3301 SEAWAY BLVD WHOLE SITE 2025-10-30

n- Mr. Greg Bertch October 25, 2016 Comment #1 The stormwater pond sits at the crest of a steep slope. The slope is comprised of dense glacial till and advance outwash soils. If the pond were to leak, slope stability could be compromised and sliding could occur. Would an underdrain be feasible that could collect any leakage and direct it to an appropriate outlet? Is there a way to ensure the pond will not leak? Response A double liner could be installed with a leak detection system installed between the liners. Such systems are common in landfill facilities where it is desired to prevent excessive amounts of hazardous substances from leaching into the ground and potentially impacting a groundwater resource. Design of these systems recognize that even a double membrane liner can leak and will establish an allowable leakage rate (ALR) based on the particular contaminant and allowed contaminate threshold. We acknowledge that the proposed Flexible Membrane Liner (FML) that will be placed in the pond can leak. In this case, the liner is being installed to prevent increases in natural groundwater seepage levels that may otherwise occur and potentially impact the current stability of the adjacent steep slopes. In our opinion, a reasonable ALR for this condition would be one that matches the current amount of precipitation that enters the ground by infiltration. Even if the liner leaks, it is more than likely that the leakage rate would be less than this amount of water and; therefore, potential impacts to the stability of the steep slopes would be avoided if not improved. Comment #2 The onsite soils are subject to periodic shallow slides/slumps due to weathering of the upper layers, particularly during extensive wet periods. As the pond crest is located along the top of the steep slope is there a potential that shallow slides could undermine the pond embankment? Resoons�e The toe of the pond embankment is setback 10 to 40 feet from the crest of the steep slope. In our opinion, this setback distance would adequately mitigate the potential for shallow surface slides on the native steep slope from impacting the stability of the pond embankment. Comment #3 The Lock and Load Wall Detail provide does not show a detail for the South Wall. Will the 518-inch minus crushed leveling pad be founded 3 feet below ground surface, as shown for the North Wall detail? Our concern is shallow sliding of the near surface soils undermining the foundation of the wall. Response The south Lock + Load wall would be constructed in accordance with our June 6, 2016 design. As this wall is adjacent a 2:1 slope the 5/8-inch crushed leveling pad will be founded 3 feet below the surface. Project No. - Page No. 2 l