Crypto and Giardia in US groundwater

Data generated from the detection of Cryptosporidium oocysts and Giardia cysts in 463 groundwater samples were compiled. Samples were taken from 199 sites in 23 of the 48 contiguous states. The groundwater sources were vertical wells, springs, infiltration galleries, and horizontal wells. Samples were analyzed using an immunofluorescence technique. Inclusion of data from all sources showed that 12 percent of the sites were positive for Cryptosporidium or Giardia or both. Cryptosporidium oocysts were found in 5 percent of the vertical wells, 20 percent of the springs, 50 percent of the infiltration galleries, and 45 percent of the horizontal wells. Giardia cysts were found in 1 percent of the vertical wells, 14 percent of the springs, 25 percent of the infiltration galleries, and 36 percent of the horizontal wells. These data suggest that springs are at a higher risk for contamination than vertical wells. Because pathogens occur frequently in infiltration galleries and horizontal wells, these sources warrant further study.