compost blankets for controlling erosion on construction sites trials under australian conditions
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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
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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)
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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.
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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.
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