (upward) making downward vertical <br /> migration unlikely. - <br /> • The following factors may have a positive contribution to protection of the deeper <br /> aquifers and retardation of contaminant migration at this site: <br /> o Gradual groundwater gradient slope <br /> o Dominant upward vertical groundwater gradient <br /> 1 <br />