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The design of VBWD's Project 1007 included an outlet for portions of this watershed. This outlet was constructed in 1990 as part of the Olson Lake Estates development. When the VBWD permit for the Olson Lake Estates development was approved, it permitted the construction of an outlet at Elevation 952.0 from the storage area in OL-18 (DNR wetland #82- 477W). The pond in subwatershed OL-18 did not have a surface water outlet (landlocked) prior to reconstruction of the pond as part of the Olson Lake Estates development. The outlet from subwatershed OL-18, constructed in 1990, was connected to an existing culvert under Olson Lake Trail. However, a drainage easement did not exist across the property between Olson Lake Trail and Lake Olson. Because of concerns regarding water quality, increased flow duration, and drainage easements, the City of Oakdale voluntarilyplugged the Olson Lake Estates pond outlet in July, 1990. However, since the Olson Lake Estates pond was not designed to operate as a seepage pond, a project is needed to carry water from the Olson Lake Estates pond to an eventual destination point. Above -average rainfall in the spring and early summer of 1993 brought substantial inflows to the Olson Lake Estates pond. VBWD declared an emergency on June 22, 1993, when the pond water level reached Elevation 961, about one foot below the lowest basements. VBWD ordered pumping of the pond to lower the water level to Elevation 952, Water was pumped from the north end of the pond to a catch basin at 49th Street North and Helmo Avenue North. The water eventually reached Long Lake. The pump was shut off and removed from the pond on July 30, 1993. On August 12, 1993, pond water levels approached Elevation 962 and VBWD declared another emergency. The plug was removed from the pond outlet pipe on August 13, 1993 and water was discharged directly to Lake Olson, The City of Oakdale replaced the plug in the pond outlet pipe on September 21, 1993, after the pond reached Elevation 952. During the week of April 25, 1994 nearly 4 inches of precipitation occurred from several intense storms and consequently the level of the pond rose to Elevation 962.3 on May 2, 1994. On May 5, 1994 the VBWD managers voted to perform a one-time alum treatment of the pond and-then-disch-arue-toLake-0lsnn-qhnrf1v-th-erPaftar T-hia approvals and acquisition of a temporary easement for the discharge pipe to Lake Olson. Following discussions with DNR staff, VBWD notified the DNR Division of Waters of its intended -discharge, and a Special Permit was granted on May 6, 1994 from the DNR Division of Fish and Wildlife to apply alum to the pond. The pond was treated with alum on May 7, 1994 and discharge to Lake Olson began May 19, 1994 following the signing of the necessary temporary easement. When the Olson Lake Estates pond water level is at Elevation 932.0, the pond can store 128 acre-feet before reaching the design 100-year flood elevation of 967; the pond can store 134 acre-feet before reaching the emergency overflow elevation of 967.5. These flood elevations are based on the pond outlet functioning as originally designed by the developer. In addition, when the Olson Lake Estates pond water level was near Elevation 957, VBWD calculated a seepage rate of approximately 0.5 acre-feet of water per day from the pond to the groundwater based on water level measurements. If the pond exceeded its overflow elevation, water would eventually reach Lake Olson, Above Elevation 965.0 water begins to backflow into the streets through catch basins in the Olson Lake Estates development. Above Elevation 967.5, water will overtop the pond embankment and flow into 45th Street North. When the water level in 45th Street North exceeds Elevation 967.2, water will flow between two homes located on the east end of 45th Street North and proceed down the hill to the ditch along Olson Lake Trail. This discharge will then flow in the ditch and enter the culvert which crosses Olson Lake Trail, eventually entering Lake Olson. 23\82\045\SEC4.RPT\KMH 24 DRAFT: June 23, 1994