Present Land Use
? APN 137-250-023: 23.62 acres - Mineral Processing, General Industry M-2
? APN 137-250-037: 45.32 acres – Field Crops- Irrigated, Agriculture I, AG-I-40
? APN 137-250-046: 68.98 acres – Open Land Use, Agriculture, AG-I-20
? APN 137-260-025: 0.15 acres – Office Buildings, Incorporated City
The project is for a revision to Reclamation Plan 88-RP-002 AM01 to: 1) conduct deep mining in Area A to a depth of 300 feet amsl; 2) backfill the deep mining area to 340 feet amsl; 3) install a drainage culvert from the mine pit to an existing sediment basin; 4) make improvements to an existing access road; 5) revise the end use of Area A from open space/habitat to agriculture; and 6) address current SMARA standards. Area A is approximately 41 acres and is located north of the river channel (Area C) and west of the processing plant (Area B), and contains an existing mine pit and sediment basin. The request for deep mining is a result of the site’s nearly exhausted shallow-depth aggregate reserves, and is limited to previously disturbed mining areas in Area A, approximately 30 to 40 feet below existing mining operations. The surrounding ground elevation outside the pit is approximately 360 feet amsl, and the existing ground elevation within the pit is approximately 330 feet amsl, creating a depression approximately 30 feet deep. Area A is buffered from the rest of the site
by manmade levees and berm roads previously developed as mitigation for expanded mining operations under Reclamation Plan No.88-RP-002 AM01. There is an approximate 130-foot buffer from the mining area to the northern property boundary, an approximate 130-foot buffer from the mining area to Area C, and an approximate 60-foot buffer from the mining area to the sediment basin.
Deep mining would generally be conducted in one phase, and is anticipated to produce 10,000 to 100,000 tons of material per year, and up to 518,149 cubic yards of material over the life of the mine. Based on this production rate, market demand, and estimated reserves, the life of the mine would be extended 20 years to 2038. Deep mining would involve excavations ranging from 30 to 40 feet deep, to a maximum depth of 300 feet amsl, which is approximately 29 feet below estimated groundwater levels. Approximately 15 percent of this total production amount is estimated to be waste material (overburden, silts, etc.). Production would be reduced from
the currently approved total production amount of up to 1,600,000 cubic yards of material. The mining pit would be excavated with side slopes of 3:1 (horizontal to vertical, h:v) and would have a maximum depth of 60 feet, from top of slope to toe of slope. The planned slopes would be predominantly cut slopes; however the upper portions of the pit slopes would involve placement of compacted fill. Fill slopes are proposed at 3:1 and 5:1 (h:v) slope ratios. No slope benches are planned
due to the relatively shallow depth of excavation. Based on exploratory borings completed as part of a geologic and geotechnical engineering investigation conducted for the project, mining operations are expected to encounter groundwater at an elevation of 329 feet amsl. Equipment used for deep mining would include both a Caterpillar D-8 dozer and a Caterpillar 623H or K scraper, or a Caterpillar
349L excavator and a Caterpillar 745C haul truck. Each equipment unit would be equipped with an engine that meets U.S. Environmental Protection Agency (EPA) Tier 4 emissions standards.
Reclamation would begin when active mining is completed, and is expected to take 10 years (2038 – 2048). Slopes in the backfilled pit would be finished at a 3:1 slope at the southern end of the pit, and a 5:1 slope at the northern end of the pit. The spoils from excavation and imported fill would be used to achieve a uniform gently sloping grade to the south. Final grading would result in a slight depression approximately 20 feet below existing grade and the established man-made levees. To date, approximately 471,484 cubic yards of fill material to be used for reclamation has been stockpiled in the northwest corner of Area A. Approximately 191,777 cubic yards of clean fill would need to be imported over the next 20 years of mining activities for
the site to begin reclamation. Stockpiled fill material plus imported fill material would equal 663,261 cubic yards, which is the amount of total backfill needed to elevate the mining pit to final grade. Some reclamation activities, such as vegetation salvage and
restoration test plot planting/monitoring would be conducted concurrently during deep mining if feasible.
Mining export would result in a maximum of 200 truck trips/day. Import to the surge pile would result in a maximum of 58 truck trips/day. Maximum daily import loads of fill material for reclamation would be limited to 100 truck trips/day. Therefore, the proposed project would result in a maximum of 358 truck trips/day. On-road equipment is assumed to meet fleet averages for 2019.
The proposed end use of Area A would be cattle and equine grazing ranch pasture or other agriculture use. Revegetation would occur in disturbed areas throughout Area A, including disturbed acreage within the mining excavation area, access roads, and desilting basin. Revegetation would consist of planting a set mixture of both grasses and legumes for forage production and erosion control NOTE: Clearinghouse will assign identification numbers for all new projects. If a SCH number already exists for a project (e.g. from a Notice of Preparation or previous draft document) please fill it in.
(three grasses and two legume species). Test plots would be established to determine if soil conditions are appropriate for the proposed seed mixes, and areas to be planted would be hydroseeded or hand-broadcast at 30-50 pounds per acre. The existing sediment basin would not be revegetated. The basin will gradually dry upon cessation of mining; however, the basin is below the river grade, and near the top of groundwater, and therefore would likely continue to receive storm runoff from the site. It isanticipated that the bottom of the basin would retain some open water and remain as a freshwater marsh post-reclamation.
The proposed end use for Areas B and C would remain the same as previously approved, consisting of commercial/industrial uses, and river channel/open space, respectively. No revegetation is proposed for these areas. Revegetation of the river channel would be left to natural processes. Required levee improvements and willow tree plantings, as required per Reclamation Plan 88-RP-002 AM01, were previously implemented.
Site improvements would be conducted at the initiation of deep mining activities, consisting of improvements to an existing east-west trending access road, located to the south of the excavation area, as well as the installation of a 24-inch culvert from the mining pit to the existing sediment basin in order to convey flows southward, and prevent standing water in the filled pit area. The inlet of the culvert would be at 339.5 feet amsl, which would be above groundwater levels and half a foot lower than the final pit elevation. The culvert would remain in place permanently through mining activities, as well as post-reclamation.
Operations and Personnel
No change in hours of operation or personnel are proposed. Project personnel consists of 15 full-time employees, and 1 part-time employee. Hours of Operation would be from 7:00 am – 6:00 pm, five (5) days per week, Monday through Friday, and to no more than eight (8) Saturdays per calendar year from 8:00 am - 4:00 pm.Other details of the proposed mining and reclamation plan are discussed and shown in the Revised Reclamation Plan prepared by the applicant.