2012-06-28_REPORT - C1982057 - Laserfiche WebLink

Home Browse Search

value is most likely and anomaly. The highest mercury value previously reported was 0.3 ug /1, while most (17 out of 21) values were less than the detection limit. NPDES Effluent Criteria (Permit No. CO- 0000221) . Four excursions of iron stream standards occurred at NPDES Outfalls 005, 016 and 017 in March, April and May of this year. Normally, the standard is 1.0 mg /l. However, in August 2008, the Colorado Water Quality Control Commission authorized a temporary modification for the total recoverable iron standard to be set at "existing quality" for Yampa Segment 13d, Dry Creek, to which these outfalls discharges into. Therefore, these excursions should not be considered NPDES violations. Also, as discussed above in the previous section, the new ambient -based standard for this stream segment went into effect on June 30, 2011. These excursions were most likely caused by snowmelt runoff. The excursions of the selenium standard at NPDES6 and NPDESI7 noted above were not NPDES permit limit excursions. On June 6, a potentially dissolved selenium value of 4.8 ug /l was observed at Outfall 006 (aka, NPDES6). The standard listed on the DMR is 4.6 ug /l. However, the total recoverable selenium value from the same sample was only 3.9 ug /l. Also, in Regulation 31 (Basic Standards for Surface Water) Footnote 4 to Table III, it states: "Both acute and chronic numbers adopted as stream standards are levels not to be exceeded more than once every three years on the average." Furthermore, on page 75, third paragraph (31.22 SBP - 1987 Revisions) it states: "Footnote 5 to Table III states that standards based on these table values are not to be exceeded more than once every three years on the average. This provision is adopted based on evidence that aquatic life can recover from impacts if not exposed to exceedances more frequently than once every three years." 22