2011-01-24_PERMIT FILE - M2011007 (8)

Home Browse Search

Reclamation Feasibility Report - Virginia Canyon waste piles and the presence or absence of a vegetation kill zone below the pile. The r? characteristics given the most weight in prioritization were proximity to a stream course and historic erosion. Intuitively, the waste rock pile contributing the largest quantity of heavy metals would be those nearest to the major streams, and those exhibiting the most erosion. Also, based upon the water quality sampling, the mine sites in Robinson Gulch and Buttermilk Gulch were given a much lower priority. The water quality from both of these drainages was significantly better than found in the main stem of Virginia Canyon, Boomerang Gulch and Seaton Gulch. In addition, there was significantly less flow from these drainages during both sampling events. Although there are several mine waste piles in Robinson Gulch and Buttermilk Gulch exhibiting severe erosion, and high metals contents, these piles occur near the headwaters, and appear to have a minor effect on water chemistry near their confluence with the mainstem. The mining sites evaluated were prioritized using a rating between 1 and 4. Mining sites given a rating of 1 are the highest priorities for reclamation. The mining sites given a rating of 4 are the lowest priorities and were evaluated as minor sources of heavy metals. Seventeen mine sites were given a rating of 1. These included 12 sites sampled and 5 sites not sampled. Twenty-two sites were given a rating of 2. Seventeen of these sites were sampled. Sixty-six sites were given a rating of 3 and 91 sites were given a rating of 4. Table 1 is a synopsis of the rankings. Where mine names are given, the names are based upon Geological Survey Bulletin 1208 (7). The mining sites are shown on Figures 3 and 4. The mining sites were evaluated for possible reclamation measures. In general, most of the mining sites evaluated did not exhibit drainage from the mine workings. The reclamation measures considered for the mine waste piles are classified as hydrologic controls. A brief synopsis of the hydrologic controls follows: • Diversion ditches are effective where run-on water is degraded by flowing over or through mine waste, or into mine workings. Diversion ditches can also be used to intercept shallow ground water that may enter mine waste. Mine waste removal and consolidation is effective where there are several small mining waste piles in an area, or where there is a large pile in direct contact with flowing water. The method is simply to move reactive material away from water sources. Stream diversion is similar to mine waste removal and consolidation. It involves moving the water sources away from reactive materials. In most cases, it is usually preferable to move mining waste rather than move the stream, since the relocated stream can require considerable maintenance, particularly following high flow events. Revegetation is often used in combination with other hydrologic controls above. Revegetation by itself can be a very effective method of reducing heavy metals concentrations, particularly where much of the metals come from erosion of mining waste into a stream. Revegetation also reduces the amount of water that infiltrates a waste pile, thereby reducing leachate production. Additionally, the roots of growing plants have been shown to produce carbonates through respiration. Reclamation of the mining sites in Virginia Canyon will require sources of soil for revegetation. Even where a waste pile is removed, the underlying soils are often highly acidic and contain high concentrations of heavy metals due to leaching. There are very few areas in Virginia Canyon where topsoil could be "borrowed°. The majority of the soils are very shallow. The terrace deposit below Delaney Gulch is one of the largest potential sources of topsoil in Virginia Canyon. There is also a moderately deep deposit of topsoil in the headwaters of the mainstem of Virginia Canyon, and a large source of topsoil in the Gilson Gulch drainage west of the Gem Mine. • 18