Laserfiche WebLink
Arequa Gulch <br />The information provided by CC&V regarding CNWAO limit exceedances included: (1) flow records and <br />sampling data taken at the two 24 inch underdrains, the North Underdrain (NUD) and the South <br />Underdrain (SUD), which confirmed that the two drains aze the principle contributing sources to the <br />CNw,,o exceedances, (2) results of sampling analyses taken from the 4 inch pipe, which captures any <br />drainage from the relocated Cazlton Mill tailings which show that this source did not exceed the CNW,~ <br />limit during this period of time, (3) sample results taken in-stream from sampling point AG l.~ + 6~0, <br />which is downstream from outfal1001A, which show no in-stream exceedances of the water quality <br />standard for CNwAp during the months of June through August of 1999, (4) records that demonstrate a <br />correlation between precipitation events and increased flow from the two 24 inch drains, (5) sampling <br />data showing high effluent CNw,~ values that exhibited some correlation with high precipitation, and <br />(6) that CN,o,~ could potentially break down in sunlight to produce forms of cyanide that aze measured <br />as CNW,~. <br />The Division has thoroughly reviewed this information and believes CC&V has provided evidence that <br />makes a strong correlation between the precipitation events, flow in the underdrains, and reported <br />exceedances of CNW,,a from May through August of 1999. The complex nature of this site and the <br />various theories as to the cause of the high CNw,~ values proposed by CC&V lead the Division to <br />believe that a definitive cause of the CNW,~ exceedances may not be identified but the heavy <br />precipitation events likely had a significant influence. A determination that an upset condition caused <br />the exceedances would only be useful as an affirmative defense in any enforcement action brought for <br />these exceedances. Given the information provided, the Division does not intend to pursue a formal <br />enforcement action regazding the May through August 1999 CNW„o exceedances. <br />If you have any questions regazding this matter, please contact me at (303) 692-3603. <br />Si er y, <br />Caz a J. enk <br />Water Quali rotection Section <br />WATER QUALITY CONTROL DIVISION <br />xc: terry Goad, AGO <br />EPA, Darcy O'Connor, Region VIII <br />Local Health Departrnent <br />Tim Vmndy, DE, Technical Services, WQCD <br />Bemham Keffelew, DMG <br />hiS-3 File <br />