Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
Yuma Marine Corps Air Station
EPA #: AZ0971590062
City: 2 miles from Yuma
Congressional District: 02
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Description and History
NPL Listing History
NPL Status: Final
Proposed Date: 06/24/88
Final Date: 02/21/90
Marine Corps Air Station Yuma (MCAS Yuma) occupies approximately 3,000 acres within the City and County of Yuma, Arizona (2nd Congressional District). The City of Yuma, the nearest municipality, is located approximately one mile northwest of the Station. Both the City and the Station obtain their drinking water from the Colorado River through an irrigation canal. The City does not use groundwater for drinking water purposes. The nearest domestic groundwater well is approximately 0.8 mile downgradient from the Station.
MCAS Yuma's mission is to provide services and materials support operations to the Marine Aircraft Wing and its subordinate units. In 1990, MCAS Yuma was placed on the Superfund National Priorities List after chlorinated solvents were detected in a groundwater monitoring well on the Station.
Starting in the mid-1940s, waste fuels and solvents from the refueling and servicing of airplanes were reportedly disposed of directly onto the ground or into unlined pits at the Station site. In addition, combustible materials such as fuel oil and organic solvents were deposited on the ground or burned during fire training exercises. Approximately 5,700 people live on-site. In the past, during maintenance work on the Colorado River irrigation canal which took place for two weeks each year, drinking water was supplemented using an on-station well. However, this practice was stopped in August 1995. The City of Yuma has a summer population of 60,000 and a winter population of 100,000.
Contaminants and Risks
- Soil and Sludges
For soil, the contaminant of concern was asbestos in the form of non-friable asbestos containing material (ACM). The ACM is scattered on top of and buried in the surface soil.
For groundwater, the contaminants of concern are chlorinated solvents (TCE, DCE and PCE). The main groundwater plume is approximately 1 mile long and 500 feet wide, and has reached the downgradient edge of the base. The maximum concentration of total solvents is approximately 500 parts per billion (ppb). All of the groundwater contamination has been detected downgradient of the old on-station drinking water well. However, the on-station drinking water well is no longer used and none of the groundwater is used elsewhere on the base. If left untreated, the plume could potentially impact private groundwater wells downgradient from the Station.
Investigation and Cleanup Activities
This site is being addressed in long-term remedial phases focusing on cleanup. There are two operable units (OUs):
Operable Unit 1: Regional Groundwater Unit which consists of basewide groundwater and vadose zone soils deeper than 10 feet.
Operable Unit 2: Surface Disposal and Landfill units which consist of the upper 10 feet of soil at 18 CERCLA Areas of Concern.
Groundwater (OU1): A remedy has been selected for the groundwater at Yuma, and construction of a groundwater treatment system has been completed. A groundwater ROD was signed in July 2000. As part of a pilot study, the Navy, with oversight from EPA under the Federal Facility Agreement (FFA), operated a groundwater treatment system to contain the chlorinated solvent plume. The treatment system was designed to intercept the plume and prevent it from migrating off the Station. The treatment system, an innovative in-well air stripping technology, ran from January to June 1997. The system was successful at diminishing VOC levels to below MCLs, but siltation problems developed effecting pumping rates. The wells were modified to work as vertical recirculation wells as part of the study. The design was incorporated into the final cleanup action for the groundwater. Monitored natural attenuation is also a part of the groundwater remedy. If the monitored natural attenuation or vertical recirculation prove ineffective, contingency plans would have been implemented. Air sparging and soil vapor extraction have treated the source area of the plume and a pump and treat system (extraction and air stripping) treated the rest of the plume. In addition, institutional controls, groundwater monitoring, and discharge to the storm drain are parts of the remedy. The system was shut down for a rebound study but is now back up and operating. The system has been extremely effective in removing contaminants and the Marines are considering options such as pulsed or phased use to maximize effectiveness.
Soil (OU2): In 1991, the Navy/Marine Corps began investigating the landfill areas and soil sites. The remedial investigation was completed in 1995. A remedy for addressing soil contamination (asbestos containing materials) was selected in December, 1997. The ROD, which addresses a total of 18 sites, describes no action at 12 sites, institutional controls at three sites and removal of asbestos containing materials (ACM) at three sites.
In 2001, all of the soil sites were cleaned and removed from the facility except the large construction debris site, but the contractor made a sweep through the debris and removed all visable ACM. The Base has placed a fence around the site and land use controls are listed in the base master plan.
The groundwater is being remediated by two treatment systems which have significantly lowered contaminant levels nearly to the MCLs. The main base system is an air-sparging/pump and treat system which attacks the main plume and the Leading Edge Plume Area system (LEPA) remediates contaminants which were beyond the main base system at the time of construction.
The Base has produced a third 5-Year review which shows the remediation to be protective.
The Base currently has a draft of a munitions response plan which is being reviewed by the regulatory agencies. At this time no decisions have been made but it does not appear that munitions are an issue.
Yuma Marine Corps Air Station is participating in the Installation Restoration Program, a specially funded program established by the Department of Defense (DOD) in 1978 to identify, investigate, and control the migration of hazardous contaminants at military and other DOD facilities. In January 1992, the EPA entered into a Federal Facility Agreement with the Yuma Marine Corps Air Station to initiate site investigations. At this time, two operable units, Operable Unit 1 and Operable Unit 2, are identified. Operable Unit 1 comprises soils deeper than 10 feet and underlying groundwater aquifers and Operable Unit 2 comprises 18 CERCLA areas of concern (soils sites less than 10 feet below surface).
Cleanup Results to Date
After adding this site to the NPL, the EPA performed preliminary investigations and determined that no immediate actions were required at the Yuma Marine Corps Air Station site while site studies and cleanup activities were in progress. At this time the soil remediations are completed and the groundwater treatment systems have performed as designed. Both systems were shut down while rebound studies were being performed but are now back up and operating.
Potentially Responsible Parties
Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.
Online information about the PRPs for the site is not yet available.
Documents and Reports
Public Information Repositories
The public information repositories for the site are at the following locations:
MCAS Yuma has established two information repositories, one at the Yuma County Library at 350 South Third Avenue and one on-base at Yuma Marine Corps Air Station. The Official Administrative Record is compiled and maintained by the Navy at the Southwest Division Naval Facilities Engineering Command in San Diego.
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