2017-08-08_HYDROLOGY - M2003016 - Laserfiche WebLink

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Heit Pit SWSP Page 2 of 5 August 8, 2017 Mine during the period of this SWSP will be replaced by fully consumable water leased from the City and County of Broomfield. In accordance with the letter dated April 30, 2010 from the Colorado Division of Reclamation, Mining, and Safety (“DRMS”), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The April 30, 2010 letter from DRMS required that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining related exposure of ground water. The DRMS letter identified four approaches to satisfy this requirement. A surety reduction was approved on March 23, 2010 by DRMS reducing the bond by $110,614 – representing the remaining 20% of the construction bond that was posted for the slurry wall. The remaining bond of $197,280 remains in place to cover the remainder of the reclamation plan. With the slurry wall installed and approved by DWR as meeting the State Engineers lining criteria for gravel pit, the Heit Mine is in compliance with the State Engineer’s requirements pursuant to § 37-90-137(11). Depletions You have estimated that up to 2.0 acres of ground water surface will be exposed at the Heit Pit in the settling ponds. Net evaporative depletions were calculated using a gross annual evaporation of 44 inches from the exposed water surface, with a credit of 9.05 inches for effective precipitation. The net depletion of ground water due to evaporation from the 2.0 acres of ground water exposed at the site was calculated to be 5.82 acre-feet. The settling pond water is used onsite for washing aggregate and dust control. The onsite production well, permit no. 66319-F (WDID 0205038), will also be used for dust suppression and the washing of mined aggregate. You have estimated that a total of 1.0 acre-foot of ground water will be used for dust control purposes at the site during this plan period. You have projected washing up to 485,000 tons of mined aggregate a year. The annual consumptive use for aggregate washing was estimated at 10.7 acre-feet using a depletion factor of 3 percent by weight because the mining is occurring inside the approved slurry wall liner and Pioneer does not have to replace the amount of water lost with the mined product inside the slurry wall, however Pioneer still anticipates washing the aggregates on site. There will be no concrete production at the Heit Pit during this plan period. The Glover method was used to lag evaporative and operational depletions to the South Platte River. The following parameters were used in the model: transmissivity (T) = 140,000 gallons per day per foot, distance (X) from the surface of the exposed ground water to the river = 2,750 feet for evaporation losses and 3,000 feet for operational losses, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 10,000 feet, and specific yield (SY) = 0.2. The location of the stream depletion is assumed to be perpendicular to the river. Lagged depletions for this plan period will total 17.42 acre-feet. Replacements The proposed source of replacement water for the Heit Pit is a total of 20.46 acre-feet of fully consumable effluent leased from the City and County of Broomfield (“Broomfield”). The existing lease was extended for a one-year period beginning September 1, 2017 and ending August 31, 2018. The replacement water will be released from Broomfield’s wastewater treatment plant (WDID 0201021), which is located on Big Dry Creek approximately 29.75 miles upstream from the Heit Sand and Gravel Mine. Of the 20.46 acre-feet of leased replacement water from Broomfield,