The background information…

The background information provided for the proposed Construction Site Dewatering exemption indicates the following: "Under the requirements of the proposed exemption, proponents would be required to implement any necessary measures to ensure that water quantity and quality are not affected upstream or downstream of the work area and that the discharge does not cause an adverse impact." If construction dewatering is exempt from the ECA process, what regulatory instruments is the Ministry proposing to use to ensure compliance with the above mentioned statement?

It is not uncommon for shallow aquifers to be contaminated (PHC, PAHC, SAR) due to historical industrial and agricultural land uses prior to the onset of any environmental legislation.
The environmental characteristics of any groundwater intended for removal by dewatering must be thoroughly understood to ensure appropriate pre-treatment technology is used to produce a high quality discharge. Construction dewatering to the storm sewer would likely result in the contamination reaching a receiving point that is considered as the natural environment.

There are numerous examples of construction dewatering projects discharging extreme volumes of contaminated groundwater to the municipal sanitary sewer because the quality of the discharge was not suitable to be discharged to the storm system. This places unnecessary hydraulic burden and cost on the WwTF and uses dilution as a treatment approach to achieve compliance since the municipal WwTF is not designed to treat many of the typical groundwater contaminants.

Extreme care in the proper management and oversight of construction dewatering projects are essential for source water protection and sustained resource management. Proper Provincial involvement would be most helpful.
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