A numerical model was developed to describe the fate and transport of hydrazinium (N2H5+) and competing Ca2+ and H+ cations applied in acidic solutions to columns of Ca2+/H+-saturated sandy soil during steady saturated flow conditions. Instantaneous ternary H+-Ca2+-N2H5+ cation exchange using the Gaines-Thomas approach was combined with second-order, irreversible, kinetic chemisorption of exchange-phase N2H5+ ions as major retention mechanisms for N2H5+. Exchange-mediated chemisorption is assumed to occur as chemical binding of N2H5+ ions located on carboxyl-group exchange sites to nearby carbonyl groups, consequently decreasing the effective soil cation exchange capacity (CEC). Comparison of simulated and observed breakthrough curves (BTCs) for concentrations of N2H5+ and Ca2+ ions in column effluent was used in model evaluation. The cation transport model with cation exchange coupled with exchange-mediated chemisorption provided a valid first approximation for N2H5+ transport.

A spill of JP-4 jet fuel at the U.S. Coast Guard Air Station in Traverse City, Michigan, contaminated a water-table aquifer. An infiltration gallery (30 ft x 30 ft) was installed above a section of the aquifer containing 700 gal JP-4. Purge wells recirculated three million gallons of ground water per week through the infiltration gallery at a rate designed to raise the water table above the contaminated interval. Ground water containing ambient concentrations of oxygen and nitrate was first recirculated for 40 days. Concentrations of benzene in monitoring wells beneath the infiltration gallery were reduced from 760 to < 1-mu-g/l. Concentrations of toluene, ethylbenzene, m,p-xylene, and o-xylene were reduced from 4500 to 17, 840 to 44, 2600 to 490, and 1400 to 260-mu-g/l, respectively. Average core concentrations of benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene were reduced from 0.84 to 0.032, 33 to 0.13, 18 to 0.36, 58 to 7.4, and 26 to 3.2 mg/kg, respectively. Ground water amended with nitrate (10 mg/l nitrate-nitrogen) and nutrients was then recirculated for 76 days. Final core concentrations of benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene were 0.017, 0.036, 0.019, 0.059, and 0.27 mg/kg, respectively. Final aqueous concentrations were < 1-mu-g/l for benzene and toluene, 6-mu-g/l for ethylbenzene, and 20 to 40-mu-g/l for the xylene isomers, in good agreement with predicted values based on residual fuel content and partitioning theory. Although alkylbenzene concentrations have been substatially reduced, the test plot is still contaminated with the weathered fuel. Based on stoichiometry, approximately 10 times more nitrate was consumed than could be accounted for by BTX degradation alone, indicating that other compounds were also degraded under denitrifying conditions.