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sequence. Therefore, the times shown on these plans are for demonstration <br />purposes only. All plans show the same geographical area at the different points <br />in time. The external boundaries of the area are defined by existing topography <br />and other diversions that do not contribute to the area shown. <br />The sixth plan view of the Arequa Overburden Storage Area provided as an <br />Attachment shows, in a summary manner, the locations of the detention ponds that <br />now exist or which will be developed as the storage area is constructed. Not all <br />of these detention structures exist at any one time (however, most of them are <br />present for the majority of the period through to reclamation). The combination <br />of those structures that exist at any particular time is shown on the respective <br />temporal configuration (i.e, on one of the five other plan views). All drainage <br />from the disturbed Arequa Overburden Storage Area is directed to one or more of <br />these ponds. Pond sizes are listed both on the plan view and in the summary <br />report in pond- specific sheets. The summary of the computations lists the <br />pertinent subbasins and the flow routing destinations in the table labelled <br />"Arequa Drainage Routing." <br />In summary form, the Tables titled "Arequa Drainage Routing" also list the <br />cumulative flow volumes for each of the five configurations and compare this <br />amount to the total capacity of the detention and retention structures (the <br />tabulation lists "capacity" based on survey data and "runoff volume "). In every <br />case but one, the combination of ponds provide more than adequate volume to <br />completely-contain the 10 - year, 24 - hour precipitation event. The exception, Pond <br />SP -3, is a water detention pond for an upland diversion that is not designed to <br />hold all runoff from a 10 -year, 24 -hour event that enters it. Therefore the <br />objective to slow flow rather than to contain it. In some cases, the <br />impoundments will also contain the computed runoff from the 100 -year, 24 -hour <br />precipitation event. The ponds will be constructed with spillways designed to <br />safely pass the peak flow from the 100 -year, 24 -hour from the structure, just as <br />the contributing ditches are so designed. <br />The temporal "Configurations" of the drainage that are depicted in the plan views <br />are individually discussed next. <br />TEMPORAL DRAINAGE CONFIGURATIONS <br />Configuration #1 represents the topography as of late 1996 and shows the start <br />of the first lift of the overburden storage area, as well as the existing <br />drainage controls. While at present, in early 1997, Configuration #2 more <br />accurately represents the drainage status of the area, Configuration #1 is <br />provided for continuity. The diversion structure constructed in 1994, which is <br />shown in operation at this stage (this structure is designated "A -B" in the <br />drawing), is the one to, ultimately, be replaced. Runoff from the disturbed area <br />of the Arequa Gulch overburden storage area located downgradient of this <br />diversion currently enters, in almost its entirety, Ponds SP -1, SP -2, SP -4, and <br />the "Sump." Upgradient detention areas assist in limiting the inflow to these <br />depressions, and, when combined, these downstream depressions completely contain <br />flows from the 10 -year, 24 -hour event. This containment occurs prior to those <br />flows reaching the current diversion channels. At this point in time, a portion <br />of the upland flow (clean water) from undisturbed lands that formerly drained to <br />diversion A -B is diverted through the small detention pond SP -3 as a management <br />practice (see drainage between subbasins B1 -6 and B1 -7). <br />Drainage from the western border outside the Cresson Mine is directed to three <br />smaller sumps, a small area draining part of the "ready line" area is drained to <br />Pond SP -12, a small area south of, and separate from, the secondary crusher (B1- <br />9) drains across the clean water diversion buried culvert to Pond SP -1, and the <br />remainder of the Crusher Area (B1 -10 and B1 -11)) is drained to the recently <br />completed clay pit sump, designated Pond SP -13. Throughout the time periods <br />represented by all of the subsequent Configurations, the drainage from the <br />Crusher area will drain into Pond SP -13, in accordance with the drainage routes <br />4 <br />