This dataset provides analytical and other data in support of an analysis of lead and manganese in untreated drinking water from Atlantic and Gulf Coastal Plain aquifers, eastern United States. The occurrence of dissolved lead and manganese in sampled groundwater, prior to its distribution or treatment, is related to the potential presence of source minerals and specific environmental factors including hydrologic position along the flow path, water-rock interactions, and associated geochemical conditions such as pH and dissolved oxygen (DO) concentrations. A DO/pH framework is proposed as a screening tool for evaluating risk of elevated lead or manganese, based on the occurrence of elevated lead and manganese concentrations and the corresponding distributions of DO and pH in 258 wells screened in the Atlantic and Gulf Coastal Plain aquifers. Included in this data release are the Supplementary Information Tables that also accompany the Applied Geochemistry journal article: Table of details on construction and hydrologic position of wells (percent distance from outcrop and percent depth to well centroid) sampled in Atlantic and Gulf Coastal Plain aquifers, 2012 and 2013. Table of general chemical characteristic and concentrations of major and trace elements and calculated parameters for groundwater samples from wells in Atlantic and Gulf Coastal Plain aquifers, 2012 and 2013. Table of mineral saturation indices (SI) and partial pressures of CO2 (PCO2 ) and O2 (PO2) computed with PHREEQC (Parkhurst and Appelo, 2013) for 258 groundwater samples from wells in Atlantic and Gulf Coastal Plain aquifers, 2012 and 2013. Table of spearman's rank correlation coefficient (r) matrix of principal components (PC1-PC6) and chemical data for 258 groundwater samples from wells in Atlantic and Gulf Coastal Plain aquifers, 2012 and 2013. Table of results of blank analysis for major and trace elements analyzed for 258 groundwater samples from wells in Atlantic and Gulf Coastal Plain aquifers, 2012 and 2013. Table of criteria and threshold concentrations for identifying redox processes in groundwater (after McMahon and Chapelle, 2008). Table of principal components analysis model of major factors affecting the chemistry of groundwater samples from wells in Atlantic and Gulf Coastal Plain aquifers, 2012 and 2013.