SANTA ANA RIVER MAINSTEM PROJECT: ALCOA EMBANKMENT - PHASE II County of Riverside, California DRAFT SUPPLEMENTAL ENVIRONMENTAL ASSESSMENT AND ENVIRONMENTAL IMPACT REPORT ADDENDUM Los Angeles District December 2020 This page is intentionally left blank. Table of Contents 1 INTRODUCTION .......................................................................................................................... 1 1.1 Introduction .......................................................................................................................... 1 1.2 Project Location ..................................................................................................................... 3 1.3 Project Authority ................................................................................................................... 5 1.4 Previously prepared documents ............................................................................................. 5 2 PROPOSED ACTION AND ALTERNATIVES ......................................................................... 9 2.1 Objectives, Purpose and Need ................................................................................................ 9 2.2 Comparison of Previously Approved Design and Proposed Action ......................................... 10 2.3 Alternatives Evaluated and Eliminated ................................................................................. 11 2.4 Project Alternatives (Alternatives Considered for Environmental Analysis) ............................ 12 2.4.1 Previously Approved Design Alternative .................................................................................................. 12 2.4.2 Proposed Action ....................................................................................................................................... 12 2.4.3 Staging Areas, Haul Routes, and Construction Activities ......................................................................... 17 2.4.4 Utilities ..................................................................................................................................................... 18 2.4.5 Future Operation, Maintenance, Repair, Replacement and Rehabilitation ............................................. 21 3 AFFECTED ENVIRONMENT .................................................................................................. 23 3.1 Air Quality ........................................................................................................................... 23 3.2 Biological Resources ............................................................................................................ 23 3.2.1 General Setting ......................................................................................................................................... 24 3.2.2 Vegetation ................................................................................................................................................ 24 3.2.3 Special-Status Plant Species ..................................................................................................................... 25 3.2.4 Jurisdictional Habitats .............................................................................................................................. 28 3.2.5 Wildlife ..................................................................................................................................................... 28 3.3 Water Resources and Hydrology ........................................................................................... 36 3.3.1 General Setting ......................................................................................................................................... 36 3.3.2 Temescal Wash and Santa Ana River........................................................................................................ 36 3.3.3 Groundwater ............................................................................................................................................ 38 3.4 Earth Resources ................................................................................................................... 38 3.4.1 Geology and Soils ..................................................................................................................................... 39 3.4.2 Seismicity and Faulting ............................................................................................................................. 39 3.5 Land Use .............................................................................................................................. 40 3.6 Aesthetics ............................................................................................................................ 41 3.7 Recreation ........................................................................................................................... 41 3.8 Noise ................................................................................................................................... 42 3.8.1 Noise Environment in the Proposed Project Area .................................................................................... 43 3.8.2 Sensitive Receptors in the Proposed Project Area ................................................................................... 43 3.9 Socioeconomics ................................................................................................................... 43 3.10 Transportation ..................................................................................................................... 44 3.11 Safety and hazards ............................................................................................................... 46 i 3.12 Cultural Resources ............................................................................................................... 46 3.13 Public Services and Utilities .................................................................................................. 47 3.13.1 Public Services ...................................................................................................................................... 49 3.13.2 Utilities and Service Systems ................................................................................................................ 49 3.14 CERCLA Hazardous Substances and Other Pollutants ............................................................. 50 4 ENVIRONMENTAL CONSEQUNCES .................................................................................... 52 4.1 Air Quality ........................................................................................................................... 52 4.1.1 Proposed Action ....................................................................................................................................... 52 4.1.2 Previously Approved Design ..................................................................................................................... 57 4.2 Biological Resources ............................................................................................................ 57 4.2.1 Proposed Action ....................................................................................................................................... 58 4.2.2 Previously Approved Design Alternative .................................................................................................. 70 4.3 Water Resources and Hydrology ........................................................................................... 70 4.3.1 Proposed Action ....................................................................................................................................... 71 4.3.2 Previously Approved Design Alternative ................................................................................................. 73 4.4 Earth Resources ................................................................................................................... 73 4.4.1 Proposed Action ....................................................................................................................................... 73 4.4.2 Previously Approved Design Alternative ................................................................................................... 75 4.5 Land Use .............................................................................................................................. 75 4.5.1 Proposed Action ....................................................................................................................................... 75 4.5.2 Previously Approved Design Alternative .................................................................................................. 76 4.6 Aesthetics ............................................................................................................................ 76 4.6.1 Proposed Action ....................................................................................................................................... 77 4.6.2 Previously Approved Design Alternative ................................................................................................... 78 4.7 Recreation ........................................................................................................................... 78 4.7.1 Proposed Action ......................................................................................................................................