spatial distribution of solutes in aquifer outcrop zones along the brazos river, east-central texas

concentrations of several solutes – nitrate, arsenic, sulfate, boron, chloride, and bromide – along with total dissolved solids (tds) in ten counties bordering the brazos river in east-central texas were compiled, mapped, and analyzed relative to regional land use and geology. agriculture and oil/gas production are major activities and potential sources of groundwater contamination in the study area. data were compiled from 104 water wells with a median depth of 446 ft (136 m) in the outcrop zones of six sedimentary aquifers: carizzo-wilcox, queen city, sparta, yegua-jackson, gulf coast, and brazos alluvium. only two observations surpassed the 44.3 mg/l drinking water standard for nitrate, and four observations exceeded the 10 ug/l standard for arsenic. the median chloride concentration was 53 mg/l; however, the maximum level was almost three times the secondary drinking water standard of 250 mg/l. chloride, bromide, sulfate, and boron concentrations resembled tds patterns, with numerous samples exceeding secondary tds drinking water standards in the yegua-jackson aquifer. most chloride/bromide ratios were between 100 and 300. overall, results of this study suggest that natural processes exert a primary control on solute concentrations in the above aquifers, with a potential for modest anthropogenic impacts from agriculture and oil/gas production.