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site many years ago. It is not the result of in-stream gravel mining. Continued gravel mining did, <br />however, prevent the hole from healing faster than if in-stream mining was not conducted. <br />A report done in January 1981 by Wright-McLaughlin Engineers encompassed a three mile stretch <br />of the Animas River from Trimble Bridge to the Bar D Pit, located further downstream. The upper <br />part of this study was still approximately 1/2 mile south of the Thomas Pit but many of the conclu- <br />sions of the study are still valid. The study concluded that this stretch of the River was highly <br />aggrading and that approximately 90,000 cubic yards of gravel could be harvested from this stretch <br />of the river in a normal year. Since the Thomas Pit is closer to the significant change in grade that <br />the Animas River makes as it leaves the San Juan mountains, it is aggrading even more at the <br />Thomas site and the gravel sizes are larger. Longtime owners of the property have said that loud <br />grinding and rumbling can be heard day and night during the spring thaw when large flows are <br />moving the larger size rocks down the river. <br />Harvesting usually occurs over a one to two month period and consists of dozers, front-end loaders <br />and trucks operating in the dry portions of the western channel. This only occurs during the lowest <br />river levels, which could be in the late fall or early spring of each year. Two ramps shown on Map <br />Exhibit C-2 allows access to the lower gravel extraction area in the dry River channel and allows <br />bringing the material up to the plant area for processing. This extraction area is approximately 120 <br />feet wide x 600 feet long. A gravel berm of 18" height is built on the east and south sides of the <br />west channel, which allows dirty water to seep back in the ground through the porous gravel mate- <br />rial. Direct discharge into the river does not occur and the old discharge permit which was active for <br />the site, CO-0033090, is not needed and has not been renewed for river mining. NPDES Permit <br />COG-500328 is active for the discharge from the entire site. This permit will be modified slightly <br />for the lake mining amendment of 2002. <br />Dozers, loaders and trucks may be used to mine the gravel and haul it to the processing plant. The <br />material extracted from the channel is stockpiled on the west bank area across from the dredge hole <br />and is then processed in the processing plant. This plant consists of a portable rock crusher and <br />screen plant to obtain the desired material sizes. Certain sizes may be used as feed for an on-site <br />portable concrete plant and portable asphalt plant. Up to 4 portable stacker conveyors are used to <br />stockpile the various sizes of material. Processing usually takes place only one [o two months of the <br />Received <br />Thomas Pit 2/02 ~ NAY Q 3 <br />Durango Meta orrice <br />Division of Minerals 3 Geology <br />