Case Study: Vapor Intrusion Mitigation System - Mission St., San Marino, CA.
Sub Slab Depressurization System on an Existing Property
THE CHALLENGE
Terra-Petra was engaged by legal counsel representing the owner of a former dry-cleaning facility in Southern California where vapor intrusion had compromised indoor air quality and stalled commercial viability.
Testing confirmed elevated levels of dry-cleaning and solvent-related contaminants (including Tetrachloroethene and others), creating both regulatory exposure and a blocked path to occupancy.
The mandate was clear: solve the problem in a way that restores asset value—without over-engineering the fix.
SOLUTION
Terra-Petra performed a full diagnostic investigation to design a precision Sub-Slab Depressurization System (SSD) to alleviate the issue.
This included:
- Pressure field extension (PFE) testing
- Permeability mapping to determine exactly how much vacuum was needed and where
- Establishing a minimum sub-slab negative pressure field of -0.016” w.c.
The result: a data-driven mitigation design that eliminated trial-and-error, avoided underperformance, and prevented costly over-design.
Terra-Petra engineered the system, secured permits, and moved directly into implementation with a clear scope, timeline, and cost control to keep the project on-schedule and within budget.
OUTCOME
The property moved from a stalled, impaired asset to a controlled and commercially viable site with a defined path to re-occupancy. The space is now occupied.
Terra-Petra’s approach delivered:
- Targeted, effective vapor intrusion mitigation
- Lower installation and long-term operating costs
- A defensible solution for regulatory and legal stakeholders