The California Department of Toxic Substances Control (DTSC) oversees cleanup of contaminated sites across the state, with a regulatory framework that prioritizes engineering‑based remediation methods such as soil excavation, off‑site disposal, and pump‑and‑treat systems for groundwater. These approaches are designed to control risk, ensure compliance with state cleanup standards, and provide predictable, measurable outcomes. It is important to acknowledge that DTSC does not endorse any specific company, service, or product.

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In contrast, in‑situ (or in place) bioremediation is a science supported and nature based method that treats contamination directly in place. For groundwater, this process involves adding organic substrates such as molasses, vegetable oils, or whey to stimulate naturally occurring bacteria. These microbes use the added organic matter as food and, in the process, break down pollutants like trichloroethylene (TCE), a common industrial solvent.

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A similar biological process can be applied to contaminated soils. Just as composting relies on food scraps, wood chips, and green waste to feed microbial communities, soil bioremediation uses organic matter to increase microbial diversity and activity. A richer microbial ecosystem improves the breakdown, transformation, or stabilization of contaminants, supporting long‑term soil recovery.

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Compared to traditional pump‑and‑treat or excavation‑and‑haul methods, in‑situ bioremediation can be more cost‑effective, energy‑efficient, and environmentally beneficial. It often shortens cleanup timelines and reduces the generation of secondary waste. Emerging approaches such as plant‑based remediation using species like hemp and willow are demonstrating additional promise for contaminants like PFAS, offering lower‑impact alternatives to conventional engineering solutions.

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As research advances, in‑situ bioremediation continues to evolve as a practical, science‑driven option for addressing both groundwater and soil contamination. As a past DTSC Branch Chief Charlie Ridenour noted, “All the new remedies are in‑situ bioremediation.”

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https://dtsc.ca.gov/proven-technologies-remedies-documents/?form=MG0AV3