The City of Wilmington proposed to develop this South Wilmington site as an apartment complex to provide housing for low-income families. Previous site evaluation performed by others indicated that near-surface soils contained elevated concentrations of metals, petroleum hydrocarbons, and PAHS. Due to the client’s desire to remove impacted soils from the site while maintaining the project schedule, excavation and off-site disposal of the soils was performed as an Interim Action under the VCP. Ten Bears personnel negotiated and managed contracts with the subcontractors responsible for the remedial excavation, waste transportation and disposal, fence installation, surveying, and laboratory analysis.
Groundwater occurred at shallow depths hindering the removal of impacted soils. In addition, a geotechnical evaluation performed by others indicated that soft soils were present beneath the impacted soils on portions of the site. Therefore, Ten Bears personnel consulted geotechnical engineers to assist in developing a program for removing the impacted soils and placing backfill with minimal impacts from site groundwater to the structural stability of the on-site and imported soils.
The restoration of the site presented other design challenges. The construction plans called for additional excavations for foundation construction to be done following the restoration of the site with structural fill during site remediation. As a result, restoring the site to finished grading during remediation would result in removal and disposal of a significant quantity of the imported fill materials. Also, restoring the site to elevations to achieve a balanced cut and fill for construction would have left the site below street level prior to construction. This alternative likely would have facilitated ponding of stormwater on the site, which would have softened the placed structural fill. As an alternative, Ten Bears personnel developed temporary post-remedial surface grading to facilitate drainage toward an on-site sump. This solution provided positive drainage of the fill while eliminating the need to remove imported fill materials during construction, resulting in considerable cost savings to the property developer and a significant improvement in the structural fill upon which the foundation work could begin.