IMPLEMENTATION OF NATURAL ATTENUATION AT A JP-4 JET FUEL RELEASE AFTER ACTIVE REMEDIATION

After eighteen months of active remediation at a JP-4 jet-fuel spill, a residual of unremediated hydrocarbon remained. Further site characte rization was conducted to evaluate the contribution of natural attenua tion to control exposure to hazards associated with the residual conta mination in the subsurface. Activities included the detailed character ization of ground-water flow through the spill; the distribution of fu el contaminants in groundwater; and the analysis of soluble electron a ccepters moving into the spill from upgradient. These activities allow ed a rigorous evaluation of the transport of contaminants from the spi ll to the receptor of groundwater, the Pasquotank River. The transport of dissolved contaminants of concern, that is benzene, toluene, ethyl benzene, xylene isomers (BTEX) and methyl-tertiary-butyl ether (MTBE) , into the river from the source area was controlled by equilibrium di ssolution from the fuel spill to the adjacent groundwater, diffusion i n groundwater from the spill to permeable layers in the aquifer, and a dvective transport in the permeable layers. The estimated yearly loadi ng of BTEX compounds and MTBE into the receptor was trivial even witho ut considering biological degradation. The biodegradation of hydrocarb on dissolved in groundwater through aerobic respiration, denitrificati on, sulfate reduction, and iron reduction was estimated from changes i n ground-water chemistry along the flow path. The concentrations of ta rget components in permanent monitoring wells continue to decline over time. Long term monitoring will ensure that the plume is under contro l, and no further active remediation is required.