Dave Hanson gets into detail about iron bacteria and the "rotten egg" odors complaints from your customers.

We get an average of 1,400 hits on our Web site (www.designwater.com) per month. What amazes me is that over 85 percent of the hits are coming from end users. These are your customers. Most of the questions are related to a frustration of our industry not being able to deal with their problems. Iron bacteria and the "rotten egg" odors are the top complaints. Last month, a general article appeared in National Driller Last month, a general article appeared in National Driller regarding well troubles in which both problems were briefly described. We will now get more specific. It's important for you to understand these problems, keep appropriate information and relay this knowledge to your customers. Copy articles and present them to customers. If you want a printed copy of this article, call National Driller or me. Study this and present the information yourself. It adds to your credibility regarding well troubles in which both problems were briefly described. We will now get more specific. It's important for you to understand these problems, keep appropriate information and relay this knowledge to your customers. Copy articles and present them to customers. If you want a printed copy of this article, call National Driller or me. Study this and present the information yourself. It adds to your credibility and elevates you above your competition when you can solve people's water problems.

Scanning electron microscope (SEM) photo of corrosion caused by anaerobic sulfate reducing bacteria. Courtesy of Metallurgical Technologies Inc.

Sulfate Reducing Bacteria (SRBs)

SRBs are anaerobic in nature, meaning they survive in an environment where there is very little oxygen. In wells, these areas could include a sump below a screen or non-producing areas of a screen. Wells that are not pumps frequently allow the oxygen in water to dissipate. The environment then becomes anaerobic and all kinds of bacteria can grow.

SRBs reduce sulfates in the water. They require sulfate levels above 50 ppm to provide the opportunity for massive growth. They can survive with only trace amounts of sulfate. However, limited nutrient would not provide significant growth. As they process sulfates, these bacteria release an organic acid that is very corrosive. You may notice corrosion and pitting along with the odors. The natural pH of water can be affected if the growth is severe. A hydrogen sulfide gas (H2S) is released during this process.

SRBs are naturally occurring soil bacteria and can be found in formations with low permeability. These areas have a low oxygen environment but must provide sulfate levels or gypsum for the bacteria to survive.

In ground water applications, we would expect as much as 95 percent of H2S gas is a result of SRBs. The other 5 percent of the H2S found in ground water is processed chemically by acids often associated with sites around oil drilling/oil production areas or solution mining applications. This chemical process may release gas from sulfur and can lower the natural pH of the ground water. This enhances sulfur in the environment and sulfur oxidizing bacteria growths can increase substantially. SRBs then have an environment in which to thrive. The bacteria often are well into the formation and the gas can be carried with water flow toward the well during pumping.

New Wells

Many times contractors have told me as soon as they start pumping a new well, they get the odor. Since these bacteria can be naturally occurring and since they are anaerobic (little oxygen), think about the type of soils that would provide that kind of environment. Think about your driller's log when you encounter these problems. The portion of a formation that would have a low-oxygen environment would generally be of low permeability and sufficient sulfate levels - like some clays or shales. If you allow flow into a well (screened or open hole) from around these areas, you increase the chance of having odors in the well. Jim Schumacher, a contractor from Algona, Iowa, tried this theory. One of the areas he generally drills in has a major problem with rotten egg odors. The formation was cemented sandstone approximately 70 feet to 80 feet thick. The upper 30 feet to 40 feet had several shale lenses and the lower portion was clean sandstone. He drilled a test hole to confirm the location of the shale lenses, reamed the test hole to below the lowest shale lens, set his casing and grouted it in. Then he reamed the clean sandstone through the casing. The result? No odors. He followed this with eight more wells in this area and seven of them also had no odor.

So can you drill wells without the rotten egg odor? I say, if you pay attention to well design and do some homework, you can increase your chances. If you are drilling in unconsolidated formations, pay attention to clay lenses and screen only the clean sands or gravels.

Sumps are sometimes used in the design of new wells. This is a casing area below the screen to collect debris from development and allow sand to settle during pumping. What a perfect environment for any anaerobic bacteria to grow. There is no water movement in this sump area during pumping and whatever advantage it provides for sand or silt retrieval during development or during the long term pumping of a well, I believe is not worth the effort. The lower portion of the screen can be cleaned during development and the well should be designed for sand-free pumping.

Some areas of a screen don't provide much water movement as water follows the path of least resistance. Specific development in all areas of the screen doesn't always take place so dead areas within a screen can also provide an environment for these bacteria. Remember, SRBs must have sufficient nutrient available to grow effectively - not all undeveloped screens will have this problem.

If you just drilled a well that has the odor, there isn't much you can do other than water treatment. Many drillers and pump installers have had great success with aeration or oxygen injection into a system to allow the gas to escape. If you pump water directly into a bladder type of tank, the only release area for the gas is the faucet and your customer will complain.

Old Wells

Older wells can suddenly develop this odor. When customers call and complain, the very first questions you should ask are: 1. How old is the well? 2. Did you or someone just replace a galvanized pressure tank with a bladder tank? 3. Did you recently install a new water heater?

1. The age of the well. If the well is older than six months and the answer to the last two questions is no, you can estimate there has been a change in the environment within the well. First, test pump the well at the well head to confirm the problem is in fact, in the well. It could be in the underground lines or in the system. You can buy a hydrogen sulfide test kit for under $50 and test (quantify the problem) the well on site. Do a test within 10 minutes of turning on the pump. Do a second test in 30 minutes and a third in an hour. If the numbers are high on the first test and decline drastically on the latter tests, the problem likely is in the well. The latter tests have a higher concentration of water from the aquifer and therefore will have lower concentrations of the gas. You can do a "highly technical" smell test by pumping water into a bucket or glass using the same time frames, but it certainly won't be as accurate.

The change in an environment can be the presence of slime bacterial growths or mineral scale deposits in the well. As a well is pumped, some of the decaying slime formers may slough, exposing these SRBs. This may cause reddish water. These bacteria are generally found under these growths and scale. This biological mass would include layers of aerobic slime formers on the surface and anaerobic bacteria at the base. This microscopic slime formation can happen within three weeks of the drilling of a well and odor problems exist within months of drilling.

You can never drill a true and straight well. Sometimes when you pull a pump, the pump will scrape this slime formation or scale on the side wells of the casing, exposing the SRBs. Even though the customer didn't complain of an odor problem originally, he may now experience the problem suddenly. This can happen with coliform bacteria, as well.

The well now has to be treated for slime forming bacteria. In a well, the H2S odor may not always be present until a well is treated (acids or chlorine) and the outside protective shell (scale or slime) is removed. You can actually make the problem worse if the products you are using are not designed to remove and kill SRBs. During any treatment for slime bacteria, we recommend wire brushing the casing and screen or open borehole. If H2S gas is observed, the wire brushing of a casing will expose more SRBs to the environment. We actually had a contractor overcome by H2S gas on a job site during wire brushing. At least be aware of that possibility.

It is possible to have SRBs present in a slime mass in a piping system or treatment vessel. Always make sure the odor is coming from the well before treating the well. If the well isn't the culprit, you can follow the problem backward by testing with the hydrogen sulfide test kit.

2. Replacements of galvanized tanks. The old galvanized tanks allowed water to contact air and the gas was released in the tank before it got to the faucets. Hence, no odor problems. If you change a galvanized tank to a bladder tank and the odor exists, either go back to the galvanized tank, to an air injection system then into the bladder tank, or to an aeration tank.

3. New water heaters. This certainly is not my area of expertise, but anode rods are put into new water heaters to act as a sacrificial anode in corrosive water. The corrosion of this rod often releases a gas with a similar odor. Ask the customer if the problem is occurring in cold water, hot water or both faucets. If it is in the hot only, look to this as a possible remedy.


We need to solve our customers' problems. If you don't know answers to questions, find someone with the expertise to help. Sometimes lab tests can be of a great help. You can't test very effectively for H2S in a laboratory as the gas escapes. The testing for H2S must be done in the field with immediate results. You can test for anaerobic bacteria and the presence of sulfate reducing bacteria, but the test is somewhat subjective.

Our industry sometimes suffers from a lackadaisical attitude. You can elevate yourself so far above your competition because it's easy, and you can command a higher price. That's profit! It's the only way to stay in business. We can't continue to cut prices and provide cheaper products. You can't survive that way. Look for different ways to build business and separate yourself from the rest. Correcting well problems is one way of doing that. Offer solutions to your customers. Most contractors want to drill wells or set pumps only. There are already too many contractors doing just that. Do something different. Learn. Find a niche in your area. It's easy because most people won't.