Agenda - Council - 06/14/2016 - Laserfiche WebLink

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Patrick Brama February 25, 2016 Page 2 To prepare the site for future development, we have proposed a number of improvements. The improvements include sanitary sewer and watermain extensions, trunk storm sewer construction, regional stoiniwater pond construction, cul-de-sac construction on the south end of Limonite Street and access removal at 142nd Avenue. The proposed improvements are shown on Exhibit 3. We are proposing to reconstruct the existing stormwater pond along the east property line of future Parcel 2. This new pond will be a regional stoiuiwater pond for the area. In our opinion, reconstructing the pond along the east property line will result in a more desirable lot for site development. The pond location is shown on Exhibit 3. The regional pond will be designed to treat the stormwater from the future parcels and to meet the water quality and rate control requirements of the Lower Rum River Watershed Management Organization (LRRWMO). The water quality requirement states that the storage below the pond outlet be equal to or greater than the runoff from a 2.5" rainfall event over the entire drainage area draining to the pond. The rate control requirement states that the proposed discharge rate from the site be less than or equal to the existing discharge rate for the 2-, 10- and 100-year storm events. A detailed review of the existing drainage areas and discharge rates will have to be completed prior to the final design of the regional pond. The final configuration and size of the pond will be reviewed based on the proposed site plans for the future parcels. One component of the LRRWMO stoiinwater requirements that will not be addressed with the proposed site improvements is volume control. The LRRWMO requires that one inch of runoff from the new impervious surfaces be infiltrated on site. Typically this is more efficient if each parcel addresses this requirement at the time of site development. Proposed Improvement Costs We have prepared an estimated construction cost to prepare the site for future development. The primary improvements include clearing and grubbing, site and pond grading, sanitary sewer and wateiiiiain extension, trunk storm sewer construction, cul-de-sac construction, salt storage building demolition and utility relocation. Based on our review, the estimated construction cost to prepare the site for future development is $417,779. A detailed cost estimate is included in Table 1. Future Development By completing the improvements discussed above, the City will create two developable parcels. An adequately designed site plan should include a balanced earthwork volume. As each parcel develops, the stormwater volume control requirements of the LRRWMO will have to be addressed. A drainage and utility easement will also have to be provided on Future Parcel 2 over the trunk storm sewer that drains from Future Parcel 1. Hakanson Anderson