Chromium-6 in San Gabriel Valley Water
Four EPA Superfund sites. More than 1 million residents on groundwater. Here is what the public data shows and how to protect your home.
The San Gabriel Valley sits atop one of California's most-documented industrial groundwater contamination zones. The EPA listed four separate Superfund sites in the San Gabriel Basin on the National Priorities List beginning in 1984, covering an aquifer that supplies drinking water to more than one million residents across Los Angeles County. Hexavalent chromium, a known carcinogen, has been detected in monitoring wells across the Baldwin Park, El Monte, South El Monte, Puente Valley, and Whittier Narrows operable units. California's public health goal for chromium-6 is 0.02 ppb. The enforceable limit (MCL) is 10 ppb, re-established in October 2024. Most utilities operate within the MCL but above the health goal, which is why many San Gabriel Valley households install NSF-certified point-of-use reverse osmosis as an additional treatment barrier. This guide covers which cities carry the greatest documented risk, how to read your utility's Consumer Confidence Report for chromium-6 levels, and which NSF-certified filtration systems reduce hexavalent chromium at the tap.
Updated October 2024: California's chromium-6 MCL
California re-established an enforceable Maximum Contaminant Level (MCL) of 10 ppb for hexavalent chromium in October 2024 following a 2017 legal challenge that had suspended the previous 10 ppb rule. Utilities must comply with the MCL. California's public health goal (PHG) of 0.02 ppb, set by OEHHA, remains the health-protective benchmark and is not an enforcement limit. Source: California OEHHA.
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Why does the San Gabriel Valley have chromium-6 in its groundwater?
The San Gabriel Valley was a center of mid-20th-century industrial manufacturing. Los Angeles County aerospace firms, chrome plating operations, metal finishing shops, and electronics manufacturers operated throughout the valley from the 1940s into the 1970s. Many disposed of industrial solvents, heavy metals, and chromium compounds directly into the ground or into unlined ponds and lagoons. Because the San Gabriel Basin aquifer underlies much of the valley and is the primary drinking water source for the region, contamination released at the surface migrated downward into the groundwater over decades.
The EPA designated the first San Gabriel Valley Superfund site in 1984 and eventually listed four separate sites covering the Baldwin Park, El Monte, South El Monte, Puente Valley, and Whittier Narrows areas. Each site contains multiple operable units where distinct contamination plumes have been identified and mapped. Cleanup is ongoing. The San Gabriel Basin Water Quality Authority, created by state legislation, manages a Section 406 remediation program that funds treatment for contaminated wells and monitors aquifer recovery.
Sources: EPA San Gabriel Valley All-Site Update and SGBWQA Section 406 Plan (2025).
Which San Gabriel Valley cities are most affected?
The four Superfund sites span a broad corridor from Azusa and Irwindale in the north to El Monte, South El Monte, La Puente, and Whittier in the south. The table below maps cities to their associated Superfund operable unit based on EPA and SGBWQA published maps. Contamination levels vary by well, blend, and treatment stage. Always verify current levels with your specific utility's Consumer Confidence Report.
| City | Superfund Operable Unit | Notes |
|---|---|---|
| Baldwin Park | Baldwin Park OU | One of the most-documented OU areas; treated blended supply from Main San Gabriel Basin Watermaster |
| El Monte | El Monte OU | VOC and heavy-metal contamination documented; active remediation ongoing |
| South El Monte | South El Monte OU | Within the southern Superfund boundary; multiple municipal wells affected historically |
| Azusa | Area 2 / Area 4 boundary | Adjacent to industrial corridor; groundwater monitoring active |
| Irwindale | Area 4 | Legacy industrial sites; hexavalent chromium detected in monitoring wells per EPA five-year review |
| La Puente | Puente Valley OU | Part of Superfund area 4 cleanup zone; residential wells should be tested |
| Whittier Narrows | Whittier Narrows OU | Active remediation; SGBWQA 406 Plan covers this zone |
Sources: EPA Superfund All-Site Update / EPA Five-Year Review, Area 4 / SGBWQA 406 Plan 2025. Chromium-6 levels at any individual property depend on your utility's current treatment and blending; verify with your CCR.
What do the Consumer Confidence Reports actually show?
For a county-by-county breakdown of water quality across Southern California, see our 2026 water quality guide. California utilities serving more than 15 connections must publish an annual Consumer Confidence Report (CCR) disclosing contaminant detections. For hexavalent chromium, utilities must report any detection above the minimum reporting level of 1 ppb. Because California's enforceable MCL is 10 ppb, a utility can be fully compliant while reporting chromium-6 at, say, 4 ppb, which still exceeds California OEHHA's 0.02 ppb public health goal by a factor of 200.
To find your utility's most recent CCR:
- Look up your water utility name on your water bill.
- Visit the California State Water Resources Control Board's Drinking Water Watch at waterboards.ca.gov or call your utility directly.
- Search for chromium-6 (hexavalent chromium) in the detection tables.
- Compare the detected level against the MCL (10 ppb) and the PHG (0.02 ppb) to understand where your supply stands relative to both standards.
If you are on a private well in an affected area, utilities' CCRs will not cover your water. Contact a California ELAP-certified laboratory to arrange independent chromium-6 testing. ELAP certification is required for official compliance testing in California.
Which filtration technologies actually remove chromium-6?
Not every water filter removes hexavalent chromium. The key is looking for NSF International certification that specifically lists chromium or hexavalent chromium as a verified reduction claim. See our chromium-6 removal systems page for installed options. The table below compares the three most common residential technologies.
| Technology | NSF Certification | Chromium-6 Reduction | Best For |
|---|---|---|---|
| Reverse Osmosis (Point-of-Use) | NSF/ANSI 58 | 90 to 97 percent (typical for chromium-6 at municipal concentrations) | Drinking and cooking water; under-sink installation |
| Strong-Base Anion Exchange (Whole-Home) | NSF/ANSI 61 (system components) | High; regenerated in place, varies by chromate loading | Whole-house chromium-6 reduction; works alongside existing softener |
| Activated Carbon Block | NSF/ANSI 42 (taste/odor only) | Low; standard carbon is NOT certified for chromium-6 removal | NOT recommended as sole chromium-6 treatment; use for taste and chlorine only |
NSF certification data: NSF International Water Treatment Certification. Always verify a specific product's NSF certification for chromium-6 before purchase.
Do San Gabriel Valley utilities treat water before delivery?
Yes. Utilities operating in the San Gabriel Basin that draw from affected groundwater basins are required to meet the California MCL of 10 ppb for hexavalent chromium. Many utilities blend contaminated groundwater with cleaner imported water from the Metropolitan Water District or treat groundwater through ion exchange, oxidation, or filtration before distribution. The San Gabriel Basin Water Quality Authority's Section 406 program has funded dozens of treatment systems across the basin since 1992.
This means tap water delivered in most affected communities has already been reduced from raw groundwater concentrations. However, treated blended water can still contain detectable chromium-6 above California's 0.02 ppb public health goal. The 406 program's annual reports and individual utility CCRs are the authoritative source for current delivery-point levels. The SGBWQA makes its monitoring data publicly available at wqa.com.
What should San Gabriel Valley homeowners do right now?
Knowing your exposure level is the first step. Here is a practical sequence:
- Request your utility's CCR. Contact your water utility and ask for the most recent Consumer Confidence Report. Look specifically for the hexavalent chromium or chromium-6 row. Compare the detected level to both 10 ppb (MCL) and 0.02 ppb (PHG).
- Test your tap if you are on a private well. CCRs only cover utility-supplied water. Private well owners in the Superfund zone should test annually through a California ELAP-certified lab.
- Install NSF/ANSI 58-certified reverse osmosis for drinking water. A properly installed under-sink RO system provides an additional treatment barrier at the point of use, reducing chromium-6 and other contaminants in your drinking and cooking water regardless of what arrives from the utility.
- Consider a whole-home filtration system with anion exchange if you want whole-house chromium-6 reduction, not just at the kitchen tap. Anion exchange is effective at removing chromate ions across all faucets.
- Schedule a professional water test. An on-site test by a trained water-quality specialist can assess chromium-6 alongside hardness, pH, TDS, and other parameters that affect which treatment approach is right for your home.
How does chromium-6 affect health at low concentrations?
Hexavalent chromium is classified by the International Agency for Research on Cancer as a Group 1 carcinogen when inhaled. For ingested chromium-6 through drinking water, the California Office of Environmental Health Hazard Assessment established the 0.02 ppb public health goal based on a theoretical one-in-one-million excess lifetime cancer risk. The National Toxicology Program found evidence of carcinogenicity in animal studies involving oral chromium-6 exposure, which informed California's risk assessment.
The risk at any given exposure level depends on concentration, duration, and individual health factors. For regulatory and policy context, California's framework distinguishes between the enforceable MCL (what utilities must meet) and the PHG (what health science suggests is protective). Both numbers matter for understanding your water quality situation.
Frequently asked questions about San Gabriel Valley chromium-6
Which San Gabriel Valley cities have the highest chromium-6 risk?
The areas closest to the four EPA Superfund sites in the San Gabriel Basin carry the highest documented industrial contamination risk. Baldwin Park, El Monte, South El Monte, Azusa, Irwindale, and La Puente are within or adjacent to identified Superfund operable units where hexavalent chromium has been detected alongside volatile organic compounds. Residents in those cities should review their utility Consumer Confidence Reports and the San Gabriel Basin Water Quality Authority monitoring data at wqa.com. Chromium-6 levels can vary by well and treatment stage.
What caused chromium-6 contamination in the San Gabriel Basin?
Industrial activity from the 1940s through the 1970s is the primary documented cause. The San Gabriel Valley was a center of aerospace, metal finishing, chrome plating, and electronics manufacturing. Solvents, heavy metals including hexavalent chromium, and other industrial chemicals were released into the soil and groundwater over decades. In 1984 the EPA listed four separate Superfund sites across the San Gabriel Basin on the National Priorities List to address this legacy contamination. Cleanup is ongoing as of 2024.
Is the San Gabriel Valley water safe to drink?
Water utilities operating in the San Gabriel Valley are required to meet California's Maximum Contaminant Level (MCL) of 10 ppb for hexavalent chromium, re-established in October 2024. Most utilities operate blended supplies and treatment steps designed to meet that MCL. However, California's public health goal for chromium-6 is 0.02 ppb, which is 500 times lower than the MCL. Utilities comply with the legal limit but many supplies exceed the health-protective goal. Households with health concerns often install NSF-certified point-of-use reverse osmosis for an additional treatment barrier.
Does a reverse osmosis system remove chromium-6 from San Gabriel Valley tap water?
Yes. Reverse osmosis systems certified under NSF/ANSI Standard 58 are tested and certified for hexavalent chromium reduction. In independent testing, certified RO membranes typically reduce chromium-6 by more than 90 percent from the feedwater at the concentrations found in municipal supplies. A certified under-sink RO system is the most practical option for drinking and cooking water in affected San Gabriel Valley homes.
What is the San Gabriel Basin Water Quality Authority?
The San Gabriel Basin Water Quality Authority (SGBWQA) is a state-created agency that oversees the Section 406 remediation program for contaminated groundwater in the western San Gabriel Basin. It funds treatment, monitoring, and well rehabilitation across the four Superfund operable units. Their publicly available 406 Plan reports document current contaminant levels and cleanup progress. You can access their monitoring data and reports at wqa.com.
How do I find out how much chromium-6 is in my specific water supply?
Your water utility is required by California law to publish an annual Consumer Confidence Report (CCR) listing contaminant levels detected during the reporting year, including hexavalent chromium if detected above the reporting threshold. You can request it from your utility directly or find it through the California State Water Resources Control Board's Drinking Water Watch database at waterboards.ca.gov. If you are on a private well, you will need to arrange your own testing through a California ELAP-certified lab.
What this guide covers vs. what it does not
This guide is based on publicly available EPA Superfund documents, SGBWQA reports, California OEHHA publications, and NSF certification data. It does not contain real-time utility monitoring data. Levels at your specific address depend on which utility serves you, their current treatment approach, and your location relative to well fields and blending stations. Always verify current levels with your utility CCR or a professional on-site water test before making filtration decisions.
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Last updated: July 28, 2026. Data sources: EPA Superfund Region 9 documents, San Gabriel Basin Water Quality Authority 406 Plan (2025), California OEHHA chromium-6 PHG (2011, affirmed 2023), California State Water Resources Control Board MCL update (October 2024), NSF International Standard 58.
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