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sow, %..� LIGHT, AIR & SPACE CONSTRUCTION ENVIRONMENTAL SERVICES COMPANY State Contractor's License Number 445403 State EPA R.E.A.Number 04072 Office 408-979-0661 10.0 Groundwater Elevation Contour and Dissolved Contaminant Maps The monitoring well groundwater elevation contours and dissolved contaminant data are presented on Figures 4, 5, 6 and 7. Groundwater flow is mapped as westerly away from the existing water well and former UST locations. 11.0 Remedial Cleanup Method The underground storage tank sources of the petroleum fuel were removed in 2004. Soil excavation of the former underground storage tank pits removed the affected soil in 2006; no groundwater was pumped from the excavations. Soil removed from the excavations was placed on a lined aeration pad and allowed to aerate. SJC/EHD directed the installation of three groundwater wells and wells sampling following a review of the soil excavation data. A groundwater extraction and treatment was not used on this site. On the basis of the chemical data attached, the excavation removed the contaminated residual soil and only one detection of TPHG in Well MW-1 in December 2008. The March 2009 well sampling requested by SJCIEHD revealed no TPHG and only one detection of MTBE in well MW-3 that was below the current MCL. Also the on-site drinking water well was tested in December 2008 and no contaminants were detected in the drinking water well. 12.0 Background Attainable with Cleanup Methods The soil analysis data indicate that only very low TPHD remain in aerated soil. Groundwater sampling shows that TPHG, TPHD, BTEX and ETBE, DIPE, TAME, TBA, 1-2-DCA, EDB, Ethanol and Methanol contaminants are not detected in the last sampling. MTBE has been detected below the current MCL in downgradient well MW-3. 13.0 Contaminant Mass Remaining in Soil and Groundwater The contaminant mass in soil is estimated from soil excavated and on the basis of the extremity soil sampling in 2006. Contaminant mass in excavated soil placed on the aeration pad has declined from about 24,000 Mg/kg to 72 Mg/kg TPHD. The laboratory reported that the 72 Mg/kg value appeared to not resemble the typical pattern for Diesel. TPHG had declined from 690 Mg/kg to none detected; Xylenes declined from a high of 1,800 Mg/kg to none detected; and BTE, MTBE and fuel oxygenates were not detected in any aeration pad soil samples (see Tables 4, 5 and 6). A rough estimate of the quantity of TPHD removed in soil by excavation indicates that about 344 gallons of TPHD was removed. A rough estimate of TPHG indicates that about 1.4 gallons TPHG was removed in soil. The residual of TPHD remaining in the soil stockpile on the aeration pad is estimated at about 2 gallons. Pa e8of16 MAIN OFFICE - 1707 LITTLE ORCHARD STREET,Surm A -SAN JOSE-CA-95125 WAILING ADDRESS a P.O.Box 36303•SAN JOSE•CA•95158-6303•4081979-0661 •4081979-0621 FAX-LASCONST@e AOL.COM E-MAIL GENERAL AND ENGINEERING CONTRACTOR-HAZARDOUS SUBSTANCE REMOVAL CONTRACTOR-SITE ENVIRONMENTAL ASSESSMENTS WETLAND AND RIPARIAN HABITAT—ASSESSMENT—DESIGN—RESTORATION—CONSTRUCTION—MITIGATION MONITORING