Appendix G Soils Characterization Report

Transcription

1 Appendix G Soils Characterization Report Draft Environmental Impact Report Beacon Photovoltaic Project July 2012

2 AECOM (805) tel 1220 Avenida Acaso (805) fax Camarillo, CA Memorandum To Heather Barone, NextEra Energy Resources Page 1 cc Subject Brandon Stankiewicz, NextEra Energy Resources; Sara Head, AECOM Beacon Photovoltaic Soils Characterization From Carmen Caceres-Schnell, P.G. #8405 Date August 16, 2011 Beacon Solar, LLC proposes to construct the Beacon photovoltaic project (Project), a photovoltaic (PV) solar facility in the Mojave Desert region of California (Figure 1). The proposed project would be a 250 megawatt net alternating current solar power generating installation. The Project would be developed over a total of about 2,320 acres (not including the transmission line right-of-way). This report presents the soil data for existing soils at the Project. Beacon Solar, LLC currently owns all Project site parcels, as well as the parcels located along the proposed transmission line route. As shown in Figure 1, the Project site is located in the Mojave Desert region of unincorporated Kern County, approximately 4 miles from the northern boundary of California City and 15 miles from the town of Mojave (in Township 31 South, Range 37 East, Mount Diablo Base and Meridian). The Project site and the surrounding areas are primarily vacant disturbed lands, formerly used for agricultural activities. State Route 14 (SR-14) runs near the western border of the Project site, and an existing Union Pacific rail line and Southern California Edison electric distribution line run through the Project site. An existing Los Angeles Department of Water and Power (LADWP) electrical transmission line runs roughly in parallel to SR-14 about 1 mile further to the west, and the existing LADWP Barren Ridge substation is located about 1 mile from the southwest corner of the Project site. The unincorporated community of Cantil/Rancho Seco is northeast of the site. The Honda Proving Ground, an automotive test track, is located about 1 mile northeast of the Project site. Regional Setting The Project is located in the northwestern Mojave Desert, in Kern County, California. The Mojave Desert is part of the greater Mojave Desert Geomorphic Province. This province lies between the northeast-trending Garlock fault on the north and the northwest-trending San Andreas Fault on the south. One strand (East Strand) of the Garlock fault is adjacent to the Project site and the other (West Strand - also referred to as the Cantil or Cantil Valley fault) is present within the Project site. The location of these faults is shown on Figure 2. The Project is located in the alluvial-filled basin of the Fremont Valley. This valley formed as a deep structural depression or a pull-apart basin formed between the two strands of the Garlock fault. The basin is bound by the southern Sierra Nevada Mountains and the El Paso Mountains on the northwest, and by the Rand Mountains on the east. Locally, the Project site is located southeast of the Tehachapi Mountain foothills and is underlain by Quaternary-age alluvium. Regionally, the ground surface slopes gently downward in a northwest direction at a gradient of less than two percent. Topography at the Project site is relatively flat with gentle slopes of one to three percent to

3 AECOM 2 the northeast, towards Koehn Lake. Ground surface elevations at the site range from 2,030 feet above mean sea level (msl) in the northeast to 2,260 feet above msl in the southwest (USGS 7.5 minute quadrangles of the project area). Characteristic landforms in the Mojave Desert include alluvial fans, plains, low pediments, and scattered buttes. The Project is underlain by recent alluvium, Holocene lacustrine and playa deposits near the surface, and older alluvium at depth. Alluvial deposits are comprised of sand, silt, and gravel and the lucustrine and playa deposits are comprised of finer-grained sands, silts and clays. 1 In the past, ground cracks have been observed in the Fremont Valley area following heavy rains. Several erosional features, ground cracks, and aligned depressions were mapped during a geotechnical site reconnaissance in Some of the most extensive ground cracks were observed in the area of Rancho Seco, which is located to the north of the northwest corner of the plant site. 1 In addition, formation of ground cracks (erosional fissuring) were observed in September 2007 during a pumping test conducted for an onsite well. The majority of the natural drainage in the vicinity of the Project site is to the northeast. The plant site is bisected by the Pine Tree Creek dry wash which is a topographically well-defined drainage channel that trends in the north-northeast direction. This channel is the larger of the two drainages considered to be State jurisdictional waters. The channel width ranges from approximately 25 to 70 feet and it has near vertical banks approximately two to four feet high. 1 The western, southern, and northeast portions of the plant site are crossed by several other drainage channels. An eroded 15- to 25-foot high escarpment trends northeast through the middle of the Project site and coincides with the mapped trace of the Cantil Valley fault. 1 The Project is located in an undeveloped area and no agricultural activities are ongoing at or in the immediate vicinity of the site. A review of the Kern County Williamson Act Lands 2005 Map indicates that the site is non-enrolled Land meaning that the County land is not enrolled with the Williamson Act Program. No lands designated as containing Prime, Statewide Important farmlands are present within the Project site. Soils in the Mojave Desert are shallow, deep, or very deep and are well drained to excessively drained. 2 The surface layer soils range from sand to clay loam. Sandy surface layers are highly susceptible to blowing, have low available water capacity and have a hazard of erosion due to slopes and insufficient plant cover. 2 These conditions can be exacerbated due to the climate in the area. Climate in the area of the Project site is highly variable because of the mountain ranges and desert areas. The Mojave Desert is generally sunny, dry, and warm. Annual precipitation in the Mojave Desert ranges from 3 to 6 inches. Precipitation in Cantil (located northeast of the Project site) averages just over 3 inches annually. 2 The majority of the rainfall occurs during December, January, and February. Winds in the Mojave Desert are prevalent from the west-southwest. They are generally light and range from 4 to 12 miles per hour. 2 1 Kleinfelder, Preliminary Geotechnical/Geologic Constraints Evaluation, Project Beacon, Kern County, Califorina, September 21 (contained in Beacon Solar Energy Project, Application for Certification, Appendix B.1, March 2008). 2 United State Department of Agriculture, Soil Survey of Kern County, California, Southeastern Part.

4 AECOM 3 Map Unit Soils at the Project Site The ground surface in the region of the Project slopes gently downward to the northeast direction at a gradient of less than 2 percent. Drainage at the Project occurs as sheet flow across the property. Much of the surface water infiltrates into the sandy alluvium. The majority of the Project site is underlain by Cajon loamy sand and Rosamond clay loam with Arizo gravelly loamy sand and Cajon gravelly loamy sand occurring on small portions of the site (Figure 2). 3 The transmission line occurs on Arizo gravelly loamy sand. Soil characteristics including drainage, permeability, and erosion hazard of individual soil mapping units are included in Table 1. Land capability classification is an indicator of the soils primary limitations for revegetation. All soil types on the Project site are Capability Subclass VIIe, which means the soils have very severe limitations that make it unsuitable for cultivation. The Project area has been heavily disturbed by past agricultural activities, and parts of the area are being recolonized with desert saltbush vegetation. Table 1 Soil Mapping Unit Descriptions and Characteristics Soil Type 104 Arizo Gravelly Loamy Sand 114 Cajon Loamy Sand 116 Cajon Gravelly Loamy Sand 172 Rosamond Clay Loam Saline- Alkali Percent Slope Drainage Permeability Runoff Water Erosion Hazard 2 to 9 Excessively drained 0 to 5 Very deep, somewhat excessively drained 0 to 9 Very deep, somewhat excessively drained 0 to 2 Deep, well drained Very Rapid Rapid Rapid Moderate to moderately slow Negligible to medium Negligible to low Negligible to low Wind Erosion Hazard Percent of Soil Type on Project Site Moderate High Slight to moderate Approx. Acres High ,385 High High Moderate Moderate Moderate Note: The acreage totals in this table include the acreage for the transmission line parcels. 3 Natural Resources Conservation Service (NRCS), United States Department of Agriculture, Web Soil Survey, accessed at: July 28.

5 AECOM 4 Erosion Potential The runoff designations for the soils potentially affected during site grading are low to negligible for the Cajon loamy sand and moderate for the Rosamond clay loam. In contrast the Arizo gravelly loamy sand has very rapid permeability whereas the Rosamond clay loam has a moderate to moderately slow permeability. The majority of site features are located on soil units that have rapid and moderate to moderately slow permeability and negligible to low runoff potential. The exception is the Rosamond clay loam-saline alkali soil unit which has moderate runoff potential. In addition, soils at the Project site have a moderate to high hazard for wind erosion. Collapsible Soil Conditions Alluvial soils in arid and semi-arid environments have the tendency to possess characteristics that make them prone to collapse with increase in moisture content and without increase in external loads. The Project is located in a geologic environment where the potential exists for collapsible soils. Collapsible soil conditions were observed in September 2007 during a pump test 4 for an onsite well. Expansive Soil Expansive soil consists of fine-grained clay which occurs naturally. It is generally found in areas that were historically a flood plain or lake area, but can occur in hillside areas also. Expansive soil is subject to swelling and shrinkage, varying in proportion to the amount of moisture present in the soil. As water is initially introduced into the soil (by rainfall or watering) expansion takes place. If dried out, the soil will contract, often leaving small fissures or cracks. Excessive drying and wetting of the soil can progressively deteriorate structures over the years because it can lead to differential settlement within buildings and other improvements. Summary Given the climatic conditions, potential for precipitation, and stormwater runoff, which historically does not reach the Project site from surrounding mountains, the implementation of best management practices (BMPs) during construction will limit the potential for soil loss from water and wind erosion. Based on preliminary geotechnical studies 1 and pump test observations done for the prior solar thermal project, the onsite soil alluvial deposits have a moderate to high potential for collapse. The expansion potential of the onsite soils within the northern portion of the Project site is high. Soils present in other areas of the Project also may be expansive. However, the potential for damage due to collapsible or expansive soils is considered to be low provided that the appropriate foundation design features and/or sub-grade soil improvements are implemented. 4 AECOM, Beacon Solar Energy Project, Application for Certification, Appendix J.3, March.

6 Munsey Neuralia Phillips Tehachapi California City Mojave Kramer Junction Rosamond Source: Beacon Solar 2010, ESRI 2011 I Miles Beacon PV Project Scale: 1:633,600; 1 inch = 10 miles Figure 1 Regional Location and Vicinity Map

7 Garlock Fault East Cantil Valley Fault (Garlock Fault West) MAP LOCATION OR ID NV UT LEGEND:!!! TRANSMISSION LINE FAULT LINES Figure 2 Fault Zones Beacon PV Project CA ALQUIST-PRIOLO FAULT ZONE ± 0 1,250 2,500 Feet Date 8-11 AZ PLANT SITE 1 " = 2,500 ' Project No

8 !!!!!! 3250ne - Jawbone Association Rock Outcrop Arizo Gravelly Loamy Sand Rosamond Clay Loam, Saline-Alkali Rosamond Clay Loam!!!!!! Cajon Loamy Sand Cajon Gravelly Loamy Sand Rosamond Clay Loam!!!!!!!!!! Arizo Gravelly Loamy Sand MAP LOCATION OR ID NV UT LEGEND:!!! TRANSMISSION LINE PLANT SITE Figure 3 Soils Map Beacon PV Project CA AZ SOIL BOUNDARIES ± 0 1,250 2,500 Feet Date 8-11 Project No. 1 " = 2,500 '