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Inconsistencies between the Summary Table of Trenching, Trench Logs and Report Text • The summary table of trenching has inconsistencies when compared to trench logs. For example, the analytical summary tables indicated all samples from T1 to T23 were collected at 5 feet bgs; however, trench logs indicate some trench excavations were shallower (e.g., trench log T1 appears to have a total depth of only 3.75 feet bgs, T2 only 4 feet bgs). How can samples be collected at depths greater than what was excavated? • The Trench Summary Table indicates that 23 trenches were excavated on April 20, 2015; however, samples are indicated as collected a day later. Samples should be collected at the time of excavation. Collecting a sample from a trench that was open overnight and analyzing it for volatile organic compounds (VOCs) and possibly also semi-volatile organic compounds(SVOCs), may not be representative of actual site conditions. In addition, how were the samples collected from open excavations at depths of 5 feet? • Although not entirely clear, it appears that the Trench Summary Table indicated that most trenches were not excavated to native soils (native soils are indicated in some logs so it is assumed that when it is not stated, that the excavation did not extend to depths of native soil). Based on this, is it possible additional wastes exist at greater depths? • The first trench log reviewed, T1, indicates wastes at approximately 2 to 2.25 feet bgs; however, the Trench Summary Table indicates wastes a foot deeper. Based only on looking at this one trench log and comparing it to the information on the table, and the inconsistencies, all information needs to be rechecked to confirm the summary table and logs match. Borings Logs A138 to AB28 and Trench Logs T1 to T23 • Based on boring logs AB8 to AB21 at the northern waste disposal area, only one boring,A1318, encountered glass waste; however, adjacent trench T10 to the north encountered glass, adjacent trench T7 to the northeast encountered glass, adjacent trench T11 to the south encountered glass, there is no log for adjacent trench T15 to the southwest (two trenches are labeled T14), adjacent trench T16 to the northwest encountered glass, and only adjacent trench T6 to the southeast did not encounter glass. Other outlying trenches also encountered glass. A review of available information provided indicates that most trenches in this area encountered (glass)waste,yet borings in the same area of exploratory trenches and in the waste disposal area did not encounter waste (glass) except at one location. Based on background information, historical aerial photographs, it does not make sense that only one boring, and most trenches in the same area encountered (glass)waste. • It is not clear whether the trench excavations extended into native soils. By only excavating to approximately 5 feet bgs and without knowing whether native soils were encountered, it is possible that wastes are present at greater depths separated by soils. Boring logs do not appear to differentiate fill soils and native soils. Trenches should be excavated one to two feet into native soils (as possible), or at a minimum, at locations where severe caving is occurring or other difficult subsurface conditions are encountered, a percentage of trenches should be excavated into native soils, depending on the WDS. Trench logs T24 to T110 • Trench logs for T24 to T110 are not available.Trench logs appear to only be available for trenches T1 to T23 and not for the other 86 exploratory trenches. • It is assumed that trench logs were prepared in the field and it may be acceptable to provide'field copies"(as opposed to drafted versions)to the regulatory agencies provided they are legible. Ninyo&Moore 1 500 E.Louise Avenue,Lathrop,San Joaquin County,California 1 104690095 1 August 11,2017