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10.5 Leachate Generation/waste water disposal

The EIA report intimates that leachate will be generated in the onsite landfill used for the storage of waste by products from the incineration process. However the report fails to indicate the volume of leachate generated per day.

With regard to the characteristics of the leachate as suggested in the EIA report49, the following observations are made:

• High Total Dissolved Solids of 34,469mg/l;
• Chloride concentration of 17,263mg/l;
• pH of 7, i.e., neutral;
• Sulfate concentration of 335mg/l;
• Nitrate concentration of 6.6mg/l;
• Very low metal concentrations.

It is observed that the concentrations of dioxins and furans in the leachate are not stated and the high TDS of the leachate (close to seawater) associated with a neutral pH needs clarification particularly as the volume of leachate is not reported.

The above characteristics of the leachate need to be validated given that the characteristics of the ashes as reported in the previous section are substantially different from those assumed in the EIA report. In particular, if the acid concentrations (HCl, HF in particular) are high as reported by Carl Bro, then the resultant residues from the Air Pollution Control System will be more acidic as the
quantity of lime used will not be able to produce a neutral pH residue.

Furthermore the EIA report considers that on the basis of their reported characteristics, no treatment will be required and the leachate will be sent to the wastewater settling basin50. Whereas, in a footnote (p6-4) mention is explicitly made that the leachate will be treated with other process waters generated from the WTE Facility. If this is not confusing enough, the EIA report further assert that the leachate generated from each cell will be collected and treated (if required) prior to reuse on site or disposal to foul sewer or surface water [4th Para. p6-5]. This assertion is further confirmed (Para. 5) with an additional statement that the discharge will be in accordance to effluent quality standards.

It is also apparent that the EIA report itself seems to be uncertain on the leachate characteristics as well as the ash characteristics. Several statements made in the report confirm these uncertainties:

í²ƒ …..The design of the subsequent phases will be reviewed based on the actual quality of the bottom ash and fly ash generated from the WTE facility and characteristics of the leachate. (Section 6.3.2 p 6-5)
í²ƒ …..The material used for the synthetic drainage will be chemically compatible with the leachate of the residues

Hence it is clear from the EIA report that the Promoters are proposing to construct a residue Storage Facility using among others a liner compatible with the leachate of the residues but simultaneously admit that they do not know the characteristics of the leachate [1st Paragraph, p6-5]

Again this is a case where under the precautionary principle the EIA report should have assessed various scenarios for leachate characteristics then identify the potential impacts and proposed mitigation measures.

The characteristics of the wastewater in the wastewater settling basin have not been given in the EIA report and whether the quality is suitable for discharge to the environment cannot be ascertained due to lack of pertinent information. However what is disturbing is that according to the EIA report, provision is made for the discharge of this wastewater to a rain water drainage channel at the site boundary and according to the same report the channel is linked to the existing road drainage system which discharges into Belle Eau River which eventually discharges to sea.51 Thus the risks of pollutants from the proposed WTE Plant entering the freshwater ecosystems of Rivière Belle Eau and the Marine ecosystem of Petite Rivière Bay are not insignificant as intimated in the EIA report.

In another section of the EIA report, disposal of leachate is stated as either to water bodies or to foul sewer, the latter route presumably meaning St Martin Treatment Works. The types of contaminants in the ashes and residues and their presence in the leachate exclude its disposal at St Martin Treatment Works as the plant has been designed to produce treated effluent for irrigation (see later) under the precautionary principle. The investments of St Martin Treatment Works and associated infrastructure are estimated at about Rs4Billion, funded by an EU grant and mostly by Government of Mauritius (see later) and disposal of leachate or any process water from the proposed WTE Plant is a direct threat to St Martin Treatment Works.

Furthermore there is confusion in the EIA report on the estimated sewage flow during the operational stage of the Proposed WTE Plant:

• In section 6.3(p6-7) mention is made of a total flow of 22.5m3/d
• Whereas in section 7.6.2 the flow is calculated at 11m3/d

The statement made in the EIA report that the wastewater will fully comply with the effluent discharge standards is not sufficient in itself as proof that this will the case.

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49 EIA report p7-15, Table 7.6b
50 EIA report p-7-14
51 EIA report p7-12

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