Why Granular Activated Carbon Beds Prioritize Contact Time Over Flow Rate
VOCs Removal Depends on Effective Contact Time
Granular activated carbon (GAC) filters work by adsorbing volatile organic compounds (VOCs) from water. The efficiency depends on the water's contact time with the carbon, not just how fast water flows through. Longer contact allows the carbon more opportunity to capture solvent compounds, reducing VOC levels effectively.
Differences in Groundwater Contamination Sources: Gasoline vs. Dry-Cleaning Releases
Gasoline Releases Leave a Distinct VOC Profile
Gasoline leaks often contribute compounds like MTBE to groundwater. However, Madison Water Utility's monitoring (2013-2015) found no MTBE above the reporting level of 5.0 micrograms per liter (µg/L or parts per billion, ppb). This suggests no significant gasoline-related VOCs in the supply.
Dry-Cleaning Chemicals Present Different VOCs
Solvent compounds from dry-cleaning, such as 1,1-dichloroethane, were detected in some water samples, with the highest recorded concentration being 0.08 µg/L (0.08 ppb), below any federal standard. This indicates trace detection but no confirmed exceedance or safety issue.
Interpreting 'Not Detected' Results and Detection Limits
Understanding Method Detection Limits in Laboratory Testing
When a compound is listed as 'not detected' for Madison's water system, it means the level is below the laboratory's method detection limit (MDL), for example, less than 0.2 µg/L for chloromethane. This does not mean the compound is absent, only that it was not measurable above the set threshold in those tests.
The Impact of Plumbing Materials and Age on VOC Presence
Plumbing Can Affect VOC Levels Independently of Source Water
Volatile organic compounds measured in public water systems represent source water quality and do not reflect any changes that may occur within household plumbing. Older materials or specific plastics can introduce or retain additional compounds, so individual testing is necessary to understand the water quality at your tap.
What Measured VOC Ranges Reveal and What They Do Not
Readings Are Measurements, Not Regulatory Exceedances
Measurements reported by Madison Water Utility for VOCs like 1,1-dichloroethane ranged up to 0.08 µg/L, with no federal maximum contaminant level assigned to these compounds. Detecting a VOC above a reporting level is simply a measurement and not a health-based violation, nor does it inherently indicate unsafe water.
Volatile Organic Compounds Detected and Not Detected in Madison's Water
Detected VOCs Include 1,1-Dichloroethane
This solvent compound appeared in two of 44 test results at low concentrations. Other VOCs such as chloromethane, bromomethane, HCFC-22, Halon 1011, 1,3-butadiene, and MTBE were not detected above laboratory reporting limits during monitoring periods.
Absence of Other Common Volatile Organics
Compounds frequently associated with industrial solvents and gasoline additives, including MTBE and various halogenated hydrocarbons, were below detection levels in all reported results.
Addressing VOCs in Household Water
To reduce the presence of volatile organic compounds and industrial chemicals potentially present in your water, consider the C-Series VOCs & Industrial Chemicals Filter. This carbon-based filtration system ships ready to configure and is designed specifically to adsorb solvent compounds effectively, helping to improve water quality at the point of use based on measured demand values you find in your own water tests.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-12-29. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Madison Water Utility (WI1130224), WI: 300 results across 7 listed contaminants, 2 detections above the reporting level; no federal MCL for these UCMR-listed VOCs