CYCLING OF ARSENIC THROUGH HUMAN WATER USAGE AND WATER TREATMENT

Arsenic is ubiquitous yet heterogeneously distributed throughout the Earth's crust and sediment. Arsenic in groundwater is also very heterogeneously distributed, particularly in fractured bedrock; wells with very high concentrations of arsenic can be found adjacent to wells with undetectable arsenic. Much study has been conducted on the cycle of natural arsenic through the hydrosphere, but the influence of human activities on this cycle has been limited to contamination sources such as pesticides, wood preservatives, mine wastes, and the like. Little research has been done on the effects humans themselves have on arsenic cycling within the environment. This study investigates the possibility that some of the heterogeneity of arsenic in groundwater is a result of human cycling of arsenic through groundwater use and waste disposal. Arsenic can be concentrated in solid and water waste by the transfer of arsenic from a diffuse water or soil source to a localized waste site. Water-treatment systems remove arsenic from drinking water either as a solid that ends up in landfills or flush it in water during backwashing to a septic system or waste-water treatment facility. In Maine, the flux of arsenic passing from bedrock aquifers through public and private water systems is estimated at 2.2 to 4.6 kg/day. This arsenic-laden water from aquifers is deposited on leach fields that provide reducing environments capable of releasing iron-bound arsenic and reducing As(V) to more soluble As(III). Arsenic is concentrated in human solid wastes, which can increase the load of arsenic to localized settings by the spreading of sludge on the land surface or by depositing it in leach fields. Modeling results will be presented on the effects of the disposal of arsenic-bearing waste water in the reducing environment of a septic system leach field.