Hazard ranking method for populations exposed to arsenic in privatewater supplies: Relation to bedrock geology

Helen Crabbe*, Tony Fletcher, Rebecca Close, Michael J. Watts, E. Louise Ander, Pauline L. Smedley, Neville Verlander, Martin Gregory, Daniel R.S. Middleton, David A. Polya, Mike Studden, Giovanni Leonardi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Approximately one million people in the UK are served by private water supplies (PWS) where main municipal water supply system connection is not practical or where PWS is the preferred option. Chronic exposure to contaminants in PWS may have adverse effects on health. SouthWest England is an area with elevated arsenic concentrations in groundwater and over 9000 domestic dwellings here are supplied by PWS. There remains uncertainty as to the extent of the population exposed to arsenic (As), and the factors predicting such exposure. We describe a hazard assessment model based on simplified geology with the potential to predict exposure to As in PWS. Households with a recorded PWS in Cornwall were recruited to take part in a water sampling programme from 2011 to 2013. Bedrock geologies were aggregated and classified into nine Simplified Bedrock Geological Categories (SBGC), plus a cross-cutting “mineralized” area. PWS were sampled by random selection within SBGCs and some 508 households volunteered for the study. Transformations of the data were explored to estimate the distribution of As concentrations for PWS by SBGC. Using the distribution per SBGC, we predict the proportion of dwellings that would be affected by high concentrations and rank the geologies according to hazard. Within most SBGCs, As concentrations were found to have log-normal distributions. Across these areas, the proportion of dwellings predicted to have drinking water over the prescribed concentration value (PCV) for As ranged from 0% to 20%. From these results, a pilot predictive model was developed calculating the proportion of PWS above the PCV for As and hazard ranking supports local decision making and prioritization. With further development and testing, this can help local authorities predict the number of dwellings that might fail the PCV for As, based on bedrock geology. The model presented here for Cornwall could be applied in areas with similar geologies. Application of the method requires independent validation and further groundwater-derived PWS sampling on other geological formations.

Original languageEnglish
Article number1490
JournalInternational Journal of Environmental Research and Public Health
Issue number12
Publication statusPublished - 1 Dec 2017

Bibliographical note

Funding Information:
Acknowledgments: The authors would like to thank all the householders who participated in the study. PHE colleagues are thanked for their support and input including the South West PHE Centre for field work co-ordination, recruitment of households and project management. Public health students also helped to recruit householders to the study. We thank the Cornwall Council Environmental Protection Team for access to the private water supplies data and for dissemination of results and advice to householders; Helen Taylor and Elliott Hamilton (BGS) for water sampling in the field and laboratory analyses; Stephen Robjohns, PHE Toxicology Group for toxicological and water advice; Zori Daraktchieva and Jon Miles (retired) of the PHE Radon Group for discussions about the application of the radon log-normal probability method are thanked. PHE designed the tracking proof of concept study, funded the study design, field collection and analysis within the Environmental Public Health Tracking programme. All other costs were met by the authors’ organisations. DM acknowledges the receipt of an NERC/CASE (with BGS) Ph.D. studentship (Contract No. GA/125/017, BUFI Ref: S204.2) PHE covered the costs to publish in open access.


  • Arsenic
  • Environmental public health tracking
  • Geology
  • Hazard and exposure assessment
  • Private water supplies
  • Public health risk


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