2013-04-11_REVISION - C1996083 - Laserfiche WebLink

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Susan Burgmaier, DRMS April 11, 2013 TR77; Review Memo Texture The texture of the coverfill material is different than the topsoil based on the soil samples results form 2003. The texture of the topsoil sampled in 2003 consists of primarily of silty loam material with less sand and clay content. The coverfill material consists of a higher percentage of sandy material and less silt and is dominantly classified as a clay loam according to the lab results. The Natural Resource Conservation Service (MRCS) soil unit for the gob pile 42 area is unit 74 the Torriorthents- haplargids unit. This map unit can be observed on Map 4a in the permit. A description of this soil unit is included on page 2.04 -97 to 2.04 -99 of the permit. This soils unit is generally comprised of sandy loam to clay loam material in the surface layers. The subsurface layer consist of sandy loam, loam and clay loam material. Given this, the texture observed in the coverfill material is comparable to the textures of the soils described in this soils unit. Percent Coarse FraLyments The initial 2003 data indicates the topsoil material sampled in this area had an average coarse rock fragments content of about 21.7 %. The samples taken from the proposed coverfill material was found to have about a 36% coarse fragments content. A higher coarse fragment content may indicate a decreased water holding capacity for the coverfill material. However, according to the soil unit description provided by the NRCS for this area, soils in this unit have a coarse fragments content that commonly exceeds 35 %. Areal Extent of the Different Soils and Materials As discussed above in the thickness of horizons and total depth section of this memo, the native soils in this area are highly variable and the topsoil salvage variance approved limits the amount of topsoil that is available to be replaced on the gob pile #2 expansion area. There is nothing to compare for this soil parameter, there is simply a deficiency of soil material and BRL would like to address this deficiency using the excess coverfill material at the site. Determinations of yH The pH observed in the topsoil in 2003 ranged from 7.2 to 8.1 with an average of 7.5 according to the 2003 soil report. The pH of the coverfill material ranges from 8.2 to 8.4 with an average of 8.3 and thus are moderately alkaline in nature. The vegetation in the affected area associated with the coal mine waste piles was classified as juniper woodlands and mixed shrub communities. The post mine land use of the area is rangeland and wildlife habitat to be reclaimed with grasses, forbs and shrubs with an emphasis on herbaceous vegetation. Section 2.05.4(2)(e) of the permit discusses the revegetation plan for the site. Seed Mix. No. 3 is to be used to reclaim juniper woodland and mountain shrub communities. A review of the species intended to be planted at the site indicate they are capable of tolerating moderate to higher amount of soil alkalinity. Only one forb species, Alfalfa (Medicago sativa) within the seed mix is less tolerant of alkaline soils, but this is only one of many species to be planted in this area. Also, BRL's revegetation plan allows for flexibility in the seed mixes and several optional species are approved to be used in a seed mix for reclamation depending on site conditions. Given this, BRL could replace Alfalfa with a species more tolerant to moderately alkaline conditions. Overall, the plant species to be established on the gob pile #2/4 area will be able to tolerate the increased alkalinity of the soils. Net Acidity or Alkalinity As discussed above, the coverfill material is on average more alkaline than the topsoil. However, the plant species to be used for reclamation of this area are species that are tolerant of moderately alkaline soils with the exception of Alfalfa. Overall, it does not appear the moderately alkaline nature of the coverfill material will significantly impact the development of the desired vegetation especially if BRL only uses this material as a supplement and still replace all of the available topsoil even if it is a lesser amount than originally projected. 0a