In low permeability but naturally fractured media. vertical leaching or vol
atilization of toxic organic compounds can lead to high exposures and unacc
eptable human health or environmental risk. A field test was recently compl
eted to evaluate in situ remediation at such sites by using hydraulic fract
uring to emplace iron metal (Fe-0) and permanganate (KMnO4) solids in the s
ubsurface to chemically treat trichloroethylene (TCE). At an old land treat
ment site, two test cells were installed in silty day soils with hydraulic
fractures filled with either iron metal or permanganate solids at 1.8, 2.4,
and 3.6 m depths. Fracture emplacement was monitored, and soil and ground
water conditions were characterized. After 3, 10, and 15 mo of emplacement,
continuous cores were collected and morphologic and geochemical data were
taken across the fracture zones. Controlled degradation tests were complete
d using site ground water with TCE concentrations near 53, 144, and 480 mg/
L, equivalent to 0.5, 1.2, and 4.1 g TCE per kg media, respectively. The ir
on-filled fractures formed a discrete reactive seam less than 1 cm thick, w
herein the Eh decreased and reductive dechlorination could occur, but effec
ts in the adjacent silty clay soils were negligible. Though the emplaced ir
on exhibited some surface corrosion after extended emplacement in the subsu
rface, its reactivity was unaffected. Iron from the fractures degraded TCE
at efficiencies of as much as 36% after 24-48 ht of contact, which is consi
stent with Fe-0 packed bed degradation half-lives of 1 to 2 hr. The permang
anate-filled fractures yielded a diffuse reactive zone that expanded over t
ime, reaching 40 cm in thickness after 10 mo. Throughout this oxidizing zon
e, the degradation efficiency was >99% after 2 hr of contact for dissolved
TCE at 0.5 and 1.2 mg TCE per g of media. When exposed to higher TCE loadin
gs (i.e., 4.1 mg per g), degradation efficiencies after 10 mo dropped to 70
% as the TCE load exceeded the oxidant capacity remaining. These efficienci
es and rates are consistent with oxidation stoichiometry and previously det
ermined half-lives of <2 min for permanganate oxidation of TCE. In both tes
t cells there were no marked effects on the chemistry or contamination leve
ls in the ground water beneath the cells. Though the results of this resear
ch are promising for emplacement of horizontal treatment zones, further wor
k is required to support full-scale application.