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<br />capital costs are associated with this alternative, but emergency expenditures would <br />be significant, perhaps as great as the culvert improvements, and unbudgeted. Lake <br />.water quality would be maintained through maintaining isolation from Vadnais <br />Lake, through monitoring of construction activities, and through public education. <br />® If allowing a periodic outflow of 63 cfs from the Vadnais chain to the RWMWD becomes <br />necessary at some time in the future, different management scenarios must be considered: <br />1. The preferred scenario would be to route the 63 cfs outflow from Vadnais Lake <br />around Twin Lake, rather than through it. This would preserve Twin Lake's water <br />quality. One possibility is to construct a conveyance system that would carry flows <br />from the west arm of Vadnais Lake around the west side of Twin Lake to the <br />County Ditch 16 system (see Figure 5}. The existing outflow from Vadnais to Twin <br />could then be abandoned. Preliminary estimates have not been prepared for such <br />a conveyance; additional study of the route is required. <br />Easements and permits would almost certainly be required for the construction of <br />this bypass system. An examination of the National Wetlands Inventory map for <br />the region indicates that wetlands permits for the work may also be necessary. As <br />a result, a separate study to evaluate the feasibility and better estimate the costs <br />would be necessary before proceeding with this alternative. <br />2. The Vadnais outflow could be routed through Twin Lake, and then through the <br />Interstate highway storm sewer conveyances, as was outlined in the 1975 Ramsey <br />County Open Space report. However, two complications exist: <br />The existing culverts beneath I-694 are not capable of handling 63 cfs; the outflow <br />system would have to be upgraded or severe flooding around Twin Lake would <br />occur. This upgrading would involve considerable expense, since over 1,600 feet <br />of additional culverts would need to be installed deep beneath the existing I-694 <br />roadway. The expense of installing the required culverts is expected to be in the <br />neighborhood of $400,000. <br />Water quality in Twin Lake would undoubtedly suffer as a result of its being <br />flushed with water bearing an elevated contaminant Load and possible exotic plant <br />species. <br />23162\264\TWINLAKE.R:I'T\KMH ~ 11 <br />