SITE INFORMATION AND CORRESPONDENCE

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David Wang • • Page 9 The RI report states that LM61 was drilled to monitor the PCE concentration at the water table surface within Contaminant Area 1. Table 3 .4-1 reports that the water level in LM61 is 16. 98 feet below ground surface. Since the screened interval is 20 to 30 feet BGS, the water level is above the top of the well screen. To obtain representative samples of the water table surface (water-air interface) , monitoring wells must be screened across the water table. 9) page 3-22 , paragraph 3 .4 . 4 . 5.7, lines 4 , 5, and 6: The RI report states: "Chemical results from groundwater analyses at LM61 indicated a PCE concentration of 15 ug/l, and a TCE concentration of 13 ug/1. " Table 3 .4-3 reports 25 ppb TCE and 85 ppb PCE in LM61 in 1988 . Clarification is requested. 10) page 3-23 , paragraph 3 .4 . 4. 5 . 8 , lines 5 , 6, and 7 : The RI report states, with reference to sample results from LM62: "These results indicate that VOCs are present at or above State Action Levels at the shallow water table surface in Contaminant Area 2 . " DHS recommends that this sentence be rewritten to clarify that the well screen of LM62 is below the water table (air/water interface) . In addition, Table 3 . 4-3 reports 7 . 6 ppb TCE and 4 . 5 ppb PCE for LM62 in 1988 . 11) page 3-26, paragraph 3 . 4 . 5.2, lines 12 through 15: The RI report states: "Plotted grain-size curves show that the installed slotted casing (0. 01 inch) and gravel pack (Lonestar Number 3 sand) retained a high percentage (approximately 90 percent) of the natural formation material, allowing passage of only very fine sand, silt, and clay particles. " The above is not the goal of an engineered filter pack. The slot size of the screen should retain approximately 90 percent of the filter pack, not 90 percent of the natural formation material .