Deep groundwater - La Rocque and St. Catherine boreholes (P.22-2007) - comments

STATES OF JERSEY

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DEEP GROUNDWATER: LA ROCQUE AND ST. CATHERINE BOREHOLES (P.22/2007) – COMMENTS

Presented to the States on 22nd February 2007 by the Minister for Planning and Environment

STATES GREFFE

COMMENTS

Background information

1. M  a nyof the Island's inhabitants share a deeply held belief that a substantial deepgroundwaterresource derives from underground streams' that flow to the Island under the seabed from mainland Europe.
2. T h a t people hold personal beliefs isnotbeingchallenged.TheMinister'sconcern is simplyto ensure that the water resources in Jersey, onwhich the Island depends, are effectively managedforthelong-term.
3. A  s part of this responsibility,anevidence-based scientific investigation to determine, onceandforall, whether groundwater beneath Jersey is sourced from outside the Island wasundertaken.
4. T h e investigation wasmeticulouslyundertakenand benefited from independent hydrogeological expertise from two leading institutions; the British GeologicalSurvey(BGS)andEntecU.K. Ltd. The investigation was overseenby the Deep Groundwater Advisory Group (DGAG).Themembersof this groupcomprised equally ofthosewho do' and do not' advocate that such streams' exist and discussion and agreement was soughtduringeverystage of the investigation.
5. A  ll DGAGmembers signed anagreement that stated, The definitive test for proving whether or not a flowing freshwater connection with mainland Europe exists will be to compare the isotopic signature of the water sampled from the two test boreholes with that of water from the surface aquifer'.
6. A  t horough scientific investigation based on the best independent scientific advice and principles has been successfully completed with the full co-operationandagreementofDGAGmembers. The methodology, the data and its interpretation has been extensivelyreviewed both by the BGS and EntecU.K.Ltd.The conclusions of the investigation are robust.Thereisno valid justification for withdrawing them or for spending further public moneyor resources in this area.
7. M  e mbers oftheStatesof Jersey have been sent a summary report ofthe investigation. Further reports, including the comprehensive technical report, canbe viewed at the EnvironmentDivision'swebsite http://www.gov.je/PlanningEnvironment/Environment/
8. I n answeringthe questions raised by Deputy Baudains, the opinions of thetwoindependent consultants, BGS and EntecU.K. Ltd. have been sought.
9. T  h e replies tothequestions raised demonstrate that Deputy Baudains' concernsdo not distract or alter either the results or the conclusionsof the investigation.
10. T h e conclusions of the investigation basedon the two test borehole sites are that –

i. th e r e is no evidence to suggest that there are underground flowing freshwater streams' entering Jersey from outside the Island;

ii . th e isotope signatures and chemistry of groundwater from the test borehole at La Rocque are

consistent with recharge from rain falling on Jersey;

ii i. t h e deep groundwater at La Rocque is hydraulically connected to shallow groundwater, so if you

pumped water from depth, neighbouring shallow boreholes would be affected;

iv . t h e deep groundwater at the two sites does not represent a separate major groundwater resource

that would be capable of significant future development to contribute to the water needs of the Island.

11. T h ese conclusions are supportedby investigations undertakenbyDGAG into the many traditional and anecdotal stories offreshwaterstreams.Noevidencecouldbefoundto support such claims.

Question

The boreholes drilled at La Rocque and St. Catherine were created for research purposes – essentially to determine whether water from France reaches Jersey.

Unfortunately, the situation is now far from satisfactory –

1. T h e siteswerechosenby diviners, butwithin certain parameters. It wassuggested they should be on the east coast, where landownerswanted boreholes, and, in the case of St. Catherine,moved to another area in order to save money.

Answer

12. T h e methodstatementofthe investigation andthe signed agreement both state that the two testboreholes sites and the depths ofthe predicted streams' at eachsite were to be identified solely bytwomembersof DGAG;Mr. GeorgeLanglois(awater diviner) and Mr. Lewis de la Haye (a well driller).
13. T h e sites were to be located wherethese two membersofDGAGconsidered that underground streams' flowing from outside the Islandwould be present.
14. M r . LangloisandMr. de la Haye stated that they were able to identify two such sites at a DGAG meeting held 12th April 2006.
15. T h e courseof the streams' was divined byMr. Langlois forsome distance toand from the proposed sites. Mr. Langlois and Mr. de la Haye markedthe final selection ofeachsite with a white painted cross The drill rig was positioned and started drilling directly over this cross in the presenceofMr. Langlois.

Suggestion that sites should be on the east coast

16. M r .  LangloisandMr. de la Hayewere not restricted to sites on the east coast and were able to choose any location within Jersey.
17. M i nutesof a DGAG meetings (7th and 21st March 2006) confirm that Mr. Langlois andMr. de la Hay themselves provisionally identified two test borehole sites ontheeast coast.

Suggestion that sites should be where landowners wanted boreholes

18. M  r. Langlois and Mr. de la Hayewerenot asked to site thetest boreholes wherelandownerswanted boreholes. The St.  Catherinetest borehole site is, in fact, in a woodedarea and the LaRocque site where the landowner already has a new borehole and is alsosuppliedby mains water. Both test boreholes therefore havenoimmediate use and remain unused.

Suggestion that St. Catherine borehole was moved to save money

19. T h e borehole at St. Catherine was not moved to save money. The initial stream' identified by Mr. Langlois and Mr. de la Haye in late May2006 bisected the road at Pine Walk,St. Catherine. Thete borehole was, in fact, drilled some ten metres further along this stream'.
20. W hen this stream' was first identified, Mr. Langlois could not find an area of sufficient size to accommodate the drilling rig. Hetherefore looked at a site further upthe same stream' at the top ofMont des Landes, St. Catherine.
21. It w as later discovered that a rig could gain accessclose to the originalchosen site. This reduced thetotal drilling depth thus increasing the accuracy bywhich the drill rig could intersect any stream'. The cost saving due to the reduced depthof the borehole was offset by the need for anaccess road to be built to get

the rig into the site. Again, Mr.  Langlois and Mr.  de la Haye identified the exact spot where the borehole was to

be drilled.

22. N o influence of the site selection was exerted onMr. Langlois or Mr. delaHaye.DGAGmemberswer advised of the final sitesselectedin a letter dated 16th August2006.No objections byDGAGmembers were received to either site and drilling proceeded as planned on 11th September 2006.

Question

2. T h e goalpostsappearto have beenmoved.The original exercise was todetermine source. That now appears to have changed to proving the existence of deep water – which we all know exists in quantity anyway.

Answer

Changes made regarding the source of deep groundwater

23. In i tially, Mr. Langlois and Mr. delaHaye informed DGAGmembers that the origin ofstreams' was in La Petite Suisse (DGAG meeting, 25th January 2006). The initial draft of the agreement therefore stated that the definitive test of the origin of the water samples will be by comparison of the isotopic signature of the sample from the test boreholes with that in the Petite Suisse region'.
24. In a letter dated22ndMay 2006, Mr. Langlois andMr. dela Haye indicated their dissatisfaction with th initial agreementand requested the reference to La Petite Suisse region to be removed as the groundwater source. Further, they recommended an agreementbasedonassessing a difference in isotopic signature between shallow and deep groundwater in Jersey.The rationale of the changewas that if shallow and deep groundwater in Jersey has different isotope signatures then it must come from elsewhere.

Size and predictability of the deep groundwater resource

25. D G  AGmembersacknowledged that, as well as the origin ofgroundwater, the size oftheresourceand how much can be safely extracted in thelong-termwasalso an important consideration. This relates to the ability of an additional deep groundwaterresourcetosupply future waterneedsofthe Island (DGAG meeting, 7th December2006).
26. T h e specification for the investigation wasconsequently drafted. This included that thetestboreholes should beof sufficient completed diameter to allow proper pump testing and also to makepossible the collection of all relevant information during the drilling process that would assist in quantifying the deep groundwater resource beneath thetwo sites.
27. D u ring the investigation byBGS and EntecU.K.Ltd., collection of data of water inflows, flow rates and groundwater levels foundnoevidenceof discrete, singleundergroundstreams.The careful assessmentof all available data concluded that –

i. th e r e was no evidence that single underground streams' were penetrated by either borehole;

ii . m o r e frequent fractures in the upper granite provide greater flow and younger groundwater than in

the deeper, less weathered section;

ii i. t h e test yield obtained for the La Rocque borehole was above average but not exceptional, whilst

that obtained at St.  Catherine was very low and the water quality was poor and not potable;

iv . t h e groundwater at depth is hydraulically connected to shallower groundwater via a network of

interconnected fractures and does not represent a separate major groundwater resource that would be capable of significant future development.

Question

3. H alfway through the exercise it was admitted the isotope test chosen was incapable of differentiating between water originating in Jersey and water originating from nearby France. In fact, it is alleged thetest result gavethesamereading as water from nearbyFrance.

Answer

Lack of French Isotope data

28. B G S and EntecU.K. Ltd. provided a joint presentation to DGAGon 12th April 2006 (prior to the letter from Mr. Langlois andMr. dela Haye of22ndMay 2006 requesting significant amendments to th DGAGagreement).During the presentation, it was stated that therewas a sufficient difference in isotopic signature for waters originating in the Petite Suisseareaand Jersey to allow a definitive distinction tobe made between the twosources.Itwas also stated that signatures for the Island and the adjacent coastal areas ofFrancewere likely tobe too smallto allow such a distinction to bemade.
29. I n recognising that nearby France has similar altitude it is also acknowledged that there would be insufficient driving head orpressurefor a stream' to flow to Jersey from this area.
30. T h e quantity of isotope data from Normandyand Brittany is very limited, nonebeing available for coastal areas adjacent to Jersey. Sinceno reliable isotope values exist for nearby France, it has neverbeen alleged' that values were the sameasthose from Jersey.
31. A reliable and published groundwater isotope value exists for the Caen area(La Petite Suisse Region which will be similar to that for the Petite Suissearea)whichshows a significant variation from the isotope values found in Jersey, proving that underground streams' do not derive from thearea that was originally advocatedas the source byMr. Langlois andMr. de la Haye.

The context of the investigation

32. It r emains true that the isotope valuesinFrance are not relevant inthe context ofthe current investigation (as specified in the DGAGAgreement) that wasdesigned to test the difference between shallow and deep groundwater in Jersey.
33. T h e conclusion remains that –

i. is o t opic signatures' obtained from the shallow' and deep' sections of each of the two boreholes are indistinguishable and are also consistent with the range of isotope signatures for Jersey groundwaters;

ii . th e r e is no evidence to suggest that either the shallow or deep groundwater beneath Jersey has a

source that is located outside of the Island.

Question

4. It is alleged the borehole atSt.Catherineprovidesvery little water.Diviners are not noted for failing to producewater,soone must assumemoving from thesitechosen to a lower one in order to save money is responsible.

Answer

34. A s mentioned above, the borehole at St. Catherinewas drilled at the exactlocationandbeyond the exact depth divined and identified byMr. Langlois andMr. de la Haye. The total depth was 5 metres below th pointatwhich they predicted an underground stream' would be penetrated.

35. A t theendof drilling Mr. Langlois wasaskedwhetherhewished drilling to continue.He replied that he did not.
36. T h e fact remains that, no single underground stream' was penetrated at St.  Catherine. Only minor inflows and low yields were recorded with the water quality being poor and not potable.Therewas evidenceof increasing salt water intrusion both with increasing borehole depthand as pump testing progressed.

Question

5. T h e LaRocque bore is a disaster – wrong materials and procedures have resulted in a borethat, despite beingre-drilled,is still obstructed halfwaydown, contains debris from a shattered lining, and bits of electrical cable (presumably from a failed attempt to fit a borehole pump).Assuch,as a testsite or a supply for water, it is useless.

Answer

The suggestion that the La Rocque bore is a disaster – wrong  materials and procedures

37. T h e borehole at LaRocquewas drilled according to the specification as laidout in the methodology. Although drilling and completion diameterswere specified, the casing materialtobe used was not, this being left to the preferencesof the drilling contractors that were invited to tender. Both contractors that submitted  tenders  proposed the use  of plastic (PVC) casings to be inserted into the  section  of  the boreholes that weretobe sealed usingcementgrout.
38. T h e plastic casingwasneverdesignedtoprovide an effective sealofthe shallow groundwater.Hence,the issue of the damageto plastic casing during the drilling out ofthecementgrout is irrelevant and does not alter the conclusions ofthe investigation.
39. T h e sealwasachieved by pumping liquid cementgroutunderpressure, to completely fill the borehole casing, borehole annulus and all of the fractures, fissuresand joints adjacent to the borehole, (from which water inflow occurred) from 43metersbelowground level (mbgl) to the surface.Oncethegrouthad hardened within the fractures it would beimpossible to remove and would prevent any further inflowof groundwater from thesehorizons.
40. A f ter the hardenedgroutwas drilled outof the inside of the plastic casing, a watertight sealremainedin the borehole.Thiscomprised the grout filled fractures and a 25mm(1inch)layerofgrout that set in the former borehole annulus from 43mbgl to the ground surface.
41. T h e cementseal is therefore extremely robustand able towithstand considerable stress caused by drilling.
42. T h e presenceofan effective sealwasconfirmedby the independentadvisors to the project (BGS and Entec U.K.Ltd.) in a report entitled Clarification toquestions relating to the constructionof the test borehole  at La Rocque, Jersey' that  can  be viewed at the  Environment Division's web site (http://www.gov.je/PlanningEnvironment/Environment/). This report is attached for information.
43. T h e report highlights the complete absence ofwaterinflow when the borehole wasre-drilled to 43mbgl as the conclusive evidence that the upper fractures were sealed out by the grout. Data of inorganic chemistry also provides proof that a seal was achieved. This absence of contamination by shallow groundwater permitted valid samplestobetaken from the depth of the predicted stream'.
44. M  r. dela Haye was originally askedbyDGAG to undertake the drilling and grouting of the boreholes, despite his tender beingmoreexpensive than other quotes. Mr. delaHayeagreedtocarryoutthework. However, his method of drilling would have only grouted the outer section of the casing and not the inside and outside asachievedby the present drilling company.

45. T h reeweeks before drilling was to commence,Mr. de la Haye informed DGAG that he wasunableto undertake theworkdue to illness ofhis staff. At this time,Mr. delaHayewasdue to sign an agreement detailing the specifications asperthe investigation method statement.
46. T h e total borehole depth was specified as 50 m (some 5 metres deeper than the level at which Mr. Langlois predicted that the underground stream' would occur. Following discussions with Mr. Langlois and the Minister for Planning and Environment,drilling continued to a final depthof55 metres below surface butas little additionalwater had been obtainedMr. Langlois agreed that drilling should beterminatedat that depth.

The blockage in the La Rocque borehole

47. T h e isotope samples taken from depth weresampled during the drilling phaseofthe borehole whenthe drill bit penetrated down to a final depth of55m.Once drilling wascomplete, a testpump and electronic measuringequipmentweresubsequently installed at a depth of 52 metres (3metresabove the total depth of the borehole). After completion ofthe investigation, thepump, all associated pipe-work and electrical cable was successfully removed from the borehole.
48. A l though there is now a reported blockage half way downtheborehole,atthe time of the investigation the borehole was not blocked.
49. T h e blockage isreportedtobewithin the cemented grouted section and was not caused by collapse of the borehole. Evidence of this is the recent film takenof the borehole column.
50. V i ewing of this film suggests that remnant plastic casing attached to the borehole wall caused difficulty to get the camera gear down. This would not have prevented the heavier sampling pump from being installed andsamples being taken from the required depth.

Question

Financial and manpower implications

I believe the La Rocque bore should be re-drilled at the Contractor's expense as it was his faulty workmanship that caused it to be useless. The St. Catherine bore was relocated at officer's request. I understand that not all the funds set aside for this experiment were utilised so I assume the Department has a balance sufficient to cover that one. Failing that, the cost will need to be met from the Department's revenue expenditure.

Answer

51. T h e evidenceatLaRocque clearly demonstrates that an effective sealwasachieved, thus isolating the shallow groundwater inflow horizons above that depthand preventing mixing via the borehole with groundwater encounteredbelow that depth. Validwater samples werethussampled from depths specified by Mr. Langlois as that wheretheundergroundstream' were predicted to occur.
52. T h e test borehole siteatSt. Catherinewas sited at a location identified by Mr. Langlois andMr. de l Haye in accordance with the agreed methodology.The siting of it was not influenced in any wayand it had a very low yield ofgroundwater.
53. T h e drilling company stepped in at a late stage, after Mr. dela Haye hadwithdrawn.Theyconstructed two boreholes that enabled a comprehensiveandvalid testing to be undertaken and the company provided an excellent service. There is no intention of asking them tore-drill either borehole.
54. T h e Environment Division has allocated considerable fundsto this investigation. All the funds set aside were utilised. The conclusions ofthepresent investigation are robust and give a definitive answerasto the originandmagnitude of deep groundwaterin Jersey.

55. T h ereis therefore no justification, and indeed nofunds available, for continued expenditure in this area. Closing remarks
56. T h e conclusions of the investigation are robustand unequivocally indicate that underground streams' flowing from outside the Islanddonotexistin Jersey.
57. T h ereisnoevidence at the two test borehole sites to indicate that thegroundwater beneath the Islandis anything other than that derived from local rainfall. It consequently represents a finite resource that could be easily depleted, endangering flora andfaunaand the waterresourcesfor Island homes, if not managed in a responsiblemanner.
58. T h is research used anagreed scientific methodology,developed in cooperationwithourmostexperienced diviners.
59. T h e value of further investigations must therefore be seriously questioned. Assuch, there is no intention of withdrawing the results or of spending further publicmoney in this area.
60. T h e Minister for Planning andEnvironmentis therefore committed, in the best interests of the Island, to bring forth the WaterResources (Jersey) Law to the States.
61. It i s believed that resourcesand energy are best utilised inachieving this next logical andimportantgoal.

APPENDIX

Clarification to questions relating to the construction of the test borehole at La Rocque, Jersey

08 November 2006

Introduction

As scientific advisors to the Deep Groundwater Advisory Group, the BGS and ENTEC have been asked by the Minister for Planning and Environment, Senator Freddie Cohen, to comment on questions raised at the DGAG meeting, 2 November 2006 concerning the construction of the test borehole at La Rocque.

A detailed site diary was maintained throughout the drilling of both test boreholes. Comprehensive records of the geology and drill penetration rate (for every 0.5m depth), together with air flush water yield, water temperature, conductivity and pH was also maintained. Groundwater samples for chemical and isotopic analysis were taken for each variation in penetration rate or water strike. These records together with the results of the chemical isotopic analyses have been used to address the questions raised.

Full documentation of the drilling and construction of the two test boreholes will be included in the final BGS/ENTEC report.

1. Evidence to prove that all surface groundwater above 43m was completely sealed off at La Rocque.

1. Air flush yields

The recorded variations in air flush water yield provide conclusive and robust evidence that all shallow groundwater flows, encountered above 43 mbgl, were successfully sealed out of the borehole by the grout emplaced above that depth.

Prior to grouting the borehole at La Rocque, the combined water yield arising from all fractures (the cumulative yield) was about 1 litre per second (l/s) at a depth of 10.5 mbgl, increasing incrementally between the depths of 10.5m and 43.0m to between 6.5 and 7.0 l/s. After grouting and re-drilling through the hardened grout, the borehole was completely dry until after the base of the grout was penetrated at 43 mbgl. This provides conclusive evidence that all productive fractures above that depth had successfully been sealed out by the grout.

The recorded water yield at 43.5m (0.5m below the base level of the grout) was only 0.6 l/s (Figure 1) but this gradually increased to 1.75 l/s at 55 mbgl, as an increasing number of fractures were penetrated below that depth. This much reduced air flush yield, together with the gradual incremental increase of yield with depth (Figure 1), is entirely consistent with the successful sealing off of all productive horizons above 43 mbgl and the yield solely being obtained from the deeper open section of the borehole below. Increases in yield obtained in the lower deep section of the borehole correspond closely to the occurrence of fractured horizons. There is no evidence of any rapid increase in yield, such as would be expected if the grout seal in the upper section of the borehole had failed or if an underground stream' were penetrated in the lower deep section of the borehole.

Flow l/sec

Bh Depth metres

5

Granitic soil and gravel Very weathered granite Weathered granite

10 10

Fairly weathered broken granite 15

Solid granite

Fractured granite

20 Solid granite 20

Fractured granite Solid granite

25 Fractured granite

Solid granite

30 Fractured granite 30

Solid granite

Fractured granite

Depth (metre

Solid granite

35 Fractured granite

40 40

Open hole Solid granite

45 Fractured granite

Solid granite Fractured granite

50

50

Solid granite Fractured granite

55 Solid granite

60

60

Figure 1 The geology and air flush yield of the La Rocque borehole.

2. Water chemistry

Groundwater was sampled for inorganic chemistry analysis at each change in drilling penetration rate and/or air flush water yield. Analysis results from the samples from 10.5 to 43 mbgl have a similar chloride concentration, this being representative of the groundwater from all of the inflow horizons encountered to a particular depth. There is little variation in concentration with depth (Figure 2). There is however a small but significant increase in chloride ion concentration for water samples obtained below 43 mbgl, likely to be indicative of an increased component of seawater. This distribution of chloride concentrations is entirely consistent with an effective seal having been emplaced above 43 mbgl, preventing flow and mixing from shallower horizons.

Chloride (mg per litre)

0 50 100 150 200 250

0 10 20 30 40 50

Borehole depth (meters bgl)

60

Figure 2. Chloride ion concentration with borehole depth.

3. Integrity of the cementgroutseal

The seal emplaced in the upper section of the La Rocque borehole was achieved by pumping liquid grout under pressure, to completely fill the borehole casing, borehole annulus and all of the fractures, fissures and joints adjacent to the borehole, (from which water inflow occurred), from 43 mbgl to the ground surface. Pressure was induced by the weight of the liquid grout column within the borehole. Additional grout was pumped into the annulus, (the gap between the permanent casing and the borehole wall), to keep the borehole topped up' as grout penetrated the fractures adjacent to the borehole. Topping up continued until the grout level stabilised at ground level. Once the grout had hardened within the fractures it would be impossible to remove and would prevent any further inflow of groundwater from these horizons.

After the hardened grout was drilled out of the inside of the plastic casing, a watertight seal remained in the borehole. This comprised the grout filled fractures and a 25 mm (1 inch) layer of grout that set in the former borehole annulus from 43 mbgl to the ground surface.

2. The cementgroutcomposition

Amplus consulted widely on the best grout mix to use to provide the most effective seal for the upper section of the borehole. After careful consideration a mix of 100 litres of water with 5 bags of cement powder was used.

Groundwater inflows occur from water bearing fissures, fractures and joints. The uncured grout mix had to have a high degree of fluidity to ensure maximum penetration of the grout into the fissures, fractures and joints penetrated above 43 mbgl, in order to completely seal out these inflows.

The addition of sand to the mix would have increased the stiffness of the grout and potentially prevented full ingress into such fractures.

A stiffer sand based mixture could also caused air pockets to occur in the borehole annulus as the tremmie pipe was removed, potentially compromising an effective seal.

3. Grout hardening

The grouting of the La Rocque borehole commenced at 1320 hrs and was completed at 1535 on 13 September 2006.

Drilling out the grout commenced at 1055 hrs on 15 September 2006.

The grout was therefore left to harden for 43.5 hours (a minimum of 24 hours was specified) before re- drilling started from the surface. Drilling inside the casing penetrated only dry hard grout.

Further, drilling of the bottom of the borehole was finally completed at 1200 hrs on 16 September 2006; a further time interval of 68.5 hours from the completion of grouting.

Rock chip samples were sampled and documented every half meter depth. The presence of hard cement chips collected from the depth interval between 43 and 44 mbgl (immediately below the base of the grout) is seen in Figure 3. This shows unequivocally that the base of the grouted upper section of the borehole (to 43 mbgl) had completely hardened and that no liquid or unhardened grout was present in the borehole.

Hard, angular cement chips sampled between 43 and 44mbgl.

Figure 3. Rock chip samples collected every 0.5m during drilling at La Rocque.

4. The plastic casing

The grout was pumped into both the permanent casing and the annulus between the casing and the borehole wall. Therefore, no pressure differential occurred between the inside and outside of the casing and buckling of the casing was not an issue.

Damage to the uppermost 13 metres of the plastic casing did occur whilst drilling out the hardened grout. There is however no evidence that the grout seal over this section of the borehole was in any way compromised. Larger diameter steel casing was grouted into the upper section of the borehole to a depth of 10 mbgl, which would have assisted in preserving the seal. It is notable that no increase in air lift water yield occurred following the occurrence of damage to the plastic casing, as would have been anticipated if the grout seal had also been damaged.

5. Conclusions

The above evidence clearly and robustly demonstrates that;

1. an effective sealwasachievedbetweenground level and43mbgl, thus isolating the shallow groundwater inflow horizonsabove that depth andpreventingmixing via the borehole with groundwaterencounteredbelowthat depth.
2. all evidenceindicatesthat the cementgrouthadcured(hardened) sufficiently toprovide a totally effectiveseal between ground level and43 mbgl.

3. the isolationof shallow inflow horizonshaspreventedany possibility of cross contamination of groundwatersamplesobtained from the depths specified bythewater diviners andwell drillers, as being where an undergroundstream' would bepenetrated.There is nopossibility that the validity ofthe results ofanalytical results forchemicalor isotopic analysis,for water samplesobtained from thedeepopen section of the borehole,havebeencompromisedby leakage from the section ofthesealedboreholeabove43 mbgl.

Mr. Colin Cheney Hydrogeologist

Groundwater Management Programme British Geological Survey

Maclean Building, Crowmarsh Gifford Wallingford, Oxfordshire

OX10 8BB

Telephone: 01491 692400 Fax: 01491 692345 E-mail: csc@bgs.ac.uk