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McGrane Water Engineering, LLC <br />4475 Driftwood Place • Boulder, CO 80301 • Phone: (303) 917-1247 <br />E -Mail: dennis(dmcgranewater.com <br />July 13, 2015 <br />Mr. JC York <br />J&T Consulting, Inc. <br />305 Denver Avenue, Suite D <br />Ft. Lupton, CO 80621 <br />RE: Loloff Pit - Slurry Wall Assessment <br />Dear Mr. York: <br />MLGrene Water Engine,ern,y <br />Via email at: jc\ork'a;j-tconsulting.coru <br />The Loloff gravel pit mine is located approximately 1 mile east of Greeley, Colorado in Section <br />4, Township 5 North, Range 67 West of the 6th principal meridian. The site is located <br />approximately `/2 mile north of the Poudre River, approximately 5 miles upstream of the <br />confluence with the South Platte River. The pit is currently being mined under permit M-1985- <br />112 by Loloff Construction Company. <br />J&T Consulting, Inc. (JT) requested that McGrane Water Engineers, LLC. (MWE) determine the <br />hydrologic impacts of installing a slurry wall around the Loloff pit during reclamation. <br />Anticipated impacts include a rise in the water table on the up gradient side of the slurry wall <br />compared to predevelopment conditions and a decline in the water table on the down gradient <br />side. Water level increases to within 10 feet of the surface on the up gradient side of the pit <br />could flood existing structures such as basements or cause water logging and phreatophyte <br />growth. A decline in water levels on the down gradient side could reduce the aquifer saturated <br />thickness and well yields if pumping rates are already maximized. <br />Results <br />Using a MODFLOW model with reasonable boundary conditions and aquifer properties, MWE <br />determined that the maximum increase in water levels up gradient from the mine will be <br />approximately 2 feet, and the maximum decrease in water levels down gradient from the pit will <br />be approximately 2 feet. The average depth to groundwater for 79 wells with reported water <br />levels located within the model area (approximately a mile from the pit in all directions) is 16 <br />feet. However, there are several wells located within the up gradient area of influence (greater <br />than 0.5 feet increase) that have reported water levels of less than 10 feet. Table 1 shows the <br />impacted wells located within the area of influence. <br />