Home hazard report for 91773 — San Dimas, CA
ZIP 91773 is served by GSWC-San Dimas: no health-based violations since 2016, latest lead result 1.2 ppb, PFAS 4.6 ppt. Los Angeles County is in EPA radon zone 2.
No health-based violations reported since 2016.
90th-percentile lead in the latest round (Jan 2026). Lead comes mostly from household plumbing and service lines, so individual homes can be higher.
Highest PFOA or PFOS result in EPA’s 2023–2025 testing was at or above 4.0 ppt, EPA’s 2024 maximum contaminant level for each. 2 PFAS compounds detected.
Predicted average indoor radon between 2 and 4 pCi/L. Test your home; many homes here exceed 4 pCi/L.
FEMA’s overall natural-hazard risk for this census tract, relative to the rest of the U.S.
The nearest active Superfund site is 7.7 miles away.
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Where ZIP 91773 is
Dashed: ZIP area · blue: utility service area · scroll or pinch to zoomDrinking water: GSWC-San Dimas
Health-based violations
No health-based violations reported since 2016.
Full record for GSWC-San Dimas →
Other systems overlapping this ZIP: Three Valleys MWD, Metropolitan Water Dist. of So. Cal..
Lead
90th-percentile lead per sampling round (90% of the homes sampled were at or below this level). Black line: EPA’s 15 ppb action level; under the Lead and Copper Rule Improvements the action level becomes 10 ppb from 2027.
PFAS (“forever chemicals”)
| Compound | Highest result | Samples with detection | EPA limit |
|---|---|---|---|
| PFBA | 20 ppt | 3 of 20 | — |
| PFOS | 4.6 ppt | 2 of 20 | 4 ppt MCL |
| PFHpA | not detected | 0 of 20 | — |
| PFBS | not detected | 0 of 20 | — |
| PFHxS | not detected | 0 of 20 | — |
| PFNA | not detected | 0 of 20 | — |
| PFDA | not detected | 0 of 20 | — |
| PFPeA | not detected | 0 of 20 | — |
| PFHxA | not detected | 0 of 20 | — |
| PFOA | not detected | 0 of 20 | 4 ppt MCL |
| HFPO-DA (GenX) | not detected | 0 of 20 | — |
EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR 5), samples 2023–2025; ppt = parts per trillion (ng/L). The 4.0 ppt maximum contaminant levels for PFOA and PFOS were set by EPA in 2024; water systems have until the end of the decade to comply.
Radon in Los Angeles County
EPA radon zone 2 — moderate potential. Predicted average indoor radon between 2 and 4 pCi/L. Test your home; many homes here exceed 4 pCi/L.
Radon is a colorless, odorless radioactive gas from soil and rock, and the leading cause of lung cancer among non-smokers. EPA recommends fixing a home at 4 pCi/L or above and considering it from 2 pCi/L. A short-term test kit costs about $15–30. How radon zones work →
Natural hazard risk
FEMA rates the overall natural-hazard risk of this neighborhood (census tract) as Relatively High, with relatively moderate social vulnerability and very low community resilience.
FEMA National Risk Index (December 2025): expected annual losses from each hazard combined with social vulnerability and community resilience, rated relative to all U.S. census tracts. Hazards not listed are not applicable here. It describes the area, not a single building; flood insurance maps (FEMA FIRMs) decide flood-insurance requirements.
Live conditions: river gauges and flood levels · tornado warnings · wildfire detections · earthquakes — our sister maps, updated from NOAA, USGS and NASA every few minutes.
Superfund sites nearby
| Site | Status | Distance |
|---|---|---|
| San Gabriel Valley (Area 2) Baldwin Park Area, California · EPA ID CAD980818512 | Active (final NPL) | 7.7 mi |
EPA Superfund National Priorities List (NPL): the country’s most serious known hazardous-waste sites, each with an EPA cleanup record (linked). Distance is measured from the ZIP center to the site’s reference point; being near a site does not by itself mean exposure — EPA site pages describe what was found and how it is being cleaned up.
What this is — and isn’t. These are records your water utility and state reported to the EPA, and the EPA’s radon map for your county. They describe the system and the area, not the water from your own tap or the air in your home. For that, read your utility’s annual Consumer Confidence Report and test: lead and radon tests are inexpensive.
Questions about 91773
Who supplies drinking water to ZIP 91773?
GSWC-San Dimas (EPA ID CA1910142), a surface water (rivers, lakes) system serving about 56,564 people.
Is there lead in San Dimas, CA tap water?
The utility’s latest 90th-percentile lead result (Jan 2026) was 1.2 ppb; EPA’s action level is 15 ppb, falling to 10 ppb from 2027. Lead mostly comes from service lines and home plumbing, so the only way to know your tap is to test it.
Does San Dimas, CA water have PFAS?
Highest PFOA or PFOS result in EPA’s 2023–2025 testing was at or above 4.0 ppt, EPA’s 2024 maximum contaminant level for each. 2 PFAS compounds detected.
Has the water system in 91773 had violations?
No health-based violations reported since 2016.
What natural hazards affect ZIP 91773?
FEMA’s National Risk Index rates the overall natural-hazard risk here as Relatively High; the highest-rated hazards are earthquake (relatively high), riverine flooding (relatively high), wildfire (relatively moderate).
Are there Superfund sites near 91773?
The nearest active Superfund site is 7.7 miles away. Sites within 10 miles: San Gabriel Valley (Area 2) (7.7 mi, Active (final NPL)).
Is radon a problem in Los Angeles County?
Los Angeles County is in EPA radon zone 2 (moderate potential). Predicted average indoor radon between 2 and 4 pCi/L. Test your home; many homes here exceed 4 pCi/L.