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Trenching between buildings may be a viable alternative to <br /> obtain a representative number of samples to better <br /> characterize this SWMU area (No. 7) . The two suggested <br /> slant borings would provide some coverage, however, they do <br /> not represent the three random samples statistically <br /> required in order to characterize likely contamination at <br /> this location. If a trench could be excavated between <br /> buildings, horizontal borings could then be inserted into <br /> appropriate locations to obtain a representative number of <br /> random samples. It should be noted that there is only an <br /> estimated 2.5 feet vertical distance between the base of <br /> this Burn Pit and the expected water table. Propose a <br /> higher number of samples and other potential techniques. <br /> 38 . Page 3-33, Section 3.2 .4.5.2.1 <br /> Installation of a monitoring well is recommended <br /> downgradient of SWMU No. 7 (Burn Pit 1) , to be "completed to <br /> a depth of 10 feet below the first water-bearing zone. " <br /> Estimated completion depth of the well is 29 feet below <br /> grade. The estimated depth is based on the boring log for <br /> LM-26 which was completed to a depth of 35 feet below grade. <br /> According to the boring log for LM-26, the well was <br /> completed in the same saturated material which was defined <br /> as the Upper Horizon. The log did not show that a lower <br /> permeability layer had been reached which would indicate the <br /> base of the Upper Horizon. Based on the range of possible <br /> contaminants in this SWMU, the well should be designed in <br /> such a way that it will screen the base of the Upper Horizon <br /> and also screen the upper portion of the Horizon. If the <br /> width of the Upper Horizon in this area is found to be <br /> greater than 20 feet, two wells should be considered, one to <br /> screen the upper portion and one to screen the lower <br /> portion. <br /> 39 . Page 3-37, Section 3.2 .5.5. 1 <br /> If significant quantities of mercury or beryllium are found <br /> here, then further soil borings will become necessary. (See <br /> also General Comment No. 14 . ) Commit to further borings <br /> should they become necessary. <br /> 40. Page 3-38, Section 3.2 .5.5.2 <br /> No monitoring well installation has been recommended for <br /> SWMU No. 8 (Burn Pit No. 2) . Sampling and analysis of <br /> groundwater from LM19 which lies 200 feet downgradient of <br /> the area is recommended. LM19 is also approximately 200 <br /> feet downgradient of SWMU No. 28, the Phostoxin Waste <br /> Storage Area, and approximately 50 feet cross- to <br /> downgradient from SWMU No. 22 , listed as a previous <br /> hazardous materials storage area. SWMU No. 30, a "salvage <br /> area" which is to be included in a geophysical survey, lies <br /> approximately 50 feet east-southeast of LM19 . With this <br /> many SWMUs in such close proximity to LM19, installation of <br /> I-14 <br />