AWWA WQTC62479

The Central Wyoming Regional Water System operates 29 groundwater collection devices in an alluvial aquifer adjacent to the North Platte River. These collection devices were previously designated as being "ground water under the direct influence of surface water" (GWUDISW). In lieu of constructing a conventional surface water treatment plant the utility opted to perform a two-year study to demonstrate that riverbank filtration (i.e. natural filtration) provides the 2.0 log reduction of Cryptosporidium required under the Interim Enhanced Surface Water Treatment Rule (e.g. riverbank filtration is the primary filtration process). Using multiple surrogates of various sizes encompassing those of Giardia and Cryptosporidium, the utility demonstrated 2.0-log reductions in over 90 percent of matched-data pairs. No Giardia or Cryptosporidium were found in any of the 170 groundwater samples. This level of removal was achieved during the summer months when infiltration rates are high due to increased river stage and well-field production. Includes 19 references, tables, figures.