Trash Capture HydraulicsOvercoming Hydraulic Head Issues

APWA ConferenceNovember 9, 2017

Agenda

Introduction &

NPDES Permits

Large Scale

Devices

Small Scale

Devices

Lifecycle and

Construction Cost

Large Scale

Hydraulics

SF Bay MRP and State Trash Amendments

Trash in the Bay Area is governed by the Municipal Regional Permit

Section C.10

100% capture of baseline by 2022

Trash throughout the rest of Northern California is governed by the

State Trash Amendments

100% Capture of baseline in 10-years

2009 MRP Trash

Begins

2014 MRP 40% Goal

2016 MRP 60% Goal

2017 MRP 70% Goal

2018 State Trash

Begins

2019 MRP 80% Goal

2022 MRP 100% Goal

2030 State 100% Goal

FTC versus Equivalency

100% Capture can be Full Trash Capture (FTC) or Equivalency

FTC = 5mm particle collection for 1-year, 1-hour storm event

Equivalency = combination of institutional controls and FTC with on-going assessment

and documentation that Full Capture System Equivalency (FCSE) is met

Benefits of FTC

Equivalency not guaranteed in future

Assessments may not always come up clean

Jurisdictional Control Credits may vary

Proving equivalency has high City staff cost

Wind Storm Water Dumping

Trash in Receiving

Water

Small Scale FTC Devices

Device Types

Connector Pipe Screens

Inside Inlet

Partial Capture ARS

Inlet Filters

On-top of inlet

Requires filter replacement

+ Quick to install

Custom design for non-standard inlets

Contingent on GIS accuracy

City ROW won’t treat private systems

- Hydraulic Impacts

Localized flooding when clogged or broken

Maintenance and Replacement

Limits on parking

Frequent (3+/year) cleanings

Shorter lifecyle

StormTek Connector Pipe Screen

Large Scale FTC Devices - Nets

Device Options

Netting

StormTrap [FreshCreek] TrashTrap

OldCastle [Kristar] Net Tech

FreshCreek – In-Line TrashTrapFreshCreek – End-of-Pipe TrashTrapOldCastle Net Tech

Large Scale FTC Devices –Hydrodynamic Separation

Device Options

Hydrodynamic Separation

Nutrient Separating Baffle Box (NSBB)

Contech CDS

Oldcastle [Kristar] DVS

Others under approval

BioClean – Nutrient Separating Baffle Box NSBBContech - CDS Oldcastle - DVS

BioClean NSBB – Solana Beach

Large Scale FTC Devices - Screens

Device Options

Screening

Roscoe Moss StormFlo

Coanda

Coanda Screens

Roscoe Moss – Storm Flo

Livermore Project Example

Large Scale FTC Head Loss

All devices, even off-line, have head loss

Upstream impacts depend on:

System slope

Depth

Capacity

Tailwater

Model in SDMP model for upstream flooding impacts

Understand device internal bypass capacity and losses

Work with manufacturers

Double check assumptions and head loss results

Consider tidal influence and sea level rise

Consider City CIP

Draining to a pump station has special hydraulic concerns

Large Scale FTC Head Loss

1-year 1-hour Storm Event

Use NOAA precipitation estimates for storm intensity at the Site

Example: Downtown Livermore 1-yr, 1-hr intensity is 0.3 in/hr

Smaller watersheds with shorter times of concentration the 1-yr can

sometimes be close to a 10-year peak event

Example: Livermore Downtown 10-year, 15-min intensity is 0.29 in/hr

Model flow to the device to

determine the actual 1-year,

1-hour peak flow rate

Modeling can reduce

overdesign and cost

Rational Method highly

conservative over 200 acres

Large vs. Small FTC Cost Comparison

Compare Capital vs. Maintenance Costs

Issue: Life time costs for Maintenance are VERY HIGH

Large Devices (high Capital vs low Maintenance)

Small Devices (low Capital vs high Maintenance)

Large Full Trash Capture Cost

Avoid!

Utility relocations

Easement or property acquisition; private property

Environmental permitting and mitigation

Constructing access roads

Extremely deep systems & shoring

Anticipate

Excavation and shoring costs; minimize footprint and system depth

Diversion structures

Traffic control on busy roads for construction and maintenance

Cast-in-place = Time; Pre-cast = Crane

Questions?