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Woolsey Oil Company 07/23/01 San Joaquin County 2 The Investigation Report recommends drilling one deep monitoring well with a screened interval from 85-100 feet bgs, and groundwater sampling for four quarters, to verify the existence of a vertical component to the hydrocarbon plume, before conducting additional investigations. One dry monitoring well, MW -1, was abandoned on January 10, 2001. The MW -1 well abandonment was observed by San Joaquin County Public Health Service/Environmental Services Department. Quarterly monitoring reports 1stQtr2001GMSR and 2ndQtr2001GMSR (and previous GMSRs) showed increasing contaminant levels in MW -6 and MW -7, and varying contaminant levels in MW -3, MW -5 and MW -9. MW -8 was not sampled, due to the presence of free petroleum product. General Comments The Investigation Report is incomplete, due to the lack of: a) Figures with groundwater concentrations isocontours and groundwater gradient contours, using the most recent quarterly groundwater monitoring event data; b) Cross-section profiles of the stratigraphy and vertical groundwater concentration isocontours, using existing boring logs and the new boring log. c) Additional clarification describing the drilling and sampling methods, to explain the observed increase of BTEX in soil samples on day two of the drilling, from 85-100 feet bgs, after BTEX was non -detect from 60-80 feet bgs. The text states that the increase may be due to cross -contamination and soil disturbance. Also, explain why groundwater samples were not taken shallower than 70 feet bgs, when the water table was at 51 feet bgs. d) Proof that the abandoned monitoring well MW -1 was inspected and approved by San Joaquin County. Subsequent reports and work plans should include information identified in a) and b). Please provide the explanation and documentation discussed in c), d), and the specific comments in the next document submittal, the monitoring well installation work plan. Specific Comments 1. Investigative Procedures, paragraph 2, page 2: The text states that soil samples were taken at five-foot intervals, from 50' to 101.5' bgs. The Drill Log (Attachment A) shows that no soil samples were taken at 70' and 80' bgs, and provides no explanation in the Description column. "No Recovery" is the Drill Log explanation for not sampling the 90', 95', and 100' intervals for soils. The Investigation Report text (Subsurface Conditions, page 3) mentions heaving sands from 90' to 101.5' bgs, although the Drill Log does not document this problem. Explain why soil samples were not taken on five-foot intervals at the missing intervals (70 and 80' bgs). See Specific Comment 2. 2. Table 1 Analytical Results --Soil and Groundwater: The Drill Log says that there was no core recovery at 100 feet bgs (heaving sands?), yet Table 1 and the Chain of Custody for 5 January 2001 lists a soil sample at 100 feet bgs. Explain this discrepancy.