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Mr. Marshall Cloud <br /> May 17, 2006 <br /> Page 3 <br /> Please correct the nomenclature discrepancies in both the provided cross- <br /> sections and figures. <br /> 5. Appendix A; DTSC reviewed CPT logs 1058 through 1063 but did not find CPT <br /> logs 1064 through 1070. Since the four cross-sections in the Technical <br /> Memorandum (TM) identify that all the CPT locations were used by the <br /> contractor to evaluate site lithology, they should be provided in the TM for <br /> reference. Please add CPT logs 1064 through 1070 to the TM so an evaluation <br /> of the site lithology can be verified. <br /> 6. Figure 6, Geologic Cross-section C-C; According to the figure, the triple nested <br /> monitoring wells MW301A/MW301AB/MW301B and <br /> MW301BC1/MW301BC2/MW301C are predominantly screened in the tighter <br /> formations, considered an aquitard by the Unified Soil Classification System. <br /> Section 2.2.2 should discuss the rationale for placing a majority of the nested <br /> wells' screened intervals in the more impermeable lithologic formations. <br /> 7. Figure 4, Geologic Cross-Section A-A; MW456B located in the North Balloon <br /> TCE hotspot, shows a concentration of 130 parts per billion (ppb) at a total <br /> screen depth of-72.00 feet mean sea level (msl). The nested monitoring wells' <br /> MW300A/300AB/300B deepest screen interval is -66.00 feet msl. A deeper <br /> monitoring well, MW456C, in the same North Balloon hotspot shows a TCE <br /> concentration of 2.2 ppb at a total screen depth of-160.50 feet msl. Since the <br /> TCE hotspot in the North Balloon is recorded six feet below the deepest screen <br /> interval in the nested monitoring well cluster MW300A/300AB/300B, and TCE <br /> concentrations continue downward 90+ feet beyond MW300B well screen <br /> interval, DTSC is skeptical as to whether the nested monitoring well will provide <br /> any useful ground water geochemical data to either the treatment technologies <br /> evaluation or monitoring program. <br /> 8. Appendix A, Well and CPT Logs Logs of MW300A/MW300AB1/MW300AB2 <br /> reveal several depth intervals where the lithology description section denotes "no <br /> recovery," but there is no attempt to provide rationale or describe any portion of <br /> the lost core. Please provide rationale in the report as to why the "no recovery" <br /> intervals occurred and whether these "no recovery" sections are indicative of <br /> "flowing sand" or a coarser grained soil matrix. If the later is true, then please <br /> explain in the report why the "no recovery" intervals from approximately -30 to <br /> -34 feet msl and -37 to -45 feet msl seem to coincide with tighter grain formations <br /> shown in the cross-sections. <br />