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

1. 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

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? + 5 cm deep compost blanket + 1:1 rock slope + Pneumatic blower used + Austin, Texas, 2002 Source: US EPA, (2006) and S. McCoy, Texas Commission on Environmental Quality (TECQ), 2005.

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. Receival and inspection Raw material processing Product blending Leachate collection / treatment Windrow composting Finished compost Aerial view of a commercial composting facilityANL, Wyong, NSW: 50,000 tpa capacity

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) 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

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) 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 a c c b

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 Control Control Comp-binder Comp-binder Comp+binder Hydromulch Comp+binder Hydromulch

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 Control Control Hydromulch Hydromulch Comp+binder Comp+binder Comp-binder Comp-binder

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)

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.