It is National Groundwater Awareness Week March 11-17, 2012, and apparently Awareness Week is in its second decade of existence. Who knew, and that’s the problem, most people are unaware of groundwater despite its importance and impact on our lives. Recently, the US Geological Survey, USGS, reported that in 2007 105 million people, about a third of the population receive their drinking water from one of the 140,000 public water systems across the United States that use groundwater as their source. In addition, 15% of the population obtains their water directly from groundwater using private drinking water wells. Groundwater is also used for irrigation. Groundwater is an important natural resource, especially in those parts of the country that don't have ample surface-water sources, such as the arid West. Groundwater is a renewable resource, but not unlimited. Groundwater recharges at various rates from precipitation and other sources of infiltration.
Unlike other natural resources or raw materials, groundwater is present throughout the world varying from place to place, depending on rainfall conditions and the distribution of aquifers (rock and sand layers in whose pore spaces the groundwater sits). Precipitation and soil type determines how much the shallower groundwater is recharged annually. However the volume of water that can be stored is controlled by the reservoir characteristics of the subsurface rocks. Generally, groundwater is renewed only during a part of each year through precipitation, but can be abstracted year-round providing a reliable and clean source of drinking water to much of the population provided there is adequate replenishment, and it is protected from pollution. We need to be aware of the source of our groundwater it’s natural recharge rate and protect our aquifers from over use and contamination.
Groundwater is usually cleaner than surface water and as source water for drinking water supplies it is often superior to surface water. Groundwater is typically protected against contamination from the surface by the soils and rock layers covering the aquifer. This water is the only available clean drinking water in many areas. However, rising population, changes in land use, agriculture and industrialization increasingly place groundwater in jeopardy of contamination. Once contaminated, groundwater is very difficult to clean and often after removal of contaminated plumes only long term abandonment of use to allow for natural attenuation is the only possible course of action. Precious groundwater resources increasingly need to be protected from contamination and well managed to allow for sustainable long-term use.
Though the water quality of the public water supply systems is regulated by the US EPA under the Safe Drinking Water Act (SDWA), drinking water supplies are only tested for slightly over 90 contaminants (many of them natural impurities) when there are over 80,000 chemicals known in the United States. In addition, the US EPA only regulates the finished water delivered to consumer through public water supply systems. The underlying groundwater quality often has not been tracked by the US EPA. In their study of the quality of groundwater sources in the United States, the USGS found trace levels of pesticide compounds (not regulated under the SCWA) or VOCs in 64% of the groundwater samples taken from public water supply wells. Three-quarters of the organic-contaminants contained an herbicide (atrazine or simazine) or an herbicide degradate (deethylatrazine), and about 40% contained the solvents perchlorethene or trichloroethene. Pesticides and VOCs were detected in a significantly greater proportion of samples from unconfined aquifers than in samples from confined aquifers. The groundwater with the greatest number of contaminants was consistently from shallower unconfined aquifers demonstrating the natural protection provided by a confining geological layer.
Groundwater typically contains geological trace elements such as arsenic, manganese, strontium, iron, and boron and radionuclides (radon, radium, and gross alpha-particle radioactivity). These contaminants originate from the rocks and sediments that contain the aquifers and are entirely natural, but there are health related maximum contaminant level standards for these elements within the SDWA. For groundwater supplies, the concentration of these geological contaminants does not change quickly over time and remains rather constant in any given region. What is changing is the appearance of modern pesticides and herbicides, substances atrazine or simazine and their breakdown products in groundwater. These chemicals slowly percolate into groundwater from land application of pesticides and herbicides used for greener lawns and gardens or for agriculture. They appear in shallower groundwater supplies. Another source of contamination of groundwater is our septic systems. It is estimated by various sources that 25-35% of all US homes use septic systems.
There are many different types of septic system designs. The most common type used for single family homes consists of a septic tank and leach field. A septic tank can be an anaerobic (without air) tank or an aerobic tank (with air). The anaerobic system is a single chamber tank that receives the toilet and drain waste from the house and allows the solids to settle down to the bottom of the tank where the anaerobic bacteria that live in the tank digest the organic materials while the effluent (water around all that stuff) flows out to the leach field to be purified by passing through soil until it reaches the groundwater. The final finishing for septic waste is the leach field or other soil absorption system, where it percolates into the soil, which provides final treatment by removing harmful bacteria, viruses, and nutrients. This is a natural process requiring suitable soil for successful waste water treatment, but even with the most suitable soil septic systems cannot remove chemicals from the water. Household cleaners, fertilizers, pesticides, pharmaceuticals and personal care products will just pass through the system and begin to appear in the recharge to the groundwater.
As our homes are filled with ever more powerful and chemical laden cleaners, antibacterial soaps, pesticides, herbicides, paints, petroleum products, insecticides and drugs-all the wonders of modern life, these things find their way into our waters. Through stormwater runoff and waste water treatment plants these things easily find their way to our surface waters. Waste water treatment plants are no more equipped to treat waste water for these chemicals than a septic system is and quite frankly none of these public supplies of water are routinely tested for these substances. Waste water treatment plants do not have chemical removal processes. Through our septic systems, and gardens and yards these contaminants are appearing in our groundwater. Although each septic system and yard can make an insignificant contribution to ground water contamination, the sheer number of such systems and their wide spread use of pesticides and herbicides in every area make them serious contamination sources. What goes down the drain or is sprayed and spread in the garden goes into the groundwater. To make a difference we all need to protect our groundwater.
The following actions to protect groundwater from contamination and are based on recommendations from the National Groundwater Association:
1. Properly store hazardous household substances like paints, paint thinners, petroleum products, fertilizers, herbicides, insecticides, and cleaning products in secure containers
2. Mix hazardous household substances over concrete or asphalt where they can be cleaned up or absorbed onto disposable media like paper towels and then properly disposed of with hazardous material waste.
3. Dispose of hazardous household wastes at an appropriate waste disposal facility or drop-off. Most landfills and city trash programs have these drop-offs.
4. Do not put hazardous household wastes down the drain or in the toilet ever,
5. Do not put any wastes down a dry or abandoned well or use sinkholes as waste disposal holes.
6. Service your septic system regularly at a minimum service it according to local health department recommendations
7. Check your private drinking water well annually to make sure the sanitary seals are intact.
8. Decommission abandoned wells on your property using a qualified water well contractor
9. Fix or replace any leaking aboveground or underground tanks storing hazardous substances. All underground storage tanks should have secondary containment to prevent contamination of the subsurface. All tanks will eventually fail.