2011-09-08_REVISION - M1977342 (35)

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Applicability of the Probable Maximum Precipitation (PMP) Portion of the Study Titled "Site- Specific Meteorological and Hydrological Study of the Williams Fork Drainage Basin" for the Henderson Mill Tailing Pond Drainage Basin Background Applied Weather Associates has reviewed the report titled "Site- Specific Meteorological and Hydrological Study of the Williams Fork Drainage Basin" for application to the Henderson Mill tailing pond drainage basin. The review was conducted by Dr Ed Tomlinson who was the project manager and principle investigator for the Williams Fork study. Although the Williams Fork study included hydrological computations along with the PMP analysis, only the PMP portion of the study was reviewed for application to the Henderson Mill location. Basin Location The Williams Fork River drainage basin is located approximately 70 miles west - northwest of Denver, Colorado. The basin is approximately 230 square miles and is relatively regular in shape, about 25 miles long and eight miles wide. The basin ranges from about 7,800 feet in elevation at the Williams Fork dam to over 13,500 feet along the Continental Divide, the eastern boundary of the drainage basin. Figure 1 shows the location of the Williams Fork basin west of the Continental Divide. The Henderson Mill tailing pond drainage basin lies entirely within the Williams Fork drainage basin on the northeast slopes of the Williams Fork Range, approximately equal distance between the top of the Williams Fork River drainage basin to the southeast and the Williams Fork Reservoir to the northwest. The top of the Henderson Mill drainage is approximately 10,000 feet with the tailing pond having an elevation of approximately 9,600 feet. The basin drains basically from southwest to northeast. Figure 2 shows the basin and major sub - basins within the Williams Fork watershed. Page 1