Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-36 - REGULATION NO. 36 - CLASSIFICATIONS AND NUMERIC STANDARDS FOR RIO GRANDE BASIN
Section 5 CCR 1002-36.12 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY, AND PURPOSE; MAY, 1989 HEARING ON MULTIPLE SEGMENTS

A. Aquatic Life Class 1 with Table Values; New High Quality 2 Designations

Rio Grande, segments, 4, 5a, 6a, 8, 9, 10, 14, 16, 17, 24, 27, 28, 30, 31a, 32, 34, 36, 38, 39, 41 Closed Basin, segments 2, 4, 12

Numerical standards for metals for these segments have in most instances previously been based on table values contained in Table III of the Basic Standards and Methodologies for Surface Water. Table III has been substantially revised, effective September 30, 1988. From the information available, it appears that the existing quality of these segments meets or exceeds the quality specified by the revised criteria in Table III, and new acute and chronic table value standards based thereon have therefore been adopted. There are also some of these segments whose previous standards were adopted. There are also some of these segments whose previous standards were based in part on ambient quality, since their quality did not meet old table values based on alkalinity ranges. However, these segments generally have much higher hardness than alkalinity, and the new table values (based on hardness-dependent equations) are now appropriate as standards.

Second, in addition to these standards changes, the use classifications have been revised where necessary so that each of these segments has the following classifications:

Recreation - Class 1

Cold Water Aquatic Life - Class 1

Water Supply

Agriculture

These classifications are appropriate because the existing quaity is adequate to protect these uses.

Third, a High Quality 2 designation has been established for each of these segments. The best available information in each case indicates that the existing quality for dissolved oxygen, pH, fecal coliform, cadmium, copper, iron, lead, manganese, mercury, selenium, silver and zinc is better than that specified in Tables I, II, and III of the Basic Standards and Methodologies for Surface Water, for the protection of aquatic life class 1 and recreation class 1 uses.

Finally, in addition to these generally applicable changes, certain specific changes were made for some segments in this group. The description of segment 10 has been revised to change the dividing line between segments 10 and 11, since the previous reference point is no longer in existence. The description of segment 14 has been revised, to correct a typographical error and make this segmentation compatible with segment 4. Segment 27 has been consolidated into segment 26 to simplify the tables, due to similarities in uses and quality, and is no longer listed as a separate segment. Segment 31a has been consolidated with segment 31b (together now designated as segment 31) to simplify the tables, due to similarities in uses and quality.

B. Existing High Quality 2 Segments; New Classifications and Standards

Rio Grande, segments 1, 26, 31b

Closed Basin, segment 1

These segments were already described as High Quality Class 2, and available information indicates that the parallel new High Quality 2 designation continues to be appropriate for each. Rio Grande segment 1 and Closed Basin segment 1 are waters in Wilderness areas, Rio Grande segment 26 is proposed for wild and scenic river designation, and Rio Grande segment 31b is the only native habitat on public lands in Colorado for the Rio Grande cutthroat trout.

In addition, the following use classifications, and associated table value standards, have been adopted for these segments:

Recreation - Class 1

Cold Water Aquatic Life - Class 1

Water Supply

Agriculture

These classifications and standards are appropriate based on the best available information regarding existing quality. These provisions would apply in the event that degradation is determined to be necessary following an activity-specific antidegradation review.

Finally, in addition to these generally applicable changes, the description of segment 26 has been revised to consolidate former segment 27 into this segment, and segment 31b has been consolidated with segment 31a, into new segment 31. These changes simplify the tables, due to similarities in uses and quality.

c. New Use-Protected Designations: No Change in Numeric Standards

Rio Grande, segments 15a, 15b, 19, 20, 23, 25

Closed Basin, segments 3, 9

These segments all qualify for a Use-Protected designation based on their present classifications. Specifically, Rio Grande segments 15a, 19, and 23, and Closed Basin segment 9 have no aquatic life classification. Rio Grande segments 15b and 25 and Closed Basin segment 3 have warm water class 2 classifications. Rio Grande segment 20 has a cold water class 2 classification. The existing standards are recommended to be retained because the segments have no metals standards or in the case of Rio Grande segment 20 have high ambient standards for some metals, exceeding table values, based on total recoverable metals data, and no dissolved metals data is available at this time.

In addition to these generally applicable changes, the description of segment 15a has been revised to correct a typographical error and make this segmentation compatible with segment 4. Also, as discussed further below, segment 19 has been divided into segments 19a and 19b.

D. New Use-Protected Designations; Revised Numeric Standards

Rio Grande, segments 2b, 11, 13, 21, 29, 33, 35, 37, 40

Closed Basin, segments 5, 6, new 7

These segments all qualify for a Use-Protected designation. Specifically, Rio Grande segments 2b, 11, 29, 33, 35, 37 and 40, and Closed Basin segments 5 and 6 and new segment 7 qualify as Use-Protected because they are classified aquatic life cold or warm water class 2. Rio Grande segment 13 is Use-Protected because existing quality for lead, mercury and silver is worse than that specified in Table III of the Basic Standards and Methodologies for Surface Water. Rio Grande segment 21 (Terrace Reservoir) is designated Use-Protected because it was identified in the 1988 Section 305(b) Report as being impacted by a combination of metals loading and fluctuating reservoir levels.

The description of segment 11 has been revised to change the dividing line between segments 10 and 11, since the previous reference point is no longer in existence.

Numerical standards for metals for Rio Grande segments 2b, 11, 21, 29, 33, 35, 37 and 40 have in most instances previously been based on table values contained in Table III of the Basic Standards and Methodologies for Surface Water. Table III has been substantially revised, effective September 30, 1988. From the information available, it appears that the existing quality of these segments meets or exceeds the quality specified by the revised criteria in table III, and new acute and chronic table value standards based thereon have therefore been adopted. There are also some of these segments whose previous standards were based in part on ambient quality, since their quality did not meet old table values based on alkalinity ranges. However, these segments generally have much higher hardness than alkalinity, and the new table values (based on hardness-dependent equations) are now appropriate as standards.

For Rio Grande segment 13, acute and chronic table value standards have been adopted except for lead, mercury, and silver. For lead and silver, ambient-quality-based standards are adopted based on the 85th percentile of available dissolved metals data. For mercury, a one-year temporary modification is established based on existing ambient quality, with an underlying standard based on the "final residual value" established in Table III of the Basic Standards and Methodologies for Surface Water, to protect human health from fish consumption. The temporary modification should allow time for collection and analyses of fish tissue for mercury. Should such analyses show no problems with mercury, the Commission will reconsider the appropriateness of the underlying standard in a subsequent hearing. Otherwise, the underlying standard will go into effect when the temporary modification expires. Also for segment 13, the recreation classification has been changed from class 2 to class 1, with a corresponding change in the fecal coliform standard, based on new information regarding existing quality.

For Closed Basin segment 5, acute and chronic table value standards have been adopted except for copper, iron, lead, mercury, silver, and zinc. For all except mercury, ambient quality-based standards have been adopted. These standards are based on the 85th percentile of available data, except for zinc which is based on the highest non-runoff value since there are only four data points. For mercury, a one-year temporary modification based on existing ambient quality and an underlying standard based on the "final residual value" have been established, in the same manner as described above for Rio Grande segment 13.

For Closed Basin segment 6, Head Lake has been removed and designated as a new segment 7. For segment 6, acute and chronic table value standards have been adopted except for iron, manganese, mercury, and selenium. For all except mercury, ambient quality-based standards have been adopted based on the 85th percentile of available data. For mercury, a one-year temporary modification based on existing ambient quality and an underlying standard based on the "final residual value" have been established, in the same manner as described above for Rio Grande segment 13.

For new Closed Basin segment 7, acute and chronic table value standards have been adopted except for iron, lead, and mercury. For all except mercury, ambient quality-based standards have been adopted based on the 85th percentile of available data. For mercury, a one-year temporary modification based on existing ambient quality and an underlying standard based on the "final residual value" have been established, in the same manner as described above for Rio Grande segment 13.

E. Other Revisions