Using an innovative remediation process, U.S. Army Corps of Engineers’ Omaha District restored unused and potentially hazardous grazing land in Arlington, Neb. and the U.S. Army Installation Management Command took notice.
On Oct. 7, 2014, an Omaha District Environmental Remediation team led by Hector Santiago, project manager, won the biennial Secretary of the Army Environmental Award in Environmental Restoration-Installation for 2013. The honor, given by IMCOM subordinate command U.S. Army Environmental Command, recognizes and rewards “excellence in the development, management, and transferability of environmental programs that increase environmental quality, enhance the mission, and support Army sustainability.” Each award is for a two-year performance period and the 2013 award covers achievements from Oct. 1, 2011 through Sept. 30, 2013.
In 2008, the Omaha District hired ITSI Gilbane Company to begin remediation efforts for a 62-acre area of trichloroethene-impacted groundwater on privately owned grazing land approximately 30 miles northwest of Omaha, Neb. The area is a Formerly Used Defense Site located at the former Offutt Air Force Base Atlas “D” Missile Site 2. In addition to Santiago, Omaha District team members include Molly Maxwell, chemist; Melissa Kemling, hazardous waste disposal and safety; Cheryl Davis, risk assessment; Carl Nardin, geologist; and Quang Le, environmental engineer.
Initially, the team detected only groundwater TCE contamination and no soil impacts. The projected remediation timeframe for the known impacts was 10 years with an anticipated site closure in 2018. In 2009 and 2010, the Omaha District and ITSI Gilbane began further soil and groundwater investigations to support the planned site-wide groundwater remedy—in situ enhanced bioremediation. The team’s pre-treatment investigations exposed a substantial soil and groundwater contamination source. Analytical results for TCE in soils were several orders of magnitude higher than previously detected at the site and indicative of a significant Dense Non-Aqueous Phase Liquid source area. The source area and elevated soil and groundwater impacts threatened to delay the site-wide groundwater remedy by as much as 100 years and add millions of dollars to the life cycle costs.
Omaha District and its contractor ITSI Gilbane selected an innovative thermal technology to accelerate cleaning up the TCE DNAPL source. Crews implemented an in situ thermal treatment using a large-diameter auger and Zero-Valent Iron to remediate the site. This unique and integrated system advanced an 8-foot diameter auger to depths of more than 40 feet at multiple cells across the treatment area. Crews treated 163 cells; 57 cells with the large-diameter augers and ZVI to create a barrier around the site and 106 cells with the large-diameter auger, steam, hot air and ZVI.
USACE selected this integrated remedial technology to address the TCE DNAPL source area for multiple reasons. “This in situ remedy provided the least disruptive alternative to the current landowner and minimized worker exposure to the soil and groundwater impacted with hazardous levels of TCE,” said Santiago. USACE based their choice on worker safety, the preferred using “green” technologies (eliminating off-site transport and disposal of hazardous waste), depth of impacted media, contaminant concentrations, treatment timeframe considerations, site-specific geologic and hydrogeologic conditions, cost, permitting considerations and the likelihood of success.
Initial drilling times of 2-to-3 hours were common to reach a depth of 40 feet. The team implemented several modifications to improve the drilling rate. These modifications and the addition of steam during the thermal treatment portion improved drilling times to 30-45 minutes to reach a depth of 40 feet. “This technology has proven to be implementable and successful in both sandy and clayey lithologies,” according to the Project Delivery Team. The Army award team recognized this transferable solution.
Pre-treatment and post-treatment soil results indicate the technology was 99.98 percent effective in reducing TCE concentrations within the source area soils. The pre-treatment and post-treatment groundwater results indicate the technology was 99.72 percent effective in reducing TCE concentrations within the source area groundwater.
Atlas “D” was used for maintenance, storage and the potential launch of Atlas “D” Intercontinental Ballistic Missiles. Constructed in 1960, the Air Force used the complex for about two years and declared it excess, an underutilized property which is disposed through demolition, transfer or sale, in 1966 . During routine rocket maintenance rocket fuel systems were periodically cleaned with TCE. The waste TCE and residual rocket fuel was washed into the Atlas “D” Flame Pit Areas and presumably burned. Additionally, the FPAs would seasonally fill with water, which eventually leached into the soil and groundwater. Omaha District’s primary contaminant concern was TCE, along with the breakdown products of cis-1,2-dichloroethene and vinyl chloride.
Before treatment, the landowner was unable to use the approximate 1-acre site because of contamination in the FPA and a steeply embanked ephemeral pond. The area had been problematic for the tenant after several small calves were lost in previous years in the FPA. Because the treatment technology required a flat working surface to implement, the problematic area was filled and leveled beforehand and re-vegetated afterwards. The current tenant now uses the site as pasture land for cattle grazing.
The team’s choice—subsurface heating and ZVI placement — benefitted the bioremediation efforts not only in groundwater at the treated DNAPL source area, but also in the surrounding areas facilitating a site-wide remedy. The site is on-schedule for closure in 2018.