Page 1
At Grades: The argument for
removing the barriers
2013 AOWMA Convention
and Trade Show
Edmonton, Alberta
February 23, 2013
Erin Motz
Angus Chu, Civil Engineering, U of C
Edwin Cey, Cathy Ryan, Geosciences, U of C
Noorellah Juma, U of A
Alf Durnie, Alberta Municipal Affairs
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Infiltration from an irrigation furrow into an initially dry soil.
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Purpose of Research
• Test the ability of an at-grade to treat
secondary treated wastewater effluent
• Provide guidance to Municipal Affairs
(At-grades in SOP)
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Woodchip LayerNo Erosion Protection @ 3:1 SlopeErosion Protection @ 2:1 Slope
Native Soil Infiltration Area
Effluent Application Area LFH LayerLFH Layer
Centre to Left Centre to RightDistance Between Chambers
Leng
th o
f At_
Grade
=
D
esign
Flow
Linea
r Loa
ding
Rate
Each Chamber RowMust be Eqivalent Width
Surface Area Under Chambers Must Be A Minimum Of80% Of Effluent Application Area
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Design 2007 Design 2002 Design
Orifice Spacing (ft) 2 3
Cover 2.25 ft chamber 8” half pipe
Loading (gal/day) 92 (1.84 gal/linear ft) 127 (2.53 gal/linear
ft)
Length (ft) 50 50
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Location
Tank
2007 Design
2002 Design
Location
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Training Day
July 3 2008
5 ft Squirt height!
• Instructions by Lew Shaw
• Thanks to Keith and Lesley for
organizing
Lunch
by
Keith
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• Installing Aquaworks pressure transducer
• Electrical connection by Tom (FCTP)
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Sampling Equipment and
Testing
Lysimeter
• Major ions
• Nutrients
• Coliform and E. coli
• BOD
• Soil Water Pressure
• Volumetric Water Content
• Electrical Conductivity
• pH
• Temperature
• Gases
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Gas
• Soil Vapor Probe - sample soil gases
– O2, CO2, N2, methane
• Tensiometer – measures soil matric potential (water pressure)
Tensiometer
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Chloride
Chloride is an excellent tracer
Week 1
Week 3
Week 7
Preliminary Results
Effluent reaches 5 ft
after 3 weeks
Most soil
concentrations now
similar to effluent
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• Non-detectable nitrate in effluent, but increasing in areas of low initial nitrate
• High ammonia in effluent (42mg/l) but less than 5 mg/l in soil
• Nearly full nitrification
Nutrients
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Volumetric Water Content
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
19:12 0:00 4:48 9:36 14:24 19:12 0:00 4:48Time
VW
C (
%)
2007 Under
2007 Between
2002 Under
2002 Between
Dec 10
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
19:12 0:00 4:48 9:36 14:24 19:12 0:00 4:48
Time
VW
C (
%)
2007 Under
2007 Between
2002 Under
2002 Between
Nov 11
• Soil under 2007 lateral maintains a lower water content
• Initially a greater distinction between under and
between orifices, but begins to balance out.
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Bacteria
• Fecal Coliform
• Total Coliform
• E. coli
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Gas
• Declining oxygen at
surface
• Increasing carbon
dioxide and nitrogen
at surface
• Change in trend with
declining
temperature
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Destructive Sampling
Dec 31, 2008
Uncovered last 10 ft of
each lateral
Excavated parallel to
lateral in 6 inch sections
Collected samples for
analysis
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2007
• Horizontal
emergence: 60
cm
• Visible depth
under lateral:
120 cm
2002
• Horizontal
emergence: 75
cm
• Visible depth
under lateral:
>160 cm
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123
Water, Air, & Soil Pollution
An International Journal of
Environmental Pollution
ISSN 0049-6979
Water Air Soil Pollut
DOI 10.1007/s11270-011-0901-y
Vadose Zone Microbial Transport Below
At-Grade Distribution of Wastewater
Effluent
Erin C. Motz, Edwin Cey, M. Cathy Ryan
& Angus Chu
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At-grade distribution of
secondary treated wastewater
appears to be a viable
alternative to conventional
distribution fields at sites
with similar climate and soils.
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• At-grade systems provide several advantages, including increasing the
size of the effective treatment zone above low permeability layers or
shallow water tables, increasing exposure to atmospheric oxygen in
the treatment zone, and reducing landscape disturbance that allows for
use in otherwise inaccessible areas (e.g., forested sites).
• The application of wastewater to the soil surface, however, also
presents a risk of incomplete treatment of several constituents.
•
• Although various forms of at-grades have been operational for over
20 years, detailed monitoring of treatment performance for many of
these systems is limited and newer designs (such as that proposed in
this study) have not been investigated.
• There are particular concerns over at- grade treatment efficacy in
colder regions because many of the biochemical transformation
processes are temperature dependent.
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• Chemical breakthrough times, geophysical monitoring and soil
dye patterns all demonstrated relatively uniform effluent
distribution in the subsurface.
• Infiltration below the at-grade was affected by capillary-driven
lateral flows, and the resulting increased fluid residence times and
increased potential for soil-atmosphere gas exchange contributed
to enhanced biochemical treatment of nutrients in the soil.
• The at-grade OWTS loaded effluent directly to the soil surface,
which allowed for enhanced treatment in the highly biologically
and chemically active zone near surface
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• Due to the temperate climate of the field site, large fluctuations in air
temperature strongly affected soil temperatures and microbial activity
below the at-grade.
• The treatment capacity of nutrients below the at-grade OWTS in this
study was highly dependent on soil temperature, with warmer
temperatures and the subsequent biomat formation providing greater
potential for inorganic nitrogen removal, and also potentially
influencing phosphate mobilization.
• Overall, the at-grade system demonstrated sufficient nutrient treatment
performance to make it a viable alternative to a traditional trenched
systems under the environmental conditions evaluated. However, it
should be noted that long term monitoring is recommended to confirm
the adequacy of at-grade system performance through time.
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Percent Soil Moisture
Orthophosphate (mg/L in soil)
Fecal Coliform (cfu/ml of soil
water)
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At Grade Draft SOP
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Acknowledgments
Lew Shaw
Clayton Foster
Daniel Morris
Jesse Berry
Chad Brooking
Alf Durnie
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Questions?
Winners of the
Husband of the
year award
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Thank You Any Questions?
Government employees really do work!!!
Where is your PPE?