5 Colo. Code Regs. § 1002-38.70
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
Pursuant to the requirements in the Basic Standards (at section 31.7), the Commission reviewed the status of temporary modifications to determine whether the temporary modification should be modified, eliminated or extended.
Segments with no change to expiration dates:
Temporary modifications provide time for sand and gravel dischargers to work with the Division to determine the most appropriate way to make progress toward resolving non-attainment of underlying selenium standards. The Commission took no action on the expiration date for the following segments. The temporary modifications will expire on 2/28/10.
St Vrain segment 6: temporary modification for selenium
Big Thompson segment 4b: temporary modification for selenium.
Because parties are working to resolve uncertainty and are on schedule to address these segments at the regularly scheduled basin-wide rulemaking (June 2009), the Commission took no action on the expiration date for the temporary modifications for the following segments:
Upper So. Platte segment 5c: (temporary modifications for ammonia). The Mountain Water and Sanitation District presented evidence that they are making progress on their study of aquatic life classification and appropriate underlying standards and will make a proposal for the June 2009 rulemaking hearing.
Big Dry Creek segment 5: (temporary modifications for nitrate, nitrite, benzene, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethene, tetrachloroethylene, and trichloroethylene). The Department of Energy submitted evidence that progress is continuing and that the temporary modifications will be addressed in the June 2009 rulemaking hearing.
Boulder Creek, segment 9, Cache La Poudre segments 11 and 12: (temporary modification for copper). The City of Boulder (Boulder Creek) and the City of Fort Collins (Cache La Poudre) submitted evidence that they are making progress on their translator studies.
Big Thompson, segment 2, Wapiti Meadow: (temporary modification for dissolved oxygen, E coli, ammonia, nitrate, boron cadmium, copper, lead, mercury, nickel, selenium, silver and zinc). The Upper Thompson Sanitation District submitted evidence that they are making progress on developing site-specific standards for the wetland and will make a proposal for the June 2009 rulemaking hearing.
Upper Clear Creek basin: The Commission considered proposals regarding temporary modifications and underlying standards for Clear Creek segments 2, 3a, 3b, 6, 9a, 9b, 11 and 13b.
Manganese acute and chronic aquatic life standards were added to segments 2 and 9b.
The Commission declined to modify other underlying standards at this time and noted that it would be willing to revisit underlying standards in the June 2009 basin-wide hearing, including any proposals from the Upper Clear Creek Watershed Association.
Since there are no permitted dischargers, the Commission deleted the temporary modification, thereby allowing the underlying standards to go into effect for the following segments:
Clear Creek segments 3a, 3b, 6 and 9b.
The numeric temporary modifications for segments 2, 9b, 11 and 13b were revised to reflect current conditions. A new temporary modification of the iron standard was added for segment 13b. A ten year period of record was used in these cases because of the wider range of hydrologic conditions that is captured by this period. These type iii temporary modifications were set to expire on 12/31/2014 as follows:
Clear Creek segment 2: Cu= 7.4 µg/l, Zn= 254 µg/l
Clear Creek segment 9a: Cu= 9.6 µg/l
Clear Creek segment 11: Zn= 325 µg/l
Clear Creek segment 13b: Cd= 4.7 µg/l, Mn= 3841 µg/l, Zn= 1582 µg/l, Fe(trec)= 7941 µg/l.
Since considerable water quality improvement in this basin has been made since 2000, the Commission adopted an alternative baseline to be used for antidegradation review for the reviewable segments (segments 1, 2, 4, 3a, 3b, 6, 9a, 9b, 10 and 13a). A notation was added to the designation column of reviewable segments "9/30/00 baseline does not apply". Pursuant to section 31.8 of the Basic Standards, the baseline will be determined at the time of the first new or increased water quality impact. This will ensure that the improved water quality will be used as the baseline.
Sand Creek, Upper So. Platte segment 16a: Suncor Energy, (U.S.A.), Inc. (Suncor) requested the Commission to extend the type iii temporary modification pursuant to section 31.7 of the Basic Standards for selenium of segment 16a of the South Platte River (Sand Creek) to 12/31/2014. More time is needed to determine what criteria are necessary to protect the use in Segment 16a and how additional treatment will be provided.
The Commission extended the selenium temporary modifications and updated the underlying narrative standard with the notation of "current condition" rather than a numeric value. The Commission's intent of using the notation "current condition" is to preserve the status quo during the term of the temporary modification. Dischargers to this segment shall maintain the existing selenium water quality and loading characteristics of their effluent, as reflected in current permits. The Commission does not intend the temporary modifications to apply to new facilities or in Preliminary Effluent Limitations.
Toll Gate, East and West Toll Gate Creeks, Upper So Platte segment 16h: The City of Aurora presented evidence that the natural or irreversible human-induced ambient water quality levels for selenium in Toll Gate Creek, East Toll Gate Creek, and West Toll Gate Creek at times exceed the relevant table value standard, and that an ambient quality-based standard, calculated in a manner consistent with Basic Standards requirements, is adequate to protect classified uses. The Commission accepts the City of Aurora's evidence as accurate. The Commission expressly finds that the natural or irreversible human-induced ambient water quality levels for selenium in Toll Gate Creek, East Toll Gate Creek, and West Toll Gate Creek exceed the relevant table value standard. Moreover, the proposed ambient quality based standard is adequate to protect classified uses and represents the highest reasonably attainable standard, based on analysis of available data that show elevated instream conditions are attributable to natural or irreversible human-induced conditions.
The Commission created a new segment, segment 16h, and adopted ambient quality-based site-specific standards for selenium applicable to Toll Gate Creek, East Toll Gate Creek, and West Toll Gate Creek in Segment 16h. The ambient quality-based standards are based on the 85th percentile (chronic) and the 95th percentile (acute) of the selenium data collected at three specific instream monitoring locations (TG6, ET1 and WT1). The instream attainment locations have been added to section 38.6(4). Percentiles are:
Toll Gate Creek (TG6): 85th percentile = 26.5 µg/l chronic (dis), 95th percentile = 29.5 µg/l acute (dis).
East Toll Gate Creek (ET1): 85th percentile = 14.3 µg/l chronic (dis), 95th percentile = 15.9 µg/l acute (dis).
West Toll Gate Creek (WT1): 85th percentile = 50.6 µg/l chronic (dis), 95th percentile = 119.2 µg/l acute (dis).
The Commission removed the temporary modification currently in place for selenium in Toll Gate Creek, East Toll Gate Creek, and West Toll Gate Creek in Segment 16c, and added "16h" to the list of exceptions in the 16c segment description.
PARTIES TO THE RULEMAKING
5 CCR 1002-38.70