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Exhibit D <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 temporarily capture and convey storm runoff from a relatively small area west of <br />the plant and north east of the mining limit for years 1 through 5. Runoff will be conveyed under the plant <br />access road and railroad and discharged to Arroyo "F" Sediment and Detention Pond (see below). <br />Diversion Ditch #2 will capture and convey storm runoff from Arroyo "B" and divert to Arroyo "G." <br />where the discharge will be protected by riprap transition. Diversion Ditch #2 is sized for runoff from <br />the tributary area of 475 acres within Arroyo "E." When mining progresses from year 6 on, the area <br />tributary to the Diversion Ditch decreases to about 75-acres, because the year 6 mining operation will <br />capture and divert storm water to the in-pit pond located in year 1 panel. Therefore, Diversion Ditch 92 <br />will have excess capacity from about year 6 through the remaining mine life. <br />To capture storm runoff within the plant area, a storm sewer system will be 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) will 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 will be <br />discharged to Arroyo "F" Sediment and Detention Pond. Runoff will be temporarily stored to facilitate <br />sedimentation of particulate matter before being released to Arroyo "E." The Pond will provide sufficient <br />storage for the entire 25-year, 24-hour flood event, plus sediment loads. Stored runoff will be tested for <br />pH, total suspended solids (TSS), oil and grease, chemical oxygen demand (COD), and, potentially, <br />blasting residuals (such as nitrates) and reported quarterly. <br />Manage Process Water <br />Although process water management is not part of this 112 Application, process water discharges were <br />considered when developing the surface water management plan. Anticipated discharge rates were used <br />to approximate the area required for an evaporative pond located north west of the plant area. Possible <br />locations for the evaporative pond were determined to have no effect on the surface water management <br />plan or the leach field for wastewater discharges (see below). <br />Manage Domestic Wastewater <br />Domestic wastewater management is not part of this 112 Application, but wastewater discharges were <br />considered when developing the surface water management plan. Anticipated discharge rates were used <br />• to calculate the area required for a septic system leach field located north west of the plant area. Possible <br />1180-Mine Permit Exhibits (Jul.05.02)FINAL.dOc D-10 <br />July 8, 2002