WND for Site Visit 022124.pptx

February 2024 Whittier Narrows Dam Safety Modification Project pre-bid conference and site visit

Contract overview Agenda Pre-Construction Services USACE Construction Offices Power Improvements

Technical requirements for the base are in 01 11 00 (with references to the Draft technical specs)

The Optional items are the remainder of the tech specs

STOP 1

STOP 2

STOP 3

STOP 4

STOP 5

STOP 6

START

FINISH

Project Location: the Los Angeles Basin

How does the dam fit in the overall LA flood protection system?

Whittier Narrows Dam Overview

West Embankment Central Embankment East Embankment Rio Hondo Outlet Capacity >75,000 cfs

N San Gabriel River Channel Capacity = 13,100 cfs

San Gabriel River Spillway Capacity = 276,000 cfs Rio Hondo Channel Capacity = 40,000 cfs Crossover Channel Crossover Weir

Typical X-Section

The dam is used primarily for flood control and is typically dry.

The earth embankment consists of 3 embankments (west, central, east).

The max cross section (55 feet) is in the west embankment. The ht of the embankment decreases to the east (typically ~40’ high in the central emb; less east of spillway). The emb terminates at ground surface elevation 234. This was the original PMF; a flood above that elevation would flank the dam.

There are two local rivers that drain into the basin: the Rio Hondo and the SGR.

There are two control structures as shown: the Rio Hondo Outlet (invert at 183 NGVD29) and the SGR spillway (invert at 200 NGVD29) .

Summarize operation: On SGR side, releases are normally limited to 500 cfs. SGR pools above 208 will result in flow over the weir and into the Rio Hondo side. During storms, SGR releases up to 5,000 cfs are typical, though temporary releases of up 12,000 cfs are permitted provided downstream capacity will not be exceeded. When the pool exceeds elevation 228.5 feet NGVD, the spillway gates begin automatic operation; channel capacity (approximately 13,100 cfs) would be exceeded before pool elevation 229 and downstream flooding would begin. The spillway discharges will reach 276,000 cfs when the pool is at the top of the dam.

[I usually emphasize that the spillway capacity is 20x channel capacity] The outlet works is capable of discharging over 75,000 cfs at top of dam, though channel capacity is only 40k cfs.

The embankment is a zoned earth embankment. The central impervious core consists primarily of CL; the shells consist of low fine content SM. The blanket drain on the d/s consists of SW’s and SP’s mined from the river. There is an existing toe drain and relief wells 26’ d/s. The RW’s are 8” CMP, 50’ deep, 50 oc on west emb and 100 oc on central and east emb’s.

The foundation is alluvial – not on hard rock

Introduction: failure modes Internal Erosion in the Foundation Overtopping

We are modifying the dam to address two “potential failure modes.”

Internal erosion in the foundation and overtopping

Modification Overview

The purpose for this contract is to address these failure modes discussed above.

We’re doing that with a combination of foundation modifications, embankment raises, and slope hardening.

We’ll get into that in more detail below, but while there are many benefits to using an IDaC contracting method, the primary reason is due to the number of impacts on other facilities and the need for the contractor on board who can and will interact with those agencies during the modification.

Contract overview Base Bid Pre-Construction Services USACE Construction Offices Power Improvements Optional Items Construct Whittier Narrows Dam Safety Modifications Construct Swale Construct Trench Drain Sta. 23+20 to Sta. 28+30 Construct Trench Drain Sta. 31+50 to Sta. 42+00 Construct Surface Chimney Filters Construct Lincoln Avenue Bike and Equestrian Trails Construct San Gabriel River Trail

Contract overview Package Development Not typical ECI Review status Pending Technical Amendment:

Source Selection Quantity updates Lincoln Subsequent Amendments

Before going into anymore detail on the scope, I wanted to discuss where we are wrt:

Package Development Not typical ECI – While ECI packages are typically awarded at 15 to 35%. we’re at 95% Review status – we’ completing our last required review Pending Technical Amendment:

Source Selection (00 22 00). There’s a re-prioritizing of a couple of selection factors and a couple of minor things, but most importantly is a change to the required personnel.

Quantity updates. As the design has matured, we’ve updated quantities.

Lincoln. There is currently a restriction in 01 14 00, prohibiting work on Lincoln between 15 Feb and 15 Aug. We’re lifting that and providing some additional discussion in Section 01 13 00.

Subsequent Amendments TBD following assessment of the last round of review comments

Preconstruction Services and Early Work Items

1. Required Personnel On Site Project Manager Construction Quality Control System Manager Materials Manager Utility Coordinator Others

2. Pre-Construction Services Constructability and Design Reviews:

Constructability evaluation Design conflicts evaluation Quantity evaluation QC review.

Borrow Plan Utility Relocation Plan Construction Schedule

3. USACE Construction Offices

4. Power Improvements

Section 01 11 00 provides project background information, as wells submittal and security requirements.

But the four key things are:

Required personnel.

Pre-Construction Services.

and two Early Work Items:

3. USACE Construction Offices. For the construction of construction offices within the USACE Baseyard

4. Power Improvements. This is to provide the power necessary to operate the pug mills or batch plant at the staging area(s)

This section provides project background and security requirements. But the four key things are:

Required personnel. The E&C team has identified a number of skills that we want to see on the team.

Some are in the source selection (note, there is a pending amendment that will include changes to 00 22 00): On Site Project Manager responsible for construction, the on-site Construction Quality Control System Manager (CQCSM), Lead Materials Manager, and Lead Utility Coordinator.

Unique (or at least unusual): Community Coordination Specialist Pre-Construction Services Constructability and Design Reviews:

Constructability evaluation – Document in a Draft Constructability Report the basis for the schedule and cost estimate. Identify the tools, equipment, methods, techniques, technology, and processes proposed to build each component Design conflicts evaluation – Identify our errors/omissions/ambiguities Quantity Evaluation – We will provide our civil models and we will work together to verify the quantities QC Review - Quality control and documentation is critical for USACE dam safety projects. Review and comment on the testing requirements, data reporting, and data management requirements in the specifications. Working with the USACE team, develop processes and tools to track and compare CQC to QA data.

Borrow Plan Evaluate available data and conduct geotechnical investigations as needed. Identify the borrow sources and quantities from each. Include a mass balance Utility Relocation Plan Coordinate impacted owners. For each utility, the Plan must document the owner, impacts to utility, owner requirements, owner approval processes, and anticipated issues. Develop a schedule showing the timing and sequence of each of impacts Construction Schedule

Typical Sections and Details

We want to spend some time discussing some of the details about how we’re addressing the PFM’s discussed above.

To address the overtopping, we’re either raising the dam (or adding parapets) or hardening the downstream surface with soil cement (aka, hardfill) to prevent erosion leading to failure during overtopping.

To address internal erosion, we’re not preventing seepage, but rather preventing that seepage from carrying particles out that could lead to the development of a pipe and ultimately failure.

Referencing this plan view, we’ve highlighted overtopping sections (purple), trench drain (red), drainage blankets (green), wells (orange), and roads (gold). Parapet walls (pink) are included in several locations but will not be discussed further in this portion but will be touched on in the reach-by-reach discussion.

The light blue indicates potential haul routes that have been coordinated through the NEPA process.

Typical Sections

As we look at the overtopping areas, there are about 10 typical sections. However, most of the key components are relatively consistent.

With each of the typical sections, we’ll have the following components:

Crest re-establishment and hardening Stepped slope face Stilling basin Runout Rock toe Some will have a trench drain; some will include new wells, some both.

Typical Sections and details

Discuss each detail The shape and material requirements are critical to getting achieving the design objectives and I’ll talk about the material requirements in a couple of slides.

Typical crest.

Stilling basin will be 17’ wide, about 2 ft deep. Hardfill about 5 ft thick.

b. Typical Slope: 15” sand, under 15” gravel, under soil cement (hori sectional width of 10’ w/0 regard to the steps). 2’ high steps, 3 ft horizontal portion, 15” of general fill and 9” of topsoil The final shape and strength of the steps is probably the most critical dam safety feature and has been the focus of a large amount of work, including lab tests, large scale model tests.

Typical Sections and details

Discuss each detail

e. General fill/topsoil over 18” of hardfill, over 18” of gravel, over 12” of sand

h. Similar dimensions for the toe

k. – trench drain. Some portions are optional

TRAINING WALLS

Six (five + one) training walls will protect the downstream faces of the “non-overtopping sections” from discharge at the overtopping sections

Lincoln Avenue

INSET MAP

To minimize (not eliminate) impacts to several compensable utilities (i.e., those that have “prior rights”), we’re relocating the road centerline about 70 to the southeast.

A parapet will be built across the existing road at dam centerline

Utilities:

SCE will relocate guy poles. The transmission lines are along the n of existing Lincoln; the guys are on the south SGVWC will move their 32” water line into new Lincoln SoCalGas will relocate and or PiP their 30” line Bike and equestrian trails. There are currently existing bike and equestrian trails on the basin side of the slope. These are not USACE trails. The owning agencies (LA County Dept of Public Works and Parks and Rec) want to restore them, but for a number of reasons, could not get a design into the contract. Section 01 13 00 call for the trails to relocated as you would an existing utility….

lincoln: Typical Section

The road will be relocated to the southeast Parapet wall added to crest Controlled Low Strength Material slurry wall will extend 7 to 8 ft below OG

Rosemead Blvd

INSET MAP

The road will be raised 5-6 ft on the existing centerline and will maintain the same approximate cross section

No major utility issues

Rosemead: Typical Section

Controlled Low Strength Material slurry wall will extend 7 to 8 ft below OG No significant utilities within the road.

Key Specifications: WORK Restrictions

FOR OFFICIAL USE ONLY

Workdays Monday – Friday, deliveries on Saturday Work hours 6 AM to 6 PM Night work on Rosemead with approval Noise/Vibration Comply with local ordinances, monitoring requirements Environmental Seasonal restrictions for clearing within the basin Rosemead Must maintain 4 lanes of traffic open (limited exceptions)

Key Specifications: WORK Restrictions

FOR OFFICIAL USE ONLY

Dam Safety General Dewatering General – groundwater, variable but typically below limit of required excavation Wet season (11/15 to 4/15)– Excavations limited to what can be backfilled in 24 hours Reach 3 specific – “deep” excavation prohibited during wet season Crest degradation Limit crest excavations during the wet season to what can be backfilled in 24 hours

General The purpose of this project is to reduce the risk to the downstream communities due to dam failure.

Everything will be view through that perspective.

Emergency plans will be required and work will be constrained

(Note: Reach 3, is between Lincoln and Rio Hondo)

Santa Fe Dam Borrow Sites Whittier Narrows Dam Google Earth Construction considerations: Borrow AREAS

SFD Basin Borrow Area SFD Stockpile Borrow Area

The pre-approved borrow source is the Santa Fe Dam basin.

This was the material that was used for our lab testing and physical models A lot of information about this source is in the Geotechnical Data Report, posted on SAMS

Two sources within that basin:

Stockpile (from clean outs and spreading ground construction) The Basin The best material is located in the active channel.

We anticipate that, should borrow need to occur during the wet season, diversion systems will need to be established

Optional Items

FOR OFFICIAL USE ONLY

Optional Items Construct Whittier Narrows Dam Safety Modifications Construct Swale Construct Trench Drain Sta. 23+20 to Sta. 28+30 Construct Trench Drain Sta. 31+50 to Sta. 42+00 Construct Surface Chimney Filters

Want to quickly identify where the options are and what we’re doing

Construct Swale Optional Items

Visible from Stop 5.

This is an option while we are getting the RE. High level of confidence that will happen Replacing the northern side slope and channel invert with sand/gravel/riprap

Construct Trench Drain Sta. 23+20 to Sta. 28+30

Optional Items

Construct Trench Drain Sta. 31+50 to Sta. 42+00

Visible from Stop 5.

This is an option because it achieves risk reduction exceeding the project objectives.

Surface Chimney Filters

These optional surface chimney filters are added in several areas to make the design more robust. This is an option because it achieves risk reduction exceeding the project objectives.

We have these at 5 locations:

At Lincoln and the west embankment Between about sta 48 and 50 – note that this is buried and has a different section than the others (as shown in the Rosemead Plans) Between sta 61 and 66+40 Between sta 115 and 118 Between sta 123 and 127

Discussed previously. Visible at stop 4

This trail would be removed if the Surface Chimney Filter option is awarded. Similar to the Lincoln trails, this is not a USACE facility. The owning agencies (LA County Dept of Public Works and Parks and Rec) do want to restore them, but for a number of reasons, could not get a design into the contract. Section 01 13 00 call for the trails to relocated as you would an existing utility….

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