Slope Stabilization Work Plan For Poplar River Management Board

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Slope Stabilization Work Plan North American Wetland Engineering, LLC. January 18, 2007 4444 Centerville Rd, Suite 140 Poplar River Management Board White Bear Lake, MN 55127 Phone: 651-255-5050 Fax: 651-255-5060 2.5 Geological Conditions 2.5.1 Summary of Geologic Conditions The Poplar River is located in a moraine complex on the border between the Rainy Lobe and the Superior Lobe that was deposited during the Wisconsinan Glaciation. The Superior Lobe traveled parallel to Lake Superior in a southwestern direction against the Rainy Lobe, which moved in a more southerly direction. The surficial geology consists of unconsolidated materials generally less than six feet deep over fractured bedrock. Dominant soil textures vary from loam to gravelly sandy loam. The glacial sediments in the Lutsen area are underlain by the North Shore Volcanic Group, a series of igneous rocks with interbeds of conglomerates and other clastic rocks. The lava rocks were formed during successive lava flows from the Mid-Continent Rift System. The Rift System is a spreading feature that formed when North America was splitting apart approximately 1.1 billion years ago. According to the USGS, the rift extends from the east end of Lake Superior to Duluth, then south along the Minnesota-Wisconsin border and west to Kansas. When the rifting stopped, a large basin was left behind that over millions of years, filled with sediments. During the last glacial period, the sediments were eroded away by the scouring action of the glacier and Lake Superior and its basin was formed. 2.5.2 Summary of Hydrogeologic Conditions Groundwater in the region originates as precipitation on the surface that has infiltrated down through the overlying sediments and into the fractured bedrock. Figure 2.5 shows a representation of the groundwater flow. Once groundwater reaches the bedrock, its movement is totally dependent upon secondary openings in the rock (fractures, joints, cracks, and cavities). Rock type has little effect on groundwater flow. At the megaslump, the groundwater is likely staying close to the ground surface, thereby saturating the soil, making it more plastic and exacerbating the effects of the slump. Figure 2.5: Representation of groundwater flow at Lutsen Mountains The average groundwater elevation at the site is approximately 1,000 feet above mean sea level. On a regional scale, groundwater flows west towards the Poplar River and then south towards Lake Superior. However, it is likely that the local groundwater direction is more variable due to pockets of 12
Slope Stabilization Work Plan North American Wetland Engineering, LLC. January 18, 2007 4444 Centerville Rd, Suite 140 Poplar River Management Board White Bear Lake, MN 55127 Phone: 651-255-5050 Fax: 651-255-5060 perched groundwater and variable subsurface deposits. The surface water is of high quality with less than 50 mg/L of total dissolved solids, but the MPCA classifies the Poplar River area as a moderaterisk zone for groundwater contamination. 13
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Page 62 and 63: The primary geogrid is approximatel

Slope Stabilization Work Plan For Poplar River Management Board

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