A new report by Snyder Geologic has raised significant concerns and issues with the analysis of the Hamilton Lane development project near the Chatham Barrel Yard remediation site.
The full Snyder Geologic Hamilton Lane Report here.
Summary of Snyder Geologic Report on Hamilton Lane
The report outlines issues with the project as proposed due to significant gaps and lack of mitigation sufficient to protect the health of the residents, the integrity of the groundwater site, and the interests of the city.
Findings include:
- Monitoring wells both above and down-gradient of the site show results indicating the plume of contamination is unstable.
- Without monitoring wells on the proposed development site, the question of whether the plume is beneath the site is unknown and should be determined.
- Analysis is insufficient to credibly show how soils on the property will be ‘balanced’ without major disruption of the site such as through blasting.
- The design of the bioretention basin is of concern; failure could send stormwater into the subsurface impacting contamination patterns.
- Significant data gaps exist, inadequate technical studies, limited/shallow soil-vapor testing, and missing historical well-by-well data.
Summary Recommendations for the City Council to require of the applicant prior to approval:
- Additional wells should be drilled and analyzed to characterize condition of groundwater at the site of construction.
- A geotechnical analysis be done prior to alteration of flow patterns of groundwater in the event of significant site disturbance.
- Because the Chatham plume is within this complex bedrock aquifer in the area of the development project and altering the bedrock aquifer by blasting should be avoided.
- Close data gaps by sampling of deeper soil and soil vapor should be conducted as well as an evaluation of the potential for perched groundwater that may be contaminated.
- Prohibition on water supply wells at the site.
- Soil vapor barriers should be added to homes and testing be conducted at various depths beneath each site.
- Remove bioretention basin or re-design with a redundant liner, monitoring, and a failure response plan if approved.
- A soils management plan should be required to describe precautions to protect neighbors during construction.
- Proponents should submit complete information and request a formal review from DTSC, specifically, input and evaluation of the potential for blasting of the bedrock during project construction, if required, to alter groundwater flow in what is a complex bedrock aquifer hydrogeologic system.
The community appeal of the project will be heard by the City Council on August 5, 5 PM at city hall.