Boron in the strata and waters of the Eocene Green River and Uinta Formations, Uinta Basin, Utah

Abstract

Boron is a naturally occurring element that can be found in the strata and water of the Eocene Green River and Uinta Formations of the Uinta Basin of Utah. Whereas boron is suspected to be a necessary trace nutrient for proper plant and animal growth and development, higher concentrations of boron can be detrimental to living things, but the element is not known to be carcinogenic. Utah has no limit on boron content in drinking water; however, for irrigation purposes a limit of 750 μg B/L (0.75 mg/L) has been established. The Green River Formation (GRF), deposited in ancient lakes in Wyoming, Colorado, and Utah, is well known for its oil shale and saline mineral deposits, particularly the thick, economic trona beds in Wyoming. Such evaporitic mineral deposits are characteristic of a saline lake environment that existed at the end stages of Eocene lacustrine deposition. In Utah they are found in the upper GRF, and to a minor extent in the lower Uinta Formation, where elevated boron is evident. Boron-bearing minerals are present in the Parachute Creek Member of the GRF in Utah, and they occur as secondary silicate minerals in at least 12 wells across Utah’s Uinta Basin. These minerals were first reported by the U.S. Geological Survey in the 1950s. This study determined that the boron mineral occurrences correlate stratigraphically and coincide with the areas delineated for the hypersaline events in the Parachute Creek Member of the GRF. This argues that boron was concentrated with other saline constituents in Lake Uinta and is an indicator of hypersaline conditions. Water quality analyses reporting boron content from surface and subsurface samples were compiled from public databases from the Utah Department of Environmental Quality, the U.S. Geological Survey, and the Utah Geological Survey. This new database consists of 155 samples from 38 sites from the upper part (Parachute Creek Member) of the GRF, and 58 samples from 26 sites from the lower part (Douglas Creek Member) of the GRF. The boron concentration was found to be different for the two GRF parts. The average boron content of the 58 lower GRF aquifer water analyses is 6338 μg/L, while the mean boron content for the 26 individual sites varies from 15 to 205,000 μg/L. The upper GRF aquifer contains at least twice the boron content of the lower GRF, and the average boron content of the 155 analyses of upper GRF groundwater is 18,172 μg/L. The mean boron content for the 38 individual sites varies 40 to 480,000 μg/L. Areas of highboron concentration in groundwater of the GRF tend to coincide with the location of GRF hypersaline paleodepocenters. Groundwater boron content in the Uinta Formation comes from 40 analyses from 36 sites. The average of the 40 Uinta Formation analyses is 3251 μg B/L, while the mean boron content for the 36 individual sites varies from 40 to 24,000 μg/L. For each interval studied, less boron tends to be found in analyses from sites near the outcrop and boron content tends to increase in the studied formations as they are more deeply buried. Additionally, boron content was compiled for surface waters and springs for 3955 analyses from 374 sites in the Uinta Basin. When the mean boron content of these surface water sites was examined by hydrologic drainage unit subareas, it was found that the tributaries in the northern Uinta Basin, north of the Duchesne and White Rivers, contain the lowest mean boron contents, whereas higher mean boron contents are common for the tributaries in southern part of the basin. The boron content of surface water from the southern Uinta Basin drainages also tends to increase northward toward the demarking water courses. The tributaries in the southern part of the Uinta Basin have higher boron contents due to their waters having contact with the boron-bearing, shallow-inclined strata of the upper GRF or member B of the Uinta Formation. The tributaries in northern part of the basin have lower boron contents because they are not in contact with the GRF, have less contact with the member B of the Uinta Formation, and are diluted by greater snow-melt runoff from the Uinta Mountains which bound the basin to the north.