40 C.F.R. § 141.23

Current through November 30, 2024

Section 141.23 - Inorganic chemical sampling and analytical requirements

Community water systems shall conduct monitoring to determine compliance with the maximum contaminant levels specified in § 141.62 in accordance with this section. Non-transient, non-community water systems shall conduct monitoring to determine compliance with the maximum contaminant levels specified in § 141.62 in accordance with this section. Transient, non-community water systems shall conduct monitoring to determine compliance with the nitrate and nitrite maximum contaminant levels in §§ 141.11 and 141.62 (as appropriate) in accordance with this section.

(a) Monitoring shall be conducted as follows:

(1) Groundwater systems shall take a minimum of one sample at every entry point to the distribution system which is representative of each well after treatment (hereafter called a sampling point) beginning in the initial compliance period. The system shall take each sample at the same sampling point unless conditions make another sampling point more representative of each source or treatment plant.

(2) Surface water systems shall take a minimum of one sample at every entry point to the distribution system after any application of treatment or in the distribution system at a point which is representative of each source after treatment (hereafter called a sampling point) beginning in the initial compliance period. The system shall take each sample at the same sampling point unless conditions make another sampling point more representative of each source or treatment plant.

Note: For purposes of this paragraph, surface water systems include systems with a combination of surface and ground sources.

(3) If a system draws water from more than one source and the sources are combined before distribution, the system must sample at an entry point to the distribution system during periods of normal operating conditions (i.e., when water is representative of all sources being used).

(4) The State may reduce the total number of samples which must be analyzed by allowing the use of compositing. Composite samples from a maximum of five samples are allowed, provided that the detection limit of the method used for analysis is less than one-fifth of the MCL. Compositing of samples must be done in the laboratory.

(i) If the concentration in the composite sample is greater than or equal to one-fifth of the MCL of any inorganic chemical, then a follow-up sample must be taken within 14 days at each sampling point included in the composite. These samples must be analyzed for the contaminants which exceeded one-fifth of the MCL in the composite sample. Detection limits for each analytical method and MCLs for each inorganic contaminant are the following:

Detection Limits for Inorganic Contaminants

Contaminant	MCL (mg/l)	Methodology	Detection limit (mg/l)
Antimony	0.006	Atomic Absorption; Furnace	0.003
		Atomic Absorption; Platform	0.0008⁵
		ICP-Mass Spectrometry	0.0004
		Hydride-Atomic Absorption	0.001
Arsenic	0.010⁶	Atomic Absorption; Furnace	0.001
		Atomic Absorption; Platform-Stabilized Temperature	0.0005⁷
		Atomic Absorption; Gaseous Hydride	0.001
		ICP-Mass Spectrometry	0.0014⁸
Asbestos	7 MFL¹	Transmission Electron Microscopy	0.01 MFL
Barium	2	Atomic Absorption; furnace technique	0.002
		Atomic Absorption; direct aspiration	0.1
		Inductively Coupled Plasma	0.002 (0.001)
Beryllium	0.004	Atomic Absorption; Furnace	0.0002
		Atomic Absorption; Platform	0.00002⁵
		Inductively Coupled Plasma²	0.0003
		ICP-Mass Spectrometry	0.0003
Cadmium	0.005	Atomic Absorption; furnace technique	0.0001
		Inductively Coupled Plasma	0.001
Chromium	0.1	Atomic Absorption; furnace technique	0.001
		Inductively Coupled Plasma	0.007 (0.001)
Cyanide	0.2	Distillation, Spectrophotometric³	0.02
		Distillation, Automated, Spectrophotometric³	0.005
		Distillation, Amenable, Spectrophotometric⁴	0.02
		Distillation, Selective Electrode^{3 4}	0.05
		UV, Distillation, Spectrophotometric⁹	0.0005
		Micro Distillation, Flow Injection, Spectrophotometric³	0.0006
		Ligand Exchange with Amperometry⁴	0.0005
Mercury	0.002	Manual Cold Vapor Technique	0.0002
		Automated Cold Vapor Technique	0.0002
Nickel	xl	Atomic Absorption; Furnace	0.001
		Atomic Absorption; Platform	0.0006⁵
		Inductively Coupled Plasma²	0.005
		ICP-Mass Spectrometry	0.0005
Nitrate	10 (as N)	Manual Cadmium Reduction	0.01
		Automated Hydrazine Reduction	0.01
		Automated Cadmium Reduction	0.05
		Ion Selective Electrode	1
		Ion Chromatography	0.01
		Capillary Ion Electrophoresis	0.076
Nitrite	1 (as N)	Spectrophotometric	0.01
		Automated Cadmium Reduction	0.05
		Manual Cadmium Reduction	0.01
		Ion Chromatography	0.004
		Capillary Ion Electrophoresis	0.103
Selenium	0.05	Atomic Absorption; furnace	0.002
		Atomic Absorption; gaseous hydride	0.002
Thallium	0.002	Atomic Absorption; Furnace	0.001
		Atomic Absorption; Platform	0.0007⁵
		ICP-Mass Spectrometry	0.0003

¹ MFL = million fibers per liter [GREATER THAN]10 [MICRO]m.

² Using a 2X preconcentration step as noted in Method 200.7. Lower MDLs may be achieved when using a 4X preconcentration.

³ Screening method for total cyanides.

⁴ Measures "free" cyanides when distillation, digestion, or ligand exchange is omitted.

⁵ Lower MDLs are reported using stabilized temperature graphite furnace atomic absorption.

⁶ The value for arsenic is effective January 23, 2006. Unit then, the MCL is 0.05 mg/L.

⁷ The MDL reported for EPA method 200.9 (Atomic Absorption; Platform-Stablized Temperature) was determined using a 2x concentration step during sample digestion. The MDL determined for samples analyzed using direct analyses (i.e., no sample digestion) will be higher. Using multiple depositions, EPA 200.9 is capable of obtaining MDL of 0.0001 mg/L.

⁸ Using selective ion monitoring, EPA Method 200.8 (ICP-MS) is capable of obtaining a MDL of 0.0001 mg/L.

⁹ Measures total cyanides when UV-digestor is used, and "free" cyanides when UV-digestor is bypassed.

(ii) If the population served by the system is [GREATER THAN]3,300 persons, then compositing may only be permitted by the State at sampling points within a single system. In systems serving [LESS THAN EQUAL TO]3,300 persons, the State may permit compositing among different systems provided the 5-sample limit is maintained.

(iii) If duplicates of the original sample taken from each sampling point used in the composite sample are available, the system may use these instead of resampling. The duplicates must be analyzed and the results reported to the State within 14 days after completing analysis of the composite sample, provided the holding time of the sample is not exceeded.

(5) The frequency of monitoring for asbestos shall be in accordance with paragraph (b) of this section: the frequency of monitoring for antimony, arsenic, barium, beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel, selenium and thallium shall be in accordance with paragraph (c) of this section; the frequency of monitoring for nitrate shall be in accordance with paragraph (d) of this section; and the frequency of monitoring for nitrite shall be in accordance with paragraph (e) of this section.

(b) The frequency of monitoring conducted to determine compliance with the maximum contaminant level for asbestos specified in § 141.62(b) shall be conducted as follows:

(1) Each community and non-transient, non-community water system is required to monitor for asbestos during the first three-year compliance period of each nine-year compliance cycle beginning in the compliance period starting January 1, 1993.

(2) If the system believes it is not vulnerable to either asbestos contamination in its source water or due to corrosion of asbestos-cement pipe, or both, it may apply to the State for a waiver of the monitoring requirement in paragraph (b)(1) of this section. If the State grants the waiver, the system is not required to monitor.

(3) The State may grant a waiver based on a consideration of the following factors:

(i) Potential asbestos contamination of the water source, and

(ii) The use of asbestos-cement pipe for finished water distribution and the corrosive nature of the water.

(4) A waiver remains in effect until the completion of the three-year compliance period. Systems not receiving a waiver must monitor in accordance with the provisions of paragraph (b)(1) of this section.

(5) A system vulnerable to asbestos contamination due solely to corrosion of asbestos-cement pipe shall take one sample at a tap served by asbestos-cement pipe and under conditions where asbestos contamination is most likely to occur.

(6) A system vulnerable to asbestos contamination due solely to source water shall monitor in accordance with the provision of paragraph (a) of this section.

(7) A system vulnerable to asbestos contamination due both to its source water supply and corrosion of asbestos-cement pipe shall take one sample at a tap served by asbestos-cement pipe and under conditions where asbestos contamination is most likely to occur.

(8) A system which exceeds the maximum contaminant levels as determined in § 141.23(i) of this section shall monitor quarterly beginning in the next quarter after the violation occurred.

(9) The State may decrease the quarterly monitoring requirement to the frequency specified in paragraph (b)(1) of this section provided the State has determined that the system is reliably and consistently below the maximum contaminant level. In no case can a State make this determination unless a groundwater system takes a minimum of two quarterly samples and a surface (or combined surface/ground) water system takes a minimum of four quarterly samples.

(10) If monitoring data collected after January 1, 1990 are generally consistent with the requirements of § 141.23(b) , then the State may allow systems to use that data to satisfy the monitoring requirement for the initial compliance period beginning January 1, 1993.

(c) The frequency of monitoring conducted to determine compliance with the maximum contaminant levels in § 141.62 for antimony, arsenic, barium, beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel, selenium and thallium shall be as follows:

(1) Groundwater systems shall take one sample at each sampling point during each compliance period. Surface water systems (or combined surface/ground) shall take one sample annually at each sampling point.

(2) The system may apply to the State for a waiver from the monitoring frequencies specified in paragraph (c)(1) of this section. States may grant a public water system a waiver for monitoring of cyanide, provided that the State determines that the system is not vulnerable due to lack of any industrial source of cyanide.

(3) A condition of the waiver shall require that a system shall take a minimum of one sample while the waiver is effective. The term during which the waiver is effective shall not exceed one compliance cycle (i.e., nine years).

(4) The State may grant a waiver provided surface water systems have monitored annually for at least three years and groundwater systems have conducted a minimum of three rounds of monitoring. (At least one sample shall have been taken since January 1, 1990). Both surface and groundwater systems shall demonstrate that all previous analytical results were less than the maximum contaminant level. Systems that use a new water source are not eligible for a waiver until three rounds of monitoring from the new source have been completed.

(5) In determining the appropriate reduced monitoring frequency, the State shall consider:

(i) Reported concentrations from all previous monitoring;

(ii) The degree of variation in reported concentrations; and

(iii) Other factors which may affect contaminant concentrations such as changes in groundwater pumping rates, changes in the system's configuration, changes in the system's operating procedures, or changes in stream flows or characteristics.

(6) A decision by the State to grant a waiver shall be made in writing and shall set forth the basis for the determination. The determination may be initiated by the State or upon an application by the public water system. The public water system shall specify the basis for its request. The State shall review and, where appropriate, revise its determination of the appropriate monitoring frequency when the system submits new monitoring data or when other data relevant to the system's appropriate monitoring frequency become available.

(7) Systems which exceed the maximum contaminant levels as calculated in § 141.23(i) of this section shall monitor quarterly beginning in the next quarter after the violation occurred.

(8) The State may decrease the quarterly monitoring requirement to the frequencies specified in paragraphs (c)(1) and (c)(2) of this section provided it has determined that the system is reliably and consistently below the maximum contaminant level. In no case can a State make this determination unless a groundwater system takes a minimum of two quarterly samples and a surface water system takes a minimum of four quarterly samples.

(9) All new systems or systems that use a new source of water that begin operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure a system can demonstrate compliance with the MCL. Routine and increased monitoring frequencies shall be conducted in accordance with the requirements in this section.

(d) All public water systems (community; non-transient, non-community; and transient, non-community systems) shall monitor to determine compliance with the maximum contaminant level for nitrate in § 141.62 .

(1) Community and non-transient, non-community water systems served by groundwater systems shall monitor annually beginning January 1, 1993; systems served by surface water shall monitor quarterly beginning January 1, 1993.

(2) For community and non-transient, non-community water systems, the repeat monitoring frequency for groundwater systems shall be quarterly for at least one year following any one sample in which the concentration is [GREATER THAN EQUAL TO]50 percent of the MCL. The State may allow a groundwater system to reduce the sampling frequency to annually after four consecutive quarterly samples are reliably and consistently less than the MCL.

(3) For community and non-transient, non-community water systems, the State may allow a surface water system to reduce the sampling frequency to annually if all analytical results from four consecutive quarters are [LESS THAN]50 percent of the MCL. A surface water system shall return to quarterly monitoring if any one sample is [GREATER THAN EQUAL TO]50 percent of the MCL.

(4) Each transient non-community water system shall monitor annually beginning January 1, 1993.

(5) After the initial round of quarterly sampling is completed, each community and non-transient non-community system which is monitoring annually shall take subsequent samples during the quarter(s) which previously resulted in the highest analytical result.

(e) All public water systems (community; non-transient, non-community; and transient, non-community systems) shall monitor to determine compliance with the maximum contaminant level for nitrite in § 141.62(b) .

(1) All public water systems shall take one sample at each sampling point in the compliance period beginning January 1, 1993 and ending December 31, 1995.

(2) After the initial sample, systems where an analytical result for nitrite is [LESS THAN]50 percent of the MCL shall monitor at the frequency specified by the State.

(3) For community, non-transient, non-community, and transient non-community water systems, the repeat monitoring frequency for any water system shall be quarterly for at least one year following any one sample in which the concentration is [GREATER THAN EQUAL TO]50 percent of the MCL. The State may allow a system to reduce the sampling frequency to annually after determining the system is reliably and consistently less than the MCL.

(4) Systems which are monitoring annually shall take each subsequent sample during the quarter(s) which previously resulted in the highest analytical result.

(f) Confirmation samples:

(1) Where the results of sampling for antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel, selenium or thallium indicate an exceedance of the maximum contaminant level, the State may require that one additional sample be collected as soon as possible after the initial sample was taken (but not to exceed two weeks) at the same sampling point.

(2) Where nitrate or nitrite sampling results indicate an exceedance of the maximum contaminant level, the system shall take a confirmation sample within 24 hours of the system's receipt of notification of the analytical results of the first sample. Systems unable to comply with the 24-hour sampling requirement must immediately notify persons served by the public water system in accordance with § 141.202 and meet other Tier 1 public notification requirements under subpart Q of this part. Systems exercising this option must take and analyze a confirmation sample within two weeks of notification of the analytical results of the first sample.

(3) If a State-required confirmation sample is taken for any contaminant, then the results of the initial and confirmation sample shall be averaged. The resulting average shall be used to determine the system's compliance in accordance with paragraph (i) of this section. States have the discretion to delete results of obvious sampling errors.

(g) The State may require more frequent monitoring than specified in paragraphs (b), (c), (d) and (e) of this section or may require confirmation samples for positive and negative results at its discretion.

(h) Systems may apply to the State to conduct more frequent monitoring than the minimum monitoring frequencies specified in this section.

(i) Compliance with § 141.11 or § 141.62(b) (as appropriate) shall be determined based on the analytical result(s) obtained at each sampling point.

(1) For systems which are conducting monitoring at a frequency greater than annual, compliance with the maximum contaminant levels for antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel, selenium or thallium is determined by a running annual average at any sampling point. If the average at any sampling point is greater than the MCL, then the system is out of compliance. If any one sample would cause the annual average to be exceeded, then the system is out of compliance immediately. Any sample below the method detection limit shall be calculated at zero for the purpose of determining the annual average. If a system fails to collect the required number of samples, compliance (average concentration) will be based on the total number of samples collected.

(2) For systems which are monitoring annually, or less frequently, the system is out of compliance with the maximum contaminant levels for antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel, selenium or thallium if the level of a contaminant is greater than the MCL. If confirmation samples are required by the State, the determination of compliance will be based on the annual average of the initial MCL exceedance and any State-required confirmation samples. If a system fails to collect the required number of samples, compliance (average concentration) will be based on the total number of samples collected.

(3) Compliance with the maximum contaminant levels for nitrate and nitrate is determined based on one sample if the levels of these contaminants are below the MCLs. If the levels of nitrate and/or nitrite exceed the MCLs in the initial sample, a confirmation sample is required in accordance with paragraph (f)(2) of this section, and compliance shall be determined based on the average of the initial and confirmation samples.

(4) Arsenic sampling results will be reported to the nearest 0.001 mg/L.

(j) Each public water system shall monitor at the time designated by the State during each compliance period.

(k) Inorganic analysis:

(1) Analysis for the following contaminants shall be conducted in accordance with the methods in the following table, or the alternative methods listed in appendix A to subpart C of this part, or their equivalent as determined by EPA. Criteria for analyzing arsenic, barium, beryllium, cadmium, calcium, chromium, copper, lead, nickel, selenium, sodium, and thallium with digestion or directly without digestion, and other analytical test procedures are contained in Technical Notes on Drinking Water Methods, EPA-600/R-94-173, October 1994. This document is available from the National Service Center for Environmental Publications (NSCEP), P.O. Box 42419, Cincinnati, OH 45242-0419 or http://www.epa.gov/nscep/.

Alternative Testing Methods for Contaminants Listed at 40 CFR 141.23(k)(1)

Contaminant	Methodology	EPA method	SM 21st edition¹	SM 22nd edition²⁸	SM 23rd edition,⁴⁹ SM 24th edition⁶⁶	SM online³	ASTM⁴	Other
Alkalinity	Titrimetric		2320 B	2320 B	2320 B		D1067-06 B, 11 B, 16 B
Antimony	Hydride-Atomic Absorption						D 3697-07, -12, -17
	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
Arsenic	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10	D 2972-08 C, -15 C
	Hydride Atomic Absorption		3114 B	3114 B	3114 B	3114 B-09	D 2972-08 B, -15 B
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
Barium	Inductively Coupled Plasma		3120 B	3120 B	3120 B
	Atomic Absorption; Direct		3111 D	3111 D	3111 D
	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
Beryllium	Inductively Coupled Plasma		3120 B	3120 B	3120 B
	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10	D 3645-08 B, -15 B
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
Cadmium	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
Calcium	EDTA titrimetric		3500-Ca B	3500-Ca B	3500-Ca B		D 511-09, -14 A
	Atomic Absorption; Direct Aspiration		3111 B	3111 B	3111 B		D 511-09, -14 B
	Inductively Coupled Plasma		3120 B	3120 B	3120 B
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
	Ion Chromatography						D 6919-09, -17
Chromium	Inductively Coupled Plasma		3120 B	3120 B	3120 B
	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
Copper	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10	D 1688-07, -12 C, 17 C
	Atomic Absorption; Direct Aspiration		3111 B	3111 B	3111 B		D 1688-07, -12 A, 17 A
	Inductively Coupled Plasma		3120 B	3120 B	3120 B
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
	Colorimetry							Hach Method 8026,³⁵ Hach Method 10272.³⁶
Conductivity	Conductance		2510 B	2510 B	2510 B		D 1125-14 A
Cyanide	Manual Distillation with MgCl₂ followed by:		4500-CN^-C	4500-CN^-C	4500-CN^-C	4500-CN^-C-99	D 2036-06 A
	Spectrophotometric, Amenable		4500-CN^-G	4500-CN^-G	4500-CN^-G		D 2036-06 B
	Spectrophotometric Manual		4500-CN^-E	4500-CN^-E	4500-CN^-E		D2036-06 A
	Selective Electrode		4500-CN^-F	4500-CN^-F	4500-CN^-F
	Gas Chromatography/Mass Spectrometry Headspace							ME355.01.⁷
Fluoride	Ion Chromatography		4110 B	4110 B	4110 B		D 4327-11, -17
	Manual Distillation; Colorimetric SPADNS		4500-F^-B, D	4500-F^-B, D	4500-F^-B, D
	Manual Electrode		4500-F^-C	4500-F^-C	4500-F^-C		D 1179-04, 10 B, 16 B
	Automated Alizarin		4500-F^-E	4500-F^-E	4500-F^-E
	Arsenite-Free Colorimetric SPADNS							Hach SPADNS 2 Method 10225,²² Hach Method 10312.⁶⁷
Lead	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10	D 3559-08 D, 15 D
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
	Differential Pulse Anodic Stripping Voltametry							Method 1001, Rev. 1.1.⁵⁷
Magnesium	Atomic Absorption		3111 B	3111 B	3111 B		D 511-09, -14 B
	Inductively Coupled Plasma		3120 B	3120 B	3120 B
	Complexation Titrimetric Methods		3500-Mg B	3500-Mg B	3500-Mg B		D 511-09, -14 A
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
	Ion Chromatography						D 6919-09, -17
Mercury	Manual, Cold Vapor		3112 B	3112 B	3112 B	3112 B-09	D 3223-12, -17
Nickel	Inductively Coupled Plasma		3120 B	3120 B	3120 B
	Atomic Absorption; Direct		3111 B	3111 B	3111 B
	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
Nitrate	Ion Chromatography		4110 B	4110 B	4110 B		D 4327-11, -17
	Automated Cadmium Reduction		4500-NO₃^-F	4500-NO₃^-F	4500-NO₃^-F
	Manual Cadmium Reduction		4500-NO₃^- E	4500-NO₃^- E	4500-NO₃^- E
	Ion Selective Electrode		4500-NO₃^- D	4500-NO₃^- D	4500-NO₃^- D
	Reduction/Colorimetric							Systea Easy (1-Reagent),⁸ NECi Nitrate-Reductase.⁴⁰
	Colorimetric; Direct							Hach TNTplus^TM 835/836 Method 10206.²³
	Capillary Ion Electrophoresis						D 6508-15
Nitrite	Ion Chromatography		4110 B	4110 B	4110 B		D 4327-11, -17
	Automated Cadmium Reduction		4500-NO₃^-F	4500-NO₃^-F	4500-NO₃^-F
	Manual Cadmium Reduction		4500-NO₃^-E	4500-NO₃^-E	4500-NO₃^-E
	Spectrophotometric		4500-NO₂^-B	4500-NO₂^-B	4500-NO₂^-B
	Reduction/Colorimetric							Systea Easy (1-Reagent),⁸ NECi Nitrate-Reductase.⁴⁰
	Capillary Ion Electrophoresis						D 6508-15
Ortho-phosphate	Ion Chromatography		4110 B	4110 B	4110 B		D 4327-11, -17
	Colorimetric, ascorbic acid, single reagent		4500-P E	4500-P E	4500-P E	4500-P E-99
	Colorimetric, Automated, Ascorbic Acid		4500-P F	4500-P F	4500-P F	4500-P F-99	Thermo Fisher Discrete Analyzer.⁴¹
	Capillary Ion Electrophoresis						D 6508-15
pH	Electrometric	⁴⁸ 150.3	4500-H⁺ B	4500-H⁺ B	4500-H⁺ B		D 1293-12, -18
Selenium	Hydride-Atomic Absorption		3114 B	3114 B	3114 B	3114 B-09	D 3859-08 A, -15 A
	Atomic Absorption; Furnace		3113 B	3113 B	3113 B	3113 B-04, B-10	D 3859-08 B, -15 B
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
Silica	Colorimetric						D859-05, 10, 16
	Molybdosilicate		4500-SiO₂ C	4500-SiO₂ C	4500-SiO₂ C
	Heteropoly blue		4500-SiO₂ D	4500-SiO₂ D	4500-SiO₂ D
	Automated for Molybdate-reactive Silica		4500-SiO₂ E	4500-SiO₂ E	4500-SiO₂ E
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
	Inductively Coupled Plasma		3120 B	3120 B	3120 B
Sodium	Atomic Absorption; Direct Aspiration		3111 B	3111 B	3111 B
	Axially viewed inductively coupled plasma-atomic emission spectrometry (AVICP-AES)	200.5, Revision 4.2²
	Ion Chromatography						D 6919-09, -17
Temperature	Thermometric		2550	2550	2550	2550-10

(2) Sample collection for antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel, nitrate, nitrite, selenium, and thallium under this section shall be conducted using the sample preservation, container, and maximum holding time procedures specified in the table below:

Contaminant	Preservative¹	Container²	Time³
Antimony	HNO³	P or G	6 months
Arsenic	Conc HNO₃ to pH [LESS THAN]2	P or G	6 months
Asbestos	4 °C	P or G	48 hours⁴
Barium	HNO³	P or G	6 months
Beryllium	HNO³	P or G	6 months
Cadmium	HNO³	P or G	6 months
Chromium	HNO³	P or G	6 months
Cyanide	4 °C, NaOH	P or G	14 days
Fluoride	None	P or G	1 month
Mercury	HNO³	P or G	28 days
Nickel	HNO³	P or G	6 months
Nitrate	4 °C	P or G	48 hours⁵
Nitrate-Nitrite⁶	H²SO⁴	P or G	28 days
Nitrite	4 °C	P or G	48 hours
Selenium	HNO³	P or G	6 months
Thallium	HNO³	P or G	6 months

¹ For cyanide determinations samples must be adjusted with sodium hydroxide to pH 12 at the time off collection. When chilling is indicated the sample must be shipped and stored at 4 °C or less. Acidification of nitrate or metals samples may be with a concentrated acid or a dilute (50% by volume) solution of the applicable concentrated acid. Acidification of samples for metals analysis is encouraged and allowed at the laboratory rather than at the time of sampling provided the shipping time and other instructions in Section 8.3 of EPA Methods 200.7 or 200.8 or 200.9 are followed.

² P = plastic, hard or soft; G = glass, hard or soft.

³ In all cases samples should be analyzed as soon after collection as possible. Follow additional (if any) information on preservation, containers or holding times that is specified in method.

⁴ Instructions for containers, preservation procedures and holding times as specified in Method 100.2 must be adhered to for all compliance analyses including those conducted with Method 100.1.

⁵ If the sample is chlorinated, the holding time for an unacidified sample kept at 4 °C is extended to 14 days.

⁶ Nitrate-Nitrite refers to a measurement of total nitrate.

(3) Analysis under this section shall only be conducted by laboratories that have been certified by EPA or the State. Laboratories may conduct sample analysis under provisional certification until January 1, 1996. To receive certification to conduct analyses for antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel, nitrate, nitrite and selenium and thallium, the laboratory must:

(i) Analyze Performance Evaluation (PE) samples provided by EPA, the State or by a third party (with the approval of the State or EPA) at least once a year.

(ii) For each contaminant that has been included in the PE sample and for each method for which the laboratory desires certification achieve quantitative results on the analyses that are within the following acceptance limits:

Contaminant	Acceptance limit
Antimony	±30 at [GREATER THAN EQUAL TO]0.006 mg/1
Arsenic	±30 at [GREATER THAN EQUAL TO]0.003 mg/L
Asbestos	2 standard deviations based on study statistics.
Barium	±15% at [GREATER THAN EQUAL TO]0.15 mg/1
Beryllium	±15% at [GREATER THAN EQUAL TO]0.001 mg/1
Cadmium	±20% at [GREATER THAN EQUAL TO]0.002 mg/1
Chromium	±15% at [GREATER THAN EQUAL TO]0.01 mg/1
Cyanide	±25% at [GREATER THAN EQUAL TO]0.1 mg/1
Fluoride	±10% at [GREATER THAN EQUAL TO]1 to 10 mg/1
Mercury	±30% at [GREATER THAN EQUAL TO]0.0005 mg/1
Nickel	±15% at [GREATER THAN EQUAL TO]0.01 mg/1
Nitrate	±10% at [GREATER THAN EQUAL TO]0.4 mg/1
Nitrite	±15% at [GREATER THAN EQUAL TO]0.4 mg/1
Selenium	±20% at [GREATER THAN EQUAL TO]0.01 mg/1
Thallium	±30% at [GREATER THAN EQUAL TO]0.002 mg/1

(l) Analyses for the purpose of determining compliance with § 141.11 shall be conducted using the requirements specified in paragraphs (l) through (q) of this section.

(1) Analyses for all community water systems utilizing surface water sources shall be completed by June 24, 1978. These analyses shall be repeated at yearly intervals.

(2) Analyses for all community water systems utilizing only ground water sources shall be completed by June 24, 1979. These analyses shall be repeated at three-year intervals.

(3) For non-community water systems, whether supplied by surface or ground sources, analyses for nitrate shall be completed by December 24, 1980. These analyses shall be repeated at intervals determined by the State.

(4) The State has the authority to determine compliance or initiate enforcement action based upon analytical results and other information compiled by their sanctioned representatives and agencies.

(m) If the result of an analysis made under paragraph (l) of this section indicates that the level of any contaminant listed in § 141.11 exceeds the maximum contaminant level, the supplier of the water shall report to the State within 7 days and initiate three additional analyses at the same sampling point within one month.

(n) When the average of four analyses made pursuant to paragraph (m) of this section, rounded to the same number of significant figures as the maximum contaminant level for the substance in question, exceeds the maximum contaminant level, the supplier of water shall notify the State pursuant to § 141.31 and give notice to the public pursuant to subpart Q. Monitoring after public notification shall be at a frequency designated by the State and shall continue until the maximum contaminant level has not been exceeded in two successive samples or until a monitoring schedule as a condition to a variance, exemption or enforcement action shall become effective.

(o) The provisions of paragraphs (m) and (n) of this section notwithstanding, compliance with the maximum contaminant level for nitrate shall be determined on the basis of the mean of two analyses. When a level exceeding the maximum contaminant level for nitrate is found, a second analysis shall be initiated within 24 hours, and if the mean of the two analyses exceeds the maximum contaminant level, the supplier of water shall report his findings to the State pursuant to § 141.31 and shall notify the public pursuant to subpart Q.

(p) For the initial analyses required by paragraph (l) (1), (2) or (3) of this section, data for surface waters acquired within one year prior to the effective date and data for ground waters acquired within 3 years prior to the effective date of this part may be substituted at the discretion of the State.

(q) [Reserved]

40 C.F.R. §141.23

56 FR 3579, Jan. 30, 1991

For FEDERAL REGISTER citations affecting § 141.23, see the List of CFR Sections Affected, which appears in the Finding Aids section of the printed volume and at www.govinfo.gov.