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23 <br />require regular maintenance. <br />Culverts C-21 through C-25 direct undisturbed runoff south of the fan and substation <br />to the Purgatoire River. Sizing data is provided in Exhibit 19 -Sediment Design <br />Specifications. Culvert C-25 was inspected and found to be draining all runoff <br />adequately. The Operator is unsure if it is a drop structure or simple culvert. (It <br />would be necessary to excavate the inlet to determine what type of structure exists. <br />Pond 004 was surveyed in 1995 and found to have 7.19 acre-feet of volume. A 10 - <br />year 24-hour storm of the contributing watershed is 0.9 acre-feet, a 25 -year 24-hour <br />storm is 1.13 acre-feet and a 100 -year 24-hour storm is 1.5 acre-feet. There are 3.78 <br />acre-feet below the lowest dewatering hole, of which SEDCAD+ estimates there are <br />three years of sediment storage between 0.98 and 1.28 acre-feet. The Operator <br />retains the option to use all 4.03 acre-feet as a combination of sediment or permanent <br />pool storage. Sediment would be cleaned out at an elevation of 7,449 feet. The <br />Operator periodically stores drilling fluids in this pond to the elevation of the lowest <br />dewatering orifice and, depending on existing water storage in the pond, there would <br />be a maximum of 2.75 acre-feet (895,950 gallons) of fluids in this pond. The <br />duration of storage will depend upon the quality of the pond's water and the size of <br />subsequent storm events. This pond is a permanent impoundment on Colorado Parks <br />and Wildlife lands. Once drilling fluids have dried, and the pond is dry, the operator <br />will selectively clean the dried material from this pond and transport to DWDA #2 or <br />DWDA #3 for permanent disposal. The operator will take care to leave as much of <br />the vegetation as possible in this pond during any sediment removal operations. <br />The Operator constructed the preparation plant in the spring of 1984. After several <br />months of operation, it was determined that a plant process pond was required to <br />accommodate plant discharges. The Operator submitted a permit revision whereby <br />Pond 006 was taken out of the surface drainage plan and modified to a plant process <br />pond. Pond 007 was sufficiently oversized to handle the additional runoff formerly <br />reporting to Pond 006. <br />Exhibit 19 -Sediment Design Specifications and West Portal Drainage Plan, <br />confirm that Pond 007 (as -built) has sufficient storage capacity to contain 10 -year, <br />24-hour storm event runoff from pond 006 and 007 drainage areas, a total of 6.6 acre- <br />feet. In addition the Universal Soil Loss equation was used to estimate sediment <br />yield from these areas at 0.3 acre-feet/year (0.9 acre-feet for three years) at a <br />conservative 1.0 sediment delivery ratio. The total required capacity for Pond 7 is <br />therefore 7.5 acre-feet. Construction of the Bates Portal will add in incremental <br />amount of water (0.21 acre-feet) and sediment (0.01 acre-feet) to pond 7. Therefore <br />the required storage volume for sediment pond 007 is 7.7 acre-feet. As shown by the <br />stage volume curve for Pond 007, 9.2 acre-feet of storage is available in Pond 007. <br />The emergency spillway is adequate for passing peak 25 -year 24-hour flows from <br />both drainage areas while maintaining 1 -foot freeboard. Exhibit 19, Section 1 <br />contains SedCad documentations that indicate Pond 005 and Pond 007 can be <br />operated with the gate valves open and that sediment effluent limitation can be met. <br />However, precipitation events sampled in 2003 indicate that under current conditions, <br />Section 2.05 RN -6 10/17/2016 <br />