2024-02-01_HYDROLOGY - M2010071 - Laserfiche WebLink

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Goose Haven Reservoir#2 Expansion SWSP Page 3 of 7 February 1, 2024 requirement from January through November 2023 was 27.13 acre-feet according to the Applicant's accounting. DewaterinQ Dewatering of Cells 2A, 2, and 4 will continue throughout the construction of a compacted clay liner in Cells 2 St 4 and a clay liner and dam embankment in Cell 2A. Dewatering will occur through two hydraulically separated trenches. Water in the southern dewatering trench system will be discharged into sediment ponds and ultimately discharged into Boulder Creek via Lafayette's return flow canal from the Boulder and Weld County Ditch Headgate. The return flow canal is a concrete lined canal that discharges to Boulder Creek into the initial reach of the Boulder St Weld County Ditch downstream of the diversion structure, but upstream of the ditch headgate and overflow canal back to Boulder Creek, as shown on attached Figure 3. The discharge of dewatering water must be measured into and from the Boulder and Weld County Ditch to ensure it makes it back to Boulder Creek. Currently, it appears the water is metered on the property before it is discharged to the ditch. Dewatering is projected to occur continuously throughout the duration of this SWSP approval period. For the dewatering analysis, it is assumed that the sediment ponds do not allow infiltration and that the dewatered water is returned to Boulder Creek the same month the dewatering occurs. As long as dewatering in the trench systems remains continuous, the net accretions should be sufficient to replace the lagged depletions. At least three years prior to the planned cessation of dewatering, the Applicant must submit a dewatering analysis that shows how post pumping depletions will be replaced. As this analysis requires knowledge of the total volume dewatered, all dewatering activities must be metered with a totalizing flow meter that is recorded and reported on the submitted monthly accounting. Any renewal request must demonstrate that the dewatering is occurring continuously at a constant rate or must account for all lagged depletions and return flows from dewatering. Replacements Replacement water for depletions under this SWSP will come from fully consumable water owned by the City to be delivered to Boulder Creek from the City's wastewater treatment plant ("WWTP", WDID 0602300) or through release from the City's Goose Haven Reservoir Complex (WDID 0603998). This WWTP discharges to Coal Creek, a tributary to Boulder Creek. Intervening water rights between the site and the Coal Creek confluence are the Boulder St Weld County Ditch (WDID 0600515), Howell Ditch (WDID 0600536), and the Wittemyer Ponds (WDIDs 0606006 through 0606010). Should one of these rights place a call, the Applicant must ensure that water is released directly from Lafayette's Goose Haven Reservoir Complex. A transit loss of 15% has been assigned to the reach of Coal Creek from Lafayette's WWTP to the confluence of Coal Creek and Boulder Creek. A letter dated June 27, 2023 from the City committing to making replacements was provided to our office on December 7, 2023 and is attached to this letter. Attached Table A1.2, column 7 provides the required replacement schedule for these deliveries. Note that actual total replacements for January through November 2023 were 31.157 acre-feet according to the Applicant's accounting. Long-Term Augmentation Final reclamation at the site will consist of lined storage reservoirs for the City's use as a part of the Goose Haven Reservoir Complex. In accordance with the letter dated April 30, 2010 (attached) from the Colorado Division of Reclamation, Mining, and Safety ("DRMS"), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral