A short primer course on hydrogeology

1. A short primer course on hydrogeology Dr Ric Horobin 30th March 2009

2. Programme • Topics • the protection afforded by the geology • preserving protection through construction at the point of exploitation • Points of view • What is the ideal? • How to spot risks? • Timing • 45 minutes presentation • 15 minutes Q&A

3. Regulatory designations • Natural mineral water • recognised • protected from all sources of pollution • stable composition • limits on TVC’s • no contaminant microbiology • no treatment • Spring Water • not recognised • same microbiological criteria at source as a Natural Mineral Water (applies when bottling) • no requirement for stability highest reliance on hydrogeology intermediate reliance on hydrogeology

4. Some terminology • geology – study of the earth • hydrogeology – study of the water flow and storage within the earth • groundwater – water in the subsurface, below the water table • water table – the level at which water in the ground is at atmospheric pressure • catchment – water appearing in the source first fell as rain on the catchment area • aquifer – a geological unit that stores groundwater and allows it to flow readily into a well, borehole or natural exit (e.g. a spring) • geochemistry – the chemistry of rocks and minerals • hydrochemistry – the chemistry of dissolved and suspended elements in water • microbiology – the microbiological population of water, which can either be natural or introduced by contamination

5. runoff condensation water table precipitation spring evaporation evapo-transpiration evaporation bedrock infiltration groundwater flow saline groundwater The hydrological cycle

6. What is a Source? • a point of abstraction AND • a natural system • a hydrochemistry and microbiology adapted to aquifer conditions • this same microbiology and hydrochemistry forced into a different state through the point of abstraction • a source is a “living entity” • reliable quantity • reliable quality • composition and taste • absence of contamination

7. shortage of water (yield shortfall) regulatory exceedance taste defect precipitation chemical contamination microbiological contamination construction failure What can go wrong? Meteorology River Borehole Bottling plant Pipeline Catchment

8. Hydrogeology - gives protection • protected catchment • unsaturated zone • filtering layers - sand • long travel time • no short travel paths • good construction Shorter travel time waters can be acceptable if the catchment is pristine, but there is a limit because of wildlife

9. confined aquifer – permeable, water bearing rock unit separated from the surface by a low permeability unit (the confining layer) http://ess.geology.ufl.edu/ess An ideal source confined aquifer, long travel time, wild catchment Confining layer

10. Real life examples • different types of source • publicly available information • covers: • hydrogeology • hydrochemistry • catchment protection

11. hydrogeology – unconfined, shallow, fractured hard rock aquifer hydrochemistry – calcium and magnesium carbonate, low dry residue (165 mg/l) catchment protection – short travel time; organic principles to catchment management Example 1 – Ty Nant

12. hydrogeology - glacial outwash gravels yield - consolidated source, several springs hydrochemistry - calcium bicarbonate, 309 mg/l dry residue catchment protection - 15 year travel time. National Park. Agreements on fertiliser use. Example 2 – Evian

13. hydrogeology – fractured limestone, major geological fault yield – fluctuates, driven by geothermal force hydrochemistry – calcium carbonate, 280 mg/l dry residue catchment protection – > 4,000 years travel time. Geological protection; National Park Example 3 – Buxton

14. Recognition – what to look for • Answers to the following questions: • What is the source aquifer? • What is it that gives the water its characteristics? • Where is the catchment area? • Are there risks in the catchment area? • Is the aquifer protected from pollution? • What is the flow rate? Composition? Temperature? Dry residue (@ 180 and 260 °C)? • Is the source stable? • Is the abstraction point protected from pollution?

15. Risks in the catchment zone • An owner needs to: • understand the term “catchment zone” • appreciate the risks associated with the catchment zone • have an idea of where the catchment is (if situation not too complicated) • understand what natural protection might exist • understand the significance of distance and travel time • be able to collate information on land use in the catchment area • understand which land use activities could represent a high risk

16. simple unconfined example uniform aquifer with vertical recharge (rainfall) only circle around the source abstraction and recharge rates define extent real situation: geometry affected by groundwater flow direction Borehole Water table Key terminology: cone of depression = depression in groundwater level around borehole Catchment identification - 1

17. borehole Catchment area Catchment identification - 2 • Confined aquifer • geology • dip • outcrop • topography • groundwater flow • Area: recharge rate vs abstraction rate • Geometry: groundwater flow paths

18. Catchment identification - 3 • hydrochemistry and modelling for complex situations

19. key issues current land use historic land use industry farming sewers and septic tanks information sources OS plans water company records Sitescope EA DEFRA local authority walkover survey Catchment land use assessment

20. industry landfill Bottling plant agriculture septic tanks and sewers Hazard identification • current and historic

21. drift low permeability – filters very low permeability – lengthens travel path unsaturated zone filters confining layers pressure against contaminant flow artesian water pressure against contaminant flow right to the surface travel time contaminant microbiology dies chemical pollutants adsorbed or breakdown catchment activity different in the past Natural protection

22. Travel time • the period between water leaving the surface (meteoric water) and appearing at the point of abstraction • key factors – distance, permeability, hydraulic gradient groundwater age – could be mixed

23. Risk assessment – best practice • assess likelihood of source aquifer contamination through step by step appraisal of: • surface protection • unsaturated zone • confining layer • travel time • hazards – use scoring system • qualitative risk assessment to assign risk rating

24. Source construction (borehole) • basic requirements • eliminate risks associated with: • surface water flow down borehole • perched water flow down borehole • cross unit contamination • permits the source water to enter • holds aquifer particles out of borehole • design ensures only desired water enters • hygienic materials

25. oil free compressors any contamination source must be bunded (drill rig engine, fuel tank etc) surface casing to keep out surface water casing stored off the ground, capped; well screen wrapped disinfection in situ after construction Well drilling - contamination and hygiene

26. casing open hole or well screen sealing of casing Mild steel, uPVC, HDPE or stainless steel Borehole construction

27. Borehole head sealed flange air filter spray balls dip tubes (sealed) for instruments and manual check valveing for wellhead CIP building above ground - no sumps access for lifting well string secure length for pipework, flow meter, etc. sampling point Headworks

28. Spring capture structure - schematic membrane

29. SUMMARY • ideal source hydrogeology • long travel time, confined, wild catchment • in practice • combination of catchment protection, unsaturated zone, filtering layers, travel time, no short travel paths • source must • be well constructed with an understanding of the hydrogeology • prevent any surface water entering • prevent any short travel time water entering • risk factors • sources which react quickly to rainfall • sources which decline markedly in summer • turbidity • occasional poor micro

30. Further information • Zenith publishes the Plain Language Guide to the Natural Mineral Water regulations • http://www.zenithinternational.com/operations_consulting/plain_language_guide.htm • UK Groundwater Forum • www.groundwateruk.org • Dr Ric Horobin • Water & Environment Director • rhorobin@zenithinternational.com Thank you * Questions