Petroleum fuels and toxic chemicals can contaminate groundwater by leaching downward through the soil after being spilled onto the ground or from underground storage tanks. This contamination is especially problematic because half of our country’s population depends on groundwater as the source of their drinking water. And of course the repercussions for the natural environment are extensive, too.
Groundwater contamination can come from landfills, underground or above ground storage tanks, industrial work sites and numerous other types of businesses. The most common groundwater contamination comes from volatile organic compounds, or VOCs. These chemicals are used in many consumer products as well as industrial processes. For instance, trichloroethelyne, or TCE, is found in cleaning fluids, degreasing agents, pesticides, fire extinguishers and spot removers.
Since groundwater contamination can include organic and inorganic chemicals, bacteria and radioactivity, as well as variable physical characteristics, a number of methods have been developed to meet remediation objectives. First you need to have a soil investigation and then their specific value depends on the traits of the site being treated.
Treatments for groundwater contamination generally fall into three technology categories:
- Biological, which can include bioaugmentation, bioventing, biosparging, bioslurping, phytoremediation and some types of permeable reactive barriers.
- Chemical, which can include ion exchange, carbon absorption, chemical oxidation, surfactant enhanced recovery and also some types of permeable reactive barriers.
- Physical, which can include pump and treat, air sparging, dual-phase vacuum extraction or monitoring-well oil skimming.
It’s sometimes more effective and faster to combine treatment methods. An example is the long-running groundwater contamination clean-up project, still underway, that is a collaboration of the US Department of Energy and New York’s Brookhaven National Laboratory (BNL). BNL’s remediation plan includes pump and treat systems, recirculation systems with in-well air stripping or carbon treatment and air sparging with soil vapor extraction to treat different areas of the site.
Pump and treat is just what the name implies, bringing groundwater to the surface for treatment then returning it to the aquifer. This is considered the standard technology within the environmental clean-up industry. It’s especially useful for applications where noise isn’t a concern, as air stripper towers tend to be loud, or where space isn’t an issue.
Re-circulation wells are usually preferred for off-site residential areas, to minimize disruptive presence, because groundwater is actually treated below the surface.
Typical goals of groundwater contamination clean-up are to arrest the spread of contaminants, remove the contaminants or reduce their levels to acceptable regulatory standards, and to ultimately return the land to a safe and usable condition.
Many factors affect design and implementation of treatment plans.
Cleaning up groundwater contamination starts with a detailed site investigation. EDMS can also help groundwater soil investigation. This investigation looks at characteristics such as:
- Geological or hydrogeological conditions such as permeability and groundwater flow
- Proximity to people
- Accessibility – some systems require little electricity and can be operated self-sufficiently in remote areas using solar panels or a wind turbines
- Chemical properties of the entire site and the contaminated plume in particular
- History of the site as it relates to when/how contamination occurred
All these traits build a composite picture that can then be used, along with project goals and objectives, to evaluate possible treatment options and design the most effective strategy. The remediation plan could include a series of steps. Ongoing monitoring is usually part of the process to facilitate any needed adjustments as clean-up is underway, and because the process itself can cause subsurface conditions to change. Monitoring following project completion ensures the results achieved are as expected.
Over the years, we’ve learned a great deal about the true danger of VOCs and other hazardous substances. As a result there are many federal, state and local regulations that strive to prevent these chemicals from entering the environment where they can endanger public health, wildlife or plants. Identifying and cleaning up sites already suffering from groundwater contamination remains a critical concern.