1,4-Dioxane Contamination

1,4-Dioxane in California Drinking Water

Ranked by max 1,4-dioxane detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR

111

Cities Tested

Over HA

50%

% Over HA

1.02 µg/L

State Avg

▲ 15% vs national

vs National

624

Health Violations

Analysis

1,4-Dioxane in California: what the data shows

California has 111 cities with 1,4-dioxane data from the EPA's UCMR 3 program (2013–2015). 1,4-Dioxane was detected above the 0.35 µg/L EPA health advisory in 55 of those cities. The state average max detected level is 1.02 µg/L. 1,4-Dioxane is a synthetic industrial chemical used as a solvent stabilizer. It enters water supplies primarily from industrial discharge and contaminated groundwater plumes near manufacturing sites, landfills, and military bases. It is highly mobile in groundwater and resistant to biodegradation. The EPA classifies 1,4-dioxane as a likely human carcinogen. Long-term exposure is associated with liver and kidney damage. Advanced oxidation processes (AOP) are the most effective treatment; conventional water treatment and standard carbon filters are generally ineffective against 1,4-dioxane.

Comparison

Cities exceeding 0.35 µg/L EPA HA (no MCL)

California

50%

55 of 111 cities

→ ▲ 15% above national rate (worse)

National avg

35%

394 of 1124 cities

City Map

1,4-Dioxane data across California

Each dot is a city with UCMR 3 1,4-dioxane testing data. Cities where 1,4-dioxane exceeds the 0.35 µg/L EPA health advisory are highlighted. Size reflects population served.

Worst Offenders

Top 10 cities by 1,4-dioxane level in California

Highest 1,4-Dioxane levels (µg/L)

All Cities

All California cities ranked by 1,4-dioxane level

#	City	Level	Over HA?	Violations	Grade
1	San Jose	7.80 µg/L	Over HA	142	F
2	Cudahy	7.60 µg/L	Over HA	3	B+
3	Bellflower	6.30 µg/L	Over HA	0	B+
4	Anaheim	6.00 µg/L	Over HA	8	C+
5	Lynwood	5.90 µg/L	Over HA	0	B+
6	Costa Mesa	5.42 µg/L	Over HA	2	A-
7	Grand Terrace	4.70 µg/L	Over HA	1	B
8	Downey	4.30 µg/L	Over HA	14	B
9	Fountain Valley	4.13 µg/L	Over HA	0	A
10	Lakewood	3.50 µg/L	Over HA	1	A-
11	Norwalk	3.30 µg/L	Over HA	1	A-
12	Vernon	3.10 µg/L	Over HA	3	A
13	Huntington Park	2.80 µg/L	Over HA	3	B+
14	Pico Rivera	2.70 µg/L	Over HA	4	B
15	Paramount	2.10 µg/L	Over HA	0	A-
16	Santa Fe Springs	1.90 µg/L	Over HA	1	B+
17	Newport Beach	1.81 µg/L	Over HA	4	B+
18	Lindsay	1.80 µg/L	Over HA	240	F
19	South Gate	1.70 µg/L	Over HA	2	B
20	Montebello	1.40 µg/L	Over HA	5	B
21	Garden Grove	1.33 µg/L	Over HA	2	B
22	Santa Monica	1.30 µg/L	Over HA	0	B
23	Compton	1.30 µg/L	Over HA	8	B
24	Bell Gardens	1.28 µg/L	Over HA	0	B
25	Huntington Beach	1.18 µg/L	Over HA	5	C-
26	Whittier	1.10 µg/L	Over HA	4	C+
27	Rosemead	1.02 µg/L	Over HA	17	C-
28	Burbank	1.00 µg/L	Over HA	1	A-
29	Los Angeles	0.93 µg/L	Over HA	94	F
30	Monterey Park	0.84 µg/L	Over HA	1	B
31	Cerritos	0.82 µg/L	Over HA	0	B
32	Bakersfield	0.80 µg/L	Over HA	690	F
33	Banning	0.78 µg/L	Over HA	15	B-
34	Jurupa Valley	0.73 µg/L	Over HA	62	B
35	Porterville	0.73 µg/L	Over HA	74	F
36	Riverside	0.70 µg/L	Over HA	13	C
37	Newhall	0.70 µg/L	Over HA	1	B+
38	Orange	0.68 µg/L	Over HA	3	B
39	El Monte	0.63 µg/L	Over HA	79	F
40	Placentia	0.59 µg/L	Over HA	0	B+
41	La Habra	0.59 µg/L	Over HA	0	A-
42	Colton	0.59 µg/L	Over HA	5	B-
43	Lake Forest	0.57 µg/L	Over HA	38	B-
44	Lathrop	0.57 µg/L	Over HA	44	B
45	Covina	0.54 µg/L	Over HA	10	B
46	Pomona	0.54 µg/L	Over HA	6	C+
47	Lomita	0.48 µg/L	Over HA	1	A-
48	Sacramento	0.45 µg/L	Over HA	425	F
49	Irvine	0.45 µg/L	Over HA	84	F
50	Ontario	0.42 µg/L	Over HA	1	B+
51	Fullerton	0.42 µg/L	Over HA	8	B
52	Buena Park	0.41 µg/L	Over HA	1	B+
53	Westminster	0.38 µg/L	Over HA	2	A-
54	Loma Linda	0.38 µg/L	Over HA	3	A
55	Brea	0.37 µg/L	Over HA	0	A
56	Norco	0.35 µg/L	No	39	F
57	Camarillo	0.34 µg/L	No	4	B
58	Monrovia	0.32 µg/L	No	0	B+
59	Glendale	0.31 µg/L	No	0	A-
60	Altadena	0.31 µg/L	No	2	B+
61	Yucaipa	0.30 µg/L	No	9	C+
62	La Crescenta	0.28 µg/L	No	3	B+
63	Fresno	0.25 µg/L	No	523	F
64	Perris	0.24 µg/L	No	0	A
65	Santa Ana	0.24 µg/L	No	8	C
66	Moorpark	0.23 µg/L	No	1	A-
67	San Dimas	0.22 µg/L	No	6	B-
68	Ripon	0.22 µg/L	No	10	A-
69	Stockton	0.21 µg/L	No	261	F
70	Rancho Cordova	0.20 µg/L	No	115	F
71	Madera	0.20 µg/L	No	564	D
72	Tustin	0.20 µg/L	No	8	B
73	Tulare	0.19 µg/L	No	61	C-
74	Yucca Valley	0.19 µg/L	No	7	A-
75	Reedley	0.19 µg/L	No	12	B-
76	Modesto	0.17 µg/L	No	76	D
77	Twentynine Palms	0.16 µg/L	No	70	B+
78	Cupertino	0.16 µg/L	No	3	A+
79	Inglewood	0.15 µg/L	No	3	A-
80	Alhambra	0.14 µg/L	No	7	A-
81	Palm Desert	0.14 µg/L	No	12	C+
82	Corona	0.14 µg/L	No	81	D
83	Farmersville	0.14 µg/L	No	20	B+
84	San Bernardin0	0.12 µg/L	No	0	A-
85	Oxnard	0.12 µg/L	No	49	F
86	Rialto	0.12 µg/L	No	6	B+
87	Los Osos	0.12 µg/L	No	0	B+
88	Santa Barbara	0.11 µg/L	No	52	F
89	Soquel	0.11 µg/L	No	1	A
90	Atascadero	0.11 µg/L	No	1	B
91	Temescal Valley	0.11 µg/L	No	2	A
92	Montclair	0.10 µg/L	No	0	B+
93	Goleta	0.10 µg/L	No	11	B
94	Baldwin Park	0.10 µg/L	No	1	A
95	Arcadia	0.10 µg/L	No	2	B
96	La Verne	0.10 µg/L	No	6	B+
97	Pala	0.10 µg/L	No	30	C-
98	Signal Hill	0.10 µg/L	No	6	B
99	Azusa	0.10 µg/L	No	2	B+
100	Hesperia	0.10 µg/L	No	2	B
101	Merced	0.10 µg/L	No	9	C+
102	Woodland	0.09 µg/L	No	52	F
103	San Fernando	0.09 µg/L	No	1	A+
104	Glendora	0.09 µg/L	No	0	A-
105	Hawthorne	0.09 µg/L	No	3	B
106	Oceanside	0.09 µg/L	No	2	A-
107	Citrus Heights	0.09 µg/L	No	2	A
108	Tracy	0.08 µg/L	No	45	C
109	Carmichael	0.08 µg/L	No	1	B+
110	Poway	0.07 µg/L	No	0	A-
111	Nuevo	0.07 µg/L	No	6	B+

FAQ

Frequently asked questions about 1,4-dioxane in California

Is 1,4-dioxane in California tap water dangerous?

1,4-Dioxane is classified by the EPA as a likely human carcinogen. There is no federal MCL, but the EPA health advisory is 0.35 µg/L. 55 cities in California exceed the health advisory level. Long-term exposure is associated with liver and kidney damage.

How can I remove 1,4-dioxane from my drinking water?

1,4-Dioxane is one of the most difficult contaminants to remove from water. Standard carbon filters and conventional water treatment are generally ineffective. Advanced oxidation processes (AOP) used by water utilities are the most reliable. At the household level, some high-end reverse osmosis systems may provide partial reduction, but no standard point-of-use filter is certified for 1,4-dioxane removal.

Where does 1,4-dioxane come from in California water?

1,4-Dioxane is a synthetic industrial chemical primarily used as a solvent stabilizer in chlorinated solvent degreasing operations. It enters water from industrial discharge, contaminated groundwater plumes near manufacturing sites, landfills, and military bases. It is highly water-soluble, does not bind to soil, and resists natural biodegradation, making it a persistent groundwater contaminant.

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