WATER RESOURCE QUALITY ASSESSMENT IN THE NORTHERN DELAWARE BASIN, NEW MEXICO
Samples were collected from 65 wells in the Rustler Formation (primarily dolomite), the Dockum Formation (aka the Chinle group, mostly mudstone and sandstone), and shallow Pecos alluvium. All strata are also known to contain evaporites. TDS in the Pecos alluvium ranged from 700-2700 mg/L, Dockum Formation waters ranged from 300-1500 mg/L and Rustler waters ranged from 800-11,000 mg/L. Approximately 90% of wells exceeded EPA secondary guidelines for drinking water quality of 500 mg/L TDS, and based on FAO guidelines for irrigation use, approximately 95% of water should be either moderately or severely restricted for irrigation based on having a TDS of >450 mg/L. Sodium Adsorption Ratio values were below 10 for most analyzed waters with a few exceptions near potash mining and livestock operations. Much of the water quality in the region is likely driven in part by the presence of evaporites and halite dissolution, with Na/Cl and Ca/SO4 ratios near 1. At least one well has likely been contaminated by nearby potash mining operations (not included in the ranges above), with a TDS exceeding 60,000 mg/L and potassium concentrations exceeding 700 mg/L.
Major data gaps still exist for the region with respect to trace and minor elements, isotopes, and gas chemistry, and the future collection of such data could help inform management decisions and the understanding of water quality evolution with changing land use.