otany Bay Project forking paper no.4 Natural water quality
HANCOCK TD189.5 TD189.5.A82B6B64 no.4. . A82 B6
B64 A.N.U. LIBRARY n o . 4 This book was published by ANU Press between 1965–1991. This republication is part of the digitisation project being carried out by Scholarly Information Services/Library and ANU Press. This project aims to make past scholarly works published by The Australian National University available to a global audience under its open-access policy. Natural water quality Botany Bay working paper no. 4 (Completed July 1978) Natural water quality Merike Johnson
Botany Bay Project Canberra 1978 First published in Australia 1978
Printed in Australia
© Merike Johnson 1978
This book is copyright. Apart from any fair dealing for the purpose of private study, research, criticism, or review, as permitted under the Copyright Act, no part may be reproduced by any process without written permission. Inquiries should be made to the publisher.
National Library of Australia Cataloguing-in-Publication entry
Johnson, Merike. Natural water quality.
(Botany Bay project working paper; no. 4) ISBN 0 7081 0340 5
1. Water, Underground. 2. Water quality. 3. Water — Analysis. I. Title. (Series).
628.161
United Kingdom, Europe, Middle East, and Africa: Eurospan Ltd, 3 Henrietta St, London WC2E 8LU, England North America: Books Australia, Norwalk, Conn., USA Southeast Asia: Angus & Robertson (S.E. Asia) Pty Ltd, Singapore Japan: United Publishers Services Ltd, Tokyo FOREWORD
One of the objects of the Botany Bay Project was to encourage environmental studies of Botany Bay on topics selected approved by the Project Committee and carried out over relatively long periods by individual investigators. This approach offered a means of having some in-depth studies to supplement the broader group research of the Project team. The Project was fortunate in being able to interest Ms Merike Johnson in a Ph.D. scholarship to work for a three- year period on a scientific investigation of water quality, with some special reference to underground water, an important resource in the area. This working paper reports in a more popular form the main outlines of her findings and offers a good deal of novel scientific appraisal of groundwater quality, particularly in relation to base-line quality evaluations. In common with other working papers of the Project, only minimal editing has been carried out in order to preserve the approach of the author. No adaptations have been made to force the scientific findings into a more explicit social relevance. This editorial constraint has been made easier by Merike Johnson’s own definite views on the matter.
N.G. Butlin June 1978
v CONTENTS
Foreword v 1. INTRODUCTION 1 2. THE EFFECT OF THE PAST ON THE PRESENT 1 2.1 Geological Events 1 2.2 The Human Element 2 2.3 Progress 5 3. RAIN WATER CHARACTERISTICS 5 3.1 The Weather 5 3.2 Salinity 7 3.3 Chemical Composition 10 3.4 The Terrestrial Component 14 3.4.1 The Sulphate Problem 14 3.4.2 Nutrients in Rainfall 19 3.5 Summary 22 4. THE UNDERGROUND RESERVOIR 22 4.1 The Nature of this Reservoir 22 4.2 The Quantity of Water 27 4.3 Characteristics of the Water 28 4.3.1 Area 1 31 4.4 The Presence of Iron 34 4.4.1 Area 2 35 4.4.2 Areas 3 and 4 36 4.4.3 Area 5 37 4.4.4 Area 6 39 4.5 The Sodium Chloride Problem 42 4.6 The I.C.I. Salt Stockpile 45 4.7 Appraisal 45 5. OUR IMPACT ON THE NATURAL WATER QUALITY 46 5.1 Scarborough Swamp - An Aquatic Environment in Distress 46 5.2 Human Influences on the Ground Water Quality 48 5.2.1 From Landfills 48 5.2.2 From Sewage 48 5.3 The Consequences 52 6. THE RIVERS OF THE BOTANY BAY CATCHMENT AREA 54 6.1 General Characteristics 54 6.1.1 Physical Aspects 55 6.1.2 Chemical Characteristics 55
vii 6.2 The Georges River 57 6.2.1 The Human Impact 59 6.3 The Cooks River 61 6.3.1 Quality Aspects 63 6.3.2 Perspective 64 7. CONCLUSION 64
References 66
viii TEXT TABLES
Table I Rain Water Composition 12 II Comparison Between Various Types of Waters 33 III Chemical Compositions of Kurnell Waters 37 IV Leachate from Sand and Iron Sulphide 41 V Leachate from Peat 41 VI Chemical Characteristics of Waters from the Botany-Banksmeadow Area 44 VII Chemical Characteristics of Wianamatta Shale Waters 56
ix TEXT FIGURES
Figure 1 Drainage Area of Botany Bay 3 2 Rain Water Sampling Locations 6 3 Monthly Rain Water Salinity 8 4 Relation Between Chloride Concentration and Distance from the Coast 9 5 Total Atmospheric Input 11 2 6 Tonnes of Atmospheric Salts/km /Annum 13 7 Sulphate Concentrations, June 1974 15 8 Tonnes/sq km/14 months of Land Derived Sulphate 16 9 Distribution of 'Excess’ Rain Water Sulphate (milligrams/litre) 18 10 Distribution of Nitrate in Rainfall 21 11 Genesis of Rain Water Salinity 23 12 Direction of Ground Water Movement within the Boundaries of the Botany Basin 25 13 Representation of Cross Section of Botany Basin 26 14 (a) Distribution of Ground Water Types 29 (b) Distribution of Sampling Points 30 15 Range of Sulphate and Calcium Concentrations 32 16 (a) Bicarbonate Distribution 38 (b) Calcium Distribution 38 17 Salty Sediments in the Botany- Banksmeadow Area 43 18 Effect of Tip Leachate on Scarborough Swamp 49
x Figure 19 Nitrate Ion Distribution, Kurnell 51 20 Relation Between Nitrate Concentration and Sewerage Pipeline 53 21 Influence of Geological Regimes on Water Salinity in the Georges River Drainage Area 58 22 Nitrate Concentrations, Georges River 60 23 Cooks River Drainage System 62
xi 1. INTRODUCTION
Water is one of the basic requirements of life and its availability is a prime determinant of human occupation of an area. Consequently the history of the development of a city is inseparable from the history of its water supply, and so too is the development of Sydney ubiquitously linked with the Botany Bay region. During more than a century of intense rural, urban and industrial activity, the region’s most important resource, fresh water, has been subjected to a multitude of extraneous stresses, but as yet we know little about the water system's capacity to absorb these intrusions. Up to the present time, hydrochemical studies have been confined to surface water data collection and rarely has any attempt been made to extend this to an interpretation of the significance of the measurements. The underground water system has received even less attention. Each body of water acquires unique chemical, biological and physical characteristics through the natural processes of environmental interaction. It is these intrinsic parameters which determine the way in which each part of the hydrological cycle responds to the increasing variety of urban and indus trial components, and a knowledge of these basic principles is imperative to effective development of water resources and waste disposal. This report describes an investigation carried out to gain some understanding of the fundamental nature of the water systems within the Botany Bay catchment area. It aims primarily to identify the relationships between the chemical character of the water and its natural environment.
2. THE EFFECT OF THE PAST ON THE PRESENT
2.1 Geological Events The past for the Botany Bay region stretches back to the Triassic Period, more than 200 million years ago, when the foundations of today’s hydrochemistry were laid with the deposition of the Hawkesbury Sandstone sediments in a fresh water lake environment and the shales of the Wianamatta Group in a brackish swamp situation. These sediments were subsequently eroded to a low plain by an anticedent drainage system bearing a close sim ilarity to the present. Earth movements during the Tertiary Period
1 unevenly warped this peneplane so that the land to the south west of Botany Bay was uplifted to form the Woronora Plateau whereas to the west, the Cumberland Plain, was relatively unaffected. As a consequence of this warping, watercourses were rejuvenated and began to incise the uplifted areas. The sea level at that time was many metres lower than it is now and the coast extended farther east. The streams draining to the coast passed through a shallow tectonic depression in the Hawkesbury Sandstone in the Botany Bay area and carved out deep trenches on the floor of this Basin as they carried their sediment load from the uplands to the sea. But sometime during the early Pleistocene the sea level rose at the end of another glaciation period and the sandstone depression was submerged. The velocity of the stream waters slowed and the sediment loads were deposited in the stream valleys. Throughout the Pleistocene Period eustatic fluctuations continued to shape the sediments of the Botany Basin. Periods of submergence resulted in marine sand, mud and shell beds being deposited; there were times when the sediments were above sea level long enough for soils to develop, and these were to become buried podsol horizons when the sea once again rose; and there were many times when extensive swamps and forests covered the area as testified by the numerous peat layers within the sediments. Much additional sand was brought into the Bay area from the seaward side by ocean currents and the wind reworked some of the sediments by depositing the sand dunes which mantle the cliff tops. These are broadly the geological processes of the past which shaped the aquatic environment of the Botany Bay region. This region is delineated, by the surface drainage area of Botany Bay and comprises the Hawkesbury Sandstone and Wianamatta shale catchment area of the Georges River and its tributaries, the predominantly Wianamatta shale catchment of the Cooks River, and the unconsolidated sediment area surrounding the Bay with i t s swamps, ponds and store of ground water.
2.2 The Human Element The geological processes formed the blue print upon which human habitation has subsequently wrought its effects. The Aborigines are known to have lived in the Botany Bay region for thousands of years, but their small numbers and lack of technology negated the need and limited their ability to modify the environment extensively; perhaps the firestick
2 Figure 1 Drainage Area of Botany Bay
BOTANY BAY
PORT HACKING
t . . I Alluvium
Hawkesbury sandstone
Wianamatta shale
3 was their main instrument of change. Two hundred years ago to Captain Cook and his crew, the Bay area still presented 'a vision of silent forests, charming meadows and extensive swamps filled with wild flowers'.1 To Captain Phillip, who arrived 18 years later with the first settlers, the extensive swamps ironically posed a threat to health as such swamps were known to do in other lands, and so he sited the settlement away from these swamps on the banks of a small stream fed by springs in the Hawkesbury Sandstone which forms the northern rim of the Botany Basin. But recurring calamitous droughts, population growth and gross pollution, soon caused the abandonment of this as a water supply and Sydney was forced to turn back to the swamps for its life-line. For several years water was brought from the Botany Basin by horse and cart and the residents paid high prices for their daily needs. This situation was improved in 1830 by the laborious excavation, by convicts, of a tunnel through the hard sandstone to reach the swamps of the present day Centennial Park. The completed tunnel delivered 13,000,000 litres per week to a standpipe in Hyde Park. The swamps formed a continuous chain of ponds to the Bay shore and from 1858 the tunnel supply was superseded by the more abundant supply from the lower swamps. The pumpage rate from this source was recorded in 1867 as 90,000,000 litres per week.2 Through the succeeding years, Sydney’s growing population necessitated continual additions to be made to this water supply in the way of diversions of water from other swamps to the main stream, and the building of a series of dams along the watercourse. It was in this way that the Botany Basin served as Sydney's only source of water for 60 years until the Nepean River Scheme took over in 1886. But by this time too, the area had experienced considerable changes. The tall timber was gone; it had been used for firewood. Many of the swamps had been drained to allow market gardening. The marshland vegetation was no more and the ground had become hardened by the trampling of cattle, resulting in flooding when it rained. Industry too, had established itself near the supply of fresh water and many of the small creeks draining to the Bay were reported to be discoloured by the foul wastes of tanneries and tallow works. Water continued to be drawn from the Basin by way of open dams, wells and spear points, and later the introduction of
4 borehole pumps resulted in an intensive utilisation of the ground water which has been maintained to the present time.
2.3 Progress The physiography of the Botany Bay catchment area today ranges from unhabited, rugged bushland, through suburban to densely habited urban and industrial regions. Many watercourses are still in their pristine state while others have been converted into cement canals. Many streams have received large flows of liquid and solid wastes. Swamps and bays have been 'reclaimed' by f i l l in g with the c i t y 's garbage. Sand mining has dug holes in the river beds and in the sand hills, and the suburban sprawl has covered the land with tar and cement. Throughout all this, what has happened to the quality of the water? What affects the chemistry of the stream more - the geology or the canalisation? What are the important factors contributing to the quality of the ground water in the Botany Basin, and has more than 150 years of European occupation influenced the water composition at all?
3. RAIN WATER CHARACTERISTICS
Since all of the surface water and ground water in the Botany Bay catchment area is derived from rainfall, a study of the chemical composition of rain water was the logical starting point from which to trace the origins of the chemical elements in our water systems.
3. 1 The Weather Outside the tro p ic s, Sydney is one of the w ettest major c itie s of the world and is certainly the wettest capital city in Australia.^ There is a high variability in Sydney's rainfall due to the influence of occasional major storms. These come mainly from the south-west during the w inter months, and the south-east in summer. The p attern is complicated by the preponderance of thunderstorms which cause marked areal v ariatio n s in the to ta l volume of rain received. Rain water was collected from the locations shown in Fig. 2 on a monthly basis over a period of 14 months, from October 1973 to November 1974. During this period several violent storms and torrential rains occurred. In fact, January 1974 heralded in some of the worst floods in Australia this century. During August 1974, a four-day downpour deposited
5 Figure 2 Rain Water Sampling Locations
VILLAWOOD
CABRAMATT, MOORE PARK WATERLOO# BE ACONSFIELD
CLOVELLY KENSINGTON
ARNCLIFFE BANKSMEADOW H IL LS D A L EPICNIC POINT HILLSDALEPICNIC
BOTANY BOTANY CEMETERY BLAKEHURST BAY
PORT HACKING
k ilo m e tre s
6 227 millimetres on the suburb of Randwick and caused severe flooding in areas south and west of Sydney. Over the 12 months’ period from December 1973 to November 1974, the recorded rainfall at the Sydney Observatory (Department of Meteorology records), was 1607 mm (63 inches) and at Randwick for the same period it was 1827 mm (72 inches). These figures illustrate the fact that it was an exceptionally wet year, although there were some months which were relatively dry.
3.2 Salinity The rain waters collected from the sampling locations, which encompassed industrial, city and suburban areas, contained a mixture of rain and dry fallout, or bulk precipitation, which represents the combined effects of all water soluble components of the atmosphere. The study has shown that the total salt content of the pre cipitation in Sydney varies in the extreme from month to month and from location to location. The electrical conductivity values, which measure the number of ions in solution, ranged from 4 micromhos/cm to 300 micromhos/cm. The salinity dis tribution for several of the sampling locations is shown in Fig. 3. As a comparison, the electrical conductivity of Sydney tap water can be taken as being 130 micromhos/cm. Notable is the much higher salinity experienced at Botany and Clovelly compared with Engadine and Cabramatta. The geographical location in relation to maritime influence is the major factor responsible for this difference. The effect of oceanic salts decreases rapidly with distance inland, as shown in Fig. 4 where the chloride ion concentration during the February and May storms is plotted against distance from the coast. There is a five-fold decrease in the chloride content for the same rain mass within a distance of 30 kilometres. Locations at similar distances from the ocean can also experience differences in salinity, as for example, Clovelly, situated less than 1 km from the coast, experiences less saline rain than Botany because Clovelly receives a predominantly easterly maritime influence, whereas the Botany location is exposed not only to the easterly winds but also to the blusterly, salt-laden southerlies coming across Botany Bay. The interaction of several factors is responsible for the variations in salinity from month to month. A major influence being the direction and strength of the rain-bearing winds. Storms predominantly from the south or south-east, carry large
7 8 I •H o u illi NOTE: No rain fell in some locations during July 1974 and hence and 1974 July during locations some in fell rain No NOTE: iue MnhyRi ae Salinity Water Rain Monthly 3 Figure c N J D N Oct I I h Jl rsls ae o en included. been not have results July the 93 4 1973 93 ♦ 1973 ______(a) Monthly rainwater salinity. rainwater (a) Monthly b Mnhy anal itiuin Randwick. distribution, rainfall (b) Monthly I ______---
■ --- 1974 » i O Nov S A J M A M F ______I I ______Waterloo Waterloo Botany Botany Engadine Engadine Clovelly Clovelly Cabramat Cabramat ta I ______I ___ I I I I I Figure 4 Relation Between Chloride Concentration and Distance from the Coast
May /
u 30 February
Cabramatta Blakehurst ClovellyPicnic Point
30 20 kilometres '0 Distance from the coast
9 quantities of oceanic aerosols and characterise the rain water by high s a l i n i t i e s . In c o n tra s t, when the ra in comes p re dominantly from the west, as the flooding rains in August 1974, the salinity is low because of the lack of oceanic a e ro s o ls . The salinity of the rain does not appear to be directly related to the volume. A saline rain from the south-east will continue to be highly saline no matter how much rain falls, but when the rainfall for the month is very low the influence of dry fallout, which consists of the water-soluble parts of city dust, soil particles, organic matter and oceanic salts, becomes predominant. This dryfall collects on the funnel and is washed into the sample bottle with subsequent rains causing the salinity of the bulk precipitation to be high as was the case during the low rainfall months of December 1973, and July and September 1974. It was found that the presence of vegetation or buildings exerted a strong influence on the total salinity of precipi tation in particular locations due to aerosol interception. Drifting atmospheric aerosols were captured by the leaves and branches of trees and by tall buildings, consequently the precipitation collected under a tree had a higher salinity than that collected in the open because the captured salt was subsequently washed off the leaves by the next rainfall. On the other hand, a location sheltered by a building which intercepted much of the dryfall during non-rain periods had a lower salinity bulk precipitation.
3.3 Chemical Composition The proportions of the various constituents of the rain water sometimes varied considerably from month to month. This was very much dependent on the direction of the wind, as can be illustrated by a comparison of the total inputs from sea and land during two different monthly periods (Fig. 5). May 1974, was a month of strong on-shore winds, and oceanic aerosols dominated the rain water composition throughout the catchment. On the other hand, during November 1973 there was an equal distribution of winds from all directions, and the atmospheric composition was dominated by aerosols derived from terrestrial sources. These two months, however, represent extreme situations under unusual atmospheric conditions. Overall, the chemical compositions varied within narrower limits and it is clear that oceanic salts are generally the major components of the
10 Figure 5 Total Atmospheric Input
10000
16000
14000
12000
10000
6000
2000
C M o *-i T3 *-» 4-» (TJ D-> O 4J rH 00 0- rH C CO U o c o —I n o DUX bulk of Sydney’s rainfall. Table I gives examples of rain water compositions (as percentages of the total concentration expressed as equiva lents) which represent the type of composition exhibited by the majority of rain waters in the city area. A comparison is made with the equivalent sea water percentages. The similarity to sea water composition is evident from the Table except for the notably greater percentages of both calcium and sulphate ions.
Table I Rain Water Composition
(a) Average composition of Sydney city rain
Cl % Na+% S0.+% Ca"<~*"% M g ^ K+% 4 Hillsdale 41.3 36.4 9.1 3.7 8.6 0.8 Moore Park 39.6 35.6 10.6 5.1 8.4 0.7 Botany 42.2 36.1 7.5 4.7 8.4 1.0 Waterloo 38.7 34.7 11.2 6.2 8.2 1.0 Clovelly 44.6 37.5 5.1 3.0 8.6 1. 1 Sea Water 45.2 38.9 4.5 1.7 8.9 0.8
(b) Approximately 30 km from the coast Villawood 24.9 22.5 26.3 18.9 5.2 2.3 Cabramatta 27. 1 22.3 26.4 9.5 10.5 4.1
As the distance from the coast increases and the maritime influence decreases, the composition of the rainfall changes to one of a le sse r percentage of sodium and chloride and a higher percentage of calcium and sulphate ions, as exemplified by the compositions at Villawood and Cabramatta. If the 14 months' period studied can be taken as represen tative of the bulk precipitation (i.e. rainfall and dryfall) in Sydney and suburbs generally, then the information gathered here shows that the annual input of atmospheric salts in the Botany Bay catchment area ranges from more than 70 metric tonnes/km2 on the exposed sand dunes at Kumell, to between 30 to 40 metric tonnes/km2 in the city area, to less than 20 metric tonnes/km2 in the western suburbs. This is illustrated in Fig. 6, together with the percentage of the tonnage which is due to sea-salt. When the sea-salt portion is subtracted from the total salts the remainder, which comprise the terrestrial portion of the
12 Figure 6 Tonnes of Atmospheric Salts/km /Annum
PERCENTAGE OF SEA-SALT IN 60-70 ’ VILLAWOOD PRECIPITATION * 1 9 / CABRAMATT/ / • 15 WATERLOO • 3* /
KENSINGTON '5efCL0VELLY / 1 l 8ANKSMEADOW J « .____ X * « « 4 7 C PICNIC POINT HILLSOALO ^ •2 4 I, I BOTANY/ BOfTANY CEMETERY BLAKI /' bay e f f e c t iv e / /CJ WIND y \ . c>—-O * DIRECTION
PORT HACKING
13 soluble salts in the rain water, accounts for between 6 to 9 metric tonnes/km^/annum and is remarkably uniformly distri buted over the whole area, except for a massive 20 tonnes at Banksmeadow where the sampling container was situated under a tree and hence received the extra salts intercepted by the tr e e .
3.4 The T errestrial Component Almost the whole of the te r r e s tr ia l component of the rain water was found to be made up of: ( 1) a year-round presence of Ca"1-** and S04~ ions, and (2) nutrient ions such as K+ in some locations and NO3- in large quantities at certain times of the year. 3.4.1 The Sulphate Problem Sulphate is an important and in terestin g component of rain water because its presence usually raises the question as to what degree it is due to either anthropogenic or natural sources. In the Botany Bay catchment, i t was found that sea-salt aerosols contribute a significant but not a major proportion of the sulphate in the rainfall. This can be seen from the sulphate concentration profile in Fig. 7, where the oceanic and te r r e s tr ia l sulphate components of the June 1974 rain waters have been separated. A noteworthy feature of Fig. 7, is the uniformity of the land-derived sulphate at the various locations. This unifor mity of the terrestrial component in individual rains is reflected in the total input of terrestrial sulphate over the catchment (Fig. 8) . Between 2-3 tonnes of land-derived sulphate fell in all suburban areas over the study period, and the total amount at Clovelly was similar to the total amount at Cabramatta, 30 km away. This may indicate that there is a regional source of sulphate which affects a ll areas of the catchment. In some locations however (notably the industrial/commercial locations), almost twice as much terrestrial sulphate fell per square kilometer as in suburban locations, indicating that industrial emissions constitute an additional source of sulphate in localised areas. Sulphate concentrations in excess of that which can be attributed to a sea-salt or an anthropogenic origin is a universal feature of rain water composition. Such ’excess’ sulphate is present in uncontaminated maritime a ir masses even
14 Figure 7 Sulphate Concentrations, June 1974
4 r AXWWWWWWWWWWWWWWWW
r~ —[ i n 30 20 10 o kilometres Distance from the coast i
15 Figure 8 Tonnes/sq km/14 months of Land Derived Sulphate
, / VILLAWOOD 1 • / CABRAMATT, \ b A y / • 2.5 WATERLOO
KENSINGTON 2j ARNCLIFFE J • • a/ \ i y.6 HILLSD^LEp PICNIC POINT \ I BOTANY J * botany cemetery BLAKEHURST BAY \ f POftT HACKING kilometres 16 in the polar regions.^ Rain waters collected during the study period (1974/75) from remote parts of inland Australia, which can be considered to be far removed from industrial pollution, were found to have sulphate concentrations which were quite comparable to those found in rain waters in the Botany Bay catchment, as can be seen from the comparison in Fig. 9. The sulphate in inland rain waters is derived primarily from the solution of gypsum which is abundantly present in the soil and which is carried aloft as soil dust by the wind. A similar particulate source of sulphate is also possible in city areas. For example, Sumi, Corkery and Monkman^ identi fied gypsum (Ca SO4 : 2H2O) as the principal crystalline component of urban dust in Baltimore, U.S.A. In Sydney, samples of city dust, when leached with water, proved to be highly soluble, and the resultant solutions contained significant amounts of SO4- ions, although the principal components were Ca-1-1" and HCO3- ions. Another significant source of atmospheric sulphate is hydrogen sulphide (H2S) produced by the anaerobic decay of organic matter. This form of sulphur emission into the atmosphere is particularly important in coastal areas where large amounts of H2S are released from inshore marine muds. The H2S is rapidly oxidised in the atmosphere to SO2, with the subsequent formation of H2 SO4 in cloud droplets. In undisturbed forested areas where there is little atmos pheric dust, this continuous emission of H2S results in the rain water composition consisting predominantly of H"*" and SO4- ions, i.e. a weak solution of sulphuric acid.^ It is probable that a substantial part of the evenly distri buted 2-3 tonnes/kmz of land-derived sulphate in the Botany Bay catchment is due to similar natural emissions. Robinson and Robbins^ evaluated that even in urban atmospheres only about one-third of the sulphur reaching the atmosphere comes from pollutant sources, whereas two-thirds is derived from natural emissions, principally in the form of H2S. Unfortunately, no measurements of H2S have been made in Sydney’s airshed which might give some indication of the extent of such natural inputs, or even gauge the effect of the thousands of sewerage vents throughout the suburbs. However, sulphuric acid droplets have been detected in the atmosphere over Sydney.^ In contrast to the dust-free atmosphere of forested regions, Sydney’s air also contains appreciable amounts of dust whose main component is calcium carbonate. The calcareous dust has a neutralising effect on 17 Figure 9 Distribution of 'Excess' Rain Water Sulphate (mi 11 i gr ams / li t r e ) ALICE SPRINGS GILES (Met Stat ° 2.2 4 .0 O OTHE OLGAS I------ COOLGARDIE WARRUMBUNGLE, 7.1 '$■' 2 7 MENINDEE O (Nat Pk ) / BALLADONIA IUNDARABILLA WA.' 1.9° o 4 .4 3 4 / 2 . 0 - . , m o s s ig e l X ESPERANCE O?,’ OLYNDHURST JERRYMUNGUB1 a Si \ 1-9 / kilometres Note: 'Excess SO^ ''means the concentration of SO^V remaining after the (SO^ ) associated with (Cl ) in a standard sea water proportion, has been subtracted. 18 the sulphuric acid, and the products of the reaction, calcium and sulphate ions, are washed down in the rainfall. There was a good correlation between high Ca++ concentra tions and high S0^= concentrations in the rain waters which could be due to the ready adsorption of either H2S or S0^= on solid aerosols where the oxidation of the gases to H2 SO^ could take place. Thus, when there is a high dust content in the atmosphere, there could be a correspondingly high proportion of calcium and sulphate in dustfall. Air pollution in the industrial and commercial locations was evidenced by the presence of a variety of heavy metals in the rain waters which were absent in the rains from the suburban locations. The approximate 1:2 ratio of S04= input in rainfall in suburban vs industrial areas, is similar to the proportion of atmospheric SO2 in suburban vs industrial areas, as measured by the State Pollution Control Commission.^ This greater amount of SO2, and consequently higher concentration of H2 SO4, outweighs the amount which can react with dust aerosols, resulting in a greater proportion of SO4" compared to Ca++, in the rainfall at the industrial locations. It seems, therefore, that the sulphate content of the precipitation in the Botany Bay catchment area comprises an oceanic component, a substantial terrestrial component, probably of natural origin and in both particulate and gaseous form, and a definite indication of added sulphate from anthropogenic sources in industrial locations. 3.4.2 Nutrients in Rainfall Rain water from locations in close proximity to trees continually contained more potassium than rain water at locations away from trees. The loss of potassium from living leaves through leaf excretion, is well documented although the precise chemical form of the potassium is still in doubt. The effect was quite localised and probably constitutes a year-round mini-nutrient cycle where the potassium washed off the leaves by rain into the soil is extracted again by the roots. In contrast to the year-round occurrence of excess potassium, the two spring periods covered by this rainfall study revealed a remarkable atmospheric phenomenon which appears to be peculiar to Australia. This phenomenon was exhibited by nitrate concentrations in the rain water such as have not been recorded in any of the voluminous literature on rain water nitrate in Europe or America. 19 During the study the nitrate concentrations ranged from 0 to 70 mg/1. The monthly distribution pattern can be exemplified by the Blakehurst, Clovelly and Picnic Point locations in Fig. 10, the peaks coinciding with the spring/ summer season with practically no nitrate being recorded in winter. This general pattern was repeated at all locations with the highest concentrations being recorded at Picnic Point and the lowest at Waterloo. The presence of ammonia and nitrate nitrogen in rain water has been known since the beginning of the 19th century but their origin is still a matter of considerable conjecture. Relatively high ammonia values have been recorded in a number of rain waters and biological activity in the soil has been inferred as the source,^ but nitrate values have always been low and although spring/summer maxima are observed in the nitrate concentrations of European and American rains, these ’high values' are usually in the 1-2 mg/1 range, i.e. in no way do they approach the high concentrations observed during the present study. There is little doubt that the nitrate content here is related to the presence of vegetation and specially to the spring season when the flowers are in full bloom. Pollen seems an obvious possibility as a source of nitrate during this period of maximum pollen dispersion. However, Richerson, Moshiri and Godshalk^ found that pollen made only a small contribution to the annual input of nitrogen to the nutrient budget of a small watershed under study in California. Furthermore, pollen, being present universally, would not explain why the nitrate concentrations in Sydney's rain are so much higher than those recorded elsewhere. At the location with the highest concentrations of nitrate, Picnic Point, it was noted that two very large Terpentine trees were in full bloom nearby during the months when the nitrate was exceptionally high. These trees are native to Australia and belong to the family Myretaceae, to which a large number of Australian plants belong, including the Eucalypts. A property peculiar to many native Australian plants is that they are unusually aromatic. The bush and trees are rich in natural oils which are emitted as droplets of oil consisting principally of hydrocarbons such as terpenes. Very little work has been done on the isolation of components other than hydrocarbons, but as early as 1913, Challinor discovered that the peculiar herring-brine odour which was given off by Rhagodia hastata, a native 'salt 20 iue 10 Figure lilligrams/litre NO milligrams/litri c. N Oct. c N Oct . itiuino irt i anal (mg/1) Rainfall in Nitrate of Distribution Clovelly 1974 inc Pt Picnic Blakehurst Blakehurst No' 0 1 21 bush* commonly growing in gardens in Sydney, was due to trimethylamine. This trimethylamine was emitted in the spring and summer months, and was most pronounced in moist w e a th e r.^ More recent research has shown the presence of cyanide containing volatiles in Eucalyptus leaves.^ Because the high nitrate concentrations appear to be unique to Australian rain waters (the inland rain waters also contained relatively high nitrate concentrations) and, considering that Australian native plants do have exceptional aromatic properties, it is possible that nitrogen containing volatiles, emitted by Australian plants during spring are responsible for the nitrate concentrations in the rain w a te rs. Whatever these as yet unidentified substances are, and what processes are responsible for the eventual formation of nitrate ions, remain a matter for speculation until more research is carried out into the effects of Australian plants on the environment. For the present, suffice to say that considerable quantities of a potential nutrient are being released into the atmosphere annually and must play a significant role in the nutrient budget of the Australian ecosystem. 3.5 Summary The rain water study has shown that there is a substantial input of salts to the Botany Bay watershed via the atmos phere, the principal source being the ocean. The rain water chemistry is controlled by a complex interaction of oceanic, mineralogical, geographical, biological and meteorological influences. Much more research needs to be done in sp ec ific field s before the in te r relationships are fully understood and the schematic diagram of Fig. 11 is merely an interpretation of some of the possible processes involved as inferred from the present data. 4. THE UNDERGROUND RESERVOIR 4.1 The Nature of this Reservoir The succession of past geological events has left a legacy in the form of a sandstone basin which is filled with a heterogeneous mixture of marine clays, shell beds, swamp peats, riv er and beach sand, and wind-blown dunes. 22 Figure 11 Genesis of Rain Water Salinity t > ? Q < i < 23 The area extent of the Basin is shown in Fig. 12,'*' and the thickness of the sediments varies from less than a metre to 80 metres. An east-west cross section of the Basin would look something like that represented by the schematic diagram, Fig. 13. The combination of an impervious sandstone base and porous unconsolidated sediments, forms a perfect rain water trap and the sediments are generally saturated to within a few metres of the surface. The topography of this area is characterised by gently undulating, irregular sand hills, with numerous swamps and ponds where the dune swales dip below the water table. On the northern and western sides of Botany Bay, houses, home units and industry have replaced the Eucalypts, Angophoras and Banksia scrub th at once covered the dunes and most of the ponds have disappeared underneath the urban and suburban onslaught. Miraculously through all this some of it has survived; perhaps not in its original form but nevertheless a large green-belt, cutting a swathe through the densest of suburbia, has preserved the chain of swamps which were Sydney's original water supply. The five golf courses and Centennial Park which made up this open area belt can be seen on the map in Fig. 12. But their survival so far is no guarantee for the future. Many of the remaining dunes are already being demolished to provide building sand for our concrete structures, while others are earmarked for the same purpose. The remaining swamps and ponds too are rapidly disappearing, and one can observe the progression, from swamp-to-garbage tip-to-sports field, taking place repeatedly. To the south of Botany Bay, the Kumell Peninsula has escaped much of the activity of civilisation because of its relative isolation. Although it has had its problems too; first the loss of much of its timber more than a century ago, then the grazing of sheep and cattle, and now sand extraction, has reduced large areas into bare, mobile sand hills. But away from the sight of roads, powerlines, sewerage vents and industry; in the swales between the dunes piled high on the sandstone cliffs which plummet steeply down to the ocean, is another world of clear reflective pools and of wilderness heathland where the wild flowers still bloom for which Botany Bay was named. However, even in that remote haven, where sand-miners have not yet reached, the delicately balanced dune vegetation is suffering because of trail-bike tracks which criss-cross the 24 Figure 12 Direction of Ground Water Movement Within the Boundries of the Botany Basin KINGSFORD m a r q u b r a Kingsford Smith Airport ARNCLIFFE LA , PEROUSE CARLTON BOTANY BAY KURNELL SYLVANIA Botany Basin CARINGBAH G reen belt Direction of ground water movement CRONULLA 0 kilo m e tre s 25 iue 3 peetto o Cos eto o Btn Basin Botany of Section Cross of epresentation R 13 Figure 26 area. The bare tops of many of the dunes bear witness to the damage already done. Steps have been taken by conservation groups and the National Parks and Wildlife Service to stop the use of this area by motorised vehicles, and in places re-stabilisation has been attempted. It is hoped that these measures will be successful otherwise this remaining natural heathland so close to Sydney will also disappear. Out of the 1,100 km of N.S.W. coastline, there are only two other areas of heath and woodland which contain sizeable fresh water swamps and lakes, these are the Myall Lakes region situated 270 km north of Sydney and the Wooli Lakes region 500 km north of Sydney. Unfortunately the sand-miners have discovered these areas too. 4.2 The Quantity of Water The volume of usable water actually contained by the Basin has been the subject of considerable interest in the past and in 1942 a governmental Commission investigated the water-bearing potential of the sand beds with a view to using the ground water to supply Sydney in the event of a national emergency.^ No such emergency arose, but it was estimated then that the northern portion of the Basin which comprises about one-third of the whole Basin, could contain in the vicinity of 136,300 million litres of water, which is quite comparable to the capacity of our surface storage reservoirs. Water is extracted from the sands by either shallow spear points where centrifugal pumps lift the water from depths of 3 to 6 metres, or gravel-packed bores where turbine line shaft pumps lift up to 90,800 litres per day from depths of 30 metres or more. Extraction has been estimated at approxi- mately 50 million litres per day,iD the bulk of which is used for various industrial purposes, but a portion is used for watering private gardens, parks, sports fields and golf courses. The current rate of withdrawal appears to be well within the capacity of the sand beds. While direct absorption of rain water by the unconsolidated sediments is the main means of ground water accession to the Basin, an important contribution to the water budget is made by the Hawkesbury Sandstone rim-rock, through direct run-off from its impervious surface and by the springs which can be seen to feed many of the ponds on the periphery of the Basin. Regional ground water movements are generally in the directions shown by the arrows in Fig. 12. It can be seen 27 that while the loss of open space areas close to the Bay would have little effect on the water yields in the rest of the Basin, open space areas on the up-slope end of the hydraulic gradient, such as Centennial Park, are intake areas for large sections of the sand beds. Thus any reduction of open space in these locations would result in a significant decline in the Basin's water storage capacity. 4.3 Characteristics of the Water As with all water supplies it is the quality rather than the quantity which is the final determinant of its usefulness. The 'purity and excellence' of the Botany Basin swamp water was a feature often commented upon by the early residents of Sydney and the first detailed chemical analysis of the water, in 1867, confirmed its low salt content. The present study of the hydrochemistry of the Basin has revealed a complex system where the interaction of a variety of factors has resulted in six distinctive chemical types of water which are distributed over the Basin as shown in Fig. 14 (a & b) . The type of salinity is represented in Fig. 14 (a) by a hexagon whose shape is determined by the concentrations of six major ions plotted along three horizontal axes to the scale indicated in Fig. 14 (a), for example: mi Hi-equivalents/lit re 1__1__1__1__1__ __1__1__1__L 1 \ / \ \ Il__ i__! 1 \\ |1 |1 --1-- 1 | HCO, \ \ 7\ \ \ \ \ \ i__i__ I I 1 1 --1--1 5 4 3 2 1 1 2 2 4 5 28 Figure 14 (a) Distribution of Ground Water Types 29 Figure 14 (b) Distribution of Sampling Points •*% • * ; . • • Bore sample A Surface sainple 30 4.3.1 Area 1 Area 1 comprises a major portion of the northern sand beds and includes the remaining ponds of the old Sydney water supply. The ground and surface waters within this aeolian dune area are characterised by their low salinity, being without exception, less than 200 mg/1. The chemical composition bears a close resemblance to the composition of rain water, particularly the rain waters containing the most terrestrial salts, i.e. the most dryfall. The ground water salts are, therefore, predominantly of oceanic origin with an excess of terrestrial calcium and sulphate ions. The excess of calcium and sulphate, however, is generally greater in the ground and surface waters than in the rain wTaters; this can be seen in the comparison of the range of concentrations in Fig. 15. The added components do not appear to be contributed by the sediments. Waters collected from flowing gutters (as distinct from drains which contain ground water) during rain storms have compositions remarkably similar to the low salinity ground waters. A comparison between a bore water and a typical gutter water, in Table II, illustrates this similar ity in terms of the absolute concentrations. The bore abstracts water from a depth of 36 metres, yet its composition is similar to that of the gutter water which has had no contact with the sediments. Pond w aters and deep ground waters show similar compositions. Clearly, therefore, the sediments do not make a significant contribution to the major ions in the water. Ground and surface waters from similar silicious coastal sand areas, such as Myall Lakes and Wooli Lakes, derive their soluble components almost entirely from rain water. The compositions of these waters generally show some excess SO^- (although this is less than the excess SO^- usually found in the Botany Basin), but of significance is the fact that there is very little, if any, excess Ca~*~+', as can be seen from the examples in Table II. S im ilarly, waters obtained from uninhabited Hawkesbury Sandstone areas which are away from the suburban areas of Sydney, also show a small excess of S0/ = , with practically no excess Ca . What these areas have in common is the fact that they are relatively undisturbed and heavily vegetated. Consequently, there is little atmospheric dust. The presence or absence of dust has a direct bearing on water composition. For 31 Figure 15 Range of Sulphate and Calcium Concentrations Terrestrial sulphate Waterloo [• • •• 7*m • Rain Vlllawood • • • • • • • • ••• • • Rain Clovelly Rain Bore Waters Pond Waters Gutter Waters milligrams/litre Terrestrial calcium Waterloo [• • • • Rain Vlllawood Rain Clovelly Rain Bore Waters Pond Waters Gutter Waters milligrams/litre 32 Table II Comparison Between Various Types of Waters Cl" Na+ S04" Ca** Mg++ K+ (mg/1) 1. September rain water at Waterloo containing a high proportion of dryfall Total concentration 24 15 11.0 3.4 1.6 0.8 T e rre stria l portion 1.6 7.8 2.9 0 0.3 2. Bore water, Rowland Park , from depth of 36 metres Total concentration 25 14 27.0 14.0 3.0 6.8 Terrestrial portion 0.1 23.6 13.5 1.3 6.2 3. Flowing gutter water at Lord Street, Roseville Total concentration 29 16 33.0 14.5 3.9 5.6 Terrestrial portion 0 29.1 13.9 2.0 5.0 4. Bore water, Myall Lakes area Total concentration 41 23 7.0 0.8 2.6 1.1 Terrestrial portion 0.2 1.5 0 0 0.3 5. Reedy Swamp, Wooli Lakes area Total concentration 33 18 18.0 1.0 2.4 0.8 Terrestrial portion 0 13.6 0.3 0.2 0.1 6. Upper Reaches of the Georges River at the ’Woolwash’ Total concentration 31 16 8.0 1.0 2.5 1.0 Terrestrial portion 0 3.8 0.3 0.4 0.3 33 example, in the elevated alpine environment of Mt Kosciusko, where both terrestrial dust and oceanic aerosols are at an extreme minimum, the salinity of the Snowy River is not much more than that of distilled water. On the other hand, much of Sydney’s dusty atmosphere is derived from cement particles swept off city streets by the wind. This is subsequently returned as calcium sulphate in dustfail, after chemical reactions in the atmosphere. The city and suburban gutters were found to be capable of releasing Ca++, HCO3- and SO4- ions into so lu tio n , and the combination of rainwater components and the ions released from the gutter material itself accounts for the composition of most of the gutter waters sampled during this study. The remarkable similarity between the chemical character istics of gutter waters and those of the low salinity waters of the Botany Basin sediments, indicates that the chemistry of the pond and ground waters is considerably influenced by the urban environment. First, by way of modification of the rain water composition due to the dustiness of the atmosphere; and secondly, through city run-off, which contributes soluble components derived from s e ttle d dust, and s tr e e t and gutter m a te ria l. 4.4 The Presence of Iron An outstanding feature of the silicious dunes of the Botany Basin, which does affect the chemical character of the natural water, is the richness of iron in the sands. This can be witnessed by the presence of podsol soils with their red, iron-rich, B- horizons; by the extensive limonite terraces bordering swamps; by the red gelatinous precipitates coating the beds of creeks, and by the irridescent films on undisturbed pools of water. Iron is one of the most troublesome components of any water supply and concentrations over as little as 0.3 milligrams/ litre begin to impart undesirable taste and colour to the water. Iron in concentrations well above this limit is a frequent component of the ground water throughout the Botany B asin. The solubilisation of the iron in the dune sands comes about due to the presence of abundant organic matter which has accumulated through the recurrent burial of soil horizons with their accompanying vegetation, and the redistribution of peaty material from old, fresh-water swamp deposits. The decay processes of organic matter require oxygen which 34 is provided by the dissolved oxygen in recharge water, but when the oxygen becomes depleted, reducing conditions prevail in the ground water environment. The iron oxide minerals coating the sand grains are no longer stable in the changed environment and the iron is reduced. This brings ferrous ions into solution thus mobilising the iron. When the mobilised ferrous ions encounter an oxidising environment, such as a swamp or pond, where the ground water intersects the surface, the ferrous ions are oxidised back to the ferric state by the dissolved oxygen in the aerated water, and re-precipitated as a ferric oxyhydroxide, to form the red terrace s on the edges of swamps. When buried, these irregular iron terraces become distinctive horizons in the strata, which are commonly called Waterloo Rock in the Botany Basin but are known by other names, such as Woolloomoloo Rock, sand rock or coffee rock, in other coastal sand areas. In spite of the abundant organic matter, however, all the ponds in the Botany Basin, including the cliff-top ponds at Kurnell, are outcroppings of the general water table and not perched on impermeable organic layers such as the dune lakes along the Queensland coast and Fraser Island. Apparently a much more profuse vegetation than that which existed in the Botany Basin is necessary for the formation of such humus- bound layers. 4.4.1 Area 2 Area 2 comprises the region surrounding Alexandra Canal, and encompasses Moore Park Golf Course which is the major intake area for this region and from where ground water flows in a south-westerly direction towards the Canal. Prior to the construction of the Canal in 1896, much of the area consisted of marshes which were drained by a small sluggish creek called Shea’s Creek. When the Canal was dug, the level of the surrounding land was raised by infilling with material from the excavation. The strata consisted of estuarine clays with many scattered shell beds alternating with sand and peat layers containing sizeable organic remains such as tree stumps. This heterogeneous strata has resulted in the ground water in this area having a very variable salinity, ranging from 200 to 700 milligrams/litre. The salinity is least around the edges of the region and highest near the northern end of the Canal. The dominant chemical characteristic of the water 35 is the presence of high concentrations of Ca*"*" and HCO^~ ions, originating from the shelly nature of the sediments. Variable concentrations of sulphate ions are also found in the bore waters. The source of this sulphate can be traced back to the swamp conditions which have existed in the area. The decay of large amounts of swamp vegetation, especially under brackish water conditions, has resulted in the formation of sulphide minerals, which have been detected in the sedi ments. On subsequent oxidation by oxygen containing ground water sulphuric acid is produced, which in these sediments, containing abundant shells, is neutralised by the calcium carbonate, forming a solution of Ca"^ and S0^= ions. A further distinguishing feature of the ground water in the central cross-hatched portion of area 2, is the Na+ ion concentrations in excess of that associated with the chloride present. Leaching experiments carried out on various peats produced similar excesses of sodium ions in solution and the present evidence suggests that the sodium is derived from sodium humates associated with the peaty strata. On the western side of the Canal only one bore was a v a il able for observation but the chemical composition of the water from this bore exhibited the typical characteristics of water associated with Wianamatta shale and it seems that the sand west of the Canal receives some seepage water from the Wianamatta shale outcropping as the rim-rock in this portion of the Basin. 4.4.2 Areas 3 and 4 Areas 3 and 4 refer to the unique hydrologic system of the Kumell Peninsula. The Hawkesbury Sandstone tip of Kurnell was once an island but became landlocked by the emergence of a tombolo about 8,000 to 6,000 years ago. Sediments forming the connecting spit were brought by ocean currents and were rich in cal careous material such as shell fragments and calcareous algae. These sediments were later subjected to considerable wind action which created large dunes reaching heights of more than 30 metres, which now cap the sandstone. One of the consequences of this wind action was a chemical sorting of the sand so that the calcareous material was left behind on the spit and almost pure quartz grains were piled up into the high dunes. This geological event now manifests itself in the two chemical types of ground water found on the Peninsula. The 36 difference between the waters can be seen when the percentage compositions are tabulated in Table III. Table III Chemical Compositions of Kumell Waters Na+ Cl" Mg'1"* Ca++ HCO3" S04= *-J • • cy cy 0/ 0/ 0/ 0/ /o /o /o /o /o /o ( 1) 840 9.7 9.7 5.2 34.0 30.2 9.2 ( 2) 540 36.7 42.7 9.1 2.5 1.0 6.9 ( 1) = water associated with marine sands of the spit (2) = water associated with the aeolian dunes E.C. = electrical conductivity in micromhos/cm. The distribution of these two types of waters is clearly delineated by the areal plots of the Ca"^ and HC03~ concen trations in Fig. 16 (a and b). The waters associated with the highly calcareous sand of the spit are often saturated solutions of calcium carbonate, although there is not a direct relationship between the Ca++ and HCO3” concentrations because some of the bicarbonate is derived from magnesium carbonate which is incorporated in varying amounts into the carbonate skeletons of organisms. Some of the calcium is also associated with the solution of gypsum crystals which are present in the spit sand.^ A distinguishing feature of all the waters at Kumell is the chloride concentrations encountered. These are generally twice as high as those found on the northern side of Botany Bay, and on the cliff tops facing the ocean and chloride values are up to 10 times higher. This is due to the direct exposure of the Peninsula to the strong salt-laden southerly winds. This effect is apparently minimised on the northern side by the buffering action of Botany Bay. Water associated with the silicious aeolian dunes of Kumell is thus characterised by its high salt content, composed almost entirely of oceanic salts transported via the atmos phere . 4.4.3 Area 5 Area 5 refers to the narrow belt of sand dunes bordering Lady Robinson’s Beach on the western shore of Botany Bay. The dunes reach a height of only 8 metres above sea level and 37 Figure 16 (a) Bicarbonate Distribution in mg/1 BOTANY BA Y 300 3fi? 7/b BA TE BA Y Figure 16 (b) Calcium Distribution in mg/1 BOTANY BAY BA TE BA Y 38 represent a series of wave-built bars alligned parallel to th e beach. Between this sand ridge and the Hawkesbury Sandstone rim- rock to the west, lies an extensive area of marshland con sisting of both shallow reedy swamp and deep open water, which drains in a southerly direction into Botany Bay. The ground water in the dune area is predominantly characterised by Ca"*“^ and HCO3- ions, reflecting the pre dominance of shells and shell grit in the strata. But the shells are randomly distributed throughout the sand and the waters are not quite as concentrated in CaCHCOß^ as those at Kumell. It seems that the calcareous sand is tempered with sand composed entirely of silica because the hydrochemical d is tr ib u tio n i s one of CaCHCOß^ ric h w aters in te rs p e rs e d a t irregular intervals with very dilute waters containing only rain water salts. These dilute waters can be found from bores within a few feet of the shore of the Bay. The marshland is fed by ground water seeping from the flanking dunes and the chemical composition of the water in the swamp is basically similar to the water pumped from the surrounding bores, however, a variety of human influences have modified some aspects of the water chemistry, these will be discussed later. Influxes of salt water from the Bay occur occasionally and this, coupled with poor circulation (accentuated by several roads dissecting the swamp area) can result in marked salinity fluctuations in the swamp water at times. 4.4.4 Area 6 Area 6 , on Fig. 12, encompasses the northern shore of Botany Bay and includes the heavily industrialised areas of Botany and Banksmeadow. This area has earned an infamous reputation for the often reported ground water pollution which has seemingly occurred due to industrial discharges. The outstanding chemical characteristic of the ground water which has led to this suspicion, is its high salinity com pared to other areas of the Botany Basin. This salinity is due to variable amounts of sodium, chloride, calcium, sulphate and iron, and associated with this salinity is a very signi ficant acidity. Acid discharges from various chemical industries and a large salt stock-pile belonging to I.C.I. Australia Limited have been the most commonly im plied sources of these components, although such conclusions have usually been based on conjec- 39 ture and only one serious attempt in the past has been made to actually study the hydrological features of the area. This study was made by J.V. Smart^ and the major finding was that the direction of the water movement in the area has been changed due to the heavy industrial pumping. The present three-year investigation of the hydrochemistry of the area has revealed that, while industrial pollution cannot be completely discounted, any effect on the ground water composition from such a source is quite over-shadowed by the overwhelming influence of the natural geological features of the region. These unusual geological properties are the result of the swamp conditions which have existed in the Botany-Banksmeadow area for many thousands of years. The sequence of peat horizons, some several metres in thickness, extends to at least 54 metres below present sea level. The radiocarbon age of a peat sample taken from a depth of 27 metres has been given as greater than 30,000 years B.P. (Before Present), but this figure is the limit of the method used and thus indicates only that the swamp sediments predate the Wurm glacial period. The many peat layers are interspersed by marine clay horizons, indicating that the sea frequently transgressed over the swamp. Swamp conditions still exist over some of the area, much of it at elevation close to sea level and a thick layer of relatively recent peat (dated 8,880 + 200 years B.P.) directly underlies the present swamp. The paleoenvironment, of swamp material with its rich store of organic matter, and subsequent sea water transgressions, resulted in severe anoxic conditions, where enormous quantities of hydrogen sulphide were produced by the metabolic reduction of sea water sulphate. The reduction process was also responsible for the extraction of iron from clay minerals and the liberated iron reacted from the hydrogen sulphide to form the range of iron - sulphur compounds, such as pyrite and marcasite, which now impregnate the sediments. These iron sulphides are unstable in the combined presence of oxygen and water, and hence any oxygen carried down to the sediments by the ground water will oxidise the iron sulphides to ferric sulphate and sulphuric acid although a range of intermediate products is possible. Hydrolysis of ferric sulphate will result in the production of more sulphuric acid and extremely acid ground waters will result. This process can be demonstrated in the laboratory by 40 leaching with water, samples of peat, clay and sand from these ancient swamp deposits. Below in Table IV, is an example of th e r e s u lta n t s o lu tio n obtained when some sand, which had become cemented into a hard sandrock by a mixture of pyrite and marcasite, was leached with distilled water. Table IV Leachate from Sand and Iron Sulphide pH Cl" Na+ Mg"1”1” Ca*H’ SO ^ Fe SiC>2 K+ 2.5 0 8 1.6 5 >2,000 1,100 15 4.5 Note: Sand + FeS2, 100 gm in 500 ml water (concentrations in mg/1). It can be clearly seen that the leachate yielded a solution of sulphuric acid and iron sulphate (both as ferric and f e r r o u s ) . But the marine transgressions also deposited in the sedi ments marine organisms with their skeletal parts made mainly of calcium carbonate. Under the very acid conditions, however, most of the shells have long been destroyed and their place taken by the reaction products such as calcium sulphate, often found in the form of large and lusterous crystals of gypsum, in the dry sediment. When sediments also containing the alteration products of marine organisms are leached, the resultant solutions show compositions similar to the example given in Table V. Table V Leachate from Peat pH Cl" Na+ Mg** Ca"1"1" SO^“ Fe SiC>2 K+ 2.8 1.5 20 70 210 1,500 30 40 7.6 Note: Peat from a depth of 30 metres in Botany- Banksmeadow a re a , 100 gm + 500 ml w ater (concentrations in mg/1). The high CaSO^ content in the leachate is evident. The silica in solution appears to be derived from the dissolution of hydrous silicon dioxide or opal, which is also a component of the skeletal material of many marine organisms. The sedimentary horizons which react with water to produce the sort of solution depicted in Table V, and which also typifies the common characteristics of many of the ground 41 waters, are most numerous in the central cross-hatched portion of area 6 on Fig. 12 but extend laterally both east and west along the northern shore of the Bay. Where these horizons are sparse and interspersed with abundant sand, the ground water is not severely affected by them, but in parts of the Botany- Banksmeadow area the ground water has no option but to move in intimate contact with these acid producing sediments. The resultant effects are visible in the creeks which are fed by this ground water. Enormous quantities of iron in solution precipitate out under the different oxidation conditions in the creek, coating the floors of the creeks with a red gelatinous mass. The chemical reactions between recharge water and the sediments are virtually instantaneous and hence there is no dilution effect even during heavy rain periods. These are intrinsic properties of the area and the chain of inter actions has been operating and will continue to operate with or without the presence of modern civilisation. It was just unfortunate that the many industries who need and use ground water chose an ancient swamp site on which to locate their b o res. 4.5 The Sodium C hloride Problem A situation has arisen in recent years where ground water has slowly increased in salinity and acidity in areas which previously produced water of low salinity. A high sodium chloride content has also been associated with this salinity increase and since the movement has been in a south to north direction, sea water intrusion into the aquifer from the Bay through heavy withdrawal by industry has been a suggested possibility. However, from both chemical and hydrological considerations, present day sea water encroachment can be discounted. But sea water did transgress once more into the low lying swamp on the edge of the Bay sometime during the past 9,000 years, to saturate the exposed deposits with salt. Whether this last transgression was due to the still controversial Late-Holocene oscillations in sea level or due to increased storminess when storm waves broke over the sand ridge which separates the swamp from the Bay, is a matter of speculation, but the effect of this transgression is still manifest today. The region where this event is most evident is in the depressed area containing near-surface peat approximating to the area in d ic a te d in Fig. 17. The ponds, ground w ater and 42 Figure 17 Salty Sediments in the Botany-Banksmeadow Area even small puddles, associated with this peat are quite saline and a major portion of the salinity is due to sodium chloride. Table VI shows some of the chemical characteristics of the water and the peat. Due to the thickness of the compressed peat in this area and the low elevation, water circulation is very slow and there has been incomplete flushing out of the connate salts trapped in the peat. This situation is not uncommon in coastal swampy areas and a very similar environment exists in the north coast swamp land of the Macleay River alluvials near Kempsey, where the excessive ground water and swamp water salinity is derived from connate sea water within the sediments.19 The waters at Kempsey are also h ig h ly co n cen trated in su lp h ates and are very acid due to the accompanying occurrence of 'acid sulphate1 sediments or cat-clays, within a few feet of the water table. What has happened in the Botany-Banksmeadow area to bring this situation to prominance is the increased industrial withdrawal to the north of the swamp which has changed the pattern of ground water flow as established by Smart^ and the salty water from the swamp area has been drawn northward. The water now being dumped from bores at some distance to the north exhibits all the chemical characteristics of the water in the southern salty area. Table VI Chemical Characteristics of Waters from the Botany- Banksmeadow Area ii to o Cl Na+ Mg"*-*" Ca4-1- (1) 490 260 24 117 236 10 13 18 (2) 1,490 950 9 110 245 6 37 9 (3) 3,024 1,900 25 240 540 0.2 5.5 18 N ote: (1) = bore water from swamp area at a depth of 24 metres (2) = pond water from swamp area (3) = leachate from surface peat in swamp area, 100 gm in 500 ml water (concentrations in milligrams/litre) 44 4.6 The I.C.I. Salt Stockpile The possibility of the I.C.I. salt stockpile being the source of sodium chloride in the ground water can be discounted on many considerations. Some of these are: (a) Past chemical records show that water to the south of the stockpile site was salty even before the salt pile was established. (b) Ground w ater a t some d ista n c e from the s a lt pile, and separated from it by two creeks, contains sodium chloride equal in concentra tion to that found in ground water near the salt pile. Such a situation is unlikely to occur with a point source of contamination. (c) The increase in salinity in previously low salinity areas has always been accompanied by a decrease in pH and in c re a se s in compon ents other than NaCl, such as Ca*"*", SO^- and Fe. The I.C.I. salt is almost totally com posed of NaCl and the near neutral solutions contain only faint traces of other ions. (d) Waters associated with the salty peat have iodide concentrations many times that of sea water. This is characteristic of connate waters where iodide is derived from the process of bioconcentration and subsequent decay. Water in newly saline areas also shows the presence of iodide, but solutions of salt from the I.C.I. stockpile contained no io d id e . 4.7 Appraisal The Botany-Banksmeadow situation has been discussed at length; because the problems there have been matters of conjecture for a considerable time. It proved to be a surprisingly complex region with a wide variety of hydrochemical factors interacting to produce the outstanding characteristics of the water. The outcome of the study clearly illustrates the need always for a basic understanding of the natural environment before pollution, as defined by human influences, can even be delineated. 45 5. OUR IMPACT ON THE NATURAL WATER QUALITY The environment constitutes a dynamic system and throughout geological time natural disturbances of both large and small magnitude have taken place, but to these natural phenomena is now added a new dimension, the human influence, and for nearly all water systems this influence is detrimental. In the Sydney region the worst urban afflictions on the water systems are garbage and sewage. The council tip is a terminal ailment for any waterbody for it quickly leads to its radical degradation and is the ultimate impact on the aquatic environment. The use of any available water habitat, be it a reedy swamp or a leafy creek gully, for the dumping of garbage for the sake of expediency, is reprehensible not only because such ’wet tipping’ causes worse chemical and biological effects on the environment than ’dry tipping' away from watercourses, but also because it results in the loss of a valuable environmental amenity. The impact of sewage on our water systems is profound and far reaching. The effects are felt in the coastal ocean water, in the rivers, creeks and swamps and even in the ground water. Some of the effects are permanent, others only temporary depending on the self-purifying capacity of the individual waterbody and the particular conditions of each s i t u a t i o n . It was not the purpose of the present study to investigate pollution per se and it is not intended here to relate all the manifestations of human influences which were unavoidably noted during the study, but one example, that of the unfortunate Scarborough Swamp, can be taken to portray many of the burdens which befall on an open waterbody in an urban s i t u a t i o n . 5.1 Scarborough Swamp - An Aquatic Environment in Distress Like any other marshland, Scarborough Swamp lying behind the dunes of the western shore of Botany Bay, would in the long term natural course of events disappear through the ageing process, as a continual build-up of nutrients causes increased biological production, heavy growth of aquatic macrophytes and accompanying silting. All the symptoms of eutrophication are clearly apparent in Scarborough Swamp at present and to what extent these conditions would have progressed under undisturbed conditions is impossible to ascertain, but the nutrient content (nitrogen 46 and phosphorous) of the Swamp water exceeds by a factor of 10 and at times by a factor of 100, the accepted threshold con centrations needed for the growth of nuisance algal blooms. Phosphate levels for example average around 0.4 to 0.9 mg/1 but the values fluctuate dramatically and concentrations as high as 4.0 mg/1 have been measured. Concentrations within the same range are observed in lakes in other countries where eutrophication is known to have been caused by cultural enrichment. Increased phosphate build-up in the sediments of Scarborough Swamp probably began late last century when much of the swamp land was drained for market gardening. The resultant agricultural drainage, rich in phosphorous, would have been scavenged and absorbed by the Swamp sediments, in later years to be mobilised again when conditions in the Swamp become anaerobic as happens when sewage flows into the Swamp to add its share to the phosphate load. The dramatic impact of a sewage inflow on the Swamp ecosystem was observed during March of 1976 when after a period of prolonged and heavy rai_n, a sewage pumping station, located on the shore of the Swamp, could not cope with the excess storm water and sewage overflowed directly into the Swamp. Water throughout the major part of the Swamp turned completely septic. There was an extremely offensive odour over the whole area, the water was coloured black from the formation of sulphides, and all fish in the Swamp were killed, the last remaining ones were seen gasping for their last breath at the surface of the water. The completely deoxygenated conditions lasted for approxi mately 10 days after which the first signs of an algal bloom (identified as the polluted water algae, Pyrobotrys) was seen as a green irridescence in the water. It took about one month for the effects of the sewage spill to abate and after five months the fish population had not regenerated beyond miniature species. This was a catastrophic event for a whole ecosystem and water pollution in the extreme, yet the Pollution Control Commission displayed no interest. Local residents worried for their children who play by the Swamp, were not informed of the cause of the awful condition of the Swamp. The Metropolitan Water, Sewerage and Drainage Board denied a sewage spill, even though similar incidents occur in many of Sydney's waterways with unfortunate regularity every time there is a heavy storm. A local council tip, located at the upstream end of the Swamp, was suggested by the Metropolitan Water, Sewerage and 47 Drainage Board as the source of the components causing the sudden severe septic conditions of the Swamp water. Leachate from the unsightly tip can be detected through increasing bicarbonate, calcium, soluble iron, silica and fluoride con centrations as the tip is approached. The distribution of silica and iron in Fig. 18 serves to illustrate this effect. There is evidence to suggest th at magnesium, chloride and sulphate ions are also being leached to some extent from the tip but it is difficult to separate the exact contribution of these ions from each of the various contributing sources. Oxygen values in the pond adjacent to the tip are con tinually low (about 20% saturation) but constant, and this pond was the only part of the Swamp still containing some oxygen during the septic conditions of March 1976, thus eliminating the tip as a possible cause of the condition. The future for Scarborough Swamp looks as bleak as that of other similar areas. Afterall, a still large tract of swamp land not yet all filled with garbage, is a situation which is not likely to last for much longer; besides the location is a proposed site for an expressway and so there is no room for a swamp anyway. But, even i f these s itu a tio n s do not eventuate, its culturally accelerated eutrophication will hasten its demise. 5.2 Human Influences on the Ground Water Quality 5.2.1 From L an d fills The ground water salinity pattern over the Basin is compli cated by the occurrence of la n d fill s ite s whose leachates enter the ground water system. The leachates can be detected in the water from nearby bores by increases in total salinity and unusually high concentrations of a variable number of components depending on the particular composition of the landfill and the stage of decomposition. These effects, while obviously operative for long periods of time, are fairly localised and with distance appear to be rapidly diluted through dispersion. 5.2.2 From Sewage The natural concentrations of nitrate are quite low in the ground waters of coastal sand areas. The nitrate contributed to a catchment area by rain water is part of the natural nutrient cycle and is therefore quickly assimilated again, and in a balanced ecosystem there is no surplus nitrate. Thus, the ubiquitous presence of significant concentrations of 48 Figure 18 Effect of Tip Leachate on Scarborough Swamp Mo. PRESIDENT BARTON — ST' Pumping / Station ------CULVER ST- SP = Reclaimed Flood gates land now sports field Ah. Bulrushes Natural Drainage Direction kilom etre 49 nitrate in the bore waters of the Botany Basin was an unusual and perplexing feature, A few of the landfill sites were found to contribute nitrate to solution, but nitrate was also found in areas where there were no landfills. Bore water from golf courses and bowling greens using fertilisers did not contain any higher concen trations of nitrate than bores in residential areas. Nor did the industrial areas show any significant differences in the range of nitrate concentrations compared to non-industrial lo c a tio n s . The possibility that the abundant peaty material in the strata could be the source of nitrate was thoroughly investi gated but the peat is past the stage of decomposition when nitrate could be formed in significant quantities and the nitrogen now in the peat is fixed in a form unavailable for so lu tio n . It was not until the nitrate situation on the Kumell Peninsula was studied, where the density of urban and suburban development is not so great, that the source of the nitrate became apparent. Figure 19 illustrates the nitrate ion distribution in both seepage waters and bore waters on the Peninsula. The natural water in the uninhabited dunes, even though rich in organic matter, does not contain nitrate. The three regions where nitrate is present are associated in one way or another with sewage. Area A contains a sewage treatment plant with sludge settling and infiltration ponds. Area B is an unsewered residential area with some bores drawing water downstream from their septic tanks. Area C is the swale between parallel dunes which follows the pipeline carrying the sewage from the treatment plant to the outfall at Potter Point. All the seepage water in puddles along this swale contained nitrate, but water between other parallel dunes did not. The creek at Woolooware containing 60^mg/l NO3 , in Fig. 19, runs parallel to a major sewage carrier and was reported to have turned black and septic during the heavy rain period of March 1976 when the previously discussed incident at Scarborough Swamp occurred. It is difficult to sort through the complex maze of nitrate distributions in the heavily urbanised sewered areas of the Basin to show that the presence of sewerage pipes is responsible for the nitrate content of the ground water, but the bores grouped near the Snape Park area in Randwick through which a main sewage carrier also passes, can serve to illustrate the s itu a tio n . 50 Figure 19 Nitrate Ion Distribution, Kurnell (mg/1) O 51 WOOLOOWARI Figure 20 shows the locations of the bores in relation to the pipe and the nitrate concentrations of the water as measured during February 1976. Approximately 280 metres away from the pipe the effect, although obviously decreased, is still apparent. It is a known fact that sewerage pipes do leak, through defective sewerage joints or through cracks developed with age and seasonal soil movement, and it is the myriads of small street sewerage carrers and individual household connections which appear to be sources of nitrate in the ground waters all over the Botany Basin. In one notably high nitrate area, Monterey, the excessive nitrate can be related to the rapid development of high-rise accommodation. The sewerage system, which was originally built for single dwelling housing, cannot cope adequately with the increased volumes from high density housing. 5.3 The Consequences While the connection between sewage and nitrate in the ground water is evident, the mechanisms through which the process takes place are not at all clear. In spite of the magnitude of the ground water nitrate concentrations, it is doubtful if large volumes of liquid sewage are actually flowing out of the underground pipes. Yet, somehow nitrate is finding its way into the ground water system apparently independently of the other components present in sewage. Cesspool leachate has been studied in cities where this has caused nitrate contamination of an underground water resource, such as Long Island, New York, and in metropolitan areas of California,^^>^2 and it has been found that ammonia released from the sewage is remarkably quickly oxidised to nitrate within a very short distance of the point of release. This would account for the fact that no ammonia or nitrite'was present in any of the bore waters studied here, even in those at Snape Park where the bores are only a few metres away from the sewerage pipeline. The nitification is apparently taking place on the solid soil/water interface and the ground water simply carries the formed nitrate away. The nitrification process can be stimulated by very minor deviations in organic matter or pH or even non-biological factors, but very little is known of these processes and, in view of the extensiveness of the effect on the ground water, it is a field which deserves further study. 52 Figure 20 Relation Between Nitrate Concentration and Sewerage Pipeline \ \ \ ------SNAPE ST— — — ------1 1 19 7 1 1 1 SNAPE PARK 1 M 17; 14 9 > STOREY ST- 13 — -GALE ST |17 ------s------— BOYCE ST...... — i 19 \ \ SEWERAGE n n PIPEUNE \ \ 14 = Nitrate concentration in bore water (February 1976) in milligrams/litre. The consequences of this added component in the ground water system cannot be considered to be entirely detrimental. Many gardens in the Basin, watered with bore water, are flourishing due to the added supply of nutrient. The possi bility of bacterial contamination can also be considered to be minimal, the sand being an extremely good filter of bacteria. The magnitude of the effectiveness was demonstrated at Kumell, where a ground water seepage pool and a sludge infiltration pool at the sewage treatment works, were in juxtapositions on opposite sides of a sand hill. The ground water seepage pool was clearly receiving nitrate (50 mg/1) from the sludge pond, but when tested for bacterial pollution, no diagnostic organisms were found. In spite of this example, however, there is always the possibility of bacterial contamination, especially with shallow bores, and this factor needs to be considered if the water is to be used for such purposes as food manufacturing processes or in public or private swimming pools. 6. THE RIVERS OF THE BOTANY BAY CATCHMENT AREA The two major rivers, the Georges River and the Cooks River, which drain into Botany Bay, have been examined by a great number of governmental, local council and independent organisations. Innumerable reports have been written in the past. Most of these have been concerned with pollution aspects and have dealt with biological parameters of the rivers such as bacterial counts and the oxygen regime. This study did not wish to duplicate these investigations but attempted to look briefly at some of the natural geo chemical processes taking place in the catchment area which might have an influence on the character of the two rivers. It is not possible, however, to study highly urbanised rivers and avoid the human impact which may often be pre dominant. Those anthropogenic factors which appeared to have a significant influence on the river environment are, therefore, also described. 6.1 General Characteristics The Sydney region has two distinct types of fresh water streams; those that traverse Hawkesbury Sandstone and those that traverse Wianamatta shale, and these two types differ markedly both in their physical and chemical characteristics. 54 6.1.1 Physical Aspects The typical Hawkesbury Sandstone creek originates on an elevated plateau from extensive areas of 'hanging swamps' where water is retained during rain periods and released slowly over a period of time. The Hawkesbury Sandstone has the property of weathering along rock joints and consequently breaks up in large slabs, so that the sandstone stream plummets down steep waterfalls and rapids and tumbles noisily over the fallen boulders. Thus, within a relatively short distance of its beginning, the stream has deeply incised into the plateau, forming the characteristic steep and inaccessible valley. In contrast, the Wianamatta shale streams are usually little more than shallow channels, with sides only a few metres deep cut into a clay of friable shale stratum. They traverse flat to undulating terrain and the channel tends to maintain its shallow depth throughout its course. Their genesis appears to be from abrupt slump-holes located in the path of major overland flow rills. At the bottom of the slump, a pool of water accumulates from water seeping through the walls. Con sequently, stream flow begins, with the volume of the water being augmented downstream by further ground water seepage from the banks. 6.1.2 Chemical Characteristics Water in contact with Hawkesbury Sandstone is characteristi cally low in dissolved salts. Under natural conditions, the salinity is less than 200 milligrams/litre and the constituents are predominantly of oceanic aerosol origin. Contribution to the salinity by the sandstone is in the form of soluble silica derived from the weathered surface layer of bedrock, and iron, which passes into solution under the mildly reducing condi tions of the ground water environment. Since the source of the salinity is rain water salts and the silica content attains a rapid equilibrium concentration, the Hawkesbury Sandstone stream will show little variation in salinity throughout its course as the addition of more run-off water will simply add water of the same composition to the mainstream. Similarly, the run-off water entering the cracks, joints and bedding planes of the ground water system, has already acquired its chemical composition while infiltrating the surface zone and will maintain this composition throughout its path of travel. During base-flow times when the river flow is maintained mainly by ground water seepage, the stream 55 will still exhibit the same salinity. Wianamatta shale streams exhibit high salinities which often exceed what is considered to be the upper limit of fresh water. The typical Wianamatta shale water is very much dominant in _1_ __ I I Na and Cl ions and contains a significant proportion of Mg ions. The ratio of Na+ to Cl- is constant and equivalent to that of sea water, but considerable variations occur in the proportions of the other major ions. Table VII shows analyses of a bore water and a creek water which have been in contact with Wianamatta shale. Table VII Chemical Characteristics of Wianamatta Shale Waters Bore Water, Moorebank, Cabramatta Creek, depth 45 metres (mg/1) Edmondson Park (mg/1) HC03" 946 600 Cl" 5,922 7,330 S04= 422 370 Ca"*-*" 124 130 Mg++ 683 640 Na+ 2,944 3,800 K+ 32 5 Total ions 11,073 12,875 The most significant feature of these examples is the exceptionally high salinities and the similarity between the creek water and the ground water. The creek water sample was taken during a non-storm period when the creek was at its normal base flow and thus contained only ground water. This accounts for the similarity between the bore water and the surface water. The very high salinity of the Wianamatta shale waters is a consequence of the original brackish water conditions under which the sediments were deposited and the lack of subsequent flushing of the retained salts due to the absence of direct external drainage. There has been very little investigation into the nature of these 180 million year old connate salts. Some of the ground waters have exhibited salt contents greater than that of sea water.^3 a cursory appraisal of the available chemical analysis shows that the most significant modification to have 56 taken place is a reduction of the potassium content and the addition of considerable amounts of bicarbonate. In contrast to the constancy of the salinity of the Hawkesbury Sandstone waters, Wianamatta shale creeks show extreme variations in salinity along their course. Fluctua tions take place within a few hundred metres because the salinity of the ground water seeping in from the banks is very variable. For example, salinity measurements of Cabramatta Creek varied from 14,000 micromhos cm~^ to 1,700 micromhos cm on the same day. Some of the variations are due to the diluting effect of low lying swampy areas adjacent to the banks. During heavy rain periods, 20 to 50 fold decreases in salinity were observed in the same part of the creek. 6.2 The Georges River The Georges River drains an area of approximately 930 sq km and the drainage system is shown in Fig. 21. The headwaters originate on densely timbered sandstone terrain of the Woronora Plateau, at an elevation of about 400 metres, but the streams fall abruptly within the first 30 km to reach the undulating topography of the Wianamatta shale region. The marked parallelism of the drainage features in the southern portion of the catchment area is a result of the tilting of the region into a ramp-like structure during the Tertiary Period. Consequently, although the Georges River rises only 10 km from the ocean, it travels a distance of 90 km before entering the sea. The southern tributaries of the River almost exclusively drain Hawkesbury Sandstone and the northern and western tributaries drain Wianamatta shale. The marked salinity divisions of the tributaries, shown in Fig. 21, reflect the two kinds of geological influences. For a considerable distance downstream the only tributaries of any significance to join the main stream come from the Hawkesbury Sandstone, and the river chemistry reflects the influence of this rock unit. It is not until only 7 km from the Liverpool Weir that the first major tributary draining the shale country joins the River. This tributary, however, has only a minor effect because of its small flow. It is in the remaining short distance to the Weir that the Georges River itself enters the Wianamatta shale and the salinity of the River increases. Prospect Creek and Cabramatta Creek, two very saline streams, join the River below the Liverpool Weir, but their influence 57 Figure 21 Influence of Geological Regimes on Water Salinity in the Georges River Drainage Area Cooks River Catchment Nepean River Catchment Port Hacking River Catchment j Hawkesbury Sandstone Wianamatta Shale kilometres 58 is overshadowed by the influx of sea water in this tidal portion of the River. During its flow eastward, the northern tributaries continue to be influenced by the shale and the tributaries from the south reflect the low salinity of the sandstone, but the effect of any of these on the river chemistry is minimal because of the over-riding influence of the tides. 6 .2 .1 The Human Impact As yet the beautiful upper reaches of the Georges River have escaped the human influence because much of the area has been a restricted military reserve. Since the catchment area of the upper reaches consists exclusively of this uninhabited bushland, the water is quite pollution free until the con fluence of Bunburry-Curran Creek which drains the newly suburbanised Campbelltown area. Between the confluence and the L iverpool W eir, the G len field Sewage Treatment Works discharges its load of effluent. Below the Weir, the water, now under tidal influence, receives another injection of sewage from the Liverpool Treatment Works and further down stream still Prospect Creek adds its load of effluent from the Fairfield Treatment Works. The effect on the River can be seen in the nitrate profile in Fig. 22. In keeping with a balanced ecosystem, the upper reaches of the River contain no nitrate, but downstream the result of the load of excess organic matter poured into the system by the sewage treatment works is clearly evident. This is a continuous input, affording the River no respite and placing an enormous stress on the water's capacity to deal effectively with the situation. At times it has failed, with drastic consequences. As the River continues on its way its environment reflects the prodigy of urbanisation. Its tributaries have been canalised and their clear waters exchanged for frothy, turbid sullage. Its banks have become receptacles for garbage, and rare is the creek gully today which is not filled or in the process of being filled with urban refuse. The effect of such garbage dumps on the River water quality must be assessed within the hydrogeochemical framework of each situation. A 'tip' immediately adjacent to the River or a creek will directly pollute the water with undegraded organic matter and bacteria. But the effect is sometimes not limited to close proximity. Due to the physical structure of the rock unit, dump locations on Hawkesbury Sandstone, even at a distance from a creek, are capable of contributing bacterial 59 Figure 22 Nitrate Concentrations, Georges River 60 pollution to the creek. The Hawkesbury Sandstone, is very impervious and leachate from a dump would enter the cracks and joints in the sandstone to later emerge as ground water seepage into a stream. Water movement through these permeable zones is rapid and bacteria would flow through these as readily as through a pipe. If, however, the ’tip’ was located in a pervious rock area, with sufficient soil cover, and at some distance from the river or creek, degradation and mineralisation of the organic matter will take place within the dump area and, since b a c te ria are removed by s o il p a r tic le s w ithin a few metres of travel, seepage from such a sanitary landfill will be confined to high concentrations of various inorganic ions. Such a saline leachate could possibly alter the biochemistry of a very low salinity Hawkesbury Sandstone creek, but would have a minimal effect on a Wianamatta shale stream which has a normal water salinity in the order of thousands of parts per m illion and where the fauna and flo ra are obviously adapted to wide and erratic fluctuations in salinity. But whatever the chemical effects of garbage tips on the River may be, these are surpassed by the visual pollution which they create and the consequent loss of so much of the aquatic environment of this River. 6.3 The Cooks River The Cooks River passes through a most densely urbanised portion of Sydney. Its recent history has been one of continuous modification by human influences. Its tributaries have been obliterated or hidden in stormwater pipes, its surrounding wetlands have been ’reclaimed', its channel has been re located, straightened and cemented, and its sides punctured with sewerage vents. Its catchment area is approximately 100 sq km and it rises at an elevation of 50 metres, 18 km west of Botany Bay. The drainage features are shown in Fig. 23. Its only tributary from the north is Alexandra Canal which drains the alluvium of the Botany Basin. The tributaries from the south predominantly drain Wianamatta shale and this is reflected by the salinities of the tributaries also shown in Fig. 23. The Cooks River can be described as a truly intermittent river. Salt water from the tidal influx encroaches for 11 km upstream and during non-storm periods this constitutes the bulk of the water in the River. A small trickle of typically saline Wianamatta shale water, which seeps in through openings 61 Figure 23 Cooks River Drainage System (Values represent salinity of river and creek water as measured by electrical conductivity in micromhos/cm) I I I I I I I I I I I1 I 1I I 1I I 1I I I1 'I I 11I 1I I 1I I I1 I I I I I 1I 1111111111Y i'iT i <>•1 I I I I 111 ii11111111111 in I ii' ■, I, I, I in, I■, I , I , I . I , I i\i ' 111/ I/ * * i\ i \ %){ 1! "II! 'i ' i ' i ' i 1 I ' l l III I11 11I 'I \ V r m W ' I I 1 / 11111111 'I ' ' I ' l l - 1 Iri'i ,1 I ,1 I ,1 Ii ,'1 Ii I 1 "II I I II 1 '•' i ' i 'i ' i ' 5'iii.i'i!i! “A I I I t I I 1 , I , I , 1 I I , z in the cemented banks, is the River's fresh water source except for occasional influxes of overflow water released from Poots Hill Reservoir, which then dilutes the shale w ater. During heavy rain periods, however, enormous quantities of run-off water from the impervious city streets pour into the River causing flash flooding. 6.3.1 Quality Aspects The unfortunate genesis of the River in the railway workshops at Chullora, resulting in an almost permanent film of oil on the water, and the floating trash thrown in by residents (a bag of dead animals and a T.V. set, have been among the floatables observed) are some of the features of this River, but the most dominant influences on the river water quality are the canalisation of the stream bed and storm sewer o v erflo w s. The cementing of a waterway, thereby turning it into a canal or drain, destroys the features of the stream channel which are essential to the River's self-purifying process. The water can no longer deal adequately with even small amounts of organic matter and the water is permanently in an unhealthy state. Such is the s ta te of the upper reaches o f the Cooks River and its tributary drains, during dry weather. The tidal p o rtio n o f the Cooks R iver, unlike the Georges R iver, does not receive a continuous input of sewage effluent and during dry weather flow periods it is relatively pollution free. During periods of moderate rainfall, dust, litter and oil from paved areas are flushed into the River, but this flushing is fairly rapid and shortly after the commencement of rain, city run-off water in gutters has been found to consist of pure rain water. The result of a severe storm on the River water is, however, quite different. While the city's gutters still discharge clean rain water, the drains, which are connected to a large number of storm sewage overflow points, discharge raw sewage into the River. Samples of water taken from the River at such times show a high bacterial content and develop growths of sewage fungus. These events were able to be chemically followed during the study period by the changes in nitrate concentrations in the River, drains and gutters. 63 6.3.2 Perspective The Cooks River, more than any other waterbody in the Botany Bay catchment area, is a parody in misdirected priorities. It has received prominent publicity; a copious number of reports have been written about it; and it has been held up as an example of the worst that industry can do to a waterway. But, surely the ultimate pollution of the River comes not from trace quantities of heavy metals in the water but from the destruction of the natural ecosystem through its trans formation into a drain. It seems pointless and futile to monitor chemical parameters in a water which no longer even resembles a viable aquatic habitat. There may be 40 or more parks surrounding the River, but there is no environmental amenity in a cement canal. 7. CONCLUSION This study has ascertained that the predominant influence on the chemistry of the water systems of the Botany Bay region is still the natural environment. It has also demonstrated the necessity for a basic understanding of the processes and relationships within the natural system before human influences can be adequately comprehended. The Botany Bay region’s close proximity to the ocean results in a large input of sea-salt aerosols to the area in the rain fall, and this constitutes a major source of water salinity. When rain water falls on Hawkesbury Sandstone and becomes a stream there is little change in chemical composition as the stream rushes through the characteristic deep and narrow gorges of this terrain. In contrast, the streams which form when rain water falls on Wianamatta shale, meander sluggishly along shallow clay-banked channels and become brackish solutions as sea-salts, left in the sediments millions of years age, are 'dissolved. In the area of Quaternary sediments surrounding Botany Bay the hydrochemical properties are determined by the varied geological history of the sediments. In the wind moulded dunes composed of quartz grains, the ground water contains only the salts brought by the rain. Where ocean currents have brought sediments to the area, the infiltrating rain water now dissolves the remains of marine organisms to form alkaline ground waters rich in calcium bicarbonate. 64 In places where there are ancient swamp deposits the chemical and biological processes of the past have left their legacy in the form of iron sulphides, gypsum and fossil sea- salts, which permeate the many peat horizons. Water in contact with these swamp sediments becomes an acidic solution containing an excess of sulphate, iron, calcium, sodium and chloride ions. Human activities influence the water chemistry by way of modification of the rain water composition through industrial emissions of sulphur dioxide, and by the removal of vegetation, which results in increased dust in the atmosphere. The continuous injection of liquid wastes from sewage treatment plants and the intermittent overflow from sewers during storms, are significant human influences on the chemistry of most surface waterbodies in the region. The ground water system is affected in a small way by leachate from municipal landfill sites but there is a more widespread effect from the network of underground sewerage pipes carrying city sewage, which results in high concentra tions of nitrate ions in the water. There are, however, much more obvious and - not infrequently - devastating human influences on the water systems which overwhelm all other considerations. The conversion of waterways into cement canals, and the use of river-bank wetlands and creek gullies as the city's garbage tips, does not affect the chemistry of the water to a significant extent but more importantly, it results in the destruction of complete ecosystems. Clearly there needs to be a change in attitude and a re appraisal of priorities regarding the use of water systems. Too often actions have been justified by false economics because there has been no accounting for intangeable social costs. In the crowded city a water resource may have its greatest value in serving aesthetic and recreational needs rather than as a carrier of wastes. 'Our water resources are a heritage of the whole nation - a heritage which must be protected both for the people of the present and for posterity.'24 65 References 1 A u s tra lia - The F ir s t Hundred Y ears. Ed. The Hon. A. Garran. Pub. Ure Smith, Sydney, 1974. 2 N.S.W. Parliamentary Papers (1869). 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The impact of Port Botany in preparation 4 Sydney's environmental policy 1870—1970 Working papers No. 1 Pamela Coward Environmental law in Sydney 2 C. Joy, W. Hickson and M. Buchanan Liquid waste management 3 W. Ryder Air pollution control 4 Merike Johnson Natural water quality ISBN 0 7081 0340 5 Distributed by ANU Press PO Box 4 Canberra ACT 2600 Designed by ANU Graphic Design