These data describe microbiological analyses performed on groundwater samples from domestic drinking water supply collected from 42 groundwater wells in the Central Valley of California. Samples were collected between January 2014 and April 2014 for the Groundwater Ambient Monitoring and Assessment (GAMA) program priority basin assessment of the Madera, Chowchilla, and Kings (MACK) groundwater sub-basins’ shallow aquifers. A total of 75 wells were sampled for the MACK study unit between August 2013 and April 2014. Samples for this dataset were vacuum filtered and plated on MI and mEI agars prior to incubation to promote colony growth. Colonies were tallied by their species into columns for various fecal indicator bacteria (FIBs): total coliforms (TCs), Escherichia coli (E. coli), enterococci. Non-target growths were also counted and tallied. Six additional replicate samples were collected for quality assurance. Of the 579 total FIB colonies detected, 106 were selected for polymerase chain reaction (PCR) analysis with the goal of sequencing their DNA. Selected colonies consisted of both target and non-target growths and were taken from 14 samples collected at 13 different wells. DNA sequencing was successful for 34 of the sampled colonies out of a total of 59 submitted. Results for these analyses were reported in FASTA format with the number of bases and their starting position indicated for each batch.

These data support the following publication:

Burton, C.A., and Lawrence, C.J., 2021, Identification of bacteria in groundwater used for domestic supply in the southeast San Joaquin Valley, California, 2014: U.S. Geological Survey Scientific Investigations Report 2021–5030, 20 p., https://doi.org/ 10.3133/ sir20215030.