ARCHIVED REPORTS XR0001353 - Laserfiche WebLink

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C A M B R I A HYDROCARBON DISTRIBUTION IN GROUNDWATER TPHg was detected in 12 of 14 groundwater samples collected from borings CPT-] through CPT-4 at concentrations ranging from 66 3 parts per billion (ppb) to 109,000 ppb The highest TPHg concentration was detected in CPT-1 at 60 fbg Benzene was detected in all 14 of the groundwater samples collected from CPT-1 through CPT-4 at concentrations ranging from 0 744 to 31,300 ppb The highest benzene concentration was detected in CPT-2 at 60 fbg MTBE (by EPA Method 8260B) was detected only in one of 14 groundwater samples from borings CPT-1 through CPT-4 at a concentration of 16 ppb, boring CPT-2 at 60 fbg Two of 14 groundwater samples from these borings contained TBA at concentrations of 91 ppb and 350 ppb Three of 14 groundwater samples from these borings contained DIPE at concentrations ranging from 2 2 ppb to 3 2 ppb Two of 14 groundwater samples collected from the borings contained 1,2-DCA at concentrations of 2 1 ppb and 3 2 ppb The groundwater chemical analytical data is presented in Table 3 and on Figure 3 Laboratory analytical data are presented in Appendix B CONCLUSIONS • Groundwater analytical data from onsite borings CPT-1 and CPT-2 suggest petroleum hydrocarbons are present in groundwater to 92 fbg Groundwater analytical data from offsrte borings CPT-3 and CPT-4 suggest petroleum hydrocarbons are present in groundwater to 92 fbg in CPT-3 and to 75 fbg in CPT-4 Groundwater samples were not collected below 75 feet in CPT-4 due to high density soils encountered The predominant gasoline constituents detected during this investigation were TPHg and BTEX This is consistent with quarterly groundwater monitoring data from existing groundwater monitoring wells at the site, which also suggests the primary concern at this site is TPHg and BTEX Some fuel oxygenates and lead scavengers were detected during this investigation, but at low levels These findings suggest the release at this site may be rather old and likely occurred prior to the introduction of fuel oxygenates into gasoline An older release may also explain why petroleum hydrocarbons are found at depth beneath this site Historically groundwater occurred deeper at this site than it does today (according the S.ICPHS-EHD April 17, 2000 letter regarding this site) If the release occurred during the period of low groundwater, then vadose soil down to 80 fbg could have been impacted by hydrocarbons released from the site As groundwater level rose, these previously unsaturated • soils became saturated and subsequently impacted groundwater that came into contact with the soil 3399 5