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MEMORANDUM _. BBA <br /> --� Water Consultants, Inc. <br /> To: Derek Slack, P.E. and Neil Thomson, P.E. <br /> E-470 Public Highway Authority (E-470) <br /> From: Austin Malotte, P.E. <br /> Subject: Sandy Acres Ponding—June 2020 Status <br /> Job: 9607.00 <br /> Date: June 24, 2020 <br /> This memorandum summarizes information collected to-date and recommended next steps <br /> regarding mitigation of water ponding issues at E-470's Sandy Acres Pit. <br /> Overview and Background Information <br /> The Sandy Acres Pit is a backfilled, inactive,unlined gravel pit located on E-470's property in the <br /> Southeast `/a of Section 26, Township 1 South, Range 67 West of the 61h P.M. near Henderson, <br /> Colorado. The former pit was permitted under Colorado Division of Reclamation, Mining and <br /> Safety (DRMS) as "Henderson Development" in Permit No. M-1980-110. DRMS approved <br /> Amendment No. 6,AM-06 on September 3, 2014 and Technical Revision No. 3 on May 12,2015, <br /> permitting E-470 to backfill the Sandy Acres Pit with washed fines from a neighboring gravel pit. <br /> The backfilling work was completed by July 1, 2016 in accordance with the conditions of the <br /> permit amendment and technical revision. <br /> Since 2014,E-470 has replaced stream depletions associated with historical evaporation of ground <br /> water exposed by the former gravel pit pursuant to a series of Substitute Water Supply Plans <br /> (SWSPs),I Stream depletions associated with Sandy Acres Pit are currently replaced pursuant to <br /> an October 25, 2019 letter from the Colorado Division of Water Resources approving SWSP <br /> operations through September 30, 2024. <br /> During a 2019 site inspection, DRMS staff noted standing water at the base of the (backfilled) pit <br /> at the southern end of the site. Representatives from E-470 and BBA Water Consultants, Inc. <br /> (BBA) visited the site and confirmed the presence of ponded water on top of the backfill material <br /> at Sandy Acres. <br /> Evaluation and Mitigation Efforts To-Date <br /> Since first identifying the ponding issue at Sandy Acres, E-470 has taken several proactive steps <br /> to identify the source or sources of the ponded water. This section describes E-470's activities to- <br /> date, including mapping and data reviews, field investigations, and a monitoring well program. <br /> 1 SWSP ID 3102 pursuant to§37-90-137(l 1)C.R.S. <br />