It follows that lining the lagoons may cause a direct reduction in the quantity of base flow discharge from the aquifer to Des Moines Creek. Fill Parameters is Uncertain SMP Appendix A, Page 1-16, provides a limited discussion of the flow data used to establish hydrologic response parameters for areas of airport fill. There is insufficient information to judge how representative the 1998 embankment fill is of proposed overall embankment conditions. However, if the sediment pond at the 1998 embankment site is intercepting interflow and base flow as stated, it is probable that the pond will intercept groundwater originating from beyond the immediate area of the fill. In particular see SMP Figure B1-3 which shows that groundwater flow in the area of the 1998 embankment will originate from well beyond the immediate footprint of the 1998 embankment.
Similar discrepancies exist on other plan sheets.
The mitigation plan drawings show a replacement drainage channel located to the west of the security road, at the toe of the embankment. This is inconsistent with the grading plans which show a replacement drainage channel located to the east of the security road, in fill soils about 10 feet higher than the toe of the embankment. That objective will not be achieved with the current grading plans because the drainage swales, as shown on the Grading Plans, will not intercept the constructed drainage blanket which will daylight at the toe of the embankment. Instead, the swales will primarily collect concentrated and flashy peak flow surface runoff from the face of the embankment, rather than naturally-attenuated groundwater seepage flows. The plans do not indicate how embankment-face runoff water will be directed into the stormwater detention ponds, as would be needed to be consistent with the stormwater management plan modeling assumptions.