An appraisal of groundwater quality in Seymour and Blaine aquifers in a major agro-ecological region in Texas, USA

摘要

Aquifer-based groundwater quality assessment offers critical insight into the major hydrochemical processes, and aids in making groundwater resources management decisions. The Texas Rolling Plains (TRP), spanning over 22 counties, is a major agro-ecological region in Texas from where highest groundwater nitrate (NO_3~-) levels in the state have been reported. In this study, we present a comparative assessment of major hydro-chemical facies pertaining to NO_3~- contamination and a host of species such as sulfate (SO_4~(2-)), chloride (Cl~-), and total dissolved solids (TDS) in different water use classes in the Seymour and Blaine aquifers, underlying the TRP. Aquifer-stratified groundwater quality information from 1990 to 2010 was obtained from the Texas Water Development Board and aggregated over decadal scale. High groundwater salinization was found in the municipal water use class in the Blaine aquifer with about 100, 87 and 50 % of observations exceeding the secondary maximum contaminant level for TDS, SO_4~(2-), and Cl~-, respectively in the 2000s (2000-2010). The NO_3-contamination was more alarming in the Seymour aquifer with 82 and 61 % of observations, respectively, exceeding the maximum contaminant level (MCL) in the irrigation and municipal water use classes in the 2000s. Salinization was more influenced by SO_4~(2-) and Cl~- in the Blaine aquifer and by NO_3~- in the Seymour aquifer. High NO_3~- (＞MCL) observations in the Seymour aquifer occurred in the Ca-HCO_3 and Ca-Mg-HCO_3 facies, the domains of fresh water recharge and anthropogenic influences (e.g., agricultural activities, waste disposal). High SO_4~(2-) , Cl~- and TDS observations in the Blaine aquifer dominated the Ca-Cl, Na-Cl, and mixed Ca(Mg)-SO_4(Cl) facies indicating evaporite dissolution, mixing and solute exchange, and lack of fresh recharge.