ARCHIVED REPORTS_XR0011915 - Laserfiche WebLink

Home Browse Search

4.0 RESULTS 4.1 Groundwater Gradient and Flow Direction Depth-to-groundwater measurements and calculated groundwater elevations are presented in Table 1 Results from previous monitoring events are included for comparison The static water level appears to have undegone a non-uniform nse since October 7 The static water level in GT-1 through GT-3 has been 1 75 feet, whereas the rise in GT-6 has been only 167 gfect and the rise in GT-5 has been only 152 feet This differential has caused a complete reversal in the mapped groundwater gradient A mound in the water table is now present alon the southern boundary of the Gillies property, where previously a trough had been mapped The water table slopes northward and southward from this linear mound toward GT-5 and GT-9 (Figure 3) Possible reasons for this reversal are discussed in section 5 0 4.2 Groundwater Contamination The laboratory results are summarized in Table 2 and the laboratory report is contained in Appendix B Groundwater samples obtained in December are considerably less contaminated than those collected in October No gasoline-range hydrocarbons (TPH-g) or volatile compounds (BTEX) were detected in any of the wells, and diesel-range hydrocarbons (TPH-d) decreased in • both GT-6 and GT-9 The TPH-d concentration increased in GT-5 Diesel was also detected in GT- 2, which had not been sampled since July 1995 because the static water level was more than 10 feet above the screened interval Apparently, rapidly purging the well with the Grundfos pump was successful in drawing down the water level sufficiently to obtain a reasonably representative sample No contaminants were detected in either GT-1 or GT-3, but judging from the map of groundwater contamination in October, both wells would probably yield contaminated water if representative samples could be obtained 5.0 CONCLUSIONS AND RECOMMENDATIONS Contrary to typical observations at most sites, the degree of groundwater contarnination declined during the fourth quarter while the static water level rose Normally, seasonal rises in the groundwater table are accompanied by an increase in the degree of contamination as water comes into contact with residual contamination trapped in the vadose zone and/or capillary fringe The decrease in concentrations is more likely due to dilution than to natural degredation of the hydrocarbons, but the reasons may become apparent after additional monitoring data are obtained in the future With fewer than five samples from most wells, the contamination record is relatively short and trends are not yet apparent We therefore recommend continued groundwater monitoring in 1997 so that any patterns or trends may be identified It is our understanding from Ms Carmen Barbot, however, that additional work remains to be completed along the Gillies-Barbot property line before she will grant permission for Upgradient to enter her property for further monitoring 2