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Critical Removal Action in Response to Contaminated Soils
1Reclamation Research Unit, Montana State University, Bozeman, MT. 2CH2MHill,
Boise, ID, 3W.B.E. Inc., Helena, MT. 4U.S. Environmental
Protection Agency, Helena, MT
.
ABSTRACT--Some
irrigated lands along the Clark Fork River, near Deer Lodge, Montana contain
elevated levels of arsenic, cadmium, copper, lead and zinc, and low soil pH.
This contamination originated from river-transported mine wastes
associated with metal mining, milling and smelting operations in the Butte and
Anaconda, Montana areas. In May
1999, the U.S. Environmental Protection Agency ordered the responsible party
(ARCO) to reduce contamination on historically irrigated lands along the
Eastside Ditch near Deer Lodge, Montana. These
lands consist of residential properties and adjacent pastures.
The preferred action for the residential yards is excavation and
replacement of soils (up to 18 inch depth) whose average arsenic values exceed
the trigger value of 120 mg/kg which is the 95% lower confidence interval value
of the human health risk-based residential concentration of 150 mg/kg.
The preferred remedial action for adjacent pastures is tilling and liming
to varying depths (up to 24 inches) to evenly distribute arsenic and metals into
the soil profile, and neutralize potential and active acidity.
The
Reclamation Research Unit, in conjunction with W.B.E, Inc. and CH2MHill
performed oversight for sampling and remedial actions along the Eastside Ditch
for the U.S. EPA. Soil samples were
collected from 17 residences and adjacent pastures, and 2 pastures
in 1998 and 1999. The soil
samples were analyzed for arsenic, copper, lead, zinc and pH.
Soils were excavated and replaced in 8 residential yards as of November
1999 (remaining soil arsenic levels are typically below 70 mg/kg). In addition, 10 adjacent pastures were tilled and limed as of
November 1999. Further sampling and
remedial activities are expected to continue in Spring 2000.
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