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Elevated hydrogen sulfide concentrations in groundwater

Elevated hydrogen sulfide concentrations in groundwater

Hydrogen sulfide is a colorless, flammable gas. It smells like rotten eggs and is sometimes called hydrosulfuric acid, stink gas, or sewer gas. It is also commonly known by its chemical formula H2S. Natural processes in the soil subsurface, like bacterial anaerobic decay, produce H2S.

Drinking water wells or groundwater sources in your area may naturally contain H2S gas. Bathing or showering with water containing elevated H2S levels may pose a significant health risk. Elevated H2S gas concentrations, released into the air from the water from shower spray or bath water, can accumulate in an unventilated bathroom.

How does exposure affect my health?

Inhalation of excessive levels of H2S gas in a confined space can result in loss of consciousness, respiratory failure, and death. A major factor in its toxicity is its ability to fatigue the sense of smell. H2S loses the typical rotten egg odor when the concentration rises, and exposed individuals may not be aware of increased gas concentrations. Inhalation of concentrations of 500-1000 ppm will cause rapid unconsciousness and death through respiratory paralysis and asphyxiation.

Because H2S is heavier than air, it can accumulate in open trenches and other confined enclosures that are open at the top. Never enter a trench or confined space that has not been tested for breathable atmosphere.

Reducing exposure

If H2S water concentration exceeds 1.3 milligrams per liter, residents should try to follow these recommendations:

  • Reduce the length of time

    Reduce the length of time for showering or bathing to 10 minutes or less.

  • Reduce the water flow rate

    Reduce the water flow rate in the shower or the volume of water in the tub.

  • Reduce the water temperature

    Because higher water temperatures cause an increase in the amount of H2S released from water, reduce the water temperature at the water heater and in the tub or shower.

  • Ventilate the bathroom

    Most importantly, ventilate the bathroom as much as possible by installing exhaust fans rated for maximum air exchange for the size of the bathroom, or by opening a window. If there are small children in the home, installation of a motion sensor or other type of sensor to activate exhaust fans should be considered.

Testing your water well for hydrogen sulfide

H2S testing has never been included in a routine test conducted for water supply approval. It is recommended that property owners located in areas where groundwater is known to contain H2S, sample their drinking water wells as soon as possible. Samples should be collected at a time that reflects typical household water use. Avoid collecting water samples after extended lack of well water use, such as following a vacation, or after periods of heavy water use, like lawn watering or laundry. Have one or more additional water samples tested on different days to confirm the H2S level.

For a nominal fee, the EGLE Drinking Water Laboratory or a commercial laboratory may be contacted to arrange for H2S testing of your water supply. Your local health department can also help by providing you with a list of laboratories or by making arrangements for the water testing by the EGLE Laboratory.

Find a drinking water laboratory

Contact your local health department

A male scientist in a lab coat and purple nitrile gloves is bending over a lab bench, holding test tubes for PFAS testing

Treatment of hydrogen sulfide

There are various methods. They should be chosen based on the level of hydrogen sulfide, the amount of water being treated, the levels of iron and manganese, and bacterial contamination. Hydrogen sulfide can be reduced or removed by activated carbon filtration, shock chlorination, oxidizing chemical injection, oxidizing filtration, or water heater modification.

residential home with trees

Incident in Monroe County

In 2001, a homeowner returned home to find about 4 inches of water in his basement. He went into the basement to find the source of the water and opened the door to the basement offset where the water pressure tank was located. When he opened the door he was overcome and passed out. His wife went into the basement to rescue him and also passed out. The fire department responded to the 911 call made by one of the children. The couple was transported to the hospital.

The fire department detected H2S at a level of 132 ppm in the basement. Upon turning the electricity back on, they noted that water was spraying out of the pressure tank in the basement offset. Monroe County is noted for having H2S in the groundwater. The water supply providing water for domestic and household purposes to the house was a hauled water system (water is hauled by truck to the residence). The on-site well was used for irrigation purposes only.

The Monroe County Health Department and the Environmental Protection Agency (EPA) investigated to determine the source of the H2S. The EPA constructed a plastic tent over the pressure tank and turned on the pump, allowing the water to spray into the confined airspace. They monitored the H2S level in the tent and within a short period of time, peaked out their equipment (>200 ppm). The permissible exposure limit is 20 ppm ceiling concentration and a peak exposure limit of 50 ppm for no more than 10 minutes if no other measurable exposure occurs.

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