Construction Dewatering…

Construction Dewatering

Supported Changes

• Stantec supports the proposed changes to allow up to 400,000 L/day for each pit based on its dewatering area of influence.
• Stantec supports not including storm water in the 400,000 L/day EASR limit

Potential Challenges

• Stantec sees challenges in the implementation of a fixed TSS limit of 25 mg/L or turbidity of 8 NTU regardless of the distance between watercourse and discharge point (whether to land, watercourse or storm sewer) as well as having this limit apply to both groundwater and stormwater discharge.
Stantec works with clients who work primarily on linear infrastructure with temporary construction dewatering at any given location, before the construction works move to a new area. For these projects achieving a TSS of 25 mg/L or turbidity of 8 NTU is incredibly challenging. The proposed fixed TSS limit does not consider the background of the watercourse that may receive discharge. If the watercourse is very turbid , the expense and time for the mitigation measures may not be warranted.
When possible, construction dewatering is directed to a low-lying area promoting recharge. This is especially true for development projects that normally create a central temporary area to receive and infiltrate dewatering from anywhere on site. Based on this setting, TSS and turbidity levels should not be required to achieve the PWQO. It would be the responsibility of the qualified professional preparing the EASR to detail the applicable discharge criteria and mitigation measures prior to discharge within a proposed development area or within a natural area.
Including this change in the EASR Regulation would likely lead to an increase in PTTW applications for projects that would otherwise qualify for an EASR just to seek relief from this condition. This would effectively counteract the goal of the proposed changes to simplify and streamline water taking activities for businesses.

Stantec suggests that the regulation state that discharge within 30 m of a watercourse meet a limit TSS of 25 mg/L or turbidity of 8 NTU or within 10% of the current background conditions of the watercourse.

• Stantec sees challenges for dewatering contractors to be able to measure precipitation events in a meaningful way in order to evaluate the impact of the generated storm water on the water taking activity and discharge. Further clarification on acceptable ways that this can be accomplished is requested.

Supported Changes

• Diversions: seepage through barrier will be included in the exemption if pumped seepage meets the limits for TSS/turbidity.

Potential Challenges
• Stantec suggests that the regulation state that discharge for diversion seepage meets a limit of 25 mg/L TSS or 8 NTU turbidity or within 10% of the current background conditions of the watercourse.