01_Edinburg PS Design Report 20151118 woA.pdf

Contract No. IBM09D0008 Task Order IBM14T0012

Rehabilitation of the Levees at Edinburg Pump Station Hidalgo County, Penitas, Texas

Final Design Documentation Report

November 18, 2015

Prepared by:

URS GROUP, INC.

Texas Registered Firm 3162 9400 Amberglen Blvd Austin TX 78729 Phone: 512-454-4797 Fax: 512-454-8807

Final Design Documentation Report Contract No. IBM09D0008 November 2015 Task Order IBM14T0012

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STATEMENT OF LIMITATIONS

This Document is being submitted as part of the final submittal for USIBWC use only. The scope of services performed within may not be appropriate to satisfy the needs of other users.

Any use or re-use of this document or of the findings, conclusions, or recommendations presented herein is the sole risk of said user.

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TABLE OF CONTENTS

Page

1.0 PROJECT INFORMATION

General Description ................................................................................................ 1 1.1 Purpose of Design Documentation Report ............................................................. 2 1.2 Project Description .................................................................................................. 2 1.3

Project Location .......................................................................................... 2 1.3.1 Existing Features ......................................................................................... 2 1.3.2 Project Objectives ....................................................................................... 3 1.3.3 Description of Alterations ........................................................................... 3 1.3.4

Project Deliverables ................................................................................................ 3 1.4

2.0 PERTINENT DATA

Design Data ............................................................................................................. 4 2.1

Controlling Elevations ................................................................................ 4 2.1.1 Hydraulics Data .......................................................................................... 4 2.1.2 Survey Data ................................................................................................. 4 2.1.3 Soil Borings ................................................................................................ 4 2.1.4

3.0 DESIGN INFORMATION AND REFERENCES

Design Standards .................................................................................................... 6 3.1 Computer Program Standards ................................................................................. 6 3.2 Computer Programs Used ....................................................................................... 7 3.3 Government-Provided Information ......................................................................... 7 3.4 Existing Utilities ..................................................................................................... 8 3.5 Project Requirements .............................................................................................. 8 3.6

4.0 ENGINEERING DESIGN

Hydrology and Hydraulics ...................................................................................... 9 4.1

Hydraulic Features ...................................................................................... 9 4.1.1 Geotechnical ........................................................................................................... 9 4.2

Objectives ................................................................................................... 9 4.2.1 Geology ....................................................................................................... 9 4.2.2 Geotechnical Drilling ................................................................................ 10 4.2.3 Geotechnical Laboratory Testing .............................................................. 10 4.2.4 Supplemental Geotechnical Information .................................................. 11 4.2.5 Geotechnical Design Features ................................................................... 11 4.2.6 Levee Materials ......................................................................................... 14 4.2.7

Environmental Considerations .............................................................................. 14 4.3 Overview ................................................................................................... 14 4.3.1 Biological Resources ................................................................................ 14 4.3.2 Cultural Resources .................................................................................... 15 4.3.3 Construction Approaches .......................................................................... 16 4.3.4

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Structural Design Features .................................................................................... 16 4.4 General ...................................................................................................... 16 4.4.1 Concrete Design ........................................................................................ 16 4.4.2 Reinforcing Steel ...................................................................................... 16 4.4.3 Steel Design Criteria ................................................................................. 17 4.4.4 Loads ......................................................................................................... 17 4.4.5 Geotechnical Design Parameters .............................................................. 19 4.4.6

Design of Floodwalls ............................................................................................ 20 4.5 Wall Sections ............................................................................................ 20 4.5.1 Load Cases ................................................................................................ 22 4.5.2 Case I1 Design Flood Loading ................................................................. 22 4.5.3 Case I2 Water to Top of Wall ................................................................... 22 4.5.4 Case I3 Earthquake Loading ..................................................................... 24 4.5.5 Case I4 Construction and Wind Short-Duration Loading ......................... 24 4.5.6 Case R1 Floodwall Usual Loading ........................................................... 24 4.5.7 Case R2 Reverse Floodwall Loading ........................................................ 24 4.5.8 Case R3 Reverse Floodwall Loading ........................................................ 24 4.5.9

Design of Drainage Structure................................................................................ 25 4.6 General ...................................................................................................... 25 4.6.1 Modifications and Design ......................................................................... 25 4.6.2

Design of Steel Bollard Wall ................................................................................ 25 4.7 General ...................................................................................................... 25 4.7.1

Civil Design Features ............................................................................................ 26 4.8 General ...................................................................................................... 26 4.8.1 Typical New Levee Section ...................................................................... 26 4.8.2 Interim Flood Protection ........................................................................... 26 4.8.3 Roadways .................................................................................................. 26 4.8.4 Utility Relocation/Removal ...................................................................... 27 4.8.5 Traffic Plan ............................................................................................... 27 4.8.6

Construction Plan .................................................................................................. 27 4.9 General ...................................................................................................... 27 4.9.1 Sequence of Construction ......................................................................... 27 4.9.2 Real Estate Information ............................................................................ 27 4.9.3 Dewatering Plan ........................................................................................ 28 4.9.4

5.0 PROJECT COST ESTIMATE

Overview ............................................................................................................... 29 5.1 Assumptions .......................................................................................................... 29 5.2

6.0 CONSTRUCTION SCHEDULE

Overview ............................................................................................................... 30 6.1 Schedule Constraints ............................................................................................. 30 6.2 Assumptions for the Construction Schedule ......................................................... 30 6.3

Rain Days .................................................................................................. 30 6.3.1 Description of Critical Path Items......................................................................... 30 6.4 Potential Delays for Construction ......................................................................... 31 6.5

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LIST OF TABLES

4-1 Geotechnical Laboratory Tests 4-2 Unit Weights 4-3 Phreatic Conditions for Floodwall Design 4-4 Load Combinations for Floodwall / Retaining Wall Design Structural Design 6-1 Monthly Anticipated Adverse Weather Delay Work Days Based on

5-Day Work Week and 0.5-Inch Rain Event

FIGURES

Figure 4-1 Uplift Forces on the Floodwall

APPENDICES

Appendix A Final Cost Estimate

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ACRONYMS AND ABBREVIATIONS

ACI American Concrete Institute

ASCE American Society of Civil Engineers

ASTM American Society for Testing and Materials

BOF Bottom of Floodwall Footing

CBP U.S. Customs and Border Protection

DDR Design Documentation Report

DHS Department of Homeland Security

FB Free Board

FEMA Federal Emergency Management Administration

HFW Height of water above the base slab on the riverside

HPW Height of water on the landside

LRGFCP Lower Rio Grande Flood Control Project

MDE Maximum Design Earthquake

NRCS National Resource Conservation Service

OPC Opinion of Probable Cost

PSI Professional Service Industries, Inc.

ROW Right-of -Way

SOW Scope of Work

TOLE Top of Levee Elevation

TOF Top of Floodwall Footing

TOS Top of Soil

TxDOT Texas Department of Transportation

URS URS Group, Inc.

USACE United States Army Corps of Engineers

USIBWC United States International Boundary and Water Commission

WSEL Water Surface Elevation

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1.0 PROJECT INFORMATION

General Description 1.1

Levees at Edinburg Pump Station is a levee rehabilitation/reconstruction project along the Rio Grande located within a portion of the Lower Rio Grande Flood Control Project (LRGFCP) in Hidalgo County, Texas. The purpose of the project is to improve flood protection for urban, suburban, and agricultural areas. This reach represents approximately 710 ft of levee in the project on the east and west sides of the Edinburg Pump Station.

The United States Section of the International Boundary and Water Commission (USIBWC) has been designing and constructing the rehabilitation of the levees within the LRGFCP to meet the Federal Emergency Management Administration (FEMA) requirements for the safe containment of 100-year flood flows since 2009.

The LRGFCP extends from the town of Penitas, Texas, at its upstream end, to 28 miles above the Gulf of Mexico, a distance of about 158 river miles. The LRGFCP has two diversion dams, Anzalduas Dam and Retamal Dam, approximately 17 and 57 river miles below Penitas, respectively, which divert portions of the flood flows into the Main Floodway in the United States and the floodway in Mexico, respectively. The LRGFCP was constructed to provide flood protection to urban, suburban, and irrigated lands in the Rio Grande delta.

The majority of the levees within the LRGFCP have been improved; however, there are several gaps that still need to be addressed. Once such gap in the levee system exists at the Edinburg Pump Station and adjacent levees. The floodwalls/border fence infrastructure has been constructed near the Edinburg Pump Station. This Scope of Work (SOW) is for the design of the levees within 10 ft of the Edinburg Pump Station up to the floodwalls/border fence infrastructure on each side of the pump house.

The SOW entitled "Scope of Work for Design of Rehabilitation Improvements for the Levees at Edinburg Pump Within the Lower Rio Grande Flood Control Project," dated 25 September 2014, was provided to URS by the USIBWC. Per the SOW, design requirements were as follows:

"The design shall include the determination of the factor of safety against failure at critical points along each levee/floodwall reach," in accordance with design standards listed in Section 3.0 of this report.

The top elevation of the levee-raising improvements will be as required to provide containment of design flood flows with a minimum freeboard of 3 ft for Water Surface Elevations (WSELs) as calculated in S&B Infrastructure's July 2008 hydraulic model titled "Lower Rio Grande Flood Control Project; HEC-RAS Hydraulic Model Update and Validation (Penitas to River Mile 28 and Off-River Floodways in Texas and Mexico)" for the Rio Grande and to accommodate the future installation of a bollard floating fence by the Department of Homeland Security (DHS). In general, work requirements in this SOW will be sufficient to lead into contracting and performance of construction of the proposed flood protection.

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Purpose of Design Documentation Report 1.2

This Design Documentation Report (DDR) presents the basis for design and the essential data, assumptions, criteria, and computations for developing the design, plans, specifications, and costs for construction of the levees and floodwalls at the Edinburg Pump Station reach. The purpose of the DDR is to provide sufficient design detail and analyses to support the preparation and review of the deliverables for this project.

Project Description 1.3

Project Location 1.3.1

The Edinburg Pump Station reach of the USIBWC levee is located within Hidalgo County in Penitas, Texas. This reach represents approximately 710 ft of flood protection in the project on the east and west sides of the Edinburg Pump Station.

The approximate length and coordinates for the limits of the Edinburg Pump Station levee rehabilitation provided in NAD83 Geodetic Position System and identified by this SOW are as follows:

Levee West of Edinburg Pump House: Approximately 345 linear ft to tie-in location at border fence wall. Approximate tie-in location at border wall (Wall Segment A) is at the following coordinates (provided in NAD83 Geodetic Position System):

Approximate wall tie-in location at Wall Segment A: N 16608345.5635 E 1001213.0041

Levee East of Edinburg Pump House: Approximately 365 linear ft to tie-in location at border fence wall. Approximate tie-in location at border wall (Wall Segment B) is at the following coordinates (provided in NAD83 Geodetic Position System):

Approximate wall tie-in location at Wall Segment B: N 16607822.6745 E 1001522.1704

Existing Features 1.3.2

In the "Final Environmental Assessment Improvements to the Mission and Common Levee Systems," February 2007, the Edinburg Pump Station was identified a historical structure. The report notes the original design configuration as shown in Dannenbaum's Construction Documents, "The existing levee system crosses the Edinburg irrigation intake channel at Project Mile 0.6. At this location, a concrete floodwall attached to the Penitas Pumping Plant is used instead of the compacted-earth levee structure. For the increase in levee height, the Penitas Pumping Plant, a potential historical site, would not be modified by the project. Levee expansion would be accomplished by construction of a new crossing, using an earthen embankment similar to that used in the remaining levee system. The embankment, placed away from the pumping plant, would provide a new roadway for traffic crossing over the channel. To maintain the operability of the pumping plant, the new embankment would be built over intake pipes with a diameter similar to those of the pumping plant intake. This crossing of the intake

URS Group, Inc. Page 3 USIBWC channel, which would be approximately 500 ft long, is the only segment of the improved Mission Levee requiring construction outside the current Right of Way (ROW)."

Project Objectives 1.3.3

The objectives for the Edinburg Pump Station Levee Rehabilitation Improvement project include:

Design and certification of the levee on the Rio Grande to withstand the 100-year flood with +3 ft of freeboard per 44 CFR for FEMA certification.

Design of a floodwall on the Rio Grande to withstand the 100-year flood with +3 ft of freeboard. The floodwall will end 10 ft from each side of the Pump Station.

Completion of an existing gatewell structure within the levee reach.

Description of Alterations 1.3.4

The alterations for the Edinburg Pump Station Levee Rehabilitation Improvement project include:

Structure:

o Design a new floodwall along the alignment that extends approximately 160 ft.

West Side of Pump Station: STA 3+56 to STA 4+62.

Approximate Length – 100 ft

East Side of Pump Station: STA 6+40 to STA 7+00 Approximate Length – 30 ft

Project Deliverables 1.4

Deliverable Due Date for Submittals

60% Construction Drawings, Specifications, DDR, Geotechnical Evaluation Report, Opinion of Probable Cost

4/26/15

90% Construction Drawings, Specifications, DDR, Geotechnical Evaluation Report, Opinion of Probable Cost

8/28/15

100% Construction Drawings, Specifications, DDR, Geotechnical Evaluation Report, Opinion of Probable Cost

9/30/15

Final Construction Drawings, Specifications, DDR, Geotechnical Evaluation Report, Opinion of Probable Cost

11/18/15

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2.0 PERTINENT DATA

Design Data 2.1

This section discusses the specific survey, geotechnical, and hydraulics data that were used to design the levee and floodwall sections.

Controlling Elevations 2.1.1

The controlling elevation is the minimum Top of Levee Elevation (TOLE), which is equal to the 100-year WSEL plus 3 ft of freeboard.

Hydraulics Data 2.1.2

The TOLE is determined based on the computed high WSEL from the HEC-RAS model results as determined in the 2008 S&B Infrastructure report titled "Lower Rio Grande Flood Control Project HEC-RAS Hydraulic Model Update and Validation (Penitas to River Mile 28 and Off- River Floodways in Texas and Mexico)."

The WSEL based on design flood at the location of the Edinburg Pump Station = 133.80 ft based on NAVD 88 vertical datum. The minimum TOLE required at Edinburg Pump Station = 133.80 + 3.0 = 136.80 ft based on NAVD 88 vertical datum.

Survey Data 2.1.3

Existing topographic data shown on the plans were produced from the field survey performed by Vickery and Associates, Inc., San Antonio, TX during January 2015. The horizontal coordinates shown on the plans are referenced to the Texas State Plane Coordinate System, South Zone, NAD83 (2011), U.S. Survey feet. Coordinates shown are surface coordinates, using a combined scale factor of 1.0000170739 (ground-to-grid factor of 0.9999829264). Surface elevations shown on the plans are referenced to NAVD88. The survey control monument for this project is National Geodetic Survey No. S 1409.

Soil Borings 2.1.4

Soil borings were provided by Professional Service Industries, Inc. (PSI) under Contract to URS1. PSI's June 2015 draft Geotechnical Data Report (GDR) (included as Appendix A of the Geotechnical Evaluation Report) includes the borings and laboratory tests performed for this Contract.

The purpose of the GDR was to provide URS with adequate information to characterize subsurface conditions and prepare a Technical Memorandum presenting geotechnical analyses

1 "General Engineering Services Report for Rehabilitation of the Levees at Edinburg Pump Station, Penitas, Hidalgo County, Texas," USIBWC IDIQ Contract No. IBM09D0008, USIBWC IDIQ Task Order No. IBM14T0012, URS Project No. 41011963; Purchase Order No.316799, October 2014.

URS Group, Inc. Page 5 USIBWC for the final design of the subject levee reach in general accordance with United States Army Corps of Engineers (USACE) documents EM 1110-2-1913 Design and Construction of Levees, ETL1110-2-569 Design Guidance for Levee Underseepage, and EM 1110-2-2502 Retaining and Flood Walls, as applicable, and the FEMA Requirements for Mapping Levees (44 CFR 65.10) as they pertain to geotechnical evaluations of levees.

A total of seven borings with varying spacing were drilled for the project by subconsultant PSI at locations prescribed by URS. The borings were drilled to depths ranging from 35 to 90 ft below existing grade. Borings were advanced through levee embankments using auger drilling techniques. Mud-rotary techniques were employed below the groundwater table to advance borings to their respective termination depth. Upon completion of drilling, bentonite-cement grout was used to backfill the boreholes using tremie methods.

Additionally, geotechnical data from previous geotechnical engineering studies within the project site performed by L&G Consultants (L&G 2008 and L&G 2009) and PSI (2012) were used to supplement the findings and analysis associated with the current study.

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3.0 DESIGN INFORMATION AND REFERENCES

Design Standards 3.1

The following design standards are a part of the requirements for the design of the project:

EM 1110-2-1913, "Design and Construction of Levees," 30 April 2000;

EM 1110-2-2502, "Retaining and Flood Walls," 29 September 1989;

ETL 1110-2-569, "Design Guidance for Underseepage," 1 May 2005;

EM 1110-2-6053, "Earthquake Design and Evaluation of Concrete Hydraulic Structures," 1 May 2007;

EM 1110-2-2104, "Strength Design of Reinforced-Concrete Hydraulic Structures," 20 August 2003;

EM 1110-2-2105, "Design of Hydraulic Steel Structures," 31 May 1994;

EM 1110-2-2906, "Design of Pile Foundations," 15 January 1991;

American Concrete Institute, ACI 318-08, Building Code Requirements for Structural Concrete;

American Institute of Steel Construction, Inc., AISC, Manual of Steel Construction, 13th Edition (ASD only);

American Society of Civil Engineers, ASCE 7-05, Minimum Design Loads for Buildings and Other Structures;

American Society for Testing and Materials (ASTM) Standards;

American Welding Society, AWS D1.1-02, Structural Welding Code;

Technical Letter 1110-2-569, entitled "Design Guidance for Levee Underseepage;"

National Engineering Handbook, Chapter 45, "Filter Diaphragms," Part 628 Dams, Natural Resources Conservation Service, United States Department of Agriculture, 210-VI-NEH, January 2007;

FEMA as found in Code of Federal Regulations, Title 44 – Emergency Management Administration, Section 65.10 - Mapping of Areas Protected by Levee Systems (44 CFR Section 65.10) and fully addresses all FEMA Levee Certification Requirements;

and

Federal Highway Administration, FHWA-IF-99-025, "Drilled Shafts: Construction Procedures and Design Methods," August 1999.

Computer Program Standards 3.2

A/E/C CADD Standard, Release 4.0, July 2009.

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Computer Programs Used 3.3

The following are the computer programs used in development of the Project:

Adobe PDF: Adobe Portable Document Format (PDF) Writer and Reader; Adobe Professional (Version 8.0); Adobe Systems Incorporated;

AutoCAD: Computer-Aided Design and Drafting (CADD) Software; AutoCAD (2012): Autodesk, Incorporated;

Culvert Master: Culvert Analysis and Design; Bentley Culvert Master (Version 3.1);

Bentley Systems, Incorporated;

LPILE: A Program for the Analysis of Deep Foundations Under Lateral Loading;

Ensoft, Inc. (2012);

Microsoft Excel: A Software for Storing, Organizing and Manipulating Data;

Microsoft Word (2003); Microsoft Corporation;

Microsoft Word: Word Processing Software; Microsoft Word (2003); Microsoft Corporation;

SEEP/W: Seepage Analysis Software; GeoStudio (2007, version 7.15); GEO-SLOPE International, Ltd.;

SLOPE/W: Slope Stability Software; Geo Studio (2007, version 7.15); GEO-SLOPE International, Ltd.; and

SAP2000: Structural Analysis Program; Computers and Structures, Inc. (2015, version 17).

Government-Provided Information 3.4

USIBWC provided the following existing project documents to URS for the preparation of this DDR and the Plans and Specifications for this project.

USIBWC Soil Boring Logs (S&B Infrastructure Technical Memorandum, 2008);

Lower Rio Grande Flood Control Project, HEC-RAS Hydraulic Model Update and Validation (Penitas to River Mile 28 and Off-River Floodways in Texas and Mexico), S&B Infrastructure, July 2008;

Final Environmental Assessment Improvements to the Mission and Common Levee Systems, Parsons, February 2007;

Horizontal and Vertical Control Survey Report, Hidalgo County Levee Restoration Project, Dannenbaum, 2008;

Geotechnical Engineering Report, DHS Segment 0-4 B, USIBWC Mission Levee Improvement Project, L&G Engineering Laboratory, 2009; and

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Edinburg Pump Levee Relocation and Channel Crossing Improvement Hidalgo County, Texas, Professional Service Industries, Inc., 2012.

Existing Utilities 3.5

The existing utilities within the Edinburg Pump Station levee rehabilitation project area include gas and adjacent overhead electric. USIBWC provided as-builts of the utilities from the Dannenbaum design. A list of known utilities and their locations is provided in the project drawings for informational purposes only.

It is the responsibility of each individual utility owner to remove, relocate, and protect their respective utility. The Contractor shall contact the utility provider at least 48 hours prior to the commencement of any construction work.

Project Requirements 3.6

The following design requirements for this project were included in the SOW:

Follow USACE and FEMA criteria for flood risk reduction design (see DDR Section 3.0).

Design a minimum 21-ft-wide levee crest to include a 21-ft-wide maintenance road at the crest of the levee consisting of a flex-base material directly placed on the finished embankment material, and additional space to permit future construction of a "floating bollard" border fence.

Design sideslopes to be no steeper than 3H:1V on the riverside and no steeper than 3H:1V on the landside.

Ensure that construction activities do not disturb existing wetlands.

Evaluate existing levee conditions and past levee performance.

Conduct a geotechnical investigation of levee embankment materials and foundation soils, and perform seepage and stability analyses to assess levee performance during the design flood event and other critical hydraulic cases.

Minimum TOLE.

Design a floodwall to withstand the 100-year flood event with +3 ft of freeboard.

Evaluate erosion potential on the levee slope.

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4.0 ENGINEERING DESIGN

Hydrology and Hydraulics 4.1

The design objective is to improve the flood control for river flooding events of the Rio Grande.

Hydraulic Features 4.1.1

The HEC-RAS analysis is provided in the report titled "Lower Rio Grande Flood Control Project HEC-RAS Hydraulic Model Update and Validation (Penitas to River Mile 28 and Off-River Floodways in Texas and Mexico), by S&B Infrastructure, July 2008.

Geotechnical 4.2

Objectives 4.2.1

The scope of the geotechnical study included drilling borings along the proposed alignment of the levee, performing laboratory testing to classify and characterize subsurface conditions, and preparing a technical memorandum presenting geotechnical analyses for the final design of the levee. The objective was to develop geotechnical recommendations for levee design and to establish anticipated subsurface conditions for use in planning and constructing the project.

Geology 4.2.2

4.2.2.1 Site Geology

The project site is located within the Gulf Coastal Plains Physiographic Province of Texas.

Specifically, the site is situated near the transition between subprovinces of the Coastal Prairies towards the east to the Gulf of Mexico and the Interior Coastal Plains towards the west.

The Coastal Prairies subprovince begins at the Gulf of Mexico shoreline and features geologic formations consisting of young deltaic sands, silts, and clays with beds that are nearly flat.

These deposits erode to form a topography characterized by nearly flat grasslands and prairies that gradually slope southeast towards the Gulf at a rate of less than 1 ft per mile. Minor steeper slopes result from subsidence of deltaic sediments along faults. Trees are uncommon, except for localized areas near streams and oak mottes where coarser underlying sediments are present

(BEG, 1996).

The Interior Coastal Plains subprovince features bedrock units consisting of alternating belts of resistant uncemented sands among weaker shales that erode into long, parallel sandy ridges (questas) and valleys. The bedding is tilted toward the Gulf, and at least two major down-to-coast fault systems trend nearly parallel to the coastline (BEG, 1996).

Mapped geology at the project site consists of alluvial soils. Mapped formations include the Lissie Formation undivided (Ql) and silty and sandy floodplain alluvium (Qas). The middle- Pleistocene-aged Lissie Formation (Ql) consists of alluvial deposits of varying proportions of sand, silt, clay, and gravel. The Lissie Formation forms a deltaic plain that parallels the Gulf

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Coast. Its deposits rest unconformably on the Pliocene and early Pleistocene Willis Formation and dips seaward beneath the Beaumont Formation. The delta plain is entrenched as much as 20 ft by streams. Topography associated with the formation is generally flat and featureless, with numerous shallow depression and small "pimple" mounds or dunes. In Hidalgo County, the formation underlies a widely irrigated and cultivated semi-arid plain featuring local veneers of thin, discontinuous stabilized eolian sand.

The younger Holocene-age silty and sandy floodplain alluvium (Qas) consists of yellowish-gray or brownish-gray quartz sand and silt, with plant debris and some biotite. Depositional characteristics of the formation include accretionary point-bars, levees, and crevasse splays formed by distributary channels on the Rio Grande delta. Point-bar deposits grade upward from cross-bedded basal sandy gravel and coarse sand to silt and fine sand up to 40 ft thick.

For further information regarding the regional geology, see the Geotechnical Evaluation Report.

The DDR only discusses the design parameters used to formulate the geotechnical basis for design.

Geotechnical Drilling 4.2.3

URS retained PSI to perform geotechnical drilling and laboratory testing. PSI drilled a total of seven borings for this study at locations prescribed by URS, labeled B-101 through B-107.

Borings B-101 through B-104 were drilled along the proposed levee alignment. Borings B-105 and B-106 were drilled on the landside of the levee, and boring B-107 was drilled on the riverside of the levee near the existing intake channel.

The borings were drilled at the locations shown on the Contract Drawings.

Geotechnical Laboratory Testing 4.2.4

Soil samples obtained from the drilling operation were classified by PSI in general accordance with the Unified Soil Classification System. Laboratory testing on select soil samples was assigned by URS/PSI for formal soil classification and determination of engineering properties.

All samples were tested in PSI’s soils testing laboratories in general accordance with ASTM standards. The geotechnical engineering properties of the strata were evaluated by the laboratory tests and tabulated in Table 4-1.

Table 4-1. Geotechnical Laboratory Tests

Type of Test Number Complete Natural Moisture Content 71 Atterberg Limits 27 Sieve Analysis 14 Hydrometer 5 Minus 200 Sieve 47 Crumb Test 6 Pinhole Test 5

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Type of Test Number Complete Consolidated-Drained Direct Shear 2 CU-Triaxial Shear w/ Pore Pressures 1 Unconfined Compression 4 Hydraulic Conductivity 2 One-Dimensional Consolidation 3

The results of the field and laboratory tests are presented in graphical or numerical form on the boring logs in the GDR prepared by PSI. The results of the remaining tests are also presented in the GDR.

Standard Penetration Test (SPT) results are noted as "blows per foot" on the boring logs, where "blows per foot" refers to the number of blows required for a 140-lb falling automatic trip hammer to penetrate 12 inches into the subsurface materials, in general accordance with ASTM D 1586. Where hard and/or very dense materials were encountered, the tests were terminated at 50 blows even if 1 ft of penetration had not been achieved. A total of 14 Shelby tube samples were collected where SPT samples indicated the presence of fine-grained soils for the purpose of performing strength, hydraulic conductivity, and consolidation laboratory testing on undisturbed samples.

Supplemental Geotechnical Information 4.2.5

Subsurface information from previous geotechnical studies at the project site were incorporated into the geotechnical design for this project. The studies were performed by PSI (PSI 2012) and L&G Engineering Laboratories, LLC (L&G 2008; L&G 2009) and included borings and laboratory test results for an alternative levee alignment at the project site. The locations of these borings and discussion of the data are provided in the Geotechnical Evaluation Report.

Geotechnical Design Features 4.2.6

Seepage and stability analyses were performed by URS at representative critical locations in the floodwalls and levees. Engineering properties of soils used for seepage and stability analyses are presented in the Geotechnical Evaluation Report. Preliminary seepage analyses indicated that exit gradients along levees and floodwalls would exceed design criteria for allowable exit gradients (maximum 0.5) on the western half of the project alignment without seepage control measures. Mitigation measures to control seepage are therefore required. Blanket and chimney drains consisting of ASTM C-33 fine and coarse aggregates and cement-bentonite cutoff walls will be used to control under seepage. These control measures are discussed in detail in the Geotechnical Evaluation Report and summarized below. The stability analyses indicated that the factors of safety are adequate for all design conditions, assuming 3H:1V sideslopes are maintained on both the landside and riverside.

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4.2.6.1 Levees

Build the levee to final grade with a compacted clay with a floodside levee slope of 3H:1V or flatter and a landside levee slope of 3H:1V or flatter. Place material in lifts that are a maximum of 8 inches (loose) thickness at moisture content between 0 and +3% of optimum moisture content to at least 95% of ASTM D1557 Modified Proctor maximum dry density.

Embankment borrow sources will be evaluated for the presence of dispersive clays, and dispersive clays will not be acceptable as borrow. Quality control of embankments will include screening to detect dispersive soils, and if disclosed, such materials will be removed.

All drain materials will be compacted to a minimum of 95% of the maximum dry density as determined by ASTM D 1557.

Levee overbuild of 0.3 ft (3.6 inches) will be provided to compensate for post-construction settlement of earthen levee sections. Settlement of drilled-pier supported floodwall sections is anticipated to be less than 0.5 inch, which is within typical construction tolerances, and therefore, floodwall overbuild is not required.

4.2.6.2 Concrete Floodwall (T-Walls)

A floodwall will be required along portions of the alignment due to limited ROW. The floodwalls will be founded on drilled piers. Drilled pier foundations were selected for the purposes of providing: 1) reduced risk of additional loading in the vicinity of the existing pump station; 2) improved floodwall resiliency in the interim period before the future tie-in with the pump station is constructed; 3) improved flexibility for the future tie-in design and construction;

and 4) improved settlement performance. The start of the floodwall alignments were offset a minimum of 30 ft from the walls of the existing pump house to ensure constructability of the future tie-in to the pump station and to avoid excavating and backfilling against the walls of the pump station.

A summary of the floodwall foundation requirements is presented below.

Project criteria for floodwall design dictates that top of wall must be a minimum elevation of 136.80 ft to provide 3 ft of freeboard above the 100-year flood.

The wall stem will be positioned at the riverside crest of the levee to provide a 16-ft-wide crest. Consequently, earthfill on the landside of the wall will be higher than the riverside.

The top of the floodwall base on the west side of the pump house will be at 122.5 ft.

On the east side of the pump house, the first floodwall reach adjacent to the pump house will have top-of-base slab at elevation 120.5 ft. The easternmost floodwall base will be set at the typical 122.5-ft elevation.

The retained side (landside) of the floodwall will consist of new levee backfill, upon which the proposed access road will be constructed.

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The resisting side (riverside) will consist of either new levee fill or cut slope into existing levee at a maximum slope angle of 3H:1V. A minimum 5-ft-wide bench in front of the wall will be provided before transitioning to 3H:1V slope. The wall footing will be embedded to provide at least 2 ft of soil cover.

Maximum anticipated unbalanced soil height (i.e., soil elevation behind the wall minus soil elevation in front of the wall) is approximately 7 ft as illustrated by the cross-sections in the Drawings.

Dimensions of the overall floodwall section are discussed in Section 4.4.4 – Structural Design Features. In general, the base slab section is 2'-6" thick x 16'-6" wide. The floodwall stem is 1'-8" thick and 14'-4" tall at the typical section and 16'-4" at the east monolith closest to the pump house.

4.2.6.3 Cement-Bentonite Cutoff Walls

Cement-bentonite cutoff walls are required between Stations 3+00 and 4+62 to reduce underseepage exit gradients to below maximum values specified by USACE. The top of levee will be excavated (de-graded) approximately 10 ft to elevation 120 ft to provide a working platform of sufficient width and to minimize cutoff wall trench depth and slurry quantities.

Cutoff walls are anticipated to be at least 3 ft wide and extend to elevation 90 ft (30 ft below interim excavation grades) with at least 5 ft of embedment into a non-pervious confining stratum.

Additional details are provided in the Geotechnical Evaluation Report and Specifications.

4.2.6.4 Blanket and Chimney Drains

Chimney and blanket drains are required to lower the phreatic surface on the landside slope, thereby reducing exit gradients and improving the slope stability's safety factor. Additionally, the drains provide internal filtration to prevent particle migration through or under the embankment that could lead to internal erosion (piping). The presence of dispersive clay soils in the existing embankments and foundation present an increased risk of piping.

Design and construction details for blanket and chimney drains are provided in the Geotechnical Evaluation Report, Drawings, and Specifications.

4.2.6.5 Pavements

Maintenance roadways will be constructed in accordance with Section 50.20.00-Flex Base. To increase pavement design life and/or reduce the thickness of flexbase aggregate to the requested thickness of 6 inches, a layer of biaxial geogrid reinforcement will be installed between the compacted embankment subgrade and the overlying flexbase. The geogrid will provide confinement of the flexbase against lateral spreading and separation to maintain the continuity of the flexbase layer.

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Levee Materials 4.2.7

4.2.7.1 Embankment

Embankment soils shall consist of soils meeting Unified Soil Classification System symbol CL or CH with more than 50% passing the No. 200 sieve, a maximum liquid limit of 60, and a plasticity index between 12 and 30. Embankment soil shall be non-dispersive and rated as Grade 1 or 2 per ASTM D 6572 (Crumb Test), 30% per ASTM 4221 (Double Hydrometer), and either ND1 or ND2 per ASTM D4647 (Pinhole Test).

4.2.7.2 Vegetative Cover

Vegetative cover is designed to minimize and/or mitigate any negative impacts to the levee during normal rain and flood events. A vegetation-free and root-free zone needs to be established per ETL 1110-2-571 - Guidelines for Landscape Planting and Vegetation Management at Levees, Floodwalls, Embankment Dams, and Appurtenant Structures, Sections 2-1 through 2-3 (supersedes EM-1110-2-301). Details for seeding and vegetation are included in Section 32 92 00 Vegetation for Erosion Control.

Environmental Considerations 4.3

Overview 4.3.1

In February 2007, the USIBWC completed an environmental assessment for flood control improvements to the Lower Rio Grande Flood Control Project, entitled "Final Environmental Assessment Improvements to the Mission and Common Levee Systems." The rehabilitation improvements for the levees at Edinburg Pump Station reach are wholly located within the project area studied in the environmental assessment.

The conclusions of the environmental assessment were based on conceptual-level design of the levee system, and the assumptions that fill material obtained from commercial sources would be added to the existing levee to meet the 3-ft freeboard criterion. An assumption made in the environmental assessment report was that typical height increases in improvement areas would range from 2 to 6 ft. A 6-ft levee height increase with 3:1 side slopes would result in a total width increase of 36 ft to the footprint. This expansion would take place within the flood control project ROW. In some instances, adjustments in levee slope would be made to eliminate the need for levee footprint expansion, when required.

A concrete floodwall will be constructed adjacent to the existing pumping station. A cement-bentonite slurry wall is required in this section of flood protection to manage seepage. The slurry barrier will be installed in a closed trench along the center line of floodwall.

Biological Resources 4.3.2

Improvements to the levee system entail clearing and placement of fill material on the existing levees. Vegetation would be impacted along the levee slopes and at locations where levee footprint expansion is required. Levee expansion, if required, would take place along the current

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No significant effects are anticipated on wildlife habitat in the vicinity of the levee system, including potential habitat for threatened and endangered species. In areas requiring levee footprint expansion, no riparian woodland communities would be impacted; impacts on vegetation would be limited to low quality vegetation along the levee slopes, of very limited value as wildlife habitat.

Cultural Resources 4.3.3

Improvements to the levee system are not expected to adversely affect known archaeological or historical resources. Architectural resources may be adversely affected by expansion of the levee footprint. Potential effects include vibration and ground disturbance from the use of heavy equipment during construction as well as effects caused by alterations to the levee itself;

however, the increased height of the levee is not expected to change the flow of water to or from architectural resources. There are no anticipated effects of dredging on archaeological resources.

Previous research has been conducted to determine if historic-age buildings and structures are known to be present along the LRGFCP (Cooper, et al. 2002). The conclusions are that the Edinburg Pump Station and associated levees is located in an area with a high probability [HPA 1 (16LJ6)] as having a high potential for historic archeological resources.

Preliminary investigations conducted for preparation of this EA indicate five major historic-age resources exist within the current levee ROW and are engineering elements of the levee and floodway systems (Neel 2006). The five engineering features are: (1) a weir gate structure at the Border Pacific Railroad crossing near Penitas, (2) the Edinburg Pumping Plant and floodwall, (3) the Mission Main Canal weir gate structure, (4) the Banker Floodway spillway structure, and (5) Anzalduas Dam. These resources, prefixed by the designation ENG, are described below. A sixth structure, the La Lomita Chapel, is located beyond the current ROW, but this structure may be visually impacted by encroachment of the expanded levee footprint.

ENG 1—A weir gate structure at the Border Pacific Railroad crossing near Penitas;

ENG 2—The Edinburg Pumping Plant and floodwall;

ENG 3—The Mission Main Canal weir gate at the Mission Levee crossing;

ENG 4—The Banker Floodway spillway structure; and

ENG 5—Anzalduas Dam.

The single water resource located within the Mission Levee project area is the Edinburg intake channel connected to the lower Rio Grande.

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Construction Approaches 4.3.4

The need for levee footprint expansion will be reduced and/or eliminated by incorporation of a floodwall and/or levee slope adjustment, where possible, when warranted for engineering considerations or space limitations. Best management practices during construction would include the use of sediment barriers and soil wetting to minimize erosion and dust.

Structural Design Features 4.4

General 4.4.1

The project consists of construction of approximately 160 ft of new floodwall with an integrated steel bollard wall and the modification of an existing partially constructed gatewell drainage structure to improve flood control measures at the site. The structural criteria outlined in this section are the basis for analysis and design of these flood control improvements. The criteria describe the structural systems and constituent components; list material properties; identify the governing design codes and technical references with which the designs shall comply; and present the design load cases for the structural and foundation analyses and designs.

The floodwall designed for the project consists of a continuous inverted T-wall with a concrete retaining wall stem and concrete base slab that are supported by concrete drilled shaft deep foundations. Analysis, design, and detailing of these structures follow the United States Army Corps of Engineer Manuals.

Concrete Design 4.4.2

The design of reinforced concrete structures requires that factored design strength equals or exceeds the factored loads imparted on structures per EM 1110-2-2104.

The strength reduction and load factors used in the design of conventionally reinforced concrete structures are in accordance with the American Concrete Institute (ACI) Building Code Requirements for Structural Concrete (ACI 318-08), except the strength reduction factor () for shear. Strength reduction factor values for design are 0.85 for shear and 0.90 for bending. Load factor values contained in the ACI Code are modified by the strength requirements for reinforced concrete hydraulic structures listed in EM 110-2-2104 (including Change 1). The Single Load Factor Method is used, which includes a load factor of 1.7 for both shear and moment design.

Due to the relatively infrequent nature of flooding in the area and unlikelihood of persistent water head at the concrete floodwall structures, a hydraulic factor of 1.0 is used for the design of these members. Allowable overstress values for individual load combinations are applied to the factored loads for design. In general, the specified 28-day compressive strength for concrete (f'c) is 4,000 psi for all structures.

Reinforcing Steel 4.4.3

Reinforcing steel conforms to ASTM A 615/A 615 M, Gr. 60, fy = 60 ksi. Per EM 1110-2-2104, the maximum flexural reinforcing requirement is 0.375 ρb. Minimum flexural requirements for reinforcing are based on ACI 318-08. Temperature and shrinkage requirements are per EM

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1110-2-2104, which specifies the total area of reinforcement in both faces must be equal to or greater than the product of 0.0028 times the gross cross-sectional area of the section. Clear concrete cover provided will be as required in ACI 318 and EM 1110-2-2104.

Steel Design Criteria 4.4.4

Steel design shall utilize EM 1110-2-2105, the allowable strength design portion of the American Institute of Steel Construction Manual, 13th edition and the Allowable Stress Design Construction Manual. Load combinations shall be in accordance with EM 1110-2-2105.

Commonly specified steels are as follows, unless otherwise noted:

Plates: ASTM A572, Grade 50;

Bolts and nuts: ASTM A325, min. 3/4 inch; ASTM A490;

Anchor Bolts: F1554, Grade 55;

Corrosion stainless steel: ASTM A304 (freshwater); ASTM A316 (saltwater);

Sheet Piles: ASTM A572, Grade 50; and

Stainless Steel Embedded Anchors: ASTM A276 or UNS S21800.

Generally, components that will be exposed to the elements will be either hot-dipped galvanized or primed, painted, and sealed with epoxy coating (10 mils min).

Loads 4.4.5

4.4.5.1 General Loading

Dead loads were determined in accordance with applicable engineering manuals and American Society of Civil Engineers…