REMOVAL_2008 - Laserfiche WebLink

Home Browse Search

Stockton Promenade—N Edison3freet USTs& Utility Corridors • Page 14 Underground Storage Tank Removal Report June 8,2009 ' WKA No, 1141,01 7.0 CONCLUSIONS Four USTs were identified and removed from a narrow access corridor between the Stockton Channel and the WOTOA parking lot during construction of the Stockton Promenade. Observation of the four USTs upon their removal identified differences in the age and condition of each tank. Although the four tanks were aligned in the same general orientation, the differing ' constructions and corrosion conditions indicate that the tanks were likely installed at different times. Additional exploratory testing of this area also identified the presence of nearby underground petroleum piping that was disconnected and previously abandoned in-place. The presence of the petroleum piping was previously identified during assessment of the adjacent ' WOTOA parking lot(Stantec, 2008). The close spacing of the USTs and their orientation together suggests that the presence of the oldest tank was known with each successive tank installation. The 90-degree routing of the underground petroleum piping around the four USTs suggests that the presence of one or more ' of the tanks was known at that time when the underground piping was installed. The orientation of these features suggests that installation of one or more of the USTs predates the installation of the underground piping and that the presence of one or more of the four USTs was known at that time when the underground piping was installed. Although the sequence of UST and underground petroleum piping installation can be inferred, the prior operational and ownership relationship of these historical features is currently unknown. Soil Analytical Results—Petroleum Hydrocarbon Constituents ' Confirmation sampling identified the presence of petroleum hydrocarbon-impacted soil beneath the UST area. Soil analytical results identified elevated petroleum hydrocarbon constituents in soil extending laterally surrounding the UST area and at higher concentrations extending south beneath the abandoned petroleum piping. The lateral extent of petroleum hydrocarbon impacted soil related to the former N. Edison Street UST area was not delineated to the southwest due to the overlapping impact to soil beneath the abandoned underground petroleum piping. 1 Soil analytical results were compared to soil clean-up goals for the Promenade project, which ' were approved by the RWQCB in a letter to the RDA dated September 5, 2008. Of the eight soil samples collected from beneath the former UST locations, only one sample (Tl-Center-6) had a TPHd concentration in excess of the corresponding cleanup goal of 500 mg/kg. Detected ' TPHmo concentrations in all eight of the soil samples from beneath the former USTs did not exceed the corresponding TPHmo cleanup goal of 500 mg/kg. Although a soil clean-up goal for