The Bonterra site is a 114-acre abandoned tree farm and former cattle ranch that is being developed into a residential community. WGI conducted an assessment to determine what fraction of the arsenic in soil was anthropogenic and what fraction was naturally-occurring. WGI delineated numerous hot spots of arsenic in soil, directed removal of the hot spots, and prepared a Source Removal Report. To streamline the sampling effort we used XRF (x-ray fluorescence) in the field to delineate hot spots. WGI prepared a Soil Management Plan and a lakefill permit application to manage the remaining soils onsite. The plan included an innovative strategy to excavate a lake and partially backfill it with soils that contained elevated levels of arsenic. During construction, WGI conducted the environmental compliance monitoring of the onsite soil management; this required thorough testing of stockpiles of muck before reuse as lakefill. WGI also installed and sampled the groundwater monitoring wells required by the lakefill permit.