Based on the Lawrence Livermore UST study and the recent letter by Walt Petit of the State Water Resources Control Board regarding site closure, active remediation systems for petroleum contamination may be unnecessary.

Oxygen Release Compound (ORC) can be used as the primary treatment method at sites where groundwater contamination concentrations require active remediation. The goal of using ORC is to prevent plume migration off-site. The treatment method described here uses a Geoprobe direct push technology rig and other equipment to install an ORC plug. In series, the plugs form an oxygen barrier across the contaminated plume. A properly designed row of ORC plugs will slowly release oxygen, enhance bioremediation, and cut off the plume in the oxygenated zone. Where remediation systems are presently installed, ORC can be used concurrently to improve clean-up results.

It appears that the limiting factor associated with the natural attenuation and mass reduction of the BTEX (benzene <50 ppm) compounds in groundwater plumes is oxygen. The ORC has the composition of milk of magnesia (magnesium peroxide). The ORC is activated by moisture, giving off a slow release of oxygen. The by-products of the reaction are oxygen and ordinary magnesium hydroxide. The ORC generates higher dissolved oxygen levels than is possible with air.

With regulatory acceptance, ORC has been placed in filter socks and placed in wells since 1994. A new pressure grouting technique has been designed to construct a passive bio-treatment zone or oxygen barrier to prevent off-site migration or to decrease site closure time. Prior to installation, intrinsic bioremediation surveys collect data such as lithology, contaminant concentration, dissolved oxygen content, enzyme activity of soils, carbon dioxide, nitrates, sulfates, temperature, pH and other data. Computer modeling is used to determine optimum ORC spacing, oxygen demand and length of treatment.

The plugs have a useful life of about I to 2 years, depending on the contaminant concentration, bioactivity, and flow rate. The passive system can be used on a leading edge of a plume, along sewer trenches, at property boundaries and as a full-scale passive remediation design. The costs for installation are a fraction of the costs of conventional treatment methods. In addition, operations, maintenance and monitoring costs are reduced. For more information please call (415) 455-1899.