Abstract: The scientific validity and rationality of soil eco-environmental baselines for informal solid waste landfills fundamentally govern the impartiality of assessment conclusions and the efficacy of remediation strategies. To address the prevalent issue whereby national risk screening values are routinely substituted for regional environmental baselines in current soil ecological damage assessments， practices that readily generate false positives in high-background areas and false negatives in low-background areas， this study investigated nine typical informal solid waste landfills in the Yangtze River Delta. Stratified soil samples were collected at depths of 0-0.5 m and 0.5-5.0 m, with two reference frameworks employed: the control-area baseline derived from on-site survey statistics, and the standard baseline represented by national risk screening values. A systematic comparison was conducted to elucidate discrepancies between these two baselines regarding pollution identification, exceedance determination, and remediation depth accounting. The results showed that the control area baseline was generally 24.2% to 99.8% lower than the standard baseline, exhibiting significant gradients with soil depth and pollutant type. When assessed against the control area baseline, the overall exceedance rate increased from 10.8% to 47.3%, revealing substantial “hidden” pollution that met regulatory standards but exceeded local baseline levels. Domestic waste landfills exhibited characteristics of “low-concentration, large-scale” non-point source accumulation, while industrial waste landfills showed “composite-deep” penetration patterns. Embedding the “real regional background” as living data that can be cited on demand will defuse the risks of “false compliance”, “excessive compensation” and “over-remediation”, promoting soil ecological environment damage assessment for informal landfills from “one-size-fits-all national line” to “true local baseline” and providing closed-loop support for precise identification, moderate remediation and fair compensation.

Key words: informal solid waste landfill, identification and assessment of eco-environmental damage, soil eco-environmental baseline, control area method, risk screening values (RSVs), pollution identification, remediation targets