A GIS SURVEY OF ARSENIC AND OTHER TRACE METALS IN GROUNDWATER RESOURCES OF TEXAS

Water quality issues have increasingly become more prevalent in local and federal politics. Most recent of which was the delayed decision to lower the drinking water standard for arsenic from 50 ppb to 10 ppb by the EPA. Reasons cited for the postponement of the Arsenic Rule included insufficient scientific understanding on the exposure pathways, occurrence and treatment methods for arsenic contaminated drinking water. Recent studies have focused on small or watershed scale arsenic hotspots and almost entirely only on arsenic, ignoring possible connections between arsenic and other trace metals.

Comprehensive surveys of water quality are far and in between. State and federal agencies offer valuable sources of data that span time and space. This study has produced the most comprehensive water quality database for the state of Texas. Data from the Texas Water Development Board (TWDB), the National Uranium Resource Evaluation (NURE) and the National Water Information System (NWIS) were collected into a GIS database. Specific attentions were placed on arsenic and other trace metals in ground water.

Geology, soil survey, land use and vegetation base maps were used to investigate controls on trace metal concentrations in groundwater. Statistical analyses of the database revealed a strong correlation between arsenic and other oxyanions including vanadium, selenium and molybdenum. Results also showed that arsenic concentrations were associated with the local aquifer geology. Iterative 2 sigma calculations for the natural background concentrations of these trace metals revealed vast regional variations. Implications and conclusions from this study showed that a GIS survey could prove to be a powerful yet easy method to investigate water quality at the state scale and also reveal regional controls on trace metal contaminants.