• Foundation conditions ranging from very soft waste clays and organic highly plastic deltaic or alluvial clays (e.g., some gypsum stacks in Florida, Louisiana), to overconsolidated glacial clays or stiff lateritic clays (e.g., gypsum stacks in Iowa, Canada and Brazil), to varying stratigraphic layering of pervious sands, clayey sands and/or bedrock formations (Florida, Middle East). Our experience with gypsum ponds located on soils containing a wide range of calcareous material include Al Kaim, Philphos and Texasgulf. Further, limestone is the bedrock for all projects in Florida.
  
• By-product gypsum resulting from varying chemical processes (hemihydrate and dihydrate phosphoric acid processes, flue gas desulfurization, etc.) using phosphate rock from miscellaneous sources (Florida, Jordan, Wyoming and Idaho, Morocco, etc.), with both highly acidic and neutralized process waters.
  Disposal ranging from simple discharge into open pits or natural depressions, to dry-stacking and wet-stacking methods (using the upstream method of construction).
  Sea water to slurry and transport the gypsum (Philphos plant in Leyte, the Philippines).
  
• Management of gypsum stacks in hot, cold and temperate climates. One-point slurry discharge in alternating compartments versus rim-ditching techniques that are used to readily drain gypsum to facilitate starter dike construction and to maintain the surface of the stack ponded and, hence, promote evaporation and improve the water balance of the plant. Stage decant versus fixed vertical riser decant structures or simply overflowing on the gypsum stack slope. Projects in arid climates in Australia, Iraq, Jordan, Syria and Wyoming.

We have worked on siting, layout, design and management of a large number of gypsum stacks and have been directly involved in permitting, as well as geotechnical, environmental, safety, surge, water balance, operating and economic evaluations.

A large number of our clients have retained us on a permanent consulting basis and, hence,our period of service for many of these projects has spanned over a period of nearly 20 years.

Over the years, Ardaman has undertaken extensive research and testing programs to overcome difficulties associated with the design and long-term performance of underdrain leachate collection and impervious liner systems used beneath some storage/disposal facilities and subjected to adverse environmental conditions. Some experience is from gypsum waste disposal systems located outside the United States where regulations are flexible, but where relatively pervious foundations, critical hydrogeologic conditions and the proximity of vital drinking water supplies necessitated the use and implementation of sophisticated liner systems and drain fields to prevent groundwater contamination.

Technical difficulties associated with clay liner or synthetic liner installation and selection of drain systems that perform satisfactorily throughout the active life of the facility without being adversely affected by process water necessitated the in-house development of specialized test equipment and testing procedures. Our research shows that some clays are not affected by process water leaching; some are favorably affected as a result of cementation and/or ion exchange while others are adversely affected by dissolution and/or ion exchange.

Ardaman engineers have developed specially designed column tests for leachate collection material evaluation that allow recirculation of process water. Probes are installed at various depths in the soil column of potential drain material to determine the head loss and changes in permeability along the full length of the tested sample. Typical results of two samples tested in this way reveal one of the soils is not affected by process water leaching, the other is shown to be adversely affected to a significant extent due to reaction with process water and the formation of various gels and crystals causing clogging. Finding a suitable soil for use in an underdrain system that performs its intended use over the life of the facility requires extensive testing. It is extremely important that drain materials selected be compatible with generated process wastes.

Ardaman has performed extensive long-term testing of synthetic liners to simulate long-term performance under stress in the adverse process water environment beneath gypsum stacks, and to determine the resistance of various synthetic liners to stress-induced corrosion. Results indicate that non-resin components of a given generic liner may be affected by process water even when the base resin is inert, thus underscoring the need to test specific liner formulations produced by manufacturers.