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CDOW Rebuttal Statement - Regulation 37 <br />December 2010 Reg. 37 Rule-Making Hearing <br />3.0 mg/L, the WQCD's alternative would retain warm-water standards for dissolved <br />oxygen (5.0 mg/L) and pH (6.5-9.0), as recommended by the CDOW (CDOW RPHS, <br />page 3) and the EPA (EPA RPHS, page 4). The CDOW believes that retention of these <br />standards is appropriate to protect aquatic life, and this practice would be consistent with <br />the approach taken elsewhere in Colorado (CDOW RPHS, page 3; WQCD RPHS, page <br />4). <br />For inorganics and metals standards, the WQCD has proposed an ambient quality-based <br />approach (WQCD RPHS, page 5). The available water-quality data suggest that it is <br />reasonable to expect exceedances of some standards typically set for protection of aquatic <br />life (CAM Exhibit 4, Table 16, page 32). However, as detailed in Reg. 31.7(1)(b)(ii), the <br />appropriateness of ambient quality-based standards is predicated by a showing that the <br />exceedances of the Table Value Standards (TVS) are the result of natural or irreversible <br />man-induced conditions. The WQCD has concluded that the streams proposed for <br />inclusion in Segment 13e are characterized by naturally poor water quality and that <br />anthropogenic activity is not expected to have resulted in worsened water quality <br />(WQCD RPHS, page 5). The CDOW notes that, while CAM has documented signs of <br />recreational use including off-road vehicle use, mountain bike use, target shooting, <br />hunting, and adult beverage consumption as well as agricultural use including livestock <br />grazing (CAM Exhibit 4, page 33), these uses appear to be relatively dispersed and are <br />unlikely to cause greater water-quality degradation than the area's naturally-occurring <br />marine shales and erosive hydrology. Additionally, the area proposed by the WQCD for <br />inclusion Segment Be does not include the BLM's Grand Valley Off-Road Vehicle Area <br />where CAM noted heavier recreational use (CAM Exhibit 4, page 33). On this basis, the <br />CDOW agrees that exceedances of the TVS in the streams proposed by the WQCD for <br />inclusion in Segment Be are likely to be naturally occurring. <br />In addition to documentation of naturally occurring or irreversible exceedances of the <br />TVS, Regulation 31.7(1)(b)(ii) requires a determination that ambient quality-based <br />standards would protect the classified uses. In this case, with regard to aquatic life, the <br />existing and proposed use classification is Warm 2, which is defined in Regulation <br />31.13(l)(c) as: <br />Class 2 - Warm Water Aquatic Lim These are waters that are not capable of <br />sustaining a wide variety of warm water biota, including sensitive species, due to <br />physical habitat, water flows or levels, or uncorrectable water quality conditions that <br />result in substantial impairment of the abundance and diversity of species. <br />The CAM Use Attainability Analysis documents that fish are likely to be restricted to <br />perennial or nearly perennial streams such as East Salt Creek. In the ephemeral or <br />intermittent streams proposed by the WQCD for inclusion in Segment 13e, the <br />expectation for aquatic life is a relatively low-diversity macroinvertebrate community <br />consistent with expectations for areas of flashy, erosive hydrology and naturally poor <br />water-quality. On this basis, it appears that the existing water-quality presently supports <br />the Warm 2 Aquatic Life Use Classification. Therefore, the CDOW believes that an <br />ambient-based approach to inorganics and metals standards in the WQCD's proposed <br />Segment Be would provide adequate protection to the expected aquatic community. <br />December 1, 2010