Polycyclic Aromatic Hydrocarbons in Soil at Groundwater Level Near an Earthen Pit for Produced Water in the Duncan Oil Field

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Abstract
Hydrocarbons, polycyclic aromatic hydrocarbons (PAH), and alkylated PAH with two to four rings were found in soil at groundwater level down-gradient from an earthen waste disposal pit for produced water, in the Duncan Oil Field of NW New Mexico. Depth to groundwater was only 1 to 1.5m in this flood plain of the San Yuan River. Complex mixtures of hydrocarbons with carbons numbers from 12 to 30 were detected in solvent extracts of soil samples collected 25m and 50m down-gradient from the waste pit. The concentration of total extracted organic mass was as large as 500 ppm at 25m, but a reduction in concentration of 90 to 100% was seen for samples at 50m on the same axes. No similar contamination was found in soil samples located on axes drawn up-gradient from the waste pit. Concentrations for total PAH in soil at 25m distance from the waste pit were as large as 4900 ppb and 37 ppb at 50m on the same axis. Detectable but trace amounts of PAH in samples up-gradient from the pit may be evidence for a secondary dispersion mechanism such as flooding of the region. While groundwater contamination with organic compounds from an earthen waste disposal pit has been demonstrated here, mobility, partition, and fate of PAH in complex mixtures in a soil/groundwater system remain undetermined.