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

Infiltration from an irrigation furrow into an initially dry soil.

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)

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

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

Location

Tank

2007 Design

2002 Design

Location

Training Day

July 3 2008

5 ft Squirt height!

• Instructions by Lew Shaw

• Thanks to Keith and Lesley for

organizing

Lunch

by

Keith

• Installing Aquaworks pressure transducer

• Electrical connection by Tom (FCTP)

Sampling Equipment and

Testing

Lysimeter

• Major ions

• Nutrients

• Coliform and E. coli

• BOD

• Soil Water Pressure

• Volumetric Water Content

• Electrical Conductivity

• pH

• Temperature

• Gases

Gas

• Soil Vapor Probe - sample soil gases

– O2, CO2, N2, methane

• Tensiometer – measures soil matric potential (water pressure)

Tensiometer

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

• 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

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.

Bacteria

• Fecal Coliform

• Total Coliform

• E. coli

Gas

• Declining oxygen at

surface

• Increasing carbon

dioxide and nitrogen

at surface

• Change in trend with

declining

temperature

Destructive Sampling

Dec 31, 2008

Uncovered last 10 ft of

each lateral

Excavated parallel to

lateral in 6 inch sections

Collected samples for

analysis

2007

• Horizontal

emergence: 60

cm

• Visible depth

under lateral:

120 cm

2002

• Horizontal

emergence: 75

cm

• Visible depth

under lateral:

>160 cm

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

At-grade distribution of

secondary treated wastewater

appears to be a viable

alternative to conventional

distribution fields at sites

with similar climate and soils.

• 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.

• 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

• 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.

Percent Soil Moisture

Orthophosphate (mg/L in soil)

Fecal Coliform (cfu/ml of soil

water)

At Grade Draft SOP

Acknowledgments

Lew Shaw

Clayton Foster

Daniel Morris

Jesse Berry

Chad Brooking

Alf Durnie

Questions?

Winners of the

Husband of the

year award

Thank You Any Questions?

Government employees really do work!!!

Where is your PPE?