PRINCETON FORCE MAIN

CONDITION ASSESSMENT

PROJECT

SAM BOARD PRESENTATION - MAY 11, 2020

PRESENTATION OUTLINE1. Purpose

2. Condition assessment team

3. Overview of Princeton Force Main

4. Methodology

5. Hydraulic assessment

6. Geologic assessment

7. External inspection process

8. Metal thickness test results

9. Soil and groundwater test results

10. Recommendations

11. Questions/discussion

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PURPOSE

• Assure reliability for next 60 years

• Determine current condition of the force main

• Proactively determine if the force main presents a risk of failure

• Settlement requirement with Ecological Rights Foundation Consent Decree

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CONDITION ASSESSMENT

TEAM

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Participant Role

SAM Operations and Collection System staff Pump station and force main operations, project

oversight, spill mitigation in emergency

SRT Consultants, San Francisco, CA Engineer of record, planning, logistics, coordination,

reporting

BAGG Engineers, San Jose, CA Logistics, planning, UT testing, soil and groundwater

sampling and analysis

Andrieni Brothers, Half Moon Bay, CA Permitting, construction support, utility locating, traffic

control, pit excavation, shoring, pipe coating

restoration, backfilling, and paving

Pipeline Inspection and Condition Analysis

Corporation (PICA)

Electromagnetic scanning, data processing, and

reporting

Ductile Iron Pipe Research Association (DIPRA) Technical assistance, observation, and guidance

OVERVIEW OF PRINCETON FORCE MAIN

• 8 inch diameter

• Ductile iron

• Age: 41 years

• Installed in 1979

• Part of the IPS

• Length: 4,200’

• Depth: +/- 4’-0”

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METHODOLOGY• Hydraulic Assessment

• Desk top model was developed in WaterCAD to assess pressure and velocity as various flow rates

• Geology and Seismicity Assessment

• Desktop study to determine geologic risks due to earthquake, faults, and liquefaction

• Force Main Alignment and Appurtenances Inspection

• Visual inspection of force main alignment

• Visual inspection of surge chamber, air release valves, and blow offs

• Non-Intrusive Pipe Wall Thickness Inspection

• Ultrasonic pipe wall thickness testing

• Electromagnetic pipe wall thickness testing

• Pipeline Subsurface Inspection

• Soil sampling and analysis

• Groundwater sampling and analysis

Removing a segment of the pipeline for internal inspection was considered but not performed because the

capacity of the Princeton PS wet well is too small to accommodate regular flow and drain back of the force main

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HYDRAULIC ASSESSMENT

Princeton Force Main

- Hydraulic modeling shows that the

force main is constantly pressurized

and there is no local high or low

points

- Hydrogen sulfide gas is not likely to

accumulate except at the high point

(connection to Montara Force Main)

- Two ARVs are installed along the

force main alignment

- One at California Avenue and Yale Avenue

- One at the high point, Princeton’s connection

to Montara Force Main

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GEOLOGY AND SEISMICITY ASSESSMENTGeology Assessment

- Site is underlain by sand and gravel deposited on uplifted marine-abrasion

platform along the coast

Seismicity Assessment

- No earthquake faults crosses the force main alignment

- Probability of major earthquake is relatively low

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FaultApproximate Distance to Site

(km)1Location with Respect to

Site

Probability of Mw>= 6.7

within 30 Years2

Hayward – Rodgers Creek 39 NE 32%

Hayward (SE Extension) 39 NE 8%

Calaveras 53 NE 25%

Monte Vista – Shannon 28 SE 1%

San Andreas (Entire) 10 NE 33%

San Andreas (Peninsula) 10 NE 9%

San Gregorio 0.3 SW 5%

SURFACE INSPECTION

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Princeton Pump Station

Surge Tank

Princeton Pump Station Pig

Launching Station

Princeton Force Main Air

Release Valve at California

and Yale Avenue

Princeton Force Main Air

Release Valve at connection

to Montara Force Main

EXTERNAL INSPECTION PROCESS

• Locate pipeline

• Excavate test pits (three total)

• Clean exposed pipe

• Wire brush scale and bituminous coating

• Perform ultrasonic thickness testing

• Perform electromagnetic testing

• Sample groundwater and send to lab for analysis

• Sample soil and send to lab for analysis

• Backfill and pavement restoration

• Conducted March 9, 10, and 11, 2020

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METAL THICKNESSClass 52 ductile iron pipe thickness for an 8-inch pipe is expected to be 0.33 inches

Manufacturing tolerance is +/- 0.05 inches

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Ultrasonic Thickness Testing

Electromagnetic

Scanning using

Bracelet Probe

ULTRASONIC AND ELECTROMAGNETIC

THICKNESS TESTING RESULTS

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Location No. Location (inches)* UT High Readings

by PICA (inches)

UT Low Readings

by PICA (inches)

Wall Loss UT Readings by BAGG

(inches)

1 (14.5, 0.0) 0.258 0.220 22% - 33% 0.248-0.261

2 (24.0, 0.0) 0.289 0.240 12% - 27% 0.252-0.259

3 (21.0, 10.0) 0.265 0.221 20% - 33% 0.251-0.253

4 (36.0, 0.0) 0.261 0.246 21% - 25% 0.259-0.261

Test Pit 1:

Location

No.

Location

(inches)*

UT High Readings

by PICA (inches)

UT Low Readings

by PICA (inches)

Wall Loss UT Readings by BAGG

(inches)

Bell Side

1 (2.2, 0.0) 0.280 0.222 15% - 33% 0.237 – 0.267

2 (11.0, 0.0) 0.250 0.168 24% - 49% 0.195 – 0.253

3 (15.0, 0.0) 0.263 0.243 26% - 28% 0.195 – 0.265

Spigot Side

4 (0.0, 0.0) 0.276 0.276 16% 0.230 – 0.303

5 (11.0, 0.0) 0.240 0.217 27% - 34% N/A

Test Pit 2:

ULTRASONIC AND ELECTROMAGNETIC

THICKNESS TESTING RESULTS CONTINUED

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Location

No.

Location

(inches)*

UT High Readings by

PICA (inches)

UT Low Readings by

PICA (inches)Wall Loss

UT Readings by BAGG

(inches)

1 (6.0, 0.0) 0.268 0.255 18% - 23% 0.266 – 0.267

2 (15.0, 0.0) 0.267 0.200 19% - 39% 0.205 – 0.277

3 (24.0, 10.0) 0.274 0.196 17% - 41% 0.220 – 0.248

Test Pit 3:

SOIL AND GROUNDWATER

SAMPLING

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Force Main Subsurface Profile in Test Pit 1 Groundwater in Test Pit 2

SOIL ANALYTICS

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Soil Resistivity (ohm-cm) Degree of Corrosivity0-500 Very High

500-1,000 High

1,000-2,000 Moderate

2,000-10,000 Mild

Above 10,000 Negligible

Correlation between soil resistivity and degree of corrosion

Correlation between soil pH and degree of corrosion

pH Degree of Corrosivity

< 5.5 High

5.5 – 6.5 Moderate

6.5 – 7.5 Neutral

> 7.5 Negligible

SOIL ANALYTICS CONTINUED

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Sulfate concentration (ppm) Degree of Corrosivity

> 2,000 Severe

1,000 – 2,000 Moderate

< 1,000 Negligible

Sulfate: Sulfate ion concentration and degree of corrosivity of soil

Chlorides: Chloride concentration and degree of corrosivity of soil

Chloride concentration (ppm) Degree of Corrosivity

> 5,000 High

1,500 – 5,000 Moderate

500 - 1,500 Mild

100 – 500 Threshold

< 100 Negligible

SOIL SAMPLING RESULTS

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Analysis/Test

Test Pit 1 Test Pit 2 Test Pit 3

Corrosion

PotentialTP-1-1 @

2.25 ft

TP-1-2 @

5 ft

TP-1-4

@ 5 ft

TP-2-1 @

2.25 ft

TP-2-2 @

4.75 ft

TP-3-1

@ 3 ft

TP-3-2 @

5 ft

Resistivity @100%

Saturation (ohm-cm)3,795 9,070 9,255 1,566 3,147 3,374 3,808 Mild

pH 7.2 7.5 5.4 7.8 7.5 7.9 7.6Neutral to

negligible

ORP (Redox) (mV) 506 526 400 520 536 421 507

Chloride (mg/Kg) 23 8 32 29 22 12 21 Negligible

Sulfate (mg/Kg) 147 65 106 29 83 63 76 Negligible

Sulfide (Qualitative

by Lead)Negative Negative Negative Negative Negative Negative Negative

Moisture Content

(%)14.6 16.6 9.9 23.1 20.6 14.2 11.8

GROUNDWATER RESULTS

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Analysis/Test

Test Pit 1 Test Pit 2 Test Pit 3

Corrosion Potential

TP-1-3 @ 5 ft TP-2-3 @ 4.75 ft TP-3-3 @ 5 ft

Resistivity (ohm-cm) 4,633 1,754 1,361 Moderate to mild

pH 7.3 7.2 7.2 Neutral

Chloride (mg/Kg) 41 84 159 Negligible

Sulfate (mg/Kg) 21 56 112 Negligible

CONCLUSIONS

• The Princeton Force Main appears to be in good condition and does not pose a threat of failure

• The pressure rating of the Force Main far exceeds the normal working pressure

• No hydraulic anomalies were observed

• There are no observed surface indications that the Force Main is leaking

• No development or other utilities are jeopardizing the Force Main

• No faults or geologic hazards pose a threat to the Force Main

• Soil and groundwater surrounding the Force Main are not corrosively aggressive

• Metal loss is moderate and does not pose of risk of failure

• There is no reason to believe the Force Main will have any less than a 100-year service life which is expected of a ductile iron pipeline

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RECOMMENDATIONS

• Perform similar inspection in 10 years

• Air release valves and blow off should be on a regular maintenance schedule

• Replace deteriorated surge tank at Princeton Pump Station

• Replace the other ARV on the force main alignment

• Install emergency bypass capability at Princeton Pump Station

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QUESTIONS &

DISCUSSION

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