Trends Summer 2017 - Page 6

on ours,” he said. “We worked together to accomplish multiple goals.” Best-Laid Plans The East Side Detention Facility (ESDF) high-hazard dam in northern Colorado is aimed at reducing flood-related damage. In 2012, Ayres conducted the site investigation for the dam, analyzing 14 locations. The site and design had to meet requirements of the Federal Emergency Management Agency and State Engineer. Groundwater testing and soils logs helped pinpoint the location, and Ayres civil engineer Chris Pletcher said groundwater was so far below the proposed construction site that it was eliminated as an issue. But when excavation started in 2014, water seeped into the site. New testing found that groundwater levels were 8 to 10 feet higher than during the pre- construction testing. “Back in 2013 we had all that flooding here,” said Stan Myers, manager of the Boxelder Basin Regional Stormwater Authority. “We had a week of solid rain, which just never happens out here. A few months after those rains, people started reporting that groundwater was at record levels.” Pletcher noted the original permitting didn’t miss anything: “It wasn’t there to be caught. There was a different condition when construction began that was going to be a long-term problem.” Because the underlying issues had changed, Ayres had to restart the permitting process during construction. And because changes during construction cost money, “we added to our permitting effort on the fly to keep the project moving,” Pletcher said. The project needed dewatering permits from the Colorado Division of Water Resources (CDWR) as well as augmentation permits to replace water lost to evaporation during construction. Despite the groundwater issues, construction moved forward, and the 30-foot-tall ESDF is complete and ready to contain floodwaters. Ayres continues to monitor groundwater levels at the site. The high groundwater levels also led to concerns related to Colorado water rights law. It’s a complicated law involving who gets to use water first and how much. Myers noted that water rights in the Boxelder Basin revolve around Colorado-Big Thompson water transfer shares. Water that evaporates from the ESDF must be replaced, potentially requiring a formal augmentation plan to be submitted to CDWR. “Our hope is that when hot weather hits, groundwater levels will drop, and we may not have to augment at all,” Myers said. “Another thing we’re contemplating is to narrow up the channel to keep the flows from spreading out so much and losing water to evaporation.” The Ayres team will work with the Authority to keep the project and any future permits on track. “Chris has always been a proactive team member and really takes ownership of things,” Myers said. 6│ TRENDS