Oil Pipeline Leak in Texas

Site Summary

Petroleum was discovered seeping from a river bank in west Texas and was traced back to 8-inch oil pipeline leak approximately 40 feet from the river bank. Investigation of the pipeline leak showed contamination in the soil around the pipeline and in the ground water below it. Petrox was used to treat the soils and ground water at the source to mitigate the source of the seepage.

Geology

The geology of the site was typical fluvial floodplain with interbedded silty sand and clayey silty deposits. While the porosity may be high, the hydraulic conductivity was relatively low.

Hydrogeology

The affected aquifer was an unconfined silty sand approximately 20 to 25 feet thick. The water table was approximately 35 feet below ground surface. There were some indications that the hydraulic gradient was reversed during flood stage in the adjoining river.

Soil and Ground Water Contamination

Petroleum was found in the soil adjacent to the abandoned pipeline at approximately 15 feet deep and spread downward in a wide cone covering about 3,000 square feet when it reached the water table. Thus, the size of ground water plume that resulted from leaching soil contaminants was about 5,000 square feet. The contamination was mainly heavy petroleum constituents, with the highest concentrations in the C12 to C28 range.

The petroleum concentrations in the soil were as high as 41,000 mg/kg for total petroleum hydrocarbons (32,000 mg/kg for C12 to C28). The petroleum concentrations in the ground water were up 580 mg/L for total petroleum hydrocarbons (460 mg/l for C12 to C28).

As regulated by the Texas Railroad Commission, the cleanup goal was to remove the sheen or free product layer. Petrox was used to reduce the contaminant mass in soil and ground water to achieve the cleanup goal. The monitoring consisted of ground water sampling for petroleum and observations of presence of absence of a sheen in the river bank seep.

Remediation Design

Two drums of Petrox (110 gallons) were injected into the contaminated soil and ground water through the existing monitoring wells. These wells were screened above and below the water table, which provided a conduit for the injection of the Petrox in the soil and ground water. Ground water samples were taken from the same wells to track the progress of the remediation. The wells were thoroughly purged prior to sampling to provide samples representative of the surrounding ground water.

Results

Petrox was injected on three occasions. After the first injection on October 5, 2005, the TPH concentrations decreased by 88%. While the contaminant concentration was continuing, two additional Petrox applications were completed and followed with calcium peroxide to increase the dissolved oxygen concentrations.

While there appears to have been some rebound in the ground water concentrations, the contaminant concentrations were much lower and the sheen was no longer observed at the riverbank seep. The responsible party has applied for site closure based on these results.

The cost for Petrox and calcium peroxide used in these three treatments was less than $6,000.