Draft Water Resources Law - Technical Assessment of Evidence - Dr S. Sutton, Entec - Submissions - 3

Scrutiny Review

Draft Water Resources (Jersey) Law

Technical Assessment of Evidence Presented

30 June 2004 Entec UK Limited

Report for

States of Jersey Scrutiny Office, States Building, Royal Square,

St. Hellier, JE1 1BA

Main Contributors Stuart Sutton

Scrutiny Review

Draft Water Resources (Jersey) Law

Technical Assessment of Evidence Presented

Issued by 30 June 2004 Entec UK Limited

Stuart Sutton Approved by

Stuart Sutton Entec UK Limited

160-162 Abbey Foregate Shrewsbury

Shropshire

SY2 6BZ

England

Tel: +44 (0) 1743 342000 Fax: +44 (0) 1743 342010

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Executive Summary

The written technical evidence provided to the Scrutiny Committee in connection with the Draft Water Resources (Jersey) Law is principally:

1. A view of the state of the groundwater resources of Jersey developed over 14 years of investigation and monitoring by the British Geological Survey (BGS);
2. Disagreements  with  the  BGS  view  presented  by  the  Water  Diviners  and  Engineers Association (WDEA).

The BGS concept of the groundwater system is of a relatively "shallow" aquifer supported by rainfall recharge. The WDEA claim that there is also a deep groundwater resource supported by recharge on the French mainland.

Up to about 1996 the BGS view of the state of the groundwater resource was of a resource under  extreme  stress  with  annual  abstraction  and  baseflow  requirements  almost  equal  to recharge. Revision of infiltration (recharge) estimates based on the Trinity Catchment Study (1996) suggest that abstraction and baseflow are equivalent to about 50% of average annual recharge. Water level and chemical monitoring data show no indication of long term decline in levels or deterioration of chemical qualityThese records do not cover prolonged periods of below average rainfall. Estimates of annual abstraction totals are poorly constrained.

WDEA provide evidence of deeper groundwater resources additional to those of the shallow aquifer but the resource is not quantified.

The BGS evidence suggests that the groundwater resources of Jersey, as they envisage them, are not deteriorating. If additional resources occur the risk of deterioration is further reduced. In the present context a key reason for abstraction licensing and regulation is to provide a reliable means of calculating total annual abstraction.

Technical discussion of questions of resource origins and quantity estimates is not proposed for the Scrutiny Hearings. Rather a series of questions to investigate whether or not the proposed law is appropriate as a means of abstraction measurement and whether or not a technically robust and defensible means of application determination has been defined, is suggested.

Contents

1. Introduction 1
2. BGS Reports 3

1. Data Collection 3
2. Conceptual Understanding 3
3. BGS Groundwater Balance and Resource Assessment 4
4. Man-made Contribution to Groundwater Recharge. 6
5. Rainfall and Groundwater Levels 7
6. Groundwater Chemistry 7

3. Alternative Technical Views 9

1. WDEA 9
2. Other Opinions 9

4. Climate Change 11
5. Summary 13

1. Technical Position 13
2. Draft Water Law 13

6. Possible Questions for Scrutiny Hearings 15

Table 2.1 BGS Water Balance Components 5

Figure 2.1a GeologicalStructure of Jersey After Page 8 Figure 2.1b Drift Deposits of Jersey After Page 8 Figure 2.2 BGS Conceptual Understanding of Jersey Groundwater After Page 8

Appendix A Borehole Hydrographs and Nitrate Trends [Reproduced from Jersey Groundwater 2002

(BGS Report CR/03/102N)]

transmit (permeability) groundwater is controlled by fractures and pores induced in the rock mass principally by surface weathering processes. Effectively in the unweathered condition each of the rock types of Jersey (see Figure 2.1a from BGS, 1988) is of very low porosity and permeability.

As such the Jersey Bedrock Aquifer is relatively shallow (thin), estimated as extending to depths  of  25-40 m bgl.  The  water  table  broadly  mimics  the  surface  topography  at  depths generally 10 m or less bgl and the saturated thickness rarely exceeds 25 m (Figure 2.2 from Hydrogeological Map of Jersey).

Locally sand deposits as at St.Ouens Bay and to a lesser extent the Royal Bay of Grouville are sufficiently thick and extensive to provide additional groundwater storage above the bedrock. Generally the surface deposits are thin and do not retain significant volumes of groundwater (Figure 2.1b from BGS, 1988).

Water resources within the aquifer are replenished (recharged) principally by infiltration of rainfall through the relatively thin overburden. Recharge will only occur when the soil moisture deficit has been satisfied i.e. generally in the winter months. This annual recharge to the aquifer supports groundwater abstraction and baseflow to the streams and rivers and other wetland habitats (see Figure 2.2). No specific data on the relationship between groundwater and stream bed levels is presented. Surplus groundwater is discharged to the sea. If abstraction exceeds the annual recharge, groundwater levels will drop, baseflow will be reduced and it is likely that contaminant levels will increase because of reduction of flushing through the aquifer system. Frequent non-specific references are made to the failure' of wells due to falling groundwater levels.

This understanding is undoubtedly a simplification of a complex natural system but it provides the  conceptual  framework  within  which  a  quantitative  appraisal  of  the  water  balance  (the balance of inflows and outflows) is made and from which the volume of resource available for use is estimated. The key indicators of over use of the resource are identified as declining water levels and deteriorating chemical water quality.

3. BGS Groundwater Balance and Resource Assessment

Rainfall  can  do  one  of  three  things  when  it  reaches  the  ground,  it  can  be  lost  by evaporation/evapotranspiration, it can flow directly over the land surface to streams and the sea (runoff) or it can infiltrate and recharge the groundwater reservoir. Stream flow measurement provides a measure of the runoff component, soil and evaporation measures provide a measure of evaporation losses and the residue is considered to infiltrate.

The components of the groundwater balance are therefore:

Inflows: Infiltration, directly from rainfall or from streams. Outflows: Baseflow to streams and wetlands;

Spring flow to the sea;

Abstraction from wells and boreholes

Natural infiltration may be supplemented by leakage from water mains, soakaways and irrigation returns. In urban areas some groundwater may be intercepted by sewers. Spring flow to the sea is generally considered as loss of freshwater, although it does represent proof that saline intrusion is limited. This flow is not readily measurable. The key balance is therefore between infiltration, baseflow and abstraction. Measurement or estimation of these parameters is usually based on a mixture of observation, experiment, experience, and local records which are extrapolated both geographically and in time. The more widespread and lengthy the records, the more reliable are the extrapolations.

Within the BGS water balance calculations no allowance is made for any additional deep sources of groundwater originating outside the Jersey rainwater catchment.

The components of the water balance quoted by BGS throughout their reports are summarised in Table 2.1.

Table 2.1 BGS Water Balance Components

Notes *(1) Includes small component of man-made recharge *(2) First indication of Trinity Catchment Study Results *(3) Based on results of Trinity Catchment Study

The  principal  revision  of  the  water  balance  estimate  is  based  on  the  experiments  and measurements of the Trinity Catchment Study which change the overall balance calculation from one in which there is no surplus to one which for an average years rainfall recharge exceeds abstraction and baseflow by close to 100% (Table 2.1).

Up to about 1996 the Jersey groundwater situation is generally described as critical in terms such as:

• under threat from overpumping and disperse pollution' (WD/91/15);

• It is concluded that Jersey is exploiting its groundwater resource at a rate that is probably unsustainable'.(WD/92/22);

• The  findings  of  the  earlier  years  of  the  study  are  confirmed;  principally  the groundwater resource is potentially being exploited beyond its sustainable capacity and that there is widespread pollution of the groundwater' (WD/93/28);

• Although the margins of uncertainty in the estimation of abstraction and recharge are  large,  problems  of  physically  unsustainable  use,  that  is  where  abstraction exceeds recharge are probably only significant in the short run during periods of "drought" and in particular localities rather than posing a longer term threat for the Island as a whole' WD/96/8.

The inference is that local control of abstraction is necessary to protect a threatened resource.

From 1996 onwards the tone of summary comments on groundwater resource changes; the resource  is  generally  inferred  to  be  adequate  but  rates  of  groundwater  abstraction  are  not reliably known. Licensing  of  abstraction  would  provide  a  method  of  determining  overall abstraction volumes.

• About half the long-term available recharge, or renewable resource, is currently used either as groundwater abstraction or as baseflow in surface water. In dry years, water levels fall, baseflow declines and many boreholes go dry particularly on higher ground' (RR/98/5);

• The  analysis  of  the  water  cycle  for  Jersey  remains  incomplete  without measurement of source abstraction volumes.(IR/01/26);

• Groundwater  levels  remained  healthy  throughout  the  year  and  in  some  areas groundwater  levels  have  been  showing  a  positive  trend  for  some  years'  also Chlorthal continues to occur in groundwater with high concentrations at some sites. Like nitrate its presence seems to be declining'. (CR/03/102H).

The principal reason for this change of emphasis appears to be the replacement of an average infiltration  estimate  of  50 mm/year  with  a  measurement  of  132 mm/year  derived  from  the Trinity Catchment study. The emphasis appears to shift from recommending licensing to protect an overdrawn resource to licencing as a measure to reduce uncertainty in the volume of groundwater abstracted. Abstraction estimates from representative metered sources ceased in 1999.

In spite of this change of emphasis the possibility of overabstraction of the resource in dry years, possibly when there is no effective recharge, remains a concern.

4. Man-made Contribution to Groundwater Recharge.

This is categorised in the BGS Report RR/98/5 as follows:

20% of Irrigation returns = 0.3 Mm³/a

Septic tanks and soakaways = 0.003 Mm³/a

Mains leakage = So small as to be negligible.

These estimates can be questioned on the following basis:

• If 4687 households discharge an average 0.6 m³/day to soakaway,  the  volume discharged to soakaway is close to 1 Mm³/year;

• Jersey New Waterworks Company provides annual supply of around 7 Mm³/year. Mains leakage is unlikely to be less than 15%, or close to 1 Mm³/year.

An  additional  2 Mm³/year  (close  to  15%)  recharge  may  therefore,  be  available  from anthropogenic sources which may make an important contribution to dry year groundwater recharge.

5. Rainfall and Groundwater Levels

Appendix 1 provides copies of long term groundwater hydrographs for 9 wells provided in the most recent BGS annual report (CR/03/102N, Report for 2002). Details of well construction and location are not provided so detailed comment is not feasible. However, it is known that 1995/97 was a particularly dry period (The BGS report for April 1995 to March 1996 is sub- titled An exceptionally dry year') and annual rainfalls were low through 1995, 1996 and up to the beginning of winter of 1997/98. During this period actual rainfall was 20% to 25% below the average of 844 mm and infiltration may have fallen to 25 mm/year or less. (Table 3 - BGS Report RR/98/5)

The groundwater hydrographs show a natural annual fluctuation of 3 to 6 m with a generally falling groundwater level from February to October and a sharp increase in November to January. Absolute levels are not reported but depths appear to be principally in the range 0- 10 m below ground level with an annual range of fluctuation of 2-8 m. Minimum levels reported  are  for  winters  1996/7. These  are  an  average  0.5 m  lower  than  general  annual minimum levels. This represents an additional reduction in groundwater levels of 10-15% resulting from a possible 80% below average annual recharge.

There is no long term trend of declining groundwater levels apparent from the data presented by BGS, nor is there any indication of significant depletion of groundwater resources in the dry years of 1995/96.

No evidence is presented of the relationship between groundwater levels and stream baseflows throughout this period.

6. Groundwater Chemistry

Overall,  groundwater  chemistry  is  consistent  throughout  the  12  year  measurement  period. Nitrate levels have been falling gradually since 1990, (see Appendix 1, reproduced from BGS report  for  2002  (CR/03/102N)  probably  as  a  result  of  improved  agricultural  practice. Organic contamination (using Chlorthal as an indicator) appears to have peaked in 2000/01 and by 2002 reduced to pre 2000 levels'(CR/03/102N) although locally high concentrations remain of concern.

Isotope studies demonstrate that the bulk of the nitrate originates from fertiliser application, suggesting that natural recharge is significantly greater than soakaway seepage. Also the results of Tritium analysis are interpreted to suggest that the bulk of the groundwater is less than 30 years  old.  (Atmospheric  testing  of  nuclear  weapons  which  ceased  in  the  1960s  is  the principal source of tritium in natural waters)

Other conclusions based on chemical data are:

1. Intrusion of sea water into the aquifer is localised to the southeast area of the island, perhaps 1 to 2% seawater in groundwater (the St Ouen's sand aquifer is protected from seawater intrusion by its shape and elevation);
2. Some older (deep circulation) groundwater may be present in the granites of the southeastern part of the island.

No data is presented on surface water quality. Of particular relevance would be river/stream water quality at low flow condition when the bulk of surface water flow is likely to be sustained by groundwater fed seepage.

recommendation for immediate legislation to protect and safeguard water resources of  the 1992 Working Party on Water Resources. This 1992 report was based on the full acceptance of the  analyses  and  conclusions  of  the  BGS  Report  WE/91/15  (Hydrogeological  and hydrogeochemical survey of Jersey) and concludes that We are persuaded that the groundwater resources are being depleted faster than they are being replenished'. And that definition of the severity of the problem will require monitoring for at least 3 consecutive years'.

maintained at (or restored to) the equivalent of Good Status' as identified by a nationwide monitoring network.

Maintaining ecological integrity is a key principal of both the present and anticipated licensing regimes and groundwater provides important support to surface water bodies and terrestrial ecosystems, particularly in summer periods.

In both the present and anticipated licencing regime, the control measure is the status of the ecology maintained by the volume and quality of surface water flows which, particularly in summer periods, are supported by groundwater.

Appendix A

Borehole Hydrographs and Nitrate Trends

[Reproduced from Jersey Groundwater 2002' (BGS Report CR/03/102N)]

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