Heap Leach Pads - Services Profile

The Smith Williams team has over 42 years of domestic and international heap leach pad experience. Our experience with heap leach pads includes permitting, geotechnical site investigation, surface water diversion design, water balance, pad and pond design, and pad closure. We have been involved in design and construction of over 60 heap leach pads, totaling over 300 million square feet (approximately 27.8 million square meters) of leach pad area. This experience has given us a thorough understanding of permitting, design, construction, and closure of heap leach facilities.

Types of Services - Heap Leach Pads

We provide a wide range of services related to heap leach pads that include the following:

• Alternative analyses and pre-feasibility studies that are focused on practical and cost-effective layout of the facilities, development of critical decision matrices, project progression planning, development of required scopes of work, and preliminary or order-of-magnitude cost estimation.
• Due diligence and bankable feasibility studies that are focused on development of detailed site element layout, production planning, detailed cost estimation (±15%) as a bankable basis.
• Geotechnical investigation, including borrow source identification, sampling/testing for design, design evaluation (slope stability analysis, settlement analysis, seepage analysis, etc.), and construction material balance.
• Hydrology and hydraulic analyses, including water balance, channel design, drop structure design, and spillway design.
• Third-party review, including review and critical analysis of designs performed by others with a focus on adding value to the project through technical and constructability reviews, targeting construction cost savings and/or operational and maintenance savings.
• Life-of-mine studies, including facility layout with phased development and construction, associated design, and financial analysis.
• Design of both valley-fill and conventional heap leach pads, including facility layout, foundation treatment, liner and leak detection systems, solution collection systems, and loading plans.
• Design of process water and storm water ponds, including siting, sizing, grading requirements, liner system, and leak detection system design.
• Design document generation including detailed design reports, technical specifications, and design drawings.
• Construction document generation and bidding, including development of special and general conditions, construction quantities (bid schedule), contract language, and bid adjudication services.
• Construction services, including construction management, construction oversight, field engineering and inspection, construction quality control (CQC), and construction quality assurance (CQA).
• Specialty studies/services, including forensic evaluation of heap leach pad, pond, and embankment failures; collection pipe and liner alternative evaluations under vertical loads up to 700 feet of equivalent heap height; thermal modeling of heap leach pads in arctic conditions; and pregnant solution management studies for valley-fill leach facilities.

Service Highlights - Heap Leach Pads

• Heap Leach Pad Design. Our experience with design of heap leach pads started in the late 1980s when leaching technology was in its infancy. A majority of the projects we worked on at that time were located in the state of Nevada. As leaching became widely used throughout the metals industry, our experience broadened and our experience was utilized as the leaching technology was transferred to foreign countries such as Peru, Chile, Uzbekistan, and Russia.
  
  Through our experience, we have found that all components of a heap leach facility must be carefully considered from cost, construction, operational, and environmental standpoints. Our designs include sound geotechnical, hydrologic, and hydrogeologic principles. In addition, we take pride in producing practical designs that are operationally friendly, cost effective, and utilize locally available materials.
  
• Geotechnical. During design, special consideration is given to geotechnical requirements for the facility. The foundation conditions are carefully evaluated to ensure that adequate stability of the heap can be maintained for the life of the facility. Geomembrane liners normally have relatively low friction coefficients in contact with low-permeability and fined-grained soil layers. This interface must be carefully evaluated for each project based on site-specific conditions. Protective and/or drainage layers are evaluated to ensure that adequate protection is provided for the geomembrane and to ensure that solution is consistently recovered from the heap even as the height of the heap increases.
  
• Water Balance. Our water balances are produced based on site-specific requirements and incorporate production rates, loading schedules, leach solution application rates, meteorological data, and solution processing rates to determine required process solution containment volumes, treatment requirements, and/or pond sizing requirements.
  We can offer several options for completing water balance analysis, including conventional modeling or dynamic systems modeling (DSM). The DSM modeling approach can add value to the project as it allows the operators to use the model and update it as conditions change. In addition, we can provide estimates for gold recovery based on the water balance information and metallurgical data provided by the client.
  
• Solution Handling Systems. We have completed designs for heap leach facilities that have external solution storage ponds and for valley-leach facilities that have storage within the heap. We have designed multiple solution collection and recovery systems in a variety of climates. Our most recent experience includes design of buried solution collection piping systems that minimize environmental exposure and allow for easier operation of the facilities.
  
• Surface Water and Storm Water Diversion. As part of our design process, we allow for diversion of surface water and storm water. Design and construction of the diversions are tailored to meet the site-specific requirements of the structure, which may be a temporary or permanent feature. Our team has experience with channels that have geosynthetic clay liners, synthetic liners, grouted and standard rip rap erosion protection, concrete culverts, CMP culverts, multi-plate culverts, sediment control, energy dissipation structures, and reinforced concrete channels and associated structures.
  
• Construction Quality Assurance and Construction Oversight. We believe it is very important to see that the materials utilized in construction and the construction methods meet the intent of the design. In addition, field conditions often vary from those in the design, and sound decisions are required to modify and/or refine the design to meet field conditions. Our engineers and technicians provide comprehensive CQA/CQC services as well as inspections to ensure work is completed in accordance with the drawings and technical specifications. Detailed specifications and quality manuals are utilized to define procedures, methods, and frequencies. CQA/CQC tasks are carefully planned and monitored to ensure full compliance with regulatory agency requirements. When required, fully equipped field laboratories are set up on project sites. All CQA/CQC activities are fully documented, as necessary, and the final construction report includes a complete record of all activities and compliance with construction methods and materials, technical specifications, drawings, and permit requirements. This document can be submitted to regulatory agencies and is often referenced for maintenance and operational activities.