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AUGUSTIN BERNAL MOUNTAIN BIKE TRAIL PROJECT DRAFT INITIAL STUDY stabilizers, revegetation,or other appropriate measures.Site stabilization and pollution prevention measures are noted on Sheets N-1 and N-2 of the trail design plans provided in Appendix A. In the absence of properdrainage controls and vegetation cover following grading and construction, long-term erosion-induced sedimentation of downstream water bodies could occur. However, implementation of MM-GEO-1 would ensure that erosion is minimized through long-term drainage control, placement of erosion control mats, and seeding following construction. With implementation of the site stabilization and pollution prevention measures identified in the trail design plans and in MM-GEO-1, construction and operational impacts to downstream drainages would not violate any water quality standards or waste discharge requirements or otherwise substantially degrade surface or groundwater quality.With implementation of MM-GEO-1, impacts from degradation of water quality or violation of water quality standards during construction and project operation would be less than significant.Therefore, impacts would be less than significant with mitigation incorporated. b) Would the project substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project may impede sustainable groundwater management of the basin? The project would not rely on any groundwater sources and would not develop or use a groundwater supply well. Further,the project does not include any paving or other new impervious surfaces that could interfere with groundwater recharge.Thus,the project would not contribute to the depletion of groundwater supplies through use of groundwater or reduction of groundwater recharge and the project would have no impact associated with the potential to impede sustainable groundwater management. C) Would the project substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river or through the addition of impervious surfaces, in a manner which would: i) Result in substantial erosion or siltation on or off site? Construction activities for the proposed project would occur over approximately 3 acres. Minor grading and vegetation removal would be required but no new impervious surfaces would be created. Under the existing condition, the project site supports unofficial user- created trails that have not been appropriately engineering to manage stormwater. This results in substantial erosion, as shown in the site photographs in Figures 7a and 7b. By replacing the user-created trail with an engineered trail that incorporates grade reversals to effectively allow stormwater to flow off of the trail surface and into adjacent vegetation, the project would reduce the extent of erosion that is currently occurring on the trail surface. Further,allowing stormwater to flow into adjacent vegetation would reduce runoff velocities, which in turn would prevent reduce the potential for erosive scour along the sides of the trail. In addition, implementation of MM-GEO-1 would ensure that erosion is minimized through long-term drainage control, placement of erosion control mats, and seeding following construction. As a result, impacts would be less than significant with 12956 DUDEK 66 April 2022