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(YVATv %MW A S S O C I A T E S I N C �.w air sparging is one approach to enhancing available oxygen. Another is oxygen releasing compound (ORCO). ATC would place ORCO in the existing groundwater monitoring wells and inject ORCO slurry into a series of approximately 20 to 25 borings located on 10-foot centers within the impacted groundwater plume. The ORCO increases dissolved oxygen into impacted groundwater via the wells and borings and then spreads throughout the ground water underlying the site vicinity. The increased oxygen enhances natural biodegradation of petroleum hydrocarbons. ORC® does not negatively affect groundwater quality and therefore, based on ATC's experience, is acceptable to the regulatory community. RECOMMENDATIONS Based on the results of therevious site characterization activities the most recent p groundwater monitoring data, and in accordance with the request of the SJCEHD,ATC proposes the following corrective actions: Based on information presented in technical reports prepared by Parker and H20GEOL, the lateral extent of soil contamination at the site appears to be generally defined. The lateral extent of shallow groundwater contamination appears to be defined except to the north in the predominantly downgradient direction. ATC recommends using cone penetration test (CPT) methodology in conjunction with soil and groundwater sampling to evaluate the vertical extent of petroleum impacted soil and groundwater, and to evaluate shallow groundwater quality north of the existing building at the site. ATC proposes advancing three CPT borings at the locations shown on Figure 13. The CPT borings will be advanced by a State-licensed (C57) drilling company. A cone mounted with sensors at the tip will be advanced into the soil using direct push rods. The sensors will test the response of the soil to the force of the penetrating cone and this will allow the subsurface stratigraphy to be characterized. One CPT boring will be advanced in the southern portion of the site to a depth of approximately 75 feet bgs to obtain a continuous description of the subsurface lithology. This location is upgradient of the USTs and fuel dispenser island, and is likely outside of the documented groundwater plume. Consequently, the potential to introduce petroleum hydrocarbons into the deeper zones should be reduced at this location with respect to the proposed CPT location in the vicinity of the USTs. The data obtained from the southern CPT location two will be used to select sampling depths at the remaining two proposed CPT locations. Depth discrete soil and groundwater samples will be collected from the CPT location adjacent to the USTs and north of the existing building. After the samples have been collected,the CPT borings will be grouted to the surface. ti The soil and groundwater samples from the CPT borings will be immediately placed in a cooler chilled with ice and delivered under chain-of-custody documentation to a State-certified analytical laboratory. Soil and �+ groundwater samples will be analyzed for total petroleum hydrocarbons quantified as gasoline (TPHg) by EPA Method 8015B; and benzene, toluene, ethyl benzene, total xylenes (BTEX), MTBE, tertiary amyl methyl ether (TAME), 1,2-dibromoethane (EDB), 1,2-dichloroethane (1,2-DCA), di-isopropyl ether (DIPE), v ethyl tertiary butyl ether(ETBE), and tertiary butyl alcohol(TBA)by EPA Method 8260B. Upon completion of the field activities, a report will be prepared describing the field activities and laboratory analytical results and will include an assessment of the extent of the petroleum hydrocarbon release along with recommendations for additional investigation and/or remediation activities if warranted. The report will be prepared in accordance with California Regional Water Quality Control Board Former Cheaper#37 January 29 2004 ATC Project Number 5425847.0037 Page 9 v