Mining has been a major part of Arizona’s history since well before it was granted statehood in 1912 and continues to be a major industry. ERC has assisted in many aspects of the development of the Hermosa Project in southern Arizona. Some of ERC’s contributions have included completing a dam breach analysis of the mine’s TSF facility to ensure all people and structures will be out of the inundation area in the event of a dam failure and conducting hydraulic and geomorphologic assessments on local ephemeral streams to determine the impact any discharges from the mine’s water treatment plant may have. ERC has also aided the mine in their water management through the development of stochastic water balance models.
Barr Lake Spillway
The State of Colorado determined that the spillway at Barr Lake was inadequate to safely pass the inflow design storm. ERC was retained to evaluate existing and future conditions and design a spillway upgrade. ERC evaluated extreme precipitation conditions and defined the Probable Maximum Precipitation of 30 inches in a 48-hour period. When routed the storm produced a peak inflow rate of approximately 40,000 cfs with a total runoff volume of 13,000 acre-feet. Hydraulic modeling showed that a 185 spillway was required to safely pass the inflows while maintaining the required freeboard without raising the dam. The design included replacing the existing earthen spillway with a composite concrete, riprap and soil cement spillway. Additionally, over three miles of perimeter dikes were designed and constructed to control water levels during the design event. ERC completed design, permitting and construction management for the project.
Boulder Creek Master Plan
Boulder Creek, like many of Colorado’s front range streams, was significantly altered by the 2013 floods. ERC was part of a team of consultants tasked with evaluating the environmental and geomorphologic conditions of the stream and developing a master plan for future resilient improvements. ERC evaluated historic aerial photographs of Boulder Creek to understand evolution of the stream’s alignment during recent and pre-development periods. From this assessment, a range of natural sinuosity and meander wavelengths were defined and alignments for future restoration were identified. Typical cross-sectional geometries that replicate natural stream conditions were determined for low flow, bankfull flow and flood flow events. Critical habitat features along the riverine corridor were defined and recommended riparian buffer zones to protect the corridor from further development were determined.
Burlington Canal Headworks
ERC designed and oversaw construction to modernize the main Burlington Canal headworks off of the South Platte River. The diversion structure included four main crest gates (two 6 foot gates and two 12 foot gates) a 4’ x 13’ crest gate for bypass flow operations and a 4’x4’ sandout gate all with flow measuring capabilities. ERC’s work included hydraulic modeling, gate design, 404 and floodplain permitting and construction observation. The completed facility has the ability to pass and measure flows up to approximately 1,000 cfs. Gates were designed to fit within the original Burlington diversion structure while improving operational flexibility and safety.
Church Ditch Headgate 53 Retaining Wall
The Church Ditch hired ERC to repair a concrete-block retaining wall holding back high banks along the ditch in Arvada. The wall showed signs of heaving and overturning in several spots due to a poor design and the expansive soils in the area. ERC designed a concrete footer for the existing blocks and a system of steel angles to tie the blocks together. Approximately 800 linear feet of wall was repaired. The sections were between 6 and 10 feet tall. Design work included hydraulics, stability analysis, and permitting. ERC also managed the project by providing construction oversight.
Church Ditch Headworks
In 2016-2017, ERC managed the project to modernize the headworks structure of the Church Ditch on Clear Creek in Golden, Colorado. During the design phase, ERC conducted hydraulic modeling to size new gates. These included two 4-ft by 4-ft Fresno slide gates, a 4-ft Rubicon overshot gate for controlling upstream head, and a 4-ft slide gate for flushing debris. We also worked with the City of Golden and Jefferson County Open Space to permit the project. In the construction phase, ERC provided bid support to select a contractor then provided oversight and observation to ensure a smooth process. The structure includes security fencing, solar power and the ability to operate the gate and measure flows remotely.
Church Ditch Leyden Flush Structure
The Leyden Flush Structure is a turn-out point for Church Ditch to bypass excess flows and flush sediment and other debris from the upper system. In 2017, the Church Ditch hired ERC to design a new structure to replace the leaky gates, old concrete rickety bridges and a manual stop-log system. ERC designed a new structure to include two concrete headwalls, a 12-ft by 4-ft canal slide gate, a 4-ft by 4-ft Rubicon SlipGate for flushing, two steel access bridges, and security fencing. The gates are solar powered and remotely operable. Design work included hydraulic modeling and gate sizing. ERC also managed the project by providing construction oversight.
Community Ditch Improvements
The Community Ditch through Eldorado Canyon was historically one of FRICO’s most difficult sections to maintain of its 400 mile canal system. Bank sloughing, icing, seepage, liner damage and limited access all contributed to operational challenges in this section. FRICO hired ERC to develop a solution that would allow water to be conveyed through this ½ mile section in a more efficient manner. ERC’s solution replaced the open trapezoidal channel with a box culvert. The culvert was designed to fit within the narrow, meandering confines of the old ditch alignment, which allowed for only inches of tolerance in the box design. Maintenance access, which had not existed through this section, was provided on the top of the culvert. Design work included hydraulic modeling, modifications to intake gates and measuring devices, evaluation of rockfall hazards and Boulder County permitting.
Cripple Creek & Victor
The gold mines that eventually became the Cripple Creek & Victor (CCV&V) gold mine were first founded in 1892. It is currently the largest producer of gold in Colorado and operates using heap leach processes to recover gold from the ore. ERC has assisted CC&V in their water management for the past several years, by means such as creating complex stochastic water balance models for different phases of the mining operations to help the mine understand their water availability and use it most efficiently. ERC has also designed diversion channels, stilling basins, and sediment ponds for mining conditions as well as runoff channels for closure conditions.
Dam Breach Modeling
ERC has completed several dam breach analyses for municipal reservoirs and mining facilities in states such as Colorado, Arizona, Montana, and South Carolina, among others. The analyses have included sizing flow hydrographs resulting from a dam breach, mapping flood inundation extents (using both one-dimensional and two-dimensional modeling methodology), and determining the downstream hazard classification of each dam in respect to local regulations. ERC has also aided in the creation of Emergency Action Plans (EAPs) for the dams where the downstream hazard potential of the dam is found to be great enough to require one.
Denver Water Moffat Project
ERC was the stream morphology and sediment transport resource specialist tasked with evaluating impacts of Denver Water’s Moffat project on front-range and west slope stream systems. Channel evaluations encompassed over 200 miles of streams including the Fraser, Williams Fork, Colorado and Blue River on the west slope and South Boulder Creek and the North Fork of the South Platte River in the front range. Field work included site assessments, surveying and sediment sampling. Existing stream conditions and recent trends in channel evolution were evaluated from this field program, evaluation of historic conditions (aerial and ground photos, assessment of USGS stream gage shifts and repeated historic cross-sectional surveys for signs of aggradation or degradation) and numeric modeling. Modeling defined sediment supply, sediment transport capacity, effective discharge, the frequency of Phase 2 sediment transport and the magnitude of specified recurrence interval flood flows. Quantitative and qualitative stream impacts anticipated as the result of the planned Moffat project were determined by defining flow changes associated with the project and overlaying these hydrologic alterations on knowledge of the behavior and resiliency of the existing stream systems. ERC’s work included design of front-range and western slope stream mitigation aimed at providing functional stream uplift to offset project impacts following the stream functional pyramid approach.
El Sauzal Closure
Water management was a significant challenge at the El Sauzal mine given the site’s steep topography and flashy rainfall history. ERC was retained to develop a diversion and water management plan for the mine’s closure. Site and historic regional precipitation records were evaluated to define the magnitude of rainfall expected at various frequencies. A risk assessment was completed to consider flow frequency and facility sizing. Based on this analysis the mine selected the 100-year storm event for design. ERC’s design included over six kilometers of channel. Design also included sediment ponds, energy dissipation structures, stilling basins and rundowns. Due to the varied flows, slopes and ground conditions a number of types of channel armoring were required with armoring including vegetation, bedrock, concrete and geowebs.
Haile Gold Mine Stream Assessment and Monitoring
The Haile Gold Mine is going to alter flows in area streams within and adjacent to the mine development. ERC was retained to evaluate and document flows and stream conditions within the mine, adjacent to development and in areas outside of the zone of influence of the mine to facilitate the long-term assessment of potential mine impacts. Baseline studies included stream surveys, sediment sampling, bank stability evaluations and flow quantification. As part of this initial assessment ERC established permanent monitoring sites and designed a system of flumes, weirs and USGS type stream gages for flow measurements. Nested piezometers were designed and installed to inform the understanding of variability in surface flows and groundwater levels and their joint contributions to the riparian wetland system that exists on site.
Haile Gold Mine – South Carolina
Gold was first discovered in Lancaster County, South Carolina in the 1820s. In 2007 Romarco Minerals acquired the property and began the process of planning, designing and permitting a modern mine at this historic location. ERC provided water resource and environmental consulting services through feasibility, permitting and final design. Environmental work included baseline wetland delineations, habitat functional assessments and impact assessments. Water resource work included climate evaluations, hydrologic and hydraulic assessments, water balance modeling, water supply assessments, spillway design and erosion control. ERC was particularly instrumental throughout the permitting process given our technical and regulatory expertise. We worked with the Corps and their third-party contractor during the EIS process and helped secure permitting which has led to operations of what will become the largest gold mine in the eastern US.
Minera Panama – Panama
With its location in the rainforest and in an environment that receives nearly 5 meters of annual rainfall, water management is one of the critical technical challenges for Minera Panama. ERC was brought into the project due to its experience characterizing and developing water management plans for mines in locations with extreme climatic conditions. Our first task was to establish estimates of design rainfall events and associated runoff for short-term and extended wet cycle conditions. Our next challenge was water diversion. The main local river, the Rio Botija, ran right through the initial mining target and needed to be diverted around the planned pit. ERC’s design included a risk based assessment of tradeoffs between design storms and allowable pit flooding. The ultimate design required lining to minimize seepage and related instability adjacent to the pit wall for the 2 kilometer channel. Finally ERC developed an operational water balance model for mine personnel use in managing pit sumps and surface water dewatering systems.
Newmont Nevada Operations
ERC has provided water resource and environmental services to Newmont Mining Corporation at their eight Nevada sites. At all locations, accurate quantification of water requirements and needed storage capacity is paramount to efficient and safe operations. Climatological conditions have been quantified to allow the mines to understand both short-term and multi-month and year weather conditions that can impact water management. Probabilistic water balance modeling has been completed to predict operational variability at tailings storage facilities, heap leaches and operations that have multiple interlinked facilities. ERC’s stochastic models have been used for project planning, permitting, design and closure scenarios. We have been involved in overall water management of facilities including estimates of fresh water requirements and design of diversion channels and sediment control measures. ERC has also provided ecological planning and design services for heap cover/closure design, revegetation planning and landscape-based closure reclamation.
Standley Lake Monitoring and Dam Break
ERC is responsible for the on-going monitoring and reporting of Standley Lake Dam in Westminster, CO. This large, high-hazard dam provides water to nearly 300,000 residential and is located in a highly urbanized area. ERC completes monthly inspections, monitors reservoir and phreatic levels, evaluates crack gages and inclinometers and provides reports to dam owners and the State Engineers Office. For emergency planning purposes ERC has modeled dam breach scenarios and prepared inundation mapping for use by local emergency managers. We have designed repairs to ancillary facilities including outlet works, the dam’s spillway and the headgate structure that diverts up to approximately 1,000 cfs into the Lake.
Trout Creek Stream Assessment
Peabody Coal’s planned Trout Creek reservoir would alter the flow regime, sediment conveyance and stream conditions in Trout Creek. ERC was hired as part of the FERC process to evaluate baseline stream conditions and assess potential impacts of the planned on-line dam. Field work included stream classification, cross sectional and longitudinal stream surveys, pebble counts, suspended and bedload sediment sampling and bank stability characterization. Using this exiting conditions data, ERC projected sediment inflows to the reservoir and changes in sediment conveyance and channel morphology that could be expected to occur as a result of the dam.