2008-12-04_PERMIT FILE - C1994082 (32)

Home Browse Search

The embankment portion of the emergency spillway consists of a rock riprap lined trapezoidal channel, underlain with Mirafi 600X geotextile, as shown on Exhibit 13-4A, The emergency spillway is constructed to safely pass the runoff volume from the 100-year, 24-hour storm {see Addendum 13-3A-C). This is a conservative design - the spillway needs to safely handle the 25-year, 24-hour event (Rule 4.05.9 (2)(c)(ii)). The design also assumes that the principal spillway was plugged and inoperable. The emergency spillway design is presented in Addendum 13-3A-D. Summary The capacity of Pond 010 is attributed partially to the embankment and partially to the pond excavation. During passage of the 10-year, 29-hour storm the discharge through the principal spillway meets effluent limitations. In addition, there is no flow through the emergency spillway. The emergency spillway was designed and constructed to safely handle a storm event equal too, or larger than, the 25-year, 29-hour event. The embankment was constructed to be stable and provide adequate freeboard. Therefore, based on the design, this structure complies with the appropriate rules and regulations for a sedimentation structure, A toe drain and horizontal discharge system were constructed to collect any seepage and discharge below the embankment. Seneca Coal Company will periodically inspect the structure for sediment storage, structural integrity, and hazardous conditions. Maintenance or remedial work will be performed in accordance with the approved mine permit. Construction Summary The earthen impoundment and spillway configurations are pre-existing. The construction of Pond 010 was supervised on site by Mr. Chuck McCulloch, Senior Engineer - Operations, at the Yoast Mine. Mr. McCulloch assured all work was performed in accordance with the design and specifications. Mr. Altavilla generally inspected the structure daily during its construction to verify the pond's conditions during construction and upon completion for the as-built. The geotechnical consultant, Northwest Colorado Consultants, Inc. (NWCC) was also on site daily to do compaction testing, soil analysis, etc. Mr. Brian Len, P.E. (of NWCC), was on site on three separate occasions during the construction of the pond. NWCC's summary report for this project is located in Addendum 13-3A-E. Pond 010 was constructed as shown on Exhibit 13-9 A, As-Built Pond 010 and originally certified by Michael G. Altavilla, a registered professional engineer in the State of Colorado experienced in the design and construction of earthen impoundments. TR-35 13-3A.5 Revised 09/07