2001-05-16_REVISION - M2000158 - Laserfiche WebLink

Home Browse Search

Memo to Erica Crosby 6 May 15, 2001 The Division will require, in accordance with the language of the TR, that no more than 500 linear feet of erosion sensitive final pit perimeter be exposed without armoring at any one time during the life of the mine. Further, the Division requests that [he Operator make every reasonable effort to complete final Lakeshore protection measures for all such areas prior to April I~' of each year. (Lakeshore sensitive azeas are those areas depicted in green on the map included with the TR. The Division considers April ]s' to be the approximate onset of snowmelt flood season on the South Platte). A cost for Lakeshore armoring per lineaz foot is developed here, and may be applied to the maximum length of the working face, plus 500 feet of unreclaimed pit perimeter, that will be committed to by the Applicant. / Cost of riprap at the quarry: $10.50 per short [on. / Pit bank riprap required, per linear foot: 6 tons (derived by rntio: 4 feet thick required in Division guidance compared to Applicant's proposed 3 foot thickness and 4.5 tons per linear foot). / Approximate haul distance from Jefferson County riprap quarries to pit: 60 miles. / Hauling cost $1/mile @ 120 miles @ 15 tons per load: $8.00 per ton. / Installation cost of riprap: $1.00 per ton. / Riprap bedding @ 1.5 tons per linear foot, cost: $3.50 per ton. / Bedding haul cost, assume source could be found within ]0 miles, $1/mile @ 20 miles @ 10 tons/load: $2.OOton. ~$10.5/Tx6T/If~+~$8/Tx6T/Ij~+~$1/Tx6T/lf~+~$3.5/TxI.ST/If~+~$2/TxI.ST/lf~ _ $125.25 per linear foot As it turns out, this per linear foot cost will not be adequate to assure stable armoring of the lakeshores. Additional armoring requirements are discussed in the next section, and another estimate of the cost per lineaz foot is developed incorporating the additional requirements. The cost developed in the next section will be used by the Division for bonding purposes unless the Applicant can provide justification for a lower cost. Timetable jor Riprap Installation The Applicant states in the TR that any armoring of [he riverbank will be optional. It is the Division's position that all cut banks or unstable portions of riverbank, as identified in the Division's forthecoming field inspection, will need to be stabilized via the approved mitigation methods/designs prior to excavation within the 100-yeaz floodplain of [he South Platte River. It is also the Division's position that riverbank armoring may also be required in certain locations prior to mining where pit excavation will occur within 400 feet of the riverbank (DMG, 1998, page D-6, copy attached). The Division recommends against armoring those portions of riverbank that are currently stable, and are characterized by gentle bank slopes and well established ripazian vegetation. Prior to installing riprap into areas of cut bank, the bank must be graded to no steeper than 2.5:1 and granular bedding and filter subgrade