Geotechnical Studies and Trenchless Planning For EBMUD’s Orinda Water Treatment Plant Disinfection Improvements Project

Justin Reeves, PE – McMillen Jacobs Associates Jeff Bandy, PE – East Bay Municipal Utility District 1897

Introduction and Background • Disinfection Improvements Project • Orinda Water Treatment Plant • Project Elements

– UV/CCB Complex – Yard piping

Geotechnical Studies • Review and research • Site investigation • Below-grade structures Trenchless Planning • Pipe connections • Methods considered

Presentation Outline

• Constructed in 1935 • Over 800,000

customers • Provides >50% of

treated water for EBMUD

• Capacity: – 175 MGD continuous – 200 MGD instantaneous

• In-line filtration via sand and anthracite filters

Orinda Water Treatment Plant

Existing ORWTP Process and Drivers for this Project

Ammonia Orinda WTP

Filters

Coagulant

Aqueducts

Aqueduct Chlorine

In-line filtration: No sedimentation basin

Disinfection upstream of filtration

No clearwell: Claremont Tunnel acts as storage

Claremont Tunnel

Drought + Aqueduct Chlorination = More DBPs

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ppb

Highest Locational Running Annual Average by Quarter

Maximum Level = 80 ppb

• Below-grade UV/CCB complex: 200 MGD low

pressure high output UV system and 1.4 MG chlorine contact basin

• New piping connections: 78- to 108-inch diameter yard piping

• Additional chemical feed and monitoring points • New electrical building and generator house to

support the new system • Modifications to the raw water spillway

OWTP Disinfection Improvements Project

Multiple benefits of selected project: • Maintains gravity flow through plant, adds storage • Multi-barrier disinfection for Giardia (UV) and virus

(CCB) inactivation • Meets regulatory approval: other large (>300 MGD)

UV facilities in California • Cuts DBPs in half by shifting to post-filter

disinfection • Comparable or lower lifecycle costs than other

alternatives • Relatively small footprint

OWTP Disinfection Improvements Project

Site layout and location of UV/CCB facility

8

UV/CCB

Filters

Claremont Tunnel to distribution

Isometric View of UV/CCB

9

1.4 MG CCB: 3 log virus inactivation

200 MGD UV facility: 1 log Giardia inactivation

Influent Effluent

Section View of UV/CCB

Flow path

• UV/CCB complex – 8,500 ft2 footprint – Basement floor 60-feet below grade

• Piping connections – 5 connections to the new complex – 78- to 108-inch diameter

Focus of the Geotechnical Studies

UV/CCB

• (Qoa) Alluvium and alluvial terrace (steam) deposits;

• Clay, sand, gravel, cobbles, and boulders

• (Tor) bedrock • Interbedded claystone,

siltstone, sandstone, and pebble conglomerate

Geotechnical Studies Project Area Geology

Pebble conglomerate (sample depth of 85ft)

• Region subject to ground shaking

• Nearest active fault is the Hayward Fault

California Earthquake Hazards

• Project subject to ground shaking

• 0.70 g (PGA)

No evidence of active faulting

Earthquake Shaking and Faulting

• Site not covered in landslide deposits

• (A) Large ancient landslide was mapped immediately west of the project area. Developed as a golf course and residences.

Slope Stability and Landslide Deposits

N

• Creeks (A) • Railroad (B)

• Previously occupied by

orchards, sheds, and barns

Historic Topographic Maps 1897 1897

N

• District Construction • Lafayette and

Claremont Tunnels • By the late 1920’s

• District garages,

bunkhouses, and offices prior to construction of the existing plant

• Creek once passed through the project area and has been captured within three 12-inch diameter pipelines to San Pablo Creek

Historic Maps 1925

UV/CCB

Historic Aerial Photos

1963 1939

2018 Plan 2010

Project Area Map Geotechnical borings and geophysical surveys

Project Test Borings

Utility potholing

Sonic boring

Test Dewatering Well Drilling

Groundwater Monitoring Wells

Test Boring Samples and Field Testing

Continuous Core Samples

Exposed rock hardness

Groundwater Level Monitoring

Identify Material Transitions

Develop Schematic Boring Profile

• Rock analysis • Site inspection • Seismic refraction

Summary Rock Strength and Rippability

Rippability

• UV/CCB floor slab 60-feet below-grade • Alluvium with cobbles • bedrock

Excavation support • Secant pile, waler, and strut • Provides groundwater cut-off • Can be installed in cobble rich

material • Incorporated structurally as

part of the final basement wall of the UV/CCB complex

Summary of Excavation Support

• Three feasible methods were considered • Open cut installation • Pipe jacking • Hand mined tunnel

Yard Piping Connections Installation Method

Performance Score

Probable Cost ($M)

Hand Mined Tunnel 73% 16.7

Open Cut 73% 10.5

Pipe Jacking 70% 8.2

Abundant below-grade utilities

• Soil with gravel and cobbles • Below the groundwater table • Bedrock

Schematic Pipe Profile

Change-in-Reach ground conditions

Tunneling Reach

Inside Diameter

(in) Length

(ft)

Invert Depth

(ft) UV/CCB Connection

A 78 45 33 Effluent No. 2

B 108 70 38 Combined Effluent No. 1 & 2

C 48 90 25 Connection to Los Altos

Pumping Plant 108 90 25 Connection to Claremont

Tunnel for distribution D 108 50 25

Hand Mined Tunnel

Grouted Canopy Tubes

Hand Mined Tunnel

1961 Effluent No. 2 and Claremont Tunnel Connection

Hand Mined Tunnel

Modern Construction

Open Cut – 1961 Effluent No. 2

Benched trench excavation

Crossing pipe support

Trench shoring

20ft

• (A) UV/CCB structure excavation as Launching Pit to launch three drives

• Thrust block

• (B) Shared Reception and Jacking Pit to launch one drive

• (C) Reception pits and connection to Effluent No. 2 and the Claremont Tunnel

Proposed Pipe Jacking and Connection Shafts

• Vertical faced shield with small sand shelves at a small vertical spacing.

• The sand lies, at its angle of repose, on each shelf as the shield is advanced.

• Shelves can be removed for full face access.

Pipe Jacking

Pumping Test

• Reduce THM’s concentrations • New disinfection process and facility • Initial design and geotechnical investigation • Yard piping installation challenges

Final Design • Data gathering • July 2020 • Construction planned for 2021

Summary and Final Design

• Carollo Engineers

- Tomas Gillogly, Chris Cleveland, Peter von Butcher, and others

• EBMUD – Matt Guihan, Chris Burquez, and others

• MJA – Tom Pennington, Dru Nielson, Mark Lawrence, and others

• Viking, Cascade, and Pitcher Drilling • NorCal Geophysical • JD Corrosion and Cooper Testing • U.S. and California Geologic Service • Exaro Technologies

Acknowledgments & Questions