Hydrostratigraphy Of Fen Wetland Recharge Zones – A Case Study From Glaciated Northeastern Illinois, Usa

Shallow (<50 ft) frequency-domain electromagnetic (FDEM) induction surveying was<br>performed over an undeveloped, 35-acre area to delineate water-bearing characteristics of<br>unconsolidated glacial deposits. The mapping was to identify the lateral and vertical extent of<br>groundwater recharge zones for two fen wetlands that border a proposed residential development<br>located in northeastern Kane County, Illinois.<br>FDEM results, correlated to boring and groundwater wells, mapped an area of shallow till<br>that acts as an east-west hydrogeologic barrier to localized groundwater movement. Waterbearing<br>depositional facies overlying till vary east and west of this stratigraphic boundary.<br>Minor variation in FDEM response (1-to-3 mS/m) correlates to generally homogeneous, wellsorted,<br>uniformly thick (~20 ft), medium-to-coarse sands east of the divide. Whereas, a more<br>variable FDEM response (up to 14 mS/m) coincides with discontinuous, poorly stratified<br>deposits of varying thickness (<1-to-40 ft) west of the stratigraphic transition zone. Groundwater<br>lies along the contact of water-bearing deposits and till and saturated thickness varies from 0.5-<br>to-12 ft.<br>FDEM methodology proved to indirectly map groundwater occurrence by mapping<br>shallow till areas and water-bearing zone characteristics. Results enabled placement of<br>subsequent groundtruthing efforts to adequately characterize fen wetland recharge zones in an<br>effort to sustain natural conditions during planned site development.