In Situ Reactive Zone (IRZ)

Through documents dated 4 August 2003 and 13 September 2003, PG&E submitted a Report of Waste Discharge to operate an in-situ pilot test at two test cell areas: one area located on the former compressor station property, and one area located at the former East Landfarm location. On 13 October 2004 the LRWQCB issued WDRs for the pilot test which involved the injection of two food-grade organic substrates (emulsified vegetable oil (EVO) and sodium lactate) into plume groundwater to create conditions in which Cr(VI) is removed from groundwater by its conversion to Cr(III).

Based on the success of the pilot test, PG&E submitted a Report of Waste Discharge, through documents submitted on 6 January 2006 and 1 March 2006, to conduct an in-situ pilot test across an area perpendicular to plume flow in the central area of the plume, near the intersection of Frontier and Fairview Roads. On 14 June 2006 the LRWQCB adopted Waste Discharge Requirements for the Central Area In-Situ Remediation Pilot Study Project located in an area approximately 1800 feet wide (cross-gradient) and 1000 feet long. Wells across the width of the project site were used to deliver a food-grade organic reductant (initially, sodium lactate solution) to groundwater, stimulating the growth of indigenous bacteria which, in turn, create chemically reducing conditions. Cr(VI) in groundwater was reduced to the insoluble Cr(III) under these conditions.

By documents submitted 2 June 2006 and 4 August 2006, PG&E filed a Report of Waste Discharge to construct a full-scale in-situ treatment system at, and immediately north of, the area within the compressor station where chromium-containing waste water was originally discharged to land. The LRWQCB approved this system, termed the In-Situ Source Area Remediation Project, on 9 November 2006. The project involved injection of food-grade organic reductant and downgradient extraction to induce flow of reductant amended groundwater over a project area approximately 2400 feet long and 1400 feet wide.

PG&E submitted a Report of Waste Discharge through documents submitted on 15 June 2007 and 28 June 2007 to modify the In-Situ Central Area Remediation Project. On 28 November 2007 the LRWQCB issued revised WDRs for the project, specifying ethanol as an additional permitted reductant, adding permitted tracer compounds, approving an expansion of the project area and the stepping-out of monitoring well locations, and specifying revised concentrations for monitoring of chromium.