Seasonal Water-Table Changes Can Shift Solvent Plumes Around Wells
A common misunderstanding about VOCs, or volatile organic compounds, is that their presence in groundwater remains static. However, the groundwater table in Cary, Mchenry County, fluctuates seasonally, causing solvent plumes—subsurface areas containing these compounds—to move relative to well intakes. This means VOC levels near a well can vary over time depending on factors like rainfall or drought conditions, groundwater recharge, and pumping rates. Your well screen's depth and location relative to these changes affect any VOC concentration it might draw, but this dynamic behavior cannot be predicted from public water system data alone.
Volatility Influences Exposure Routes Beyond Drinking Water
Volatile organics are notable for easily evaporating into air from water. In household use, this means that inhalation and dermal contact during activities such as showering or dishwashing can represent significant exposure routes—not just ingestion by drinking. As vapors enter indoor air, they can be inhaled, which differs from less volatile contaminants typically bound to water particles. Understanding this characteristic highlights why some residents concerned about VOCs in Cary's water may experience effects even when dissolved concentrations are low. The public system data informs on water concentrations but does not address vapor-phase exposure in homes.
Gasoline Releases and Dry-Cleaning Solvents Leave Different Groundwater Fingerprints
Another common confusion is that all VOC contamination comes from similar sources. In Cary’s groundwater, solvent compounds may arise from various origins, including gasoline leaks and industrial solvents used in dry-cleaning. Gasoline-related VOCs often consist of compounds like 1,1-dichloroethane, while dry-cleaning solvents may include chloromethane and HCFC-22. The Cary public water system monitoring found no detection of 1,1-dichloroethane but did detect chloromethane and HCFC-22 at low levels. These differing chemicals result in distinct groundwater impact patterns and persistence, influencing treatment needs.
Start With Simple Checks Before Pursuing Detailed Laboratory Tests
Determining whether your household water has problematic levels of volatile organics requires laboratory testing of your own water source. Before this step, homeowners should verify system water reports, understand the public supply data for Cary, and assess visible water characteristics or odors that sometimes accompany VOCs. Professional lab analysis specifically for VOCs requires collecting samples under controlled conditions to avoid volatilization loss. While the Cary public water system serves thousands, its data is an average from multiple connections and does not substitute for private testing.
Which Volatile Organic Compounds Were Found in the Cary System Record?
The EPA Unregulated Contaminant Monitoring Rule 3 (UCMR3) results for the Cary public water system, serving about 17,826 people, report these VOC detections from 2013 to 2015:
- Chloromethane: Detected in 4 of 16 samples above the reporting level of 0.2 micrograms per liter (µg/L), with a highest measured concentration of 1.322 µg/L (1.322 parts per billion or ppb) and a median of detected values at 0.72 µg/L.
- HCFC-22: Detected once above the reporting level of 0.08 µg/L at 0.245 µg/L (0.245 ppb).
- Other VOCs: 1,1-dichloroethane, bromomethane, Halon 1011, 1,3-butadiene, and MTBE were all either not detected or detected below their respective reporting levels in all samples.
Importantly, none of these detections represent violations of federal health standards, as there are currently no maximum contaminant levels (MCLs) established for these specific VOCs under UCMR3. This means the presence alone does not indicate unsafe conditions for the public water system.
Concluding: The Essential Test for Understanding Your Household Water
Given the variability of VOC presence and the limits of area-wide data, the definitive way to know your household water quality in Cary with respect to volatile organic compounds is to have your water tested by a qualified laboratory for VOCs. This test measures actual concentrations specific to your well or connection, considering seasonal changes and source variability. Should VOC levels be detected above your comfort or any guidance level, technologies such as the C-Series VOCs & Industrial Chemicals Filter can then be considered to reduce volatile organics effectively. The C-Series System ships ready to configure for residential water treatment needs related to these compounds, offering a tailored approach to managing solvent compounds in drinking water.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2013-11-22. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Cary (IL1110100), IL: 108 results across 7 listed contaminants, 5 detections above the reporting level; no federal MCL for these UCMR-listed VOCs