Project Number:
DNR-192
Funding Year:
2006
Contract Period:
7/1/2006 - 6/30/2007
Funding Source:
DNR
Investigator(s) and affiliations:
Abstract:
Background/Need
Guidance for disinfection of domestic wells in arsenic-sensitive areas of Wisconsin calls for a treatment at 20 percent of the chlorine strength and 10 percent of the contact time recommended for non-arsenic impacted wells. This guidance is based upon an assumption that the oxidizing strength of chlorine causes chemical oxidation of arsenic-rich sulfide minerals. However, microbially-mediated reductive dissolution of arsenic-bearing iron (hydr)oxides also contributes arsenic to groundwater in some areas of Wisconsin. Therefore, a low-dose chlorination treatment may not be a preferred method of disinfection in all settings where groundwater and wells are arsenic impacted.
Objectives
Investigate geochemical and biogeochemical mechanisms of arsenic release to well water from arsenic-rich sulfide minerals and iron (hydr)oxides during in situ disinfection with chlorine
Methods
In laboratory batch experiments, arsenic-rich aquifer sediments were subjected to deionized water with 8 mg/L O2 or chlorine disinfection solution at 1200 mg/L Cl- . Solution chemistry was monitored during 24 hours of reaction. The second portion of this project utilized a field setting to monitor microbial populations and water chemistry in a test well completed in the St. Peter sandstone. The well was subjected to periods of routine pumping, periods of non-use, and treatment with a low-dose chlorine disinfection.