Hydrogeology
Water, Springs and Mine-Water Pathways
In a historic mining district, the question is not how far apart two points are on the surface. It is whether they are connected underground.
Intact granite has relatively low matrix permeability: water does not move easily through the body of the rock itself. That fact is often used, incorrectly, to argue that groundwater cannot travel far.
In historic mining districts, groundwater movement is instead dominated by secondary permeability — the openings created by geology and by three centuries of mining:
- Fractures
- Joints
- Mineral veins and lodes
- Shafts
- Adits and drainage levels
- Stopes
- Tunnels
- Flooded workings
- Artificial drainage routes
These features can transmit water rapidly and over distances that bear no simple relationship to surface geography. Water can also move in directions that surface topography would not predict.
The investigation must therefore examine underground connections rather than simply surface distance. Establishing or excluding connectivity is a hydrogeological question, answered by mine plans, water-level monitoring, hydrochemistry and, where justified, tracer testing.
Conceptual pathways
Routes that must be tested, not assumed
The following are conceptual pathways only. Each is a working hypothesis requiring hydrogeological investigation. None is asserted to be occurring.
Rainfall to spring
- 1Rainfall infiltrates the soil and weathered zone
- 2Water enters fracture and joint networks
- 3Flow intercepts a historic mine working
- 4Water moves through the flooded workings
- 5Groundwater re-emerges at a spring line
Conceptual pathway requiring investigation. Whether any such connection exists in this location is not established.
Mine-water to stream
- 1Water standing in historic workings
- 2Movement along a fracture or vein system
- 3Discharge to a drainage level or seepage point
- 4Entry to a surface watercourse
Conceptual pathway requiring investigation. Mine-water discharge to watercourses is well documented across Cornwall generally; its occurrence at any specific point here is unverified.
Altered groundwater to woodland
- 1A change in groundwater level or chemistry
- 2Altered saturation in the shallow soil profile
- 3Stress or decay affecting the fine-root zone
- 4Reduced anchorage and tree health decline
Conceptual pathway requiring investigation, linking hydrogeology to the tree-failure question. Not established.
Water evidence
How water testing is recorded here
Water results are only meaningful with their context. Every result published on this site carries the information needed to judge it.
Historic water tests
Awaiting verificationAny pre-existing test results held by residents, landowners, Environmental Health or previous owners. These are the closest thing to a baseline the area has, and are actively sought.
Current water tests
Awaiting verificationSamples taken now, at defined points, by a stated person, using a stated method, analysed by a named laboratory.
Control samples
Awaiting verificationSamples from comparable sources outside the area of concern. Without controls, no result can be interpreted as unusual.
Analytical suite
Determinands under consideration
The suite below reflects the geology of the district and the receptors present. Final scheduling should be set by an environmental geochemist and, where relevant, an explosives-residue chemist.
pH
Field and laboratory pH; mine-influenced water can be acidic or neutral.
Electrical conductivity
A rapid indicator of total dissolved ion content.
ORP / redox potential
Indicates oxidising or reducing conditions in the source.
Sulphate
Commonly elevated where sulphide minerals are oxidising.
Iron
Responsible for the familiar orange staining of mine-influenced water.
Manganese
Often accompanies iron; has its own drinking-water standard.
Arsenic
Naturally associated with Cornish mineralisation; requires careful comparison.
Lead
Can arise from mineralisation, historic processing or plumbing.
Copper
A principal historic ore metal of the district.
Zinc
Frequently mobilised with other base metals.
Cadmium
Often present with zinc mineralisation at trace levels.
Nitrate
Primarily agricultural; important as a control on interpretation.
Nitrite
Indicates incomplete nitrification or other processes.
Ammonium
Agricultural, organic or, in specific cases, energetic-material related.
Energetic / pyrotechnic compounds
Specialist determinands only where professionally indicated, using an accredited laboratory with appropriate methods and detection limits.
Evidence status
Water: where this stands
Secondary permeability dominates
That groundwater flow in fractured, historically mined granite terrain is dominated by fractures, veins and mine voids rather than rock matrix is established hydrogeological understanding, reflected in published BGS and mine-water literature.
Changes to springs and streams
Residents report changes in flow, colour, sediment or odour at particular sources. These reports are logged, but none has yet been supported by paired sampling with controls.
Underground connectivity
That specific springs or watercourses are hydraulically connected to particular underground features is a hypothesis testable by water-level monitoring, hydrochemistry and tracer testing.
Any contaminant pathway
No demonstrated contaminant pathway from any operation to any water receptor exists on the present evidence. Establishing or excluding one is a task for independent specialists.