1

Compost blankets for controlling erosion on construction sites

Trials under Australian Conditions

Compost Australia Seminar Series

‘A New Standard in Erosion Control’

Dr Mark JacksonDepartment of Environment and Conservation NSW

2

Outline

What are compost blankets?

Advantages

Applications

Compost production in Australia

Overseas developments

Barriers to compost blankets

R&D trials by Uni of Western Sydney

Trial results

Siting and design considerations

Source: Rexius Inc.

3

What are compost blankets?

Fine, surface applied compost

Applied with plant/shrub/tree seed, fertiliser and tackifier (optional)

Surface applied via blower (usually) for soil protection and as plant germination layer

Compost usually manufactured from kerbside collected garden organics

M7 Motorway, Blacktown, Sydney

4

What are compost blankets?

Source: US EPA, (2006) and S. McCoy, Texas Commission on Environmental Quality (TECQ), 2005.

+ 5 cm deep compost blanket

+ 1:1 rock slope

+ Pneumatic blower used

+ Austin, Texas, 2002

5

Compost blankets are a potentially better alternative

Conventional soil erosion control techniques

- Hydroseeding (seed, water, dye, fertiliser, tackifier)

- Hydromulching (seed, water, dye, fertiliser, tackifier, straw or fibre)

- Geotextile blankets (US EPA, 2006)

6

Advantages of compost blankets

Provides immediate protection of soil from wind and rain

Reduces sheet and rill erosion by absorbing rainfall

Prevents soil compaction and crusting and facilitates rainfall infiltration

Organic matter improves soil fertility and structure

Source: The Hills Bark Blower / Rexius Inc.

7

Advantages of compost blankets…

- Compost can retain pollutants Heavy metals

Nitrogen

Phosphorus

Oil and grease

Fuel

Herbicides & pesticides

Other potentially hazardous substances from storm water

- Improves downstream water quality

8

Advantages of compost blankets…

Provides a nutrient and organic matter rich soil layer for rapid plant establishment

Plant establishment provides long term erosion control

Highly effective two stage integrated soil erosion control solution

Road cutting stabilisation, Bella Vista, Sydney

9

Applications for compost blankets

Erosion control and vegetation establishment:

- Road construction- Roadside cuttings / slopes

- Road shoulders, verges and medians

- Earth embankments

- Soil stockpiles

- Stream banks / riparian works

- Land sub-divisions

- General civil works

10

Applications for compost blankets

US EPA (2006) recommends:

- Most effective on slopes 1:1 to 4:1

- Control of sheet flow

- Not effective for concentrated flow (e.g. channels / earth drains)

Excellent erosion and sediment control on difficult terrain —including steep, rocky slopes

M7 Motorway, Blacktown, Sydney

11

Compost production in Australia1

Over 3 M tonnes of organics recycled in Australia in 2005

140 commercial composting facilities around the country

Compost markets traditionally domestic and commercial landscaping, horticulture and some agriculture

Council collected garden organics largest feedstock

Industry sold ~ 3.7 M m3 of compost nationally in 2005

1 Compost Australia National Processor Survey (2005).

Survey results for NSW, VIC, SA and WA.

12

Aerial view of a commercial composting facilityANL, Wyong, NSW: 50,000 tpa capacity

Windrow composting

Finished compost

Receival and inspection

Raw material processing

Product blending

Leachate collection /treatment

13

Drivers for developing markets for compost

State Government policies driving recovery of organics from landfill

Major sustainability benefits from organics recycling

Improves sustainability of local environment

- e.g. reduced need for virgin materials in landscaping and construction (e.g. sand, gravel, soil, woodchip, pine bark)

Organics recycling can deliver benefits of ECO$114/tonne when recycled

14

Development of markets for compost blankets overseas

1993: First technical studies by Ettlin and Stewart, in Oregon, USA

- Compost applied to bare soil slopes up to 42%

- Soil loss reduced by more than 96-97% with compost blankets compared to bare soil; similar to hydromulch

2001: Ros et al. reports compost blankets reduced runoff by 54% compared to bare soil control

15

Development of markets for compost blankets overseas…

2003: Texas DOT adopts compost blankets as erosion control BMP

2003: AASHTO provisional standards adopts compost blankets

23 DOTs in USA adopt the spec

2005: Faucette et al. reports total runoff after 1 year for compost blankets was 50% of control; hydroseeding only reduced it by 30%

2006: US EPA adopts compost blankets as new best practice for erosion control on construction sites

16

Barriers to developing the market for compost blankets in Australia

Hydromulching is an industry standard

- e.g. NSW RTA QA Spec R178 – Vegetation – hydromulching for erosion control on road projects

- e.g. NSW Landcom blue book – Managing Urban Stormwater

Little experience with compost blankets under Aus climatic conditions

Key issues:

- Performance and cost relative to hydromulching

- Erosion control (sediment and nutrient loss)

- Plant establishment success

- Effect of local climate and rainfall frequency / intensity / duration

17

Program undertaken to overcome barriers

DEC consulted industry on priorities

Pioneering work being done, e.g. The Hills Bark Blower in (Sydney), Groundworks (Brisbane) and We Blow Landscapes (Melbourne)

Need for independent assessments

Little knowledge of opportunities in composting industry

R&D project developed in consultation with industry

18

Key questions

Performance of compost blankets compared to hydromulching

Assess effects of the following factors on erosion control and plant establishment:

- Slope angle

- Level of soil compaction

- Rainfall intensity

- Binder or tackifier

Dr Charles Morris, University of Western Sydney contracted to undertake project

19

R&D trials

Scientific trials undertaken to establish performance of compost blankets

Trial under glasshouse conditions

Difficult to undertake work under field conditions

Soil flats constructed to simulate road verge construction process

50 mm sandy loam overlying 120 mm

Bringelly shale derived clay

20

R&D trials - overview

Four treatments were compared:

- Compost blanket (25 mm) with binder

- Compost blanket (25 mm) without binder

- Hydromulch (RTA QA R178); and

- Bare soil.

Compost blanket – AS 4454 (2003) composted soil conditioner applied at US EPA spec 25 mm deep

Other variables:

- Two angles of slope (20 and 45)

- Uncompacted and compacted

21

R&D trial – Set-up

Japanese millet applied via compost blanket and hydromulch

Soil flats set at angle and watered for 5 weeks

Rainfall simulation at week 6 to test erosion control performance

1 in 10 year design rainfall event (67 mm/hr for 30 mins)

Actual was 90 mm/hr for 30 mins:

- 1 in 75 yr event for Sydney

- 1 in 100 yr event for Melbourne

- 1 in 10 yr event for Brisbane

Hydromulch (LHS)Compost blanket (RHS)after 3 weeks

Rainfall simulation

22

Parameters measured

Total and steady-state runoff

Soil in runoff

Total suspended solids in runoff

Nutrients in run-off (total N and P)

Plant establishment (density and biomass)

23

Results – runoff hydrograph (low angle)

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40

Time (mins)

Mea

n r

un

-off

per

5 m

ins

(mL

)

Compost blanket – compacted soil

Compost blanket – non-compacted soil

Hydromulch – compacted soil

Hydromulch – non-compacted soil

Control – non-compacted soil

Control – compacted soil

excellent

poor

24

Results - runoff

Compost blankets reduced steady state runoff by 46 - 49% compared to bare soil

Compost blankets performed 2 times better than hydromulch (23% reduction in steady state runoff) (P<0.05)

More rainfall held and infiltrated into compost blankets

Steeper slope significantly increased total run-off

25

Results – soil loss (or erosion)

0

10

20

30

40

50

60

70

80

Control Hydromulch Compostblanket - binder

Compostblanket +

binder

Mean total soil loss across

different slopes and

levels of compaction (g

DW per soil flat)

a

b b b

26

Results – soil loss (erosion)

Both hydromulch and compost blankets highly effective in soil erosion control

Almost complete control of soil erosion

At the steep slope, soil loss was reduced by 91% under hydromulch, and even more under compost blankets (99.8 to 99.9%) compared to bare soil control

Soil loss increased at the steeper slope

27

Results – total suspended solids

0

500

1000

1500

2000

2500

3000

Control Hydromulch Compostblanket -binder

Compostblanket +

binder

Mean total suspended

solids in runoff across

different slopes and

levels of compaction

(mg/L)

a

b c c

28

Results – total suspended solids

Both hydromulch and compost blankets highly effective in reducing TSS in runoff

Hydromulch slightly better in reducing TSS (TSS reduction of 98.5%) compared to compost blankets (95.9 - 97.3%)

Compaction and slope angle had no effect on TSS

29

Results – nitrogen in run-off

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

bare

soil

hydr

omulch

RO-b

inder

RO +

binde

r

bare

soil

hydr

omulch

RO-b

inder

RO +

binde

r

low angle high angle

Me

an

to

tal N

(m

g/L

compacted

non-compacted

Contro

l

Hydro

mul

ch

Comp-

bind

er

Comp+

bind

er

Contro

l

Hydro

mul

ch

Comp-

bind

er

Comp+

bind

er

30

Results – nitrogen in run-off

Total nitrogen (N) slightly higher in run-off from the compost blankets (1.25 – 1.35 mg/L) (P<0.05) compared to control and hydromulch

Total N levels released still low

31

Results – phosphorus in run-off

00.1

0.20.3

0.40.5

0.60.7

0.80.9

1

bare

soil

hydr

omulch

RO -b

inder

RO +

binde

r

bare

soil

hydr

omulch

RO -b

inder

RO +

binde

r

low angle high angle

Me

an

to

tal P

ho

sp

ho

rus

(m

g/L

)

compacted

non-compacted

Contro

l

Hydro

mul

ch

Comp-

bind

er

Comp+

bind

er

Contro

l

Hydro

mul

ch

Comp-

bind

er

Comp+

bind

er

32

Results – phosphorus in run-off

No difference in total P on non-compacted slopes

Small increase in total P in compost blankets on compacted slopes

Levels of total P released were low

33

Results – cover crop growth

Rapid plant establishment occurred on hydromulch and compost blankets

No difference in amount of biomass produced

Plant densities ranged from 2,000 – 5,000 /m2 - reduced by soil compaction, and the compost blanket + binder treatment.

34

Summary of key results

Performance results for hydromulch and compost blankets very similar to US field trials

Compost blankets performed at least equally as well as hydromulch on slopes up to 45

Compost blankets twice as effective as hydromulch in terms of reducing runoff after heavy rainfall events

Nutrient load in stormwater likely to be lower due to reduced runoff

No observed benefits of using a binder

35

Siting and design considerations

Trials suggest US EPA specs likely to be suitable for Australian application

Factors that need to be considered on the job site:

- Existing vegetation

- Climate

- Structural attributes of the site (steepness of slope)

- Annual rainfall

- Rainfall erosivity

Critical for determining appropriate blanket depth

Source: The Hills Bark Blower

36

Siting and design considerations…

Compost quality- Specs set out by US EPA (2006)

and AASHTO (2003)

- Particle size, chemical properties and maturity similar to a composted soil conditioner in AS 4454 (2003)

- CSC successfully used in trials

- CSC in AS 4454 has tighter specs for most parameters

- Moisture content of 30-50% as in US EPA specs may need to be set to enable easy blower application

Source: The Hills Bark Blower

37

Siting and design considerations…

Application rates at different rainfall rates: US EPA (2006)

AnnualRainfall/

Flow Rate

Total Precipitation /Rainfall Erosivity

Index

Compost BlanketDepth (Vegetated

Surface)

Compost BlanketDepth (Unvegetated

Surface)

Low25 – 635 mm

20 – 9012.5 – 19 mm 25 – 37 mm

Average635 – 1270 mm

91 – 20019 – 25 mm 37 – 50 mm

High>1270 mm

>20125 – 50 mm 50 – 100 mm

38

Installation

US EPA (2006) recommends:

- Compost should be applied to the soil surface in a uniform thickness

- Easiest applied with a pneumatic blower, especially on steep slopes or difficult to access areas

- The compost blanket should extend at least 1 m over the shoulder of the slope to ensure that storm water runoff does not flow under the blanket

- Thicker compost blankets are recommended for areas with higher annual rainfall or rainfall intensity and coarser compost is recommended for areas subject to wind erosion

39

Further information and advice

Contact your local compost blanket service provider

Can provide advice regarding sediment and erosion control planning

Specific advice to maximise the success of your project

40

Acknowledgements

Dr Charles Morris (Uni of Western Sydney)

Compost NSW committee

Jon Moon and Penny Smith (The Hills Bark Blower)

Further information Mark Jackson, (02) 8837 6010.