Laserfiche WebLink
Mr. Michael Cunningham <br /> CEMEX Sandstone Quarry—Response to Preliminary Adequacy Review Comments <br /> Permit M-1977-361 <br /> July 1, 2014 <br /> CEMEX Response 6: The one road that will remain has been added to the revised Figures E-1, E-2, and <br /> E-4 attached to this letter. <br /> Comment 7. The Reclamation Plan Map shows the outlet channel will have erosion control features. <br /> Please specify the types of erosion control features to be used and indicate if the outlet channel will be <br /> armored. <br /> CEMEX Response 7: Hydromulch, flexible growth media, or erosion control blanket will be applied to the <br /> steep reclaimed slopes along the re-routed irrigation ditch. Erosion control blanket was used for <br /> reclamation cost estimates for these areas. The outlet of the drainage culvert under the irrigation ditch will <br /> be riprapped; a total of 97 cy of riprap was included in the reclamation cost estimate in Section D-15. <br /> Comment 8: Please demonstrate that the 48"culvert in the outlet channel is adequate to convey surface <br /> runoff from a 100 year/6 hour storm event, provide any calculations used to size the outlet channel and <br /> culvert. <br /> CEMEX Response 8: The contributing watershed for the outlet culvert was delineated based on an aerial <br /> topographic survey. The total watershed is 31.3 acres. An area-weighted composite curve number(CN) <br /> was calculated for the watershed based on the composition of soils present. The undisturbed upgradient <br /> watershed includes both the Baller(CN 85)and Sixmile (CN 80) soil types. The pit highwalls were <br /> assigned a CN of 96. All 2:1 slopes were assigned a CN of 85, and the reclaimed pit floor(sloping at 2%) <br /> was assigned a CN of 78. The composite curve number for the watershed is 83.5. The 100-year, 6-hour <br /> storm was modeled with a Type—II rainfall distribution using SEDCAD 4.0 by applying the rainfall depth <br /> (4.01 inches)to the watershed. The 4.01-inch point rainfall is the site specific 100-year, 6-hour rainfall <br /> amount as specified in NOAA Atlas 14. The modeled discharge for the 100-year, 6-hour storm is 108.5 <br /> cfs. The SEDCAD Culvert Utility was used to size the culvert. The 48-inch diameter corrugated metal pipe <br /> culvert modeled in SEDCAD will pass the 100-year, 6-hour design storm with a headwater to depth ratio <br /> of 1.5. The headwater to depth ratio is the ratio of maximum headwater(measured from the culvert invert) <br /> to the culvert diameter. Generally, culverts should be sized to pass the design storm with a headwater to <br /> depth ratio of 1.5 or less. The culvert shall be installed at a 3% slope, which is slightly steeper than the <br /> inlet and outlet channel, which will promote self-cleaning of sediments. <br /> The culvert outlet channel was modeled with the SEDCAD channel utility to determine the channel <br /> capacity and the stable riprap size gradation (See Appendix D-1). The outlet channel was modeled with a <br /> 3.0-ft bottom width having 2:1 sideslopes and the proposed 1.7%channel gradient. SEDCAD modeling <br /> results in a stable riprap gradation characterized as follows: Dmin: 3 inches, D50: 6 inches, Dmax: 9 <br /> inches. <br /> 6.3.5 Exhibit E-Map <br /> Comment 9: The Applicant submitted a map labeled as Figure E-1: Sandstone Quarry Existing <br /> Topography. Please clarify is this map was intended to serve as the Mining Plan Map. Either revise <br /> Figure E-1 or provide a separate map which includes the following elements: (a) Signature of the person <br /> who prepared the map; (b) Label the names of owner(s) of record of the surface area and of the land <br /> within two hundred feet of the affected area, identify the owner of the substance to be mined, and the type <br /> of structure and owners of record of any permanent man-made structure within two hundred feet of the <br /> affected area; (c) Outline and label all major features to be used in connection with the proposed <br /> operation including:existing roads, topsoil stockpiles, overburden stockpiles, product stockpiles, etc.; (d) <br /> Indicate the direction material extraction will proceed. <br /> CEMEX Response 9a: Figures E1, E2 and E3 are preliminary and conceptual drawings for permitting <br /> purposes and should not be used for construction. Figure E1 is not a formal Mining Plan, but rather a <br /> conceptual drawing for permitting purposes that shows the general progress of future mining. Water and <br /> Page 3 of 4 <br />