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TETRA TECH RMC Ms. Madoline Wallace <br />January 5, 2004 <br />Page 4 <br />5) Short radius bends should be avoided. <br />6) At least 10-feet of unobstn~cted access shall be provided along the west side of the new <br />ditch. At least 30-feet of unobstructed access shall be provided along the east bank of the <br />new ditch. The remainder of the 70-foot ditch easement shall be reasonably accessible to <br />the Ditch Company. <br />7) . Until the Smith &, Emmons Ditch is relocated, we recommend that Lafarge be prevented <br />from mining within 120 feet of the ditch banks. This is based on a depth to bedrock of up <br />to 23 feet, the 50-foot minimum offset from waterways as recommended in their <br />Geotechnical Stability Exhibit, and the representation in the application that mining will <br />be to a neaz vertical face. As an alternative, Lafarge can mine to within 50 feet of the <br />existing ditch banks if they will commit to leaving an unmined 3:1 slope extending from <br />that point to bedrock. <br />8) We could not find any mention in the application assessing, or proposing mitigation of, <br />the potential for inducing additional leakage from the existing Smith & Emmons Ditch <br />due to dewatering of the mine site. The dewatering of the mine site will undoubtedly <br />lower the groundwater table below the Smith & Emmons Ditch. Whether this results in <br />additional leakage from the Ditch depends on the difference between the condition prior <br />to mining and the dewatered condition. Lafarge should provide for review, all depth to <br />water table information it has obtained during its exploration of the Duckworth property. <br />The information needed would be the location of each of the borings, the depths to water <br />after groundwater levels stabilized in the drill holes, and the dates of the depth to <br />groundwater measurements. Once we have been provided the data, we will review the <br />information to assess how adequately it represents the pre-mining condition, will offer an <br />opinion regarding the probability that mining of the site could induce additional seepage <br />from the Smith & Emmons Ditch, and will offer suggestions for mitigating any potential <br />losses. <br />9) The Ditch Company must be allowed continuous and unrestricted access to both sides of <br />the Ditch through the mine property. Thus, mining activities should not be allowed to <br />block that access in any way. <br />Conclusio~r <br />There is insufficient information presented in Lafarge's current mining permit application to <br />adequately assess the potential impacts on the Smith & Emmons Ditch, or to be able to assess the <br />acceptability of their proposal to relocate the ditch. We cannot at this time recommend that the <br />Ditch Company agree to the proposal to relocate the Ditch, and can only recommend that mining of <br />the property be allowed subject to the proximity limits described at #7 above, and subject to Lafarge <br />