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1 December 22, 1998 41017 002 Harding Lawson Associates Mr Michael Kith PHS/EHD Page 8 concentrations of detectable TPHd and TPHmo in these samples ranged from 230 to 8,100 mg/kg and from 540 to 9,600 mg/kg, respectively No detectable concentrations of soluble TPHd or TPHmo were reported for any of these samples SUMMARY AND DISCUSSION ' On July 9, 1998, with approximately one half of the UST removed from the excavation and PHS/EHD staff onsite to direct UST-removal sampling operations, field observations of discolored soils with apparent hydrocarbons odors indicated that impacted soils were present in a narrow, discontinuous nm outside and adjacent to the UST sidewall Mr Kith (PHS/EHD) stated that pnor to performing any overexcavatton a work plan would be required to be approved by the PHS/EHD Site Mitigation Group Sampling performed July 9th at the direction of PHS/EHD, included one UST removal sample (T-3) from soils beneath the former bottom of ' the UST,three samples (T-1, T-2, and T-3) from impacted soils adjacent to the sidewall (which were later excavated), and four discrete stockpile samples (SP-1, SP-2, SP-3, and SP-4) (Plate 3) PHS/EHD indicated that the remaining UST-removal samples and confirmation sampling following overexcavatton could be performed on the same day Removal of the remainder of the UST, without overexcavation, was completed on July 13, 1998 On July 13, 1998, HLA submitted the requested workplan (HLA, 1998e) which was approved by the PHS/EHD Site Mitigation Group on the same afternoon v r xcavation of impacted soils was performed in two phases, each followed by confirmation sampling O ee p p p , Impacted soil was restricted to a narrow discontinuous band immediately adjacent and outside of the concrete sidewall and was not observed beneath the former UST's concrete bottom The first phase of confirmation sampling was performed on July 15, 1998 Mr Kith, from the UST group, selected the remaining two UST- removal sample locations (T-5 and T-6) from soils beneath the former bottom of the UST Ms Lagono, from the Site Mitigation group, selected locations for ten confirmation samples (T-7 through T-15) along the circular trench generated by overexcavatton In accordance with the approved analytical program, Ms Lagono designated sample T-8 for semi-volatile analyses with method EPA 8270 The analyses of the three UST removal samples (T4, T-5, and T-6) did not detect TPHd, TPHmo or BTEX above respective reporting limits Based on field observations made during removal activities and sampling ' operations and on the analytical results from the three UST removal samples, impacted soil was not present in soils beneath the bottom of the former UST 1 Analyses of the ten confirmation samples indicated that TPH-impacted soils had been removed in all but two locations, one on the northwest side (samples T-8 and T-9, depths of 10 and 9 5 feet bgs, respectively) and one on the northeast side of the excavation (samples T-11 and T-12, depths of 10 and 9 5 feet bgs, respectively) Semi-volatile analysis of sample T-8, with the exception of 2_methylna htt[5.0 mgLkg) and hn enanrene (3 0 mg/kg), did not detect any other analytes Soils in proximity to sample location T-8 were subsequently removed during the second phase of overexcavation A second limited phase of overexcavatton was performed in two areas and proceeded carefully to avoid encountering groundwater The purpose of the second phase of overexcavatton was to determine the vertical and lateral extent of impacted soil in these two locations Overexcavation on the northwest side of the 1