Interceptor System Master Plan B 2000 GEOTECHNICAL AND
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Technical Memorandum 3 / Interceptor System Master Plan - 2000 June, 2000 Prepared for the Sacramento Regional County Sanitation District Interceptor System Master Plan B 2000 GEOTECHNICAL AND HAZARDOUS WASTE SITES OVERVIEW OF POTENTIAL IMPACTS Technical Memorandum 3 España Geotechnical Consulting Technical Memorandum 3 / Interceptor System Master Plan - 2000 June, 2000 Project No. J146 Technical Memorandum 3 / Interceptor System Master Plan - 2000 June, 2000 TABLE OF CONTENTS 1.0 Introduction ......................................................................................................................... 1 1.1 Purpose and Scope .................................................................................................. 1 2.0 Geotechnical Data ............................................................................................................... 1 2.1 General .................................................................................................................... 1 2.2 Regional Geology.................................................................................................... 2 2.3 Regional Groundwater Conditions.......................................................................... 2 3.0 Geotechnical Conditions of Potential Significant Impact ................................................... 3 3.1 Slope Instability and Liquefaction........................................................................... 3 3.2 Very Dense Cobbles and Boulders within the American River Channel................ 3 3.3 Landfills .................................................................................................................. 4 3.4 Dredge Tailings ....................................................................................................... 4 3.5 Cobbles and Boulders in Older Alluvium............................................................... 5 3.6 Groundwater and Perched Water ............................................................................ 5 3.7 Bedrock ................................................................................................................... 6 3.8 Lineament Features ................................................................................................. 7 4.0 Hazardous Waste/Material Site Information....................................................................... 7 4.1 General .................................................................................................................... 7 4.2 Guidelines for Use of Hazardous Waste/Materials Site Data ................................. 8 References Figures Project Vicinity Map - Figure No. 1 Regional Geologic Map - Figure No. 2 Ground Water Contour Map - Figure No. 3 Hazardous Materials/Waste Regional Base Map - Figure No. 4 Appendix I - General Geology References Estimated Subsurface Conditions - Tables I-3 to I-10 Regional Geologic Map - Figure No. I-1 Regional Geologic Map - Figure No. 4b Appendix II - Groundwater Conditions References Depth to Groundwater Analysis - Figure No. II-1 Appendix III - Environmental Records Review Key Map - Hazardous Materials Waste Sites - Figure No. III-1 Detail Maps - Figure No.’s III-2 to III-49 Hazardous Materials/Waste Sites Data - Table III-1 Technical Memorandum 3 / Interceptor System Master Plan - 2000 June, 2000 1.0 Introduction 1.1 Purpose and Scope Design and construction of a wastewater collection system of below ground interceptor pipelines can be substantially effected by geotechnical information on subsurface conditions. Additionally, if conditions of significant potential cost impact can be identified prior to or during right of way planning and evaluation, they can be avoided or minimized where possible. Similarly, right of way planning and acquisition can benefit from preliminary assessment of potential hazardous waste/materials conditions and/or knowledge of potentially adverse conditions during construction. The purpose of this Technical Memorandum is to gather and report on selected geotechnical and hazardous waste site data that would be useful during master planning and costing. The selected geotechnical data are those needed for identification of general zones or areas within the collection system service area that have unusual soil or groundwater conditions potentially impacting interceptor construction methods and project costs. The hazardous waste/materials data to be reviewed includes relevant listings of reported sites that will be of importance to right of way acquisition and construction planning. Gathered data are to be displayed on summary maps and tables to facilitate understanding and use. Suggestions for use of hazardous waste/materials data in evaluating alternative alignments during master planning and for guideline considerations in right of way acquisition are included. Data and information to be gathered and evaluated are readily available from public agency references, SRCSD files, and consultant reports on SRCSD projects. 2.0 Geotechnical Data 2.1 General The substantial size of the collection system service area necessitates data sources on a similar scale in order to depict geologic and soils units as well as regional groundwater information. Regional geologic mapping and groundwater monitoring has been performed by several agencies (Helley and Harwood, 1985; USGS, 1970; Department of Water Resources, 1990; and the County of Sacramento, 1997) for many years. Site specific studies by agency (CDMG, 1975 and 1988) and private sources (España, 1999; Kleinfelder, 1997, 1998a & 1998b; Tong and Chang, 1999) are also useful for basic characterization of geologic units to supplement the general data from regional mapping and monitoring. The basis of the regional data reported are therefore existing maps created for Sacramento County and its vicinity. Figure 1 shows the boundaries of the SRCSD service area and base map features of selected roadways, railroads, and other community improvements. Figure 2 presents a regional geologic map for the service area. Soil and rock units of similar properties and characteristics are shown as boundaries labeled with geologic abbreviations. The abbreviations 2 Technical Memorandum 3 / Interceptor System Master Plan - 2000 June, 2000 correspond to surface materials and named surface formations deposited over a sequence of geologic time, typically listed from youngest to oldest in age. The specific depths of surface units are not readily shown on the map, and so other underlying units may control actual excavation and support conditions at invert elevations. The alignments of various planned interceptors are also shown on Figure 2. Planners can use the information to identify soil and rock types that will be encountered, reroute where to less costly alternative routes are possible, or refine master plan cost estimates based on known properties of the particular units being crossed. Figure 3 presents an evaluation of regional groundwater elevations for a particular period in time. Shown are groundwater elevation contours from measured well data representative of Spring 1997 (County of Sacramento, 1997). This map uses the latest data readily available in contour format. These data have been selected as representative of regional conditions that can be used in near term (1 to 2 years) forecasting of alignment areas that will encounter groundwater within the excavation depths to the pipeline’s invert. Water levels encountered during construction can effect the properties and stability of certain soils encountered within the excavation or cause construction delays and therefore result in increased construction costs. Unlike geologic units, groundwater levels fluctuate within short time frames due to seasonal rainfall, groundwater pumping, aquitard zones and other influences. Use of historical high and/or low levels may not be representative of future fluctuations. Periodic updates to regional groundwater elevations will be necessary for longer planning horizons. These data maps can be used as a basis for discussion of unusual soil or ground water conditions that potentially can impact construction methods and project costs. 2.2 Regional Geology Summaries of the regional geology of the Sacramento area have been presented in most of the private investigation reports listed in this memorandum’s reference list. For completeness, a similar summary is presented in Appendix I. It provides details of the soil and rock units shown on Figures 2 and I-1 as well as the structure and stratigraphy of the region, information on faulting affecting the area, and an estimate of general subsurface conditions expected along each planned interceptor alignment. 2.3 Regional Groundwater Conditions A discussion of the groundwater aquifers and conditions in the service area is presented in Appendix II. A specific analysis of the location of areas where depths to groundwater are expected to be at or above the invert depths of the interceptors is also presented in Appendix II. 3 Technical Memorandum 3 / Interceptor System Master Plan - 2000 June, 2000 3.0 Geotechnical Conditions of Potential Significant Impact 3.1 Slope Instability and Liquefaction Generally the weakest soil units, statically and under earthquake loading, are young in age and are those deposited in low energy environments. In addition, reprocessed soils such as uncontrolled manmade fills, levees and dredge tailings can be weaker than their original, natural state. Geologic units termed stream channel deposits (designated