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a • SITE CONCEPTUAL MODEL Shell-branded Service Station 6131 Pacific Avenue, Stockton, California Site Address: 6131 Pacific Avenue Incident Number: 98996189 San Joaquin County Environmental Health City: Stockton, California Regulator: Department Item Evaluation Criteria Comments/Discussion 1 H drocarbon Source 1.1 Identify/Describe Release Inventory records indicate a product loss from the regular unleaded Source and Volume(if known) tank(Aegis,June 1990). 1.2 Discuss Steps Taken to Stop The tank referenced above was emptied on February 29, 1990. Release Three USTs were removed on June 7, 1990. New USTs were installed in a different location. 2 Site Characterization 2.1 Current Site Use/Status The site is an operating Shell-branded Station 2.2 Soil Definition Status The vertical extent of TPHg (above 66.5 fog),benzene(above 60.5 fbg),and MTBE(above 61.5 fbg)in soil is defined by borings SB_4 SB- 5,and SB-6. The lateral extent of TPHg abgveroundw ter is defined N,( onsite in all dir7tions by rlls/borings MW-1, SB=1, M4, MVf_3, 6�, o o 9 5 B-7,Geo3, B-2,and MW-2. The lateral extent of benzene above groundwater is defined in all directions surrounding the site by wells/borings MW-1,SB-1,MW-4, MW-3,B-6,MW-5,Geo-3,and MW- 2. The lateral extent of MTBE above groundwater is defined to the northeast of the former UST complex by SB-3,to the east by SB-4, SB- 1,and MW-4,to the southeast by MW-6,to the south by SB-5,and to the west by MW-5. Note that MTBE analysis was not required when borings B-1 through B-14 and Geo-1 through Geo-3 and wells MWA through MW-3 were drilled. The constituent detections in soil at depths below groundwater and in the capillary fringe in some of these wells and borings are most likely caused by impacted groundwater,as the constituents were not found in shallow soil. Soil results are included on Table 1�nd a site map is included as Figure 2. 2.3 Separate-Phase Hydrocarbon Separate-phase hydrocarbons were observed in well MW-3 during Definition Status 1991 through 1993. None have been observed in a monitoring well since April 1993. 2.4 Groundwater Definition Status Groundwater monitoring results suggest the extentXPHg is defined (BTEX) to below reporting limits�o the north by wells MW-1✓1 and MVy'2 and to the west by well MW-5(with the exception of 4 events since 1998). Benzene is defined below 1 ppb to the north by wells MW-1 and MW-2 and to the south by MW-11. Note that MW-5,to the west, is also frequently ND. Groundwater results are included in Attachment 1. C (./ L 0854 Page I of 3 Date Modified: 1013/2003