2014-10-29_REVISION - M1998013 - Laserfiche WebLink

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0/_3 MEMORANDUM - TO: /RMS, Bestway Concrete, Project File FROM: ✓Civil Resources, LLC DATE: ✓October 29,2014 RE: DRMS TR-2 Review Comments via email October 16,2014 The responses to the DRMS email comments from October 16,2014 are summarized in bold below. 1) What is the current minimum depth to static groundwater in the Burch parcel? The current minimum depth to groundwater varies from 6 feet to 8 feet in the northwest and southeast corners of the proposed mining area. The groundwater in northeast portion of the mining area is 8.2 feet deep indicating a gradient to the northeast toward the St.Wain River. Groundwater by the current mining area(Pond D)is 18 feet below grade. See groundwater mitigation plan. 2) What is the proposed depth of excavation at the Burch Parcel? The excavation varies from 16 feet in the west cell to 25 feet in the east cell based on recent monitoring well drill logs. 3)How many cubic yards of material will be required for each stage of proposed mining to backfill the excavations to at least two feet above static water level, and will there be sufficient overburden/backfill available on-site to achieve this without importation of additional material. The west cell has a total depth to bedrock of 16 feet with 9 feet of gravel and 7 feet of overburden. In order to backfill above groundwater which is at 7 feet Bestway would require 11 feet(9 feet+2 feet)of backfill. Using the footprint in the attached plans the average-end-area is 11.96 acres at 11 feet deep equals 212,206 cubic yards of material. The overburden at 7 feet deep and using the 11.96 acre average-end-area equates to 135,040 cubic yards. The east cell has a total depth to bedrock of 26 feet with 16 feet of gravel and 10 feet of overburden. In order to backfill above groundwater which is at 7 feet Bestway would require 21 feet(19 feet+2 feet)of backfill. Using the footprint in the attached plans the average-end-area is 6.45 acres at 21 feet deep equals 218,716 cubic yards of material. The overburden at 10 feet deep and using the 6.45 acre average-end-area equates to 104,039 cubic yards. The approximate gravel quantity is 340,084 cubic yards using fines loss of 18%equates to an additional 61,215 cubic yards of material for backfill. The north portion of the site has approximately 1.89 acre of overburden at 5 feet deep which is another 15,242 cubic yards of material. Therefore the site requires 430,922 cubic yards (212,206 cubic yards plus 218,716 cubic yards)of backfill material and the site has available 315,536 cubic yards(135,040 cubic yards plus 104,039 cubic yards plus 61,215 cubic yards plus 15,242 cubic yards). This would require an additional 115,386 cubic yards to be mined from the site which is available from the mining areas in the main Shores gravel mine as those area all have approved slurry walls and require no backfill. The Table below summarizes what is available onsite per the above discussion and site layout.