Boreholes drilled to determine the source of Jersey's deeper water

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WRITTEN QUESTION TO THE MINISTER FOR PLANNING AND ENVIRONMENT BY DEPUTY G.C.L. BAUDAINS OF ST. CLEMENT

ANSWER TO BE TABLED ON TUESDAY, 30th JANUARY 2007

Question

1. W i th regard to the twoboreholes recently drilled in order to determinethesourceofJersey'sdeeper water, would the Minister inform members –

1. w  h ether the bore at St. Catherine was drilled where the waterdivinerswanted and, if not, whether the alternativesitewaschosenin order to save money?
2. w h e th er the drill-rig wasbrought back to re-drill the bore atLaRocque?

2. W i th regard to the LaRocquebore,wouldthe Minister advise –

(i )  w h e th er the bore had to be re-drilled and, if so, whether it now meets specification?

2. th e depthofthebore?
3. at what depthflow-rate and samplesweremeasured?
4. w hether the contractor has been paid for his work?

Answer

1. The  investigation  was managed through DGAG and  the  process  has  been  open throughout.  Two consultants  (The  British  Geological Survey and  Entec UK Ltd)  were  appointed  by DGAG to independently oversee and quality-assure the experimental design, delivery, analysis and subsequent reporting. All aspects of the investigation were discussed by the DGAGgroupandmemberswere kept regular updated.Membersshowed interest in the drilling work and took the opportunity to regularly visit the drill sites and todiscuss various aspects with the consultants.

B o th water diviners, Mr George Langlois and Mr Lewis de la Haye are members of the Deep Groundwater

Advisory Group (DGAG). An essential part of the agreed methodology was that Mr  Langlois and Mr de la Haye would identify two locations in Jersey which they considered to be the most probable sites where underground streams' exist. As well as the location, they informed DGAG that they would also identify the depth of the stream' below ground level.

M  r L anglois and Mr de la Haye were given an absolute free hand and as much time as they wished to

identify the sites and depths to be drilled. They were given a window' of up to a depth of 750 feet below ground level in which to locate the stream'. Both the diviners gave this task their utmost attention to detail, as well as identifying spots to be drilled they further took the time to divine the respective streams' for some distance to and from the site. The final locations and depths identified were presented to and agreed by DGAG members.

M r L anglois and Mr de la Haye marked the spots they had chosen with a paint cross and Mr Langlois was

present when drilling commenced to ensure that the drill bit entered directly on the mark that they had identified.

O n e of the initial sites considered by Mr Langlois and Mr de la Haye at St Catherine was towards the top of La Vielle Charrière above Pine Walk. This was later changed when Mr Langlois discovered that the

same stream' could be accessed and effectively drilled into on lower ground toward the coast at Pine Walk.

T h e advantage of the second site was that the same stream' could be drilled into without pre-drilling

through the overlying hill. This minimised the drilling depth (from 450 to 250 feet) and so maximised the chance of hitting' and drilling into the identified underground stream'. The cost saving of this second site was offset as an access road had to be constructed to get the drilling rig in.

(i i)  T he first stage of the investigation involved the drilling out of the borehole to the depths specified by Mr

Langlois and Mr de la Haye as being where the stream' could be located. All the planned sampling of chemistry, isotopes and recording of air-flush yields, groundwater levels, rock type and hardness were successfully completed during this stage.

T h e second stage of the investigation involved hydraulic testing of the aquifer to determine the yield of

each borehole. This required that submersible test pump was lowered to just above the base of the borehole. The drilling rig was brought back to the site to clear some plastic debris at about 25 m depth that was preventing the pump from being lowered any further. This was cleared with no difficulty and the pump was installed at the specified depth. The hydraulic testing of the aquifer and further sampling of isotope and age then was successfully completed.

2. A s above,at the LaRocqueborehole the rig successfully cleared plastic debris without re-drillingof the borehole.

T h e borehole at La Rocque fully conformed with the stringent specification as demanded by the

investigation and agreed by DGAG members. The major evidence of this was that all the shallow groundwater (7 litres per second) was effectively sealed out permitting valid samples to be obtained from the depths of the predicted streams' specified by the water diviners.

T h e d rilling process was supervised throughout by a consultant from the British Geological Survey who

has extensive experience in drilling and supervising such boreholes worldwide. All information pertaining to the drilling process is included as part of the comprehensive technical report.

A l l m embers recently viewed a video of the inside of the borehole at La Rocque. This showed that the

borehole was solid. This was clearly evidenced in that the cement could withstand some superficial scratching by the drill bit. The video showed no signs of having been compromised.

(i i)  T he investigation specified that both the La Rocque and St Catherine borehole should be drilled through

the stream' and to a total depth below the stream' predicted by Mr Langlois and Mr de la Haye. At the request of the Minister for Planning and Environment the La Rocque borehole extended some 3 m beyond this to further try to locate a high yielding stream'. At the request of Mr Langlois the open uncased section at St Catherine was increased, again to maximise the chance of locating a stream'.

T h e f inal drilled depths were: La Rocque 55.5m (182 ft) below ground level (bgl) and St Catherine 79.5

m (261 ft) bgl. Both these depths exceed the predicted stream' depths by Mr Langlois and Mr de la Haye streams (La Rocque 45.7 m (150 ft) bgl, St Catherine 76.2 m (250 ft) bgl).

D e ta i ls of the drilling depths are given in the summary and technical reports.

(ii i) All samples and flow rates taken were fully in accordance with the experimental design of the

investigation. As much data as possible was collected during the investigation.

D u r in g the first stage of the investigation (the drilling of the borehole) –

A   t o t al o f 13 water samples for inorganic chemistry were taken at La Rocque at 10, 19.5, 22, 28.5,

34.5, 37.5, 43, 44, 46.5, 47.5, 48.5 50.5 and 55m bgl. Isotope samples were analysed for depths 10, 19.5, 22, 34.5, 37.5, 43, 46.5, 50.5, 55 m bgl.

A t o ta l o f 9 water samples for inorganic chemistry were taken at St Catherine at 58, 68, 70.5, 72, 73.5,

75.5, 77, 78.5 and 79.5 m bgl. Isotope samples were analysed for 58, 68, 75.5, 77, 79.5 m bgl. Above these depths no suitable groundwater was found that could be sampled.

I sotope samples for analysis were taken for every depth where a variation in air-flush yield was

recorded.

I n b o t h b o reholes specific electrical conductance, pH and temperature were measured every 0.5  m.

In b o t h boreholes  rock chip  samples  were  taken  and a  description  of  rock  types  and hardness

(penetration rate) was made every 0.5m.

A  t L a R o cque, 35 measurements of the air flush yield were taken. A total of 31 were taken at St

Catherine. Rest water levels and water inflows were also recorded.

D etailed measurements and further isotope, inorganic chemistry and age-dating tracer gases samples

were also taken during the hydraulic testing of the aquifer and from neighbouring boreholes.

F ull details of all samples and results taken during the investigation, as well as, the comprehensive

reporting of all activities are included in full technical report and summarised in a summary report. These can be accessed on the Environment site on the States of Jersey web site:  www.gov.je.

(iv )  The contractor constructed both boreholes to the required specifications and has been paid.