Laserfiche WebLink
GSGM <br /> www. s9 1-n-i tic. com <br /> Wetlands Delineation Finding <br /> The National Wetlands Inventory (NWI) provides the user with information to conduct an initial desktop <br /> assessment and generate maps for an area of interest. The NWI for the Rifle Pit#1 property (Property) <br /> indicated that most of the area is wetlands (Figure 1). A site visit and delineation performed by SGM on <br /> July 17, 2019 generally confirmed that this parcel contains large areas of wetlands, although not as <br /> extensive as suggested by the NWI (Figure 2). The wetland areas are concentrated on the west end of <br /> the property and are well-developed and relatively high-quality from a biological and functional <br /> perspective. The east end is mesic pasture meadow rather than jurisdictional wetlands, and development <br /> of the gravel resources in this area could be accomplished without Section 404 permits. <br /> Parcel Geology <br /> The Parcel is underlain by river gravels which are saturated and in direct contact with the water table. The <br /> surface soil is generally an alluvial silty clay loam, with areas of heavy clay. Boring logs and direct <br /> observation suggest that many areas of wetland vegetation are underlain by a clay aquitard layer at a <br /> depth of approximately three feet. <br /> The site visit and supplemental subsurface documentation suggests that the wetlands are supported <br /> primarily by surface water discharge onto the property via pooling of that water on the shallow clay <br /> aquitards. Shallow groundwater may be supplementing the wetland hydrology in some areas, but drilling <br /> data suggest that the water table is approximately seven feet below the surface across most of the <br /> Parcel, and that 3 or 4 feet of dry gravel underlies the clay pans and wetlands. Surface water reaches the <br /> property exclusively via artificially-excavated channels off the Last Chance Ditch. This includes the large <br /> lateral/tailwater ditch that bisects the property from east to west, and several smaller ditches that <br /> discharge underneath the interstate and onto the southern boundary of the property (Figure 3). <br /> Based on this understanding of the hydrology, if the tailwater seepage and direct discharge onto the <br /> property are stopped (by closing headgates, re-routing and/or piping the ditches, or other similar <br /> methods), the primary water source for the wetlands could be removed. Groundwater modeling also <br /> suggests that pit dewatering activities in adjacent upland areas (east) will significantly and rapidly depress <br /> groundwater levels throughout the Parcel, further isolating the wetlands from groundwater hydrology (See <br /> attached Letter Report, Hahn Water Resources, LLC, August 2, 2019). <br /> The combination of pit dewatering adjacent to the wetlands, and removal of irrigation-derived water <br /> discharges onto the property, could remove the hydrology supporting the wetlands throughout the Parcel, <br /> and will likely result in the loss of wetland status within two growing seasons. <br /> Army Corps Section 404 Permitting Considerations <br /> The Army Corps of Engineers (Army Corps) regulates the discharge of sediment into wetlands through <br /> Section 404 of the Clean Water Act. The eastern portion of the Parcel does not contain jurisdictional <br /> waters or wetlands, and development could proceed in that location without Section 404 permitting. <br /> SGM's site investigation completed on July 17, 2019 would be formalized in a wetland delineation report if <br /> the property is purchased which would provide confirmation of regulatory compliance for the initial <br /> development activities. <br /> 2 <br />