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Understanding What a 'Not Detected' Result Means Under Lab Detection Limits

The EPA’s unregulated contaminant monitoring rule (UCMR3) provides occurrence data for various volatile organic compounds (VOCs) in public water systems, including Sacramento Suburban Water District. When a lab reports a compound as 'not detected,' it means the concentration was below the method detection limit (MDL) for that test – the smallest amount the instrument can reliably measure. This designation does not indicate absence of the compound, only that it was not measurable above that threshold during sampling.

Which Volatile Organic Compounds Appear in Sacramento Suburban Water District Records

The UCMR3 monitoring from 2013 to 2015 showed several VOCs tested in the public system serving Sacramento County. Notably, 1,1-dichloroethane and HCFC-22 were detected at low levels in some samples, while chloromethane, bromomethane, Halon 1011, 1,3-butadiene, and MTBE were not detected above reporting limits. None of these detections correspond to any federal maximum contaminant levels (MCLs), as these VOCs are unregulated under current EPA standards.

Interpreting Terms: 'Detected', 'Median', and 'Range' in Sampling Data

'Detected' means the compound’s level measured above the MDL but does not imply a violation. The 'median' of detections refers to the middle value among samples where the compound was present above the MDL, helping to illustrate typical concentrations during that monitoring period. The 'range' covers the lowest to highest detected levels, showing variability across samples. For example, HCFC-22 had a highest detected concentration of 15.0 micrograms per liter (µg/L or parts per billion) with a median detection around 13.0 µg/L.

Distinguishing Public Water System Records from Private Well Testing

Data from the Sacramento Suburban Water District reflect system-wide monitoring of surface water sources serving nearly 195,000 people, not conditions in individual household plumbing or private wells. Private well owners must conduct their own comprehensive VOC testing to understand their home's water quality because localized factors such as well depth, soil composition, and nearby sources of contamination greatly influence VOC presence and concentration.

Fixtures and Household Processes Sensitive to VOCs

Volatile organic compounds may affect household fixtures and water use differently. Because VOCs are volatile, inhalation exposure can occur during showering and dishwashing as residues evaporate. Water used in drinking and cooking is another exposure pathway. Existing home water equipment that once managed VOCs may struggle as VOC levels fluctuate or increase, especially in residences using older or undersized systems. Equipment specifically designed for removing VOCs, such as the Fleck VOCs & Industrial Chemicals Filter, ships ready to configure and can provide enhanced reduction of these solvent compounds.

Deciding when to upgrade water treatment is often driven by the need to maintain effective control over VOCs to address health-conscious user expectations and mitigate exposure routes.

Recap and Reference

This briefing is based on Sacramento Suburban Water District’s EPA UCMR3 records, monitoring several VOCs without any health-based violations recorded. These data are system-wide and do not replace individualized water testing. For official data and further details, consult the EPA’s public water system records under UCMR3 occurrence data at epa.gov.

Where this information comes from

Source: EPA SDWIS public water system record. Sampled 2015-08-19. These figures describe the public water system's record, not the plumbing inside any individual building.

On record: EPA UCMR3 monitoring (2013-2015) for Sacramento Suburban Water District (CA3410001), CA: 758 results across 7 listed contaminants, 6 detections above the reporting level; no federal MCL for these UCMR-listed VOCs