['Water Programs']
['Water Quality', 'Safe Drinking Water', 'Maximum Contaminant Levels']
06/27/2024
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(a) [Reserved]
(b) The maximum contaminant levels for inorganic contaminants specified in paragraphs (b) (2)-(6), (b)(10), and (b) (11)-(16) of this section apply to community water systems and non-transient, non-community water systems. The maximum contaminant level specified in paragraph (b)(1) of this section only applies to community water systems. The maximum contaminant levels specified in (b)(7), (b)(8), and (b)(9) of this section apply to community water systems; non-transient, non-community water systems; and transient non- community water systems.
| Contaminant | MCL (mg/l) |
| (1) Fluoride | 4.0 |
| (2) Asbestos | 7 Million Fibers/liter (longer than 10 µm). |
| (3) Barium | 2 |
| (4) Cadmium | 0.005 |
| (5) Chromium | 0.1 |
| (6) Mercury | 0.002 |
| (7) Nitrate | 10 (as Nitrogen) |
| (8) Nitrite | 1 (as Nitrogen) |
| (9) Total Nitrate and Nitrite | 10 (as Nitrogen) |
| (10) Selenium | 0.05 |
| (11) Antimony | 0.006 |
| (12) Beryllium | 0.004 |
| (13) Cyanide (as free Cyanide) | 0.2 |
| (14) [Reserved] | |
| (15) Thallium | 0.002 |
| (16) Arsenic | 0.010 |
(c) The Administrator, pursuant to Section 1412 of the Act, hereby identifies the following as the best technology, treatment technique, or other means available for achieving compliance with the maximum contaminant levels for inorganic contaminants identified in paragraph (b) of this section, except fluoride:
BAT for Inorganic Compounds Listed in Section 141.62(B)
| Chemical Name | BAT(s) |
| Antimony | 2,7 |
| Arsenic4 | 1, 2, 5, 6, 7, 9, 125 |
| Asbestos | 2,3,8 |
| Barium | 5,6,7,9 |
| Beryllium | 1,2,5,6,7 |
| Cadmium | 2,5,6,7 |
| Chromium | 2,5,62,7 |
| Cyanide | 5,7,13 |
| Mercury | 21,4,61,71 |
| Nickel | 5,6,7 |
| Nitrate | 5,7,9 |
| Nitrite | 5,7 |
| Selenium | 1,23,6,7,9 |
| Thallium | 1,5 |
1BAT only if influent Hg concentrations ≤10µg/1.
2BAT for Chromium III only.
3BAT for Selenium IV only.
4BATs for Arsenic V. Pre-oxidation may be required to convert Arsenic III to Arsenic V.
5To obtain high removals, iron to arsenic ratio must be at least 20:1.
Key to BATS in Table
1 = Activated Alumina
2 = Coagulation/Filtration (not BAT for systems < 500 service connections)
3 = Direct and Diatomite Filtration
4 = Granular Activated Carbon
5 = Ion Exchange
6 = Lime Softening (not BAT for systems <500 service connections)
7 = Reverse Osmosis
8 = Corrosion Control
9 = Electrodialysis
10 = Chlorine
11 = Ultraviolet
12 = Oxidation/Filtration
13 = Alkaline Chlorination (pH ≥8.5)
(d) The Administrator, pursuant to section 1412 of the Act, hereby identifies in the following table the affordable technology, treatment technique, or other means available to systems serving 10,000 persons or fewer for achieving compliance with the maximum contaminant level for arsenic:
Small System Compliance Technologies (SSCTs)1 for Arsenic2
| Small system compliance technology | Affordable for listed small system categories3 |
| Activated Alumina (centralized) | All size categories. |
| Activated Alumina (Point-of-Use) 4 | All size categories. |
| Coagulation/Filtration 5 | 501-3,300, 3,301-10,000. |
| Coagulation-assisted Microfiltration | 501-3,300, 3,301-10,000. |
| Electrodialysis reversal 6 | 501-3,300, 3,301-10,000. |
| Enhanced coagulation/filtration | All size categories. |
| Enhanced lime softening (pH> 10.5) | All size categories. |
| Ion Exchange | All size categories. |
| Lime Softening 5 | 501-3,300, 3,301-10,000. |
| Oxidation/Filtration 7 | All size categories. |
| Reverse Osmosis (centralized) 6 | 501-3,300, 3,301-10,000. |
| Reverse Osmosis (Point-of-Use) 4 | All size categories. |
1 Section 1412(b)(4)(E)(ii) of SDWA specifies that SSCTs must be affordable and technically feasible for small systems.
2 SSCTs for Arsenic V. Pre-oxidation may be required to convert Arsenic III to Arsenic V.
3 The Act (ibid.) specifies three categories of small systems: (i) those serving 25 or more, but fewer than 501, (ii) those serving more than 500, but fewer than 3,301, and (iii) those serving more than 3,300, but fewer than 10,001.
4 When POU or POE devices are used for compliance, programs to ensure proper long-term operation, maintenance, and monitoring must be provided by the water system to ensure adequate performance.
5 Unlikely to be installed solely for arsenic removal. May require pH adjustment to optimal range if high removals are needed.
6 Technologies reject a large volume of water-may not be appropriate for areas where water quantity may be an issue.
7 To obtain high removals, iron to arsenic ratio must be at least 20:1.
[66 FR 7063 Jan. 22, 2001; 66 FR 28342 May 22, 2001; 69 FR 38855 June 29, 2004]
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