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• CAMBRIA <br /> CONCLUSIONS <br /> Petroleum hydrocarbons were not detected in soil and groundwater samples from any of the <br /> borings or Shell well MW-5 These results indicate that petroleum hydrocarbons previously <br /> detected in shallow soil have not migrated vertically or horizontally and have not impacted <br /> groundwater beneath the northern dispenser area <br /> MTBE was not detected in soil or groundwater samples from borings SB-1, SB-3, and SB-4 <br /> These results indicate that MTBE in soil and groundwater has been delineated to the east, <br /> south, and southwest of the northernmost dispenser islands <br /> Soil samples from SB-2 (MW-5) indicate that MTBE has been defined vertically and does not <br /> extend to, or below 45 5 fbg Since groundwater occurs approximately 58 to 59 fbg, these <br /> data suggest MTBE has not impacted groundwater beneath this site However, the <br /> groundwater samples collected from MW-5 (SB-2) indicated MTBE is present in groundwater <br /> at low levels <br /> • Based on the information Cambria collected regarding the upgradient former Chevron site, it <br /> is possible MTBE from this site has impacted groundwater beneath the subject site <br /> Analytical data from Chevron's well MW-5 suggests MTBE has migrated offsite and in the <br /> direction of the subject site Although Chevron's downgradient well MW-8 has not contained <br /> detectable levels of MTBE, it may be that this well is located eastward of the plume axis <br /> The low level of MTBE detected in Shell's well MW-5 may be the downgradient end of <br /> Chevron's MTBE plume <br /> RECOMMENDATIONS <br /> Cambria recommends monitoring and sampling well MW-5 quarterly The groundwater <br /> sample will be analyzed for TPHg, BTEX, and MTBE Because no fuel oxygenates (other <br /> than MTBE) were detected, analysis for fuel oxygenates will be discontinued If MTBE is <br /> reported in the groundwater sample by EPA Method 8020, it will be confirmed by EPA <br /> Method 8260 <br /> Cambria also recommends the installation of three additional groundwater monitoring wells at <br /> the subject site Due to the proximity of municipal well No 12 to the subject site, we feel it <br /> is prudent to place two additional monitoring wells between the site's UST system and the <br /> municipal well The recommended location of these wells is shown on Figure 3 In addition, <br /> we recommend installing a monitoring well northeast of Shell's MW-5, and approximately <br /> 1346 7 <br />