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September 30, 1999 47491 1 Harding Lawson Associates Margaret Lagono, Supervising REHS San Joaquin County Public Health Services Environmental Health Division Page 2 sump located within the courtyard of main plant building (Plate 2) The second area consisted of a 210,000- gallon Number 6 UST located in the southeast corner of the Newark facility(Plate 2) For a detailed ' presentation of the sites history and the results of these investigations, the reader is referred to HLA's reports entitled Closure Report, 210,000-gallon UST Removal Project, and Summary Report, Limited Phase 11 Investigation, Courtyard Tanks and Sump, both dated December 22, 1998 (HLA 1998b and 1998c) Presented below is a brief synopsis of previous work in the courtyard and a brief summary of HLA's investigations in both areas Courtyard Tanks and Sump In October 1990, American Environmental Management Corporation (AEMC) submitted a report(AEMC, ' 1990)titled "Unauthorized Release Report for Newark Paperboard Corporation, Stockton, California " The report summarized results of July 1990 soil sampling and recommended closure procedures for the No 6 fuel delivery pipeline and the courtyard tanks (concrete vaults) and sump ' In October/November 1993, the courtyard tanks and sump were closed in-place by Resna Industries Inc (RESNA) by removing the remaining contents, cleaning, and backfilling with a cement slurry (RESNA, 1994) This work was presented in RESNA'S report entitled Underground Fuel Storage Tank Closure, dated July 12, 1994 In September 1997, PHS/EHD correspondence to Newark requested further investigation of the extent of ' petroleum hydrocarbons in the courtyard area In April 1998, in accordance with the approved work plan, HLA conducted a field investigation and prepared a summary report entitled Limned Phase II investigation, Courtyard Tanks and Sump, dated December 22, 1998 (HLA 1998c) The scope of work for the investigation ' was developed after discussions with Ms Lagorio of PHS/EHD The objectives of the investigation were to assess the maximum concentrations and lateral and vertical distribution of petroleum hydrocarbon-impacted soil A further objective of the investigation was to assess the potential threat to groundwater quality and to assess the feasibility of insitu passive bioremediation of impacted sods Based on the results of this and previous investigations,HLA concluded the following ' • Potential leaks have been eliminated by closure activities which removed all former product, cleaned, and backfilled the USTs/sump with concrete • The lateral extent of the impacted soil associated with the courtyard USTs/sump location has been determined • The vertical extent of impacted soil has been determined and does not extend to depths of 20 feet bgs at ' the source • The areal extent of impacted soil is less than 700 square feet 1 • The Hydropunch groundwater data are suspect and groundwater is not likely to be impacted based on • the available data ' • The lack of detectable benzene in all soil samples collected to date and the lack of detectable polyaromatic hydrocarbons (PAHs) in the soil with the maximum TPH concentrations indicates that