2016-09-09_REVISION - M2004031 - Laserfiche WebLink

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As mentioned above,the Drain addresses infiltrating surface water, surface water from groundwater seepage, and groundwater. Mitigation effects will be monitored in existing wells. The previous Temporary Drain was successful in mitigating surface and groundwater, as documented in a DRMS site visit in the summer of 2015. The Temporary Drains were set at an elevation of 5,038. The new Drain will be at an elevation of 5,036.5 and will be more effective in lowering the groundwater levels. Groundwater levels will be tracked by measurements in the existing wells mentioned above. D. Al will be responsible for the operation of the Drain for as long as the site is under DRMS permit. The City of Thornton is aware of the Drain and will continue operation of the Drain. E. Al agrees that the elevations stated in the Tetra Tech Memo are accurate as they were surveyed by the Al surveyor. Furthermore, Tetra Tech agrees that the HZMW-2 groundwater data mentioned in the Equity Response is important. That is why Al plans to monitor groundwater levels in HZMW-2, HZMW-11 a, and HZMW-11 b after completion of the Drain. The depth to groundwater of 3.75 feet mentioned by Equity is at well MW-2. At well MW-11 a, pre-slurry wall groundwater levels were near the surface. At well MW-11 b, pre-slurry wall groundwater levels were within approximately 1-foot of the surface. F. Based on interviews with Mr. George McDonald(the Fulton Ditch Superintendent),turnouts from the ditch in the non-irrigation season are typically 5 to 6 cubic feet per second(cfs). Tetra Tech measured flows through the Temporary diversion pipes(at elevation 5,038)after the turnout had been closed between March 9 and April 14,2016. The average flow during this period was 1.2 cfs. The maximum flow was 2.4 cfs. The minimum flow was 0.56 cfs. G. Al will reclaim and maintain the channel of the Bull Seep as required under the USACE permit. H. As documented in the DRMS site visit in the summer of 2015, (inspection performed by the DRMS on August 19,2015),the Temporary Drain at elevation 5,038 had successfully lowered surface water at the site. At the recommendation of Division staff,the Drain will be lowered to an elevation of 5,036.5 to improve the situation. The Equity response is correct in mentioning that there were wetlands on the NW corner of the property. However, Equity fails to note the wetlands were mapped adjacent to the NE part of the Orr property. These were mapped to the property line and likely extend onto the Orr property. In addition, as mentioned above,groundwater levels in wells HZMW-11a and HZMW-11b were at or within a foot of the ground surface prior to slurry wall construction and relocation of the Bull Seep. Furthermore, a test hole drilled on the Orr property during March of 2004 showed groundwater at a depth of approximately 1 foot(Test Hole TH-24 reading on March 31,2004). Wetlands likely extended on the Orr property over a much greater area than the NW corner. Again the Bull Seep will be reclaimed and maintained as required by the USACE permit. Al has no obligation to maintain the Fulton Ditch. The re-alignment of the Bull Seep was done with the concurrence of the Fulton Dich Company and the previous owners of the Orr property. I. As mentioned above,the Drain addresses infiltrating surface water, surface water from groundwater seepage, and groundwater. Mitigation effects will be monitored in existing wells. It appears that Equity is misrepresenting the 11-foot increase by comparing water levels in HZMW-2 to levels in in HZMW-11 b. Water level variations must be made using the same well, not by mixing readings from different wells. J. If the pipes are blocked at the outlet and the river spills into the reservoir,the Drain is equipped with a gate that can be closed, blocking flow onto the Orr Property. Furthermore, much of the Orr property is within the 100-year flood plain and will be subject to flooding. Consequently, a flooding scenario with a river elevation 5040.8 will likely result in flooding of the Orr property without regard to the Drain. PA23514\133-23514-16002\Docs\Memos\Response to Equity Funding\AI Hazeltine Equity funding response 2016 09 23 Final.docx 2 Tetra Tech