BergerWorld: 2nd Quarter 2006

Since wetlands naturally filter water, it's not surprising that wetlands can be designed and constructed to optimize their filtering capability. Used mostly to treat domestic sewage, constructed wetlands require little energy to operate,

while providing greenspace and wildlife habitat. In addition to domestic wastewater, constructed wetlands have also been used to treat mine drainage, mostly from coal mines, but little is known about treating drainage from molybdenum mines. In an innovative project, Klohn Crippen Berger (KCB) is employing treatment wetland technology to treat molybdenum, copper, zinc and ammonia in drainage from a high altitude mine in Peru.

The Compañía Minera Antamina S.A. (CMA) copper-zinc-molybdenum mine is located in the rugged high Andes in Peru, 4,200 meters above sea level in the upper Amazon drainage basin. Ore is excavated from an open pit at the rate of 360,000 tons per day, processed through an on-site crusher and concentrator plant, transported

through a 302-km underground pipeline to the Peruvian coast, and then shipped overseas. CMA required treatment of drainage from the waste rock dump and tailings pond water prior to discharge to the Ayash River which serves as drinking water for downstream villages.

KCB prepared a feasibility study and recommended an innovative treatment wetland to remove ammonia and molybdenum from incoming mine drainage. In 2005, KCB completed detailed design plans and specifications and provided construction supervision services. The 4.2-hectare (10.3-acre) wetland comprises 30 treatment cells using on-site topsoil to support the wetland vegetation and the water treatment processes. Discharge pipes situated above rock berms where mine drainage outflows by gravity prevent high-intensity discharges from scouring the wetlands, enhance solids removal and even loading of the wetland, and prevent anoxic conditions at the inlet area.

Selection of vegetation focused on two species-Scirpus californicus and Juncus arcticus-both adapted to the local environment and variable hydrological conditions, and growing in nearby Lake Pajoscochas. The planting effort required approximately 10,500 transplants. KCB provided Antamina with technical information regarding transport and establishment of the wetland plants.

KCB also prepared an operation and maintenance manual to insure optimal wetland performance. The manual discusses periodic maintenance requirements and necessary monitoring procedures-information that will be used to document wetland health, mass loading rates and pollutant removal efficiencies. KCB staff is overseeing the operation of the wetland for several years.