Evaluation of Environmental Impacts Generated by Pulp and Paper Sludge Leachate Stored in Winter, 1999 Environmental Conference Proceedings

André D’Astous & Gilles Fortin

Envir-Eau Inc.

Louis Désilets

Association des Industries Forestières du Québec Limitée (AIFQ)

The Quebec Association of Forest Industries (AIFQ), mandated by member companies, is involved with the Quebec Ministry of Environment and Fauna (MEF) in finding ways to reuse combined primary and secondary sludge for agriculture. MEF acknowledges the importance of reusing biosolids as fertilizer for agriculture, but expresses some concern about the potential environmental impact created by winter storage of these biosolids. Therefore, MEF transitory regulations forbids the storage of sludge on agricultural land for several months for biosolids having a total solids content less than 30%.

AIFQ mandated Envir-Eau Inc. to conduct a study of the potential environmental impacts related to the winter storage of biosolids. We used three different mathematical models (HELP, LEACHM, MODFLOW) to simulate worst case scenarios of leachate production, migration in the unsaturated soil zone and transport in the groundwater from an uncovered sludge piles stored directly on the soil over the winter period in selected Quebec region. Nitrogen in form of nitrates, the most hazardous contaminant, was chosen to simulate worst case contamination problems.

Results show that the environmental impact created by storage of uncovered mixed sludge residues, of solids content between 20% and 35%, is minimal for all simulated conditions. Drinking water standard are only exceeded for a short period of time in loams and sand. Nitrate concentration decrease rapidly under the 10 mg/l drinking water limit within a small area around the contaminant source. Most problematic results were found for the sand unit. Additional data on some physical and chemical characteristics of Quebec biosolids and the leachates that are generated from them would be useful to complement existing data and will permit model validation.