Geoflow SDD in Freezing Conditions

Transcription

Geoflow Subsurface Drip Dispersal Systems in freezing conditions
2011 WCOWMA Conference
Geoflow
Subsurface Drip Dispersal
FREEZING CONDITIONS
Introduction to SDD design for cold
climates
Agenda
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Cold climate experience and research
Design concepts for cold climate
Example system
Further design concepts
Questions and discussion
Geoflow
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What is SDD?
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Application of effluent by drip emitters
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Applies water directly into the root zone (6-12
inches deep)
More evapotranspiration
Puts effluent in the most biologically active soil
zone
Keeps soil drier for better treatment and
greater horizontal dispersal
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Geoflow
Drip emitters
PC emitters usually have lower flow rates
Each dripper has a filter
built in at the entry port.
Dose Mode
When WASTEFLOW PC is pressurized,
the rubber diaphragm flexes across
the compensating chamber to regulate
flow regardless of pressure variances
WASTEFLOW Classic
Flow varies with pressure
Flush Mode.
As the pump is powered on and
again powered off, system pressure
relaxes across the exit hole
enabling the dripper to
self flush every cycle.
Effluent travels through a turbulent flow path
that helps keep any fine particles from
settling inside the dripper. And slows the
flow until flow is laminar at discharge
PC = Pressure
compensating
WASTEFLOW PC = pressure compensating
Geoflow
Gives same output flow even if emitters are at different levels
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Water movement from emitter
Subsurface drip
Surface drip
Geoflow
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Typical Sites
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If severely constrained for conventional
drainfields
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Depth
Slope
Shape and slope alignment
Size or setbacks
Heavy soils
Sand/gravel soils
Geoflow
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Other typical sites
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Where site or ecosystem impact must be
reduced
Where in soil treatment must be
maximized
Where irrigation/reuse is a priority
For cost savings on large systems
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Geoflow
Typical SDD layout
Air valve
Shows single lines (not looped)
Air valve
Dose manifold
Dose forcemain
Flush main
Returns to trash tank inlet
Geoflow
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Geoflow
SDD IN COLD CLIMATES
Geoflow
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Research and experience since the
1990s
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Wisconsin—Bohrer and Converse
Minnestota—Scott Wallace, NAWE
Wetland applications (various)—NAWE
New Zealand—Peter Gearing, URS
Colorado and Utah high altitude systems
BC (Southern Interior, Prince George)
Eastern Washington state (Scott Jones)
Small, medium and large systems
Geoflow
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Large Systems under Freezing Conditions
Aluminum Smelter (Invercargill, NZ)
Disposing 78,000 gallons of human effluent per day over
12.35 acres.
Installed May 1998
Consulting Engineer:
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Peter Gearing, URS
Auckland, NEW ZEALAND
mailto:peter_gearing@urscorp.com
Geoflow
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Yosemite West (Yosemite National Park)
115,000 gpd – about 260 homes.
Steep wooded slope down to a fragile
stream which is monitored by Fish &
Game.
Reference: Matt Freeman, DPW, Maricopa
County, California.
Geoflow
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Tenaya Lodge (Fish Camp, CA)
Installed Summer 2000.
Slope in excess of 50% at the top of the section.
20,000 gpd.
Designed by: Summit Engineering
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Tel: 707-527-0775
Project overseen by Jack Niblett
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Tel: 559-692-5340
Geoflow
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NAWE cold climate wetlands
B.P. Casper, Wyoming. Wetland 3.3mgpd by
NAWE
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Shenyang, China vertical flow wetland
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SSD used for distribution to reed planted
wetland with subdrain discharge
-25 to -30 C in February/March
Improved efficiency
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1 sqm/pe vs more normal 2 sqm/pe
6000 person equivalent = 750 cum/day size
Blumberg Engineering and NAWE, 2004
Images: Blumberg Engineering.
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Geoflow
SDD distribution system
Geoflow
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Geoflow
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Minnesota
Geoflow
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Minnesota
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Minnesota
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Drip mounds in E. Washington
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Cold, dry climate
Type 1 to sand mound
Many systems
Only one freezing issue to date
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Due to winter startup with cold water
Short term
Geoflow
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BC experience
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Prince George
Kelowna
Penticton
Kamloops
No freezing issues
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even where some conventional systems froze.
Even in cold dry climates
CAREFUL DESIGN AND INSTALLATION
Geoflow
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Research papers on Geoflow website
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http://www.geoflow.com/research_w.html
Drip Distribution Soil Performance and
Operations in a Northern Climate by R.
Bohrer
Bohrer Thesis
Design & Performance of Drip Dispersal
Systems in Freezing Environments by S.D.
Wallace
Geoflow
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Soil temperature
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Soil temperature measurement in dispersal
systems
Temperature found to be higher than ambient
Example Roger Shafer, Colorado
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Septic tank, textile filter and polishing sand filter
Standard pressure distribution system
Use of a Recirculating Textile Filter followed by a Polishing Sand Filter for Onsite Wastewater Treatment in
Colorado’s Fractured Bedrock Environment Roger J. Shafer, P.E., Fractured Rock Aquifers 2002 conference,
Denver Colorado, 2002
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Sand filter temperature maintains above freezing at 1
inch below surface
Geoflow
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Biological activity and freezing
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Bernhart research (Ontario)
Opinion that biologically active, aerobic
systems keep warmer
And have higher winter evaporation from soil
This favors use of Type 1 effluent
Geoflow
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SDD in frozen soils
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Bohrer and Converse paper and others
SDD lines in soil that is below freezing point
SDD still functions
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Bohrer and Converse
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Soil < 0 C at and also < 0 C 4ʺ below dripline
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Temperatures as low as – 12 C in soil observed
Ice crystals found in soil cores, but pores still
open
Effluent dosing does warm the soil
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Warm effluent is important
Geoflow
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8 systems monitored in Minnestota,
Scott Wallace
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7.5 to 60cm cover over dripline
Soil below freezing at dripline
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Temperature between doses lower than
surrounding soil with light loading
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Temperature probes and soil cores
Heavier loading showed more dose impact
Air valve enclosure design to reduce impact
of freezing conditions
Geoflow
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Residential system—light loading
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Elementary school
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Saturation issues
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Installation error led to standing water in
dripline at the school in January 2000
Field froze due to high water in tank backing
up into dripline
Geoflow
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Air circulation on systems with two air
valves
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Scott Wallace’s paper shows soil at dripline
to be cooler between doses than surrounding
soils
Theorizes this is due to air circulation
Effluent warming soil only supported for
heavier loadings
Consider:
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Single air valve system
Sealed air valve boxes
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What helps SDD to work in frozen
soil?
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Soil is not saturated
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Larger pores are not clogged with ice crystals
Small doses do not lead to clogging
Water has short distance to travel vertically to
non frozen soil
Some frozen water will sublimate
Dripline and manifolds drained down between
doses—design and installation is critical
Geoflow
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Geoflow
KEY DESIGN CONCEPTS
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Drain back
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Drain manifolds and dripline back
Drain rapidly
Any more than 15 mins may freeze
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Keep it to 10 mins or less
Design and also TEST at commissioning
Make sure forcemains slope properly
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And are lower than the dripline
Geoflow
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Insulate
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Insulate dose and flush forcemains
Even when draining back
Insulate headworks (if not in pump chamber)
Insulate air valves
Geoflow
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Keep the dripline warm
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Install with 8ʺ cover minimum.
Consider temporary insulation (peat, sawdust
etc) for first year.
Revegetate.
Trap snow.
Geoflow
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Keep the effluent warm
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Insulate lid of tanks and riser lids
Create heat island by extending insulation
laterally
Try to get heat island next to house
Use treatment that keeps effluent warmer
Type 1 is warmest
Keep draining volumes low
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(reduce cooling of effluent)
Geoflow
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Special case effluent temperature
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Caution with cold water systems
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Example highway rest area
Caution with startup in winter
Caution with seasonal use systems that get
used at Christmas…
Geoflow
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Continuous flush
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Do NOT use continuous flush in cold climates
Cools effluent by running it through the field
Reduces treatment performance
And greater risk of freezing
Geoflow
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Soil type
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Consider soil drainage
Design for the soil
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Do not allow saturation around emitters
Do not allow water to drain along driplines
Do not damage soils at installation!
Do not use Type 1 in low permeability soils
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Reduced activity in winter may lead to biomat and
saturation near emitters/line
Geoflow
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Site
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Sloping sites are easier
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Drainage
Frost drainage
South facing best
Steep slope is even better
Tanks below field area preferable
But can use less favorable sites
Geoflow
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Climate
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Heavy snow cover insulates
More care where snow is not reliable
Consider microclimate
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12ʺ cover where shaded, frost hollows
Geoflow
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Site use—some considerations
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Keep people off the field in the winter
Do not compact or remove the snow
Try to trap snow
Deep vegetation or forest cover preferable
Do not compact soils
Geoflow
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Geoflow
AIR VACUUM VALVE DESIGN
Geoflow
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Drainback design—Air valves
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SDD systems need to draw air from air
vacuum valves when draining
Caution not to allow cold air to circulate
through valves and pipes
Risk of air valves freezing and either leaking
or not allowing air back in for drain down.
Prefer to draw warmer air into air valve
Air valves are most likely part of system to
freeze
Try to keep it to one or two valves
Regular inspection of air valves
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Insulated air valve installation
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Creates heat island at valve
Valve draws warm air from deep in soil profile
Concept developed from NAWE research
In sealed valve box
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Polylok riser/lid suitable
Geoflow
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Geoflow
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Air valve detail
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Sizing of excavation
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Base on void space in drainrock fill
Geoflow
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Sealed, insulated air valve boxes
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Less likely to lead to air circulation in situation
with more than one air valve
Air is warmer if it does circulate
Geoflow
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Air valve in tank
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Can install air valve in pump chamber
With filter headworks
Site specific (tank above field)
Will need to drain the manifolds and line to a
secondary tank lower down
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Geoflow
Line slopes
down to field
Air valve
Filter
Note unions
Geoflow
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Site near Kamloops
Design: Chad Meir and
Ian Ralston
Install: John Pavlovich
Drains to tank below
field, with small pump
to return flows to trash
tank.
Geoflow
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Geoflow
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Geoflow
Summerland system.
Design Karen Halliday and Ian Ralston Install Gary Dicken
SYSTEM EXAMPLE
Geoflow
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Site and soils
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Steeply sloping site
Slope 40 – 50%, slope to SW
Soil Silt Loam BK/2, sl hard. Perk. 34 mins.
Shallow soil over shale
Constrained soil area
Geoflow
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Single air valve design
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Sloping dripline
Dose and flush connections with pressure
test ports
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Insulated valve boxes!
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Geoflow
Flush
connections
Air valve
Dripline,
sloping from
dose to flush
Second
dripline
Setback
Dose and
flush mains
Headworks
and tanks in
insulated
heat island
Geoflow
Flush and
dose
connections
with
pressure
test ports 60
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Headworks flow paths
Geoflow
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NO drain
valve, open
when
pump off
Filter drains
to pump
discharge
orifice
Pressure
regulator
Geoflow
NC Flush
valve.
Opens to
drain
system 62
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Air valve
Dripline
Geoflow
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Effective drainback
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System drains back completely in less than
8m 30s
Despite small diameter forcemains
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1ʺ CTS dose, 3/4ʺ PEX CTS flush
Single air valve design
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Prevents air circulation
Reduces complexity
Geoflow
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Small diameter forcemains
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Reduce recirculation volume
Improve time for pressurization
Better dose uniformity
Lower HAR
Proper scouring
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Attached to 2ʺ PVC with access points.
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Geoflow
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Geoflow
FURTHER DESIGN
CONSIDERATIONS
Geoflow
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Drain back with filter bypass
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Instead of using drain valve
Use a loop around filter with check valve and
drain back to pump discharge orifice
OK if head is not too high
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Large orifice for rapid drainage
Too much bypass flow with very high head
Would not have been suitable at Summerland
Geoflow
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Bypass
loop
Ball Check
valve
From pump
Pump with
discharge
orifice
To field
Flush valve
Geoflow
Quesnell
system
Sean
Pitcher 68
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Drainback design—orifice
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Allow for orifice flow in pump selection
Make sure the system drains back fast
enough
Test drain time at commissioning
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Geoflow
Valves for drainback (incl. flush valve)
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Motorized ball valves
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Model with anti-condensation heater
Solenoid valves do not drain effectively
Don’t let these end
up below water!
Geoflow
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Control panel
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Must allow for control of drainback and flush
drain back
Must be able to power motorized ball valves
(24VAC)
Do not use continuous flush systems
Geoflow
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Drainback with field below tanks
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Use drain tank at base of field to collect water
Send back to trash tank with small pump
Options for draining:
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2 motorized valves, dose and flush manifolds
Single motorized valve to drain flush manifold
Geoflow
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2 motorized valves
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Quick drainage
Best for lower slope sites
Works with central air valve as well
Higher cost and complexity
Geoflow
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Single motorized valve
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Dripline slopes dose to flush
Drain flush manifold with valve, drains
dripline also
Dose forcemain and dose manifold drain via
orifice at lower tank
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So they don’t have to drain through the field
Adjust orifice at commissioning
Check pressures with test ports
Geoflow
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Design for maintenance
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All pressure regulating valves accessible
Ensure can measure pressure at end of
dripfield (to make sure it isnt frozen)
Steel pin at air valve boxes
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Attach dose and flush mains to 2ʺ pipe to
allow steam lance defrosting
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Find it in the snow
Helps to keep grade for drainage also
Pre-install heat tape at air valves and
headworks
Geoflow
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Drainback on low slope sites
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NAWE (Scott Wallace) uses system with
drainage to low manifolds
Darryl Brizan (Prince George) built one
system with air clearing
Geoflow
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Drainback on low slope site—modified from
NAWE design
Recommend using air
valve on central manifold
(NAWE uses valves on
Geoflow manifolds)
dose and flush
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Air clearing
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Small diaphragm blower used to clear lines
between doses
Blower in heated basement
Continuous flush system
Sawdust (few inches) for first season
insulation
No freezing issues seen
Geoflow
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Geoflow
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Compressor and dripline trenches
Geoflow
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SDD works in cold climates
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Careful design and installation
Don’t try to cut corners
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For technical support contact:
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Ian Ralston, Geoflow
250-597-3155
Onsite@traxdev.com
Geoflow website http://www.geoflow.com/
Geoflow
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Geoflow SDD in Freezing Conditions

Transcription

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