Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-31 - REGULATION NO. 31 - THE BASIC STANDARDS AND METHODOLOGIES FOR SURFACE WATER
Section 5 CCR 1002-31.11 - BASIC STANDARDS APPLICABLE TO SURFACE WATERS OF THE STATE

Universal Citation: 5 CO Code Regs 1002-31 § 11

Current through Register Vol. 47, No. 17, September 10, 2024

All surface waters of the state are subject to the following basic standards; however, discharge of substances regulated by permits which are within those permit limitations shall not be a basis for enforcement proceedings under these basic standards:

(1) Except where authorized by permits, BMPs, 401 certifications, or plans of operation approved by the Division or other applicable agencies, state surface waters shall be free from substances attributable to human-caused point source or nonpoint source discharge in amounts, concentrations or combinations which:

(a) for all surface waters except wetlands;

(i) can settle to form bottom deposits detrimental to the beneficial uses. Depositions are stream bottom buildup of materials which include but are not limited to anaerobic sludges, mine slurry or tailings, silt, or mud; or

(ii) form floating debris, scum, or other surface materials sufficient to harm existing beneficial uses; or

(iii) produce color, odor, or other conditions in such a degree as to create a nuisance or harm existing beneficial uses or impart any undesirable taste to significant edible aquatic species or to the water; or

(iv) are harmful to the beneficial uses or toxic to humans, animals, plants, or aquatic life; or

(v) produce a predominance of undesirable aquatic life; or

(vi) cause a film on the surface or produce a deposit on shorelines; and

(b) for surface waters in wetlands;

(i) produce color, odor, changes in pH, or other conditions in such a degree as to create a nuisance or harm water quality dependent functions or impart any undesirable taste to significant edible aquatic species of the wetland; or

(ii) are toxic to humans, animals, plants, or aquatic life of the wetland.

(2) The radioactive materials in surface waters shall be maintained at the lowest practical level. In no case shall radioactive materials in surface waters be increased by any cause attributable to municipal, industrial, or agricultural practices or discharges to as to exceed the levels in 31.11 Table A below, unless alternative site-specific standards have been adopted pursuant to subsection (4) below:

31.11 TABLE A - RADIONUCLIDE STANDARDS

TABLE A RADIONUCLIDE STANDARDS**
Parameter	Picocuries per Liter
Americium 241*	0.15
Cesium 134	80
Plutonium 239, and 240*	0.15
Radium 226 and 228*	5
Strontium 90*	8
Thorium 230 and 232*	60
Tritium	20,000

*Radionuclide samples for these materials should be analyzed using unfiltered (total) samples.

**These Human Health based standards are 30-day average values.

(3) The interim organic pollutant standards contained in 31.11 Table B Basic Standards for Organic Chemicals Table below are applicable to all surface waters of the state for which the corresponding use classifications have been adopted, unless alternative site-specific standards have been adopted pursuant to sub-section (4) below.

Note that all standards in the 31.11 Table B Basic Standards for Organic Chemicals Table are being adopted as "interim standards." These interim standards will remain in effect until alternative permanent standards are adopted by the Commission in revisions to this regulation or site-specific standards determinations. Although fully effective with respect to current regulatory applications, these interim standards shall not be considered final or permanent standards subject to antibacksliding or downgrading restrictions.

31.11 TABLE B - BASIC STANDARDS FOR ORGANIC CHEMICALS

TABLE B BASIC STANDARDS FOR ORGANIC CHEMICALS (concentration in µg/L)
Parameter	Human Health Based1			Aquatic Life Based4
CAS No.	Water Supply2	Water + Fish3	Fish Ingestion8	Acute	Chronic
Acenaphthene	83-32-9	420	420	---10	1,700	520
Acetochlor	34256-82-1	140	---	---	---	---
Acetone	67-64-1	6300	---	---	---	---
Acrolein	107-02-8	3.5	3.5	9.3	3	3
AcrylamideC, 13	79-06-1	0.022	---	---	---	---
AcrylonitrileC	107-13-1	0.065	0.051	0.25	7,500	2,600
Alachlor	15972-60-8	2M	2	140	---	---
Aldicarb	116-06-3	7M	---	---	---	---
Aldicarb Sulfone	1646-88-4	7M	---	---	---	---
Aldicarb Sulfoxide	1646-87-3	7M	---	---	---	---
AldrinC	309-00-2	0.0021	4.9X10-5	5.0X10-5	1.5	---
AnilineC	62-53-3	6.1	---	---	---	---
Anthracene (PAH)	120-12-7	2,100	2,100	40,000	---	---
AramiteC	140-57-8	1.4	---	---	---	---
Atrazine	1912-24-9	3M	---	---	---	---
AzobenzeneC	103-33-3	0.32	---	---	---	---
BenzeneC, 12	71-43-2	2.3 to 5M	2.2	51	5,300	---
BenzidineC	92-87-5	0.00015	8.6X10-5	0.00020	2,500	---
Benzo(a)anthracene (PAH)C, 13	56-55-3	0.16	0.0051	0.0053	---	---
Benzo(a)pyrene (PAH)C, 12, 13	50-32-8	0.016	0.00051	0.00053	---	---
Benzo(b)fluoranthene (PAH)C, 13	205-99-2	0.16	0.0051	0.0053	---	---
Benzo(k)fluoranthene (PAH)C, 13	207-08-9	1.6	0.051	0.053	---	---
Benzo(g,h,i)perylene (PAH)	191-24-2	---	0.0038	0.018	---	---
BenzotrichlorideC	98-07-7	0.0027	---	---	---	---
Benzyl chlorideC	100-44-7	0.21	---	---	---	---
BiphenylC	92-52-4	4.4	---	---	---	---
Bis(chloromethyl)ether (BCME)C	542-88-1	0.00016	0.0001	0.0003	---	---
BromateC	15541-45-4	0.050	---	---	---	---
Bromobenzene	108-86-1	56	---	---	---	---
Bromodichloromethane (HM)C	75-27-4	---	0.55	17	11,000	---
Bromoform (HM)C	75-25-2	---	4.3	140	---	---
Butyl benzyl phthalate	85-68-7	1,400	1,400	1,900	---	---
Carbaryl	63-25-2	---	---	---	2.1	2.1
Carbofuran12	1563-66-2	35 to 40 M	---	---	---	---
Carbon tetrachlorideC, 12	56-23-5	0.5 to 5M	0.43	3.0	35,200	---
ChlordaneC, 12	57-74-9	0.10 to 2M	0.00080	0.00081	1.2	0.0043
ChlordeconeC	143-50-0	0.0035	---	---	---	---
Chlorethyl ether (BIS-2)C	111-44-4	0.032	0.030	0.53	---	---
Chlorobenzene11	108-90-7	100 M	100	1,600	---	---
Chlorodibromomethane (dibromochloromethane) (HM)11	124-48-1	---	54.0	1,700	---	---
Chloroform (HM)C	67-66-3	---	3.4	110	28,900	1,240
Chloroisopropyl ether(BIS-2)	108-60-1	280	280	65,000	---	---
4-Chloro-3-methylphenol	59-50-7	210	---	---	30	---
Chloronaphthalene	91-58-7	560	560	---10	2,300	620
Chlorophenol,2-	95-57-8	35	35	150	4,380	2,000
Chlorpyrifos	2921-88-2	21	---	---	0.083	0.041
Chrysene (PAH)C, 13	218-01-9	16	0.51	0.53	---	---
Dalapon	75-99-0	200M	---	---	---	---
DDDC	72-54-8	0.15	0.00031	0.00031	0.6	---
DDEC	72-55-9	0.1	0.00022	0.00022	1,050	---
DDTC	50-29-3	0.1	0.00022	0.00022	0.55	0.001
Demeton	8065-48-3	---	---	---	---	0.1
Di(2-ethylhexyl)adipate	103-23-1	400M	---	---	---	---
Diazinon	333-41-5	---	---	---	0.17	0.17
Dibenzo(a,h)anthracene (PAH)C, 13	53-70-3	0.016	0.00051	0.00053	---	---
1,2 Dibromo-3-Chloropropane (DBCP)	96-12-8	0.2M	---	---	---	---
Dibromoethane 1,2C	106-93-4	0.018	---	---	---	---
Dicamba	1918-00-9	210	170	860	---	---
Dichloroacetic acidC	79-43-6	0.7	---	---	---	---
Dichlorobenzene 1,211	95-50-1	600M	420	1,300	---	---
Dichlorobenzene 1,3	541-73-1	94	94	960	---	---
Dichlorobenzene 1,411	106-46-7	75M	63	190	---	---
DichlorobenzidineC	91-94-1	0.078	0.021	0.028	---	---
Dichloroethane 1,2C, 12	107-06-2	0.38 to 5M	0.38	37	118,000	20,000
Dichloroethylene 1,1	75-35-4	7M	7	3,600	---	---
Dichloroethylene 1,2-cis12	156-59-2	14 to 70M	---	---	---	---
Dichloroethylene 1,2-trans11	156-60-5	100M	100	10,000	---	---
Dichloromethane (methylene chloride) C, 13	75-09-2	5M	4.6	590	---	---
Dichlorophenol 2,4	120-83-2	21	21	290	2,020	365
Dichlorophenoxyacetic acid (2,4-D)	94-75-7	70M	---	---	---	---
Dichloropropane 1,2C, 12	78-87-5	0.52 to 5M	0.50	14	23,000	5,700
Dichloropropylene 1,3C	542-75-6	0.35	0.34	21	6,060	244
DichlorvosC	62-73-7	0.12	---	---	---	---
DieldrinC	60-57-1	0.002	5.2X10-5	5.4X10-5	0.24	0.056
Diethyl phthalate	84-66-2	5,600	5,600	44,000	---	---
Diisopropylmethylphosphonate (DIMP)	1445-75-6	8	---	---	---	---
Dimethylphenol 2,4	105-67-9	140	140	850	2,120	---
Dimethyl phthalate	131-11-3	70,000	70,000	1,100,000	---	---
Di-n-butyl phthalate	84-74-2	700	700	4,500	---	---
Dinitro-o-cresol 4,6	534-52-1	0.27	1.3	28	---	---
Dinitrophenol 2,4	51-28-5	14	14	5,300	---	---
Dinitrotoluene 2,4C	121-14-2	0.11	0.11	3.4	---	---
Dinitrotoluene 2,6C	606-20-2	---	---	---	330	230
Dinoseb	88-85-7	7M	---	---	---	---
Dioxane 1,4- C	123-91-1	0.35	---	---	---	---
Dioxin (2,3,7,8 TCDD)C, 12	1746-01-6	2.2x10-7 to 3.0x10-5, M	5.0X10-9	5.1X10-9	0.01	0.00001
Diphenylhydrazine 1,2C	122-66-7	0.044	0.036	0.20	270	---
Diquat12	85-00-7	15 to 20M	---	---	---	---
Endosulfan	115-29-7	42	---10	---	0.11	0.056
Endosulfan, alpha	959-98-8	42	---10	---	0.11	0.056
Endosulfan, beta	33213-65-9	42	---10	---	0.11	0.056
Endosulfan sulfate	1031-07-8	42	---10	---	0.11	0.056
Endothall	145-73-3	100M	---	---	---	---
Endrin	72-20-8	2M	----10	---	0.086	0.036
Endrin aldehyde	7421-93-4	2.1	0.29	0.30	---	---
EpichlorohydrinC	106-89-8	3.5	---	---	---	---
Ethylbenzene11	100-41-4	700M	530	2,100	32,000	---
Ethylene dibromideC, 12 (1,2 - dibromoethane)	106-93-4	0.02 to 0.05M	---	---	---	---
Ethylene glycol monobutyl ether (EGBE) (2-Butoxyethanol)	111-76-2	700	---	---	---	---
Ethylhexyl phthalate (BIS-2)C, 12 (DEHP)	117-81-7	2.5 to 6M	1.2	2.2	---	---
Fluoranthene (PAH)	206-44-0	280	130	140	3,980	---
Fluorene (PAH)	86-73-7	280	280	5,300	---	---
FolpetC	133-07-3	10	---	---	---	---
FurmecycloxC	60568-05-0	1.2	---	---	---	---
Glyphosate	1071-83-6	700M	---	---	---	---
Guthion	86-50-0	---	---	---	---	0.01
HeptachlorC, 12	76-44-8	0.008 to 0.4M	7.8X10-5	7.9X10-5	0.52	0.0038
Heptachlor epoxideC, 12	1024-57-3	0.004 to 0.2M	3.9X10-5	3.9X10-5	0.52	0.0038
HexachlorobenzeneC, 12	118-74-1	0.022 to 1.0M	0.00028	0.00029	---	---
Hexachlorobutadiene	87-68-3	0.45	0.44	---10	90	9.3
Hexachlorocyclohexane, AlphaC	319-84-6	0.0056	0.0026	0.0049	---	---
Hexachlorocyclohexane, Beta	319-85-7	0.019	0.0091	0.017	---	---
Hexachlorocyclohexane, Gamma (Lindane)	58-89-9	0.2M	0.2	---10	0.95	0.08
Hexachlorocyclohexane, TechnicalC	608-73-1	---	0.012	0.041	100	---
Hexachlorocyclopentadiene11, 12 (HCCPD)	77-47-4	42 to 50M	40	---10	7	5
Hexachlorodibenzo-p-dioxin (1,2,3,7,8,9-hcdd)C	19408-74-3	5.60E-06	---	---	---	---
HexachloroethaneC	67-72-1	0.88	0.5	1.2	980	540
Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)	121-82-4	0.42	---	---	---	---
Hexanone 2-	591-78-6	35	---	---	---	---
Hydrazine/Hydrazine sulfateC	302-01-2	0.012	---	---	---	---
Indeno(1,2,3-cd)pyrene (PAH)C, 13	193-39-5	0.16	0.0051	0.0053	---	---
Isophorone11	78-59-1	140	130	3,600	---	---
Malathion	121-75-5	140	---	---	---	0.1
Methanol	67-56-1	14,000	---	---	---	---
Methoxychlor12	72-43-5	35 to 40M	---10	---	---	0.03
Methyl bromide (HM)	74-83-9	---	9.8	1,500	---	---
Methyl chloride (HM)C	74-87-3	---	5.6	180	---	---
Methylene bis(N,N'-dimethyl)aniline 4,4C	101-61-1	0.76	---	---	---	---
Metribuzin	21087-64-9	180	160	1,700	---	---
Mirex	2385-85-5	1.4	---	---	---	0.001
Naphthalene (PAH)	91-20-3	140	140	---10	2,300	620
Nitrobenzene	98-95-3	14	14	2,800	27,000	---
Nitrophenol 4	100-02-7	56	56	9,700	---	---
Nitrosodibutylamine NC	924-16-3	0.0065	0.0043	0.012	---	---
Nitrosodiethylamine NC	55-18-5	0.00023	0.00023	0.0083	---	---
Nitrosodimethylamine NC (NDMA)	62-75-9	0.00069	0.00069	3.0	---	---
N-NitrosodiethanolamineC	1116-54-7	0.013	---	---	---	---
Nitrosodiphenylamine NC	86-30-6	7.1	3.3	6.0	---	---
N-Nitroso-N-methylethylamineC	10595-95-6	0.0016	---	---	---	---
N-Nitrosodi-n-propylamineC	621-64-7	0.005	0.005	0.50	---	---
Nitrosopyrrolidine NC	930-55-2	0.017	0.016	36	---	---
Nonylphenol	84852-15-3 and 25154-52-3	---	---	---	28	6.6
Oxamyl (vydate)12	23135-22-0	175 to 200M	---	---	---	---
PCBsC, 9, 12	1336-36-3	0.0175 to 0.5M	6.4X10-5	6.4X10-5	2.0	0.014
Parathion	56-38-2	---	---	---	0.065	0.013
Pentachlorobenzene	608-93-5	5.6	1.4	1.5	---	---
PentachlorophenolC, 12	87-86-5	0.088 to 1.0M	0.080	0.91	196	156
Perchlorate	7790-98-9	4.9	---	---	---	---
Phenol	108-95-2	2,100	2,100	---10	10,200	2,560
Picloram	1918-02-1	490	---	---	---	---
Prometon	1610-18-0	100	---	---	---	---
Propylene oxideC	75-56-9	0.15	---	---	---	---
Pyrene (PAH)	129-00-0	210	210	4,000	---	---
QuinolineC	91-22-5	0.012	---	---	---	---
Simazine	122-34-9	4M	---	---	---	---
Styrene	100-42-5	100M	---	---	---	---
Tetrachlorobenzene 1,2,4,5	95-94-3	2.1	0.97	1.07	---	---
Tetrachloroethane 1,1,2,2C	79-34-5	0.18	0.17	4	---	2,400
Tetrachloroethylene (PCE)C	127-18-4	5M	5	62	5,280	840
Tetrahydrofuran	109-99-9	6,300	---	---	---	---
Toluene11, 12	108-88-3	560 to1,000M	510	5,900	17,500	---
ToxapheneC, 12	8001-35-2	0.032 to 3M	0.00028	---10	0.73	0.0002
Tributyltin (TBT)	56573-85-4	---	---	---	0.46	0.072
Trichloroacetic acid	76-03-9	0.52	---	---	---	---
Trichlorobenzene 1,2,411	120-82-1	70M	35	---10	250	50
Trichloroethane 1,1,1 (1,1,1-TCA)	71-55-6	200M	---	---	---	---
Trichloroethane 1,1,2 (1,1,2-TCA)11, 12	79-00-5	2.8 to 5M	2.7	71	9,400	---
Trichloroethylene (TCE) C	79-01-6	5M	2.5	30	45,000	21,900
Trichloropropane 1,2,3 C, 13	96-18-4	3.7E-4	---	---	---	---
Trichlorophenol 2,4,5	95-95-4	700	700	3,600	---	---
Trichlorophenol 2,4,6C	88-06-2	3.2	1.4	2.4	---	970
Trichlorophenoxypropionic acid (2,4,5-tp) (Silvex)	93-72-1	50M	---	---	---	---
Total Trihalomethanes (HMs)	(total)7	80	80	---	---	---
Trimethylbenzene 1,2,3	526-73-8	67	---	---	---	---
Trimethylbenzene 1,2,4	95-63-6	67	---	---	---	---
Trimethylbenzene 1,3,5	108-67-8	67	---	---	---	---
Vinyl ChlorideC, 12	75-01-4	0.023 to 2M	0.023	2.3	---	---
Xylenes (total)12	1330-20-7	1,400 to 10,000M	---	---	---	---

Table B - Footnotes

(1) All standards are chronic or 30-day standards. They are based on information contained in EPA's Integrated Risk Information System (IRIS) and/or EPA lifetime health advisories for drinking water using a 10-6 incremental risk factor unless otherwise noted.

(2) Only applicable to segments classified for water supply.

(3) Applicable to all Class 1 aquatic life segments which also have a water supply classification or Class 2 aquatic life segments which also have a water supply classification designated by the Commission after rulemaking hearing. These class 2 segments will generally be those where fish of a catchable size and which are normally consumed are present, and where there is evidence that fishing takes place on a recurring basis. The Commission may also consider additional evidence that may be relevant to a determination whether the conditions applicable to a particular segment are similar enough to the assumptions underlying the Water + Fish ingestion criteria to warrant the adoption of Water + Fish ingestion standards for the segment in question.

(4) Applicable to all aquatic life segments.

(5) Deleted.

(6) Standards are pH-dependent. Those listed are calculated for pH = 7.8. Acute = e[1.005(pH)-4.869]; Chronic = e[1.005(pH)-5.134].

(7) Total trihalomethanes are considered the sum of the concentrations of bromodichloromethane (CAS No. 75-27-4), dibromochloromethane (Chlorodibromomethane(HM), CAS No. 124-48-1), tribromomethane (bromoform, CAS No. 75-25-2) and trichloromethane (chloroform, CAS No. 67-66-3).

(8) Applicable to the following segments which do not have a water supply classification: all Class 1 aquatic life segments or Class 2 aquatic life segments designated by the Commission after rulemaking hearing. These class 2 segments will generally be those where fish of a catchable size and which are normally consumed are present, and where there is evidence that fishing takes place on a recurring basis. The Commission may also consider additional evidence that may be relevant to a determination whether the conditions applicable to a particular segment are similar enough to the assumptions underlying the fish ingestion criteria to warrant the adoption of fish ingestion standards for the segment in question.

(9) PCBs are a class of chemicals which include aroclors, 1242, 1254, 1221, 1232, 1248,1260 and 1016, CAS numbers 53469-21-9, 11097-69-1, 11104-28-2, 11141-16-5, 12672-29-6, 11096-82-5, and 12674-11-2 respectively. The aquatic life criteria apply to this set of PCBs. The human health criteria apply to total PCBs, i.e. the sum of all congenor or all isomer analyses.

(10) The chronic aquatic life standard is more stringent than the associated Water + Fish or Fish Ingestion standard, and therefore no Water + Fish or Fish Ingestion standard has been adopted.

(11) The Water + Fish and Fish Ingestions standards for these compounds have been calculated using a relative source contribution (RSC).

(12) Whenever a range of standards is listed and referenced to this footnote, the first number in the range is a strictly health-based value, based on the Commission's established methodology for human health-based standards. The second number in the range is a maximum contaminant level, established under the federal Safe Drinking Water Act that has been determined to be an acceptable level of this chemical in public water supplies, taking treatability and laboratory detection limits into account. Control requirements, such as discharge permit effluent limitations, shall be established using the first number in the range as the ambient water quality target, provided that no effluent limitation shall require an "end-of-pipe" discharge level more restrictive than the second number in the range. Water bodies will be considered in attainment of this standard, and not included on the Section 303(d) List, so long as the existing ambient quality does not exceed the second number in the range.

(13) Mutagenic compound, age dependent factors were used in calculating standard. (C) Carcinogens classified by the EPA as A, B1, or B2.

(M) Drinking water MCL.

CAS No. - Chemical Abstracts Service Registry Number.

(HM) - Halomethanes

(PAH) - Polynuclear Aromatic Hydrocarbons.

-------------------------

(4) Site-Specific Radioactive Materials and Organic Pollutants Standards.

(a) In determining whether to adopt site-specific standards to apply in lieu of the statewide standards established in sections (2) and (3) above, the Commission shall first determine the appropriate use classifications, in accordance with section 31.13 . If such a determination would result in removing an existing classification, the downgrading factors in section 31.6 (2)(B) shall apply.

(b) The Commission shall then determine whether numerical standards other than some or all of the statewide standards established in sections (2) and (3) above would be more appropriate for protection of the classified uses, taking into account the factors prescribed in section 25-8-204(4), C.R.S. and in section 31.7 . The downgrading factors described in section 31.6 shall not apply to the establishment of site-specific standards under this section.

(c) Site-specific standards to apply in lieu of statewide standards may be based upon consideration of the appropriateness of the assumptions used in the risk assessment based potency factors and reference dose values, including, but not limited to, consideration of the uncertainty factor, exposure assessment, bioaccumulation factor, exposed population factor, assumed consumption factor, risk comparisons, uncertainty analysis, and the availability of the toxics in the water column, considering persistence, hardness, pH, temperature or valence form in the water column.

(5) Nothing in this regulation shall be interpreted to preclude:

(a) An agency responsible for implementation of the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), 42 U.S.C. 9601 et seq., as amended, from selecting a remedial action that is more or less stringent than would be achieved by compliance with the statewide numerical standards established in this section, or alternative site-specific standards adopted by the Commission, where a determination is made that such a variation is authorized pursuant to the applicable provisions of CERCLA.

(6) Except where the Commission adopts or has adopted a different standard on a site-specific basis, the less restrictive of the following two options shall apply as numerical standards for all surface waters with a "water supply" classification, if water supply is an actual use of the waters in question or of hydrologically connected groundwater:

i. existing quality as of January 1, 2000; or

ii. the following table value criteria set forth in Tables II and III:

Iron	300 µg/L (dissolved)
Manganese	50 µg/L (dissolved)
Sulfate	250 mg/L (dissolved)

Provided, that if the existing quality of these constituents in such surface waters as of January 1, 2000, is affected by an unauthorized discharge with respect to which the Division has undertaken an enforcement action, the numerical standards shall be the ambient conditions existing prior to the unauthorized discharge or the above table value criteria, whichever is less restrictive.

Data generated subsequent to January 1, 2000 shall be presumed to be representative of existing quality as of January 1, 2000, if the available information indicates that there have been no new or increased sources of these pollutants impacting the segment(s) in question subsequent to that date.

For all surface waters with a "water supply" classification that are not in actual use as a water supply, the water supply table value criteria for sulfate, iron and manganese set forth in Tables II and III may be applied as numerical standards only if the Commission determines as the result of a site-specific rulemaking hearing that such standards are necessary and appropriate in accordance with section 31.7.

(7) Methylmercury Fish Tissue: Fish tissue concentrations shall not exceed 0.3 milligrams methylmercury per kilogram (0.3 mg/kg) of wet-weight fish tissue. Attainment of the standard will be assessed by comparing the average fish tissue methylmercury concentration for each species and size class to the 0.3 mg/kg standard.

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