When it comes to protecting freshwater resources from man-made disasters, surface water gets almost all the attention, but groundwater or underground aquifers play a major role in the fresh water supply. Chronic groundwater contamination can break the balance between supply and demand, leading to socioeconomic crises and even wars.
It’s true that surface water provides drinking water to half the U.S. population and is more vulnerable to pollution from pipelines, agriculture and urban runoff. But the other half rely on groundwater, which are just vulnerable to man-made disasters but are often assumed to be uncontaminated.
The soil and rock above an aquifer help filter water as it seeps underground. Sometimes aquifers are used to dilute contaminated water supplies, but groundwater contamination is hard to detect, and the natural purification processes can take decades or even hundreds of years.
There are about 542,000 underground storage tanks (UST) in the U.S., storing thousands of gallons of fuel and hazardous substances. Over the last 33 years, there have been 502,786 UST fuel leaks and a backlog of about 60,000 clean-ups.
Fuel tanks hold a toxic mix of heavy metals and chemicals that can contaminate water supplies, affecting the health of humans, wildlife, and lands and forests. Heavy metals can build in the soil and affect vegetation growth, while benzene and toluene—toxic chemicals found in fuel— move quickly through soil, contaminating groundwater and surface water.
The largest UST facility in the United States is the Red Hill Bulk Fuel Storage Facility in Oahu, Hawai’i—a perfect example of how these tanks pose a significant threat to aquifers.
Not only is Hawai’i battling underground tanks that have been leaking for decades, but a lack of oversight and regulations needed to protect groundwater, which provide 99 percent of Hawai’i’s water.
The Red Hill facility has twenty underground fuel tanks containing up to 12.5 million gallons of fuel, located 100 feet above Oahu’s sole-source groundwater aquifer, supplying water to Honolulu residents from Halawa to Hawai’i Kai.
There have been 73 documented fuel leaks at Red Hill. One of the most significant leaks occurred in 2014 when 27,000 gallons of jet fuel leaked from a tank at the facility. The most recent was in 2021 when approximately 1,000 gallons of jet fuel leaked during a refilling operation.
On Jan. 7, the Hawai’i Department of Health (DOH) ordered the Navy to shut down Red Hill and de-fuel the underground tanks. However, the DOH gave the order months after the Navy shut down two of their wells, the Red Hill well and Aiea-Halawa well, after military families reported smelling fuel in their water and feeling sick.
The Navy’s water system supplies water to approximately 93,000 residents at the Joint Base Pearl Harbor-Hickam and surrounding military housing. After flushing a part of the system, water tests showed that total petroleum hydrocarbons-diesel contamination—a mixture of chemicals found in diesel and gasoline—exceeded 200 parts per billion at 620 parts per billion.
Although tests haven’t detected widespread contamination in the Oahu aquifer, they raised concerns over the safety of Oahu’s only water source. Cleaning up a contaminated aquifer is a costly and challenging process, and current technology is limited, but one option is as simple as heated wood or activated carbon.
A study published in the Journal of Water Process Engineering showed that remediation strategies to remove trace fuel chemicals originating from diesel and gasoline, specifically the chemical benzene, need more than a traditional water treatment system.
The researchers found that powdered activated carbon (PAC) is an effective adsorbent that significantly reduces trace chemical concentrations in contaminated water. A dosage of 80 milligrams of PAC brought trace concentrations far below U.S. EPA recommendations. However, whether the contaminants originated from diesel or gasoline impacted PAC absorption.
Since gasoline is cleaner than diesel, benzene removal was higher in gasoline-contaminated water, but adding PAC without coagulant improved absorption for diesel and gasoline-contaminated waters.
During the rapid mixing stage in a water treatment system, a coagulant such as ferric sulfate or alum helps remove particles from drinking water. Not only did the study find that adding PAC before coagulant improves absorption, but ferric sulfate outperformed alum in reducing benzene concentration in diesel and gasoline contaminated water.
To remediate the contaminated wells and restore safe drinking water, the Navy works with the DOH and EPA to flush and test the Navy’s water system, but the Navy is also tasked with installing a water treatment system with an industrial filtering system.
They plan on constructing massive pipes to discharge up to 5 million gallons of treated water a day. For the Navy to discharge treated water onto the soil or into storm drains or sanitary sewers, their filtering system must have diffusers and granulated activated carbon (GAC).
The main difference between PAC and GAC is their particle size and use. Although both remove chemicals from drinking water, and their inherent adsorption and pore structures are the same, PAC’s smaller particle size helps it absorb chemicals faster and is usually added directly to water and discarded after use. After the coagulation stage, GAC is typically used as filtration media and can be reactivated and reused.
GAC filters are proven to remove certain chemicals, but the Navy’s filtration system could benefit from adding PAC and ferric sulfate since diesel contaminated water is harder to clean than gasoline, ensuring contaminated water is free of toxic chemicals before discharging it into the environment.
States can avoid UST leaks altogether with laws and regulations that protect groundwater resources. For example, only recently was a bill amended to give the City and County of Honolulu the power to issue, modify, suspend or deny underground storage tank permits that may threaten an aquifer.
The amendment also states that underground storage tanks with a capacity of more than 100,000 gallons require a permit. To obtain a permit, an applicant must demonstrate that the tank system will not leak into the environment during its working life.
In the case of Red Hill, the DOH issued several notices stating the facility failed to properly maintain corrosion protection, adequate leak detection, piping tests and visual inspections.
Only last year did Hawai’i tighten UST regulations for better leak detection, leak investigations and visual inspections, but given the threat underground fuel tanks pose to aquifers, all underground tank systems should be held to the same standards and requirements, regardless of size or location.
Stopping fuel leaks completely is impossible, but states can mitigate future clean ups with stricter laws and regulations that require state and management oversight, UST training, leak detection and cleanup plans that follow the science to protect aquifers.
Image courtesy of Flickr. Originally published by S&S on February 16, 2022.