THE CHEMICAL COMPOSITION AND DISTRIBUTION OF
GROUNDWATER IMPACTED BY PETROLEUM PRODUCTION
OPERATIONS: THE OSPER A SITE, OSAGE COUNTY, OK
Yousif Kharaka*
U.S. Geological Survey
Mail Stop 427
345, Middlefield Rd.,
Menlo Park, CA 94025
Voice: 650-329-4535
Fax: 650-329-4538
E-mail: ykharaka@usgs.gov
Robert A. Zielinski
Bruce D. Smith
U.S. Geological Survey
Denver, CO
We are involved in a multidisciplinary investigation to study the transport, fate, natural attenuation and impacts of released petroleum compounds and inorganic salts in produced water at the Osage-Skiatook Petroleum Environmental Research (OSPER) A and B sites in Oklahoma. In this report, we summarize the impacts on the groundwater at the OSPER A site, where ~1.5 hectare of land has been affected by oil operations that started in 1913 and were largely terminated by 1937. Groundwater impacts are being investigated by repeated sampling of 35 wells (1-36 m deep), completed with slotted PVC tubing. The well locations were based on: (1) The presence of salt scars, excessive soil and rock erosion, brine and asphalt pits, degraded oil, dead trees and shrubs and other visible surface features; (2) results of electrical conductance, Cl, Br and SO4 measurements on aqueous leachates from samples of shallow soil (0-15 cm), selected soil profiles (0.5-1.7 m) and core samples from prior drilled wells; and (3) results of shallow penetrating (<10 m) electromagnetic (EM) and deeper (30-60 m) DC resistivity surveys used to map the subsurface distribution of saline water, soil and bedrock.
Results of water analysis are in general agreement with those obtained from soil and core samples and the geophysical surveys. We are mapping a 3-D plume of high salinity water (5,000-30,000 mg/L TDS) with chemical and isotopic characteristics similar to those of the source produced water. The depth of this plume is not currently well defined; the one well that penetrates into a deeper aquifer has lower salinity (~2,000 mg/L TDS), but high Fe, Mn and dissolved organics. The horizontal plume boundaries are also not well delineated, since all wells deeper than 2 m at the site encounter the plume. A background well, drilled 0.6 km to the NW of the site has freshwater (450 mg/L TDS) and other characteristics of the pristine local groundwater, but also has relatively high dissolved organics, including BTEX. Results to date clearly show that large amounts of salts and organics remain in the local groundwater after more than 65 years of natural attenuation.