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State Water Resources Control Board Division of Water Quality GAMA Program History of Occurrence Nitrate is the most common chemical contaminant in the world's groundwater aquifers. The USGS has estimated that nitrate exceeded background concentrations in 65 percent of shallow wells (<100 feet) in agricultural and urban areas. According to 2010, US Geological Survey publication, up to 7% of 2,388 domestic wells sampled in agricultural and urban areas have nitrate levels above the MCL. Concentrations exceeding the MCL were less common in public-supply wells (about 3 percent of 384 wells sampled). In California, multiple areas have elevated levels of nitrate contamination in groundwater including the San Joaquin Valley, Santa Ana Valley, and Salinas basins. Contaminant Transport Nitrate dissolves rapidly in water and once dissolved is difficult to Characteristics remove. Some natural degradation (denitrification) can occur under low or no-oxygen groundwater conditions. However, evidence suggests that aquifer-scale denitrification does not occur, and that once nitrate enters groundwater it can remain there for decades. REMEDIATION & TREATMENT TECHNOLOGIES There is no simple way to remove nitrate from water. Boiling, softening, and filtration as a means of purifying water do not reduce nitrate concentrations. The following methods can reduce or remove nitrate: Demineralization • Distillation - Removes nitrate and all other minerals from the water. Distillation is one of the most effective types of demineralization. This process involves boiling the water, then collecting and condensing the steam by using a metal coil. • Reverse osmosis -Water is placed under pressure and forced through a membrane that filters out minerals and nitrate. Both distillation and reverse osmosis are costly and require time and energy to operate efficiently. They are low-yield systems, and storage space for treated water is required. Ion-exchange -Water containing nitrate flows through a tank filled with resin beads that are charged with chloride. As the water flows through the tank, the resin takes up the nitrate and exchanges with chloride. Electro-dialysis —Water containing nitrate flows across anion-exchange and cation exchange membranes in a constant electric field. The use of these mono-anion- selective membranes offer additional possibilities of nitrate removal by enabling preferential flow of mono-valent anions (Rozanska A. and J. Wisniewski, 2003). Other potential options include: phytoremediation and above ground biochemical denitrification. Revised November 2017 4