02/07/2011 Council Packet - Laserfiche WebLink

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HoustonEngineering Inc. and infiltrate 2% of the total runoff volume from a two-year event for the project. The loss of this function is also relatively small. Impacts on Water Quality One purpose of RCWD infiltration requirements, besides control of downstream runoff volumes, is to maintain water quality by reducing downstream loads. Although Basin E2 does not currently provide an infiltration function, it does provide some treatment of stormwater runoff settlement of particulates. However, this water quality treatment is likely less than what would have been provided if the basin functioned as it was designed. Because the contributing drainage area of Basin E2 is so small compared to the total project area and the receiving waters immediately downstream from the site, any improvement to water quality leaving the basin would provide no measurable change in the water quality of its receiving waters (including the downstream ponds, Anoka County Ditch 10- 22 -32, and eventually Marshan Lake). Alternative 2 proposed in the January 11 memorandum would result in improved water quality leaving the site due to its filtration function. Conclusions From purely a technical perspective, the no -action approach fails to comply with the original permit conditions. The current poor function of Basin E2 does result in an incrementally small decrease in water quality and volume control function compared to its intended design. However, from a practical perspective, the no-action approach is expected to have little or no impacts to downstream water bodies. Should the Board decide as a matter of Principal that absolute permit compliance is necessary, then one of the corrective alternatives at a cost ranging from $64,000 to $90,000 can be implemented.