We provided process-engineering support for a remediation system that had been shut down for exceeding permit limits. The system used air stripping and granular activated carbon to treat ground water containing MTBE and BTEX. The system experienced unexpected breakthroughs. By analyzing process data we showed that sudden spikes in influent MTBE concentration caused the breakthroughs. We recommended operational and design improvements to accurately predict carbon life, schedule change-outs and make the system less vulnerable to sudden changes in concentration. The overseeing regulatory agency directed the client to startup the system conditional upon implementing our recommendations.