Waye Cottage Water.

Stephen Crittenden 14/03/2008

1

The drilling of a borehole to provide an additional Water Supply at Waye. by Stephen Crittenden BSc, MSc, PhD. Independent Geological Consultant. April - May 2004. Introduction. This document records the drilling of a borehole at Waye Cottage to ‘tap’ a groundwater source in order to supplement the existing well supplied Domestic Water, in the hamlet of Waye. It is stressed that the comments and discussion in this document are made purely from surface observations by and from the best judgement of Dr Stephen Crittenden, Independent Geological Consultant. For this study no scientific measurements or tests have been performed to assess the underground water situation at Waye. Such tests, measurements and procedures may be carried out in the future. Accordingly the correctness or accuracy of the information and interpretation herein cannot be warranted and under no circumstances should any such information or interpretation be relied upon as the sole basis for any drilling or financial decision. In no event will Dr Stephen Crittenden be liable for any damages including but not limited to, indirect, special or consequential damages, resulting from the use of any information or interpretation provided. Prior to 2004 the three houses at Waye; Waye Cottage, Waye Farm and Lower Waye Farm, were each supplied with domestic water by their own dug well /cistern. Each well is in the order of 10metres deep (30 – 35 feet) and at some time in the past hand dug. The three wells are approximately within 50 metres of each other. The two wells supplying the medieval long houses of Waye Farm and Waye Cottage were dug probably in the 14 / 15th Centuries in fractured / jointed rotten granite to a depth of about 10metres (30 - 35 feet). They are unlined and are about 1 metre square in cross section. The well at Lower Waye Farm is topographically lower than the other two but is also dug predominantly in granite. It is lined with dressed granite setts / bricks and was probably dug some time in the 19th century. Further investigation of this well may reveal that it is dug partially in growan /alluvium above granite.

Simple Geology, Bedrock and Groundwater The storage and circulation of ground water at Waye is very dependent on the local geology. At Waye Cottage the bedrock is hard ‘blue’ Dartmoor Granite which is overlain by a thin veneer of soil. In the Waye hamlet area there is in some places a thin veneer of alluvium, which has been worked for tin some time in the past, and ‘growan’ – rotten decomposing granite. There are no Culm Measures or rocks of the metamorphic aureole at Waye. Granite is pervious due to the presence of interconnected open joints and fissures (both macro and micro sized) through which water can flow. At Waye the water migrates through the rock by the most permeable routes and emerges by natural openings (to form springs and seeps), by the three artificial openings (hand dug wells) and by direct feed into the small streams. The actual water storage capacity of the granite beneath Waye Cottage is probably not high and is

Waye Cottage Water.

Stephen Crittenden 14/03/2008

2

controlled by the density and volume of the open fractures and joints for a given volume of rock. Below a certain level beneath the ground surface at Waye Cottage all porous, permeable and fissured rocks are saturated with water (ie. groundwater). The upper surface of the groundwater is termed the water table. The water table surface follows in general the topography of the ground above; it is arched up beneath hills and curves down beneath hollows and vales. Beneath the ground surface three successive zones are recognized. These zones are dynamic.

a) The uppermost zone is the Zone of Non-saturation. b) The Zone of Intermittent Saturation extends from the highest level ever

reached by groundwater (after prolonged wet weather), the water table, down to the lowest level to which the water table drops after drought. The three wells at Waye are mostly in this zone and the upper part of the Zone of Permanent Saturation.

c) The Zone of Permanent Saturation extends down to the limit beneath which groundwater is never found.

The Borehole It was decided to drill a borehole at Waye Cottage into the granite deep into the Zone of Permanent Saturation. The hope was that a number of fresh and drinkable water bearing fissures, fractures and joints would be intersected by the well bore thus providing multiple sources of water influx into the well bore. If a deep (about 65metres) borehole were drilled then the chances of obtaining water were considered to be good but….how much water and of what quality could not be determined. The site of the borehole at Waye Cottage was decided by the available surface area and a thorough site survey was deemed unnecessary although existing water rights and contamination possibilities were considered. According to the Government Department of the Environment it was not necessary to seek permissions for the site and drilling of a borehole and for the eventual abstraction of water for domestic use. Unfortunately at Waye Cottage there was not the possibility that a borehole could be sited such to tap two sources of water; one from an overlying alluvial aquifer where the water is possibly more mobile but thus prone to contamination, and one from the granite aquifer beneath. There are no alluvial deposits in the curtilage of Waye Cottage. The borehole was sited in front of the shippon adjacent to the original cross passage entrance on the northern side of the Waye Cottage Longhouse. Saxton Drilling Ltd was contracted to carry out the drilling of the borehole while Waterwise Engineering was contracted to complete and ‘plumb-in’ the borehole to the existing pipe system of Waye Cottage. The 6 inch diameter borehole was drilled, using a tractor mounted compressed air and rotary / percussion drill, to a depth of 226 feet (69m). A plastic slotted liner was placed in the borehole together with an electric downhole submersible pump and pipes to a large storage tank in the shippon. The water is passed through a UV light system, a Ph correction unit and a chemical treatment system. A separate surface pump transports the water to the house. The downhole pump is switched on automatically when the level of water in the storage tank falls down to and below a pre-set level.

Waye Cottage Water.

Stephen Crittenden 14/03/2008

3

Rate of Abstraction The rate of abstraction of water for domestic use from the borehole at Waye Cottage is regulated by a number of factors.

A. The water level in the borehole will fall if the “granite aquifer” is not able to transmit the percolating water to the borehole at the rate with which water is being withdrawn.

B. A localized cone of depression – draw down of the water table, may occur if excessive rates of abstraction are used in a borehole even if it is penetrating the Zone of Permanent Saturation.

C. The rate of abstraction of water through the borehole tapping the storage must not exceed the rate at which the storage is being recharged by infiltration. If it does it results in the lowering of the water table and emptying of the aquifer that may have taken decades to fill. It may then take some years for the aquifer to recharge and the water table to rise to its former level in the area.

D. It is never sensible to pump a borehole dry. Such a practice runs the risk of permanently damaging the water transmission ability of the fractures and fissures that ‘feed’ the borehole and indeed can adversely affect the water table level for some considerable radial distance from the borehole. Water travels by preferred routes in the fractured granite aquifer and routes can in some instances become plugged /blocked such that a borehole may become semi-bypassed.

A typical borehole in Granite in Devon usually flows less than 3 – 4 cubic meters /day. The Waye Cottage borehole ‘struck water’, probably at a number of fractures toward the bottom half of the borehole as evidenced by a spectacular water and mud spout shooting into the air – caused by the compressed air used for the drilling. Previous to that the granite cuttings / flour brought to the surface by the compressed air was dry / damp. Prior to the completion of the well the bore was pump tested in the following manner. The downhole pump was lowered into the borehole which was left to stabilize for a day and the final height of the water column measured at 6.3m (20.67ft) from the surface. Pumping commenced and a final flow rate of 9.8 litres / min (2.15 gallons / min) was established that maintained the water height in the borehole. An increase in the pump rate caused the level in the borehole to fall. The borehole was then left for two days pumping at slightly below the 9.8 litres / min rate in order to clean up the water and the borehole. The daily rate of flow is equal to 14,112 litres / day (3,104.27 gallons / day) more than sufficient to meet the domestic daily demands of Waye Cottage.

Water Quality The quality of the water was measured by the South West Water Scientific Services Exeter Laboratories between 13th May and 25th May 2004. The Manganese (102micrograms per litre), Aluminium (440 micrograms per litre) and iron (2450 micrograms per litre) levels were above the maximum level standards set by the UK

Waye Cottage Water.

Stephen Crittenden 14/03/2008

4

Government for drinking water. This necessitated the installation of treatment procedure equipment by Waterwise Engineering Ltd. The iron levels were by far the biggest worry in terms of excess above the government maximum of 200 micrograms per litre.

Borehole Water Supply Cost Saxton Drilling drilled the borehole and supplied all drilling equipment, slotted liner and personnel at an all in cost of £1000.00 (no VAT). The drilling took three days. Waterwise Engineering Ltd costs were £2818 (excluding VAT). Total Cost : £3818.00 VAT : £649.01 £4467.01

Photographs of the Job The photographs show the setting up of the drilling equipment, including polythene sheeting to protect the interior of the shippon; the tractor mounted drill, the pneumatic compressor, the drill pipe and the cuttings pile, and the completed well head with the liner in place and the down hole pump and cable all protected by an upturned bucket prior to the final well completion.

Waye Cottage Water.

Stephen Crittenden 14/03/2008

5

Waye Cottage Water.

Stephen Crittenden 14/03/2008

6