Table 1.

Pollutants whose concentrations exceed or potentially exceed 10⁻⁶ cancer risk levels at > 50% of monitoring locations.

Pollutant	No. of locations	Percent locations with concentrations > 10−6 cancer riska	Percent locations with concentrations potentially > 10−6 cancer riskb
Benzene	305	100	0
Formaldehyde	163	0 (100)c	0
Acetaldehyde	163	99	0
Chromium VI	21	10 (96)c	0 (4)c
Carbon tetrachloride	278	85	15
Ethylene oxide	16	81	19
1,3-Butadiene	276	70	30
Arsenic PM2.5	432	67	11
Arsenic PM10	37	59	38
Nickel PM10	35	57	9
Acrylonitrile	124	52	48
Arsenic TSP	82	40	60
Tetrachloroethylene	271	37	51
Cadmium PM10	36	36	22
Naphthalene	39	33	51
1,4-Dichlorobenzene	202	33	51
Nickel TSP	101	26	56
Cadmium TSP	105	15	57
Benzyl chloride	110	13	71
Hexachlorobutadiene	153	8	89
1,1,2,2-Tetrachloroethane	226	5	94
1,2-Dichloropropane	227	5	78
Vinyl chloride	252	4	70
Ethylene dichloride	251	4	95
1,1,2-Trichloroethane	211	3	96
Ethylene dibromide	233	3	97
Cadmium PM2.5	261	2	98
Dibenzo[a,h]anthracene	30	0	63

^aSites where < 85% of measurements were reported as below the MDL and the site average concentration was above the 10⁻⁶ cancer benchmark.

^bSites where > 85% of measurements were reported as below the MDL and the 10⁻⁶ cancer benchmark was below the MDL.

^cResults change depending on the cancer benchmark value used (OAQPS or IRIS for formaldehyde, OAQPS or IRIS or CalEPA for chromium VI).