Car Dealership’s Diesel Problem, San Diego, California

The Problem: A car dealership owned a underground storage tank. The tank leaked diesel into the underground, potentially threatening the groundwater. The agency standard of practice at the time was a linear universal strategy. That meant, first investigate the vadose impact extent, second the groundwater impact extent and third do cleanup before case closure. The problem with this strategy is it results in many years at great cost to plod through each step. The average case age took 16 years. The average case cost ranged from $400,000 to $800,000.

Our Solution: We invented a case closure risk model based on site specific conditions. Our team mathematically assessed risk probabilities with the boundary limits of a shallow diesel impact. We measured lab results, migration pattern through the underground geology, the distance to the deeper groundwater table, and the groundwater flow direction risks. The modelled results revealed that the diesel would weather to harmless byproducts over 1,000 years migration to groundwater and that there was no impact risk to groundwater. We drilled out a deep high-risk core in one day by a behemoth drill rig. The low-risk outer impact was left in the underground. The agency accepted our risked-based case closure proposal to set a precedent for new policy.

The Benefit: Our new strategy enabled site-specific, risk-based case closures to result in savings of time, cost, and rigor. This strategy was adopted locally and eventually statewide. Our solution was revolutionary over the earlier linear discovery strategy, due to low risk parts of the impact that could be left in the underground and limiting cleanup to the high-risk core. This car dealership benefited by this kind of case closure in a fraction of time and cost consequence compared with others using the non-risk based linear discovery.