2018-05-23_HYDROLOGY - M2004009 - Laserfiche WebLink

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Turnpike Mining Resources Page 2 of 7 May 23, 2018 During this SWSP period, depletions will consist of evaporation losses from the exposed ground water, water lost with the mined product, water used for dust control and dewatering. The pit will remain continuously dewatered until reclamation is completed. The dewatering trenches will be approximately 4 to 5 feet wide and oriented approximately parallel to Boulder Creek. A turbine pump mounted on a float will be used to pump the water from the trenches to the historic Plumb Creek, which is tributary to Idaho Creek a tributary to Boulder Creek, or directly to Boulder Creek. Upon completion of mining, the site will be reclaimed by installing a compacted clay liner on excavation slopes to prevent groundwater seepage. The proposed replacement of depletions for this site will come from a lease of fully consumable water from the City of Louisville. In accordance with the letter dated April 30, 2010 (copy attached) 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 requires 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 identifies four approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, you have indicated that a bond has been obtained for $1,114,000.00 through the DRMS for lining of this site to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, that would lead to the abandonment of the Pit. Depletions The projected depletions for the period of this SWSP consist of net evaporation from exposed ground water surface area, water removed in the mined product, dust suppression, and dewatering. The SWSP anticipates that ground water will be exposed within Cell 3, Cell 2A and Cell 2B as shown in Table 1 below: Table 1: Exposed Surface Area by Cell Time Period Cell 3* (Acres) Cell 2A (Acres) Cell 2B (Acres) Total Jan-May 2018 4.7-3.0 2.0 0.3 7.0 June-Dec 2018 0.0 2.0+0.3 5.0 7.3 Jan-Dec 2019 0.5 1.0 5.0 6.5 *The existing wash ponds in Cell 3 will be drained and moved to Cell 2B by the end of May 2018 (Figure 2) The Applicant proposed to replace evaporation from exposed ground water at the site based upon evaporation atlases in NOAA Technical Report NWS 33 and the SEO monthly distribution factors for sites below 6,500 feet, as shown in attached Table AI.1. Gross annual evaporation at the gravel pit location is estimated to be 39.00 inches per year. Net evaporation is defined as gross evaporation less the consumptive use of water by vegetation that naturally occurred at the site prior to construction of the pit. The historical consumptive use was assumed to be equal to the effective precipitation, which was estimated based on the data from the Longmont South (record 1973-2015) NCWCD weather station. The net evaporation from the exposed water surface is estimated at 2.36 acre-feet/exposed surface acre/year.