12/19/2001 Env Bd Packet - Laserfiche WebLink

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Wards Lake is situated in a Natural Environment Basin. Wards Lake is Public Waters. As presented in the Environmental report in September, keeping volume and discharge rates to predevelopment numbers is important. Water from Sherman, Centerville and CD 25 south of Birch flows into Wards Lake. In effect, in has been pointed out that Wards Lake is now a "settling pond" for Reshaneau Lake (Exhibit 7). Water from virtually all directions flow to the Reshanear Lake inlet. This includes water from the South side of the island. Any contaminants leaving the North end of the island will eventually reach Roundeau Lake and the very sensitive ground water on the West end of the island. The effects of increased water storage in this basin can be seen during spring melt and storm events. Water seems to be backing up into the George Watch basin to the North. A recent watershed calibration study has shown that the lower part of the watershed district is now experiencing a basin storage shortage. High water levels for storm events seem to be changing. All efforts should be made in development proposals to consider this in structural planning and surface water volume management. Buffers: The September, 2001 Environmental Board report also states the need to maintain vegetation buffering on the shore areas. Table 1, Buffer Strategy of the Applied Ecological Services Technical Report, suggests a 200 foot buffer in high -risk ecological resource areas (Exhibit 3). Pheasant Hills Preserve is located in a high -risk natural resource area. The 200 buffer width is recommended in areas where there are lake margin wetlands. Surface Water Treatment: Attenuation of hydraulic pulses is needed in a case like Wards Lake Island. Storm water treatment train techniques can positively effect this pulse attenuation. The pulse occurs because storm water is conveyed to holding ponds and released over 1 or 2 days, flushing contaminants with in the process. Attached please find literature Open Space Through Stormwater Management (Exhibit 9). The developer obviously does not have the room for a 200 -foot buffer in this area. Maintaining existing vegetation as much as possible, restoration with proper and incorporating any of the best management practices as developed by Barr Engineering (exhibit 4), could help to attenuate hydraulic pulsing, surface water volume evacuation, and mitigate contamination of the Lake and ground water systems. Ponds 1 & 2: Create a Hydraulic Spike. These are located in ineffective soils. These ponds do not have enough elevation difference between the bottoms of the pond and the water table. Soils: The Regional Hydrologic Assessment —Anoka County Sand Plane, Minnesota shows the area to the West of the island, including the western most tip of land, as very sensitive to ground water pollution. (Exhibit 5). Travel time for contaminants is from hours to