Concerns About the Proposed…

Concerns About the Proposed Nitrate Limit and Unit Errors in the ACS

Nitrate is not typically included as an effluent parameter for surface water discharges in Ontario. Nitrate limits are generally applied to groundwater discharges, not surface water, unless the receiving watercourse is extremely low flow or highly sensitive. While it is not impossible for an ECA to include a nitrate limit in a surface water context, it is unusual and requires strong technical justification.
The expert review also identified a technical issue in the assimilative capacity calculations: the proponent appears to have mixed nitrate as N and nitrate as NO₃ units. This is a common source of error, but it has important implications for interpreting water quality criteria.

Specifically:
• The CCME guideline of 13 mg/L applies to nitrate as NO₃.
• When expressed as nitrate as N, the equivalent value is 2.93 mg/L.
• The river data in the ACS is reported as nitrate as N, meaning the proponent should have compared it to 2.93 mg/L, not 13 mg/L.
Despite this unit error, the expert concluded that correcting the calculation would not change the overall outcome. The receiving watercourse has sufficient assimilative capacity according to the ACS so it’s unclear why a nitrate limit is imposed.

Given this, I respectfully request that MECP:

1. Review the nitrate unit conversion issue in the ACS to ensure the analysis is technically correct. Also are the other values used properly.

2. Explain why a nitrate limit is appropriate, given that nitrate is not a standard parameter for surface water discharges and the corrected ACS indicates adequate assimilative capacity.

3. Ensure that any effluent limits included in the ECA are supported by defensible, receiver specific technical rationale, rather than by unit errors or assumptions.

These steps are necessary to explain why that effluent limits is scientifically justified and aligned for this surface water discharges.