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MEMORANDUM <br />© MONTGOMERY WATSON <br />To: Kate Drewry, District Administrator Date: November 17, 1999 <br />Rice Creek Watershed Dist ict <br />From: Derek Knapp, P.E. Reference: <br />Subject: Otter Lake Drive Hockey Rink/Easement <br />Vacation <br />The purpose of this memorandum is to summarize my review of the Otter Lake Drive Hockey <br />Rink/Easement Vacation situation based upon the updated survey data sent by Bob Adamson, <br />dated November 2, 1999, received November 15, 1999. <br />RECENT ACTIONS <br />The new data was submitted in response to my October 12, 1999 memorandum requesting 1) <br />more detailed survey data on the Melton pond at the eastern end of Otter Lake Drive, 2) <br />verification of the pond's runout elevation, 3) recalculation of the pond's live storage volume <br />between the newly surveyed pond runout elevation (911.3) and Otter Lake's HWL of 912.9, and <br />4) survey data along the centerline of the swale between the Melton pond and a low area on the <br />northeast corner of the Schwartz's property. <br />The requested survey data was satisfactorily completed. <br />COMPENSATORY STORAGE <br />The Rice Creek Watershed District's (RCWD) permit (90-14) for the Oak Brook Peninsula <br />development specified 640 cubic yards of compensatory floodplain storage volume to mitigate <br />for fill in Otter Lake's floodplain. The RCWD permit was issued based upon plans showing the <br />compensatory storage basin to be excavated at the eastern end of Otter Lake Drive. This storage <br />area was not constructed as approved. <br />Instead, the requisite 30' x 30' water quality pond (dead storage only) at the eastern end of Otter <br />Lake Drive was enlarged during site construction to approximately 220' long x 30' wide (on <br />average). As approved, this water quality pond was intended to function separately from the <br />compensatory storage basin. As constructed, this pond provides approximately 525 cubic yards <br />of live storage below Otter Lake's HWL. <br />An additional 30' x 30' water quality pond was required by the RCWD to pretreat roadway <br />runoff prior to discharge to Otter Lake. This pond is located on the south side of Otter Lake <br />Drive approximately 800' west of the permitted compensatory storage area. The pond appears to <br />