SITE INFORMATION AND CORRESPONDENCE

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IRM Prove-Out Reports -5- 29 August 1991 DDRW, Tracy 4. Figures 6 to 9. The cross-sections are inaccurate and incomplete. The report does not indicate whether the lithologic logs or the geophysical logs or both were used to construct the cross-sections. The cross-section need to be revised. My specific comments on the cross-sections are discussed below. a. The screened intervals were not plotted on the cross-sections. The cross- sections need to be revised to include this information so that the screened interval can be related to the lithology. In addition, a representative and consistent water level measurement, such as the SWL in all of the wells prior initiation of the extraction system, would be beneficial . b. The lithology of a particular unit for a particular well changes from one cross-section to the next section. For example, the upper coarse-grained unit from about 20 to 30 feet ii IW-3 is depicted as an well graded sand (SW) on B- B' (Figure 7) , but is depicted as a silty gravel (GM) in A-A' (Figure 9) . The cross-sections need to be revised to have consistent lithologies for the same well on each cross-section. c. The depth of a particular lithologic interval in a particular well is different on different cross-sections. For example, on cross-section B-B' there are four coarse grained intervals in IW-3. However, in A-A' this same well shows that there are three coarse grained intervals in this well . Specifically, the lowest coarse grained interval in IW-3 in B-B' extends from about 75 to 100 feet below ground surface (bgs) and has a clay stringer, but on A-A' the deepest coarse-grained interval is depicted as extending from about 90 to 100 feet bgs without a clay stringer. The cross-sections need to be revised to have consistent lithologic intervals for the same wells for each section. d. The cross-sections D-D' (Figure 6) and B-B' (Figure 7) both trend along the northern boundary of the site. It is unclear why these two cross-sections were not combined into one cross-section because both sections trend in the same direction. The distance between EW-4 on D-D' and IW-1 on B-B' is unknown. However, as depicted on D-D' the upper 50 feet of the subsurface is primarily a lean clay (CL) with two thin coarse grained intervals centered around 20 and 30 feet bgs. However, as depicted in B-B' , IW-1 has only one coarse grained interval above 50 feet bgs at about 30 to 38 feet bgs. The coarse grained intervals do not correlate between sections and are not depicted as potentially pinching out. These cross-sections need to be revised to correlate to each other. e. Lithologic contacts below the depth of the wells have been depicted in D-D' and A-A' . Convention for cross-section construction does not permit a contact to be drawn without data and requires that dashed lines be used where the data are inferred (or the correlation is not clear) . The cross-sections should be revised to delete contacts below total borehole depths and to use dashed lines where appropriate. f. The screened interval for EW-1 is unknown and cannot be added to the cross- sections. The report does not indicate what existing well was converted to use as an extraction well . This information should be provided in this report and the cross-sections revised accordingly for EW-1.