Laserfiche WebLink
David Wang • <br /> Page 6 <br /> o page 7-1, paragraph 7 . 3 , lines 1 through 4 : <br /> The RI report states: <br /> "The vertical extent of contaminant Area 4 has not been <br /> fully defined. A well should be installed approximately <br /> 200 feet downgradient of LM17 with a screened <br /> zone between 35 and 45 feet which should delineate the <br /> extent of vertical contamination in this zone. " <br /> DHS recommends this monitoring well be screened from <br /> approximately 45 to 55 feet BGS. The intent of this well <br /> is to screen near the base of the gravelly sand unit <br /> above the silty clayey sand depicted on the revised <br /> geologic cross-section C-C' . <br /> o page 3-33 , lines 27, 28, and 29: <br /> The RI report states: <br /> "A slight vertical gradient in the direction of groundwater <br /> flow is noted with increased distance off-site. " <br /> Clarification of this statement is requested. It appears <br /> to DHS that there is an abrupt decrease in the vertical <br /> gradient with increased distance off-site (i.e. , there is <br /> very little vertical gradient north-northeast of the well <br /> cluster consisting of LM55, LM56, and LM57) . <br /> o DHS has reviewed the recommended well locations in the Data <br /> Analysis Supporting Task 36 report. DHS will not provide <br /> specific comments on the five new monitoring well locations <br /> until the additional hydrogeolgic information requested in <br /> our comments is provided. <br /> 4) Section 3 . 4 .2 , Groundwater Movement: <br /> This section of the RI report should comment on the magnitude of <br /> the hydraulic gradient in the horizontal and vertical direction. <br /> There is ample hydraulic data to calculate such parameters. <br /> paragraph 3 .4 . 4 .4. 3 , page 3-20, lines 16 through 19 : <br /> The RI report states that a sandy clay layer was noted at a depth <br /> of approximately 46 feet when Well LM50 was installed and that <br /> this clay could be forming a localized lithologic barrier impeding <br /> the vertical migration of contaminants in this zone. <br /> DHS suggests that consideration of possible lithologic <br /> barriers to groundwater flow be included in Section 3 . 3 .2 <br /> (Local Geology) and/or Section 3 . 4 . 2 (Groundwater Movement) of <br />