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�r 16r �( <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. Boring B-4 water sample taken immediately under the tank pit <br /> showed 690 ug/l (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/1 at the upgradient 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 in 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 drilled 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/l in B-2 in a downgradient location. No BTEX or MTBE or related oxygenates were <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. <br /> On the basis of this data collected for this study, limited leakage from the former underground <br /> tank had occurred that is attributed 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 />