9.0 selection of preferred alternative 9.1 Trunk ewer Alignment The initial evaluation if alternatives resulted in the selection of Route DS4 and US2 as the overall recommended alignment (figures 6 and 9), as was presented at the second public meeting (June 27, 2007). Through the public consultation process it became apparent from the "friends of Stoney creek", that additional details were required before they could support the US2 portion of the option. The group felt that the environmental assessment needed to address issues relating to the construction of a trunk sanitary sewer within the ESA area located west of Highbury Avenue and north of Stoney Creek. Concern was expressed with respect to both short and long term impact to the ESA area and the potential benefit of mitigation/compensation measures. In addition, the group wanted to ensure that section 15.3.3 of the Official Plan was upheld which indicates that as a condition of approving infrastructure projects in natural heritage areas, the city may require specific mitigation and rehabilitation measures and/or compensation for the damage to naturel features and functions caused by construction or maintenance of the infrastructure. As such, additional environmental evolution of the preferred option was deemed necessary to father assess impacts and required mitigation, rehabilitation and/or compensation measure. In general, the additional investigations and reassessment of mitigation measure of option US2 consisted of the following: 1. The portion of US2 located just east of the Stackhouse avenue crossing was further investigated with respect to slope stability. Golder associates outlined in their letter dated November 5, 2007 (see appendix B) that there were no adverse impacts to either the future sewer or the existing slopes in the area with respect to slope stability issues. 2. A floral life science reconnaissance along US2 was completed to ensure any atypical species would not be impacted. (If atypical species were identified an appropriate mitigation plan was to be required.) 3. Tree protection zones would have to be established at or beyond the drip line of all trees to be maintained. 4. Overhanging branches that may be impacted from construction equipment activity would require trimming. 5. Silt fencing was recommended around stockpiles adjacent to woodlands. 6. A replanting strategy was recommended where possible. 7. A qualified hydrogeologist was to make recommendations during detailed design and construction in order to ensure that baseflows to waterways were not impacted. 8. During construction it was to be ensure that mitigation and/ or compensation was provided in accordance with the city of London policies in place at the time. 9. A replanting strategy was recommended where possible. 10. A qualified hydrogeologist was to make recommendations during detailed design and construction in order to ensure that baseflows to waterways were not impacted. 11. During construction it was to be ensured that mitigation and/or compensation was provided in accordance with the City of London policies in place at the time. The UTRCA provided a comment that it preferred to have the new Stackhouse Avenue construction / flood control facility coordinated with the new sanitary sewer construction in order to avoid disturbing the creek corridor more than necessary. As noted in Section 5.2 of this report trenchless construction was not considered feasible along any portion of this section due to the type of soil. Therefore in consideration of this comment and the soil conditions, it was determined in 2008 that the EA was far enough along with the presentation of the recommended options that the installation of a casing at this crossing would not change the outcome of this EA. Therefore a 1050m dia. Concrete casing was installed on the upstream side of the Stackhouse Avenue crossing in 2008 in order to facilitate the installation of the sanitary sewer at some point in the future. Figure 14 shows a detail of the sanitary crossing concept. The potential of installing a watermain at the Stackhouse Avenue crossing was also considered, however it was determined by the City that the water distribution network did not require a linkage at this location. Following these investigations, the City decided to defer finalizing this EA pending the update of the City's Official Plan policy of section 15.3.3 regarding construction within environmentally sensitive areas. As a result of this update, the City had Deican prepare an "Environmental Impact Study (EIS) for the Stoney Creek Trunk. Sanitary sewer and Warermain CROSSING Class EA, "dated March 2010 to assess mitigation and compensation options for the routing through an ESA as a result of the various mitigation and compensation options for the routing through an ESA as a result of the carious mitigation and compensation measures required as part of the EIS, updated costing, and timing implications of developments the preferred alignment was chosen as US4 and DS5 as shown on Figure 13. 9.2 Rationale for the selection of route US4/DS5 as the recommended Alternative: Route US4 1. Potential to service a portion of Marsman lands; 2. Low to moderate construction costs; represents an effective use of capital; 3. Shallow sewer allows for ease of construction/ less disturbance; 4. Timing of Marsman development coincides with sewer construction plans; 5. Avoids creek corridor and ESA; 6. Ease of construction; 7. Availability of property; Route DS5 1. Avoids Natural Environment disturbance along the creek banks; 2. Minimizes the number of creek crossings required; 3. Least construction impact with respect to disturbance behind existing homes, especially homes with foundation settlement issues in the past; 4. Public prefers construction along existing streets rather than along creek corridor; 5. Low to moderate construction costs; represents an effective use of capital; 6. Good flexibility with respect to servicing future development areas; 7. Ease of construction; 8. Availability of property; 9.3 Implementation One of the key concerns expressed by the development community was a desire to expedite the implementation of the construction of the critical downstream section. Subject to final budgetary approval, the City advised that it is intended to proceed with the construction of the downstream section (DS5) as a capital project with construction in 2011. A major portion of the upstream section (US4) wold be located within a development block located south of Stoney Creek and east of Stackhouse Avenue. It will be necessary to coordinate with affected property owners the means by which trunk sanitary sewer will be constructed within future road allowances. The sections of the trunk sanitary sewer along Highbury Avenue south of Stoney Creek will be coordinated with road improvements. The crossing of Stoney Creek will be done trenchlessly. Sections of the trunk sanitary sewer north of Stoney Creek would be carried out in the future.