Elsinore Valley Municipal Water District Elsinore Valley Subbasin Groundwater Sustainability Plan Chapter 3 HYDROGEOLOGIC CONCEPTUAL MODEL DRAFT | January 2021 CHAPTER 3 | ELSINORE VALLEY SUBBASIN GROUNDWATER SUSTAINABILITY PLAN | EVMWD Contents Chapter 3 Hydrogeologic Conceptual Model 3-1 3.1 Physical Setting and Topography 3-1 3.2 Surface Water Features 3-2 3.3 Soils 3-2 3.4 Geologic Setting 3-3 3.4.1 Pull-Apart Basin 3-3 3.4.2 Geologic Units 3-4 3.5 Faults 3-6 3.6 Aquifers 3-6 3.6.1 Description of Principal Aquifer Units 3-6 3.6.2 Physical Properties of Aquifers 3-7 3.6.3 Description of Lateral Boundaries 3-7 3.7 Structures Affecting Groundwater 3-8 3.8 Definable Basin Bottom 3-8 3.9 Cross Sections 3-8 3.9.1 Available Data and Information 3-9 3.9.2 Cross Section Construction 3-10 3.9.3 Hydrostratigraphic Evaluation 3-10 3.10 Recharge and Discharge Areas 3-11 3.11 Primary Groundwater Uses 3-11 3.11.1 Elsinore Hydrologic Area 3-11 3.11.2 Lee Lake Hydrologic Area 3-12 3.11.3 Warm Springs Hydrologic Area 3-12 3.12 Data Gaps in the Hydrogeologic Conceptual Model 3-12 3.13 References 3-12 DRAFT | JANUARY 2021 | i pw://Carollo/Documents/Client/CA/EVMWD/11585A00/Deliverables/RPT01/Ch03 EVMWD | ELSINORE VALLEY SUBBASIN GROUNDWATER SUSTAINABILITY PLAN | CHAPTER 3 Figures Figure 3-1 Subbasin Topography 3-17 Figure 3-2 Surface Water Bodies Tributary to Elsinore Valley Subbasin 3-19 Figure 3-3 Tributary Watershed 3-21 Figure 3-4 Subbasin Soil Hydrologic Properties 3-23 Figure 3-5 Surficial Geology 3-25 Figure 3-6 Cross Section Orientations 3-27 Figure 3-7 Cross Section A to A’ 3-29 Figure 3-8 Cross Section B to B’ 3-31 Figure 3-9 Cross Section C to C’ 3-33 Figure 3-10 Cross Sections D to D’ and E to E’ 3-35 Figure 3-11 Cross Section F to F’ 3-37 Figure 3-12 Groundwater Recharge and Discharge 3-39 ii | JANUARY 2021 | DRAFT CHAPTER 3 | ELSINORE VALLEY SUBBASIN GROUNDWATER SUSTAINABILITY PLAN | EVMWD Acronyms and Abbreviations DWR California Department of Water Resources EVMWD Elsinore Valley Municipal Water District GIS geographic information system gpd/ft gallons per day per foot Metropolitan Metropolitan Water District of Southern California NED National Elevation Dataset NRCS U.S. Department of Agriculture, Natural Resources Conservation Service SSURGO Soil Survey Geographic Database Subbasin Elsinore Valley Subbasin of the Elsinore Groundwater Basin USDA United States Department of Agriculture USGS United States Geological Survey DRAFT | JANUARY 2021 | i pw://Carollo/Documents/Client/CA/EVMWD/11585A00/Deliverables/RPT01/Ch03 CHAPTER 3 | ELSINORE VALLEY SUBBASIN GROUNDWATER SUSTAINABILITY PLAN | EVMWD Chapter 3 HYDROGEOLOGIC CONCEPTUAL MODEL This chapter describes the hydrogeologic conceptual model of the Elsinore Valley Subbasin (Subbasin), including the boundaries, geologic formations and structures, principal aquifer units, and recharge and discharge areas. The Hydrogeologic Conceptual Model presented in this chapter is a summary of relevant and important aspects of the Subbasin hydrogeology that influence groundwater sustainability. While the Chapter 1 Introduction and Chapter 2 Plan Area establish the institutional framework for sustainable management, this chapter, along with Chapter 4 Groundwater Conditions and Chapter 5 Water Budget, sets the physical framework. Later sections including the water budget and sustainability criteria will refer to and rely on the technical material contained here. 3.1 Physical Setting and Topography The Elsinore Valley Subbasin (8-4.1) underlies a portion of the Elsinore Groundwater Basin (8.4) in southwestern Riverside County and covers approximately 200 square miles. Elsinore Valley Subbasin is adjacent to two other groundwater basins/subbasins: the Bedford-Coldwater Subbasin of the Elsinore Groundwater Basin (8-4.2) to the north and the Temecula Valley Basin (9-5) to the south. Ground surface elevation in the Subbasin range from just over 1,000 feet above sea level in the northwest at the boundary with the Bedford-Coldwater Subbasin to over 2,000 feet above sea level at the western boundary in the Santa Ana Mountains. Figure 3-1 illustrates the topography of the Subbasin and surrounding uplands. Note that this map and all others in this section have been reoriented (relative to maps in Chapter 2) in order to maximize the basin area and to better show detailed information; as shown, the north arrow does not point to the top of the page. The Subbasin consists of three general hydrologic areas (Figure 3-1): the Elsinore Hydrologic Area (Elsinore Area) that is the main, southern portion of the Subbasin, the Lee Lake Hydrologic Area (Lee Lake Area) located at the northern downstream portion of the Subbasin, and the Warm Springs Hydrologic Area (Warm Springs Area) in the northeastern Subbasin. The Elsinore Area is the largest area of the Subbasin and provides most of the groundwater production. It is located in the southern and central Subbasin and is bounded on the west and north by the highlands of the Santa Ana Mountains, to the south by the Temecula Valley Basin, and to the east by bedrock outcrops in the pediment of the Temescal Mountains. The Lee Lake Area is the northernmost part of the Subbasin bounded by the Santa Ana Mountains to the west and the Temescal Mountains to the east. The Lee Lake Area has limited hydraulic connection with the Elsinore Area to the south through narrow alluvial valleys between bedrock highs and a similarly limited connection to the Bedford-Coldwater Subbasin to the north through the narrow and shallow alluvial channel of the Temescal Wash (Todd and AKM 2008).The Warm Springs Area is located in the northeast of the Subbasin and is bordered on the north and east by the Temescal Mountains. The Warm Springs Area is connected to both the Elsinore and Lee Lake Areas through the Temescal Wash. DRAFT | JANUARY 2021 | 3-1 EVMWD | ELSINORE VALLEY SUBBASIN GROUNDWATER SUSTAINABILITY PLAN | CHAPTER 3 3.2 Surface Water Features Figure 3-2 shows surface water features including rivers, streams, lakes, and ponds within and surrounding the Subbasin. The sub-watersheds (USGS 2020a) that drain into and through the Subbasin are shown on Figure 3-3. The Subbasin covers portions of the Dawson Canyon-Temescal Wash, Arroyo Del Toro-Temescal Wash, and Lake Elsinore subwatersheds and the low-lying part of the Railroad Canyon Reservoir-San Jacinto River subwatershed. Most of the Subbasin is within the Lake Elsinore watershed. Lake Elsinore is a natural lake with an area of approximately 3,300 acres. In the past the lake has varied in size from 6,000 acres in very wet years to a dry playa in drought years. In 1995, a levee was constructed to maintain the lake at a fixed size and to moderate historical variations in lake surface area. (MWH 2005). Railroad Canyon Reservoir, located upstream of the Subbasin in the San Jacinto River Watershed, is a reservoir that is fed by the San Jacinto River watershed and, occasionally, untreated imported water from connections to the Metropolitan Water District of Southern California (Metropolitan) Colorado River Aqueduct and the State Water Project. Canyon Lake spills into Railroad Canyon which in turn flows to Lake Elsinore (MWH 2002). 3.3 Soils Soil characteristics are important factors in natural and managed groundwater infiltration (recharge) and are therefore an important component of a hydrogeologic system. Soil hydrologic group data from the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey Geographic Database (SSURGO) (NRCS2020) are shown on Figure. 3-4 The soil hydrologic group is an assessment of soil infiltration rates determined by the water transmitting properties of the soil, which include hydraulic conductivity and percentage of clays in the soil, relative to sands and gravels. The groups are defined as: • Group A – High Infiltration Rate: water is transmitted freely through the soil; soils typically less than 10 percent clay and more than 90 percent sand or gravel. • Group B – Moderate Infiltration Rate: water transmission through the soil is unimpeded; soils typically have between 10 and 20 percent clay and 50 to 90 percent sand. • Group C – Slow Infiltration Rate: water transmission through the soil is somewhat restricted; soils typically have between 20 and 40 percent clay and less than 50 percent sand. • Group D – Very Slow Infiltration Rate: water movement through the soil is restricted or very restricted; soils typically have greater than 40 percent clay, less than 50 percent sand. The hydrologic group of the soil generally correlates with the potential for infiltration of water to the subsurface. However, a correlation does not necessarily exist between the soils at the ground surface and the underlying geology or hydrogeology. The hydrologic group information relates to the material in the top six feet of the subsurface. Soils with high infiltration rates can be underlain by low permeability materials (silts and clays), or vice versa. As shown on Figure 3-4 the hydrologic characteristics of soils in the Subbasin range from Group A to Group D. The Elsinore and Lee Lake hydrologic areas generally have more high infiltration rate soils, while those in the Warm Springs area generally have lower infiltration rates. 3-2 | JANUARY 2021 | DRAFT CHAPTER 3 | ELSINORE VALLEY SUBBASIN GROUNDWATER SUSTAINABILITY PLAN | EVMWD 3.4 Geologic Setting The Subbasin is located within one of the structural blocks of the Peninsular Ranges of Southern California. The groundwater basins in this region occupy valleys in linear, low-lying areas between the Santa Ana and Elsinore Mountains on the west and the Temescal Mountains, Perris Plain, and Gavilan Plateau on the east (Norris and Webb 1990).