Windrow Composting to Treat Explosives-contaminated Soil at Umatilla Army Depot Activity, Hermiston, Oregon (Full-scale Remediation)

Site Name:

Umatilla Army Depot


Hermiston, Oregon

Period of

March 1994 - September 1996 (anticipated end date)


Full-scale remediation


Wilder Construction Co. (Phase I)
Bioremediation Services, Inc. (Phase II)

Composting (Windrow)
- Soil excavated and stored on site (Phase I)
- Soil treated inside 200 x 90 ft structure (Phase II)
- Moisture content maintained at 30-35%
- Turning frequency was once every 24 hrs for first 5 days followed by less frequent turning on subsequent days
- Composting batches required approximately 22 days to reach cleanup goals
- Full-scale treatment based on 3 trial tests

Cleanup Authority:
- ROD Date: September 1992

SIC Code:
9711 (National Security)
Point of Contact:
Remedial Project Manager
Umatilla Army Depot Activity
Hermiston, OR

- Primary soil contaminants include 2,4,6-Trinitrotoluene (TNT); Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX); Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX); and 2,4,6-Trinitrophenylmethylnitramine (Tetryl)
- TNT and RDX soil concentrations ranged from 100 to 2,000 ppm; and HMX from <1 to 100 ppm
- Contamination present in top 6 ft of soil

Waste Source:
Surface Impoundment/Lagoon

Type/Quantity of Media Treated:
- 10,969 cubic yards (13 windrows with 810 cubic yards each and 1 windrow with 439 cubic yards)
- Predominantly Quincy fine sand and Quincy loamy fine sand
- Soil pH gradually increased from 7 (at ground surface) to 8.5 at 5 ft below ground surface

Purpose/Significance of Application:
First full-scale application of windrow composting to biodegrade explosives-contaminated soils

Regulatory Requirements/Cleanup Goals:
Concentrations of explosives in soil of less than 30 ppm for each of target compounds - TNT and RDX

- Windrow composting generally reduced the levels of target explosives to below the cleanup goals
- Average concentrations prior to composting were 190 ppm for TNT and 227 ppm for RDX
- 27 x 30 cu. yd. grids sampled in each batch
- Through 11 batches, only 2 of almost 300 grids did not meet cleanup goal after initial phase of treatment

Cost Factors:
- Actual total project cost of $5,131,106, corresponding to a unit cost of $346 per ton from mobilization to demobilization
- Phase I cost $1,320,162 (soil excavation and storage)
- Phase II cost $3,810,944 (soil treatment)
- Costs specific to biological treatment ($1,989,454) correspond to unit cost of $181/cubic yard soil treated

From approximately 1955 to 1965, the UMDA operated a munitions washout facility in Hermiston, Oregon, where hot water and steam were used to remove explosives from munitions casings. About 85 million gallons of heavily-contaminated wash water were discharged to two settling lagoons at the site. The underlying soils and groundwater were determined to be contaminated with explosive compounds, primarily TNT, RDX, and HMX, and the site was placed on the NPL in 1987.

Windrow composting was used for a full-scale remediation at UMDA, with treatment taking place from July 1995 to September 1996 (anticipated completion date per September 1996 report). A total of 10,969 yd3 of contaminated soil were treated at UMDA, in 14 batches. Analytical results indicated that average concentrations were reduced from 190 to <30 ppm for TNT, and from 227 to <30 ppm for RDX. Through 11 batches, only two of almost 300 grids did not meet the cleanup goal (30 ppm) after an initial phase of treatment.

Detailed information on actual costs for this application are provided in the report. Actual costs are shown according to an interagency Remedial Action-Work Breakdown Structure (RA-WBS). Factors affecting costs that were identified for this application included climate, soil characteristics, and amendment availability and cost. For example, the semi-arid cool climate and sparse vegetation at UMDA contributed to fairly low preparatory site work cost. Amendment availability and cost are significant factors for composting and are driven by the proximity, seasonality, quality, and consistency of the materials to be used. At UMDA, the majority of the amendments were readily available in the Umatilla area.