EPA's MCLG and MCL do not distinguish between arsenate and arsenite. NRC noted that these assumptions set an upper bound on the contribution from food, which is about 10 g a day for adults. The NRC report was inconclusive about the health risks to the pregnant woman, developing fetus, infants, lactating women, and children. EPA identified waste disposal options that will likely be used for arsenic treatment residuals. Ultimately, liquid wastes would be disposed at sanitary sewers, evaporation ponds, or be directly discharged.
Chemical precipitation is assumed to be an intermediate step for the disposal of some brines.
Sludges would be either mechanically, or non-mechanically dewatered prior to ultimate disposal at a landfill. Solid wastes would typically be disposed at non-hazardous landfills. EPA assigned national selection probabilities to each of these options in a decision tree. These probabilities are an estimation of the likelihood of a treatment plant opting for a particular disposal option given the size of the system, whether it is surface water or groundwater, and the type of arsenic removal treatment technology used. Although six of the drinking water standards have changed, the TC values have not.