Groundwater Pollution: Sources & Prevention

Nov. 1, 2005
Overview of regulations and contamination factors

About the author: Marianne R. Metzger is general products business unit manager for National Testing Laboratories, Ltd. She can be reached at 800.458.3330, ext. 223, or by e-mail at [email protected].


Updated 9/28/21

What Contaminants are Found in Groundwater

Contamination is defined as the introduction of any undesirable physical, chemical or microbiological material into a water source. There are two types of groundwater contamination sources: point sources and non-point sources. Point sources include landfills, leaking gasoline storage tanks, leaking septic tanks and accidental spills; as the name implies we can point directly to the source of contamination. A point source is technically defined as any discernable, confined and discrete conveyance from which pollutants are or may be discharged.

Non-point sources can be less obvious and can include naturally occurring contaminants, such as iron, arsenic and radiologicals and runoff from parking lots, pesticides and fertilizers that infiltrate the soil and make their way into an aquifer. There are numerous regulations that address both point sources and non-point sources of groundwater contamination. In addition to these regulations, it is important for citizens to become aware of how their actions can affect the groundwater contamination and take action to reduce any potential contamination.

Groundwater Pollution Regulations

The Clean Water Act passed in 1972 was enacted to reduce point source pollution. The act requires an NPDES permit to discharge any pollutant from a point source, specifically industrial facilities and publicly owned treatment works. Before this regulation, many facilities were discharging contaminants directly into waterways. This regulation is aimed at protecting surface water. However, point sources do not just contaminate surface water; they can contaminate groundwater as well. Point sources that can contaminate groundwater include landfill leachate and leaking underground storage tanks. These discharges are normally accidental and therefore, not regulated. The Water Quality Act of 1987 set up specific permitting guidelines for storm water discharge. This made industries become more aware of the effect their operations were having on the environment and held them accountable for anything they discharged into the sewer systems. In 1987, the Clean Water Act was amended to establish the section 319 Non-Point Source Management Program. This program allows states, territories and Indian tribes to receive grants to address non-point pollution. In 1991, the National Monitoring Program was established and supported by the funds authorized under Section 319 of the amended Clean Water Act. The primary objectives of the program include evaluating the effectiveness of watershed technologies designed to control non-point source pollution and improving our knowledge about non-point source pollution.

Groundwater Contamination Factors

Many factors can affect how groundwater contamination occurs. The depth of a well is an obvious factor because a contaminant has to travel farther in deeper wells. The soil and formations the contaminant travels through act as a natural filter. The underlying geologic formations additionally affect the possibility of groundwater contamination in two ways. First, the geological formation can be a source of groundwater contamination; there are various rock formations that contain minerals such as calcium, magnesium, iron, arsenic and various radiologicals. While some of the minerals may not cause any known health effects, naturally occurring arsenic and radiologicals are known carcinogens. Second, the formation can slow the contaminant or it may have the opposite effect.

For example, contaminants can travel more quickly through sand than clay. The amount of rainfall in a given area will contribute to contamination as well; the more rain that falls, the more water is filtered down to recharge the aquifer. Rainfall that seeps into the ground can carry these contaminants into the aquifer.


There are several properties to consider when looking at groundwater contaminants. Some of these properties include: persistence, adsorption, solubility, volatility and molecular size.

Persistence refers to the staying power of a contaminant. Certain groundwater contaminants do not breakdown easily and will persist in the environment for a long time. PCBs are an example of persistence in the environment.

In 1976, the Toxic Substances Control Act prohibited the manufacture and distribution of PCBs, yet they are still found in our environment today. Adsorption refers to how tightly a compound will attach to soil particles. Compounds that are strongly adsorbed are less likely to leach into the groundwater.

Solubility is the ability of a substance to dissolve in a solvent. Compounds that are highly water-soluble will dissolve in water percolating through the soils down to the water table. Methyl Tertiary Butyl Ether (MTBE) is an example of a contaminant with a high water solubility, which is one of the reasons MTBE contamination is so widespread.

Volatility of a substance refers to its tendency to change from a liquid or solid into a gas. One group of contaminants called Volatile Organic Chemicals readily change from liquid or solid to gas when exposed to the atmosphere. The more volatile a substance is, the more likely it will be lost to the atmosphere.

Lastly, the molecular size can play a role. The smaller the molecule, the more likely it will be able to travel between soil particles.

More Regulations for Groundwater Protection

The Environmental Protection Agency (EPA) has enacted several programs that are designed to protect groundwater. These programs include the Safe Drinking Water Act (SDWA), the Resource Conservation and Recovery Act (RCRA), the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the Toxic Substance Control Act (TSCA) and the Clean Water Act.

In addition to setting standards for public water supplies, the SDWA regulates underground disposal of waste into deep wells. The SDWA has also developed a nationwide program for the states to implement wellhead protection programs in an effort to protect groundwater sources.

RCRA regulates hazardous waste storage, transportation, treatment and disposal. CERCLA authorizes the government to cleanup contamination sites, which are commonly referred to as Superfund Sites. FIFRA regulates pesticides that have the potential to contaminate groundwater. TSCA allows the EPA to control the manufacture, use, storage, distribution and disposal of toxic chemicals. The CWA, as previously explained, aids in the development of programs to protect water sources. This includes public education; consumers need to become aware that anything they dump into the sink or down a drain will influence water quality.

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