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Stockton Promenade—N Edison3Treet USTs& Utility Corridors • Page 16 Underground Storage Tank Removal Report June 8,2009 WKA No.7345.09 Portions of the former N. Edison Street UST area were later over-excavated for the placement of Iunderground utilities and a roadway as part of the Stockton Promenade construction project. Cadmium and zinc impacted soil from former Tank#2 were ultimately over-excavated and transported for off-site disposal to a licensed landfill facility. Documentation of soil assessment, excavation, and removal activities will be reported to the RWQCB as part of the Stockton Promenade construction project. 1 Water Analytical Results IOne tank rinsate sample from Tank No. 1 and three grab groundwater samples from surrounding I the UST area were collected during this assessment. Analytical results for the rinsate sample from Tank#1 identified elevated petroleum hydrocarbons primarily in the fuel and motor oil range. The water was ultimately removed and soil sample Tl-C was collected from a depth of 6 ' feet bgs in the Tank#1 excavation and did not reflect saturated conditions. ' Grab groundwater analytical results for the direct-push borings identified elevated petroleum hydrocarbon constituents in each of the three sampling locations. TPHg was detected in grab groundwater sample EB-3 (6,200 µg/L) from beneath the former UST area and in EB-1 (23,000 µg/L), approximately 17 feet southeast of the former UST area. The highest TPHd and TPHmo concentrations were detected in EB-2, located approximately 15 feet northeast and presumably upgradient of the former UST area. Benzene was detected in direct-push boring EB-1-GW (2.9 µg/L) and EB-3-GW (9.3 µg/L) in excess of water quality standards (RWQCB, 1998). The distribution of petroleum hydrocarbon impacted groundwater was identified beneath, to the southeast, and to the northeast of the former UST area. Because the former UST area is in close proximity to the seawall for the Stockton Channel, the relationship between shallow groundwater and surface water in the Channel are currently unknown. Ongoing groundwater monitoring conducted by Stantec shows in irregularity in shallow groundwater flow directions along the ' southern side of the Stockton Channel, which suggests that the Channel may represent a hydrogeologic boundary or a source of recharge to shallow groundwater beneath the site. General Conclusions Based on the results of UST removal activities and the exploratory assessment findings, WKA concludes that the presence and overall distribution of adversely impacted soil and groundwater in the former N. Edison Street UST area is the result of multiple long term operational activities that have since been discontinued and/or removed. These former historical land use activities ' include the following: �`�