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Section 780.21 <br />• <br />816.72. Drainage control with respect to excess spoil stockpiles, <br />especially in relationship to the protection of surface water quality, <br />involves three fundamental concepts: 1) Placement of an underdrainage <br />system; 2) Diversions around the spoil; and 3) A drainage system on top of <br />the spoil. <br />The placement of a durable rock underdrain will help prevent saturation of <br />the spoil. This will reduce the amount of leaching activity and decrease <br />the impact on TDS concentrations downstream. The rock underdrain system <br />will be installed in accordance with 30 CFR 816.71(1) and 816.72(b) and is <br />more fully discussed under Section 81G.72(b) and in Exhibit 9, Excess Spoil. <br />Diversion structures for the excess spoil structures have been designed and <br />will be constructed and maintained in accordance with 30 CFR 816.43(f) to <br />safely pass the runoff from a 100-year, 24-hour precipitation event. These <br />diversion ditches are located on Eckman Park Hydrology (Map 14) and Permit <br />• Renewal Map 9A Hydrologic Features/Sediment Control and their specific <br />designs are set forth under Section 816.43 and shown on Figure 32, Permanent <br />Diversion Structures. The purpose of the diversions will be to divert <br />surface runoff from areas upstream of and surrounding the spoil around and <br />away from the spoil. This diversion will not only prevent erosion and <br />subsequent TSS loading of surface water, but will minimize saturation of <br />the spoil material so that leaching and possible TDS loading of surface <br />water is minimized. <br />• <br />89-23 780-156(a) Revised 02/22/89 <br />