water stream over rocks


Groundwater Modeling Services for Risk Assessment Red Hill Fuel Storage Facilities, NAVFAC Pacific, Oahu, Hawaii

Groundwater Modeling Services for Risk Assessment Red Hill Fuel Storage Facilities, NAVFAC Pacific, Oahu, Hawaii

TEC Incorporated

01/01/06 - 02/28/07

The US Navy's bulk fuel storage facility at Red Hill is located in the ridge between south Halawa Valley and Moanalua Valley on the island of Oahu. The facility was constructed in the early 1940's and consists of 20 buried steel tanks each with a capacity of about 12.5 million gallons. Currently, the tanks contain JP-5 (jet fuel) and Diesel Fuel Marine. The bottoms of the tanks are situated about 100 feet above sea level and about 80 feet above the basal water table. The geology of the site is primarily basaltic lava flows within which clinker beds, fractures and interflow boundaries serve as the primary route for the migration of fluids through the site.

An investigation found evidence of releases from several tanks. The evidence ranged from rocks saturated with a petroleum-like product to elevated readings on a photo ionization detector (PID) and total petroleum hydrocarbon (TPH) analytical results above Hawaii Dept. of Health Tier 1 action levels. The investigation was limited to a narrow horizontal zone beneath each tank. Two vertical borings, one of which was converted to a groundwater monitoring well, were installed hydraulically downgradient to identify and monitor potential migration of contamination to a major potable water source in proximity to the tank farm.

Based on the presence of petroleum contamination found in the basaltic formations surrounding the tanks, the investigation recommended an evaluation to assess the risks posed by the contamination on site. The Navy's PWC Red Hill Shaft potable water pump station, located hydraulically downgradient from the fuel storage facility is a potential point of exposure, as well as the Halawa Shaft and the Moanalua Wells, which belong to the Honolulu Board of Water Supply.

After review of the site investigation report and conducting a site visit, the State of Hawaii Department of Health (DOH) indicated that additional information was required to meet the requirements of their Technical Guidance Manual to facilitate their decision process for the site. In accordance with DOH regulations, the owners and operators of USTs cleaned contaminated soil and groundwater to levels that are protective of human health and the environment.

A numerical model of the regional hydrogeology at the Red Hill Fuel Storage Facility (RHFSF) was created to support the development of a comprehensive fate and transport model to provide supporting data for risk assessment. This model simulated the fate and transport of potential contamination from the site and the effect on the saltwater/freshwater transition zone of various pumping scenarios.

The Groundwater Modeling System (GMS) model developed for the State of Hawaii Department of Health, Safe Drinking Water Branch's Source Water Assessment Program (SWAP) by WRRC was modified to assess flow and transport of potential contamination from the bulk fuel storage facility.