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1 hydrocarbon plume In February 2003, Thnfty submitted a workplan for additional site assessment activities which was approved by the SJCDEH on May 30, 2003 From November 18 through 21, 2003, Advanced GeoEnvironmental, Inc (AGE) completed site ' assessment activities that consisted of drilling three locations using cone penetrometer testing (CPT) Selected figures from the AGE report including cross sections illustrating the distribution of TPHg and benzene in groundwater are provided in Appendix D The results of the CPT ' testing were summarized in the Cone Penetrometer Testing/Sate Assessment Report prepared by AGE dated March 31, 2004 and are briefly discussed below ' Soil collected during the CPT investigation from depths of near surface to approximately 65 feet bgs, 75 feet to 90 feet bgs, between 100 feet and 105 feet bgs to 110 feet bgs and from 115 feet bgs to total depth consisted dominantly of clay, silt, clayey silt, and silty clay ' Coarse-grained soil consisting of silty sand and fine- to medium-grained sand were identified at depths of between 65 and 75 feet bgs and between 90 to 100 feet bgs ' A total of eleven grab groundwater samples and thirty nine soil samples were collected from the soil borings and submitted for laboratory analysis TPHg concentrations were detected in twelve of the thirty-nine soil samples analyzed The highest TPHg concentrations were ' reported in samples collected from CPT-4, ranging from 408 mg/Kg in sample CPT-4-40 to 9,110 mg/Kg in sample CPT-4-75 TPHg was detected in only one of the twelve samples collected from CPT-2, at a concentration of 88 mg/Kg (CPT-2-75) The highest benzene concentrations were reported in samples collected from CPT-4 at 25 3 mg/Kg benzene (CPT- 4-75) MTBE was detected in one soil sample from CPT-3 and two samples from CPT-4 at ' concentrations of 0 0018 mg/Kg (CPT-3-50), 0 072 mg/Kg (CPT-4-85), and 0 068 mg/Kg (CPT-4-90) TPHg, benzene, and MTBE concentrations appear to decrease laterally and may not extend much beyond CPT-2 towards the west and CPT-3 towards the southeast Based ' on the results, AGE concluded that the vertical extent of TPHg, benzene, and MTBE in soil do not appear to exceed 100 feet bgs, which indicates that the fine-grained interval at between 75 and 90 feet bgs does retard the vertical migration of contaminants, however, low ' concentrations of the remaining BTEX compounds toluene, ethylbenzene and/or xylenes were present to total depth in borings CPT-3 (120 ft) and CPT-4 (112 ft ) ' TPHg was detected in all grab groundwater samples except CPT-2-94-98, at concentrations ranging between 104 µg/L. and 15,200 µg/L Benzene was detected at a maximum concentration of 156 Rg/I benzene (CPT-4-65-70) MTBE was detected only in one grab ' groundwater sample (CPT-3-65-69) at a concentration of 3 7 µg/L AGE concluded that the vertical extent of TPHg-impacted groundwater is not defined However, it does appear that the vertical extent of benzene and MTBE are defined Low concentrations (below California ' Department of Health Service's Maximum Contaminant Level) of the BTEX compounds ethylbenzene and/or xylenes were detected in groundwater samples collected at all sampling depths in borings CPT-3 and CPT-4 1 ' 4