Effectiveness of compost erosion control blankets and compost filtersocks to control runoff and erosion from engineered slopes

This three year project evaluated critically the use of BSI PAS 100 Compost as Compost Erosion Control Blankets (CECBs) and as filter media in Compost Filtersocks (CFs) for the prevention and control of soil erosion, nutrient loss and runoff from engineered slopes in the UK. This will be achieved through a two-phase experimental program located within the A421 Widening Scheme in Bedfordshire, UK. Phase I involved a 12 month field trial project on soil stock piles derived from the A421 Widening Scheme and engineered to replicate a highway embankment. Optimum CECB and CFs treatments derived from Phase I were taken forwards into Phase II for comparison against current erosion and runoff control Best Management Practices (BMPs) adopted by the UK construction industry. The intensive data collection program has answered key performance and environmental questions pertaining to the use of CECBs and CFs. In summary, optimum performance in terms of runoff control was achieved by the CFs treatment with or without CECBs. In Phase I, for all nine runoff generating rainfall events, the 25 mm depth CECB with CFs treatment was associated with 100% reductions in runoff volume, Total Suspended Solids, Total Soil Loss and Total loss of Sediment Bound-P as compared with the bare soil control plots. Further, all CECB and CFs treatments were are associated with 98.6–100% reductions in Total Soil Loss and 98.4–100% reductions in Total Sediment Bound-P as compared with the bare soil controls. In Phase II optimum performance was associated with the bare soil CFs treatment which for three out of four runoff generating rainfall events was associated with 100% reductions in runoff volume, Total Suspended Solids, Total Soil Loss and Total loss of Sediment Bound-P as compared with the bare soil control plots. In addition, for both Phase I and Phase II, all ortho-phosphate-P concentrations in runoff derived from CECB, CFs and bare soil control treatments, were orders of magnitude below the maximum permissible levels for ortho-phosphate-P as specified in the Water Framework Directive of the UK Environment and Condition. Further, Total Oxides of Nitrogen (TON) concentrations in runoff derived from CECB, CFs and bare soil control treatments were significantly lower than the maximum permissible level of <50 mg l-1 for nitrates (NO3-) as specified in the EU Council Directive 91/692/EEC concerning the quality required of surface water intended for the abstraction of drinking water in EU Member States (91/692/EEC).