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A Fairfax County, VA, publication

Department of Public Works and Environmental ServicesWorking for You!

Let’s Talk PrioritizationAPWA Mid-Atlantic Chapter Conference May 3, 2018

December 14, 2017

Let’s Talk Prioritization

Stormwater/Maintenance and Stormwater Management Division

Agenda

• Background• Fairfax Stormwater Likelihood of Failure• Fairfax Stormwater Consequence of Failure• Things to Look out for• Scoring/Ranking• What Next?

2


Who am I

• Engineer at Fairfax County Stormwater Maintenance• Working with Prioritization/Asset Management for three years• Primarily worked with Stormwater Pipe Prioritization but

dabbled in Sanitary Pipe Prioritization• Attended Prioritization Presentations for:

– Stormwater Pipe– Sanitary Sewer Pipe– Water Lines– Pump Stations – Ponds

3

Fairfax County Stormwater Pipe Prioritization Program


Fairfax County – Prioritization Background

• Program was solely complaint driven• Started CCTV in 2009

– 950+ out of 1300 miles complete– Provides internal condition of pipes

• NASSCO PACP grading system allows capability to rank– Ranks pipe defects by structural score– Reviewed highest ranked pipes, added proactive projects to the Work

Plan

• Started to create a Prioritization system, using a consultant– Likelihood of Failure (LOF) parameters– Consequence of Failure (COF) parameters

• Currently Refining LOF and COF Parameters

4

- Engineers

- Project Managers

- Senior Management


Fairfax County - Background - Staff Workshop

• May 2017• Staff from varied aspects participated

‒ Customer Service – call takers‒ Complaint Technicians‒ Maintenance Professionals

• Two Agencies Represented

• Surveyed participants prior to workshop– Typical problems– History of complaints they hear about or see

• Consultant developed initial parameters• Fairfax team vetted, expanded, refined and ranked the parameters

5

- Stormwater MSMD - CAP (Wastewater)




Likelihood of Failure

9 LoF Parameters:• PACP Structural QuickScore• Joint Defects• PACP Operation and Maintenance (O&M) QuickScore• Hydraulic Capacity• Pipe Material• Installation Date• Cover Depth/Surface Features• Groundwater Level• Soil Type

6




• PACP Structural QuickScoreThe Structural QS represents the severity and quantity of defects in a pipe. Severe defects are assigned higher grades.

Need to complete CCTV of entire storm conveyance network.

• Pipe Joint DefectsOffset/separated joints are a major problem in storm pipes, but the PACP grade is not adequate to depict their severity.

Need to complete CCTV of entire storm conveyance network and identify pipes with joint defects

• PACP Operation and Maintenance (O&M) QuickScoreO&M defects can also cause structural failure. O&M allows us to prioritize cleaning.

Need to complete CCTV of entire storm conveyance network and identify pipes with O&M defects

7




• Hydraulic CapacityIf a pipe is unable to contain a 10-year storm causing nuisance flooding or doesn’t have Overland Relief, it is considered a failed pipe.

Need to determine drainage area to each pipe. Need to confirm pipe dimensions.

• Pipe MaterialSome materials are more susceptible to damage or accelerated deterioration.

Need to update GIS with pipe material, including renewed pipe.

• Installation DateSome deterioration is expected to occur as a pipe ages.

Use easement dates to estimate the age.

8

Need to determine what you consider failure.

Under capacity may cause flooding but may not

cause damage to the pipe


Age of Pipes

9Stormwater/Maintenance and Stormwater Management Division




The following parameters were identified as affecting LoF. However, they are more constant parameters that may not

change with repair or rehabilitation.

• Cover Depth/Surface FeaturesPipes are more susceptible to damage when in shallow circumstances.

Need to determine pipe depths.

• Groundwater LevelGroundwater fluctuations can displace surrounding soil, and affect load capacity.

Need to determine groundwater depths around pipes.

• Soil TypeSoil properties can affect pipe settlement and damage.

10



Consequence of Failure

5 CoF Parameters:• Potential Damage to Critical Facilities• Pipe Flow Rate• Population Density• Site Accessibility• Water Quality Impacts

11




• Potential Damage to Critical FacilitiesPipe failure near critical facilities could create problems that impact loss of life or emergency response.

Need to determine where pipes are located relative to the critical facilities.

• Pipe Flow RateA pipe with greater flow will have more displaced water should it fail.

Need to update pipe dimensions and slope.

• Population DensityThe surrounding population density may indicate the number of people impacted or the magnitude of property loss caused by a potential pipe failure.

12


Choosing Scoring Ranges

13

y = 261.14e-0.19x

0

50

100

150

200

250

300

350

400

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 26 28 29 33 37 47 54

Freq

uenc

y

Population Density(people/acre)

Frequencies of Population Densities

Notes: Densities rounded up to a whole numberAreas delineated by subwatershed boundaries




• Site AccessibilityPipes that are more difficult to access could require more time and effort to repair when they fail.

Need to determine surrounding conditions, such as topography, buildings, foundations, pipe depth, to access each pipe.

• Water Quality ImpactsA failed pipe could transport surrounding contaminants into a protected area

Determining non-natural contaminant sources

14


Parameters should be based on your own circumstances

What type of asset? Where is it located? What are the geographic circumstances

• Stormwater tends to be shallow– Less focus on crossing utilities since they tend to be below our system

• Less contaminants than sewer pipes– Typically less sever environmental impacts when failure occurs

• VDoT in Fairfax owns the stormwater pipe under the road.– Our focus is less road damage more residential damage

15


Building up Data

• Baby Steps– What data do you have?– What can you get? How fast can you get it?– Are there interim steps that can be taken?

We have people walking grids to do above ground inspections. We can add a section of site accessibility to their forms.

16

Site Accessibility

Have Need

GIS layers• Buildings• Tree cover• Contours• Roads• Some invert depths

Where the pipe is relative to buildings?What is the density of nearby trees?What is the depth through the length of the pipe


Things to look for

• Same Data but Opposing Parameters

If looking at the parameters on an individual basis, this could be helpful.

17

Depth

Cost – Accessibility Likelihood – Damage

The deeper the pipe is the more expensive it will be to fix

Deep pipes would have a more critical score

The more shallow a pipe is the more damage it will receive from live loads

Deep pipes would have a less condition score


Things to look for

• “Double Dipping”

18

Holes

PACP Quick Score Cave-in – Joint and Hole

Holes have a Score of 5.If a hole is coded in a pipe it will automatically be within the highest score range.

If a Hole is coded in a pipe it will be given the highest score

Cave-ins can be caused by joints and holes. If there is a hole or a large joint offset it is within the highest score range.

If a Hole is coded in a pipe it will be given the highest score

Unconnected Joints do not have the capability of getting a PACP score of 5, but they cause

major problems in out Stormwater pipes

…But what about joints?



Scoring – Ex. Refining: Pipe Diameter/Capacity

19

Date GroupScore

1 2 3 3.1 4 5

10/16 Consultant

The pipe is measured or

determined to be less than 24-inches

in diameter

N/A

The Pipe is measured or determined to be grater than or equal to 24-

inches and less than or equal to 42-inches in diameter

X N/A

The pipe is measured or determine to be greater

than 42-inches in diameter

3/17 ConsultantThe pipe capacity is determine to be less than 22 cfs (14 mgd)

N/A

The pipe capacity is determine to be greater than or equal to 22 cfs (14

mgd) and less than or equal to 67 cfs(44 mgd)

X N/AThe pipe capacity is

determine to be greater than 67 cfs (44 mgd)

5/17 Consultant < 22 cfs N/A 67 cfs ≥ capacity ≥ 22 cfs X N/A >67 cfs

7/17 Consultant

< 22 cfs - basis is range of 15" to 24"

dia. Pipes with scouring velocity at

7 ft/sec

N/A67 cfs ≥ capacity ≥ 22 cfs - basis is

range of > 24" dia. To 42" dia, scouring velocity at 7 ft/sec

Unknown pipe diameter N/A

> 67 cfs; basis is range of > 42" dia. Pipe with scouring

velocity at 7 ft/sec

11/17 Fairfax* Qmax < 2.5 cfs N/A 2.5 cfs ≤ Qmax ≤ 25.1 cfsUnknown

pipe diameter or slope

N/A Qmax >25.1 cfs

* data based on PFM 2 ft/s



Scoring

• Scoring Range 1-5 (good – critical) used– Range 1-3 does not differentiate the conditions enough– Range 1-10 is an acceptable alternative and differentiates parameters

more successfully, complicates with more choices• 1-5 keeps it simple as we form and we can see if it doesn’t differentiate

adequately

Unknown Information :Any Parameter with no knowledge is scored as 3.1

20



Scoring - Calculating Final Score for Ranking

• Likelihood of Failure– Uses highest scored parameter

• Can dilute information for critical condition pipes• If it has failed in one category, it’s failing

– Should there be a count of the scores? Should those with multiple parameters with a score of 5 be elevated

• Consequence of Failure– Parameters are weighted based on perceived criticality – Balances all the different impacts

21



Ranking - Weighting for CoF

Workshop initial estimate:

• 46% Potential Damage to Critical Facilities• 25% Pipe Flow Rate• 15% Population Density• 12% Site Accessibility• 2% Water Quality Impacts

If something is only at 2% is it worth keeping?Fine-tuning will be needed once the final parameters are defined and refined.

22

What’s important to you? Stormwater doesn’t have as much

risk as sanitary.


Weighting

• Watch when you Weight multiple times

23

Criticality Category

Category Weight Parameter Parameter

Weight Final Weighting

Level of Service 40%

Option #1 40% 16%

Option #2 60% 24%

Environment 40%Option #3 30% 12%

Option #4 70% 28%

Cost 20%

Option #5 20% 4%

Option #6 45% 9%

Option #7 35% 7%

Is 4% really worth keeping?



Ranking - Problems with Calculated Risk

• ‘Risk’ = LoF x CoF• ‘Risk’ is a very linear way of looking at pipes.

– Which pipe is worked on first vs. How should we handle this pipe

• It can dilute information and decrease ability to find the correct pipes to rehab

24

A pipe in fair condition will be looked at for rehabilitation

before a pipe in critical condition

18.35

11.85

10.329.66

9.33

8.48

7.727.14

5.95.43

4.92

4.163.77

2.712.18

Like

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Ranking - Calculated Risk Graph

25

18.35

11.85

10.329.669.33

8.487.72

7.14

5.95.43

4.924.16

3.77

2.712.18

1

25

1 25

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Ranking - Prioritization Table

26

Like

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5

4

3

2

1

0 1 2 3 4 5



What Next?

• Planning– What information are we deficient in?– Cost of obtaining that information– Weighting CoF Parameters once defined

• Implement– Test Parameters– Evaluate Results

• Differentiation• Matrix Definitions

– Adjustments• Parameters• Weighting• Matrix

27

Additional Information

For additional information, please contact

www.fairfaxcounty.gov/dpwes

Stormwater Pipe Prioritization Program

Stormwater/Maintenance and Stormwater Management Division 28

Amy Linderman

703-877-2872

[email protected]



Condition Assessment Progress

29

0.8% 1.2% 1.5% 2.5%1.7% 2.4% 3.1% 4.1%

9.6%14.7%

19.2%22.8%

28.6%

37.9%

40.5%

42.0%

0.7%

0.8%

0.9%

1.0%58.6%

43.0%

34.9%27.5%

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

7/1/14 7/1/15 7/1/16 7/1/2017

Structural

Additional Review Required Failed or Failing Minor Defects Good Rehabbed Not Assessed Yet


Quick Score Delineation

30

Rehabbed1%

000037%

1000-1z005%

2000-2z1z7%

3000-3z2z12%

4000-4z3z1%

5000-5z4z4%

Additional Review Required 2%

Need to CCTV31%

Based on data from July 2017



Diameter of Pipes in System

31Stormwater/Maintenance and Stormwater Management Division



Scoring - LoF

32

Likelihood of FailureScore

Parameter 1 2 3 3.1 4 5

1 PACP Structural QS

No defects or like new, Structural QS = 0000

Minor defects, Structural QS 100 to 3100 Structural QS 300 to 4100 No information on

pipe condition Structural QS 4100 to 5100 Abandoned survey or Structural QS =/> 5100

2 Joint and Hole Defects No visible joint defects

Joint infiltration stains verified to be without joint

seals

Any separated joint or hole with infiltration stains and >1 cave-in

complaint

Any separated joint or hole with active infiltration, >3

cave-in complaints

Any offset/misaligned joint or hole with active infiltration, > 6

cave-in complaints

3 PACP O&M QuickScore

Pipe is clear or O&M QS is 0000 to 2100

Sediment, debris or roots present, or O&M QS is 2100

to 3100

>10% of the cross-sectional area is blocked, flushing or root cutting is

required more than once/yr, or O&M QS is 3100 to 4100

O&M QS of 4100 to 5100Cross bores or intrusions (pipe break-ins) present or O&M QS

is 5100 or greater

4 Hydraulic Capacity

Pipe can adequately convey the 10-yr storm and sufficient OLR exists

Pipe cannot adequately convey the 10-yr storm and OLR is sufficient

Pipe capacity is unknown

Pipe can adequately convey the 10-yr storm and works

with OLR

Pipe cannot adequately convey the 10-yr storm and OLR does

not exist

5 Pipe Material

Reinforced Concrete (RCP) or rehabilitated

with structural integrity (ex. CIPPL)

Non-Reinforced Concrete or rehabilitated with non-

structural integrity (ex. Slip-line or coated)

Masonry block, brick or clay Unknown Corrugated Metal (CMP) or High Density Polyethylene

(HDPE)

6 Installation Date

Installed or renewed after 1995 1984 through 1995 1974 through 1983 Unknown 1961 through 1973 Before 1961

7Cover Depth/ Surface Features

Average cover is greater than 8 feet

Average cover is between 2 feet and 8 feet, and lies only under an unpaved

area or sidewalk

Average cover is between 2 feet and 8 feet, and lies partially under a roadway

or building

Pipe cover depth or type is unknown

Average cover is 2 feet or less and lies only under an

unpaved area or sidewalk

Average cover is 2 feet or less and at least partially lies under

a roadway, driveway or building

8 Groundwater level

Groundwater level stays below the pipe invert

Groundwater level remains above the pipe invert and below the pipe crown

Unknown groundwater level

Groundwater level fluctuates from above the pipe crown to

below the pipe invert

9 Soil Type Sand or Gravel Unknown or classified as Urban

Acidic/corrosive, Silt, Loam or Marine Clay



Scoring - CoF

33

Consequence of FailureScore

Parameter 1 2 3 3.1 4 5

A

Potential Damage to Critical Facilities

Failure would cause minimal or no property

damage

Failure may cause erosion or temporary yard flooding

Non-Critical - Failure would cause damage to transit, park & ride, or

transportation facilities

Degree of failure damage is unknown

Essential - Failure would cause damage to dwellings, government buildings

Critical - Failure would cause damage to a fire or police

station, sanitary sewer pump station, electrical sub-station,

hospital or health center

B Pipe Flow Rate Qmax < 2.5 cfs Capacity 2.5 cfs through 25.1 cfs Pipe size or slope is unknown Q max > 25.1 cfs

C Population Density

Pipe lies in area of 0-25 persons per acre



Population density is unknown


Pipe lies in area of 101 or more persons per acre

D Site Accessibility

Equipment access is through an easily

accessible right-of-way or easement

Equipment access is through County property or

an easily accessible road right-of-way

Equipment access is through County property, without a cleared accessway.

Access may involve tree removal or installation of construction

entrances/roads

Equipment access may involve: removing fences,

sheds or other semi-permanent structure: cutting

trees or installation of temporary construction

entrances/ roads; obtaining permission over private or

non-Co property

Pipe is located behind/under permanent structures/buildings

with no equipment access. Building foundations are close

to easements. Accesswayscontain steep slopes or utility

obstructions.

E Water Quality Impacts

> 200 feet from a BMP, floodplain, wetland or Resource Protection

Area, and containment of contamination within

or nearby the asset exists

> 200 feet from a BMP, floodplain, wetland or

Resource Protection Area and containment of

contamination within or nearby the asset not

available

<200 feet from a BMP, floodplain, wetland or Resource Protection Area

If an incident that causes water-borne contaminants or

sedimentation cannot be contained by natural or

constructed features, would potentially contribute to water

quality impairment

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