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?