Our ‘hidden’ and undervalued resource: groundwater

This week is National Groundwater Awareness Week. In the majority of Minnesota, though, this week should really be named “National Drinking Water Week” because that’s the easiest way for people to connect to how groundwater influences their daily lives.

For our area, groundwater is THE water source – not just A water source. We interact with it over and over every day – when we go to the faucet to get a glass of water or to wash our hands, to flush our toilets, or water our plants. We see it irrigating crops out in the fields and/or helping cool operations in industrial settings. ALL groundwater. All of it.

Yet, for being so incredibly interwoven in our lives, groundwater is still an abstract concept for many – it’s hard to really grasp how much water is under our feet, how it connects and interacts with the water we see on the surface, and how our actions and land use as individuals and communities can influence the quality and quantity of the resource.

So let’s spend a few minutes to learn about our groundwater and what we can do to protect it.

Geology is Destiny

The fact that we have such extensive groundwater resources at all is due to Minnesota’s geologic history. For millions of years, Minnesota was actually a shallow marine environment, with sandy beaches, coral reefs, and deeper calm waters. This period led to the deposition of sand and silt hundreds of feet thick that eventually consolidated into sandstone, siltstone, and limestone. These formations are the foundation of our local groundwater resources – as rain and melted snow infiltrated into the ground over millennia, the water took up residence between the pore spaces of the sandstone layers until they were completely saturated. We refer to these water-bearing layers as ‘aquifers.’

Minnesota, about 450 million years ago. Yes, really.

Our more recent glacial history also plays a part, too – as glaciers came and went in this region through the last ice age, they deposited sand and gravel that blankets a large portion of the region. These unconsolidated sediments form surficial aquifers in our area.

Unconsolidated sediment deposits with underlying bedrock layers form the aquifers we source for our water. Figure from the Groundwater Digest of the Metropolitan Council.

Groundwater acts as the the ultimate ‘bank’ account.

Think of our relationship to groundwater like a checking account. We make ‘withdrawals’ by pumping water from the ground but we also need to make sure we don’t ‘overdraw’ our aquifers by pumping too much. This is especially important in years of drought (like in 2021), and as we consider how our population continues to increase throughout the basin (in Washington County alone, population is projected to increase by 43% to over 360,000 people by 2030).

We also need to make sure we are making enough ‘deposits’ by allowing water to recharge the aquifers and replace the water we are pumping out. This means being very mindful of minimizing new impervious surfaces as development increases and protecting known recharge areas, including lands where the aquifers are close to the surface and lakes that collect and store water that recharge the aquifers.

Groundwater pollution is tough to fix.

With groundwater ‘out of sight,’ it’s hard to realize how our actions above ground can lead to contamination of this underground resource. Land use practices, including waste disposal, fertilizer use, and negligent upkeep of septic systems, can eventually lead to pollutants seeping into our groundwater. While soil can act as an effective filter in many cases, the geology of the region can work against us too. Southern Washington County has pervasive ‘karst’ topography, which is a type of landscape where the limestone has become eroded to form extensive holes and fissures underground. Such open cracks in the ground can provide direct pathways for surface water and contaminants to enter our groundwater. Unsealed abandoned wells in other areas can also be a direct source of contamination.

Once groundwater is polluted, it is extremely difficult and costly to remediate. The best defense against groundwater pollution is a good offense – prevention! Aside from protected recharge areas, many municipalities establish ‘wellhead protection areas’ around their public supply wells that guide land use practices and waste disposal within those areas to protect groundwater from contamination.

The flow in Brown’s Creek in Washington County is sustained by groundwater. Photo Credit: Angie Hong

Groundwater sustains much more than our immediate water supply.

Groundwater is intimately connected to our surface water resources. Groundwater serves as the primary water source for several lakes and streams throughout the Lower St. Croix watershed, including Lake Elmo, Lake Edith, Trout Brook, Valley Creek, Brown’s Creek and Mill Stream. Keeping our groundwater clean also translates into keeping the aquatic ecosystems – plants, macroinvertebrates, fish, etc. – in those surface waters healthy and thriving.


You can help keep our groundwater resources plentiful and healthy with a few easy actions. Make sure you properly dispose of any chemicals or hazardous materials versus dumping them on the ground, build less impervious surfaces (narrower driveway, smaller patios), test your water regularly if you have a private well, and practice reducing your overall water use in your house and yard!