2015-07-10_INSPECTION - M1999034

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PERMIT #: M-1999-034 INSPECTOR'S INITIALS: TOD INSPECTION DATE: July 2, 2015 This inspection was conducted to observe and evaluate the site conditions described by the City's representative. During the inspection, the Division observed an earthen berm along the western bank of the River (Photo 1). The earthen berm was created by the Urban Drainage and Flood Control District (UDFCD). The Division believes that the earthen berm was created by UDFCD in an effort to keep the River within its channel. The earthen embankment between the River and the reservoir complex appeared to have been damaged downgradient from the southeast corner of Phase 2 (Figure 1). It appeared that the damage to the UDFCD earthen berm provided a path for flow to be diverted from the River around the berm, thereby allowing the flow to overtop the southeast corner of reclamation phase 2 (Figure 1). During the inspection, the Division observed a breach between the River and Phase 2 (Photo 2). The breach occurred in the southeastern portion of phase 2 (Figure 1 and Photo 2). The breach was estimated to be approximately 150 feet wide. The breach has headcut back to the River, eroding the land between the River and phase 2. The breach eroded the upper portion of the slurry wall. A smaller breach previously occurred at the same location during the fall 2013 flood. The Division observed the fall 2013 flood damage during a previous monitoring inspection conducted in June of 2015. The Operator never repaired the 2013 flood damage. A headcut feature is visible on a Google Earth image dating back to October 2013, just after the 2013 flood. A large erosion channel is visible on the October 2013 Google Earth image. The feature spans from the southeast corner of phase 2 and towards the River (October 2013 Google Earth image). The October 2013 and October 2014 Google Earth images clearly show erosion of the land located between the River and Phase 2. The October 2014 Google Earth image clearly shows deposition of material into the bottom of Phase 2. After reviewing the Google Earth images it appears that the UDFCD earthen embankment was repaired shortly after the 2013 flood; however, it appears that no repair work ever took place at the breach and headcut. The most recent breach occurred at the same location as the 2013 flood breach. The 2013 flood damage provided a preferential path for flow, the most recent occurrence caused the breach to be enlarged and divert a portion of the River through the reservoir complex. The breach in turn has diverted a portion of the South Platte River flow into phase 2 and throughout the reservoir complex. Figure 1 on page 5 details the flow path of the diverted flow. During the inspection the flow in the South Platte River was approximately 2400 to 3000 CFS (Chart 1). The flow of the River diverted into the pit was estimated to be approximately 1/3 of the current river flow (approximately 750 to 1500 CFS). The water from the River was flowing through the breach into phase 2. The diverted flow had completely filled all 3 phases of the reservoir complex. After all 3 phases were inundated, water was flowing over the earthen berms between all of the phases. The diverted flow was circuiting through the reservoir complex and draining back to the River. The diverted flow was overtopping the earthen embankment between phases 2 and 3. A portion of the earthen embankment between phases 2 and 3 had been completely eroded away (Photo 3). After the diverted flow entered phase 3, the water flowed overtop of the earthen embankment between phases 3 and 4 (Photo 4). After the diverted flow entered phase 4, the majority of the flow returned to the main River channel through an emergency spillway. The emergency spillway was constructed along the eastern side of Phase 4 (Photo 7). Some of the excess flow is overtopping Phases 3 and 4, flowing directly into the River (Photos 5 and 6). The flow overtopping Phases 3 and 4 has damaged land between the River and the reservoirs (Photo 5). On July 8, 2015, the Division received an email from the Operator's representative (enclosed). In the email the Operator's representative notified the Division about a pit breach in phase 3. The Operator's representative explained that the eastern bank of phase 3 had failed. The Operator's representative explained that water was flowing from phase 3 back to the River. The Division conducted a follow up inspection on July 9, 2015, to observe and evaluate the site conditions described by the Operator's representative. Aggregate Industries - WCR, Inc., was notified of the inspection date and time. Aggregate Industries was not present during the follow-up inspection. The City of Thornton was represented by Josh Redman, and Walt Jenkins during the follow-up inspection. During the follow-up inspection, the Division observed a breach between the River and Phase 3 (photo 8). The breach occurred in the eastern portion of phase 3 (Photo 9). The Page 3 of 11