title: Natural attenuation of perchlorate in denitrified groundwater.
abstract: Monitoring of a well-defined septic system groundwater plume and groundwater discharging to two urban streams located in southern Ontario, Canada, provided evidence of natural attenuation of background low level (ng/L) perchlorate (ClO4⁻) under denitrifying conditions in the field. The septic system site at Long Point contains ClO4⁻ from a mix of waste water, atmospheric deposition, and periodic use of fireworks, while the nitrate plume indicates active denitrification. Plume nitrate (NO3⁻ -N) concentrations of up to 103 mg/L declined with depth and downgradient of the tile bed due to denitrification and anammox activity, and the plume was almost completely denitrified beyond 35 m from the tile bed. The ClO4⁻ natural attenuation occurs at the site only when NO3⁻ -N concentrations are <0.3 mg/L, after which ClO4⁻ concentrations decline abruptly from 187 ± 202 to 11 ± 15 ng/L. A similar pattern between NO3⁻ -N and ClO4⁻ was found in groundwater discharging to the two urban streams. These findings suggest that natural attenuation (i.e., biodegradation) of ClO4⁻ may be commonplace in denitrified aquifers with appropriate electron donors present, and thus, should be considered as a remediation option for ClO4⁻ contaminated groundwater.
authors: Environment Canada, Burlington, Ontario, Canada.
authors: William D
authors: WD
authors: Robertson
authors: James W
authors: JW
authors: Roy
authors: Susan J
authors: SJ
authors: Brown
authors: Dale R
authors: DR
authors: Van Stempvoort
authors: Greg
authors: G
authors: Bickerton
mesh_terms: D001673:Biodegradation, Environmental; D058440:Denitrification; D004784:Environmental Monitoring / Q000379:methods*; D060587:Groundwater / Q000032:analysis*; D009566:Nitrates / Q000032:analysis; D009864:Ontario; D010472:Perchlorates / Q000032:analysis* / Q000378:metabolism*; D045483:Rivers; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000378:metabolism
chemical_list: D009566:Nitrates; D010472:Perchlorates; D014874:Water Pollutants, Chemical; C494474:perchlorate