SITE INFORMATION AND CORRESPONDENCE 1995-2004

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• 0 Mr. Fernando . -3- 14 December 1995 8. Page 4-3, Section 4.2.1, Area I Subsurface Soil The FS states that soil samples were collected at depths of one to 100 feet bgs with most samples collected within the upper 25 feet bgs. The FS should explain the rationale for the preponderance of samples at this interval. 9. Pages 4-3 and 4-6, Section 4.2.1.1, Potential Source Area 1 (S1) The FS states that S1 is characterized by borings MW-9, MW-19, SB-313, SB-2-95, SB-3-95, SB-4-95, and SB-23-95; boring logs show that concrete or wood barriers were encountered at depths of 15-23 feet bgs; PNAs were detected at significant levels at 24 feet bgs in MW-9 and at 19.5 feet bgs in SB-4-95; and chemical data are summarized in Table 4-1. The sampling program is inconsistent in sampling depths and types of analyses performed. Following are the sample locations and their sampling intervals: MW-9: 2.6-40.5 feet bgs; MW- 19: 50 and 100 feet bgs; SB-2-95 and SB-3B: 3-8 feet bgs; SB-3-95: 11.5-12 feet bgs; SB-4-95: 10.5-20 feet bgs; and SB-23-95: 7.5-24 feet bgs. At MW-9, soil samples were analyzed for total PNAs and total petroleum hydrocarbons as diesel (TPHd) at the first sampling depth of 2.6-3.0 feet bgs. At the next sampling depth of 3.0-3.5 feet bgs, the sample was tested for total volatile organic compounds (VOCs) and TPH as gasoline. This alternating sampling procedure was used throughout the sampling depth. As a result, the vertical extent of contamination has not been identified. For example, at 24.0- 24.5 feet bgs, total PNAs and TPHd were detected at 1,875 and 5,425 mg/kg, respectively. The next available data for total PNAs (1.28 mg/kg) and TPHd (9.68 mg/kg) were taken from the interval at 35.0-35.5 feet bgs . Thus, there are more than 10 feet of undefined soil layer beyond the point where the highest concentrations of total PNAs and TPHd were detected. If remediation is proposed to go down to about 35 feet bgs, at least in this particular spot, further characterization will not be necessary since remediation will address the interval which lacks data. MW-19 was not tested for total VOCs. SB-3B was not tested for TPHd/g. Table 4-1 lists `Total VOCs' as one of the column headings. The table should define `VOCs'. The term is typically associated with solvents such as carbon tetrachloride, tetrachloroethylene, trichloroethylene, etc. If the table is referring to aromatic compounds associated with petroleum hydrocarbons, the term `BTEX' is more appropriate and should be used. The lateral and vertical extent of soil contamination in S I has not been defined except to the east of SB-23-95. To the west, MW-12 may define S1's lateral and vertical extent. However, I could not find the soil sample results for MW-12 in Appendix B which contains the soil data for the site. To the north is MW-9. As stated above, MW-9 is highly contaminated at about 25 feet, lacks data for 10 feet beyond this depth and is still contaminated at 35 feet. Lateral and vertical definition of this contamination to the north is necessary. To the south, SB-3B and SB-3-95 were sampled at maximum depths of only eight and 12 feet bgs, respectively. Laterally, the definition of the extent of contamination is acceptable. However, the data are limited to make a determination of the vertical extent.