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McGrane Water Engineering, LLC <br /> } <br /> 4475 Driftwood Place•Boulder,CO 80301 •Phone:(303)917-1247 <br /> E-Mail:dennis@mcgranewater.com <br /> McGrane Water Engineering <br /> July 13, 2015 <br /> Mr. JC York <br /> J&T Consulting, Inc. <br /> 305 Denver Avenue, Suite D Via email at Ick ork aj-teonsit 1trng.com <br /> Ft. Lupton, CO 80621 <br /> RE: Loloff Pit- Slurry Wall Assessment <br /> Dear Mr.York: <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 '/z 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 />