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08 September 2000 AGE -NC Project No. 97-0372 Page 16 of 18 Migratory pathways through the vadose zone are controlled primarily by soil composition, conduits created by man or nature (excavations, fractures, root traces, etc.). At this time, AGE has no knowledge concerning these factors, other than the spill excavation in the tank storage area. The importance of these factors must be inferred from the soil samples collected at the time of the investigation and which must be evaluated at that time. The exception will be the soil samples collected directly under the backfill in the former excavation will be given a high priority for analysis. At the time of preparation of this work plan, there is no knowledge that any releases to the subsurface have occurred on the site, much less the volume of possible releases. AGE will assume that the volume of possible releases was sufficient to follow migratory pathways to ground water in selection samples for analysis. This means that samples will be selected for analysis if observations from other samples indicate that one or more releases have occurred and that horizontal migration along preferential pathways overlying less permeable strata is likely to have occurred. Thus, the selection process for soil samples for analysis will rank proximity to suspected points of release and soil composition. If sand underlies by a foot or two the suspected release point and is underlain by silt or clay, the upper portion of the recovered fine-grained material will be selected for analysis. On the other hand, if the suspected point of release is underlain by a thick sand on the order of 10 feet or so, then a sand sample directly underlying the release point will be selected; professional judgement, with concurrence of the DTSC, will be exercised for cases in between. If significantly impacted soil is encountered, soil samples from greater depth in adjacent borings, if available and appropriate, will also be analyzed to define the descending and laterally spreading plume. However, it should be kept in mind that the objective of this work plan is to identify areas of contaminant releases and to get an indication of the potential magnitude of any releases encountered, and is not intended as a complete assessment of any contamination encountered. If significant contamination is encountered and identified, an addendum work plan for complete assessment will be prepared. The samples selected for analysis will be analyzed in accordance with the following analytical methods and practical quantitation limits (PQL), providing there is no matrix or competing analyte interference: • EPA Method 9045 for pH; • EPA Method 6010 for total lead, cobalt, copper, nickel, chromium, and zinc (PQL 5 mg/kg chromium and lead, 10 mg/kg cobalt, copper, nickel and zinc); • EPA Method 335.2 for total cyanide (PQL 0.20 mg/kg). Advanced Geo Environmental. Inc