Water in McHenry County, Illinois, commonly comes from groundwater wells tapping the 110QRNR aquifer. Water drawn from these wells travels through plumbing to household taps. Understanding the local sulfide content helps determine potential causes behind a sulfur odor, often described as a 'rotten egg' smell, which may affect water aesthetics.
If your well or source depth differs within the aquifer
The 47 USGS groundwater samples taken from 45 wells in this area ranged between 14 and 344 feet in depth. The sulfide concentrations measured showed a median level of 0.0105 mg/L and varied from undetectable to 0.15 mg/L. Because sulfide levels can depend on well depth and the location of the water source within the aquifer, your individual well might have differing sulfide characteristics. Knowing your well depth and its position can help anticipate what to expect regarding sulfur odor presence.
If you want to understand how sulfide enters groundwater here
Sulfide in groundwater typically arises from natural geological and biological processes, including the reduction of sulfate minerals by bacteria in anaerobic conditions underground. In McHenry County's 110QRNR aquifer, these processes lead to the observed sulfide range. Sulfide itself is colorless but can give water a noticeable sulfur or rotten egg aroma, causing aesthetic concerns without necessarily indicating a health issue.
If you want to interpret sulfide levels versus federal standards
None of the 47 samples exceeded federal thresholds for sulfide or related constituents. Detected sulfide is not a violation or health hazard by itself but may impact water taste and smell. It is important to recognize that a detection means the instrument measured sulfide at some concentration—not that the water is unsafe. Federal limits focus on health risks; secondary standards address aesthetic factors like odor. The measured range indicates what occurs naturally in the aquifer rather than a problem specific to any individual well.
If you have a large household, a seasonal residence, or a second home
Water usage patterns affect how often water with sulfur smell is noticed. Larger households may cycle water faster, potentially limiting odor development in plumbing. Seasonal homes or properties with intermittent use might experience stronger or more persistent sulfur odors due to water sitting longer in pipes, allowing hydrogen sulfide gas to accumulate. Knowing your usage can help decide if sulfur smell relates to water source conditions or plumbing stagnation.
If you consider changes over seasons and multi-year trends in water quality
The USGS sampling occurred over two years from mid-2010 to mid-2012, revealing sulfide remains within the documented range without clear upward or downward trends. Seasonal and annual variations are common in groundwater quality, influenced by factors like precipitation and aquifer recharge. The data show sulfide is regularly detected in this aquifer but with variation that does not signal worsening conditions or acute events.
What you should not conclude from area data: This regional sulfide information does not define your individual water quality or health risk. Only testing your own well water can confirm its sulfide content and odor causes. A detection in the aquifer samples is not a violation or indication of unsafe water. Sulfur smell often has aesthetic causes which do not imply federal health standard exceedances.
For households concerned about sulfur odor, equipment like the C-Series Rotten-Egg Sulfur Smell Filter ships ready to configure to reduce hydrogen sulfide-related smell in water. Testing your water to determine sulfide levels can guide whether such treatment is appropriate for your situation.
Where this information comes from
Source: USGS groundwater sampling. Sampled 2012-08-23. These figures describe groundwater sampled in this area. They are not a test of any individual private well - only a test of that well can establish its own water.
On record: U.S. Geological Survey sampling of Sulfide in the 110QRNR aquifer (McHenry County): 47 results from 45 wells, median 0.0105 mg/L, range 0.0-0.15 mg/L; none above any federal threshold