2014-11-14_PERMIT FILE - M2014043 (3)

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Albert Frei & Sons, Inc. Hatchery Pit Groundwater Monitoring Plan. Page 1 Permit # M- 2014 -043 The plans to install slurry wall liner around the 2 excavated areas and then backfill them present two different scenarios that have to be addressed in a different manner. They also have common issues that can be addresses in general. Phase 1 involves mining an alluvial deposit of gravel where the slurry will be place at grade around the area to be mined and backfilled. Phase 2 is mostly a terrace deposit with the water table located approximately 33 feet below the surrounding sur- face. The top of the slurry wall will be no higher then z31 feet below the surface. As part of the Certificate of Designation Albert Frei & Sons, Inc. needs from Adams County will include a groundwater monitor- ing requirement. The plans are to install 7 piezometers around the mine site which will be installed once the Notice to Proceed is received from Adams County (prior to mining commencing). Map Exhibit Gm -1 shows the approximate locations of the proposed piezometers. Their exact location may be different from the map due to installation problems but, they will be placed in the vicinity of the locations shown. Once installed, data will be collected on a monthly basis for 1 year to establish background water levels and the monitoring will then go to quarterly collec- tion as required in CD. The Groundwater Monitoring Data Analysis discussion explains how the data collected will be used to address the proposes mitiga- tion measures if problems occur to the surrounding groundwater table. This site and surrounding properties have existing groundwater and surface water features that impact groundwater elevations due to their proximity to the mine. On the north is an old gravel mine that was backfilled with inert materials similar to what is proposed at this site. Along the west side the Bull Seep paral- lels the property line from the SW corner, from where the prop- erty line turns back to the east, to the northwest corner where it leaves the site. The Bull Seep is a warm water slue that carries water year around. West of the Bull Seep is a slurry wall liner installed by the City of Thornton around a water storage reservoir that runs the entire length of the west side of the permit area. An old gravel lake is located in the northwest part of the mine area and previous owners installed lateral ditches and ponds along the interface of the terrace deposit and the alluvial deposit to divert water that comes to the surface, around the site and back to the Bull Seep. All of these water 1