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Geological TecluuesInc Page 6 Groundwater Momtonng Report Project No 425 2 November 12,2001 3 Vertical groundwater gradients have been found to be flowing upward during winter and early spring and downward during late spring and summer This may be due to the ' annual cycle of groundwater pumping needs of the community The negative shallow and positive deep gradients recorded for the September 2001 event are consistent with = the September 1999 & 2000 events - 4 The dominance of upward vertical flow of groundwater may be the primary reason the contaminants has not impacted the drinking water aquifer During heavy pumping, the ' contaminants would be moved into deeper portions of the aquifer and a slower rate then they would be moved back to a shallower depth in low pumping periods of the year 5 The shallow water table groundwater plume is laterally defined except to the west The data indicate that the contamination does attenuate toward the west 6 Petroleum hydrocarbon concentrations in the groundwater at the site fluctuate with each monitoring event The residual contamination in soil up gradient of MW-2 remains a significant source of impact to the groundwater plume 7 The deeper groundwater plume is defined vertically since MW-102 and MW-202 remain non-detect for contaminants S The three domestic wells sampled for the event remain non-detect Recommendations MThe following recommendations are made 1 The impacted soils in the vicinity of the former UST field were excavated during the week of July 23, 2001 The current quarterly monitoring schedule should be maintained to determine contaminant trends 2 The 12 monitoring wells and 3 domestic wells should be sampled for natural attenuation ' parameters during future monitoring events so it may be determined if remediation by natural attenuation is occurring This testing should be performed six to 9 months after the excavation is complete ' 3 Prior to backfilling the excavation, bra-venting piping was installed and the gravel pored in around it This bio-venting system should be installed this winter to continue the contaminant removal in the vicinity of MW-2 ' 4.0 LIMITATIONS ' This report was prepared in accordance with the accepted standards and practices of the field of environmental geology, groundwater hydrology and good business practices It should be recognized that definition and evaluation of environmental conditions is a ' difficult and inexact science Judgments leading to conclusions and recommendations are generally made with an incomplete knowledge of the site-specific conditions present The tasks proposed and completed during this project were reviewed and approved by the local regulatory agency for compliance with the law No warranty, expressed or implied, is made