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11 , <br /> 11 <br /> 0) <br /> • Discussion <br /> Soil chemical data from the vadose and capillary fringe shows that contaminants were not <br /> detected Groundwater chemical data show that relatively low levels of TPHD were detected in <br /> groundwater samples from each borehole with sample B-2 showing 33,000 micrograms per liter <br /> (ug/1) Boring B-2 is located in a downgradient position (about 70 feet) from the former <br /> underground storage tank pit Bonng B-4 water sample taken immediately under the tank pit <br /> showed 690 ug/I (see Figure 1) Boring B-3 located in an upgradient position showed similar <br /> results at 660 ug/1 BTEX, MTBE and related fuel oxygenates were not detected in any soil or <br /> groundwater sample <br /> The laboratory reported that the chromatographic pattern of the water samples did not match the <br /> Diesel standard This indicates that the TPHD in the samples is highly degraded and depleted in <br /> volatile content The detection of 660 ug/l at the upgradaent boring location B-3 may suggest that <br /> some contribution of wastewater organics since this also did not match the chromatographic <br /> pattern The B-4 water sample collected under the former tank pit is only slightly higher than the <br /> 580 ug/1 observed u1 1998 Relatively low levels of TPHD were detected during the tank <br /> removal and the most elevated dissolved TPHD occurs in a downgradient position form the <br /> former tank pit In our opinion, these data suggest a limited residual TPHD from the tank that is <br /> attributed to historic overspill A small dissolved plume of highly degraded TPHD has migrated <br /> a short distance from the former tank pit in a north-northwest direction <br /> Conclusions and Recommendations <br /> Four exploratory borings were dnlIed and sampled around the former underground tank pit at the <br /> Wastewater plant The tank source has been removed and tank removal data from 1998 showed <br /> low levels of TPHD in soil and groundwater samples The current backup diesel tank is a surface <br /> mounted facility <br /> Soil boring samples discussed herein showed that contaminants were not detected Groundwater <br /> samples showed very low levels of dissolved TPHD, with one relatively elevated occurrence of <br /> 33,000 ug/1 in B-2 in a downgradient location No BTEX or MTBE or related oxygenates were y <br /> revealed in any soil or groundwater sample It is our understanding that portions of this area are <br /> scheduled for future expansion of wastewater plant surface operations t <br /> On the basis of this data collected for fts study, limited leakage from the former underground <br /> tank had occurred that is attnbuted to historic overspill The small dissolved plume has migrated } <br /> a short distance downgradient of the former tank pit to the north-northwest This area lies within ' <br /> the Wastewater plant property and between treatment ponds for Municipal Wastewater use It is <br /> our opinion that given the plant use and past source removal, the remnants of this highly <br /> degraded plume should continue to degrade with time and future movement would be limited <br /> Further work is not recommended at this time <br /> Page 4 of 6 <br /> i� <br /> t <br />