Compost blankets for controlling erosion on construction sites Trials under Australian Conditions

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Compost blankets for controlling erosion on
construction sitesTrials under Australian
Conditions
Compost Australia Seminar Series A New Standard
in Erosion Control Dr Mark Jackson Department
of Environment and Conservation NSW
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Outline

• What are compost blankets?
• Advantages
• Applications
• Compost production in Australia
• Overseas developments
• Barriers to compost blankets
• RD trials by Uni of Western Sydney
• Trial results
• Siting and design considerations

Source Rexius Inc.
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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
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What are compost blankets?
5 cm deep compost blanket 11 rock slope
Pneumatic blower used Austin, Texas, 2002
Source US EPA, (2006) and S. McCoy, Texas
Commission on Environmental Quality (TECQ), 2005.
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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

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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 11 to 41
• 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
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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
  ECO114/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
• RD 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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RD 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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RD 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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RD 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)
poor
Control compacted soil
Control non-compacted soil
Hydromulch non-compacted soil
Hydromulch compacted soil
Compost blanket non-compacted soil
Compost blanket compacted soil
excellent
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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)
  (Plt0.05)
• More rainfall held and infiltrated into compost
  blankets
• Steeper slope significantly increased total
  run-off

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Results soil loss (or erosion)
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
a
c
c
b
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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
Control
Control
Comp-binder
Comp-binder
Compbinder
Hydromulch
Compbinder
Hydromulch
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Results nitrogen in run-off

• Total nitrogen (N) slightly higher in run-off
  from the compost blankets (1.25 1.35 mg/L)
  (Plt0.05) compared to control and hydromulch
• Total N levels released still low

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Results phosphorus in run-off
Control
Control
Hydromulch
Hydromulch
Compbinder
Compbinder
Comp-binder
Comp-binder
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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
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Siting and design considerations

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

Annual Rainfall/ Flow Rate Total Precipitation / Rainfall Erosivity Index Compost Blanket Depth (Vegetated Surface) Compost Blanket Depth (Unvegetated Surface)
Low 25 635 mm 20 90 12.5 19 mm 25 37 mm
Average 635 1270 mm 91 200 19 25 mm 37 50 mm
High gt1270 mm gt201 25 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

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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

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Acknowledgements

• Dr Charles Morris (Uni of Western Sydney)
• Compost NSW committee
• Jon Moon and Penny Smith (The Hills Bark Blower)
• Further information
• Mark Jackson, [phone].