Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-41 - REGULATION NO. 41 - THE BASIC STANDARDS FOR GROUND WATER
Section 5 CCR 1002-41.5 - GROUNDWATER QUALITY STANDARDS

Universal Citation: 5 CO Code Regs 1002-41 ยง 5

Current through Register Vol. 47, No. 5, March 10, 2024

The water quality standards specified in subsection B below are deemed necessary and appropriate to protect groundwater uses as specified in section 41.4 , and shall be adopted to protect such classified uses. The standards specified in subsections A and C apply to all State groundwaters, unless alternative site-specific standards have been adopted for a specified area pursuant to subsection D below.

A. Narrative Standards

1. Groundwater shall be free from pollutants not listed in the tables referred to in section 41.5 , which alone or in combination with other substances, are in concentrations shown to be:
a. Carcinogenic, mutagenic, teratogenic, or toxic to human beings, and/or,

b. A danger to the public health, safety, or welfare.

2. Determinations made pursuant to section 41.7 of specific numerical limitations under this subsection shall be based upon the best scientific information currently available.

B. Numeric Standards

1. The numeric standards shall be measured as total concentrations unless otherwise specified in Tables 1 through 4.

2. When a groundwater has a multi-use classification, the most restrictive standard for a parameter shall apply.

3. The following numeric standards shall apply:
a. "Domestic Use-Quality" - The Human Health and Secondary Drinking Water Standards listed in Tables 1 and 2, respectively, except as specified in section 41.5(B)5 or 41.5(B)(6).

b. "Agricultural Use - Quality" - The Agricultural Standards listed in Table 3, except as specified in section 41.5(B)5.

c. "Surface Water Quality Protection" - The standards necessary to prevent the exceedance of surface waters standards.

d. "Potentially Usable Quality" - appropriate standards considering those factors listed in section 41.4 (B)(4)(d).

4. The TDS limitation listed in Table 4 shall apply to the following classes:

"Agricultural Use - Quality"

"Surface Water Quality Protection"

"Potentially Usable Quality"

5. For groundwater classified "Domestic Use - Quality" or "Agricultural Use - Quality," where a table value is exceeded by the background level, the applicable standard for that parameter shall be either 1) the table value or 2) the background level for that parameter. This determination shall be made considering the increased risk to public health, crops, or livestock associated with the background levels, the extent of the exceedance above the table value, the degree to which the pollution is deemed correctable and subject to treatment; and the economic reasonableness of such treatment requirements.

6. The Commission may adopt site-specific standards in lieu of those listed in Tables 1, 2, 3 and 4 taking into account the factors prescribed in Section 25-8-204(4), C.R.S. and section 41.4 . The downgrading factors described in Regulation No. 31, section 6(2)(B) of the Basic Standards and Methodology for Surface Water shall not apply to the establishment of site-specific standards under this subsection.

C. Statewide Standards

1. Radioactive materials and Organic pollutants in groundwaters shall not exceed the following levels, unless alternative, site-specific standards for these substances have been adopted by the Commission:
a. For radioactive materials and organic pollutants listed in subsections 2 and 3 below, levels shall not exceed those specified in those subsections.

b. For all other radioactive materials and organic pollutants, they shall be maintained at the lowest practical level.

c. Where site-specific standards have been adopted, they shall apply in lieu of the standards set forth in this subsection.

2. Radioactive Materials Standards:

Radioactive Materials Standards1

Parameter

Standard

Americium2

0.15 pCi/l

Cesium 134

80 pCi/l

Plutonium 2392, and 2402

0.15 pCi/l

Radium 2262 and 2282

5 pCi/l

Strontium 902

8 pCi/l

Thorium 2302 and 2322

60 pCi/l

Tritium

20,000 pCi/l

pCi/l = Picocuries Per Liter

1 In site-specific cases, when it has been demonstrated that there are negligible differences between the results of dissolved (filtered) samples and total (unfiltered) samples, then dissolved results may be utilized for implementing the radioactive material standards.

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

3. Interim Organic Pollutant Standards:

Note that all standards in table A 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 restrictions such as antibacksliding or downgrading.

TABLE A

GROUNDWATER ORGANIC CHEMICAL STANDARDS

(in micrograms per liter)

Parameter

CAS No.

STANDARD1

Acenaphthene

83-32-9

420

Acetochlor

34256-82-1

140

Acetone

67-64-1

6300

Acrolein

107-02-8

3.5

AcrylamideC, 8

79-06-1

0.022

AcrylonitrileC

107-13-1

0.065

Alachlor

15972-60-8

2.0M

Aldicarb

116-06-3

7.0M

Aldicarb Sulfone

1646-88-4

7.0M

Aldicarb Sulfoxide

1646-87-3

7.0M

AldrinC

309-00-2

0.0021

AnilineC

62-53-3

6.1

Anthracene (PAH)

120-12-7

2100

AramiteC

140-57-8

1.4

Atrazine

1912-24-9

3.0M

AzobenzeneC

103-33-3

0.32

BenzeneC, 2

71-43-2

5.0M

BenzidineC

92-87-5

0.00015

Benzo(a)anthracene (PAH)C, 8

56-55-3

0.16

Benzo(a)pyrene (PAH)C, 8

50-32-8

0.016

Benzo(b)fluoranthene (PAH)C, 8

205-99-2

0.16

Benzo(k)fluoranthene (PAH)C, 8

207-08-9

1.6

BenzotrichlorideC

98-07-7

0.0027

Benzyl chlorideC

100-44-7

0.21

Bis(chloromethyl)ether (BCME)C

542-88-1

0.00016

BiphenylC

92-52-4

4.4

BromateC

15541-45-4

0.05

Bromobenzene

108-86-1

56

Bromodichloromethane (THM)C, 7

75-27-4

0.56

Bromoform (THM)C, 7

75-25-2

4

Butyl benzyl phthalate

85-68-7

1,400

Carbofuran6

1563-66-2

35 to 40M

Carbon tetrachlorideC, 6

56-23-5

0.5 to 5M

ChlordaneC, 6

57-74-9

0.10 to 2M

Chlordecone C

143-50-0

.0035

Chlorethyl ether (BIS-2)C

111-44-4

0.032

Chlorobenzene

108-90-7

100M

Chloroform (THM)C, 7

67-66-3

3.5

Chloroisopropyl ether (BIS-2)

108-60-1

280

4-Chloro-3-methylphenol

59-50-7

210

Chloronaphthalene

91-58-7

560

Chlorophenol, 2-

95-57-8

35

Chlorpyrifos

2921-88-2

21

Chrysene (PAH)C, 8

218-01-9

16

Dalapon

75-99-0

200M

DDDC

72-54-8

0.15

DDEC

72-55-9

0.1

DDTC

50-29-3

0.1

Di(2-ethylhexyl)adipate

103-23-1

400M

Dibenzo(a,h)anthracene (PAH)C, 8

53-70-3

0.016

1,2-Dibromo-3-Chloropropane (DBCP)

96-12-8

0.2M

Dibromochloromethane (chlorodibromomethane) (THM)3a, 7

124-48-1

14

Dibromoethane 1,2C

106-93-4

0.018

Dicamba

1918-00-9

210

Dichloroacetic acidC

79-43-6

0.7

Dichlorobenzene 1,2

95-50-1

600M

Dichlorobenzene 1,3

541-73-1

94

Dichlorobenzene 1,4

106-46-7

75M

DichlorobenzidineC

91-94-1

0.078

Dichloroethane 1,2C, 6

107-06-2

0.38 to 5M

Dichloroethylene 1,1

75-35-4

7M

Dichloroethylene 1,2-cis6

156-59-2

14 to 70M

Dichloroethylene 1,2-trans6

156-60-5

140 or 100M

Dichloromethane (methylene chloride) C, 6, 8

75-09-2

5.6 or 5M

Dichlorophenol 2,4

120-83-2

21

Dichlorophenoxyacetic acid (2,4-D)

94-75-7

70M

Dichloropropane 1,2C, 6

78-87-5

0.52 to 5M

DichlorvosC

62-73-7

0.12

DieldrinC

60-57-1

0.002

Diethyl phthalate

84-66-2

5,600

Diisopropylmethylphosphonate (DIMP)4

1445-75-6

8

Dimethylphenol 2,4

105-67-9

140

Di-n-butyl phthalate

84-74-2

700

Dinitro-o-cresol 4,6

534-52-1

0.27

Dinitrophenol 2,4

51-28-5

14

Dinitrotoluene 2,4C

121-14-2

0.11

Dinoseb

88-85-7

7M

Dioxane 1,4-C

123-91-1

0.35

Dioxin (2,3,7,8 TCDD)C, 6

1746-01-6

2.2x10-7 to 3.0x10-5, M

Diphenylhydrazine 1,2C

122-66-7

0.044

Diquat6

85-00-7

15 to 20M

Endosulfan

115-29-7

42

Endosulfan, alpha

959-98-8

42

Endosulfan, beta

33213-65-9

42

Endosulfan sulfate

1031-07-8

42

Endothall

145-73-3

100M

Endrin

72-20-8

2M

Endrin aldehyde

7421-93-4

2.1

EpichlorohydrinC

106-89-8

3.5

Ethylbenzene

100-41-4

700M

Ethylene DibromideC, 6

(1,2-dibromoehtane)

106-93-4

0.02 to 0.05M

Ethylene glycol monobutyl ether (EGBE) (2-Butoxyethanol)

111-76-2

700

Ethylhexyl phthalate (BIS-2)C, 6 (DEHP)

117-81-7

2.5 to 6M

Fluoranthene (PAH)

206-44-0

280

Fluorene (PAH)

86-73-7

280

FolpetC

133-07-3

10

FurmecycloxC

60568-05-0

1.2

Glyphosate

1071-83-6

700M

HeptachlorC, 6

76-44-8

0.008 to 0.4M

Heptachlor epoxideC, 6

1024-57-3

0.004 to 0.2M

HexachlorobenzeneC, 6

118-74-1

0.022 to 1.0M

Hexachlorobutadiene

87-68-3

0.45

Hexachlorocyclohexane, AlphaC

319-84-6

0.0056

Hexachlorocyclohexane, Gamma (Lindane)

58-89-9

0.2M

Hexachlorocyclopentadiene6 (HCCPD)

77-47-4

42 to 50M

Hexachlorodibenzo-p-dioxin (1,2,3,7,8,9-hcdd)C

19408-74-3

5.60E-06

HexachloroethaneC

67-72-1

0.88

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)3b

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

193-39-5

0.16

Isophorone3

78-59-1

140

Malathion

121-75-5

140

Methanol

67-56-1

14,000

Methoxychlor6

72-43-5

35 to 40M

Methylene bis(N,N'-dimethyl)aniline 4,4'C

101-61-1

0.76

Metribuzin

21087-64-9

180

Mirex

2385-85-5

1.4

Naphthalene (PAH)

91-20-3

140

Nitrobenzene

98-95-3

14

Nitrophenol 4

100-02-7

56

Nitrosodimethylamine NC(NDMA)

62-75-9

0.00069

N-NitrosodiethanolamineC

1116-54-7

0.013

Nitrosodiphenylamine NC

86-30-6

7.1

N-Nitrosodi-n-propylamineC

621-64-7

0.005

N-Nitroso-N-MethylethylamineC

10595-95-6

0.0016

Oxamyl (vydate)6

23135-22-0

175 to 200M

PCBsC, 5, 6

1336-36-3

0.0175 to 0.5M

Pentachlorobenzene

608-93-5

5.6

PentachlorophenolC, 6

87-86-5

0.088 to 1.0M

Perchlorate

7790-98-9

4.9

Phenol

108-95-2

2,100

Picloram

1918-02-1

490

Prometon

1610-18-0

100

Propylene oxideC

75-56-9

0.15

Pyrene (PAH)

129-00-0

210

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

Tetrachloroethane 1,1,2,2C

79-34-5

0.18

Tetrachloroethylene (PCE)C, 6

127-18-4

17 or 5M

Tetrahydrofuran

109-99-9

6,300

Toluene6

108-88-3

560 to 1,000M

Total Trihalomethanes (TTHMs)7

N/A

80M

ToxapheneC, 6

8001-35-2

0.032 to 3M

Trichloroacetic acidC

76-03-9

0.52

Trichlorobenzene 1,2,4

120-82-1

70M

Trichloroethane 1,1,1 (1,1,1-TCA)6

71-55-6

14,000 or 200M

Trichloroethane 1,1,23a, 6 (1,1,2-TCA)

79-00-5

2.8 to 5M

Trichloroethylene (TCE)

79-01-6

5M

Trichloropropane 1,2,3C, 8

96-18-4

3.7E-4

Trichlorophenol 2,4,5

95-95-4

700

Trichlorophenol 2,4,6C

88-06-2

3.2

Trichlorophenoxyproprionic acid (2,4,5-tp) (Silvex)

93-72-1

50M

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, 6

75-01-4

0.023 to 2M

Xylenes (total)6

1330-20-7

1,400 to 10,000M

Notes and Abbreviations:

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 The standard for Benzene has been established at the MCL (q.v. 41.17)

3a Standard for Group C compound that has both a published reference dose (non-cancer) and carcinogenic toxicity data and is calculated based on reference dose (non-cancer) toxicity data and then adjusted downward using an uncertainty factor of 10.

3b Standard for Group C compound that has both a published reference dose (non-cancer) and carcinogenic toxicity data and is calculated based on the toxicity data (i.e., non-cancer-based or cancer-based) resulting in the most protective (lowest) water quality standard.

4 The Diisopropylmethylphosphonate (DIMP) standard was adopted in 1993 (q.v. 41.16)

5 PCBs are a class of chemicals that 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 human-health criteria apply to total PCBs, i.e. the sum of all congener or all isomer analyses.

6 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 has been determined to be an acceptable level of this chemical in public water supplies, taking treatability and laboratory detection limits into account. The Commission intends that control requirements for this chemical be implemented to attain a level of ambient water quality that is at least equal to the first number in the range except as follows:

* Wherever the Commission has adopted alternative, site-specific standards for the chemical, the site-specific standards shall apply instead of these statewide standards.

* The implementing agency has determined that setting the protection level to the second number in the range is consistent with the current and reasonably anticipated future uses of the groundwater, factoring in site-specific information, such as: existing prohibitions on groundwater use; whether the location is within the boundaries of an existing or reasonably anticipated public water supply; the proximity of the site to existing and reasonably anticipated water wells; whether or not the aquifer can produce water at a rate capable of supporting the anticipated use; or it can be demonstrated that access to groundwater is prohibited, unavailable or present at insufficient quantities for reliable use.

The Commission does not intend the adoption of this range of standards to result in changes to clean-up requirements previously established by an implementing agency, unless such change is mandated by the implementing agency pursuant to its independent statutory authority.

7 For aquifer storage and recovery facilities, if the source of this chemical in groundwater is potable water provided by a drinking water system with a Colorado PWSID that meets all applicable federal Safe Drinking Water Act and corresponding State requirements at the time that it is utilized for aquifer storage and recovery or artificial recharge, then the separate total trihalomethane standard will apply to the groundwater in question, rather than the individual standards for bromodichloromethane, bromoform, chloroform, and/or dibromochloromethane. For any parameter for which there is a Maximum Containment Level (MCL) established by the Safe Drinking Water Act, as identified in Table A with Footnote "M", the MCL shall apply as the standard for groundwater when potable water is used for ASR or artificial recharge.

8 Mutagenic compound, age dependent factors were used in calculating standard. N/A - not applicable

C Carcinogens classified by the EPA as A, B1, or B2.

M Drinking water MCL.

CAS No. - Chemical Abstracts Service Registry Number THM - Halomethanes

4. Whenever the practical quantitation limit, or PQL, for a pollutant is higher (less stringent) than a standard listed in subsection 2 or 3 above, the PQL shall be used in regulating specific activities. PQL's may be established by the applicable implementing agency or in consultation with the Water Quality Control Division.

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 and a point of compliance that are more or less stringent than would be achieved by compliance with the statewide numerical standards established in this subsection, 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; or

b. An agency responsible for implementation of Subtitle C of the Resource Conservation and Recovery Act (RCRA), 42 U.S.C. 6901, et seq., as amended, or the Colorado Hazardous Waste Act, C.R.S. 25-15-101, et seq., as amended, from applying background levels or establishing "alternate concentration limits" and a point of compliance that differ from the statewide numerical standards established in this subsection, or alternative site-specific standards adopted by the Commission, for purposes of establishing hazardous waste management or corrective action requirements, where a determination is made that such background levels or alternate concentration limits are authorized by the regulations adopted pursuant to these statutory authorities; or

c. An agency responsible for implementation of a storage tank (ST) program, pursuant to C.R.S. 25-18-101 et seq., as amended, from issuing a regulatory determination, including a point of compliance, that is more or less stringent than would be achieved by compliance with the statewide numerical standards established in this subsection, or alternative site-specific standards adopted by the Commission, where a determination is made that the groundwater quality protection criteria identified in applicable ST regulations are satisfied.

6. Interim Narrative Standard
a. The "Interim Narrative Standard" in 41.5(C)(6)(b)(i) below is applicable to all groundwater, to which standards have not already been assigned in the state, with the exception of those areas where the total dissolved solids (TDS) are equal to or exceed 10,000 mg/l. This standard is applicable independent of and in addition to the statewide standards for radioactive materials and organic pollutants established in this section 41.5.C.

b.
i. Until such time as use classifications and numerical standards are adopted for the groundwater on a site-specific basis throughout the state, and subject to the provisions of subsection (ii) below, ground-water quality shall be maintained for each parameter at whichever of the following levels is less restrictive:
(A) existing ambient quality as of January 31, 1994, or

(B) that quality which meets the most stringent criteria set forth in Tables 1 through 4 of "The Basic Standards for Groundwater."

ii. The interim standard shall not be interpreted or applied as defining or limiting the potential need for remediation of contaminated groundwater where remedial requirements are established under state or federal law. It is the Commission's intent that, to the maximum degree technically feasible and economically reasonable, remedial efforts should be directed at cleaning up groundwater contaminated by human activities to a degree such that it is usable for all existing and potential beneficial uses; this interim narrative standard is not intended to define when such remediation is or is not feasible. Where contamination already exists, this interim standard is merely intended to assure that conditions are not allowed to deteriorate further pending remedial action. The appropriate level of clean-up to be achieved may be addressed by this Commission in a future classification and standard-setting proceeding, or by other agencies with jurisdiction over remedial actions.

iii. In applying this interim narrative standard, the Commission intends that agencies with authority to implement this standard will exercise their best professional judgment as to what constitutes adequate information to determine or estimate existing ambient quality, taking into account the location, sampling date, and quality of all available data. Data generated subsequent to January 31, 1994, shall be presumed to be representative of existing quality as of January 31, 1994, if the available information indicates that there have been no new or increased sources of groundwater contamination initiated in the area in question subsequent to that date. If available information is not adequate to otherwise determine or estimate existing ambient quality as of January 31, 1994, such groundwater quality for each parameter shall be assumed to be no worse that the most stringent levels provided for in Tables 1 through 4 of "The Basic Standards for Groundwater," unless the Commission has adopted alternative numerical standards for a given specified area.

D. Site-specific radioactive materials and organic pollutant standards

1. In determining whether to adopt site-specific standards to apply in lieu of the statewide standards established in subsection C above, the Commission shall first determine the appropriate groundwater classifications within a specified area, in accordance with section 41.4.

2. The Commission shall then determine whether numerical standards other than some or all of the statewide standards established in subsection C 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 section 41.4. The downgrading factors described in Regulation No. 31, section 6(2)(B) of the Basic Standards and Methodologies for Surface Water shall not apply to the establishment of site-specific standards under this subsection.

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