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Technical Report WRD83051

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REVIEW OF THE DARWIN RURAL

AREA GROUNDWATER POLI,UTION

STUDY

N R Allen & S A Townsend Water Division Department of Transport and Works Darwin

November 1983

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l CLASS NO. I L_

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CHAPTER

1.

3 .

4.

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CONTENTS

SYNOPSIS

INTRODUCTION

OBJECTIVES

AN OVERVIEW OF THE DARWIN RURAL AREA GROUNDWATER POLLUTION STUDY

3. 1 Selection of liater Quality Parameters

3 "} . ~ Selection of Sample Point Locations

3.3 Selection of Sample Frequency

3.4 Data Collection and Interpretation

3.5 Stati.stical Analysis

REVIE~1 OF DARWIN RURAL AREA GROUNm'lATER POLLUTION STUDY BACTERIOLOGICAL DATA COLLECTION AND ANALYSIS

4.1 Hydrologic Units

4.2 Sample Point Selection

4.3 Differentiation of Bores and Wells

4.4 Frequency of Sampling

4.5 Data Analysis Methodology

4.6 Bacteriological Water Quality and Rainfall

4.7 Assessment of Bacteriological Drinking Water Quali ty


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7.

8.

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10.

11.

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AN ALTERNATIVE INTERPRETATION OF THE DARWIN RURAL AREA GROUNm"lA'l'lm POLLUTION STUDY BACTERIOLOGICAL DATA

5.1 Application of Criteria

5.2 Temporal Distribution

5.3 Aquifer Source

5.4 Septic Tank/Bore Separation Distance

5.5 B.coli/Faecal Streptococci Ratio

5.6 Chlorination

SEP'rIC TANK UlVESTIGA'l'ION STUDIES

6.1 Fluorescein Tracer Tests

6.2 Sodium Chloride/Conductivity Trials

6.3 Phosphate Study

6.4 Review of Waste Disposal Systems

REVIEI,/ OF SAMPLE POINT CONSTRUCTION STANDARDS

SmlNARY

RECOMHENDATIONS

9.1 Recon~endations based on the Darwin Rural Area Groundwater Pollution Study Report

9.2 Recommendations for Project 2001, Danlin Rural Area Pollution Hanagernent Study

REFERENCES

APPENDICES


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9.

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Bore and l'Iell Numbers per Hydrologic Unit

Application of the Desirable Drinking vlater Quality criteria to DHAGPS Sample Point Data

Explanation of Sample "Failures" (as defined by the Criteria)

Bore Sample Unacceptability (According to the Criteria) for Rainfall and Non-Rainfall Periods

Well Sample Unacceptability (According to the Criterial for Rainfall and Non-Rainfall Periods

Sample Unacceptability (According to the Criteria) and Aquifer Source

E.coli Sample Concentrations for Chlorinated Bores and Wells

E.coli Sample Concentrations for Fluorescein Tracer St"udy Sample Points

B.coli Sample Concentxations for Sodium Chloride/Conductivity Tracer Study Bores


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LIs'r OF FIGURES

FIGURE

1. Danrin Rural Area Hydrologic Units

2. Geology of the Danlin Rural Area

3. Honthly Rai.nfall Totals at Howard Springs Meteorological Station for the DRAGPS "\>let" and "Dry Seasons"

4. (a) Percentage of Bore Samples which have Unaccept.able Coliform Concentrations and Monthly Rainfall Tot.al

(b) Percentage of Bore Samples which have Unacceptable E:.col~ Concent.rat.ions and Monthly Rainfall Totals

5. (a) Percentage of ,'leI 1 Samples which have Unacceptable Coliform Concent.rat.ions and Monthly Rainfall Totals

(b) Percentage of \>lell Samples which have Unacceptable E.coli Concentrat.ions and Mont.hly Rainfall Totals

6. (a) Percent.age of Bore Samples with Unacceptable Coliform Concentrations and Septic Tank/Bore Separation Dis·tance

(b) Percent.age of Bore Samples wit.h Unacceptable E.coli Con~entrations and Septic Tank/Bore Separation Distance

7. (a) Percentage of Bores which Fail the Coliform Portion and the Criteria and Septic tank/Bore Separation Distance

(b) Percentage of Bores which Fail the E.coli Portion of t.he Criteria and Septic Tank/Bore Separation Distance

8. E.coli/F.S. Ratio Frequency Distribution for Bore Samnles which are Unacceptable to t.he Criteria

9. E.coli/P.S. Ratio Frequency Distribution for Well Sam:?les which are Unacceptable t<: the Criteria

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SYNOPSIS

The Darwin Rural Area Ground¥later Pollution Study has shown that there is bacteriological pollution of bores and wells. Whilst the direct source of contamination has not been c learl v identi fied, three distinct factors have been identified which could have a cause/effect on the level of pollution. 'Phese faotors are:

(i) (i i) (iii)

bore construction septic tanks (design and operation) land management.

From surface inspection very few of the bores and wells satisfied Department of Health Regulation 58, with the fa i lure to install simple items such as coping and fencing one mus': question the care taken with the sub-surface structural requirement.s. The absence of pollution indicators in the aquifer \Vaters would tend to indicate that the pollution is localised in the bores. Whilst this may appear to be a ;;atisfactory condition at present with respect to the groundwao:er, the poorly constructed bores could become a major point-source of pollution for groundwater in the future. The problems associated with bore construction methods :3hould be addressed by the specialist.s in groundwater hydrology.

Sep~ic tank construction, and disposa 1 systems may not be adeqcatoe in tehe Darwin Rural Area. Investigations are r<ilquired to assess parameters sui table to develop minimum design criteria for septic tank installations.

The topography of the area, location of animal pens and proximity of septic tanks should all be considered when siting the bore or well. It is apparent that this is not the case in many sItuations.

v'hi.lst pollution appears to be localised in the systems, chlorina'~ion on a once only bas Ls appears to produce long term benefits. This aspect of treatment should be further invest.ig.lted.

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1. INTRODUCTION

'l'he Darw in Rural Area Planning Zone RLl has been subjected to increase:! pressure for development and domestic exploitation of groun:lwater. A responsibility of the Water Division under the Water Supplies Development Act is to provide advice and assistan::e to landholders regarding water supply development. In order to have a sound basis of advice, a hydrogeological study of the Darwin Rural Area was undertaken, and completed in 1980 {see Reference ll. During, and prior to this study, bacteriological water samples were collected from bores and wells at the request of landholders. The results indicated a "high incidence of pollution" (Reference 2, Section 1.1) of groundwater domestic supplies. This raised concern for the health ef residents using groundwater for domestic use, and also fo,~ the potential pollution of Darwin's groundwater supply.

As most samples were collected under "wet season" conditions, further samples were collected during August, 1981 in order to obtain "dry season" bacteriological results. An intecpretation of the results confirmed the previous finding of unacceptable sample "pollution". A discussion of the data realised its' limitations, in particular the possibility of sample bias, and questioned any conclusions which could be drawn from the data (Reference 3).

In August 1981 Water Division recommended a "stat.istically based 12 months sampling programme" (Reference 3, Sect:.on 1.4) be implemented to investigate groundwater pollution of t.he Darwin Rural Area. The recommendation was agreed teo by Cabinet. As a result the Darwin Rural Area Groundwat.er Pollution Study (herein referred to as DRAGPS) was instigated. The objectives of the study were to:

(i) ( iiI (iii) ( iv)

(v)

identify source(s) of pollution gauge the extent of pollution examine the reasons for pollution occurrence determine development constraints associated with water provisions and waste disposal determine water management requirements to protect public health and '.'later resource.

After thr~,e months of data collection an interim report was published (See Reference 4). The report examined the relationship between bacteriological water quality and sample site sanitary conditions, "wet" and "dry seasons", landholding size, pH and phosphate concentrations.

During the Study, a moratorium on subdivision in the Darwin Eural Area below 8 hectares was imposed, except where reticulated water suppJ ies ,.;ere proyided. The DRAGPS was completed in September 1981 and a report published in that month (See Reference 3).

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2. OBJECTIVES

The objectives of this Report are to:

(i) review the Darwin Rural Area Groundwater Pollution Survey, it s data interpretation and conclusions;

iii} propose recollliuenda tions for the Darwin Rural Area Pollution Management Study.

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3. AN OVERVIEW OF 'rHE DARWIN RURAL AREA GROUNDWATER POLLUTION STUDY

The DR1\CPS objectives necessitate a comprehensive water quality survey. The essential components of any water quality survey include selection of (i) water quality paramet_el's, (ii) sample point locations and (iii) sample frequency. The collected data is collated and interpreted in accordance with the statistical design of the survey.

3.1 Selection of "later Quality Parameters

\'later <.{tlality parameter selection is determined by the survey's obj ectives. Generally I selection is based on the known cha:::acteristics of t.he waterbody and that of the pollution source.

Bio:ogical, chemical surveyed by the DRAGPS.

and physical parameters were

3.1.1 Bio:cogical water quaIl ty parameters

(a) Coli from organisms - these are a group of indicator organisms which include the genera Escherichia, Klebsiella, Enterobacter and Citrobacter. The Coliform group of micro-organisms are widely distributed in the environment. They are present in large numbers in the faeces man and other warm blooded animals, and non-faecal sources such as soil and vegetation.

(bl Escherichia coli are indicator organisms found in the faeces of man and other warm blooded animals.

(c) Faecal streptococci streptococci commonly occurring in large numbers in the faeces of man and other warm blooded animals. The organisms also originate from reptiles and insects. It has also been assoc iated "i. th non-faecal sources. 'l'he presence of faecal streptococci is reqarded as an additional indication of the presence of enteric bacteria from warm blooded animals.

(d) 37°C viable plate count - provides an estimate of the number of bacteria which will grown at 37°C.

'l'he term "indicator organisms", as used in water mic::obiology, refers to micro-organisms whose preSence is eVldence of enteric pollution. Indicator organisms may be accompanied by pathogens. The most probable number and membrane filter count provide an index of numerical expression of enteric_ pollution. Indicator org,lnisms, rather than pathogens, are employed to assess

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wat,er quality because of their relative ease of detection and enumeration. Pathogens are usually more diff ieul t to grown, isolate and identify t,han indicator organ~sms, and often require special media and procedures. Pathogens appear in smaller numbers than indioator organisms, and are therefore less likely to be detected.

An indicator organism should have the following characteristics:

( i) (ii)

(iii)

(iv) (v) (vi) (vii) (viii)

(ix) (x)

applicable to all types of water present in sewage and polluted waters when pathogens are present number is correlated with the amount of pollution present in greater numbers than pathogens no aftergrowth in water greater survival time than pathogens absent from unpolluted waters easily detected by simple laboratory tests in the shortest time consistent with accurate results has constant characteristics harmless ,to man and animal.

No group of organisms meet all these criteria, but the "Coliform group" do fulfil most of them. The group have beon used extensively and have providnd a valid and reliablo index of onteric pollution in the majority of waters.

Difficulties have been encountered in the interpretation of Coliform and E.celi rosults, p<lrticularly in tropical and monsoonal regions. Bioc~emical confirmation of E.coli has been complicated by the presence of bacteria producing reaction patterns intermediate between E.coli and Enterobacter aerogones.

Coliform organisms, including E.coli, have exhii:>ited growth in natural waters. Data are not available on the concurrent growth of pathogens. The public health significance of Coliforms in natural waters is questionable, as is their ability to satisfy chan,cteristics (1), (iii) , (v) and (vii) of an indi'~=~dtor organism.

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In cases ,,"'here the results of the Coli form and E.coli test.s are difficult to interpret, Bifidobacteria should also be included (Reference 5). Bifidobacteria are anaerobic, gram pos~tive ofljanisms which are present in c;:mcentrations of 10 to 10 /g wet weight of faeces. 'rest procedures are at present under development (Heference 6) based on membrane filtration, using a modified Gyllenberg medium, and anerobic incubation at 37°C for two davs.

"

3.1.2 Chemical water quality parameters

(a) Phosphate - thjs inorganic ion is present in high concentration is sewage effluents. Its selection was based on the premise that phosphate concentration could be used as an index of effluent contamination of groundwater.

(b) Pesticides - the toxicity of particular pesticides is well known. The pesticides analysed were mainly the pesticides of the chlorinated hydrocarbon group. Pesticides of this group are of interest not only because of their toxicity, but also this 9r'ouP of pesticides is insoluble in water and absorb to clay particles. Detection of pesticides of this group in the groundwater would indicate particulate movement through the aquifer.

(c) General chemical p.arameters - the general chemical parameters will allow identification of particular groundwater sources i. e. doland tic or lateritic sources. The data would also indicate changes in chemical matrix due to recharge of the aqui::ers.

3.2 Selection of Sample Point Locations

The location of sample points in t.he Darwin Rural Area should take intc account those spatial factors which influence water quality. These factors include:

( i) (ii) (iii) (iv)

(v) (vi) (vii) (viii)

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Sample point type (bore or well) Sample Point construction standards Catchment land-use The nature and proximity of point sources of pollution Groundwater level Soil characteristics (e.g., permeability) Aquifer Geology


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The approach adopted by the DRAGPS was to subdivide the Dan/in Hural Area into hydrologic units. These were of approxiol."!tely equal area, and based on inter fluvial boundaries. A random selection of sample points was made from each hydrologic unit. The above spatial factors did not appear to influence sample site selection. The DRAGPS criteria for sample site selection will be examined in detail in Sectians 4.2, 4.3 and 4.4.

3.3 Selection of Sample F.requency

'['he sample frequency should depend on the variability of the data. Therefore, a foreknowledge of the variability of the paramete r-s of interest is necessary. Bacteriologioal data from 1976 was available to the DRAGPS Study team to evaluate variability. Sampling frequency should be flexible, and adjusted after suffioient data has been collected to permit <"n evaluation.

The frequency of sampling should also be related to changes in factors ~Jhich are known to influence water quality (e.g. rainfall).

The production of bacteriological data has associated with it inherent statistical unceTtainties. Increased sample frequency, including resampling, would minimise these uncertainties.

The DRl\.GPS data collection programme was based on a monthly sampling frequency. The programme was strictly adhered to and did not include :-esampling. A detailed examination of the DRAGPS sampling frequency is presented in Section 4.5.

3.4 Data Collation and Interpretation

3.4.1 The information collected from a water quality survey must be collated and interpreted ~;ith respect. to the surveys' objectives. Data evaluation methods, including statistical analyses, need to be determined in conjunction with the detalls of data collection. For example, if a survey is to rely heavily on the statistical interpretation of data, the data base must be statistically designed.

'I'he DHAGPS was intended to be a "statistically based 12 month sampling progranune" (Reference 3, Section 1.4). There is, however, little or no discussion of the statistical design of data collection or the use of i3tatistical methods to interpret the data. The only statistical interpretation of the DRAGPS data is undert.aken in the DRAGPS Interim Report (See Reference 4) •

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3.4.2

3.4.3

\-,aL,r quality data needs to be compared with scientific criteria to rationalise its acceptability for a designated number of uses. Criteria have been developed for drinking wat.er, public recreational waters, agricultural waters, industrial waters, and the preservation of aquatic and marine ecosystems. Groundwa ter in the DaI>.;in Rural Area is exploited for dr inking and irrigation uses. The DRAGPS was concerned only with its drinking use.

Water quality criteria need obj.2ctives and standards. apply (Reference 5):

to be distinguished from The following definitions

Criteria: A scientific requirement on which a decision or judgement may be based concerning the suitability of water quality to support a designated use (i.e. a scientific rationalisation of water quality data) .

Objectives, guides, goals: ."'. set of levels of water pollutants or water-quality parameters to be attained in water-quality management programmes which also involve cost/benefit considerations (i.e. a political process).

Standards: Legally prescribed limits of pollution which are established under statutory authority.

3.4.4 i'mstralian drinking water quality criteria and objectives have been jointly prepared by t.he Australian Water Resources Council and the National Health and Hedical Research Council for the Commonwealth Department of Health (Reference 7, Appendix A). The criteria sets out drinking water quality levels which are regarded as acceptable under Australian conditions. Health investigat_ions levels are utilised by the criteria to assess sample acceptability. When a sample exceeds the heal th investigation levels t tJ1e minimum requirement is imrnediate resampling. The recomiuended 1 evels are set we 11 below those a t which health risk \"ould occur. The current desirable drinking water quality criteria states 90% of all samples, throughout any year, should not contain levels in excess of the health investigations .Levels. Implicit in the criteria are minimum sampling frequency and sample number, and sampling techniques. These are based on W.!l.O. (Reference 8).

The criteria are largely designed for public water sUFplies. In very small communities it is often impractical, due to the remoteness and/or cost effectiveness to undertake routine bacteriological water quality monitor-ing. When samples are collected less than once a month - the W.H.G. recommended maximum

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3.5

inturval between successive samples there is insllfficient historical data available from which the rel.lability of the source can be assessed. In such circumstances disin faction, although desirable, is not always practical. Assessment of water quality must not be based exclusively on the results of bacteriological eXBloinations, but also on a sanitary inspection of the immediate catchment area. The objective of the inspection is to identify and remove obvious sources of con l:ami na tion.

The bores and wells of the Darwin Rural Area are examples of small communi ties, in this case household, water supplies. The new W.H.O. document, Guidelines for Drinking Water Quality will address the application of criteria to very small untreated water supplies.

'I'he DRAGPSi mplementedthe long term drinking water quality objective for purposes of assessment. Clearly, from the above definitions I the objective is not designed for this use. Criteria are designed for assessment purposes. The DRAGPS should have employed the current desirable drinking water quality criteria.

Sta~istical Analysis.

Aft'=r three months of data collection an Interim Report was produced (See Reference 4). The objectives of that Report, although not stated, were to review the DRAGPS. Imy review of a study shOUld aim to assess the value of the water quality parameter data, and also to assess the data collection system (ie. sample point number and locations, and sample frequency). These items of assessment were poorly convered by the Report; nevertheless it "as concluded "a correct assessment was mad,? regarding the amount of sampling needed to satisfy statistical criteria" (Reference 4, Page (ii». The Int,=rim Report deals mainly with data interpretation.

The Interim Report contains the only statistical int8rpretation of the DRAGPS data. Correlation co-efficient and regression analyses were determined for t.he "variables":

percentage bores polluted according to long term drinking water quality objectives

percentage bores meeting Public Health Hegulation 58, excluding the requirement for a fence surrounding the bore/well.

If the fence requirement of the Public Health RegcJlation is included, nearly 'all sample points fail the Regulation; and as such no correlation could be soucJht.

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The "variables" were based on hyJrologic unit data. It was assumed the percentage of samples which failed the drinking water quality obJective was equal to the percentage of bores which fail the objective. This is on I:! correct \vhen each bore is represented by a single sample.

The actual variables under examination are dlchotomous scaled, ie. the variables contain two classes or categories. The bore pollution variable has the two values: polluted and not polluted. The bore construction variable has the two values: satisfy Reg'llation 58 (excluding fence requirement) and fail Regulation 58. Both variables are binomally distributed, and require non-parametric statistical analysis. The application of the Pearson correlation in the Interim Report co-efficient is not appropriate bec'1use an underlying assumption of that analysis is the normal distribution of test variables. The translation of the raw data to percentage values does not alter the frequency distribution of t.he two variables.

The application of Pearson correlation co-efficient and regression analyses to the bacteriological and bore construction data demonstrates a misunderstanding and miss-use of statistics. Consequently the statement "Strong correlation between good sanitary conditions and low pollution incidence is apparent for the bores during Nov,",mber" (Reference 4, Section 4) has no scientific, nor statistical, basis.

The intention of the DRAGPS was to collect and analyse water quality data according to statistical principles and methods. There is, however, no discussion of the Study's statistical basis, nor a rational use of statistical methods to interpret the data. In chapter. 5 of this Review no statistical analyses of the data have been :nade, this is due to t.he uncertain statistical validity of the data base and also insufficient time to research appropriate statistical analyses and undertake computations.

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4. REVTEW OF THE DARWIN RURAL AREA GROUNDWATER POLLUTION STUDY BACTERIOLOGICAL DATA

COLLEC'fION AND ANALYSIS

It is essential that data collection for assessment provides a statistically sound statistically based study should include features:

water quality data base. A the following

A number of samples points statistically valid proportion of of points.

representing a the total number

A spatial distribution of sample points which takes into account areal and depth variability of relevant parameters, such as geology and aquifer.

A sampling data base, associated data.

frequency which will provide a sensitive and minimise st.atistical uncertainties

wi th the production of bacterio logical

The maintenance of the same water supply management pract.ices, collection and transportation of samples, and Laboratory techniques throughout the data collection period.

The methodology used by DRAGPS to collect and analyse bact€riolog~cal data is evaluated in this chapter according to the above set of features.

4.1 Hydrologic Units

For the purpose of the DRAGPS, the Darwin Rural Area was subdi vided into ten hydrologic units (See Figure 1). An understanding of the method of selection of the units is crucial to an evaluation of the results presented in Appendix H, of the DRAGPS Report. (Reference 3). The unit.s were delineated according t.o approximate interfluvial zones (creek boundaries), which do not, generally, permit the passage of shallow (phreatic) aquiter water. The units represent a surface areal interpretation of the Darwin Rural Area.

The hydrogeological variability of the Area, and exploitation of different aquifers (dolomite, sandstone and laterite) by rural residents were not considered when the units ~lcre delineated. 'I'he units, therefore, do not define areas of homogenous domestic groundwater sources, and should not be used as a units of data analysis.

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4.2 Sample Point Selection

The DRAGPS sought a minimum number of nine sample points from each hydrologic unit, which the Report states, "would loosely correlatf, to subdivision/population density" (Reference 3, Section ';.l. 1). The statistical basis of this correlation is unclear, as is the statement itself. The" correlation" is not substantiated in the DRAGPS Report.

Sample points were selected randomly in each hydrologic uni t, c}:cept where geological factors were taken into account. Other spatial factors, which could influence sample water qUc3lity, I"ere not considered. These included:

, i) (; . ) ,~l

(iii) ( iv)

IV)

(vi) (vii)

Sample point type Sample point construction standard Catchment land-use The nature and proximity of point sources of pollution Groundwater level Soil characteristics Aquifer

The inclusion of geology in hydrologic unit sample point selection indicates geology (or rather the waterbody pertaining to a geologic strata) needs to be considered when evaluating the bacteriological quality of groundwater. This recogni tion of the importance of geology, however. was not extend<xl to t.he delineation of hydrologic units (See Figure 2) . Therefore the requirement to assess water qual i ty in relation to geology has not been satisfied. This becomes evident in the DRAGPS Report as there has been little or no discussi{m of hydrogeology and water quality.

4.3 Differentiation of Bores and Wells

The initial selection of hydrologic unit sample points seems to have assumed no diffE,rencE' between bores and wells. The selection procedure simply specified a minimum number of nine sample peJints per hydrologic unit (See Section 4.2). There is howe-.;er, a necessity to differentiate bet.ween the bacterio~ogical water quality of bores and wells, due to the susceptibility of wells to surface run-off and atmospheric contanlina tion ..

well bacteriological Report during data during sample point

The need to differentiate bore and data wa'3 recognised by the DP.AGPS interpretation, but was not recognised selection. When the two types of differen;:iat.ed, the ORl,CPS requirement points· per hydrologic unit is negated:

sample point are for nine "sample

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Two hydrologic units have less than nine bores, and all have less than nine wells (See Table 1)

Consequently, the nuwber of \'1ells, and in two cases the number of bores, representing a hydrologic unit do not satisfy the criteria designed to select a statistically valid proportion of the bore and well populations. Given that bores and wells are to be exam:ined separately, to correctly implement the DRAGPS selection criteria, nine bores and nine wells should have been chosen to represent each hydrologic unit.

4.4 Frequency of Sampling

P. strict monthly sampling programme was implemented to produce the DRAGPS dat.a base. During the study, twelve samples were collected from each sample point (except where a bore punp was not operational, access to a bore denied, or deletior; of the sample point from the Study). The collection of one sample per month is the minimum sampling recommended by the tl.H.M.R.C. (Reference 7). The N.H.M.R.C. also states that the minimum action to be taken if a sample bactericlogical count_ exceeds the health investigation levels is immediate resampling. If the repeat sample results reach the hea:cth investigation levels, it is concluded the source is pollLted.

ThE- basis of any water quality survey sampling frequency is discussed in Section 3.4. An examination of DRAGPS Appendi~ A data (Reference 3), will reveal a high degree of bacteric·l count variability. It can be assumed that an Jncrease of sampling, included resampling I would minimise this variability, as wall as other statistical uncertainties associated with bacteriological data production. These include sampling procedure, collection of an adequate sample volume, transportation to laboratory, sample processing and tha enu·:leration of the true bacterial organism density. A greater number of samples, including resamples, would have produced a more sensitive, and statistically sound, data base. The DRAGPS sampling programme is not statistically based, and t.herefore does not lend itself to st.atistical analysin.

The practice of resampling is essential to the developnent of a statistically sound bacteriological data base. Only one sample exceeding the health investigation level was resampled during the DRAGPS. A sample collected from bore RN 20115 produced an E.coli count of 94 organisms per 100 mL. "hen the bore was resampled, the count was reduced to zero E. coli per 100 mL. I t is 1 ikely the high initial count was due to one or several of the statistical uncertainties associated with bacteriologioal data production.

12: HYDR04


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w

I I I I I I I

Tl~BLE 1

I HYDROLOGIC j , ,

UN I '!' I i I ! I I , ,

2 I i , I !

I I 4

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I 5 I

I I

6 I

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1 7

I

~ I 8 I I I

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., -

10

--

I I

'rOTAL

L 1-

12:EYDR04

BORE AND WEl.L NUMBERS PER HYDROLOGIC uNIT

SAMPLE POINT TYPE

BORE WELL

12 4

9 0

13 3

8 0

I I 6 3 I

I

! I I 14 3

, I \

I 10 2

11 1

- -

'-83 16


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Sampling technique is integral to the implementation of any sampling programme. Duri ng the DRAGPS Study, samples were collected after the bore had been pumped 10 minutes. In SOIUe cases this may be insufficience time to extract all the standing bore water. A bore water sample, rather than aquifer sample may have been collected. It is recommended an investigation of th,~ bacteriological quality of the bore stem \"Jater and aqui fer be undertaken by sampling throughout a pump cycle t.o establish sampling techniques, and the source of con tamina t,ion.

4.5 Data Ana lysis !4ethodol.!23Y

The pril11ary ~mit of bacteriological data analyses of the DRAGPS was the hydrologic unit. The approach adopted by the Study was t.o view each nnit as a single reticulation system, where each sample poi.nt represented a "tap" drawing water from a "'common pipeline" - the groundwater reservoir. The sample results from each sample location in a hydrologic unit were grouped and collectively examined.

The methodology suffers from hlO major weaknesses. Firstly, the sample points do not draw water from a common aquifer, and therefore there are no grounds for their collect.ive analysi.s. Secondly, no account is made of the sanitary characteristics unique to each sample point (ego proximity to point sources of pollution, sample point construction standards, and cat.chment land-use).

Furthermore, chlorinated and management and as

the fact that some sample points were others not, reflects differences in

such excludes their collective analysis.

<1.6 Bacteriologica 1 Wat.er Quality and Rainfall

The collated hydrological unit sample data was analysed for an association between rainfall and bacteriological contamination. The broad based definitions 0 f "wet" and "dry" seasons "ere used in the Study. These seasonal classifications really refer to the occurrenco of box jelly fish and safe bathing periods, and do not necessarily represent actual changes in catchment hydrology, in particular rainfall. By t.hese seasonal classifications the "wet" SE'aSon is the period November to April, and the "dry" season May 1"0 October. The DRAGPS should have used actual rainfall periods rather t.han loosely defined seasons. Groundwater level could also have been monitored.

As shown in F 19ure 3, the "dry" season included two months ",hen rain fell. The DRAGPS methodology does not permit a meaninqful association between rainfall and bacteric.logical sample contamination to be considered in any deptch.

Future samplinq should be sensitive to rainfall, with rain gaLqcs should be installed at selected bores.

12: HYDR04


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I I I I I I I 600

1-'00

I 400 ~ g ~

300 H

I H ~ r... :z

200 H

I ~

100

I I I

w

I I I I I I

FIGURE 3

\4 E T

--

I - I

I _I

I -

-

HONTHLY RAINFALl, TOTALS AT HOWARD SPRINGS NETF.OLOGICAL STATIONS FOR THE "WET" AND "DRY SEASONS".

SEASON

\ I I •

I

I I

I 1

DRY SEA SON

NOV. DOC. JAN. FEB. t·IA..<l,. APR. MA.Y. JUN. JULY. AlJG. ;lEI'. CCT.

TlllE ( I'ONI'lIS)

>

I I I

I

I 1

I


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4.7 Assessment of Bacteriological Drinking Water Quality

The DRAGPS implemented the N.H.M.R.C. long term drinking water quality objective. The objective sets out a "stringent level" (Reference 7, Page 2) of the water quality. As discuss~,d in Section 3.5, the objective is not designed for assessmEcnt, this is the function of criteria. An assessment of drinking water quality criteria in general, and their applicat,ion, will be undertaken in "A Review of Bacteriological Drinking Water Quality Criteria", which is presently in preparation.

The objective level was applied to each DRAGPS sample. Those samples which failed the objective level were termed "polluted". The DRAGPS Report concluded 30% of all dry seasons n sources" (ie. samples) and 42% of all wet season "sources" were polluted. The objective level should have been applied to the bacteriological data pertaining to each sample point, thereby providing information on the number of sample points which meet the objective. When this is undertaken, 96 of the 99 bores and wells (approximately 97% of all sample points) fail the objective. This contrasts with the above percentage values of "jjlource" pollution, and, more importantly, represents the correct implementation of the objective.

ThE' poor compliance (97%) is a result of the application of a "stringent" water quality objective, not designed for assessment of bacteriological water quality, and a statistlcally weak data base which did not include resampling.

In order to afford the evaluation of bacteriological water quality I the current desirable drinking water quality criteria, utilizing health investigation levels, is recommended. This approach is supported by the lack of epideminological data implicating :drinking water as a vector of enteric complaints. l

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5. AN AI,TERNATIVE INTERPRETATION OF THE DARWIN RURAL AREA GROUNDWATER POLLUTtoN STUDY BACTERioLOGICAL STUDY

Data interpretation in this chapter will be restricted to DRAGPS samples points which were unchlorinated, and represented by ten or more samples.

5.1 Application of Criteria

The most applicable assessment level to the DRAGPS sample point da{:a is the current desirable water quality criteria. The criteria is currently utilized to evaluate town and community drinking waters in the Northern Territory.

Less than half of all sample points complied to the criteria (See 'l'able 2). The "failure rate", as defined by the criteria, for wells was considerable higher than that for bores .

A large proportion of samples "failed" due to excessive Coliform counts only (See Table 3), in particular well samples. This indicates a non-faecal pollution source, such as soil and dust, could be important contributor to sample point water contamination.

TABLE 2

Application of The Desirable Drinking Water Quality Criteria to DRAGPS Sample Point Data.

SAMPLE POINT TYPE

BORg

WELL

12:HYDR04

TOTAL NUMBER

70

12

DESIRABLE DRINKING WATER QUALITY CRITERIA COMPLIANCE

SATISFY NOT SATISFY

30 43% 40 57%

1 8% 11 92%


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..,

TABLE 3

Explanation of Sample Failures (as defined by the Criteria)

SAMPLE POINT TYPE

BORE

WELL

EXPLANATION OF SAMPLE "FAILURE" (as defined by the criteria)

EXCESSIVE E.COLI

COUNT ONLY

9%

9%

EXCESSIVE COLIFORM COUNT ONLY

44%

57%

EXCESSIVE E.COLI & COLIFORM

COUNT

47t

34%

5.2 Temporal Distribution

An examination of the temporal distribution bacterio:cogical data will provide an insight into associat:con between Darwin Rural Area hydrology, groundwai:er contamination.

of the and

The hydrologic parameters which vary be important in the bacteriological groundwa ;:er inc 1 ude:

with time, and may contamination of

(i)

(ii 1

(iii)

Surface run-off from sample point catchments.

Infiltration to the groundwater body.

Change in groundwater level.

(lv) Groundwater velocities.

(v) Laternal water movement through the unsaturated soil zone (interflow).

As there is little or no data available on the above hydrolog:'.c parameters, rainfall will be used as an index to changes in Darwin Rural Area hydrology. Rainfall records from the Howard Springs Meteorological Station No. 014149 will be Iltilized.

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1-. I 1 I I 1 I I

Ideally, it would have been preferable to rainfall total for the 24-72 hours prior to collection, and bacteriological sample quality. limitations of time and manpower, however, this possible. Instead, sample "failure" per cycle was with monthly rainfall total. The weaknesses of the include:

compare sample

Due to was not compared analysis

1. The use of rainfall as an index of catchment hydrology.

2.

3.

The index does not successfully account for changes in groundwater levels.

The four week sample cycle was not based on a calender month.

Rainfall at Howard Springs cannot be extrapolated to every sample location in the Darwin Rural Area.

Rainfall prior to sampling is represented by a monthly total, rather than the actual rain which fell.

The percentage of bore samples which fail the desirable drinking water quality criteria is greater during the months of rainLlll (See Figure 4). The association between the two variable:; ~s not linear, and in fact could not be expressed mathematIcally. Table 4, provides a summary of bore bacteriological water quality for periods of rainfall and non-rainfall. A bore sample is twice as likely to be unacceptdble, as defined by the criteria, when collected during t.he a rainfall month compared to a "non-rainfall" month.

A similar examination of well bacteriological sample data has been undertaken. Only E.coli sample concentrations appear t·) be associated with monthly, rainfall (See Figure 5). No such association is eviden:t for coliform sample concentration. This may be due tol the entrance of coliform bearing dust down uncovered wells. Nevertheless, the incidence of unacceptable well samples during the rainfall months is higher than "non-rainfall" months (See Figure 5).

l\lthough no clear relationship between catchment hydrology and sample water quality can be stated, there does appear ::0 be an association between the two parameters. Further investigation is warranted.

5.3 Aquifer Source

From an examination of sample point . log data, presented in Appendix A of the DRAGPS Report, the geologic strata supplying groundwater to rural residents was estimated.

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FIGURE 4(a) PERCENTAGE OF BORE SA}1PLES WHICH HAVE UNACCEPTABLE COLIFORM CONCENTRATIONS AND MONTHLY RAINFALL TOTALS.

f-In STOG RZl.M : RAINFALL

LINE ~ % SAHPLE UNACCEPTABLE

600 - c-

500 . '" ..

400 -

300 - i-

200 ---/ \. - r

100 i .. .

I A

o ..JuL AUG .rT SEP DEC NOV JAN I.w< FEB APR w.y JUN

:)RAGPS MJN'TI! (NORMAL DISTRIBlJrION )

FIGURE 4(b) PEiRCEN'l'AGE OF BORE SAHPL8S WHICH HAVE UNACCEPTABLE E.COLI CONCENTRATIONS AND MONTHLY RAINFALL TOTALS. . - "-

HISTOGRAH ,. RAINFALL LINE .. % SAHPLE UNACCEPTABLE

600

500

400

300

200

100

o

JUL AUG OCT SEP DEC NOV JAN MAR ~EB APR MAY JUNE .

DRAGPS H?NTH ( NORAAL.~3~S~'f~~T:I:?N ~urll'C:E[JrABLE l\CCORDIN3 TO 'l.'HE DESIR'lBLE DRINKING 1'l".TER QUALITY CRl'l'ERU>

SO

70

60

50

40

30

20

10

o

BO

70

60

50

40

30.

20

i<

~ I ~ ~.

i ~


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TABLE 4

BORE SAMPLES UNACCEPTABILITY (ACCORDING TO THE CRITERIA) FOR RAINFALL AND NO RAINFALL PERIODS

PERIOD

Rainfall rronths (8 rrcnths)

No rainfall IlDnths (4 rrDnths)

TABLE 5

T'JI'AL NO. OF SAMPLES

561

281

NO. OF SAMPLES

UNl'CCEF'l'ABLE

147

37

26%

13%

AVERAGE N:).

OF SAMPI.ES l.JNACCEl?T1l.B

PER M:lNI'H.

18

9

WELL SAf.1PLE UNACCEPTABILITY (ACCORDING TO THE CRITERIA) FOR RAINFALL .l\.ND NO RAI~~ALL PERIODS

w I ~--------------------,----~------~ TCII'AL N:). N:). OF PEK'ENI'AGE AVERAGE N:).

OF SAMPLES SAMPLR; SN-lPLE OF S/\MPLES

I UNl'CCEPl'ABLE UNACCEPTABLE UNACCEPTABLE PERIOD PER M:lNI'H

I I I I I I

Rainfall rronths (8 rrDnths)

No rainfall nnnths ( 4 n=ths)

96 36

48 12

38% 4.5

25% 3

-.


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500

400

300

200

100

600

J 500

~ 400

1300

~ 200

~ 100

o

J1]L

FIGL'RE 5 (a) PRECEN'ICIfuE OF WELL SAI,lPLES \'lllICH HA ~ lJNA02EPI'ABLE* OJLlFOru~ CCNCENI'RATICNS AND Inl'rHLY RlUNE'ALL TOl'AIS.

\ \

fr •

V AUG 0Cl' SEP DOC N:JI1 JAN MAR FEB . APR Ml\Y JUNE

DRAGPS MJNI'H ~ NJRMl\L DISTRIBUTICN )

FIGURE 5 (b) PERCENI'AGE OF w'ELL Si\M!?LES WHICH HAVE lJNi\CCEP'I'ABLE* E. COLI CON8ENl.'RATlrnS AA1p M:W'HLY RAINFALL TOl'AlS.

HISTCGRAM3 = PAINFALL LINE = t SA/-lPLE 1JNI\CCEPTl\BLE

I

~.~

AU::; CCT SEP DEC NOV JAN MAR PEa ---APR -~~y JUNE ;.!'"

DRAGPS MJNl'H ( NORWIL DISTRIBUPION ) I I *u."lACCEPTl'BI£ ACC03DIN3 TO ':'HE DP'sIRABLE DRINKDlG WATER QUI\LJ.'"TY CRI'I'BRIA •

. ¥,

80 «

70 i 60

50

40 f!l

30 ,

(': , .'.:

20

20

b

80

70

60

50 h

40 ~. .. €':1

30 tB.

20 .~ .. ill,' ..

10

a


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I I I I I .41 I

• I I I I I

Due to the paucity of log data, only half of all sample point aquifer sources could be estimated. The wells were of shallo,,, depth, and drew from the upper laterite aquifer. Bores, of deeper construction, drew water from three major geologic strata: sandstone, slate and dolomite.

The percentage of samples collected from the same aquifer source, which exceed the health investigation level, are presE,nted in Table 6. Surprisingly, the percentage of unacceptable samples from each source was approximately the same. '1'1:.e dolomite aqui fer, in particular, was expected to show low contamination. The aquifer is typically 55-75m below the surface I water percolating to this depth should have suf Eicient time to become bacteriologically "clean". High bacterial counts (in one case in excess of 1000 coliform organisms per 100 roLl from bores which tap the dolomite aquifer may be due to contaminated bore stems.

The relations between aquifer source and bacteriological sample contamination is unclear, and warrants investigation.

TABLE 6

SM~PLES UNACCEPTABILITY (ACCORDING TO THE CRITERIA) ~JD AQUIFER SOURCE

GEDIlX',IC STRATA

Sandst.ane

Dolanite

Shale

Laterite

12:HYDR04

NUMBER OF

BORES

22

6

10

o

WELLS

o

o

o

8

264

72

120

108

70 27%

17 24%

25

33

21%

31%

j"


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5.4 Septic Tank/Bore Separation Distance and Bacteriological Water Quality

An underlying supposition of the DRAGPS was the resident domestic groundwater supplies by effluent. Such contamination is a function of:

pollution of septic tank

effluent bacterial concentration bacteria die off rates

(i 1 (ii) (iii) soil hydrology (infiltration rate, distance to the

saturated zone) (iv) groundwater velocity, and recharge rates

Surface run-off from soils draining septic tanks may also contribute to groundwater contamination. Run-off water may enter the groundwater body by percolating down the bore stem casing.

A comparison of criteria) and septic presented in Figure 6.

sample failure (as defined by tank/bore separation distance

Interpretation of Figure 6 is limited by the following:

the is

1. The septic tank/bore separation distance does not take into account direction of groundwater or surface water movement.

2. The diagram does not detail the distribution of samples between bores, nor does it detail sample distribution for individual bores.

" failed" "failed"

The distance ranges are represented by approximately the same number of samples. There is a decreasing incidence of sample "failure" with increasing separation distance (Reference 3, l',ppendix ll). A similar diagram, a plot of E.coli sample concentration and sepa~ation distance, was used to derive the "reasonable" minimum separation distance of 100 meters. Note, however, the percentage of "failed" samples does not decline to zero for samples collected from bores with a separation distrance of at least 90 m (330 m in one case). Also, at least 75% of samples, regardless of separation distance, complied with the desirable water quality criteria.

The number of bores which failed the desirable water quality criteria and their distribution amongst septic tank/bore distance ranges is summarised in Figure 7. The proportion of bores which did not meet the E.co1i part of the criteria decreased significantly for bores located at least 70m from a septic tank.

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FIQJRE 6 (a) PER!::ENI'AGE OF EO..~ SAMPLES WITH llNACCEPTABLE* E.COLI CON~ENTRATIONS AND SEPTIC T.ANK/BORE: SEPARATIO" .. DISTAN:E.

~

<if' ~

§

~ 35

30

25 -p 20 -

~ 15

~ 10 P<

-5 -

FIGUP.B 6 11.»

~ 35 . "" ~ § 30 .

~ 25' .

20

15 .

10 . E]

~ p,

5 _

•

I l

10-29 30-49 50-69 70-89 90

SEPTIC 'TI\NK/BORE: SEPARATICN DISTAN::E (m)

PERCll,"l1\GE OF OORE SAl<lPLES WITH l1Nl\CCEPTABLE* COLIFORM CONCENI'RATlOOS* AND SEPTIC TANK/OORE SEPARATION DISTfu'iCE.

I I

10-29 30-49 50-69 70-89 90

SEPl'IC TllNK/I'ORE SEPARATICN DIS'I~NCE . (m)

* ACCORDING 'TO DESIPABLE DFXNKING \i'\.TER c;ul\LITY CRITERIA.

I. 1: ! I ~.


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FIGURE 7(a) PERCENTAGE OF BORES WHICH FAIL THE E.OOLI PORTION OF THE CRI'I'ERI.l\, Ai'ID SEPTIC TANK/BORE SEPARATION DISTANCE.

70

. 60

~ 50 ,,; ~

fil i!l

40

fjJ 30

~ tl :n ffi il; 10

BIQJRE 7 (b)

70

60 .

~ 50

f11 40 f2 @

30 (3 Wi 20

~ 10 Po<

I \ I

I I

-? -' - .., -30 ~9 50 69 ,0 89 90

SEPrIC TANK/BORE SEPARATION DISTAt-x:::E (m)

PErCENTAGE OF roRES WHICH FAIL THE COLIFORH PORI'ION OF THE ,[TERIA, AND SF.Pl'IC TANK/OOPE SEPAF.M'ICN DL~.

i

j i !

I I

-.

10..,.29 30-49 50-69 '70-89 90

SEPTIC TA."lF'./l3OHE SEPARATION DIS'OOKE (m)


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The same trend is not evident when the Coliform portion of the criteria is applied to the same bore samples. In fact, th.~ proportion of bores which failed the Coliform criteria showed no relationship with septic tank/bore distance.

When the desirable water quality crite):"ia are applied, about 50% of all bores fail, and 20% of .all samples fail. Sample points located 70m or more from a septic tank are likely to fail the criteria because of high coliform counts only. The relatively low faecal contamination of these samples, and long separation distance indicates the samples are not being polluted by septic tank effluent. Sample contamination is due to an unidentified source, which is most likely of non-point source origin, and accentuated by poor bore com;truction which does not satisfy Health Regulation 58.

Bores sited within 70m of a septic tank are likely to fail the criteria because of high E.coli and Coliform counts. E.coli contamination appears to be associated with the close proximity of septic tanks. Septic tank effluent may contribute directly to the E.coli contamination of bore water, or it may provide nutrients which are capable of maintaining bacteria viability and growth. Coliform contamination of the bore samples might be attributed to septic tank effluent. H~~ever, as with bores with a separation distance of greater than 70m, an unidentified non-point source of pollution may be responsible for samples failing t.o meet the Coliform criteria. Bore construction which doE'S not meet Health Regulation 58 (eighty-two of the eighty three study bores) may render bores susceptible to poliution from point and non-point sources.

The analysis of the association between bacteriological water quality and septic tank/bore separation distance examined the number of samples and bores which fail the desirable water quality crite~ial the complementary situation, the number of samples and bores which satisfied the criteria, has not been discussed. If any association between bore "failure" and distance from a septic tank can be put forward, an explanation must also be found for the 50% of bores and 80% of samples which satisfy the desirable quality criteria.

The lack of any clear relationship between septic tank/bore separation distance and bacteriological water quality is a result of the complex nature of bacteriological contamination of bore waters. A similar analysis for wells was not possible due to the small number of sample points.

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'"

'" 1


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~I

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5.5 Faecal Coliform/:&'aecal Streptococci Ratio

The fa€:cal coliform (F.C.) /faecal streptococci ratio (F.S.) ratio is used to assess the faecal origin of bacteriological pollution. The basis of the ratio is tr-e observation that faecal streptococci numbers tend to be high in animal faeces, but IO~1 in human faeces. A predominately human pollution source should exhibit a F.C./F.S. ratio greater than 4.0, whereas animal sources exhibit ratios of less than 0.7. Intermediate values indicate a mixed source. Due to differential die-away rates of the faecal coliform and faecal streptococci groups, the ratio is only use.fvl for assessing the source of recent pollution.

E.coli rather than faecal coliforms, were enumerated during the Study. Consequently an E.celi/F.S. ratio has been utilized. It has been assumed the E.coli/F.S. and F.C./F.S. ratios are little different. A zero count of either E.coli or faecal streptococcus organisms has been treated as < 1 organism per 100 mL. Samples containing coliform organisms, but zero E.coli and faecal streptococci, have no ratio and are recorded as such.

FIGURE 8

E.COLI/F.S. RATIO FREQUENCY DISTRIBUTION FOR BORE SAMPLES WHICH ARE UNACCEPTABLE TO THE CRITERIA

50

percentage 40

of bore 30

samples 20

unacceptable 10

0

<.0.7 0.7-4.0 > 4.0 no ratio

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I

• I

• • • t I

• • • • ,., .' • • • • I

•

Due to the monthly sampling frequency, many ratios are likely to refer to faecal pollution not of a recent nature. Therefore r no sound interpretation of the ratio frequency distribution oan be made. Nevertheless, the data can be examined for a trend. A summary of the frequency distribution of B.coli/F.S. ratios for DRAGPS bore samples, which ar,,, unacceptable according to the desirable water quality criteria, is presented in Figure 8. Nearly half of all "cont.aminated" samples had a ratio of less than 0.7. This would tend to suggest animal faecal matter may be an important contributing factor to groundw;;;.ter bacteriological pollution. Also, the large percentage of samples containing no faecal organisms indicates soil and dust contamination of the bore stem and/or groundwater body.

The E.coli/F.S. ratio frequency distribution for wells which fail the criteria reveal a similar trend to that exhibited by bore samples (See Figure 9). The majority of ratios were less than 0.7. The E.coli/F.S. ratio data is of limited 'Talue due to the monthly sampling frequency and unknown age of any faecal pollution. Nevertheless, they do emphasis the need to consider animal faecal matter and, to a lesser e·xtent, soil particulate matter as sources of groundwater pollution.

FIGURE 9

E.COLI/F.S. RATIO FREQUENCY DISTRIBUTION FOR WELL SAMPLES WHICH ARE UNACCEPTABLE TO THE CRITERIA

percentage of bore sanplea unacceptable

12 : HYDR04

80

70

60

50

40

30

20

10

o

(0.7 0.7-4.0 > 4.0 no ratio

E.COLI/F.S. RATIO


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• w I I

• • I I

•

5.6 Chlorination

During the Study, eight bores were chlorinated by landholders. Calcium hypochlorite was added to the bore stem. Following chlorination, bacterial counts, notably E.coli, were markedly reduced for the remainder of the Study (See Table 7); in one case 10 months after chlorination.

Whils't chlorination can be held responsible for the initial bacterial die-off, its direct effect cannot extend to periods up to 10 months.

If the initial source of contamination was septic tank effluent, and this contamination was continuous, then it could be assumed samples collected more than a month after chlorination would be contaminated similar to pre-chlorination samples. Contamination did not return (See Table 7). There are two possible explanations for this phenomena: (1) coincidental ceasation of bore pollution and bore chlorination - at> vrlflkl!ly event; (2) a pollution event may have "seeded" the groundwater or bore stem with bacteria which did not die-off, proved 'viable and capable of growth. Chlorination destroyed this viable bacteria population.

Bact.eria growth cannot occur however, without a nutrient source. Two possible nutrient sources are the detrital material of bacterial slime growths on bore stems, and septic tank effluent. The viability of bacteria in bore stem and nutrien~ sources requires investigation.

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,

* = c.fU=ination by landholder - = no sanp1e =llected

E.COLI PER 100 rnL. ~,,-,,-

CYCLE

£OllE,/\\lEIL llN 1 2 3 I 4 5 6 7

!

WELL 20178 13 30* 2 2 0* 0* 0

, roBE 9117 2 200 2 170 8 120 16*

i 1

I £ORE 9784 500 1000*1 0 0 2 0 a

i I I • BORE 9835 1220* 0 a 2 Q 0 6

i

I .'

, WELL 9751 0 2 I 2 40* 0 2 Q

! i !

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• 1

\ 0

1 I

BORE 8966 0 3 50 I 8* 4* 0 i ,

• I

WELL 9712 96 0 4 24 a 2* 0

BORE 9943 0 1 300 290* 0 0 -

I

8 9 10 II 12

0 - I - - -

0 I 12 a 0 0 ,

! , ! i

0 0 0 0 4 1

I I I

0 0 0 0 0 I

0 0 12 0 0

I

. " .. :

0 0 0 I a 0 I

t 0

I 0 0 0 Q.

I t

0 0 0 0 o I

. ;.'


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6. SEPTIC TANK INVESTIGATION STUDIES

6.1 Fluorescein Tracer Testinq -Fluorescein tracer testing was undertaken as part of the Dar..;in Rural A.rea Study to investigate hydraulic connection and travel rates between septic tanks and bores. Thirteen sites, ·"hich "showed consistent E;coli presence in water" (Reference 3, Section 4.2.3), Were selected for the investigation.

Prior to the additional of flourescein to septic tanks, the background flourescence at each sample point was examined. Samples exhibited flourescence of variable concentration, sometimes of an "unexpectedly high magnitude" (Reference 3, Appendix D). This flourescence was most likely due to crganic molecules which flouresce in wavebands similar to flourescein. An intensive sampling programme should have been undertaken to fully determine background flourescence variability at each sample point.

Samples were collected, in most cases, every morning and evening from sample points for a 39 day period after flourescein addition. Flourescence detection, defined as twice the "background level", was recorded. The DRAGPS results are presented in Appendix B. Detection counts tended to be scattered, the period between flourescein detections range from 12 hours to thirteen days. There were few 3-4 day consecutive detections of flourescein.

Flourescein concentration, rather than detection, should have been determined. This would have permitted calculation of the flourescein plume peak, and removed interference from background flourcscence. The test results were held to be "in doubt and display some uncertainty" (Reference 3, Appendix D) dueLo unknown levels of/background flourescence. Nevertheless, the injected flou~escein was held to be detected in the bore well samples - an opinion of the study team (Reference 3). The bores and wells "deduced" to be flourescein positive, and hence to have a hydraulic connection between the septic tank and sample point, did not generally exhibit sample contamination typical of sewage effluent (See Table 8). High bacterial counts were not consistent for "flourescein positive" sample points. In fact, zero E.coli concentrations account for over half of all samples collected from seven of the ten bores and wells "hydraulically connected" to septic tanks.

To derive travel times the septic tank/sample point distance was plotted against the time· between flourescein injection and its first "detection" .. (See Appendix C). Two lines drawn to encompass five point.!!~ were used to defin~ maximum and minimum travel times. Six points were not included in the derivation, three for unstated reasonli ... and remainder because they were considered "dubio\1s~ (Reference 3, Appendix D).

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,. " , '

Technical R

eport WR

D83051

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age 41 of 64.

- -- - -- - - .,~- - - - - ~ ~,~;~. - - - - -TABLE 8 E.COLI SAMPIE ~TIONS FOR FIl.DRE.9:::EIN TRl\CER SWDY SAMPlE IDINI'S

E.CDIJ: PER 100 mI,. FIWRESCEIN , .----- T&l\CER

ac:m:/WELL RN i I I I TEST 1 2 3 4 5 6 7 8 1 9 10 11 12 RESUL'1'*

BOP'" 9795 0 0 i 26 --;._- -;,- 10 560 0 0 0 2 0 +

OORE 20297 1 4 0 320 2 12 220 240 6 2 0 2 _

oom:: 9117 2 200 2 170 8 120 16 0 12 0 0 0 +

oom:: 9784 500 1000 a 0 . 2 0 0 0 0 0 0 4 +

OORE 9423 9 24 28 10 1000 80 260 180 400 2 0 680 +

OORE 9059 0 4 1 2 2 4 a 0 0 0 0 +

OORE 8927 1 1 400 0 48 2 0 0 0 0 0 0 + ~

OORE 8872 0 8 4 12 0 2 4 0 0 0 0 0 + --""

BORE 7792 I 0 0 0 0 2 2 0 12 0 0 0 0 +

WELL 8940 0 0 0 0 2 2 2 0 0 68 0 0 -

weLL 21079 4 0 1 56 2 0 2 2 0 0 0 0 +

WELL 9712 96 0 4 24 0 2 0 0 0 0 0 0 -

WELL 9944 145 1000 4 30 10 10 6 400 0 0 0 0 +

~,

" + "" HYnRl\DLIC CXNNa:TlON BElWEl'N SEPTIC TANK AND BrnE/WELL .

.• · ... ·:i;;~~~-AlrJ~~~iH~::~'F~~;.::f'~;,:.· ... '~'-"~~"'~iiriijii¥ii,~~~~~9Z:6±il:~;:i: ;~:;::":


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Travel rates of 1.3 to 3. 5m/ day were calculated, one sample point however, had a "travel time of at least 20m/day" I (Reference 3, Section 5.2.4). As stressed in the DRAGPS Report, though, the rates were only an "indication of contaminant travE;1 rates" (Reference 3, Appendix Dj. How "indicative" the rates are is not detailed. I

The DRAGPS investigation of hydraulic connection and travel rates between septic tanks and sample points were not based on sound scientific method. Background flourescent was not fully determined, nor was the flourescein plum peak. Also, tr~vel rate calculations have been restricted to only six of tne twelve sample point studies. Consequently, the travel rates and flourescein results in general, are of questionable value.

Although only "indicative" the travel rates have been utilized to derive a "first pass limit of pollution" (Reference 3, S~ction i.l). The D~_GPS Report does not clearly define ;this parameter. A value of 90m was calculated, thijil, the Report states, is "an indicative minimum separation distance for bores/wells and sewage disposal systems of the type in common use in the Rural Area". 'rhe value 90m was calculated by multiplying the travel r,:l.te 3.1m/day by 30 days the "maximum life of bacteria' (Reference 3, Section 7.1). The use of this bacterial survival period is unreferenced, and may be based on the desirable retention period of a sewage lagoon. If so, it is not necessarily applicable to bacterial survival of sewage effluent in soil. The methodology used to derive the "'first pass' pollution limit", is based on study team opinion, doubtful and uncertain data, selective use of data and the unsubstantiated use of a bacteria survival period.

6.2 Sodium Chloride/Conductivity

The aim of sodium chloride/conductivity trials was to assess groundwater movement close to sample points. Four bores were selected for the study. The selection of these bores (Registration numbers 9059, 9681, 9624 and 9835) appears to be a poor choice as they did not show consistent contamination (See Table 9). Up to six observation bores (maximum depth 8 meters) were sited in the vicinity of each sample point. Most observation bores were located between the sample point and the household septic tank.

Each observation bore was dosed with two kilograms of sodium cl1,loride L and flushed with 50 litre of water in April, 1982. Six sampl,es were collected during the following four weeks from each' sample point, and sodium concentration and conductivity determined.

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TJlBLE 9

,

E.COLI s..Z,NPLE CONCENTRATIONS FOR SODIUM CHLORIDE/CONDUCTIVITY TRACER STUDY BORES.

E.COLI PER 100 mI..

C\''CLE

BORE RN ,

2 3 4 5 6 7 8 9 10 11 12 1.

,

9059 - 0 4 1 2 2 4 0 0 0 0 0

I

9281 0 0 500 0 4 6 0 6 4 0 I 0 0

I I I I 9624 0 0 0 4 2 0 2 240 8 0 0 I 0 I

1 I ,

I ,

9835 220 0 0 2 0 0 6 0 0 0 0 0

I .

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I I I - .. _- .. ,--~ . -


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During that time the water from a tank, this discharge. The results sodium ,'onductivity peak sample points.

observation bores were charged with crudely approximates a septic tank reflected background levels. A

was not detected from any of the

The sodium chloride concentration and conductivity results indicate no hydraulic connection between the observation bores and the sampling point, not supporting the supposition that septic tank effluent was contaminating the groundwater. The Report states, however, that the failure to demonstrate a hydraulic connection was due to "rapidly falling water tables" (Reference 4, Section 5.2.3). Drawdown rates were of the order of 0.5 to 10m (reduced SI'7L) for an eighteen day period, for three of the four bores. The reduced SWL for the other bore fell below the depth of the observation bore.

6.3 Phosphate Study

Septic tank effluent typically exhibits phosphate concentr~tions of 45rng P0

4/1itrc (Reference 9). This

observation formed the basis for the use of phosphate as a chemical tracer of septic tank effluent. It was held that phosphat<: dispersion from septic tanks would parallel indicator organism dispersion.

Phosphate concentrations of five samples from every sample p0int were determined. Generally, concentrations were 10Vl, approximating 10 ug/litre. This is 1110 OOOth the concentration of phosphate in septic tank effluent. A similar "dilution" of E.coli from effluent would yield concentra.tions of 10 E.coli per 100 rnL. Sample phosphate concentrdtion of 10 ug/litre were not accompanied by E.coli concentrations of 10 per 100 mL. In fact, the study results sho~led no correlation, nor association, between phosphate concentr,ltion and indicator organism concentrations. This may be a~tributed to one or more of the following:

( i) (ii) (iii) (iv) (v)

effluent bacteria die-off phosphate absorption by soil phosphate uptake by bacteria groundwater dilution of septic tank effluent insignificance of septic tank effluent to sample point "pollution".

The DRAGPS bore and well phosphate concentrations were of the same order of magnitUde as Government test bores not associated with Rural Land-Use. It is likely phosphate from septic tank effluent did not reach the sample points, and that sample concentrations reflected b.ackground levels.

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The phosphate investigation produced about 500 results. These are not discussed in the body of the DRAGPS Report. The implicit assumption involved in examining phosphate concentration was not born out by the results.

6. <\ Review of ,'laste Disposal Systems

Septic tanks are the most common form of domestic sewage disposal systems in the Darwin Rural Area. The tanks function as sedimentation chambers for suspended solid matter which is decomposed anaerobically by bacteria. The tank effluent typically pass into an absorption trench where organ.Lc matter and bacteria are retained by the soil and subject t.o aerobic bacterial decomposition.

Septic tank construction is regulat.ed under the Public Health Act. The Act does not include absorption trenches. The minimum septic tank capacity, as recommended by the Department of Health, is 2,500 litres. Officers of the Department, under the authority of the Public Health Act, can inspect septic installations, and direct the clearing and even renoval of septic tanks which are a danger to public health.

During tank s ,,·ere observed:

the course of the DRAGPS approximately 25 septic inspected. The following inadequacies were

1. siting of absorption trench uphill of septic tank

2. unsealed septic tank t.ops (septic tank a large pipe)

3. improper sealing of septic tank base

insufficient accumulation

holding capacity caused by sludge

5 • septic tank infrequently pumped out. not aware of this maintenance need.

6. unbaffled tanks

Landholder often

7. tank construction of 200 rom blocks which were not reinforced

8. anaerobic absorption trenches

Septic tank construction and disposal systems in t.he Darwin "ural Area may not be adequate. In Australia and overseas the multi-chambered tank system is the preferred system, the size of the tank is such that the "clear zone" capacity is equivalent to one days retention time. To maintain this detention time, regular- inspections and sludge

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removal is required. The design of sub-surface trenches is related to percolation and infiltration rates, with particular emphasis given to construction finish of trenches, ego scazification of trenches to improve lateral dispersion and the application of straw or water permeable paper over the acrgregate base to prevent si 1 tation. Basic design/performance parameters are not detailed in the Public Health Act. Investigations will require to assess parameters suitable to develop minimum design criteria for septic tank installations.

Even when a septic tank disposal system is correctly designed, constructed and constrained by local environmental conditions. During the Terri tory's heavy summer rainfall, groundwater level rises and may "drown" absorption trenches. Also, solution cavities and channels of the Darwin Rural Area lateritic soils detract from the soil's suitability as a filtration medium for effluent organic matter and bacteria.

siting are separation

is at least regulations

bet-ween the

Twc approaches to regulating septic tank currently in practice. The W.H.O. utilize a distance (Reference 10), the recommended distance 15m. 'I he other approach is to implement regarding the depth of unsaturated soil absorption trench and the groundwater level.

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• , • ;: , , • • • • • ~ '. • • '. • 0

• • • • • • •

7. REVIEW OF SAMPLE POINT CONSTRUCTION STANDARDS

Groundwater in the Darwin Rural Area is extracted from bores and wells. The former is defined as any shalf of less than " metre diameter, and the latter as shal f s over J., metre diameter and suitable for lowering a basket into (Reference 4). As ·::If September 1982, There was 628 Bores and 133 wells in the D3.rwin Rural Area (Reference ~l).

vlater Division has standards for bore and well construction under the cont.rol of Waters Act (Reference 11). Hinimum standanls 0 f bore and well construction are detailed in Appendix D. These f however f are not at present legally enforceable. The Act requires the driller to obtain a permit prior to commencement of bore or ~/ell construction, and to notify the Rural Advisory Section of the Water Division of the completion of drilling and casing. An 1nspection of the site is then undertaken by the Rural Advisory Section. No further inspections are made •

The following construction inadequacies have been noted by the DRAGPS:

(a) Bores:

(b) Wells:

1. improper seal between casing and pumphead or pump delivery hose

2. inadequate coping around casing

3. casing cut off at coping surface, or near ground level

4. slotted casing near ground surface

5. slotted casing for full depth of bore

6. insufficient casing depth

7. liverstock and poultry access to borehead

8. inadequate borehead drainage

1. exposure to atmosphere

2. casing cut off at groundlevel

3. perforated casing near ground surface

4. liverstock access

5. inadequate surface drainage from well

No inspection of bore or well groutin~ was possible.

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A large number of bores and wells are of sUb:;;tandard construction. For example, most sample points were unfenced (Reference 4) - a requirement of the N.T. Public Health Act. Only one of the 99 DRAGPS sample points complied with Health Regulation 58. To compound any pollution problems associated with substandard construction, some bores and wells were located in or near animal yards. Of .the 83 DRAGPS bores, the two which produced the poorest bacteriological water quality were lOC.lted within and adjacent to poultry sheds.

'I'o reduce groundwater pollution, W.D. Scott (Reference 8) have proposed present construction standards be upgraded. The proposed standards are designed to prevent the ingression of contamination from "polluted" upper groundwater and surtace water to the lower aquifer. Of the existing bores and wells in ::he Dan-an Rural Area, none comply with the W.D. Scott proposed constl-uctiol1 standards.

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8 . SUMMARY

of the DRAGPS a different a different the previous

The two previous Reports (Reference 3 and 4) were reviewed, and the data manipulated in manner. As a result of this manipulation, interpretation can be placed on many aspects of Reports, thus arriving at different conclusions.

The use of the long term drinking water quality objective for assessment is not supported in the recognised literature (Reference 7 and 8). The Health investigation level, cf the drinking water quality criteria, should be used for assessment purposes.

The selection of DRAGPS sample sites and sample frequency is open to debate. Selection of sample sites have been in1: luenced mot-e by surface topography, than any of the other spatial factors (eg. land-use, hydrogeology and pollution point source) which may influence water quality. A monitoring programme was initiated which conformed to the N.H.H.R.C.; ie. minimum of 1 sample per month, to provide for a data base. However, N.H.~1.R.C. also states that when a count is unacceptable, a repeat sampling is an immediate requirerrent to remove any uncertainties associated with sampling and laboratory techniques. This basic recommended approacr. ~laS not implemented by the DRAGPS.

Seasonal conditions, as defined in the previous Reports, were related directly to calender seasons, ie. May-October "dry seasons", November-April "wet season". Examination of rainfall data indicated this is not the case, a quite heavy rainfall event can be experienced in the "dry season" period. The incidence of samples with bacterial counts exceeding the health investigation level was highest during the periods of rainfall. Changes in the Darwin Rural Area hydrology appear to be associated with bore/well bacteriological water quality.

Of the 99 sample points surveyed in the study, only one cOlnplied \>lith t.he construction standards of Health Regulation 58. The sanitary conditions of many bores and \.;ells were inadequate; some were located within or adjacent to animal yards. The construction standards of septic tanks a potential point source of pollution - were also inadequate in wany cases.

The limited tests associated with chlorination indicated, in the majority of cases, the concentration of pollution indicator organisms could be reduced for several months after sterilization. This t.ends to indicate growth of these organisms in the bore stem. The source of these organisms is yet to be established.

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9. RECOHHENDATIONS

9.1 Recommendations Based on the DRAGPS Report

1. Bores and l'io11s

2.

(d) Bore construction. All bores should satisfy Health Regulatlon 58 requirements. Prior to testing of the bores, the bore stem should be sterilized using a chlorine solution. On completion of bore construction a bacteriological sample should be collected in addition to the normal inorganic chemical sample. Samples should be collected during the pump cycle.

(b)

When a bore is serviced, it should be practice to sterilize the bore stern prior to it being placed back into service.

Wells. it is syste:n.

The use of wells should be discouraged, as extremely difficult to provide 'a safe'

SeVldge DisDosal Systems

(a) Location (separation distance) • Whilst the stparation-aIstance of 100m between sewage disposal system and bores would be satisfactory to protect the water source, alternative separation distances can be acceptable provided soil permeability is adequate for the removal of bacteria. A minimum distance, wi th satisfactory soil permeability should be approximately 20 metres. '1'he onus is upon the landholder to show f i 1 tration media are satisfactory for effluent bacteria removal. Sewage disposal systems should preferably be located down hill of bores. .

(b) Construction. The se\vage disposal system chamber should be baffled to prevent grease and oil transfer to the filtration media. Where problems may be experienced with poor suitability the site should excavated and backfilled with suitable filtration media.

l.n alternative to the provision of an adequate filtration media, in cases of minimum separation distance, is a surface disposal system. These are only recommended as a final means of sewage disposal due to the problems associated with odour, flies, mosquitoes, mechanical failure and cost.

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9.2 Recommendation [or the Darwin Rural Area pollution Management Study

1. Further laboratory investigations to establish suitability of the Coliform group of organisms by themselves, as suitable indicator organisms for this investigation.

2. In conjunction with the Depart.ment of Health derive a working bacterial concentration level to afford a satisfactory basis for water quality assessment purposes in the private bore/well situation.

3.

4.

Bores that indicate consistent high sample bacterial concentrations (maximum 10) will be examined in depth to establish the source of pollution and reason for pollution. Investigations will include:

Bacteriological testing through a pump cycle

viability stud~es

chlorination studies

comparative studies between contaminated and uncontaminated bores

in conjunction with the groundwater engineers, investigate surface and subsurface bore construction.

Investigate basic design parameters of subsurface drainage septic tanks. Septic tank performance be evaluated in terms of:

clear zone space

percolation rates

dispersion rate (tracer studies)

clogging factors

subsurface trench design

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1.

3.

4,

5.

6.

7 .

8 •

9.

10 ..

11.

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REFERENCES

Hydrogeology of the Darwin Rural Area, Report No. 8/1980. Nater Division, Department of Transport and Norks (1980).

Kingston, Survey:

D. "Dan-an Rural Area, Water Pollution Report to the Department of Lands,

September Transport

1981" Water Division, Department of and Works (1981).

Kingston, !), & Port, G. "Danvin Rural Area Groundwater Pollution Study: Report 7/1982 Volume 1 and 2, Water Division, Department of Transport and \'larks (1992).

Kingston, D. "Darwin Rural Area Water Pollution Survey Interim Report Decewber 1981", Water Div ision, Department of Transport and Works (1981).

I.R.D, - W.H.O. Natio:ls (1978).

"Water Quality Survey" United

Evision, L.H. & James, A. "Bifidobacterium as an Indicator of Faecal Pollution in Water". Progress in Water Technology 7(2) pp 57-66 (1975) .

Commonwealth Department of Health "Desirable Quality for Drinking Water in Australia". Australian Government Publishing Service (1980).

Iv.!!. O. Water"

"International Third Edition,

Standards (1971) •

for Drinking

Whelan, B. R. et. al. "Movement of Phosphate and Nitrogen from Septic Tank Effluent in Sandy Soils near Perth, Western Australia" In Proceedings of the Groundwater Pollution Conference. Australian Government Publishing Service. (1980).

Wagner, E.G. Rural Areas (1958) •

& Lanoix, J.N. "Excreta Disposal for and Small Communities". W.H.O.

N.D. Scott & Co. Pty Ltd. "Darwin Rural Area Water Supply Study" September 1981.


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APPENDIX A

HICROBIOLOGICAL DESIRABLE QUALITY FOR DRINKING WA'l'ER

(FROM REFERENCE 7)

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Criteria, objectives and investigation levels in the following Table:

Column 1

Desirable current criteria sets out maximum levels which may be used as current criteria appropriate to present Australian conditions to give a drinking water of satisfactory quality.

Column 2

Long term objectives sets out more stringent levels which could be aspired to as long term objectives, and which, if achieved, result in drinking water of excellent quality. These levels are based on WHO International Standards for Drinking Water, 1971.

Column 3

Health investigation levels - sets out, in respect of those characteristics and constituents which may affect human directly or indirectly, levels above I.-hich the authority should be notified in order t.hat it may advise on action necessary to prevent the occurrence of a situation potentially dangerous to health. This the levels recommended, are set well below those of which a health risk would actually occur.


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DRINKING WATER QlALLTY - CRITERIA, OBJECTIVES AND INVESTIGATION LEVELS

1 , .... ~ '! 0' -'''''r'm' _ vU[/l.--Jv ,i;>

c' 0 l. /Arm 1 !)CSilubtc i..: l-iJlY'cn t: Criter-ia

Thr.-ougllQut auy year, 90" of all samples shoulrl not cont.lin levlJls in excess of those spe{_, i f i ed in Column 3.

C:o.zumn ::;

Long tePm obJec-tll..les

niQximun leveZs

Column .3 Health investigat{on levels

it leveZs exceed

1. Throuyhout any 20 per 100 mL. year 90% of samples shuuld not contain any coliform organisms in 100 mL.

2 .No. sample should conta.in more th<3.n 10 col i form oryan.isms per 100 mL.

3.Coliform organisms should not be detectable in 100 mL of any two consecutive samples 4

(!:lee Int.(;rprC!tation (;f results, parapqrd..pIls 3.1, 3.2.2" and Collection of Samples, paragraphs S~1.7. a.nd 5~1.8)

11. E. e::oZ.i 'l'hr0 uqhou t any year/ 9U% of all samples should not con LtJ.in levols in excess of lhose. specified jn Column 3.

No sample shoulr.l contain r. DoZi in 100 mL.

2 ;)£~:C 100 mL.

(Sec IntcL-prctation of results, paragraphs 3.1, and 3.2~:2, and Collection ot sarop1.es, paragraphs 5.1.7. a.nd 5.1.B)


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3.

3. 1

3.2

3.2.2

4.

4.1

4 .1.1

4.1.2

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Interpretation of results

J: t should be not_cd that col iform organisms may occur in an otherwise satisfactory water supply system for reasons not associated with faecal f)ollution. Consequently, in some cases, low levels of coliforms may be allmyed in the absence of B.coli without causing concern.

If, however, a marked rise in coliform occur in a regularly monitored supply, should be taken to ascertain the cause.

should action

Health investigation level exceeded.

action required if

Microbiological

I f more than 20 Coliforms or 2 E. coli per 100 mL are present in any sample the minimum action necessary is immediate resampling. If the health Lnvestigation level is reached in the repeat, immediate steps should be taken to ascertain the cause and to remove the source of contamination. T f these measures are unsuccessful, urgent steps should be taken either to disinfect the supply, or to provide an alternative.

Frequency of Sampling*

Sampling for microbiological examination.

In order to ensure the continuing safety of public water supplies it is necessary to carry out regular microbiological examinations of water in all distribut.ion systems irreSpective of whether the water is chlorinated or I not • The frequency of sampl ing and the minimum number of samples to be examined depend upon the characteristics of the supply and upon the population served. The World Health Organisation recommendations for sampling are given in the following table!

~laximum intervals between successive samples and min~mum number of samples to be taken.


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4.1.3

4.1.4

4.1. 5

4.1. 6

5

5. 1

!,XlPulation served

LeSiJ than 20 000 20 000 to 50 000 50 000 to 100 000 More tha!1 100 000

HaximJrn inte.-,,,a 1 between successive sarrples

1 lIDnth 2 l>'Ceks

4 days 1 day

~1inimJrn nurrber of samples to be taken fran the ~tole distribution systems each rronth

1 sarrple per 500 p:JpUlation per rronth 1 sarrple per 100 000 population per m:mth

Bot.h of the above criteria should be satisfied in every di£tribution system.

The minimum number of samples may be redued to one per 10 000 population per month ,,,hen the population served exceeds 100 000, since in system serving populations of this size some locations are examined each day. In very small and isolated cowmunities, a lesser trequency would be acceptable subject to ttle concurrence of the health authority.

The Samples should not necessarily be taken from the sample point on each occasion, but expert advisers determine the points in the distribution systems from which samples should be collected.

It should be emphasised that, in rout.ine control, it is far more important to examine numerous samples by means of a simple test than occasional samples by a more complicated test. or series of tests.

The frequencies recommended are the m~nimum necessary to routine microbiolog1ca 1 examination, and, in unfavourable circumstances or in the event of an epidemic or im.Ttlcdiatc danger of pollution, or when more stringent control is necessary, much more trequent microbiological examination will be required.

Collection of samples*

Collect~on of samples for microbiological examinat.ion

12:HYDH04


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Scrupulous care in the collection of samples for microbiological examination is necessary to ensure that the samples is representative of the water it lS desired to examine, and to avoid accidental contamination of the sample during collection. The \vay in ",;hich samples are collected has an important bearing on the results of their examination and it is important, therefore" that sample collectors should be properly trained for the work.

Where several samples are being collected on the same occasion from the same source, the sample for microbiological examination should be collected first, in order to avoid the danger of contamination of the sampling point during the collection of the other samples.

Sterilised glass bottles provided with a ground-glass stopper or a metal screw-cap should be used, the stopper and neck of the bottle at least should be protected by a paper or parchment cover, or by thin aluminium foil, disposable sample bottles of plastic materials may be used provided it can be shown that results comparable to those from glass containers can be obtained.

If the water to be sampled contains, or is likely to contain, tracer of chlorine, chloramine or ozone, it is necessary to add to the sampling bottles, before sterilisation, a sufficient quantity of sodium thiosulphate (Na 2S2 )" 5H 20) to neutralise these substances. I t has Leen shown that 0.1 mL of a 3% solution of crystaline sodium thiosulphate in a 170 mL bottle has no significant effect on the coliform or E.coli content of unchlorinated water during 6 hours storage. This amount of sodium thiosulphate is SUfficient to neutralise up to at teast 3mg/L of residual chlorine, and it is therefore recommended that it be added to all bottles used for the collection of samples for microbiological examination.

If samples of chlorinated water are taken, it is desirable to determine the content of chlorine at the sampling point, at the time of sampling.

The sampling bottle should be kept unopened until it is required for filling. During sampling, the stopper and neck of the bottle should not be allowed to touch anything which may contaminate the sample. The bottle should be held near its bottom. The bottom should be filled, without rinsing, and the stopper should be repiaced immediately. The sample should not completely fill the bott:e.


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If a sample of mains water is to be taken from a tap, the tap chosen should supply water from a service pipe directly with the main and not, for ins tar.ce , one se rved f rom a roo f cis ten. The tap should be cleaned and then flamed to sterilise it. The water should be run to waste from the tap for at least two minutes before the sample is collected, in order to cle.ar water ~lhich has been standing in the service pipe.

!lased on WIlO International Standards for Drinking Water, 3rd Edn, 1971.

12:!lYDR04


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APPENDIX C

DKUVATION OF TRAVEL TINES (FROM RE~'ERENCE 3)

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NO'1'E OF CAUTION

~/hiZst these aer)ived ~e$ults ape by no means acaurate, they provide an indication of aontaminant travel !lates.

It is thought that most of these pates are induced by poo~ bore or well ef'fieieny and ove'P-pu.mping~

LEGEND

• Time when [ZttoreRcain first detected in samples.

-0 Dtibious results (ehloY'ophyZl or other' fluoTJeseent interference).

FIGURE' Dl

f1TRA. VRL TIME'S OF PLUORESCEIN 11R4CE'-R l! LU1"JES.

-. / //'" V ~----4------0------8------1-J------1-2------1-4------1-6------1-8------


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APPENDIX D

CURRENT W1\TER DIVISION MINIMUl1 STANDARDS FOR BORE CONSTRUCTION

( a)

(b)

(c)

(d)

(e)

( f)

(g)

(h)

12:HYDR04

(FROM REFERENCE 11)

An annular betltleen borecasing and holewall of not less than 20 rom and to a minimum depth of 6 m shall be cement grouted by the driller in a manner approved by the Controller.

The driller shall notify the Controller when ready for grouting.

A concrete block must be constructed at the surface.

Minimum dimensions . . 1 metre square 300 rom above final ground

surface 100 rom below final ground

surface

The surface of the concrete to be self-draining.

TOp of the borecasing shall be a minimum of 75 rom above the top of the concrete block.

A distance of 5 metre radius around the bore shall be well drained.

If unfenced stock or poultry has access to the bore a stock and poultry resistant fence shall surround the bore at a distance of·5 metres.

i

Prior to equipping the bore the casing shall be securely capped, either by tag welding a steel plate to the casing or other secure means.

When the bore is equipped the space between the casing and the pump components shall be sealed against vermin and dirt.

When a diesel or petrol driven pump is installed the engine shall be installed on a separate concrete block, this block shall be provided with a concrete gutter and sump or other means to catch any spilled oil and fuel.


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Bore and maintained occur.

pumping equipment shall be installed and so that leakage and spillage do not

The first tap than 5 metres tap shall be a of the bore.

on the pipeline shall be not less from the borehead, preferably this co~mon garden tap to enable sampling

The bore is to be maintained at all times to the above minimUl!l standards.

If a bore is no longer required, the casing shall be securely capped or the borehole backfilled in a manner approved by the Controller.


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AP?ENDIX D (CONT)

CURRENT W.i\TER DIVISION t4INH1UM STANDARDS FOR CONSTRUCTION OF A WELL

(FROM REFERENCE 11)

The well shall be lined with a water proof liner to a depth not less than 3.5 metres, with an annular space not less than 20 mm between the lining and the hole wall.

The annular space shall be backfilled and cement grouted by the driller in a manner approved by the Controller. The driller shall notify the controller Ivhen ready for backfilling and grouting.

A concrete apron shall surround the well and a collar installed to extend a minimum of 500 rom above ground level.

Dimensions of the apron shall be:

Minimum 500 rom w~de Minimum 150 mm thick

and shall drain away from the well.

A weather proof cover shall be installed to prevent ingress of dirt and vermin.

When a pump is installed, the and cover shall be sealed to dirt and vermin .

space between pump prevent ingress of

A 25 Dlm diamet.er. in the cover to readings.

hole with plug is to be installed provide access for water level

A distance of 5 metres from the well shall be well drained.

A stock and poultry resistant fence shall surround the well at a distance of 5 metres.

When a diesel or pe'trol driven pump is installed the engine shall be installed on a separate concrete block, this block shall be prov1ded with a concrete gutter and sump' or other means to catch any spilled oil and fuel.


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12:ilYDR04

Well and pumping equipment shall be installed and maintained so that leakage and spillage do not occur.

The first tap on the pipeline shall be not less than 5 metres from the well, preferably this tap shall be a common garden tap to enable sampling of the well. .

The well is to be maintained at all times to the above mini.mum standards.

If a well is no longer required, the hole shall be backfiled in a manner approved by the Controller.

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