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)

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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].