The City of Modesto public water system, serving over 218,000 people in Stanislaus County, uses surface water and has no EPA health-based violations recorded. The EPA's Unregulated Contaminant Monitoring Rule (UCMR3) data collected between 2013 and 2015 provides insights into volatile organic compounds (VOCs) detected in the system's water.
Why Volatility Matters: Exposure Through Showering, Dishwashing, and Inhalation
VOCs can evaporate during household water use
Volatile organic compounds are solvent compounds that can vaporize into air during common activities like showering or washing dishes. This creates additional inhalation exposures beyond drinking water consumption.
Routes of exposure include skin contact and breathing
Aside from ingestion, VOCs may enter the body through skin contact or inhalation of vapors, making their volatility a factor in household exposure assessments.
Why a Granular Activated Carbon Bed is Sized for Contact Time Rather Than Flow Alone
Longer contact time improves removal efficiency of volatile organics
Granular activated carbon filtration relies on the water's retention time within the carbon bed to adsorb VOCs effectively, not just the volume passing through per minute.
Flow rate alone does not determine VOC reduction
System design prioritizes sufficient contact time to maximize interaction between water and carbon, enhancing solvent compound removal.
What the Measured Range Means Against Federal Standards, and What It Does Not Mean
Detected VOCs do not indicate violations or unsafe water
The EPA's UCMR3 sampling found some VOCs at levels above laboratory reporting thresholds, but none above any established federal maximum contaminant levels (MCLs), because no MCLs exist for these specific compounds under UCMR3.
Detection is a measurement, not a health risk determination
Presence above detection limits reflects laboratory sensitivity, not a safety concern. Household water can only be characterized by direct testing of that home's supply.
Which Volatile Organic Compounds Appear in This Record and Which Do Not, Named From The Facts
Detected VOCs in Modesto include 1,1-dichloroethane and HCFC-22
- 1,1-Dichloroethane detected twice above 0.03 μg/L, highest at 0.06 μg/L (0.06 parts per billion)
- HCFC-22 detected six times above 0.08 μg/L, with a maximum of 7.2 μg/L (7.2 ppb)
Other tested VOCs not detected above reporting levels
- Chloromethane, bromomethane, halon 1011, 1,3-butadiene, and MTBE were not detected above their respective reporting levels
How the Documented Treatment Technology Removes or Neutralises the Constituent
Autotrol VOCs & Industrial Chemicals Filter uses granular activated carbon
This system is designed to adsorb volatile organic compounds effectively through a carbon media bed, requiring proper contact time to trap solvent compounds like 1,1-dichloroethane and HCFC-22.
Carbon adsorption reduces both taste-impacting and volatile chemical concentrations
The Autotrol System reduces solvent compounds by binding them to the carbon surface, mitigating potential inhalation and ingestion pathways of VOCs in household water.
Ordering a Water Test to Confirm Your Household VOC Levels
The only way to know your home's specific VOC concentrations is through a certified laboratory water test for volatile organic compounds. A comprehensive VOC analysis will determine if VOCs are present above detection limits relevant to your water supply.
A result showing nondetect or levels consistent with the City of Modesto's public system record would clarify that no additional household treatment is needed beyond standard precautions.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2014-02-06. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for City of Modesto (CA5010010), CA: 825 results across 7 listed contaminants, 8 detections above the reporting level; no federal MCL for these UCMR-listed VOCs
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