Frequent Questions

Under the Long Term 1 Enhanced Surface Water Treatment Rule, what is the definition of ground water under the direct influence of surface water (GWUDI)?

The definition of ground water under the direct influence of surface water (GWUDI) means "any water beneath the surface of the ground with significant occurrence of insects or other macroorganisms, algae, or large-diameter pathogens such as Giardia lamblia or Cryptosporidium, or significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or pH which closely correlate to climatological or surface water conditions. Direct influence must be determined for individual sources in accordance with criteria established by the State. The State determination of direct influence may be based on site-specific measurements of water quality and/or documentation of well construction characteristics and geology with field evaluation. (67 FR 1812, 1836; January 14, 2002).
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