Occurrence of Benzene, Toluene, Ethylbenzene, and Xylenes in Water Wells near Oil and Gas Development in the Wattenberg Field of Colorado
Abstract
Monitoring of groundwater quality near oil and gas development has revealed evidence of contamination of water wells near drilling and production facilities, but the frequency and severity of water well contamination is not well known. To assess the frequency and severity of water well contamination, we used a water quality database provided by the Colorado Oil and Gas Conservation Commission to search for occurrences of benzene, toluene, ethylbenzene, and xylenes (BTEX) in the Wattenberg Field, the most productive region of the Denver-Julesburg Basin in northeastern Colorado, from 2001 to 2019. In this database, we found at least one of the BTEX compounds above its detection limit in 72 of 1,837 water wells (3.9%) from which samples were collected and analyzed for BTEX. In 16 of the 72 water wells, more than one BTEX compound was detected, which resulted in a total of 88 occurrences of BTEX compounds above their detection limits. These occurrences were examined as 51 cases of contamination owing to proximity of some of the contaminated water wells. Toluene most frequently occurred at a concentration above its detection limit. Benzene most frequently occurred at a concentration above the maximum contaminant levels for Colorado drinking water. BTEX compounds most frequently occurred in the Laramie-Fox Hills aquifer with an average depth of 217 m, which indicates that surface spills were not likely to be contaminating the water wells. The rate of BTEX detection increased from 1.5 to 9 water wells per year in 2015, likely in response to the introduction of mandatory water well sampling near oil and gas drilling in 2013. Of the 72 water wells in which BTEX was detected, dissolved methane was measured in 35, and in twelve of these 35 water wells, the methane was identified as thermogenic by carbon-13 isotope analysis, which suggests that BTEX occurrence could be attributed to oil and gas development and that BTEX compounds may have followed the same path of release taken by methane. BTEX occurrence with microbial methane (23 of the 35 water wells in which carbon-13 was measured) suggested that the BTEX origin was coal seams interbedded into the Laramie-Fox Hills aquifer.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMSY15C0433R