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Page G-2 of the application states that ground water recharge occurs from the south and west and that discharge of ground water is into the St. Vrain and the South Branch. At times of low ground water conditions the St. Vrain may be recharging the ground water. Page G-1 states that the site is chazacterized by flood plain features. Page G-2 also states that the ground water table is typically two to three feet below the ground surface on the average, but it may rise to the surface during the spring and early summer runoff periods or fall as low as six feet below the ground surface during the late fall and winter. Finally, the January 28, 1997 RMC letter to Scott Gudahl states that surface and ground water features north of the valley will be protected by a slurry wall constructed parallel to St. Vrain Creek and the South Branch With this information, it appears that there is a strong hydrologic connection between the St. Vrain (and South Branch) and the surrounding flood plain, i.e.: riparian, wetland, subirrigated meadow complex. The applicant will need to explain how the normal and essential hydrologic functions of recharge and discharge for this alluvial- ground water system will occur following installation of the slurry wall and what long-term impacts or changes to the system might be expected. In particular will the reclaimed floodplain complex be able to resume a naturally occurring hydrologic interchange with the main stem and south branch of the St. Vrain for the 2200 lineaz feet of channel passing through or adjacent to the site? Also, the applicant should explain how the upgradient and downgradient ends of the slurry wall will be keyed or configured into the surrounding alluvium. Response: The Division is referred to Attachment #8, "An Analysis of Possible Groundwater and Surface Water Impacts Resulting from the Lyons- Rockin' WP Gravel Pit," prepared by Bishop Brogden Associates, Inc. 28. Comment: The applicant will need to cleazly identify on all appropriate map the location of all proposed slurry walls. In addition, the applicant will need to provide specific information regazding the construction of the slurry walls including the depth, thickness, description of bedrock key cuts, construction materials, construction methods, and quality controVquality assurance procedures. The applicant will need to supply cross sectional engineering designs for the features noted above. The applicant will also DMG Adequacy Review Response Page I I