5 Colo. Code Regs. § 1002-38.81
The provisions of C.R S. 25-8-202(1)(a), (b) and (2); 25-8-203; 25-8-204; and 25-8-402; provide the specific statutory authority for adoption of these regulatory amendments. The Commission also adopted in compliance with 24-4-103(4) C.R.S. the following statement of basis and purpose.
BASIS AND PURPOSE
The Commission adopted on a permanent basis the revisions to Regulation # 38, Classifications and Numeric Standards for South Platte River Basin, Laramie River Basin Republican River Basin, Smoky Hill River Basin, which had been adopted on an emergency basis on December 13, 2011, and extended the expiration date of the temporary modification. The Commission is readopting the rationale for that temporary modification at this time, while anticipating a future review of arsenic criteria and standards in an April 2013 rulemaking
Prior to the December 2011 emergency rulemaking, the Colorado Department of Transportation ("CDOT"), the Regional Transportation district ("RTD") and the City and County of Denver ("Denver"), requested an emergency adoption of a revision to the water-plus-fish (W+F) arsenic standard for Segment 14 of the Upper South Platte River Basin in order to facilitate the issuance of Colorado
Discharge Permit System (CDPS) permits to segment 14 with chronic arsenic effluent limitations that are achievable with current and reasonable treatment capabilities.
In August of 2005 the Commission adopted revisions to the Basic Standards and Methodologies for Surface Waters (Regulation #31) to add a W+F table value standard of for chronic arsenic of 0.02 micrograms per liter (µg/L). W+F standards are numeric human health-based water quality standards that are calculated protective values that take into account the combined exposure from the pollutant in drinking water and the pollutant accumulated in fish flesh. This criterion was generally adopted for water bodies with drinking water and aquatic life class 1 use designations in the basin hearings between 2006 and 2009.
The proposal on December 13, 2011 was to revise the W+F water quality standard for arsenic on Segment 14 from 0.02 micrograms per liter (µg/L) to a range of 0.02 -7.6 µg/L. The Division proposed the revision to the chronic arsenic standard for Segment 14 based on circumstances where entities that have been assigned chronic arsenic effluent limitations in a CDPS permit at or near the 0.02 µg/L cannot achieve their chronic arsenic effluent limitations with treatment that may be beyond the current reasonable limit of technology. The Division examined the basis for the W+F standard and provided the Commission a policy option for an alternate W+F table value standard for chronic arsenic that it believed would be protective of human health for Segment 14 (7.6 is below the Safe Drinking Water Act protective level of 10 µg/L). Testimony was presented that as a practical matter, 3.0 µg/L is the lowest level that is technologically achievable. Testimony was also presented that there is uncertainty regarding the arsenic level necessary to protect the W+F use and regarding the extent to which the arsenic levels are reversible (i.e., whether the levels in the ground water and the river are natural or human-induced irreversible).
As a matter of policy, the Commission decided that since the technologically achievable arsenic level is less stringent than the calculated W+F criterion, the W+F criterion for segment 14 will be a hybrid, based on a range of 0.02-3.0 µg/L. The first number in the range shall be the strictly health-based value, based on the Commission's established methodology for human health-based standards that protect against the combined exposure of drinking water and eating fish. The second number in the range is the technologically achievable value of 3.0 µg/L. The Commission adopted this revision in the form of a temporary modification in recognition of the uncertainty regarding use-protective values and achievability. In the emergency action, the temporary modification was adopted with an expiration date of December 12, 2012. In this rulemaking, the Commission is extending the expiration date to October 31, 2013. The Commission anticipates that there will be a rulemaking hearing in April 2013 to address the substantive issues regarding arsenic criteria in Regulation #31 and arsenic standards in all basins. The extended expiration date is intended to provide time for that additional review.
Control requirements, such as discharge permits 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 during the effective period for this temporary modification.
The Commission found that the revision was necessary since achieving arsenic discharge permit limitations that result from the current arsenic standard appears to be technologically unachievable. CDOT, RTD, and the City and County of Denver (CCD) have expended significant public funds for multiple projects administered by these entities in attempting to comply with the limits.
5 CCR 1002-38.81