08-02-94 CCM - Laserfiche WebLink

Home Browse Search

The three homes along the southwest side of the Olson Lake Estates pond, on Upper 45th Street North, were built below the minimum building elevation (El. 966.9) set by the VBWD permit for the project. The lowest home (Lot 2, Block 3) has a basement elevation of 961.7 and a top of foundation elevation at 969,9. Another low home (Lot 1, Block 3) has a low window sill elevation of 965.5 and an estimated basement elevation of 963.5. The third low home (Lot 3, Block 3) has a basement elevation of 964.3. If water levels in the pond remain high for extended periods of time, these basements could be flooded by groundwater moving horizontally from the pond. VBWD's previous Water Management Plan showed the 100-year flood elevation of Lake Olson to be 931.5. This flood elevation was obtained from hydrologic computer models which were used in the design of Project 1007. The computer model included watersheds OL-17 through OL-25 as tributary to Lake Olson. However, watersheds OL-1 through OL-12, OL-15 and OL-16, which are naturally tributary to watersheds OL-17 through OL-25, were not assumed tributary in the computer model. Therefore, VBWD determined the impact of the additional tributary area on the flood level of Lake Olson. The results of the hydrologic computer modeling showed that there was a threat of additional flooding if six or more inches of runoff over the watershed were to occur. The threat was found to be alleviated if the control elevation of Lake Olson could be lowered 0.5 foot, from 927.0 to 926.5. In March, 1991, VBWD received approval from the DNR to modify the Lake Olson operating plan to allow for the additional lowering of the lake water level when high spring runoff is imminent. Information regarding this request and DNR approval is available from VBWD. No negative impacts further downstream in the system were predicted in the modeling. 4.2.8.3 VBWD Water Quantity Management Goals At various times between 1990 and 1993, VBWD considered multiple options for the ultimate discharge of the water from the Olson Lake Estates pond, many of which were suggested by Lake Olson area residents. The options can be generally grouped into the following categories: discharge to Lake Olson, discharge to Project 1007 system, downstream of Lake Olson, treatment of Olson Lake Estates pond water, and other combinations of these discharge options. The existing control structure for the Olson Lake Estates pond is located north of the 45th Street North cul-de-sac, inside the 15" RCP on the east side of catch basin #25. From this point, the pipe system connects to the existing manhole and storm sewer on the west side of Olson Lake Trail. This existing manhole and storm sewer system is undersized and does not include piping from the pipe under Olson Lake Trail to Lake Olson. In addition, re-routing of the main inlet pipe to the north end of the Olson Lake Estates pond to maximize water quality benefits, should be included in each of the outlet options listed below. Based on public workshops addressing the various discharging options from the Olson Lake Estates pond, VBWD identified the following four options for the pond outlet: 1. Outlet to Lake Olson without treatment of pond water. This option would include re-routing of the pond's main inlet pipe and upgrading the downstream system to handle the pond outflows. 2. Outlet to Lake Olson with treatment of pond water. This option would include the pipe system improvements in option 1, along with treatment of the pond inflows by a continuous alum treatment facility or an acceptable equivalent treatment methodology. 23\82\045\SEC4.RPT\KMH 25 DRAFT: June 23, 1994