geoflow subsurface drip dispersal · geoflow subsurface drip dispersal systems in freezing...

Geoflow Subsurface Drip Dispersal Systems in freezing conditions2011 WCOWMA Conference

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Subsurface Drip Dispersal

Introduction to SDD design for cold climates

FREEZING CONDITIONS

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Agenda

Cold climate experience and research

Design concepts for cold climate

Example system

Further design concepts

Questions and discussion

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What is SDD?

Application of effluent by drip emitters 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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Dose Mode

When WASTEFLOW PC is pressurized,

the rubber diaphragm flexes across

the compensating chamber to regulate

flow regardless of pressure variances

Each dripper has a filter built in at the entry port.

Effluent travels through a turbulent flow path

that helps keep any fine particles from settling inside the dripper. And slows theflow until flow is laminar at discharge

WASTEFLOW ClassicFlow 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.

WASTEFLOW PC = pressure compensatingGives same output flow even if emitters are at different levels

Drip emitters PC emitters usually have lower flow rates

PC = Pressure compensating

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Water movement from emitter

Subsurface drip Surface drip

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Typical Sites

If severely constrained for conventional drainfields Depth

Slope

Shape and slope alignment

Size or setbacks

Heavy soils

Sand/gravel soils

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Other typical sites

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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Typical SDD layout

Dose manifold

Shows single lines (not looped)

Dose forcemain

Flush main

Returns to trash tank inlet 8

Air valveAir valve

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SDD IN COLD CLIMATES

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Research and experience since the 1990s 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

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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: Peter Gearing, URS

Auckland, NEW ZEALAND

mailto:[email protected]

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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.

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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 Tel: 707-527-0775

Project overseen by Jack Niblett Tel: 559-692-5340

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NAWE cold climate wetlands

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B.P. Casper, Wyoming. Wetland 3.3mgpd by NAWE


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Shenyang, China vertical flow wetland

SSD used for distribution to reed planted wetland with subdrain discharge

-25 to -30 C in February/March

Improved efficiency 1 sqm/pe vs more normal 2 sqm/pe

6000 person equivalent = 750 cum/day size

Blumberg Engineering and NAWE, 2004

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SDD distribution system

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.

. Minnesota

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.Minnesota

Minnesota

Drip mounds in E. Washington

Cold, dry climate

Type 1 to sand mound

Many systems

Only one freezing issue to date Due to winter startup with cold water

Short term

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BC experience

Prince George

Kelowna

Penticton

Kamloops

No freezing issues even where some conventional systems froze.

Even in cold dry climates

CAREFUL DESIGN AND INSTALLATION

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Research papers on Geoflow website

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

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Soil temperature

Soil temperature measurement in dispersal systems

Temperature found to be higher than ambient

Example Roger Shafer, Colorado Septic tank, textile filter and polishing sand filter

Standard pressure distribution system

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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

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Biological activity and freezing

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

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SDD in frozen soils

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

Soil < 0 C at and also < 0 C 4ʺ below dripline 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 Warm effluent is important

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8 systems monitored in Minnestota, Scott Wallace 7.5 to 60cm cover over dripline

Soil below freezing at dripline Temperature probes and soil cores

Temperature between doses lower than surrounding soil with light loading Heavier loading showed more dose impact

Air valve enclosure design to reduce impact of freezing conditions

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Residential system—light loading

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Elementary school


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Saturation issues

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

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Air circulation on systems with two air valves 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: Single air valve system

Sealed air valve boxes

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What helps SDD to work in frozen soil?

Soil is not saturated 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

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KEY DESIGN CONCEPTS

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Drain back

Drain manifolds and dripline back

Drain rapidly

Any more than 15 mins may freeze Keep it to 10 mins or less

Design and also TEST at commissioning

Make sure forcemains slope properly And are lower than the dripline

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Insulate

Insulate dose and flush forcemains

Even when draining back

Insulate headworks (if not in pump chamber)

Insulate air valves

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Keep the dripline warm

Install with 8ʺ cover minimum.

Consider temporary insulation (peat, sawdust etc) for first year.

Revegetate.

Trap snow.

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Keep the effluent warm

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 (reduce cooling of effluent)

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Special case effluent temperature

Caution with cold water systems Example highway rest area

Caution with startup in winter

Caution with seasonal use systems that get used at Christmas…

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Continuous flush

Do NOT use continuous flush in cold climates

Cools effluent by running it through the field

Reduces treatment performance

And greater risk of freezing

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Soil type

Consider soil drainage

Design for the soil 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 Reduced activity in winter may lead to biomat and

saturation near emitters/line

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Site

Sloping sites are easier Drainage

Frost drainage

South facing best

Steep slope is even better

Tanks below field area preferable

But can use less favorable sites

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Climate

Heavy snow cover insulates

More care where snow is not reliable

Consider microclimate 12ʺ cover where shaded, frost hollows

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Site use—some considerations

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

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AIR VACUUM VALVE DESIGN

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Drainback design—Air valves 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

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Insulated air valve installation

Creates heat island at valve

Valve draws warm air from deep in soil profile

Concept developed from NAWE research

In sealed valve box Polylok riser/lid suitable

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Air valve detail

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Sizing of excavation

Base on void space in drainrock fill

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Sealed, insulated air valve boxes

Less likely to lead to air circulation in situation with more than one air valve

Air is warmer if it does circulate

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Air valve in tank

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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Line slopes down to field

Air valve

FilterNote unions

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Site near Kamloops

Design: Chad Meir and Ian RalstonInstall: John Pavlovich

Drains to tank below field, with small pump to return flows to trash tank.

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SYSTEM EXAMPLE

Summerland system.

Design Karen Halliday and Ian Ralston Install Gary Dicken

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Site and soils

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

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Single air valve design

Sloping dripline

Dose and flush connections with pressure test ports Insulated valve boxes!

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Dripline, sloping from dose to flush

Setback

Headworksand tanks in insulated heat island

Air valve

Second dripline

Flush connections

Dose and flush mains

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Headworks flow paths

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Filter drains to pump discharge orifice

NC Flush valve. Opens to drain system

NO drain valve, open when pump off

Pressure regulator

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DriplineAir valve

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Effective drainback

System drains back completely in less than 8m 30s

Despite small diameter forcemains 1ʺ CTS dose, 3/4ʺ PEX CTS flush

Single air valve design Prevents air circulation

Reduces complexity

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Small diameter forcemains

Reduce recirculation volume

Improve time for pressurization

Better dose uniformity

Lower HAR

Proper scouring

Attached to 2ʺ PVC with access points.

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FURTHER DESIGN CONSIDERATIONS

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Drain back with filter bypass

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 Large orifice for rapid drainage

Too much bypass flow with very high head

Would not have been suitable at Summerland

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From pumpPump with discharge orifice

Bypass loop

Ball Check valve

To field

QuesnellsystemSean Pitcher

Flush valve

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Drainback design—orifice

Allow for orifice flow in pump selection

Make sure the system drains back fast enough

Test drain time at commissioning

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Valves for drainback (incl. flush valve)

Motorized ball valves Model with anti-condensation heater

Solenoid valves do not drain effectively

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Don’t let these end up below water!

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Control panel

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

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Drainback with field below tanks

Use drain tank at base of field to collect water

Send back to trash tank with small pump

Options for draining: 2 motorized valves, dose and flush manifolds

Single motorized valve to drain flush manifold

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2 motorized valves

Quick drainage

Best for lower slope sites

Works with central air valve as well

Higher cost and complexity

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Single motorized valve

Dripline slopes dose to flush

Drain flush manifold with valve, drains dripline also

Dose forcemain and dose manifold drain via orifice at lower tank So they don’t have to drain through the field

Adjust orifice at commissioning

Check pressures with test ports

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Design for maintenance 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 Find it in the snow

Attach dose and flush mains to 2ʺ pipe to allow steam lance defrosting Helps to keep grade for drainage also

Pre-install heat tape at air valves and headworks

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Drainback on low slope sites

NAWE (Scott Wallace) uses system with drainage to low manifolds

Darryl Brizan (Prince George) built one system with air clearing

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Drainback on low slope site—modified from NAWE design

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Recommend using air valve on central manifold (NAWE uses valves on

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Air clearing

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

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Compressor and dripline trenches

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SDD works in cold climates

Careful design and installation

Don’t try to cut corners

For technical support contact: Ian Ralston, Geoflow

250-597-3155

[email protected]

Geoflow website http://www.geoflow.com/

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