2006-06-28_REVISION - M1982015 - Laserfiche WebLink

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Clarification of Recommendations for Lake Embankment Slope Protection Terracon Bayshore Development -Weld County, Colorado Terracon Project No. 25045300 i. The rip rap slope protection is a significant change from the previously submitted grading plans and present site configuration. ii. The adequacy of the rip rap protection to resist undercutting along the St. Vrain River channel. Additionally, cross sections of typical sections of the rip rap placement and plan view of the extents of rip rap placement are requested. iii. Impacts to the St. Vrain River and downstream parties due to placement of the rip rap. iv. The width of the embankment used in the global stability analyses. Based on these comments, we submit the following clarifications/responses: i. The grading of the lake embankment to the proposed 2-1/2:1 slope is not considered to be a major change to the extent of the overall grading plan, only a modification of the slope inclination. The result of the slope inclination modification is that the lake embankment crest of the slope will extend closer to the proposed lake body (north) and is considered necessary for the overall global stability of the lake embankment and slurry wall. Based on field documentation of the existing lake edge conditions, a majority of the southern lake edge consists of recycled concrete armoring varying in size from minus 6-inches to greater than 4 feet in diameter (see attached photos taken on June 23, 2006) with the thickness observed to be on the order of 3 to 5 feet in thickness. It should be noted that, in the locations where the proposed lake embankment encroaches adjacent to the St. Vrain River channel edge, it appears that the existing concrete armoring extends fully to the bottom of the river channel. Addition of the geotextile fabric and rip rap protection above/behind the existing concrete armoring is not considered to be a negative modification of the existing condition along the southern edge of the lake embankment. Furthermore, it would be considered a formalization/improvement of existing erosion/scour protection along a majority of the embankment. ii. Generally, five areas along the proposed lake embankment are directly adjacent or will coincide with the St. Vrain river channel. All other areas of the lake embankment along the southern edge do not encroach within reasonable distance from the existing river channel and are located within the existing subjected floodplain. The five areas which are directly adjacent or will coincide with the St. Vrain river channel are located at approximately Station 4+50 to 12+00, Station 19+50 to 24+50 (spillway location), Station 40+50 to 43+50, 2