1970: Beginning in the 1970s, numerous studies and investigations were conducted at the installation sites, excluding the OB/OD area, investigated include:

• tank areas
• landfills/waste/ash piles
• igloos/storage areas/pads
• paint/maintenance shops/wastewater lagoons/retention ponds/demolition/ demilitarization areas/training areas
• asphalt plants

1982: Operational control of the base was transferred from the Secretary of the Army to the AZ ARNG. After the transfer, the mission for the AZ ARNG was primarily training, with the secondary support mission of leasing storage space to other federal and state entities. Past activities led to known and suspected contamination of several environmental media outside the ammunition demolition areas. These areas included: ammunition workshops, munitions storage, munitions testing and training ranges, operations facilities (including automotive maintenance and fueling), hazardous materials storage, and solid waste disposal facilities.

1991 - 1993: The U.S. EPA and ADEQ completed the RCRA facilities assessment and visual inspection at Camp Navajo in fall 1993. EPA also completed a preliminary assessment/site inspection re-evaluation of Camp Navajo under the Comprehensive Environmental Response Compensation and Liability Act (CERCLA) in April 1993. The report incorporated records contained in the 1991 master environmental plan and subjected available sampling data to Hazard Ranking System scoring. In October 1993, EPA notified the AZ ARNG that Camp Navajo did not score high enough to be placed on the National Priorities List (NPL). However, the facility is still subject to CERCLA, state (delegated RCRA, Water Quality Assurance Revolving Fund (WQARF) etc.) and local laws, and must comply with applicable remedial standards established by the IRP for all federal facilities.

In 1993, operational control was transferred under BRAC 1 to the AZ ARNG, and the name was changed to Camp Navajo. The installation is subdivided into three “zones” with several parcels of land leased to tenants. The interior zone of Camp Navajo is utilized for storage igloos, General Service Administration warehouses, and ammunition and surveillance workshop areas. The southern zone of the installation was formerly used as a demolition area to train ammunition handlers and to demilitarize obsolete munitions. For activities in this zone, the OB/OD Area is described elsewhere. Administrative, military training, and tenant activities are conducted within the buffer zones.

1995 - 2000 The Former Construction Debris Landfill #5 was first investigated in 1995, with a supplemental investigation in 1999. In 2000, 6,000 cubic yards of debris and soil were transported and disposed at a permitted hazardous waste landfill.

2000: Major removal actions performed included the excavation of TNT contaminated soils at the TNT washout facility, a.k.a. Building 318/319; the demolition of Building 319, and the dewatering and treatment of TNT contaminated groundwater from the perched aquifer immediately beneath buildings 318/319. The contaminated soils and groundwater were treated by biocomposting on site.

2001: The former Sanitary Landfill was first investigated in 1998, with supplemental investigations in 1998, 1999, and 2000. Based on these investigations, an environmental engineering and cost analysis was finalized in May, which proposed recontouring, capping and re-seeding of the site. The remedial action was completed in October.

2002 - 2003: Thirty-four sites were involved in investigation and remediation activities under CERCLA in 2002 and 2003. They are summarized as follows:

• Remediation at seven sites was completed.
• Twenty-seven sites were investigated and removal actions conducted during field work in summer 2002 and 2003 and were slated for closure.
• Contamination at these sites appeared to be limited primarily to the surface. However, additional soil and groundwater characterization was performed to verify the vertical and horizontal extent of contamination, or to verify remediation completion recommendations.
• For those sites with soil contamination above the applicable regulatory standards (Arizona Soil Remediation Standards Rule, A.R.S. 49-151-152; A.A.C. R18-7) a removal action, combined with long-term groundwater monitoring, was the preferred remedial action.

Proposed plans were prepared for the closure activities. Closure activities at Camp Navajo are conducted in accordance with the Army’s IRP for non-NPL sites as authorized by the Defense Environmental Restoration Program 10 USC Chapter § 2701-2708 and 2810.
2006: Record of Decisions (ROD's) were pending for 29 of the sites. After the RODs are approved those sites will be considered closed. Five sites required LTM. The LTM activities included groundwater monitoring and five-year reviews (FYR).

2007: The annual technical project planning meeting was held in February. Representatives from the NGB and the ADEQ agreed that RODs will replace decision documents for all future activities related to the LTM of the facility. ADEQ reviewed the LTM groundwater monitoring report for NAADs 11B, 14D, 14G, 40 and 43. ADEQ recommended the continuing monitoring of perchlorate in the wells. Camp Navajo continued to conduct groundwater monitoring and reporting at all LTM sites.

2008: ADEQ and the NGB reviewed the LTM reports and discussed the decreased monitoring activities for the IRP long-term sites. The NGB prepared monitoring reports for fall 2008 which will be evaluated to determine what remedial actions will be taken for closure of the area.

2009: The NGB prepared the LTM sites for decreased monitoring activities and closure.

2010: A FYR report for five installations, IRP sites was submitted in the summer. The LTM sites started ramp-down procedures as outlined by the LTM sites workplan. The five sites LTM decision document was approved in the fall.

2011: In May 2011, the groundwater monitoring results were submitted in the fall 2010 LTM report for NAADs 11B, 14D, 14G, 40 and 43. In accordance with an approved ramp-down process, select groundwater monitoring wells would continue to be sampled for select analytes. NGB explored funding sources to continue monitoring and reporting.

2012: In July, a revised workplan to continue LTM sites groundwater monitoring was developed. Select wells and limited analyses continued (approved ramp-down procedures).

A former outdoor storage yard (furnace debris storage area) was targeted for minor surface clearance and clean-up in fall.

2013: NGB is continuing LTM at several sites. Long-term protectiveness of the removal actions will continue to be monitored by groundwater sampling during the LTM program. Current data indicates that the remedies are functioning as intended at the sites.

A former outdoor storage yard (furnace debris storage area) was surface-cleared during fall 2012.

ADEQ executed a decision document which administratively closed seven sites deemed ineligible for the IRP. The seven sites were either duplicates of other sites, resulted from IRP-ineligible activities, or involved IRP-ineligible contaminants. Concerns associated with the seven sites were addressed by other site-specific IRP activities or other programs. No further response action was deemed necessary and the IRP status is considered response complete.