Adaptive Groundwater Management: Tiered Environmental Health Risk Assessment and Zonation at Complex Contaminated Sites

“One toxicant at a time”
regulations overlook the
joint risks posed by realistic coexposure to complex toxicant mixtures
in groundwater. Here, 1,016,590 quarterly concentration records for
277 toxicants from 367 monitoring points were integrated into an adaptive
zonation and classification framework for mixture-oriented risk management.
Ecological mixture risk was quantified with species-sensitivity-distribution
models combined in a tiered concentration addition → response
addition (CA → RA) scheme, while Monte Carlo simulations captured
probabilistic carcinogenic and noncarcinogenic human health risks.
These dimensions were merged into an environmental health risk index
(EHRI; 0.42 ecology: 0.58 health). Quadrant analysis identified four
coexposure patterns and showed that ≤10% of detected toxicantschiefly
inorganics, metals, BTEXs, haloalkanes, and phenolsdrive >95%
of cumulative EHRI. Spatial interpolation converted point-level EHRIs
to grid-scale and, when embedded in a “source–plume–buffer”
treatment train, reduced the great concern zone (EHRI > 0.60) from
19 km2 to <0.1 km2 after removal of 45 highest-leverage
toxicants. The framework unifies deterministic and probabilistic perspectives,
pinpoints priority toxicants and zones, and supplies tier-graded actionable
triggers for adaptive intervention. This study provides the first
field-scale evidence that mixture-aware risk assessment can be directly
coupled to risk-zoned management, offering a transferable blueprint
for the sustainable regulation of complex, multipollutant groundwater
systems worldwide and a framework potentially relevant to other management
zones such as surface water.