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How mitigating contamination risks maximizes remedial outcomes
While news sources are not calling the recent extended levels of rainfall “El Niño,” it is apparent that in some regions of the Pacific, El Niño-like storms have delivered on a promise to usher in impressive precipitation. Particularly in rain-thirsty Northern California, reservoirs have rapidly refilled and snowpack is at an all-time high of 184%. Cities across the state of California have recorded their highest rain levels in years. That is good news for formerly drought-stricken Southern California.
Though considered by regulatory agencies as separate resources, groundwater and surface water are inextricably intertwined and essentially one resource physically connected and controlled by the hydrologic cycle, which involves the storage and movement of water from reservoirs found in the atmosphere, rivers, streams, lakes, oceans, glaciers, snowfields and groundwater. In other words, water finds a way.
In today’s highly industrialized societies, rushing waters are not always a welcome sight, particularly when viewed from the perspective of remediation professionals who work to eliminate or mitigate the levels of hazardous materials from both private and public soil and groundwater. Aside from the visible devastation caused by a forceful El Niño at the surface, there are far more troubling conditions percolating at another level—out of sight and perhaps out of mind among the general population—which have the potential to compromise human safety in both the short- and long-term.
In 1997 and 1998, during one of the strongest El Niños in recorded history, regions in the Pacific were hammered by extreme wind and rainfall. In California, particularly in the north Santa Monica Bay, extraordinary storms increased sewage runoff and dumped high concentrations of contaminants into the ocean and beaches where residents and tourists swam and surfed. Originating from the Santa Monica Mountains, the contamination prompted beach advisories and closures well into the summer, affecting some of the area’s most popular destinations and causing public health outbreaks that ranged from skin rashes to serious respiratory illnesses. With El Niño’s influence on the quality of ocean waters dauntingly apparent, experts began to shift the focus to a much deeper level and evidence of contaminated groundwater, including the spread of contaminants at the subterraneous level, prompted concerned scientists and environmentalists to work diligently to find ways to prevent such disasters before they occur.
It is now understood that excessive precipitation from events like El Niño—or any superstorm—has the capacity not only to spread contaminants at the surface but also to increase the spread of these contaminants underground, adversely affecting freshwater fisheries, wetlands, rivers and coastal waters, as well as municipal and industrial water supplies. That is a real concern, particularly in the U.S., where some 105 million people—or one-third of the population—receive their drinking water from public groundwater systems, which can be vulnerable to man-made contaminants like trichloroethene, benzene and fertilizers, as well as naturally occurring contaminants such as radon, uranium and arsenic.
The amount of contamination that reaches underground aquifers and the wells that supply that resource depends on the paths that directly connect the surface and the underlying aquifer systems. This connectivity affects the in-ground time of groundwater, and groundwater age plays a significant role not only in how fast the water recharges the aquifer reserves but also how it affects its chemistry.
During heavy rain events such as those associated with El Niño, storm water not only picks up and transfers surface contaminants like fertilizer and petroleum to storm drains and waterways but also infiltrates or soaks into the ground. Deep beneath the surface, the water carries and spreads contaminants into the underlying aquifer systems and—in worst-case scenarios—those contaminants end up in municipal wells. Over long periods of time, groundwater monitoring wells installed and used to analyze the quality of local groundwater at contaminated sites can become compromised by age or accidental damage. During heavy rain events, surface storm water runoff can make its way through compromised well covers and gain direct access to the underlying groundwater aquifer. Surface runoff water often carries oil and grease as well as many other contaminants directly into the underlying groundwater system.
Of the most common groundwater contaminants, trichloroethylene (TCE) is a significant environmental hazard to human health. A halocarbon commonly used as an industrial chlorinated solvent, TCE was once widely used as a metal degreaser, chemical extractant and intermediate, and component of various consumer products. In September 2011, the U.S. Environmental Protection Agency (EPA) concluded a 20-year toxicological review of TCE and listed it as a known carcinogen.
Other common groundwater contaminants at risk of spreading through groundwater during heavy rain events include petroleum hydrocarbons such as benzene, toluene, ethylene and xylene, along with gasoline additives like methyl tertiary butyl ether. These contaminants typically are found in underground storage tanks associated with gasoline service station operations and military clean-up sites. While the movement of contaminants like gasoline and TCE through the subsurface is complex, most contaminants are introduced to the subsurface by infiltration of these materials from surface spills or industrial processes through the soil matrix and into the underlying aquifers. Upon introduction of contaminants into the aquifer, the process of contaminant migration often is exacerbated by heavy rain events and can result in greater risk to human health and the environment.
For landowners, developers and government agencies in various stages of soil and groundwater remediation, the consequences of El Niño water-influx-related spread of contaminants are significant, both environmentally and financially. Therefore, it is essential to address potential risks before they occur. In fair weather conditions, a site’s groundwater concentration may meet state and EPA compliance. However, when affected by a large rain event, those once-acceptable levels have the potential to rise— particularly at sites that have incompletely removed contaminants either by design or otherwise. Increases in aquifer water levels after large rain or flooding events cause previously untouched contaminants to become soluble and subject to spread into previously remediated aquifer sections. This results in a renewed threat to the environment and human health as well as causes significant losses of time and money for those responsible for cleanup.
Remediation has played a key role in reducing or eliminating contaminants from soil and groundwater for decades. In the early-to-mid-1980s, the most common method for groundwater remediation was a simple pump-and-treat solution, with the contaminated soil either excavated and delivered to a treatment facility, composted or incinerated on site, or left unaddressed.
By 1990, however, progressive environmental consulting and engineering firms began searching for more cost-effective and environmentally compatible solutions. As a result, innovative in situ groundwater remediation technologies have been designed and improved upon over the past two decades to address the challenges of time and end-point uncertainty. One method of treatment uses highly dispersible, fast-acting, sorption-based technology, such as PlumeStop liquid-activated carbon, that captures and concentrates low level dissolved-phase contaminants within its matrix-like structure. Once contaminants are sorbed onto the regenerative matrix, biodegradation processes achieve complete remediation at an accelerated rate and prevent contaminant migration. It also is an effective tool for controlling and treating groundwater contamination associated with low-permeability porous formations and matrix back-diffusion, promoting diffusion out of the immobile porosity while preventing groundwater impact, and for treating sites with very low contaminant concentrations.
As the demand for environmental remediation increases, researchers and scientists who possess a greater knowledge of the potential risks associated with changes in climate conditions are working to provide smarter and more cost-effective solutions. Preparing for a natural disaster in conditions of uncertainty, requires public awareness and commitment by all stakeholders—private landowners and government agencies alike. This challenge requires all parties to take preventive measures to minimize risks to the environment and human health. It is critical that our highly industrialized world begin to judge the suitability of a given innovation, technology or process not on its simple economics but on the total footprint. The positive impact on economics must be judged against and outweigh the hazards (and costs) presented to the environment.
Migration of contaminants, such as fertilizers, often is exacerbated by heavy rain events.