Which substances, found in leachate, commonly cause problems if discharged to a public sewer?
A. Clearly, methane either conveyed in the sewer airspace, or in solution, must not be discharged to a sewer in view of explosion and asphyxiation risks this would entail. The maximum permissible safe concentration of dissolved methane in water (or leachate) is 1.4 mg/l. Most authorities responsible for sewers, require a factor of safety against methane hazard of 4 to 10, when setting the maximum permissible limit. The discharge to sewer of sulphides, and a variety of other odour producing substances, must also be avoided as these odours may affect properties further down the sewer. Discharge of sulphates in high concentrations, must be avoided in concrete sewers, in view of potential concrete attack. In addition the discharge of all toxic and biologically inhibitory substances must be avoided. It is advisable for expert technical advice to be sought on the suitability of any leachate discharges, for all but the most innocuous low concentration leachates, in view of the chemical comple
