The Sandia Canyon Wetland is an effluent supported wetland sustained by three National Pollutant Discharge Elimination System (NPDES) permitted outfalls. The wetland sediments contain an inventory of chromium released from historic operations. Maintaining physical and geochemical stability in the wetland is intended to keep the chromium inventory in its reduced trivalent state to minimize mobility and subsequent offsite migration. Upgrades to the Sanitary Effluent Reclamation Facility (SERF) decreased the amount of water used in nearby cooling towers, and therefore reduced the volume of effluent discharged into the wetland. SERF provides tertiary treatment to treated sanitary effluent creating water of improved quality to allow for additional cycles of concentration in the cooling towers. In November 2013, a grade control structure was installed at the terminus of the wetland to provide physical stability, to help maintain high groundwater levels in the wetland, and to maintain reducing conditions within the wetland. A network of alluvial piezometers and surface water gages, above and below the wetland, was used to monitor changes of hydrology and geochemistry within the wetland that may have resulted from the decreased effluent volumes and installation of the grade control structure. Water samples were collected from the monitoring network between November 2012 and March 2014. Piezometer water levels showed stable groundwater elevations in the wetland while the presence of ammonium and sulfide suggested reducing conditions were present even after the effluent volumes decreased. The manganese, iron, and chromium concentrations in groundwater and surface water samples further indicate that anaerobic conditions were present in the wetland. Over the monitoring period reported in this project, the results indicate the wetland has sustained reducing conditions to maintain the chromium inventory in the reduced trivalent state.
Sandia Canyon Wetland, effluent, geochemistry
Iacona, Brian M.. "Evaluation of the Geochemical Stability of the Sandia Canyon Wetland." (2015). http://digitalrepository.unm.edu/wr_sp/9