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The access road and railroad spur are important to the operation of the cement manufacturing facility and <br />will be protected from major damages during a 100 -year flood event. Culverts are provided where the <br />road and railroad crosses an existing arroyo or creates a sump condition with an embankment. Multiple <br />culverts are specified and are designed with low head (that is, headwater -to -depth ratio of 1.5 or less) to <br />minimize erosive velocities at the outlet. This approach also minimizes turbulence in the transitions into <br />and out of the culverts, because the broad, shallow flow of the natural arroyos is mimicked. Each culvert <br />will have either flared - end - sections or saddle headwalls to facilitate transitions. Erosion at the outlet will <br />be minimized by constructing rock - lined, pre - formed scour basins. Locations and details of the culverts <br />are provided in Appendix F. <br />Storm water runoff from the embankments will be collected in ditches located at the base of the <br />embankment and conveyed to the nearest arroyo culvert. The potential for ditch erosion will be controlled <br />by ditch -check structures (that is, small rock checks or geo- synthetic check dams with heights up to 2 <br />feet). Embankment slopes will be protected from erosion with vegetation. Steeper slopes will use either <br />geotextile wrap or geogrid reinforcement to protect the slope. <br />Protect the Plant Operation From Storm Water Run On <br />Protection of the cement manufacturing area will include the use of diversion ditches and an internal <br />storm drainage system. <br />Diversion ditches are designed to convey a 100 -year flood event with a maximum depth of 2 feet plus 1 <br />foot of freeboard. Disturbed surfaces and embankment slopes will be seeded to protect them from wind <br />and rain erosion. Depending on the longitudinal slope of the diversion ditch, additional erosion protection <br />may be required in the flow area, such as a rock lining or reinforced turf mat. Where diversion ditches <br />discharge into existing arroyos, the transition area is protected by riprap to prevent excessive erosion. <br />Specifications for diversion ditches are provided in Appendix F Surface Water Management Plan. <br />Diversion Ditch #1 will captures and conveys storm runoff from a relatively small area west of the plant <br />and north east of the mining limit for years 1 through 5. This runoff is discharged to Arroyo B via the <br />culvert under the railroad tracks. <br />Diversion Ditch #2 captures and conveys storm runoff from Arroyo "E" and diverts to Arroyo "G." where <br />the discharge is protected by riprap transition. Diversion Ditch #2 is sized for runoff from the tributary <br />area of 475 acres within Arroyo "E." When mining progresses from year 6 on, the area tributary to the <br />Diversion Ditch decreases to about 75- acres, because the year 6 mining operation will capture and divert <br />storm water to the in -pit pond located in year 1 panel. Therefore, Diversion Ditch #2 will have excess <br />capacity from about year 6 through the remaining mine life. <br />To capture storm runoff within the plant area, a storm sewer system has been constructed with a 25 -year <br />flood capacity. This design frequency exceeds typical storm water standards for industrial land uses, often <br />in the 5- to 10 -year design frequency. The system consists of curb and gutter, storm inlets, and storm <br />sewer to collect local runoff for discharge to Arroyo "F" Sediment and Detention Pond (see below). An <br />oil /water separator device (or an alternate oil control measure) may be constructed with the storm sewer <br />before discharging into the Arroyo "F" Sedimentation and Detention Pond. The discharge into the pond <br />will be protected by riprap transition. <br />Control Runoff from Disturbed Areas <br />Storm runoff collected by the storm sewer in the plant area and runoff from the fill area is discharged to <br />Arroyo "F" Sediment and Detention Pond. Runoff is temporarily stored to facilitate sedimentation of <br />Technical Rev No. 4 <br />April 26, 2013 <br />D -9 <br />