we have a project site situated in the rural mountains where infiltration is not even possible due to geological conditions. The site consists of very low permeable soil, with high groundwater level (only 2 m below grade). The site is currently drained off into existing water surface streams situated 1) on site and 2) at the boarder of the site. One of the streams is drained into underground pipe also situated on site that releases water outside the LEED Site. This pipeline was constructed in the past to prevent the whole area from flooding. Both of the streams are then leading to a local dam (situated roughly 100 m from the LEED Site).
We would like to approach the credit SSc4 LEED NCv4 ideally through option 2: to manage all the incremental runoff volume on site compared the project status after the construction to full natural undeveloped land cover.
But the project team is suggesting not to design on site bioretention ponds but rather to use the already built dam to catchup the incremental runoff from the LEED Site. This sounds very logical to utilize the already built dam nearby that was designed specifically for the flooding prevention purpose.
Is it possible to include retention dam outside the LEED Site to fulfill the requirements of the credit nevertheless what option is used? This approach was possible in LEED v3 by assuming all the credit requirements to be applied for the whole water collection areas including the LEED Site. What approach should be used within LEEDv4 for option 1 vs. option 2?
Is it possible to consider the proposed solution as a low-impact development strategy? The dam is natural based structure – regional soil and stone based bearing structure (layers of stones and soil with different granularity) but of course made by hard mechanization. Dam is equipped with 16 kW output hydro plant. The top of the surface is surrounded by paved concrete road. Also the overflow bypass is concrete based structure. The rest of the embankments is pedestrian based with natural slope into the water.
Thanks in advance for any kind of help
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