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Ms. Jennifer S. Lindahl Page 3 of 9 <br />June 28, 2018 <br />shown in attached Table 1. Gross annual evaporation at these gravel pit locations is estimated to <br />be 44.27 inches per year. Net evaporation is defined as gross evaporation less the consumptive <br />use of water by vegetation that naturally occurred at the site prior to construction of the pit. <br />The historical consumptive use was assumed to be equal to the effective precipitation, which <br />was estimated based on the data from the Fort Lupton 2SE (ID 3027, record 1950-1976) and <br />Brighton 1 NE (ID 950, record 1976-2014) NOAA weather stations. The net evaporation rate for <br />the exposed water surface is estimated to be 2.92 acre-feet/acre, as shown on the attached <br />Table 1. <br />The projected maximum exposed groundwater surface area at each stage is described below. <br />Stage 1-The southern portion of Stage 1 is currently 6 acres which will continue through <br />the end of this SWSP amendment. The northern portion of Stage 1 was allowed to fill in June <br />2017 and the expose ground water surface area for all of Stage 1 is now a total of 13 acres (6 <br />acres from the southern portion and 7 acres from the northern portion) which will remain <br />throughout the end of this SWSP approval period. <br /> <br />Stage 2 - Stage 2 was allowed to partially fill in October 2017 and additionally fill in <br />December 2017 under free river conditions. The current exposed surface area of Stage 2 is 7 <br />acres and if additional free river conditions allow, or other fully consumable replacement water <br />supplies are obtained, the surface are of Stage 2 could increase to as much as 14 acres. <br /> <br />Stage 6A – Mining at Stage 6A is completed. Currently 3.0 acres are exposed, which will <br />exist through the end of the mining plan. <br /> <br />Stage 6B - Stage 6B previously exposed 1.0 acre which increased to 5.0 acres in March <br />2018 due to the fill during free river. The 5.0 acres exposed surface area will remain throughout <br />the period of this SWSP. <br />Stage 3 - Stage 3 currently exposes 1.0 acre and is expected to be reduced to 0.5 acres in <br />May 2018. Stage 3 is anticipated to be backfilled with overburden from other stages by the end <br />of May 2018. In the future Stage 3 will be completely backfilled and will result in no permanent <br />exposed surface areas or first fill depletions. <br />Stage 4 – RMCC is currently installing a slurry wall at Stage 4. The surface area at Stage 4 <br />is anticipated to be 1.0 acre from September 2017 through the end of this SWSP approval period. <br />Stage 4 will continued to be dewatered throughout the period of this SWSP. <br />The projected maximum net evaporation volume during the period of March 2018 through <br />December 2018 is 94.1 acre-feet, based on a maximum surface area of 36.5 acres, as shown in <br />the attached Table 2, column 2. <br />In addition to the evaporation, water is lost with the mined product removed from the mine <br />sites. RMCC projected that they will produce approximately 1,354,391 tons of gravel during the <br />remainder of 2018, as shown in Table 2, column 3b. The mining occurring during this SWSP <br />amendment will primarily occur at Stage 4. The gravel production may consist of one of the <br />following: gravel mined above the ground water table and washed, gravel mined below the <br />ground water table in a dewatered state and not washed, or stock piled material that is washed, <br />therefore the ground water lost with the mined product is estimated at 2 percent by weight. The <br />water lost with the mined product is projected to total 19.9 acre-feet. The estimated water <br />used for dust suppression is 1.2 acre-feet/month for March-July, 1.0 acre-foot/month for August,