Groundwater: Frequently Asked Questions

What is groundwater, and why it is important to protect it.

Table of Contents

What is groundwater?

Groundwater is water below the ground surface in the cracks and spaces in soil, sand, and rock. Groundwater is contained in formations known as aquifers, which consist of materials such as sand and gravel that are permeable (having large connected spaces between the materials that allow water to flow through). The area where water fills the aquifer is known as the saturated zone, and the top of this zone is known as the water table.

How much groundwater exists in the US today?

Scientists estimate that there are approximately 33 TRILLION gallons of groundwater in the U.S.

How much do we use?

Every day approximately 76 BILLION gallons of water are pumped from the ground for use in the U.S.

Why is it important to protect groundwater?

Approximately one-half the population of the United States uses groundwater as a drinking water supply. Most groundwater is naturally clean and free of pollutants, but contamination of groundwater can cause serious health effects from harmful bacteria and nitrates. Elevated nitrate levels can pose a risk to infants. Babies under six months of age are particularly susceptible to health problems from high nitrate-nitrogen levels, resulting in the condition known as methemoglobinemia (blue baby syndrome). Wildlife can also be harmed by contaminated groundwater. Excessive levels of nutrients such as nitrogen and phosphorus can harm the health of freshwater and marine ecosystems. See the Massachusetts Estuaries Project and Reports for information on Massachusetts coastal waters polluted by excess nitrogen in groundwater.

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How is groundwater contaminated?

There are many potential sources of contamination to groundwater. Improperly treated wastewater from malfunctioning treatment facilities and on-site systems is one major source. Other sources include:

  • Leaking underground storage tanks
  • Landfills
  • Hazardous waste sites
  • Excessive use of road salts and fertilizers.

Why is clean groundwater important to lakes, rivers, and streams?

Rivers and streams are called surface water bodies. Groundwater provides much of the flow for surface water bodies, contributing approximately 492 BILLION gallons per day to U.S. surface waters and habitat. If the groundwater is polluted, it can impact the use of these surface water bodies for drinking water. High levels of nutrients, such as nitrogen and phosphorus, can cause eutrophication, algal blooms or fish kills.

How long does it take groundwater to get clean again after it is contaminated?

Groundwater moves very slowly and can take years to naturally cleanse itself even if the source of the pollution is removed. It is possible to employ sophisticated treatment processes to remove contaminants, but that can be very expensive. Rather than clean contaminated groundwater, it is better to prevent the pollution from happening in the first place.

What factors are considered before allowing wastewater to be discharged into the ground?

A hydrogeologic study must be performed first. Key factors in the study will include wastewater flow rate, depth to groundwater, direction of groundwater flow, type of soil, distance to sensitive receptors such as drinking water supplies, wetlands, and surface water bodies, and the proposed level of wastewater treatment.

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