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11 1 M • Appendix A - Historical Background River City Petroleum and Connell Motor Lift Truck Page 4 of 14 collected two shallow soil samples under the concrete apron, one at the surface and one at a depth of 15 feet Laboratory analysis detected elevated levels of diesel and what appeared to be weathered gasoline,these levels were substantially reduced(90%)within the first foot of depth Amherst concluded that limited subsurface contamination posed little threat to the environment, and that additional work would not required for site closure by the owner (Connell Motor Truck) • On 11 June 1998,UST Numbers 5,6 and 7 were removed Thorpe Oil of Lodi excavated and removed the fueling facility as well as piping discovered during removal of the former UST system in 1986 The soil under the three USTs was analyzed and reported as non-detect for all analytes, however, hydrocarbon-impacted soil was found beneath the dispenser and the old piping Subsequently,a limited volume of impacted soil was removed and the excavation was backfilled with pea gravel • On 29 July 1998,Connell Motor Truck and River City Petroleum received an official Notice of Responsibility letter from EHD informing them that the site has been assigned to the Local Oversight Program for assessment and remediation • On 09 October 1998,an EHD memo noted receipt of an incomplete work plan for site over- excavation,submitted by Foothill Engineering(FE) An expanded work plan and Executive Summary for public review were needed • On 20 October 1998,a revised work plan was submitted by FE that proposed excavation of all contaminated soil from the dispenser and piping area FE noted that the fuel contamination was concentrated near the surface and diminished as depth increased The estimated size of the proposed excavation area was+/- 20'X 30'to a depth of+/- 8', with a volume of+/-200 cubic yards The removed soil would be stockpiled on site until removed to a regulated landfill or was reclaimed on site • On 04 January 1999,FE issued a memo to the EHD on the analysis of three samples taken during over-excavation of the pump area FE assumed that contamination would be found under the pump island and to the east of the excavation area Samples BS-2 and side sample SW-1 from the west side of the excavation showed discoloration and FE determined that it might be from the pre-1986 fueling operations FE interpreted the data to show that contamination may extend deeper than suspected and recommended that a work plan be developed to assess the horizontal and vertical extent of contamination and that the work plan should include ground water sampling under the fuel islands • In September 1999, three shallow ground water monitoring wells were installed near the former western fuel dispensing island, surveyed and later sampled Dissolved petroleum hydrocarbons were detected in ground water samples from each of the ground water wells • In September 2000, three shallow and four depth-discrete ground water monitoring wells were installed and sampled Hydrocarbon-impacted soil was encountered from 20 feet to 70 Advanced GeoE.nvironmental,Inc