Daniel B. Stephens & Associates, Inc. Table of Contents Section Page Executive Summary .................................................................................................................. 11 1. Introduction .........................................................................................................................1 1 1.1 Site Background .......................................................................................................... 11 1.1.1 Overview and Problem Statement ..................................................................... 11 1.1.2 Regulatory Background ..................................................................................... 44 1.1.3 Recent Community Involvement ....................................................................... 88 1.2 Project Area Definition ................................................................................................. 99 1.3 Purpose and Overview ............................................................................................. 1111 1.4 Document Organization ........................................................................................... 1212 2. Summary of Previous Work ............................................................................................. 1414 2.1 Historical Documents, 1957-1997 ............................................................................ 1414 2.2 1997 Ehlig and Yen Feasibility Study ....................................................................... 1717 2.3 2000 Leighton Feasibility Study ............................................................................... 2020 3. Physical Characteristics of the PBLC Vicinity .................................................................. 2222 3.1 Topography ............................................................................................................. 2222 3.2 Watershed Hydrology .............................................................................................. 2424 3.3 Soils ......................................................................................................................... 2626 3.4 Geology ................................................................................................................... 2929 3.5 Landslide Characterization ....................................................................................... 3131 3.6 Hydrogeology........................................................................................................... 3434 3.6.1 Groundwater Recharge ................................................................................. 3535 3.6.2 Groundwater Occurrence .................................................................................. 38 3.6.3 Water Wells .................................................................................................. 4040 3.7 Geotechnical Modeling ............................................................................................ 4141 4. Feasibility Study .............................................................................................................. 4545 4.1 ARARs ..................................................................................................................... 4545 4.1.1 Definitions ..................................................................................................... 4545 4.1.2 Identified ARARs ........................................................................................... 4646 4.2 Remedial Action Objective ....................................................................................... 4747 4.3 General Response Actions ...................................................................................... 4848 4.3.1 Stormwater Control ........................................................................................... 49 4.3.1 Subsurface Dewatering ..................................................................................... 49 4.3.2 Stormwater Control ........................................................................................... 49 4.3.1 Engineered3 ................................................ Enineered Slope Stabilization Measures 51 4.3.24 Eliminate Septic System Discharge ................................................................... 52 4.3.5 Coastal Erosion Control .................................................................................... 53 4.4 Identification and Screening of Technology Alternatives .......................................... 5353 4.4.1 Stormwater Control Option 1 – Repair Existing Corrugated Piping System ....... 53 4.4.1.1 Description ......................................................................................53 53 4.4.1.2 Screening Summary ............................................................................54 i Daniel B. Stephens & Associates, Inc. Table of Contents (Continued) Section Page 4.4.2 Stormwater Control Option 2 – Install Concrete Channels ................................ 54 4.4.2.1 Description ..........................................................................................54 4.4.2.2 Screening Summary ............................................................................54 4.4.3 Stormwater Control Option 3 – Install Liner and Channel System ..................... 55 4.4.3.1 Description ..........................................................................................55 4.4.3.2 Screening Summary ............................................................................55 4.4.4 Stormwater Control Option 4 – Seal Surface Fractures ..................................... 56 4.4.4.1 Description ..........................................................................................56 4.4.4.2 Screening Summary ............................................................................56 4.4.5 Subsurface Dewatering Option 1 – Groundwater Extraction Pits ................... 5656 4.4.5.1 Description ......................................................................................56 56 4.4.5.2 Screening Summary ............................................................................57 4.4.6 Subsurface Dewatering Option 2 – Groundwater Extraction Wells .................... 57 4.4.6.1 Description ..........................................................................................57 4.4.6.2 Screening Summary ........................................................................57 57 4.4.7 Subsurface Dewatering Option 3 – Directional Subsurface Drains ................ 5858 4.4.7.1 Description ......................................................................................58 58 4.4.7.2 Screening Summary ........................................................................58 58 4.4.8 Engineering Slope Stabilization - Buttressing (Engineered Fill) ..................... 5959 4.4.8.1 Description ......................................................................................59 59 4.4.8.2 Screening Summary ........................................................................60 60 4.4.9 Engineering Slope Stabilization Measures - Mechanically Stabilized Earth Wall ................................................................................................................... 60 4.4.9.1 Description ......................................................................................60 60 4.4.9.2 Screening Summary ............................................................................61 4.4.10 Engineering Slope Stabilization Measures – Drilled Piers (CaissionsCaissons) ......................................................................................... 61 4.4.10.1 Description ..........................................................................................61 4.4.10.2 Screening Summary ............................................................................61 4.4.11 Centralized Sewer System ................................................................................ 62 4.4.11.1 Description ..........................................................................................62 4.4.11.2 Screening Summary ............................................................................62 4.4.12 Coastal Erosion Control (Breakwater) ............................................................... 63 4.4.12.1 Description ..........................................................................................63 4.4.12.2 Screening Summary ............................................................................63 4.4.13 Summary of Retained Technologies ................................................................. 63 4.5 Detailed Analysis of Remedial Technologies ............................................................... 63 4.5.1 Concrete Channels ........................................................................................... 64 4.5.2 Liner and Channel System ................................................................................ 65 4.5.3 Seal Surface Fractures ..................................................................................... 66 4.5.4 Groundwater Extraction Wells ........................................................................... 67 4.5.5 Directional Subsurface Drains ........................................................................... 68 4.5.6 Centralized Sewer System ................................................................................ 70 ii Daniel B. Stephens