Tetra Tech is providing Military Munitions Response Program (MMRP) support to the U.S. Army Engineering Support Center, Huntsville (USAESCH) for environmental investigation at the U.S. Army Garrison, Hawaii’s Kipapa Ammunition Storage Site (KASS) on the island of Oahu.

During World War II the U.S. military dug 80 underground storage tunnels into the rock formation of both sides of Kipapa Gulch near Mililani, Hawaii. The tunnels were reportedly constructed for storing chemical warfare materiel (CWM), incendiaries, and high explosives. Photographic evidence suggests chemical agent (CA) leaked from CWM stored in the tunnels, creating a potential environmental concern.

Although the site is closed, the National Oceanic and Atmospheric Administration (NOAA) uses one of the tunnels in Lower Kipapa to house geophysical equipment for earthquake detection as part of the Pacific Tsunami Warning Center.

Tetra Tech characterized the interior tunnels and exterior areas of the KASS munitions response site (MRS); assessed the presence, type, density, and distribution of chemical agent, munitions constituents, and hazardous and toxic waste (HTW); and evaluated the potential risks and hazards to human health, safety, and the environment posed by these substances.

Tetra Tech conducted the remedial investigation (RI) to characterize the 40-acre MRS, including 54 tunnels in Upper Kipapa, 26 tunnels in Lower Kipapa, and six former loading and unloading areas (FLUAs). Our work included surface clearance, vegetation removal, air monitoring for CA, tunnel inspection, field sampling, and tunnel closure. The project presented multiple safety challenges—confined spaces, potential for heat stress and biological hazards, and exposure to HTW-contaminated materials. We completed more than 27,000 hours without a recordable or lost-time injury. Tetra Tech also prepared a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) Proposed Plan and Decision Document to support closure of the MRS.

The potential presence of CWM/CA required a USAESCH survey of Tetra Tech’s operations at the MRS. We identified appropriate protocols and followed the Department of the Army’s Interim Guidance for Chemical Warfare Materiel Responses and Related Activities during project preparation, and conducted rigorous training prior to the survey. Tetra Tech’s execution of survey scenarios received outstanding marks, and USAESCH issued approval to begin the investigation.

Tetra Tech investigated six potential sources associated with the MRS: the interior of the ammunition storage tunnels; environmental media beneath and adjacent to the exterior of the tunnels; soil and structures within the entrance corridor; natural and man-made drainages; soil at the FLUAs; and other observed releases or suspect items. The RI included detector-aided visual inspections, air monitoring, and biased discrete grab and incremental sampling, followed by tunnel closure and site restoration.

During the 300-day field investigation, Tetra Tech collected approximately 300 incremental concrete and soil samples that were analyzed for CA, munitions constituents and HTW, and collected nearly 1,600 samples for an asbestos survey. Upon completion of sampling, 79 tunnels were welded shut and warning signs were posted on the exterior. Tetra Tech scientists evaluated the sampling data and completed a baseline human health risk assessment and screening-level ecological risk assessment. Risk assessment results indicated minimal risk to human health and the environment at the MRS, thereby eliminating the need for a feasibility study. Tetra Tech then prepared the CERCLA Proposed Plan and Decision Document to support a recommended No Further Action determination at the site, which was approved in December 2018. Our team consistently earned outstanding reviews from the client for quality, schedule, budget, and project management.