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idnuary 8 1998 �•� ) Page 2 . (2) The specific ac/mll of the local agency (1'H.1;1EH1)) which the .Slate Boal d it i egiie ted to i eiueil, On behalf of UNOCAL, PEG hereby requests that the SWRCB review the PHS/EHD's deternimation, dated December 10, 1997, that a proposed work plan was deficient and requiring additional soil borings and groundwater monitoring wells for the lateral and vertical delineation of petroleum hydrocarbons in soil and groundwater, and for air sparge and soil vent testing UNOCAL proposes to install a single downgradient monitoring well and continue the current groundwater monitoring program for a minimum of one year (3) The crate oil which IWV E- HD acted The date on which the PHS/EHD acted was December 10, 1997 A copy of their letter dated December 10, 1997, is included in Attachment A as Document A-2 (�) .Statemew of the 7eacoils the action was wappjclpl rale of mill neer PHS/EHD is requiring actions that are not necessary for protection of public health and/or groundwater resources Specifically, the requested additional soil borings and groundwater monitoring wells will not provide data that will have meaningful use in risk • assessment or remediation beyond the data already available Performance of the requested sparge/vent pilot study is inappropriate given the low risk of hydrocarbons to impact groundwater resources The subject site is currently a vacant lot located in Stockton, California (Attachment B, Figure 1) Two 1,000-gallon gasoline underground storage tanks (USTs), located in the southeastern corner of the site, and one 550-gallon waste oil UST, Iocated east of the station building, were removed from the site in 1967 These first generation USTs were replaced with two I0,000-gallon gasoline USTs and one 280-gallon waste oil UST, all located immediately south of the station building In 1992, the service station ceased operations and all the second generation USTs, associated piping, hydraulic lifts and oil/water separator were removed and the station facilities demolished A site map which depicts former site features is included in Attachment B as Figure 2 Site investigations have determined that impacted soil and groundwater are in the vicinity of and associated with, the first generation USTs removed in 1967 Cross sections showing the distribution of hydrocarbons in soil beneath the site are included in Attachment B as Figures '), 4 and 5 The plume is relatively small with highest levels of hydrocarbons concentrated immediately downgradient of the former source area Analytical data collected from fourteen consecutive quarterly monitoring events indicate that hydrocarbon concentrations have decreased over time in most wells No separate- phase hydrocarbons (SPH) have been detected during any sampling event, except the z 101507A 0187REN IEW