Evaluation of Arsenic Contamination in Texas

Abstract

Lowering the federal standard for arsenic in drinking water from 50 µg/L to 10 µg/L has led to a much wider spread of arsenic contamination in groundwater across Texas. This study aimed to (1) determine the distribution of arsenic in Texas groundwater, (2) assess the potential impact of past arsenical pesticide applications on groundwater in the southern High Plains and southwestern Gulf Coast, (3) evaluate the role of phosphate fertilizers in mobilizing arsenic, and (4) assess geologic sources of arsenic in Texas. The focus was on areas with domestic drinking water wells affected by high arsenic levels.

The Bureau of Economic Geology (BEG) undertook several tasks to achieve these objectives. Firstly, they reviewed groundwater arsenic concentrations in neighboring states and analyzed existing research on elevated arsenic studies in the US. Secondly, potential anthropogenic sources of arsenic, such as arsenical pesticides, were examined using GIS overlay analyses and soil sampling in the southern High Plains and southwestern Gulf Coast. Thirdly, potential geologic sources of elevated arsenic concentrations in groundwater were evaluated in these regions by studying the relationships between arsenic concentrations and different geologic units. Additionally, the impact of various redox conditions on arsenic distribution was explored. Limited additional groundwater sampling was conducted in Duval County in the Gulf Coast.

Arsenic contamination is widespread in neighboring states, particularly in New Mexico, where 16% of wells exceed the MCL (10 µg/L). In Oklahoma, only 5% of wells surpassed the MCL, with contamination primarily found in Permian formations in central Oklahoma. Arsenic contamination in Arkansas affects 8% of wells and is associated with alluvial aquifers in eastern Arkansas. In Louisiana, arsenic contamination is limited.

In Texas, groundwater arsenic contamination is widespread, with approximately 6% of wells exceeding the MCL of 10 µg/L. The contamination is particularly concentrated in the southern High Plains (32% of wells exceed the MCL) and the southwestern Gulf Coast (29% of wells exceed the MCL).

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