The objective of this study was to assess the potential of applying enhanced landfarming system on the treatment of diesel-oil contaminated soils. Laboratory reactors were conducted to determine the optimal operational conditions of the modified landfarming. Except of frequent soil tilling for air replacement, different additive was added in each reactor enhance the removal efficiency of total petroleum hydrocarbon (TPH). The additives used in this study included kitchen waste compost, petroleum-hydrocarbon (PH) degrading bacteria, rice husks, and activated sludge. PH-degrading bacteria were isolated from PH contaminated soils and activated sludge was collected from a wastewater treatment plant containing PH in the influent. PH-degrading bacteria and sludge were added to increase the microbial population and diversity. Rice husk was used as the bulking agent (soil to bulking agent volume ratio = 3:1) to increase the soil permeability. The compost (soil to compost volume ratio = 3:1) was used as organic amendment to increase both the microbial population and soil permeability. Results indicate that the highest first-order TPH decay rate and removal ratio were approximately 0.1 day-1 and 92.4%, respectively, observed in reactor containing compost. In the compost reactor, TPH dropped from 5,900 to 450 mg/kg and total viable bacterial counts increased from 9.4×105 to 7.2×108 cfu/g of soil within 25 days of incubation. This indicates that the kitchen waste compost contained high microbial population and organic content, which could cause the rapid bacterial growth and enhance the TPH degradation. The TPH removal ratios for sludge, PH-degrading bacteria, rice husks, and control reactors were 86.9, 83.1, 79.7, and 54%, respectively. This indicates that the soil tilling played an important role in the landfarming system, and significant amount of TPH removal was due to the volatilization mechanism. Adding sludge or PH-degrading bacteria could cause the increase in both the total microbial population and specific PH-degrading microbial consortia, which caused the increased TPH removal efficiency.

The industrial solvent, trichloroethene (TCE), is among the most ubiquitous chlorinated compounds found in subsurface contamination. Operation of an avionics repair shop at a military base has resulted in past release of solvent chemicals including TCE and other chlorinated aliphatic hydrocarbons. The objectives of this study were to investigate the occurrence of natural remediation process and the feasibility of using natural remediation as the remedial option at this site. The following tasks have been performed: (1) site characterization to delineate the lateral and vertical extent of contaminants in the subsurface; (2) field investigation of natural remediation; and (3) efficiency of TCE removal through natural remediation in the field. Results indicate that TCE biodegradation occurred at this site, and natural remediation is a possible remedial alternative for TCE plume containment. Evidences for the TCE natural remediation included: (1) decreased TCE and other chlorinated compounds concentrations along the transport path; (2) production of the TCE degradation byproducts (including ethane); (3) decreased total organic carbon along the transport path, (4) deceased pH in the spill source area; (5) production of chloride ion and carbon dioxide. Experiences obtained from this study would be helpful in developing a site remedial protocol for other DNAPL sites.