www.tetratech.com

Felix Belanger, P.E. August 26, 2013

US EPA Region 6 CMOM Workshop

PresenterPresentation NotesIt’s a pleasure to be here. I’d like to consider with you today the topic of SSOs.

While I’ll be using the term SSO, by it today, I mean wet weather SSOs, not dry weather SSOs; and the solutions we discuss will primarily apply to wet weather SSOs, though there may be some applicability to dry weather SSOs as well.

• When you’ve finished the projects in your Consent Decree? • When you’ve eliminated all your current SSOs? • Will you need an I&I abatement program??? SYSTEM DEGRADATION !!

NEW SSOs ??

• How will you prioritize I&I abatement after you’ve completed your existing programs and solved your existing

SSOs?

• We all experience SSOs.

• Typically reactive solutions

• At risk for Consent Orders and fines

• Is it possible to be proactive?

PresenterPresentation NotesWhat about SSOs??

SSOs are a very common problem. I have yet to run into a community with separated sewers that doesn’t experience them, and if there is such a community they’re probably not represented here today!

And when they occur we take remedial action. However, we usually do so only after we begin to experience SSOs, or worse, after we find ourselves negotiating with the state regulators or the EPA.

Let’s look at mid-sized community in the region. Their problem will sound very much like your problems.

• Tulsa, Oklahoma • SSO Avoidance Strategy

• Concepts

• Implementation Status

PresenterPresentation NotesTo summarize.

SewerTown is serious about effectively managing its collection system and bringing it’s SSOs under control.The Strategic level processes are designed to keep SSOs from developing, but if they do, The Tactical level processes provide for aggressive response and accountability toward solving the problem.

The Strategic and Tactical level tools that have been developed will help them work toward that goal. This is a new initiative for them and undoubtedly changes will be

• Population: 400,000 • 2,025 miles of sanitary sewer • 60 pump stations • 4 WWTPs • Annual rainfall: 40 inches

• Two Consent Decrees 1990 - 2005

2008 - 2013

• Spent $300 M+ on collection system improvements addressing wet weather SSOs

• After first CD some 20-year old SSOs were still occurring Reduced frequency – but not eliminated

New SSOs at new locations

• Unfortunately, this is not uncommon!

PresenterPresentation NotesSewerTown is a mid-sized city with a sewered population of about ½ a million people.

They received their first collection system Consent Decree in the early 1990s and embarked upon a 15 year program to address SSOs. About 5 years ago they received a 2nd Consent Decree.

In all, over 20 years they’ve spent over $300 million on their collection system, and an additional $200 million on their treatment system.

Recently, it was brought to their attention that about 1/3 of the SSOs that were listed in their first Consent Decree had reoccurred in the past 5 years.

PresenterPresentation NotesTulsa’s Consent Order program began in 1990 and was completed in 2005.Everything seemed to be going well until 2007 and 2008, when they experienced heavy spring rains, and a large number of SSOs. These rains were less than a 2-year event, but because they had so many rain events, they had tremendous soil saturation and elevated flows due to groundwater saturation, such that there was no more available storage in the ground.

Transition from a reactive mode of I&I Abatement to a proactive mode of I&I Abatement by understanding and tracking changes in the system's wet weather performance anticipating and preempting new SSOs

PresenterPresentation NotesOf course that raised a lot of eyebrows, caused quite a bit of consternation, and got them asking some very good questions.

Review the questions.

You don’t have to have had the same experience to want to have a better solution.

They asked us to help them develop questions to these answers.

Reappearance of old “solved” wet weather SSOs

Appearance of new wet weather SSOs

Ongoing system degradation

PresenterPresentation NotesThe SSO challenge faces both technical issues and managerial problems.

First, I&I response is not linear. Twice as much rain might produce 2, 3, 4, or more times as much I&I. Thus, the less intense, but much more common rains may not give you the information you need to solve the problem.

Second, rainfall patterns are different from year to year and the year that you’re doing your study you may only experience the lighter, less intense rainfalls.

Now let’s compound this by introducing a Consent Decree schedule that requires you to move forward with a solution, whether truly adequate or not, and it’s easy to see how some of the solutions that are implemented don’t solve the problem the first time around.

Lastly, we often get so caught up with managing the details of the engineering and construction processes that we lose focus on the ultimate goal, which is to eliminate SSOs.

These issues are familiar to most of you, so we won’t go examine them in detail here. Let’s turn to the solutions tha

Strategic Level Processes

Wet weather surcharging

Wet weather I&I rates

Flow monitoring

•52 Permanent flow monitors

•2,025 miles of pipe

•Average basin size - 200,000 lf/meter

Rainfall data

•Gauge Adjusted Radar Rainfall (GARR)

•1km x 1km resolution

•Provides 623 rainfall profiles over the collection system

•Supported by 40 permanent rain gauges

PresenterPresentation NotesHere are the tools that SewerTown is using as part of its Strategic Level process.

• 52 permanent flow monitors • Additional meters in current SSES areas • Add new meters in at risk areas • Evaluating use of manhole depth monitors

PresenterPresentation NotesSemi annually, the flow and rainfall data will be reviewed and the system response in each flow monitoring basin will be calculated.

• Visit critical locations after significant rainfall Historical SSO Locations

Susceptible locations based on hydraulic model

Evaluating use of manhole depth monitors

• Classify surcharging severity Depth/severity of surcharging

Evaluate cause

• Localized overloading

• Systemwide overloading

• Overview of 8 RDII Prediction Methods (WERF 1999) Constant unit rate Percentage of rainfall Percentage of stream flow Synthetic unit hydrograph Probabilistic method Rainfall/flow regression method Streamflow regression method Methods embedded in hydraulic models

“Using Flow Prediction Technologies to Control Sanitary Sewer Overflows” Water Environment Research

Foundation, Project 97—CTS-8, 1999

For any particular storm:

R = % of the total rainfall that appears in the sanitary flow R = I&I Volume / Rainfall Volume I&I Volume = Wet Weather flow - Dry Weather Flow Rainfall Volume = Rainfall depth X Basin area

Uses readily available data Flow meter data GARR rain data Hydraulic model subcatchment

definitions

Does not require model calibration or recalibration Not affected by basin size, geometry, or surcharging.

• R Value Calculated for every significant storm

Tracked from year to year

Currently have 3 years of data ( 2011 -2013 )

PresenterPresentation NotesThe first step is to establish benchmarks. The benchmarks will be established for every flow monitoring basin. As time goes on, current data will be compared to the benchmark and degradation or improvement calculated.

The rainfall coefficient – R – is used extensively and is a common measure of a system’s leakiness.It is expressed as a percentage of rainfall that makes its way into the collection system.

The inflow coefficient – I – is a measure that SewerTown has used for a number of years. It’s a measure of the peak inflow response at the design storm event.

Compare changes in R value over time

Normalize for variation

Soil moisture

Rainfall intensity

Rainfall duration

PresenterPresentation NotesAnd the current I&I response in every basin will be compared to the benchmark for that basin.

• Proactive Approach Will allow Tulsa to initiate action before SSOs occur

Evaluate surcharging at each storm event

Continually monitor and track improvement and degradation in I&I

rates using the R value

• Developing relationship curves between R and rainfall. Rainfall intensity

Rainfall duration

Soil moisture/saturation

• Analysis and interpretation of surcharge data Extent of surcharging / backwater

Timing of surcharge events relative to rainfall occurrence

PresenterPresentation NotesSewerTown is currently in the early stages of implementation and undoubtedly the processes will change as time goes on.As they do, we hope that Raj will allow us to provide updates at future CMOM conferences.

Thank you

Questions??

SSO Avoidance Strategies – Year 2!What will you do next??How do we deal with SSOs?OverviewTulsa, OklahomaTulsa, OklahomaTulsa SSO HistoryTulsa I&I HistoryTulsa's Goals Why???Strategic Level ProcessesTracking System PerformanceTools / Data neededSlide Number 14Slide Number 15Wet Weather Surcharging AnalysisSlide Number 17Slide Number 18SSO MonitoringSurcharging AnalysisI&I Rate AnalysisMeasuring I&I ContributionPercentage of RainfallAdvantages of R-Value MethodologyMeasuring I&I ContributionSlide Number 26Evaluate I&I responseDocumenting PerformanceSlide Number 29Slide Number 30SummaryTasks for the coming yearQuestions??