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" SITE DESCRIPTION: HYDROLOGY FOR NW COLLEGE ROSEVILLE, MN The site is located on a 3,05 acre tract of land located between Snelling Ave, and Lincoln Drive at Lydia Ave, in Roseville, MN, The existing site is an on grade parking lot that drains both west and south to a retention pond on the south side of the property via an in place storm sewer system, The pond outlets south through a 21 inch storm sewer, eventually entering Lake Johanna. Proposed site improvements include an on grade parking lot with a 72 vehicle parking ramp overhead, Storm drainage will flow to the existing pond via a storm sewer for the on grade parking lot. The parking ramp will drain via floor drains through the deck, METHOD: TR-55 was used for this hydrologic study, using a Type" rainfall, Assumptions used in the calculations include; a time of concentration (Tc) of 10 minutes and a soils classification of B, Peak runoff calculations were done for both pre-development and post-development using the 1, 2, 5,10, 25, 50 and 100 year storms events, SUMMARY: The proposed modifications to the site will decrease the hard surface area that drains to the south pond as follows: DESCRIPTION GRASS (ACRES) IMPERVIOUS (ACRES) TOTAL (ACRES) EXISTING 1,33 1,72 3.05 PROPOSED 1,37 1,68 3,05 The existing pond has a dead storage capacity of 0,27 ac-ft, between elevations 904,0 and 909,5 according to JC Johnson Consultants storm water calculations dated 6/15/93, (attached), Also, the calculations indicate a 0.60 ac-ft of live storage between 909,5 and 912,5, From calculations based on contour areas from the current Bolton and Menk survey, the pond has 0.4 ac-ft of live storage between contours 909,5 and 912.5, The change in impervious surface will decrease the peak storm water discharge rates as follows: EVENT YEAR 1 2 5 10 25 50 100 PRE 3 cfs 5 cfs 7 cfs 1 0 cfs 12 cfs 14 cfs 16 cfs POST 3 cfs 4 cfs 7 cfs 9 cfs 11 cfs 13 cfs 15 cfs A 2.5 inch rainfall requires 0,24 ac-ft of dead storage for the site,