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., o 0 MR. ROBERT J. SHUKLE CDPS N0. CO-0027154 OCTOBER 3, 1985 PAGE 2 The results of the sampling program indicate that: 1. Metals that are present exist primarily in the suspended, and not dissolved, state. 2. Suspended silver and zinc, which are of particular concern, appear to be composed of finer particles than are most suspended solids. 3. The primary source of suspended solids is the underground mine dis- charge. Although not necessarily the primary source of suspended metals, the underground mine discharge contributes a significant proportion of suspended metal particles. 4. The discharge from the underground mine occurs typically in surges. This condition and the proximity of the mine discharge point to the Pond D outlet probably increases suspended sediment concentrations through a churning effect. Based on these results, CYCC plans to implement the following treatment measures at Pond D. CYCC believes that these measures, along with the consi- derations set forth below, are sufficient to meet the proposed water quality limitations at Pond D. 1. Rerouting of underground mine discharge into the Area 2 pit, rather t an channe ing the water directly in o on as currently is done. See figure 1. This rerouting is expected to reduce suspended ~~Q, solids at Discharge Point 005 because solids from the underground Rio mine discharge (which account for as much as 99% of suspended solids ~ entering Pond D) will nave substantially more time to settle out. I' p f` In addition, the surging effect which currently exists for under- I ground mine discharge will no longer be present. An application for a revision to reroute the underground mine dis- charge into the pit and then into Pond D is being developed and will be submitted to the Colorado Mined Land Reclamation Division in early October, 1985. Preliminary discussions with the Mined Land Reclamation Division indicate that the application may be approved as a minor revision. 2. CYCC's consultant, Applied Hydrology Associates, believes that pre- liminary evidence indicates that a relatively large amount of fine suspended material resides in the near surface zone of the Area 2 pit (see AHA's attached report}, Applied Hydrology Associates has recommended obtaining a suite of samples at 10 foot depth intervals ~~ in the Area 2 Pit to determine if this is indeed the case, particu- b larly for suspended metals. If a relatively large amound of sus- pended metals are found in the upper waters of the pit, a baffling system in the Area 7 pit may significantly reduce metal contribu- tions to Pond D. Baffles, which are illustrated in figure _2, may