Environment Act Proposal Rapid City Lagoon Expansion Rural Municipality of Oakview Environment & Geoscience 4 October 2019 Internal Ref: 648290 Environment Act Proposal Rapid City Lagoon Expansion Notice to Reader This report has been prepared and the work referred to in this report has been undertaken by SNC-Lavalin Inc. (SNC-Lavalin), for the exclusive use of the Rural Municipality of Oakview, who has been party to the development of the scope of work and understands its limitations. The methodology, findings, conclusions and recommendations in this report are based solely upon the scope of work and subject to the time and budgetary considerations described in the proposal and/or contract pursuant to which this report was issued. Any use, reliance on, or decision made by a third party based on this report is the sole responsibility of such third party. SNC-Lavalin accepts no liability or responsibility for any damages that may be suffered or incurred by any third party as a result of the use of, reliance on, or any decision made based on this report. The findings, conclusions and recommendations in this report (i) have been developed in a manner consistent with the level of skill normally exercised by professionals currently practicing under similar conditions in the area, and (ii) reflect SNC-Lavalin’s best judgment based on information available at the time of preparation of this report. No other warranties, either expressed or implied, are made with respect to the professional services provided to the Rural Municipality of Oakview or the findings, conclusions and recommendations contained in this report. The findings and conclusions contained in this report are valid only as of the date of this report and may be based, in part, upon information provided by others. If any of the information is inaccurate, new information is discovered or project parameters change, modifications to this report may be necessary. This report must be read as a whole, as sections taken out of context may be misleading. If discrepancies occur between the preliminary (draft) and final version of this report, it is the final version that takes precedence. Nothing in this report is intended to constitute or provide a legal opinion. SNC-Lavalin disclaims any liability to third parties in respect of the use of (publication, reference, quoting, or distribution), any decision made based on, or reliance on this report or any of its contents. RM of Oakview 648290 4 October 2019 © SNC-Lavalin Inc. 2019. All Rights Reserved. Confidential. i Environment Act Proposal Rapid City Lagoon Expansion Executive Summary SNC-Lavalin Inc. (SNC-Lavalin) was retained by the Manitoba Water Services Board (MWSB) on behalf of the Rural Municipality (RM) of Oakview to prepare this Environment Act Proposal (EAP) for the proposed Rapid City Lagoon Expansion. The lagoon currently services a population of 440 people in Rapid City and is being expanded to bring the lagoon into compliance with current legislation. The proposed expansion includes adding winter storage capacity through the construction of a new secondary treatment cell, as well as a new concrete truck dump spillway into the primary cell. It will utilize the existing pump station / forcemain infrastructure and will provide an additional 25 years of wastewater treatment capacity. SNC-Lavalin completed an assessment of the existing lagoon to determine its physical condition and current loading capacity. The current loading capacity was compared to the current and 25-year future service population. The wastewater treatment lagoon at Rapid City was found to be structurally sound with a suitably impermeable liner based on visual observations and geotechnical testing. The hydraulic conductivity of the clay liner sample was measured to be 7.19 x 10-8 cm/s. The hydraulic and organic loading assessment found the lagoon suitably sized to handle the organic loading from the 25-year design population but significantly undersized to handle the current and future winter storage requirements. Based on the 25-year design population of 500 people and the wastewater generation rate of 220L/cap/d the lagoon requires approximately 8,500 m3 of additional storage volume to satisfy the 230-day winter storage requirement. SNC-Lavalin evaluated three options for upgrading the lagoon to bring it into compliance with current legislation: (1) add additional winter storage capacity by constructing a new secondary cell; (2) build a new lagoon in a new location with sufficient winter storage capacity; and, (3) implement tertiary treatment with a submerged attached growth reactor (SAGR) system to allow for continuous or nearly continuous discharge from the lagoon, significantly reducing, or eliminating the need for winter storage capacity. Option 1 was the recommended system, as it was the least expensive and simplest option to upgrade the Rapid City lagoon. It will maximize the use of the existing infrastructure and continue with facultative treatment which is simple to operate and maintain. The proposed expansion includes adding winter storage capacity through the construction of a new, soil- lined secondary treatment cell, as well as a new concrete truck dump spillway into the primary cell. The expansion will utilize the existing pump station / forcemain infrastructure. The new lagoon cell will be roughly 0.75 ha in area at a standard 1.5 m operating depth. Treated water will be discharged intermittently along the existing discharge route down to the Little Saskatchewan River. The lagoon has been designed in accordance with the Manitoba Sustainable Design Objectives for Wastewater Treatment Lagoons (MSD 2017a). It has also been designed such that the effluent will meet the water quality limits outlined by the Manitoba Water Quality Standards, Objectives, and Guidelines. Construction is tentatively scheduled to commence in May 2020, pending receipt of regulatory approvals and funding, and is expected to take four to six months to complete. The design life of the facilities is 25 years. A geotechnical investigation will be required to demonstrate whether it will be feasible to construct a recompacted soil liner with the in-situ soil in that location. A geotechnical investigation was conducted immediately west of the existing lagoon, however, the soils do not meet the MSD guideline for hydraulic conductivity, hence would require importing clay or installation of a synthetic liner. Since the investigation, the proposed site for the expansion was moved to the south of the existing lagoon, and the wide variability of the soils encountered west of the existing lagoon do not allow a good estimation of the soil type expected south of the existing lagoon. The RM of Oakview will conduct a geotechnical investigation within the RM of Oakview 648290 4 October 2019 © SNC-Lavalin Inc. 2019. All Rights Reserved. Confidential. ii Environment Act Proposal Rapid City Lagoon Expansion footprint of the proposed expansion to determine if it is feasible to construct a recompacted soil liner with the in-situ soil in that location. If not, the lagoon will require the importing of clay or construction of a synthetic liner. The RM of Oakview is committed to design the lagoon to meet the MSD (2017a) Design Objectives for Wastewater Treatment Lagoons. Rapid City is located within the Hamiota Ecodistrict of the Aspen Parkland Ecoregion of the Prairies Ecoregion and on the banks of the Little Saskatchewan River. Data were compiled from provincial surficial geology maps, the provincial groundwater well database, and the project’s geotechnical study to understand the surficial geology of the area. Much of the area appears to consist of diamicton till with layers of sand and gravel in the first several metres. The Manitoba Conservation Data Centre (MBCDC) was contacted for a search of their database for rare species within the project footprint plus a two-kilometre buffer, and no occurrences were found. The Manitoba Historic Resources Branch (HRB) examined the proposed area of disturbance in conjunction with their records and did not have any concerns with the project at its proposed location. The potential and/or expected project effects were evaluated, and include: › Dust and noise emissions during construction activities; › Odours and air emissions during operation from the release of methane, H2S and NOX; › Permanent displacement of soils to construct the lagoon; › Removal of a small tree stand to accommodate the new cell; › Treated effluent discharge which will flow into the Little Saskatchewan River and may include coliforms, organic wastes, suspended solids and other contaminants; and › Potential for effects to soils / groundwater if the wastewater leaks/seeps through the lagoon liner into the groundwater or in the event of an accidental spill. The RM of Oakview is committed to avoiding or reducing adverse environmental effects associated with the proposed project wherever possible and has developed numerous mitigation and environmental design measures to minimize these effects. Overall, the expansion is expected to improve the water quality of the effluent and provide the community with a wastewater facility that can accommodate its long-term needs. RM of Oakview 648290 4 October 2019 © SNC-Lavalin Inc. 2019. All Rights Reserved. Confidential. iii Environment Act Proposal Rapid City Lagoon Expansion List of Abbreviations and Acronyms Term Definition BOD biological oxygen demand CBOD5 5-day carbonaceous biological oxygen demand ECCC Environment and Climate Change