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. C700kg&A TeChAks lnc. Page 6 Groundwater Monitoring Report Project No. 1030.2 October 22,2004 2.4 Groundwater Parameters Field measurements from the July 19,2004 sampling event indicate the following: ' • The average pH recorded during this event was 7.25. This pH is conducive to maintaining aerobic biodegradation activity. ' • The average E.C. recorded during this event was 2307 (Dmhoslcm. • The average temperature recorded during this event was 67.6°F. This temperature is conducive to'maintaining aerobic biodegradation activity. ' • Oxidation-reduction potential (ORP) was positive in five of the six monitoring wells and was negative in MW-1 (location of the former USTs). Positive ORP readings suggest the site conditions may be conducive to maintaining aerobic biodegradation activity. ' • Measured dissolved oxygen (DO) levels in the water table wells ranged from 0.33 ppm in MW4 (edge of plume) to 0.65 ppm in MW-3 (background conditions). All water table wells and the deep well had DO measurements <1 ppm. DO levels below 1 ppm are not ' conducive to aerobic degradation A summary of groundwater parameters is included as Table 4. 3.0 CONCLUSIONS AND RECOMMENDATIONS Petroleum Hydrocarbons • MW-1 has low levels of BTEX and TPH-G constituents and MW-4 has trace levels of ' some BTEX constituents. The concentrations do not appear to be decreasing in concentration. • MW-2, MW-3, MW--5, MW-101 and the domestic well were no above laboratory reporting limits for all analyzed constituents. Site Characteristics • The plume is defined laterally by MW-2 to the southeast, MW-3 to the southwest and MW-5 to the north (all screened from 5 to 20-feet bgs) • MW-4 appears to be located near the leading edge of the plume • Groundwater slope is gradual, averaging 0.0038 ft/ft, and likely slows down the migration tof the plume. ed from 29.5 to 34.5-feet bgs) The plume is defined vertically by MW-101 (screen • • The clay layer at 19 feet bgs provides a significant barrier to vertical plume migration. • vertical groundwater gradient is historically positive (upward) making downward vertical 1 migration unlikely. • Measurements of dissolved oxygen in the shallow monitoring wells range between 0.33 and 0.65 ppm, suggesting conditions at the site may not favor biodegradation (Table 4). ' • Measurements from MW-2, MW-3, MW4, MW-5 and MW-101 indicate a positive oxidation-reduction potential (Table 4).