2010-02-11_APPLICATION CORRESPONDENCE - C2009087

Home Browse Search

Mr. Vern Pfannenstiel February 11, 2010 16. Please add to the permit application the following historic reclamation information pertaining to the Seneca II lands that will be transferred to the PSCM: (Responses to items a and b of this Comment 16 are adequate as submitted.) c) A summary of past husbandry practices; i. Weed control measures; method-chemical, biological, or mechanical, describe, and what species was being controlled. Although the weed management plan provided says what will be done if weeds are found, the history of weed control measures previously employed are needed. ii. (This response is adequate as submitted.) iii. Mowing, location and dates (year would be adequate, for example: Mowed parcel 89-2 in 2001). This information is needed because mowing can be used as a weed control measure. 48. Please revise the calculation of ground water flow velocity on page 2.04-52 using a value for porosity that is significantly less than 14% (we suggest a value of 10%), and revise associated analyses or references in the permit application. Although Robson and Stewart reported 14% as an average and used it in their numerical simulation, it represents total porosity, rather than the effective porosity value that is required in a calculation of Darcy seepage velocity. SCCC's bulk density logs show that total porosity of the beds in the underburden (the only interval logged) that are most likely to be permeable (sandstone) are around 15%, but the low hydraulic conductivity values shown for the lower member of the Williams Fork in Table 2.04.7-T2 indicate effective porosity would be significantly less than the total porosity shown on the logs. Based on Williams and Clark's (1992) study, it is probable that clay minerals reduce effective porosity to a value that is significantly less than total porosity. Their mineralogic analysis (Table 15) found that core samples from the lower member of the Williams Fork contained abundant clay minerals (mainly kaolinite). Their comparison of hydraulic conductivity and permeability to air (page 23 of their report) concluded that permeability was reduced to less than the theoretical maximum probably as a result of clay minerals plugging the sandstone pores. Although Williams and Clark's data may suggest effective porosity would be only a fraction of the value of total porosity, they analyzed permeameter samples which would not have had fracture porosity; therefore, an effective porosity value of 10% is suggested relative to total porosity of 14% or 15%, rather than some smaller effective porosity value. 49. Please revise the calculation of mine water discharge to alluvium at the top of page 2.05-85 so that it uses the 2.5 ft/day hydraulic conductivity value noted above in our Comment 14. 50. Please revise the mine inflow and drawdown calculations in Section 2.05.6(3)(b)(iii) as follows: Page 4 a) Extend the time period to include the end of the first 60-month permit term and 30 years after the end of the 60-month permit term.