Clarifying What 'Not Detected' Means in Lab Results
Method Detection Limits Set What Counts as Measurable
When the government records show that a volatile organic compound (VOC) was 'not detected', it means its concentration was below the laboratory's method detection limit. For example, if 1,1-dichloroethane is not detected above 0.03 micrograms per liter (µg/L), it could still be present at a lower level, but not measurable by that method. This threshold is not a health benchmark, just the technical boundary of the test.
Which Volatile Organic Compounds Were Measured and Found in This System
Cross County Rural Water System’s VOC Sampling Results
- Eight VOCs listed under EPA's Unregulated Contaminant Monitoring Rule (UCMR3) were tested from 2013 to 2015.
- No detections above the laboratory reporting limits occurred for 1,1-dichloroethane, chloromethane, bromomethane, HCFC-22, Halon 1011, or 1,3-butadiene.
- Methyl tertiary-butyl ether (MTBE) was also tested twelve times with no detections above the 5.0 µg/L reporting level.
These VOCs are examples of solvent compounds and industrial chemicals sometimes found in groundwater due to urban or industrial activities.
Why Secondary Aesthetic Standards Are Distinct From Health-Based Limits
Appearance and Taste Thresholds Differ From Safety Benchmarks
Some VOCs have secondary standards addressing their taste, odor, or staining effects, but these are not health-based limits. The Cross County Rural Water System has two EPA-recorded health-based violations, but none related to VOCs listed here. Therefore, the presence below detection limits of these VOCs does not indicate a health risk or system violation.
Designing a Granular Activated Carbon Filter: Contact Time Over Flow Rate
Effective VOC Removal Requires Sufficient Water-Carbon Interaction
Filters that target volatile organics like VOCs rely on adsorbing contaminants onto activated carbon. The key performance factor is contact time—the duration water spends within the carbon bed. Merely passing water quickly through a filter does not ensure removal. Systems configured to provide adequate contact time allow the carbon to trap solvent compounds more effectively.
Interpreting Terms: 'Detected', 'Median', and 'Range' in Public Data
Understanding Sampling Record Language
- Detected: A measured concentration above the method detection limit.
- Median: The middle value of all measurements when listed in order.
- Range: The span from the lowest to the highest measurement.
In this Cross County data, no measurements of the listed VOCs exceeded detection thresholds, so these statistical terms do not indicate any detected solvent compounds in the sampled system during the monitoring period.
What You Should Not Conclude from This Area’s VOC Record
This water system’s VOC monitoring data shows no detectable concentrations of the tested volatile organic compounds above established detection limits. This does not guarantee every household’s water is free of VOCs, since these results represent system-wide groundwater source sampling rather than individual home plumbing or well tests. To understand your own water quality, consider professional laboratory testing of your tap water.
Addressing VOC concerns effectively involves choosing treatment technology designed for solvent compounds and industrial chemicals. The C-Series VOCs & Industrial Chemicals Filter ships ready to configure for point-of-entry use. It uses granular activated carbon sized for optimal contact time to reduce VOCs commonly found in groundwater from industrial sources.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2014-01-14. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Cross County Rural Water System (AR0000459), AR: 60 results across 7 listed contaminants, 0 detections above the reporting level; nothing detected above the method reporting level