2017-06-26-minutes-public-works-study-session

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KITTITAS COUNTY DEPARTMENT OF PUBLIC WORKS PUBLIC WORKS — BOARD OF COUNTY COMMISSIONERS STUDY SESSION STAFF REPORT ,STUDY SESSION DATE: June 26, 2017 TOPIC: Blackhorse at Whiskey Creek ACTION REQUESTED: Informational — No Action Required LEAD STAFF: Mark R. Cook RECOMMENDATION: Informational — no action required. BREIF NG SUMMARY: • Proposed revised storrnwater management strategy failed • County's flood study has been sent to DR Horton and Ellensburg Water Company BACKGROUND: During the past several winters, the onsite stormwater ponds supporting improved runoff within the Blackhorse subdivision have not worked properly since construction. It appears that the ponds are being influenced by a high water table. Responding to the height of the water table, DR Horton recently attempted to construct a shallow infiltration gallery (excavation filled with round rock) setting the bottom elevation approximately three feet below the existing ground surface. The excavation began filling during construction. Over the following weekend, groundwater filled the excavation to approximately eight (8) inches of depth. Staff met with DR, Horton on 06-15-2017 discussing the issue. Public Works (PW) does not have a plan from DR Horton at this time. Recently, PW conducted a lrmrted flood analysis of the DR Horton property (Black Horse) using a recently completed two dimensional flow model developed by the Flood Control Zone District of Whiskey Creek. The preliminary results were shared with the Board of County Commissioners several weeks back and later with two residents bordering Black Horse. Watershed Science and Engineering has since completed a final flood study that has been sent to the Board of County Commissioners, The final study was transmitted to DR Horton and Ellensburg Water Company on 06-20-2017. A meeting with DR Horton has not been scheduled at this time. Page 1 of 2 PUBLIC WORKS BOARD OF COUNTY COMMISSIONERS WORK SESSION STAFF REPORT