2024-08-05_REVISION - M1986123 (4)

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Patrick Lennberg, Colorado DRMS 2 Kirtright Pit DRMS M1986-123 Reclamation Plan Amendment August 1, 2024 • In practice, based on the"O'Brien Pond" performance over the last several years, we're concerned the local alluvial groundwater flow into the ponds may no longer be reliable to maintain desirable pond levels. • Further, based on the lack of local alluvial groundwater recharge that followed the Spring 2023 Big Thompson River overbank flood events on the Kirtright Pit property, we have concerns the pond bank soils may be sealing up, preventing the intended and necessary interaction with the groundwater intended for these ponds. • Overall, the effect is reduced turnover of water in the ponds, reduced regular pond depths, and slower-receding/slower-recharging overbank flood waters, as well. • If the ponds adjacent to the O'Brien property are to be left in-place, it appears they would need to be rehabilitated for groundwater infill and recharge function. Kir&A7fit Pit F/oodv/ain • The O'Brien family and technical support team remain concerned that the Big Thompson River floodplain may have been adversely impacted by modifications to the Kirtright Pit properties in terms of function, limits/extents, overbank diversions and direction, and overbank velocities, in addition to the overbank flow post-flood impoundments discussed further in this letter. • The O'Brien family and team supports all appropriate, needed and required floodplain modeling and physical protections, including any indicated stability improvements, and including accurate documentation and approvals for additional floodplain earthwork. • We are concerned that the Kirtright Pit floodplain work is not covered under a current floodplain permit, and that there has been and continues to be potential for a jurisdictional gap between DRMS and Larimer County regarding floodplain management on the Kirtright Pit activities. • We understand there is intent for floodplain modeling of the property and proposed reclamation, and we request the modeling and analysis efforts be expedited, in order to best address the adequacy of the Reclamation Plan in leaving the Kirtright Pit properties in a stable, sustainable conditioned for planned land after-uses. • We have made the previous request that the Kirtright Pit Amendment provide for additional fill protection near the O'Brien residence, for maximum flood protection. • We recognize this must be within the requirements for good floodplain management practice, and are aware of the floodway proximity. • The floodway as illustrated by Weiland Inc mapping indicates fill can only be placed within approximately 200 feet of the O'Brien home, or an additional 150 feet beyond the existing residential fill area, without floodway encroachment. ft Thompson River Overbank Stora4e • We appreciated the operator's prior Exhibit F effort to provide an overbank drainage channel northeast of the O'Brien property, to evacuate overbank flood storage flows back to the Big Thompson River as the river flood stage recedes. • This is consistent with the prior O'Brien family request from last year that the property be provided with a system and means to actively drain flood waters from the property following a rainfall or flood event, consistent with the State Division of Water Resources requirements for 3-day (97 percent) and 5-day (99 percent) evacuation of water impoundment areas, unless covered by augmentation. DANGIROUX@TERRAMAX.US 0 (303) 929-3194