Agenda Packets - 1997/02/24 - Laserfiche WebLink

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Non-Benefits Does not get rid of the existing hole for the pond. • Will have short term ponding during rainfall events Option 4. New Pipes - Surge Manhole Remove existing storm sewer and raise the storm sewer which eliminates the need for sump manholes. Excavate the existing pond to native material. Fill the pond with granular material to elevation 906.0 (elevation of the existing water in the pond) Connect sump manholes to surge and rate control manhole next to highway ditch This eliminates standing water by raising the storm sewers so the discharge elevation is above the invert of the outlet pipe in the highway ditch(904.58). However,it does not eliminate the detention function of the area;therefore,the existing"hole" would remain. This option allows the pond to be filled an additional 1.5 to 2 feet. This puts the bottom of the pond around elevation 906.0 which is near existing normal water elevations. The sump manhole would control the water that gets into the highway drainage system. If water cannot flow through the small 6-inch orifice opening, it would surge out of the manhole and into the detention area. For the most part the water quality function of the pond would be lost which may require a new pond offsite. Only difference between this option and option 2 is the sump manholes are eliminated. • Project Cost. $95,500 Benefit(s): No annual sump maintenance Pond Bottom is near existing normal water elevation. Non-Benefits Does not get rid of the existing hole for the pond. Will have short term ponding during rainfall events Option 5. Bury storage including retention storage. Create sump catch basins at each inlet to the pond which drain to the pond. Excavate the existing pond to native material. Replace the lost pond volume using large CMP culverts which allows the pond to be - completely filled. - With this option the existing ponding is eliminated by using Corrugated Metal Culverts (CMP). Enough CMP's are buried in the pond location to compensate for the lost storage. This will allow the site to be filled to near the elevation of the existing land. Sump catch basins are installed prior to discharging into the underground CMP system to collect a portion of the sediment. Some of the CMP should be perforated to take advantage of the natural infiltration of the soils. For the most part the water quality function of the pond would be lost. However, with proper maintenance of the sump catch basins, an additional water quality pond should not be required. • Project Cost. $165,000