Report on bioventing of petroleum contaminated soils at 108-3C: Active extraction and passive injection (barometric pumping) of a gaseous nutrient

A bioventing system was constructed with horizontal extraction wells and vertical injection wells in an area which had previously been excavated and then backfilled. Initial in-situ respiration rates (air addition only) suggest that hydrocarbon degradation may be nutrient limited. The rate of TPH degradation was maximum (0.8-1.2 mg/kg/day) between 10-15 ft (bgs), but dropped to essentially zero 30 ft (bgs) within the contaminated zone (even though previous analysis at this depth indicated a TPH concentration of 3800 ppm). Analysis of the soil at 17 ft showed that NO3 and PO4 were below detection limits (0.5 ppm), indicating that nutrient limitation may be occurring. Nitrate levels were highest at 10 ft (bgs), correlating with the highest respiration rates. However, phosphate levels were at/or below detection levels throughout tile site (indicating possible PO4 limitation). Viable cells increased from 3 x 106 cfu/g at 3 ft (bgs) to 1 x 107 cfu/g at 10 ft (bgs) and remained relatively constant down to 17 ft. Cell numbers in the control area were significantly lower than in the contaminated zone (4.5 x 103). Gas phase nutrients (triethlyphosphate and nitrous oxide) will be injected to see if the hydrocarbon degradation rate can be increased