By Daniel Theobald, "Wastewater Dan"
It supplies drinking water for more than half of the total U.S. population and greater than 95 percent of the rural population. It helps grow our food because more than 60 percent of it is used for irrigation to grow crops. It's an important component in many industrial processes, and it’s a source to recharge lakes, rivers, and wetlands.
“It” is groundwater — the water found underground in the cracks and spaces in soil, sand, and rock, stored in and moving slowly through geologic formations of soil, sand, and rocks called aquifers.
And it's under threat.
Groundwater depletion, a term often defined as “long-term water-level declines caused by sustained groundwater pumping,” is a vital issue associated with groundwater use, and many areas of the U.S. are experiencing it.
Groundwater depletion is recognized by measuring the lowering of the water table — the point below which the ground is saturated with water. For example, in the Atlantic Coastal Plain area of New York state, pumping water for domestic supply has lowered the water table, reduced or eliminated the base flow of streams, and has caused saline groundwater to move inland. Depleting groundwater has also been measured throughout the U.S., including the Pacific Northwest, Desert Southwest, and West-central Florida, among other areas.
The effects of depleted groundwater include the following:
Lowering of the water table
The lowering of the water table is the most severe consequence of groundwater depletion. For water to be withdrawn from the ground, it must be pumped from a well that reaches down below the water table. If groundwater levels decline too far, the well owner might have to deepen the well, drill a new well, or, at least, attempt to lower the pump. As water levels decline, the rate of water the well can yield may decline as well.
Increased costs for the user
As the depth to water increases, the water must be lifted higher to reach the land surface, thereby increasing cost.
Reduction of water in streams and lakes
There is more of an interaction between the water in lakes and rivers and groundwater than most people think. Some, and often a great deal, of the water flowing in rivers comes from seepage of groundwater into the streambed.
Groundwater pumping can alter how water moves between an aquifer and a stream, lake, or wetland — either by intercepting groundwater flow that discharges into the surface-water body under natural conditions, or by increasing the rate of water movement from the surface-water body into an aquifer. A related effect of groundwater pumping is the lowering of groundwater levels below the depth that streamside or wetland vegetation needs to survive. The overall effect on the environment is a loss of riparian vegetation and wildlife habitat.
The basic cause of land subsidence is a loss of support below ground. When water is taken out of the soil, the soil can collapse, compact, and drop.
Deterioration of water quality
Compromises to groundwater can impact the quality of the overall water supply itself. One water-quality threat to fresh groundwater supplies is contamination from saltwater — salt water intrusion. Not all of the water in the ground is fresh water; much of the very deep groundwater and water below oceans is saline. Pumping deep wells can cause saltwater to migrate inland and upward, resulting in saltwater contamination of the water supply.
One high-volume option to replenishment of depleting groundwater is the conversion of sewage to tap water. This process involves treating and recycling wastewater from municipal sewer systems, converting it into drinkable water in a timely period.
Sewage is converted into drinkable water using three processes. The first process uses ultrafiltration to remove the physical solids. The second uses reverse osmosis (RO) to remove the dissolved solids, and the third and final process is disinfection with ultraviolet (UV) light, which kills bacteria that transmit waterborne diseases.
The drinkable water is then pumped into the environmental waters to replenish depleting groundwater. And this can be a life-sustaining business model for other communities throughout the U.S.
Other options using artificial methods to replenish groundwater include the following:
Rainwater harvesting is another method to replenish ground water. But this method can be used only during the rains. In urban and rural areas, the rooftop rainwater can be conserved and used for recharge of groundwater. This approach requires connecting the outlet pipe from the rooftop to divert the water to existing wells/tube-wells/bore-wells or specially designed wells.
Raingardens to recharge groundwater
A raingarden is designed to hold rainwater runoff from rooftops, driveways, patios, or lawns. It contains native shrubs, perennials, plants, etc. Every time it rains, water runs off impermeable surfaces such as roofs or driveways, collecting pollutants like particles of dirt, fertilizer, chemicals, oil, garbage, and bacteria along the way. The pollutant-laden water enters storm drains untreated and flows directly to nearby streams and ponds. Raingardens collect rainwater runoff, allowing the water to be filtered by the vegetation and percolate into the soil, thereby recharging groundwater aquifers. This process filters out pollutants.
Advantages offered by raingardens include:
Use of injection wells is a more energy-intensive method of groundwater replenishment, utilizing high-pressure pumps to actively ‘push’ water into aquifers. Sources of water for injection wells include treated wastewater, stormwater, and agricultural runoff.
Municipal wastewater and industrial wastewater are suitable sources for replenishing groundwater by pumping through RO process units.
These are only some options to replenish depleting groundwater. If you have other options to share, please submit them here.
About Dan Theobald:
Known in the industry as “Wastewater Dan,” Daniel L. Theobald, proprietor of Environmental Services (www.esdlt.com), is a professional wastewater and safety consultant/trainer. He has more than 24 years of hands-on industry experience operating many variants of wastewater treatment processing units and is eager to share with others his knowledge about water conservation.
Theobald serves as an active consultant for industries looking to achieve and maintain improved wastewater treatment at reduced cost. He is a Lifetime Member of the Who’s Who Registry of Professionals and holds numerous certifications from wastewater management regulatory boards and professional organizations. Theobald contributed one chapter to the Water Environment Federation’s (www.wef.org) Manual of Practice #37 (MOP-37), a technical manual resource guide for biological nutrient removal, published in 2013.
Image credit: "...and the rains came," © 2005 Neil Piddock, used under an Attribution 2.0 Generic license: http://creativecommons.org/licenses/by/2.0/