2009-12-11_REVISION - M1977036 (13)

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TETRA TECH Page 3 of 5 Mr. Jared Ebert December 11, 2009 Area Reclamation T Approximate Fill Depth to Wetland Approximate Fill Depth to Upland South Part of South Central Pit N/A 20 to 25 feet North Part of South Central Pit 13 to 21 feet 19 to 27 feet East Pit 0 to 20 feet 5 to 29 feet F. Please address item 21 from the first adequacy review: 21. How much material is on site currently to backfill the South Central and East Pit excavations? The majority of the fill will be silt fines produced as a byproduct of aggregate processing. The aggregate processing plant will continue processing sand and gravel from other sites after mining is complete at the 35` Avenue Mine. The processing of material from other sites will result in ample amounts of fill to meet the reclamation plan. Other sources of fill are available if necessary. These other sources include an approximately 10 foot thick clay lens that makes deeper mining in the West Pit uneconomical. This clay lens could potentially be borrowed if needed for reclamation. In addition, if needed, bedrock could potentially be borrowed from the bottom of areas to be reclaimed as ponds. Lafarge is confident that ample amounts of fill are available. G. Please address item 22 from the first adequacy review: 22. It states in the Exhibit L narrative that 114 acres of the affected land will remain as open water. However based on the reclamation plan map, 5 open water ponds will contain 140 acres. Please explain this discrepancy? As indicated in our October response letter, the reason for the discrepancy is that we had assumed the 26 acre North Central Pit was already reclaimed as a pond and so it was left out of the calculation. However, because you have requested topographic information for this pond to confirm that it was reclaimed with the required slopes and have agreed to delay requiring this information until prior to release of the site, we have added some money to the Exhibit L spreadsheet to account for some minor adjustments to the slopes in this pond. H. Please address item 24 from the first adequacy review: 24. What are the current conditions of the pit slopes around the west pit, south central pit and the east pit in terms of horizontal to vertical slope ratio? The current conditions of the pit slopes above water surfaces are shown on the Exhibit C Pre - Mining Plan. The slopes in the West pit range from 1.5:1 to 10:1(the slopes in the areas that are currently being mined have generally have 3:1 slopes); the slopes in the South Central Pit range from 0.5:1 to 5:1 with the area that has already been backfilled having a less than 1% slope to the northeast; and the slopes in the East Pit that are above the waterline range from 1.5:1 to 4:1 with the area that has been backfilled being relatively flat with a 1% slope to the southeast. 1. The response to item 25 of the Division's adequacy review indicated topsoil would be brought in from offsite. Please provide an estimate of the amount of topsoil that