By Roy Evans, P.E., M.SAME, and Varut Guvanasen, Ph.D., P.E.
The former Fort Ord encompasses approximately 28,000-acres in the Monterey Bay area in central California. From its founding in 1917, the base served primarily as a training and staging facility for infantry troops.
In the early 1960s, Fritzsche Army Airfield was completed in the northern part of Fort Ord. Fire training activities at the airfield’s Fire Drill Area (FDA) began in 1962 and ended in the early 1980s. During training, fuel and some solvents were poured into the unlined burn pit, ignited, and extinguished. Unburned liquid infiltrated into underlying groundwater and traveled under sensitive habitat designated for federally and stateprotected plant species.
Fort Ord was identified as a National Priorities List site in 1990. Operable Unit 1 (OU-1) was established to define and remediate groundwater contamination resulting from the training activities.
In 1991, Fort Ord was placed on the Base Realignment and Closure list, and then on Sept. 30, 1994, it was officially closed down.
SCOPE OF INVESTIGATIONS
The 1995 OU-1 Record of Decision identified 10 volatile organic compounds, including trichloroethene, total 1,2-dichloroethene, and benzene, as chemicals of concern (COCs). The trichloroethene plume footprint encompassed the individual plumes of all 10 of the COCs.
Site investigations began in 1984, and contaminated soils were removed in 1986. A groundwater extraction and treatment system was constructed near the FDA and began operation in 1988 (this strategy was adopted as the selected remedy in the record of decision). The Army subsequently realized the system was not fully containing the COC plume and estimated that groundwater contamination had extended 1,850-ft beyond the system’s capture zone.
To manage the financial risk associated with expanding the groundwater remedy, the Army adopted a performance-based, fixed-price remediation with insurance (PB-FPRI) contract to complete cleanup. This significantly reduced its financial obligation for OU-1 remediation. Field investigations found that the volatile organic compound plume had extended nearly 4,100-ft beyond the limit of the groundwater extraction and treatment system capture zone. The additional resources needed to define and remediate the much-largerthan-anticipated contaminant plume were absorbed by the contractor and insurer. Although the larger contaminant plume could not be remediated fully within the PB-FPRI contract term, which expired in 2013, considerable progress was made.
At the end of the effort, the plume was well-defined and remedial efforts were on track to meet the cleanup goals. Trichloroethene was the only COC that still exceeded the cleanup targets, with the maximum concentration 6.7-µg/l (above the cleanup target of 5-µg/l).
The Army was able to contract HydroGeoLogic Inc. (HGL) using low-risk, fixed-price task orders with well-defined scopes of work to complete the OU-1 remediation and closeout.
UNIQUE REQUIREMENTS
In June 1996, 600-acres of the former Fort Ord property were incorporated into the University of California Natural Reserve System and designated as the Fort Ord Natural Reserve (FONR). The entire on-post OU-1 groundwater plume was located within the reserve.
FONR serves as a unique outdoor laboratory for the study and protection of threatened and endangered plants, as it contains critical habitat for the federally endangered and state threatened Sand Gilia and the federally threatened Monterey Spineflower. Both the Army and the U.S. Fish & Wildlife Service agreed to parameters for protecting the reserve— requiring habitat and plant restoration if remediation activities resulted in unacceptable impacts to the protected species.
HGL developed and enacted protective construction protocols, including biological monitoring and field staff training, to identify sensitive environmental situations. Pre-construction biological surveys and mapping of plant populations were incorporated into the remedy design. Locations for extraction wells and treated-water recharge facilities were selected to avoid the rare plant populations and especially sensitive habitat.
MINIMIZING IMPACTS
To preserve the seed banks of threatened and endangered plants in sensitive areas, the top 6-in of soil removed during construction was segregated, saved, and applied as surface topping during postconstruction restoration. The field crew placed temporary mats on roadways to protect seed banks and dormant plants from heavy equipment traffic.
Construction activities were limited to late June through early October to avoid disturbing rare plants and habitat during critical reproductive and growth periods. HGL performed annual rare plant population surveys from 2003 through 2017 and did not identify any significant impacts to the FONR rare plant populations.
IMPLEMENTING TECHNOLOGY
To develop and compare alternatives for expanding the groundwater extraction and treatment system, a 3D groundwater masstransport model for the OU-1 area was developed using MODFLOW-SURFACT. Based on the modeling results, HGL added eight extraction wells, two injection wells, two infiltration trench systems, and a new 200-gal/min granular activated carbon treatment facility. The wells were placed in locations that would not affect the ongoing remediation of a nearby carbon tetrachloride plume. The new system began operating in July 2006.
The project team aggressively optimized operation of the groundwater extraction and treatment system from startup of the expanded system in 2006 through termination of active remediation in 2014. Qualitative optimization (identifying trends through analysis of groundwater sampling results, performing sensitivity runs to assess parameter impacts, and converting a monitor well to extraction well) was used to obtain regulatory acceptance for reducing long-term sampling requirements and pumping rates at selected wells.
In 2011, HGL implemented its innovative Physics-Based Management Optimization technology to evaluate alternative pumping strategies using both existing and potentially new extraction well locations.
Results led to regulatory acceptance of significantly reduced pumping rates and further sampling reductions projected at that time to reduce overall cleanup costs by an estimated $310,000 while still completing the cleanup on time. Operational modifications resulting from implementation of the Physics-Based Management Optimization reduced greenhouse gas emissions by an estimated 59,000-lb/year (based on the Pacific Gas & Electric Company estimation tool).
EXITING TO SUCCESS
Although now recognized as potentially significant environmental hazards, the emerging contaminants perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were not on the national radar when site investigations began in the mid-1980s, or when the OU-1 Record of Decision was signed in 1995. However, they had been recognized as potential threats to groundwater quality when the OU-1 groundwater cleanup targets were achieved in September 2014.
Given the high probability that compounds containing PFOA/PFOS were used in training activities at FDA, the regulators overseeing the cleanup required site-specific data to support the Army’s site closeout request. HGL developed a strategy to reach site closure that included attainment monitoring for the COCs and PFOA/PFOS along with follow-up criteria based on the Provisional Health Advisory. The attainment monitoring was performed in 2015, and although results showed PFOA and PFOS were present in the OU-1 groundwater plume, the concentrations were below the action criteria set in the exit strategy.
The Environmental Protection Agency subsequently issued a health advisory in 2016 with values more conservative than those in the preliminary version. At two wells, PFOA/PFOS concentrations exceeded the new guidance. The Army and HGL presented information showing that the existing institutional controls, absence of an exposure pathway and limited PFOA/ PFOS extent, would provide protectiveness if the OU-1 site was closed.
In February 2017, regulators concurred with the Army’s recommendation to close OU-1. HGL decommissioned the expanded OU-1 groundwater extraction and treatment system. The final site closure report was approved in December 2017.
Roy Evans, P.E., M.SAME, is Principal Engineer, and Varut Guvanasen, Ph.D., P.E., is Principal Engineer and Vice President, Research & Development, HydroGeoLogic Inc. They can be reached at revans@hgl.com; and dguvanasen@hgl.com.
[Article originally published in the May-June 2018 issue of The Military Engineer]
