Starting in the early 1950s and continuing over a period of several decades, arsenicals and organochlorine pesticides, including DDT and Lindane, and production raw materials and intermediates, were released into soil, groundwater, and surface water adjacent to Greens Bayou, a part of the Houston Ship Channel system. These contaminants were transported into Greens Bayou and local tributaries to the bayou via industrial discharges, surface water runoff, and groundwater discharge and upwelling. Geosyntec was retained by counsel to the Port of Houston Authority (PHA) to evaluate remediation strategies and develop remediation cost estimates to mitigate the impacts associated with this contamination loading to Greens Bayou and the tributary waterways, the most significant tributary being a large Harris County Flood Control Channel (HCFCC).
Geosyntec conducted a comprehensive review of topographical, bathymetric, geological, hydrogeological, and environmental data for the project area and constructed a geographic information system (GIS) and conceptual site model (CSM) for the area. The CSM included stormwater runoff, groundwater fate and transport, groundwater/surface water interaction, and sediment erosion, scour and transport. The GIS employed advanced applications of geostatistics, environmental chemistry and forensics, and data visualization techniques. The CSM model was used to characterize site conditions, describe the site-specific processes for contaminant transport from upland areas via stormwater runoff and sediment transport in the flood control channel, and contaminant transport in groundwater that migrated from site source areas to discharge points in Greens Bayou.
Geosyntec prepared design plans, specifications, and cost estimates for several remediation components, including: excavation and containment of contaminated upland soils, groundwater hydraulic containment system (soil-bentonite and cement-bentonite cutoff walls), groundwater extraction and treatment system, and sediment excavation and capping in the HCFCC. These soil, groundwater, and sediment remediation designs were intended to prevent recontamination of Greens Bayou after remedial dredging of the bayou (designed by others) was complete. Our scope of work also included extensive geotechnical analyses of waterfront structures and of a dredge spoil disposal area adjacent to the project site to assure their geotechnical stability during and after remediation and dredging activities.
Geosyntec prepared a GIS and CSM for contaminated soil, sediment, and groundwater resulting from historical operations of a pesticide production facility adjacent to Greens Bayou. Using this CSM, we prepared remedial design plans, specifications, and cost estimates for mitigating pathways by which contaminants could recontaminate the bayou. The remedial design developed by Geosyntec on behalf of PHA became part of a court-ordered remedy to restore water quality in Greens Bayou, remediate impacted sediment and upland soil, and prevent recontamination of sediments by impacted groundwater.