Page 1

SEPTEMBER 1986 JOURNAL OF THE AUSTRALIAN WATER AND WASTEWATER ASSOCIATION


water

ISSN 0310-0367

Official Journal AUSTRALIAN WATER AND WASTEWATER ASSOCIATION

Vol. 13, No. 3, September 1986 FEDERAL PRESIDENT A. Lloyd , G.H. & D., GPO Box 668, Bri sbane 4001 .

FEDERAL SECRETARY G. Dooley, Bo x A232 P.O. Sydney Sth., 2001.

FEDERAL TREASURER J . D. Molloy, Cl- M.M.B.W. 625 Lt . Collins St. , Melbourne, 3000. '

BRANCH SECRETARIES Canberra, A.C.T. M. Sharpin , Willing & Part ., P.O. Box 170, Curtin , A.C.T. 2605. (062) 815 811

New South Wales M. Hann on, P.W.D. Sewerage Branch , 74 Philli p St. , Sydney , 2000. (02) 270 4488

CONTENTS Viewpoint-R. M. Hillman, Chairman Water Authority of Western Australia . ... .. . ...... . .. . .......................... .. .. .

5

Association News, Views and Comments . . . .. . ...... . ........... .

6

IA WPRC News . . .. . .................... ..... ............ .... .

12

Augmentation of the West Pilbara Water Supply- The Harding Dam Project -R. J. Wark, G. C. Meink and C. R. Tenby ...... .. ...... .... .. .

14

Industrial Waste Disposal-Victoria -The MMBW Proposal ........ . ....... ....... . ... . .... ... .

19

Cape Peron Environmental Monitoring -P. N. Cha/mer and L. W. Edmonds

20

People-Conferences-Courses . .. .......... ....... ........... .

26

Products-Plant-Equipment .. : . .... ..... .. . ... . . .......... .. .

27

Swampy Odour in the Drinking Water of Perth, Western Australia -J. E. Wajon, B. V. Kavanagh, R. I. Kagi R. S. Rosich, R. Alexander and B. J. F/eay ............. ..... .

28

Products-Plant-Equipment . . ............. ... .............. . .

34

Water Hammer Alleviation - A Western Australian Case Study - Y. H. Ng and A. J. Gale ........ .. ........................ .

35

Calendar ..... .. ... . . . .... .......... ... ... ............ ..... . .

38

Victoria J . Park, Water Trai ning Cent re, P.O. Box 409, Werribee , 3030. (741 5844)

Qu eensland D. Mac kay, P.O. Bo x 412, Wes t End 4101 . (07 44 3766)

South Australia A. Glatz, State Water Labora tori es, E. & W.S . Pri va te Mail Bag, Salisbury, 5108. (259 0319)

Western Australia Dr B. Kavanag h, Water Auth. of W.A. , PO Box 100, Leedervi lle 6007 (09) 420 2452

Tasmania T. Denne, 675 Nel son Rd ., Mt . Nelson. (002) 23 2267 (A. H.)

North ern Territory M. Lukin , P.O. Box 37283 Winnelli e, N.T. 5789.

ED ITORIAL & SUBSCRIPTION CORRESPONDENCE G. A. Goffin , 7 Mossma n Dr., Eaglemont 3084 03 459 4346

water

COVER PICTURE The cover photo shows the recently completed Harding Dam and its reservoir, Lake Poongka liyarra. The works were constructed by Leighton Contractors Pty. Ltd. in 1983/84 for the Water Authority of Western Australia. The Dam supplies water to the towns of the West Pilbara region. Front cover photograph, courtesy the Water Authority of Western Australia; cost donated by Leighton Contractors Pty. Ltd.

The statem en ts made or opinions expressed in 'Water' do not neces sa rily reflect the views of the Australian Water and Wastewater Association, its Coun cil or committees.

WATER September, / 986

I


Augmentation of the West Pilbara Water Supply T¡he Harding Dam Project R. J. Wark, G. C. Meinck and C.R. Temby ABSTRACT The West Pilbara Water supply is the second largest country water supply in Western Australia. T he stimulus given to the region by the development of the North West Shelf Gas Project required major augmentation of the scheme and planning studies for augmentation of the headworks resulted in the decision to construct the Harding Dam and associated works. The Pilbara is an arid region with irregular rainfall, high evaporation and low topographic relief. The particular form of conj unctive use of the surface and underground resources adopted to overcome these problems is unique in this country. The remote location and the climatic conditions posed a number of problems in the construction of the 42 m high earth core rockfill dam requiring special attention which are described in the paper with the wide ranging environmental and social evaluations undertaken.

INTRODUCTION The Harding Dam is located on the Harding River , in the Nort h of Western Australia. The dam, constructed in I 983 and 1984, is the first surface storage to be incorporated into the West Pilbara Water Supply (Figure 1). The original scheme, based on groundwater drawn from the Millstream aquifer, was first constructed in 1969 to meet the needs of the iron ore mining and export trade through the towns of Dampier and Karratha. In 1971 the scheme was expanded to supply water to Wickham and Cape Lambert, and is now the second largest country water supply in the State.

R. J. Wark

G. C. Meinck

l

C.R. Temby

Bob Wark, B.C.E., B.App., Sc., M.l.E.Aust. is Principal Engineer Dams and Garry Meinck, A. W.A.l. T., M.l.E. Aust. is Supervising Engineer, Dam Projects, with the Water Authority of Western Australia. Both were involved in the planning and regional investigation phase of the West Pilbara Water Supply augmentation and in the detailed investigation and design of the Harding Dam. Colin Temby, B.E.(Hons.), M.S.C.E., M.l.E.Aust. is Principal Engineer, Water Supply Design of the Water Authority of Western Australia and was the Project Manager for the construction of the Harding Dam.

DEMAND FOR WATER Projected Use The major component of water use in the West Pilbara is the domestic demand of the population. Following the initial rapid rise in the demand (Figure 2) which followed the development of iron ore mining and export, the demand remained relatively stab le during the late 1970s . However, in this initial domestic supply phase, the Nort h West Shelf Gas project has caused a marked increase in demand. Development of the export phase of that project in the late 1980s is expected to result in a demand for water of around 15 x 10• m' per ann um by the mid 1990s.

Demand Management One aspect of the water industry in the Pilbara of considerable concern has been the high per capita consumption which approximates around 1500 m 3 /service/yea r - some two to three times the consumption rate in other comparable countr y towns. While recognising the social and recreational benefits derived by the communities from such water use , there is a need to conserve the scarce water resources of the region. Also significant economic and environmental benefits which can accrue as result of reduced need for supply capacity increases. Restrictions on Lhe use of sprinklers during the daylight hours have applied in the West Pilbara since 1974. Apart from an early initial impact, there is no indication that per capita water consumption has been reduced. While the restrictions are remaining in force it is fairly clear that they are not an effective tool for generating long-term reductions in demand. The pricing structure in country areas normally penalizes high water consumers but the problem in the West Pilbara is that many consumers enjoy significant free water allowances, the cost being borne by their employers, the major companies. Water consumption statistics indicate consumers with free water allowances use two to three times the quantity of water consumed by those paying for their own consumption. Changes to the pricing policies are accordingly unlikely to be effective and would unduly penalize those meeting their own water charges. The most effective demand management activities have been those of local committees and the Western Australian Water 14

WATER September, 1986

~ N I

Figure 1. Locality plan.

Reso urces Council. This work has shown consumers that it is possibie to generate a pleasant and attractive urban environment


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Decision to take ac tion

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LEGEND

- - Projected aquifer depletion volumes with Harding Dam

Figure 2. West Pilbara demand projection.

with low water use gardens. The local population and the mining companies are now well aware of the economic and environmental benefits of reducing consumption and this is starting to become apparent.

- · - · - Projected aquifer depletion volumes without Harding Dam - - - - - - Actual aquifer depletion volume

NOTES 1. Aquifer depletions are maximum va lue in any yea r. 2. Percentiles represent the probability that aquif er depletions would be grea ter than the va lue shown.

MILLSTREAM AQUIFER The Millstream aquifer is a basin of calcrete covering a total area of approximately 600 square kilometres. The water surface is 20 to 25 metres below the ground surface and the saturated zone is up to 26 metres thick. The main water bearing calcrete is cavernous and the water flows freely to the extraction bores. Current estimates indicate that the primary calcretes have some 600 x 10• m3 of water in storage and total storage could amount to 1700 x Io• m3 • Due to the high lime content of the rocks forming the aquifer, the water is hard and the total soluble salts (TSS) content of water supplied to consumers is generally in the range of 900 to 1000 mg/ L. The aquifer is recharged naturally by direct rainfall, runoff from the surrounding hills and from flood flows in the Fortescue River, the estimated average recharge rate being 17 x 106 m3 / year. Water from the aquifer discharges through springs on the perimeter . These springs feed several large pools in the Fortescue River . One of the most important environmental issues occurs at Millstream where the flow from springs and permanent water supports a large variety of vegetation formations and their associated ecosystems (Figure 3). Many of these are unique to the area, the Millstream palm is of particular significance as major populations are found only in this locality . The palm together with the sedge and heathlands are among the most importarl1: ecological features. A National Park has now been created over the area of major environmental significance. As water supply extractions increase and water levels in the acquifer fall, natural flows from springs are decreased, reducing the supply of water to the pools and riverine forests. Supplementation of these flows by pumping from the aquifer has been an essential part of aquifer management policy for some time. Thorough understanding of the hydrogeological processes has been a key factor in the management of the aquifer system and has led to the successful development of the hydrologic model of aquifer behaviour. Using this tool it has been possible to predict with confidence the performance of the aquifer under a range of operating conditions, a factor which has been vital in the development of the water management strategies for the region.

REGIONAL INVESTIGATIONS OF ALTERNATIVE RESOURCES Planning Studies

By the late 1970s it was evident that the development of the North West Shelf Gas Project would have a major impact on the future water demand . Studies showed that , without augmentation

Figure 3. Millstream aquifer performance.

of the headworks, the reserves of storage available in the Millstream aquifer would be rapidly depleted. (See Figure 3) . Collection of the basic hydrological data and the assessment of the underground and surface water resource potential of the region began in the 1960s. Planning studi~s in the early 1970s showed that supply from surface water resources within the region was both feasible and economic. However, this work highlighted the need for a comprehensive review of the engineering (particularly the hydrologic,v factors), economic, environmental and social parameters to permit a multi objective assessment of the relative merits of the various alternatives. This work commenced in earnest in 1974 with engineering investigations of two dam sites on the Fortescue River. Consultants were engaged to investigate environmental aspects and the Western Australian Museum undertook the social assessments. In conjunction a number of public meetings were arranged and discussions held with various community groups. In 1976 the studies were broadened to include a thorough evaluation of the regional alternatives including both surface and groundwater resources . These investigations were completed by late 1977 so that the Government, in making decisions on augmentation the West Pilbara supply, could do so on the basis of firm planning data. Conjunctive Use

Although development of the known groundwater reserves could double the nominal yield from the Millstream aquifer, to meet the sustained expansion of the region, utilization of the large surface water sources is necessary. Development of the surface water sources was complicated by three factors : • poor storage characteristics of the major dam sites, • high evaporation rates, • erratic stream flows. The combination of these three factors meant that none of the surface storages could supply significant quantities of water if operated as independent storages. These factors together result in rapid deterioration in the quality of water retained to provide drought security . The conjuctive use strategy has been adopted to utilize efficiently the surface resources, and involves top priority to using water from surface storage when water of suitable quality is available . The full water supply demand is drawn from the Millstream aquifer when the surface storage is depleted or contains unusable water. Operating this way, the bulk of the supply is WATER September, 1986

15


drawn from the surface storage with the Millstream aquifer providing drought reserve. Environmental Studies

The comprehensive environmental work carried out in the region was, in many cases, the first review carried out since the times of early exploration. While the environmental studies generated some very detailed information on the ecology of the region, they were primarily aimed at identifying the broad characteristics of each of the various surface and groundwater alternatives. In general, the surface storage proposals had the largest direct impacts and much of the effort was directed to evaluating these . Social Impact Studies

The studies fairly quickly identified the impact upon Aboriginal culture of the various alternatives as the most significant aspect. Most of the early investigative work was undertaken by experts familiar with the culture and the traditions of the area. Ir, order to assess the impact of the proposed alternative developments on specific aspects of the culture, direct consultation between the project engineering staff and the local people was necessary. This led to a better understanding of the issues and had a significant bearing on the decision making process. s~Iection of the Harding Dam Option

The Harding Dam proposal was found to be the most economic soludon of the alternatives studied. The impact on social values is low and the direct environmental impact of the dam and the reservoir was not high in absolute terms. The improved scope for -management of the Millstream aquifer resulting from a dam development was considered to be a more significant environmental consideration. The all groundwater alternative was some 2507o more costly than the Harding Dam, although it has a low direct social and environmental impact. The reduced scope for management of the Millstream environment was considered a serious disadvantage. Also, the average quality of the water supplied from groundwater would be inferior to that supplied from the dams.

HARDING DAM In June 1981 the State Government approved in principle construction of the Harding Dam and at that stage, detailed engineering, environmental and social impact studies commenced. These led to the final detailed engineering design and included a review of the system yield and flood hydrology, field investigations and materials testing. The selected arrangement of the works is shown on Figures 4 and 5. Tenders for construction of the major civil works were called in October 1982 after approvals had been obtained under the appropriate environmental statutes. In February 1983 a contract was awarded to Leighton Contractors Pty Ltd for substantial completion by November 1984. The overall cost of the project, including the dam and ancillary works, pipelines and Millstream headworks was $45 million (1985 values) . Geology

Figure 4. Harding Dam -

la. out of works.

imum rainfall, with appropriate freeboard. The 12 hour duration storm gave the largest peak inflow flood of 24 200 ml/sec from a rainfall of 790 mm. However, peak levels in the storage were generated by the 36 hour duration storms with rainfalls of 1365 mm and a peak inflow rate of 19 200 ml/sec. The large flood surcharge (16 m) and flood storage causes significant attenuation of the flood peak, with peak design outflows amounting to just over 6000 ml/sec on the main spillway and 2300 ml/sec on the auxiliary spillway. Embankments

The 64 x 10' ml capacity storage is formed by the construction of two 45 m high embankment in the river valley and a 15 m high auxiliary embankment closing off a saddle located south of the embankment in the reservoir flood zone. Both embankments have a central impervious core protected on both sides by sand and gravel filters supported by rockfill shoulders .

The dam and reservoir are located in a group of pyroclastic rocks including tuffs, agglomerates and interbedded sandstones which have been intruded by a dolerite sill structure known as the Cooya Pooya Dolerite. The pyroclastic rocks occupy the areas of Excavation and Foundation Treatment low relief and the dolerite forms a hilly terrain with extensive scree Excavation for the rockfill foundation involved removal of the slopes. The dam is located in a gorge where the Harding River has scree, slopewash and alluvial deposits, as well as highly and comcut through the dolerite. The river valley is approximately 160 metres wide, with up to 9 pletely weathered rock. This exposed a foundation surface of metres of highly permeable river bed alluvium overlying the moderately weathered to predominantly fresh rock. Some local dolerite bedrock. Tuff occurred as rafted blocks within the excavations were required on the main embankment to remove dolerite sill structure, particularly on the abutments. Some out- deeper pockets of completely and highly weathered dolerite . Moderately and slightly weathered rock was removed during crop was visible but both abutments were predominantly covered with a layer of scree of both rock types, several metres thick, lying excavation of the impervious core and filter foundation, revealing predominantly fresh rock or fresh rock with stained joints. In at close to the angle repose. particular, in the river bed area of the main embankment, very little further excavation was required after removal of the alluvial Flood Hydrology deposits of sand and shingle - an even, flat work surface of fresh The dam is considered to be a 'high hazard' dam as defined in rock being exposed. Curtain and blanket grouting of the impervious core foundathe ANCOLD 'Guidelines on Design Floods for Dams ' and has been designed to pass the flood generated by the probable max- tion was carried out using cement grout. The design envisaged 16

WATER September, 1986


Filter Materials Maiumum Flood Level AL 76 Om 0 l

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The key to the problems of the potentially dispersive core material and the possibility of cracking due to shrinkage and settlement lies in the design of the filters. These consisted of a twolayer system of fine and coarse filters processed from existing river gravel deposits in the Harding River. Following an extensive round of laboratory testing, including tests of the interaction of the cracked core and filter, an effective size (d 15) for the fine filter of not greater than 0.4 mm was selected. Spillway

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The spillway channel provided the main source of rockfill for the embankment and the design was based on balancing the quantities from the excavation with those which were required for the rockfill zones of the embankment and the rest of the works. The 70 metre wide unlined spillway channel discharges into the river downstream of the dam. At the maximum flood level of 16 metres over the spillway crest the design discharge is 6000 m3 / s.

¡,

Outlet Works

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Tne Full Supply Level Is tnat level at w hich Che Spill w ay starts 10 overflow

Figure 5. Harding Dam -

typical cross sections.

The intake tower is a 49 metre high reinforced concrete structure with multi-level intakes. The base section of the tower was cast initially and the stem slip formed over a four day period . The multi-level intake arrangement permits selective withdrawal of water from the reservoir when stratification occurs and enables the simultaneous supply of good quality water to water supply and the release of poor quality water through the scour. ' The outlet culvert consists of two 1220 mm OD steel pip'es incased in concrete, 140 metres in length, leading to the pump station. Small river flows occurring during the embankment construction were diverted through the culvert. Water can be scoured from the dam through a 700 mm diameter jet dispersal valve. This valve is also used to maintain water levels in the recreation pool downstream of the dam . Pump Station

that blanket grouting would extend over the entre core extract area of both embankments. Grout takes were found to be very low and a much reduced pattern was then adopted for the majority of the blanket grouting. Apart from three holes, gro ut takes over the site average 3.5 kg of cement/metre of hole. Earthfill

The earthfill material for the impervious core was obtained from deposits adjacent to the river in the vicinity of the dam site . Priority was given to using materials from within the storage area, with the balance being obtained from an area immediately downstream of the dam. Contact earthfill to be placed against the dam foundations was obtained from slopewash and residual deposits within the borrow areas . All the deposits exhibited a wide range of engineering properties, showed a random tendency for some samples to disperse and contained increasing proportions of calcrete with depth. Upper limits were placed on the percentage of calcrete which could be placed in the impervious core. The inherent natural variability of the material was controlled by working the borrow pit over the full depth of usable material, stockpiling, conditioning and reworking. The moisture content ranges for compaction of the core material were initially set to provide a relatively plastic core material which would not be susceptible to cracking, dut to either settlement or drying shrinkage. Appropriate compaction procedures for the core material were developed in a trial embankment placed prior to the start of construction. However, as the work on progressed, it became increasingly clear that when the material was placed close to the wetter specification limits, the contractor was unable to achieve the compaction standard . Additional studies were then carried out to examine in more detail the susceptibility of the core to cracking at lower moisture contents. As a result, the decision was made to allow the contractor to place the material 1OJo drier than the original specification. The contractor took this opportunity to carry out some further roller trials using a variety of compaction equipment and increased layer thickness with the marginally drier core material. These trials indicated that the core could be successfully compacted in 300 mm layers (instead of the original 150 mm layers specified) using a heavy vibrating roller .

The pump station delivers water through two pipelines to tanks located at Yannery and Plat from whence it flows to the various towns. The installation comprises three electric pumping units with a total capacity of 1025 Lisee housed below ground level in reinforced concrete cells which pro'fide security against flooding during spillway discharge. The station is controlled automatically from the Karratha control centre, which also monitors and controls conditions at various sites throughout the West Pilbara Water Supply area. The control system also allows for manual control of the pump station from Karratha. Construction

Construction commenced in June 1982, with the Department's day labour force being used for the establishment of site facilities including access roads, accommodation , sewerage disposal and power distribution aro und the site. The construction programme required placement of the main embankment in two stages during the 1983 and 1984 dry seasons, with the embankment completed ready to store water by mid November 1984. This date was critical to avoid any risk of overtopping and hence catastrophic failure in floods resulting from early season cyclones. This deadline was met, and the balance of the civil works were completed by February 1985, followed by installation and commissioning of the pumping station, rising main and water treatment plant. Floods during construction were a major cause for concern in planning the embankment construction programme . The area is subject to the intense tropical cyclones typical of the region. In the period from December to March there was a 250Jo chance of receiving a flow event with potential to significantly damage the partially completed works if they were not protected. This probability drops to about 80Jo in the months of May and June, although the wettest two weeks on record are the last week in May and the first week in June. The first stage of embankment construction involved excavation and treatment of the foundations, construction of the outlet works and placement of the embankment back to river bed level prior to the onset of the 1983/ 84 wet season. The second stage completed placement of the main embankment . WATER September, 1986

17


The two season construction programme resulted in the need to provide "flood-proofing" to the first stage of construction to prevent major damage to the rockfill embankments. This floodproofing involved mesh reinforcement to the downstream toe of the embankment and covering the core and filter zones with a protective layer of rockfill. In March 1984 rainfall on the catchment from tropical cyclone Chloe resulted in the largest flood ever recorded on the Harding River . The flood was estimated to have a peak flow rate of some 3000 m3 /s and water 9 metres deep flowed over the protected embankment. The works suffered no significant damage during this flood and, in particular, the protected embankment required no remedial work. Particular care was taken in the design and construction of concrete works to minimize the effects of thermal si1ock and shrinkage which are likely to occur in the hot dry conditions. Control was achieved by paying particular attention to the mix designs and limiting concrete placement temperatures and temperature rise during hardening.

70 000

700

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400

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The First Filling of the Reservior

Tropical cyclone Gertie produced 155 mm of rainfall on the Harding catchment over a period of 18 hours starting at 2.00 a.m. January 31, 1985. Water level in the reservoir rose to within three metres of the full supply level by the morning of the following day. The peak storage volume reached in the reservoir was about 34. million cubic metres . Monitoring of the quality of the water in the reservoir, known as Lake Poongkaliyarra, has been carried out at approximately monthly intervals. This involves sampling for temperature, conductivity, dissolved oxygen, pH, colour and turbidity over a full depth profile at six locations. The results of the TSS (conductivity) monitoring is shown in Figure 6 and verifies the salinities predicted by the hydrologic modelling of the reservoir. The behaviour of the turbidity, colour and dissolved oxygen parameters after the first filling, is also shown in Figure 6. Turbidity and colour levels decreased to acceptable levels within 20 days of the storage filling . Vertical stratification of the water body occurred soon after the lake filled. This temperature stratification resisted mixing by the wind and lasted for about two and a half months. Towards the end of the period, lower dissolved oxygen levels were observed in the lower layers of the lake . As the water temperature of the lake profile became more uniform, the dissolved oxygen values increased throughout the profile. Coincident with periods of higher water temperatures and 18

WATER September, 1986

§.

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Environmental and Social Aspects

Aesthetic values were considered to be of particular importance. The arid environment, spinifex plains and widespread screeslopes coloured with the 'desert varnish' are particularly sensitive to disturbance and are not readily rehabilitated. Particular care was taken in planning and construction of the project to limit site disturbance to those areas which would be covered by the final works. Of necessity some areas have been disturbed downsteam of the dam for road, pipelines, and borrow areas. Rehabilitation is now in progress . Recreational activities are not permitted on the lake but a recreation area has been established immediately downstream of the dam. The immediate vicinity of the damsite is of traditional significance to the aboriginal people of the area . A number of studies were undertaken to identify the important aspects. In consultation with the Department of Aboriginal Sites some rock engravings were moved from the foundation areas of the embankments. Over the balance of the site care was taken to avoid disturbance to sites. In late 1982 the local aboriginal community made it known that a number of important sites had not been identified in the existing studies. Action was taken to ensure that those sites that would not be inundated by the reservoir would not be desecrated during construction. As a result of further discussions a number of other initiatives occurred. These included the formation of a consultative group to examine the impact of the project on aboriginal people, specific studies of aboriginal culture, increasing aboriginal employment on the project and the appointment of an aboriginal ranger to monitor the catchment. Close contact with the aborigines was maintained through the project.

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Figure 6. Lake Poongkaliyarra water quality.

stratification, a strong earthy-baggy taste ma~ifested itself within the storage, reaching a taste threshold number of around 30. During this period supply was taken from the Millstream Aquifer. With the advent of cooler weather an~ with natural mixing of the reservoir the taste problem disappears. An aerator has been installed in the reservoir to destratify the water column and prevent the development of water with low dissolved oxygen contents. The effectiveness of this measure in controlling the taste problem is being assessed. •

AUSTRALIAN WATER & WASTEWATER ASSOCIATION

MEMBERSHIP Membersh ip is in four categories: qualif ications suitable for • Member membership in the Inst. of Engineers (Aust.) or other su itab le professiona l bod ies ($27 p.a.). • Associates - experience in the water and/or wastewater industry ($27 p.a.). • Student ($5 p.a.). • Sustaining Member - an organisation invo lved in the Industry wish ing to susta in activit ies of the Association ($110 p.a. plus State lev ies where app licab le). Application forms and further information are available from Branch Secretaries, see page 1.


INDUSTRIAL WASTE DISPOSAL The MMBW Proposal lmmobHINtlon plant pre-treatment ot residues betore landtilling to immobilise wastes

lnt1rmedl1t1 storage area storage ol materials prior to immobilisation

Stormwater pondege all stormwater collected and monitored betore discharge from plant

VICTORlA

Main waste storage 1ra1 separate tanks contain inorganic and orgamc wastes

High tamperatura Incinerator accepts liquids . sludges and solias extensive gas cleaning system_..

Phyalcll/ chemical tr111tment plant aqueous inorganic treatment aqueous organic treatment solvent and oil separation

Orum and solids racelvel building equipment to empty. clean and crush drums. storage tor drums of wastes., 1 , receive and store loose solid wastes â&#x20AC;˘

M1lnt1nanc1 and 1menltlH building maintenance for buildings and plant

Odour control building trea1ment lor odorous air extracted lrom unloading bays and 1ransfer areas

Admlnlatratlon and laboratory building general ottices and ma1or p1ant control room and laboratory Gatel!OuH and weighbridge controls access to treatment plant monitors incoming waste loa4s

Chemical r11agent 1tor11 reagent chemicals kept separate from wastes

Figure I : In 1985, the Melbourne and Metropolitan Board of Wor ks was given responsibility to build and operate industrial was te storage and treatment fac ilities to service the whole of Victoria. Since that date, Board officers have been examining different aspects of waste management, including local and overseas practices, avai la bl e and preferred treatment technology and developing criteria for siting of faci li ties. Victoria produces abo ut 35 million tonnes of waste from industry and commerce each year, most of which can be safely consigned to municipal type tips or discharged to sewers. About 100 000 to nnes of this total cannot be disposed of safely in this way and requires special treatment to render it environmentall y ha rmless. These wastes include contam inated acids from th e metal industry, so lve nts and waste oils from the oil and paint industries, residues from refinery processes, used oils from service stations and chemicals used in schools and hospitals. Many are treated on-site by industry, but faci lities for offsite disposa l of residues are limited . The Board now proposes to estab lish a comprehensive system to manage the State's special wastes, comprising a single integrated high-t ec h treat m ent a nd disposal fac ility, a number of small collection depots and a sec ure landfill. It is expected th at this system will be operational by 1990, when app lication of liquid wastes

An artist's impression of the facility

to '!and at the waste treatment facility at Tullamarine must cease. An integrated fac ility has a number of advantages over separate treatment plants catering for different parts of the waste stream; establishment costs are lower because on ly one site is needed and elements such as laboratories and bulk liqu id holding areas can be shared by different treatment processes . Such facilities have a proven record of effective operation overseas, part icularly in Europe. The major operations of the integrated fac ility will include physical and chemical treatment, oil and solvent recovery, high temperature incinerat ion and chemical immobilization . T he largest proportion of wastes will be taken to the p hysical/ chemical plant where inorganic and organic aqueo us wastes and ot her organic liquid wastes wi ll be treated . T he treatment of inorganic aq ueous wastes is expected to involve chemical pretreatment as necessary; neutralisation fo llowed by floccu lation; gravity settling of solids fo llowed by gravity thickening; disposal of treated effluent to sewer or further treatment as required; pressure filtration to produce a dry solid filter ca ke a nd disposal of th e cake to landfi ll or to th e immobiliza ti on plant if haza rd ous. Organic aq ueous wastes will be treated initiall y by separatin g water and solids from the organic (oil) phase by grav it y settling; centrifuging the wate r phase to remove solids; se paration of any remain-

ing organic material from the water phase by em ulsion breaking and dissolved air flotation; disposal of the water phase to sewer or further treatment and incineration or recovery of organic material. A high temperature incinerator capable of disposing of some 15 000 tonnes of organic waste per year will be a major feature of the facility. It will also be capable of safely disposing of unstable and potentially the most hazardous (or intractable) wastes. The incinerator will be a rotary kiln lined with firebrick and is expected to be operated at temperatures greater than 1000 degrees Celsius and have the abilit y to deal with liquid, solid and pasty wastes and to burn wastes in 200 L drums. Before being disc harged to the atmosphere, exhaust gases will be passed through a heat recovery system for temperature reduct ion and then through a gas cleaning system to remove fine particles and acid gases produced during combustion. Heat energy recovered will be used for heating of other treatment processes or for power generat ion. The int egrated faci lit y wi ll be essentially a medium sized chemical processing plant. A site will be chosen after an extensive cons ult a ti on programme with Local Government, various interest gro ups and the communit y. The Board ack nowledges communit y concern that the fac ility be separate from residential and environmentally sensitive areas, final siting criteria wi ll include specific separation distances. WATER September, 1986

19


Cape Peron Enviro.nmental Monitoring P. N. Chalmer and L. W. Edmonds undertaken by Binnie & Partners Pty Ltd in association with G. B. Hill & Partners. With the information already available from the Garden Island Causeway Study and the Cockburn Sound Study as a basis, detailed oceanographic studies were undertaken by R. K. Steedman & Associates and ecological studies and seabed surveys were conducted by Le Provost, Semeniuk & halmer. An Environmental Technical Liaison Committee, chaired by Dr. Graham Chittleborough of the Department of Conservation and Environment, provided an independent review and assessment of the studies. The outlet was designed to satisfy the 'Water Quality Criteria for Marine and Eustarine Waters for Western Australia' which was produced in April 1981. The aim of the criteria, which have no statutory force at present, is to suggest guidelines for water quali ty which would fully protect all possible users of water in each area. Users include marine flora and fauna as well as man. The criteria are based on the concept of 'Beneficial Uses' and from these, four

ABSTRACT The Water Authority of Western Australia's newest and largest effluent outlet was commissioned in June 1984. The 1400 mm outlet discharges into 20 m of water in the Sepia Depression, 4 km offshore. This paper describes the environmental monitoring carried out before and after commissioning. The monitoring reveals that the discharge from the outlet is generally behaving as predicted and shows that no adverse environmental effects have been detected.

INTRODUCTION Most of the wastewater from Perth's southern suburbs is treated at the Woodman Point Wastewater Treatment Plant. Commissioned in 1966 the plant discharged primary effluent through a 1800 m ocean outlet into about 20 m of water in Cockburn Sound. Several major industries also discharged effluent into the sound. In 1976, concern over the deterioration of the environment in and around Cockburn Sound resulted in the Western Australian Government allocating funds for a three-year environmental study. Published in 1979, the report of the Cockburn Sound Environmental Study showed that: • The sound behaved as a tidal 'lake' for much of the time and thus effluents did not move out of the sound readily; • the seagrass dieback was related to the increase in nutrient input to Cockburn Sound; • the water quality deteriorated through the occurrence of undesirable blooms of free drifting algae, also attributable to nutrient input; • some of the biota, sediments and inshore waters were contaminated by heavy metals or bacteria; • the nutrients, heavy metals and bacteria originated from industrial or sewage effluents. The Cockburn Sound Study suggested two main alternatives for the long term solution of the problems in the sound greatly improved standards of effluent treatment, or disposal to deep ocean waters. Most of the major industries around Cockburn Sound were planning and implementing changes to reduce the quantities of pollutants being discharged . For the Woodman Point Wastewater Treatment Plant a number of options, including ocean disposal, advanced treatment with disposal to Cockburn Sound and advanced treatment with land disposal, were considered. It was concluded that the most economic solution was to discharge primary effluent into the open waters of the Sepia Depression through a 4 km outlet off Cape Peron (Fig . 1). In January 1981 it was decided to proceed with the full feasibility study of ocean disposal off Cape Peron . This was 20

WATER September, 1986

P. L. Chaim er

L. W. Edmonds

Dr Phillip Cha/mer is a marine biologist having completed a B.Sc.(Hons) and Ph.D. at the University of W.A. He has been involved in environmental consulting since 1975 and is a director of the Environmental Consultants Le Provost, Semeniuk and Cha/mer. Mr Lindsay Edmonds has been involved in the design and operation of wastewater treatment facilities since he graduated with a B.E. from the University of W.A. in 1974. He is currently Technical Services Engineer in the Wastewater Treatment Section of the Sewerage and Drainage Branch of the Water Authority of Western Australia.

0

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\

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WARNBRO SOUND

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2-5

Figure 1. Location plan.

5 Km


were selected as providing the most stringent requirements applicable to establishment of targets for the location and design of the diffuser outlets, these being: • drawing of boundaries for Direct Contact Recreation • definition of a zone for Harvesting of Aquatic Life • setting of boundaries for Mollusc Harvesting • designation of the whole of the area for the maintenance and Preservation of Aquatic Ecosystems. An Environmental Review and Managment Programme (ERMP) was prepared, and published in January 1982. This was considered by the Environmental Protection Authority (EPA) which found that the proposal was environmentally acceptable providing a number of conditions, in. eluding a detailed monitoring programme, were agreed to by the Water Authority. The outlet commissioned in June 1984 and approximately 55 MLd- 1 of primary effluent is being discharged.

MONITORING PROGRAMME

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The following monitoring programme, which was developed to meet the recommendations of the EPA is being carried out by the Water Authority of Western Australia: • Monitoring of the shape and extent of the detectable plume, to determine if it conforms to the predictions of the ERMP. This is to be done by annual grid sampling, beach sampling and water quality analyses. • Suspending filter feeding sentinel organisms (mussels) in the upper part of the water column at selected sites to determine whether reef shellfish (abalone) are being exposed to faecal bacteria. • If monitoring under the items above indicated that the discharge was extending further and at higher concentrations than predicted in the ERMP, the Authority would immediately: advise EPA, intensify sampling of receiving waters and biota to determine the extent of the impact and, report to EPA on the further steps the Authority proposes to take in order to safeguard other users of the area. • Surveying of the fauna within both the sediment and the rock fill close to the outlet, for changes in species of food value to rock lobsters and any accumulation of faecal bacteria. The results to be passed to the Department of Fisheries and Wildlife for consideration and advice to EPA. • Underwater checking of pipeline each spring; EPA to be advised of any damage or alteration which could affect any other users of the area. • Estimation of bacterial die-off in the discharge area under various conditions as soon as possible after the discharge commenced . These new values to be used to re-calculate the distribution of bacterial concentrations. The results to be reported to the EPA and to the Public Health Department.

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LOCATI ON S

ANN UAL GRID ~EAC H wt.H R QUALITY SENTINE L MU SSELS BE NTHIC INFAUNA

Figure 2. Sampling locations.

MONITORING RESULTS ANNUAL GRID SAMPLING

At Cape Peron, as at all the Authority's major outlets, an annual grid sampling programme was organised. A grid with 143 sample points at 500 m intervals was established, centred over the diffuser (Figure 2). Surface samples are taken from 80 of these points, according to the direction of the current. A background survey was conducted in April 1984. Position-fixing was carried out by Associated Osiris Surveys using a Trisponder DDMU 260, an HP85 computer and three shore stations. A drogue was dropped at the sample point over the diffuser and its movement monitored. Once the current direction was established, the relevant grid was selected and sampling commenced. Samples were also taken at the point the drogue was dropped and at the point it was retrieved after the grid sampling was completed.

These samples were analysed for temperature, conductivity, dissolved oxygen, biochemical oxygen demand, turbidity, ammonia, total Kjeldahl nitrogen, nitrate, reactive phosphorus, cadmium, lead and bacteria (Total Coliforms, Faecal Coliforms and Faecal Streptococci). Two post-discharge surveys have been conducted, in March 1985 and April 1986, and results have been generally as predicted with the plume being well defined and to the north of the diffuser section. As with all Perth's outlets, the plume is driven by the current with the wind having only miminal effect. A plot of the Total Coliforms from the 1986 Survey (Figure 3) is reasonably typical. BEACH SAMPLING

The beaches around Cape Peron are in the Shire of Rockingham which undertook beach sampling before and after commissioning at five locations in Cockburn Sound, five adjacent to the WATER September, 1986 2 1


Data on pre-discharge water quality conditions were available from MarchSeptember in 1981 and March-May in 1984. These parameters were sampled at 13 set grid points within a I km radius of the outlet (Figure 2). At each site, samples were collected from the surface , midwater and the bottom. Because of time limitations, bacterial samples were collected on separate days from those for other parameters. Of the above parameters, total phosphorus , total nitrogen, chlorophyll 'a' and bacteria were most useful, and only those parameters are considered below .

42 14

<Ii

Nutrients

F. Strep

Salmonella % pos

500/ 100 mL

M edian No / JOO mL

91.5

97.3

13

0

2

94.0

98 .3

3

0

Warnbro S & South

2

97.5

99.4

3

0.8

Cockburn Sound Cape Peron

6

88 .9

97. 3

15

0

High ammonia concentration ( ~ 5 Âľg L- 1 ) were used as a tracer for the wastewater plume (e.g. Figure 4 for January 1985) . Within the wastewater plume, average total nitrogen and phospohorus levels fluctuated widely and reached relatively high levels (Figures 5 and 6). However, these levels generally occurred within a restricted area and reduced rapidly with distance from the outlet (e .g. Figure 7). While it was expected that nutrient levels would be elevated within the wastewater plume as it dispersed from the outlet, it was also of importance to examine the nutrient concentrations from the sample sites outside the plume . Outside the immediate effluent plume, average total nitrogen and phosphorus levels also fluctuated, but generally remained s imilar to pre - discharge background conditions for the area (Figures 5 & 6). However, on two occasion s (September-November 1984, January-March, 1985) total nitrogen values were also observed to rise substantially . Whether these increases in nitrogen concentrations were due to wastewater discharge is unknown, but they should be viewed with caution as, together with phosphorus, these nutrient levels approached those recorded by Chiffings (1979) in Cockburn Sound when eutrophication was considered a problem there.

98.6

99.3

2

0

Chlorophyll 'a'

Warnbro S & South

2

3

0

500

Figure 3. Total coliforms (No. per 100 mL) -

1500 m

14.4.86.

TABLE A: SUMMARY OF BEACH SAMPLING Faecal Co/iforms Period Pre-discharge July 1982May 1984

Post-discharge July 1984July 1985

Location

Median No / JOO mL

% < 1501100 mL

Cockburn Sound Cape Peron

6

Cape Peron outlet (shown in Figure 2) and ten more stretching 15 km southwards from the north end of Warnbro Sound. Samples are collected each fortnight during the winter and weekly during the summer, and are analysed for bacteria by the Public Health Department. The results of the pre-discharge sampling taken from July 1982 to May 1984 and post-discharge sampling taken from July 1984 to June 1985 are summarised in Table A. These show that the levels of bacteria are within acceptable levels in each area. The levels are highest in the enclosed waters of Cockburn Sound and decrease southwards where there is less residential and industrial development. The post-discharge levels are slightly higher in Cockburn Sound and slightly lower around Cape Peron. It is apparent 22

WATER September, 1986

96.9

%<

100

that the discharge of effluent is having no detectable effect at the beaches . WATER QUALITY

The water quality parameters specified for the monitoring programme were salinity, temperature, light attenuation (Secchi disc), total phosphorus, total nitrogen, chlorophyll 'a', and bacteria (Total coliforms, Faecal Coliforms, Enterococcus, Salm onella) . Samples were collected on 13 occasions over each of the December-May periods in 1984-85 and 1985-86 when usage of the area and potential exposure of the public to the effluent were likely to be greatest and when disperson conditions were likely to be worst. Some additional samples were collected immediately after the outlet commenced operations in August-November 1984.

Chlorophyll 'a' levels were the best indicator as to whether the nutrient input to the Sepia Depression was causing increased productivity. Table B shows that, after discharge commenced, chlorophyll 'a' levels were similar to the pre-discharge levels, and thus phytoplankton levels had not increased. Bacteria

The water quality criteria applying to bacteria , in relation to the most stringent beneficial use, i.e . harvesting of molluscs for food, state that the median reading of five water samples over a 30 day period should not exceed 15 faeca l coliforms/ 100 mL, or 20% of such samples should not exceed 50/ 100 mL. While the number of samples collected during this programme greatly exceeds the suggested number, the same statistics (median and upper 20th percentile) have been applied . The samples collected from the outlet have


4TH OF JANUARY 1985

TABLE B: CHtOROPHYLL 'a' LEVELS RECORDED WITHIN 1 KM OF THE OUTLET

I

e

Date

116

Surface

6

Midd le

3

Bottom

\

PRE-DISCHARGE March-Sept. 1981 (n = 89) March-May 1984 (n = 11 7)

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3 4

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2

2

11

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292

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2

3

3 3

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2 2

500 m

2

2

1

2

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3 4

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3

2

4

2

Figure 4. Ammonia values (/Lg L-') at the sa mpling stations shown in Figure 2. T he wastewater plume as determined from th ese values is indicated by the broken line.

abalone (Haliotis roe1) are harvested. Mussel samples were attached to submerged moorings at stations located betwen the outlet and the inshore abalone reefs as shown in Figure 2. These mussels were collected from Southern Flats Bank in Cockburn Sound and were first analysed to show they were free of faecal bacteria. The mussels were then left at the stations for approximately two weeks. Simultaneously an additional mussel sample was suspended above the outlet to confirm that the mussels were detecting

been omitted from these calculations because that point obviously exceeds the guidelines. Table C shows that the median E. Coli level was zero both before and after wastewater discharge commenced, and that only 6 to 12% of samples exceeded 50 E. coli. per 100 mL. SENTINEL MUSSELS Mussels (Mytilius edulis) were used to detect bacterial contamination extending from the outlet to the inshore reefs (Figure 2), where shellfish , particularly

Median Percentage of Samples Reading Faecal exceeding 50 Coliform Faecal per 100 mL Colijorms per JOO ml

,oo ,00

0

~

8

P, • • d, 1cl, or9, 1000

• •

PRE-DISCHARGE March-Sept. 1981 (n = 26) Apr. -May 1984 (n = 39)

Po1 t-d11char9,

1951

0

19U / 8.5

19U

D

198.S / 86

.34 ± .27

The sea floor of the Sepia Depression in the vicinity of the outlet consists of bare sand with no living seagrass or algae. The benthic fa una of the area consists of infauna dominated by biv alve a nd gastropod molluscs, polychaete worms and amp hipod crustaceans. The benthic infauna of the Sepia Depression are

z

~z

.44 ± .32

BENTHIC INFAUNA

Date

,oo

~

.71 ± .52

bacterial contamination. The mussel samples were analysed for Total Coliforms, E. co li, E nterococcus and Salm onella. P re-discharge data were collected from these mussels on three occasions in early 1984. After discharge commenced, 12 sets of samples were analysed in 1984-85 and 13 in 1985-86 over the December-May periods . The mussels were usually free of bacterial contamination and thus only maximum bacterial contamination in each sampling period is shown in Table D. While Total Coliforms and Enterococcus were occasionally detected in the mussels, these levels were low, and their presence may have been due to sources other than faecal contamination. E. coli, which is the best indicator of faecal contamination was only detected in the mussels in extremely low numbers, and those levels were sufficiently low that they may have been due to the sampling and anlysis procedures. Salmonella wjlre not detected from any mussels.

600

-

.39 ± .32

TABLE C: BACTERIA LEVELS IN SEAWATER SAMPLES

PLUME

1000

.45 ± .3 1

POST-DISCHARGE Aug.-Nov . 1984 (n = 156) Dec. 1984-May 1985 (n = 468) Dec. 1985-May 1986 (n = 546)

2

I

3

I

I •

239 11

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2

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Chlorophyll 'a' (ug/ L, x ± S.D.)

NON - PLUME

000

0

0

0

0

0

12%

0

6%

0

8%

600

,oo ,00

AUG

SEP

OCT

NOV

DEC

JAN

FEB

MAR

APR

MAY

MONTH

Figure S. Nitroge n levels within 1 km of the effluent outlet.

JUN

JUL

POST- DI SC HARGE Sept. -Nov . 1984 (n = 144) Dec. 1984-May 1985 (n = 432) Dec 1985-May 1986 (n = 432)

Th ese sa mpl es were coll ected within I km of the outlet (see Fig. 2), but sa mples from the out let site a re excl uded from the table.

WATER September, 1986

23


PLUME

100

.

. 60

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NON- PLUME

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Figure 6. Phosphorus levels within 1 km of the effluent outlet.

4TH OF JANUARY 1985

e

\ \ \ \

188 1 99

241

e

211

231

232

235

232

209

e 323

Surface

198 198

Bottom

Middle

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427

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186 186

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e 542

208 218

229

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239

219

2 28

2 27

187

218

218

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PIPELINE INTEGRITY CHECK

e 219

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naturally sparse (L'!JC, 1981). Only the cockle Glycymeris striatularis is sufficiently large and abundant for bacterial analyses to be carried out. Consequently benthic infauna sampling has been directed specifically at Glycymeris. The abundance of Glycymeris was estimated at sites 50 m, 150 m and 300 m north of the outlet. At each site sediment to a depth of 100 mm from five replicate I m 2 quadrants was sieved through 3 mm mesh using a Venturi airlift. The number of Glycymeris collected was counted and the Glycymeris were then analysed for bacterial contamination. The abundance of Glycymeris is shown in Figure 8. While the number of Glycymeris has decreased 50 m north of the outlet 1 it has increased 150 m & 300 m north of the outlet. However despite these variations, the abundance of Glycymeris has not increased over the maximum values recorded in the area prior to the outlet commencing discharging . Bacterial contamination of Glycymeris also remained low after discharge commenced (Table E). While bacteria have been recorded from the cockles, levels of Total Coliforms, E. coli and Enterococcus have remained extremely low, and Salmonella have not been detected . Each December , Authority divers swim along the full length of the outlet to check the structural integrity of the pipe. After two years operation the pipe is in good condition, there has been no significant build-up or scouring ' of sand, and the ports are flowing freely. BACTERIA MORTALITY RATES

The reduction in the numbers of bacteria released in the effluent is governed by three processes: dilution, dispersion and die-off. The initial dilution is determined from e 218 e 198 • 21e the measured concentrations at the outlet 240 208 230 and the surface (assuming the effluent reaches the surface) once background 207 219 260 concentrations of nitrogen and phosphorus are determined. These background concentrations vary widely and the calculated value of the initial dilue 208 tion depends greatly on the background 227 500 m concentration assumed. (Table G) . Therefore it is not possible to determine 198 the exact value of the initial dilution, but it would appear that it is approximately equal to the design value of 100. Similarly,' Figure 7. Total nitrogen values (µg L· 1 ) at the sampling stations shown in Figure 2. The dispersion values were also calculated but wastewater plume from the ammonia values in Figure 4 is indicated by the broken line. again these varied widely. TABLED: BACTERIA LEVELS OF MUSSELS TABLE E: BACTERIA ANALYSIS OF THE COCKLE GLYCYMERIS IN THE VICINITY OF THE OUTLET Date Maximum Bacterial Contamination Detected (organisms per g of mussel flesh) Total Colijorms PRE-DISCHARGE March-April 1984 (14 samples) POST-DISCHARGE Dec . 1984-May 1985 (53 samples) Dec. 1985-May 1986 (130 samples)

4

WATER September, 1986

4

278

2

70

33

• present in one sample only . •• present in only seven of 130 samples.

24

E.coli

Date

Enterococcus Salmonella

5.3

0

PRE-DISCHARGE June & Dec . 1983

50 m, 150 m & 300 m north of outlet

POST-DISCHARGE May 1985 and June 1986

50 m, 150 m & 300 m north of outlet

0

••

0

Distance from Outlet

Maximum Number of Organisms Recorded per JOO g of Cockle Total Coliforms

E. coli

Enterococcus

Salmonella

4

4

4

0

79

2

0


In determining aie-off, the mortality rate is usually expressed as the time taken for the concentration to reach l0OJo of its original value, this time is called the T90 (in hours) . T90 values based on the mean subsequent dilutions and the measured numbers of Total Coliforms, Faecal Coliforms and Faecal Streptococci have been calculated . T90s ranged from -19.6 hours to 28.5 hours, with 71 % of the results within the range from Oto 10 hours. The negative results are meaningless and illustrate the effect of turbulence on the measured data and two calculated T90 values exceed 10 hours and also seem likely to be in error . The remaining calculated values of T90 follow roughly the curves for T90 developed for the outfall design .

50 U")

C

,o

0

50 m Nor th of out l•t

e

150 m Nort h o f outl•t 300 m Nor th of outl• t

6

NE

"'w 0..

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i:31

30

20

0 O<

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10

z

1983

1985

19 84

198 6

YEAR

CONCLUSION

Figure 8. Abundance of the Cockle gly cymeris.

TABLE F: CALCULATED VALUES OF INITIAL DILUTION BASED ON ALTERNATIVE BACKGROUND CONCENTRATIONS Date

(A)

18 Feb. 85 27 Feb . 85 12 Mar . 85 19 Mar. 85 26 Mar. 85 30 Apr. 85

N

p

N

106 66 65 30

69 146 169 134 225 57

127 581 226 128 197 39

145 43 5 209 130 218 96

82 153 100 95 36

76 164 192 153 263 59

60

133

216

206

87

151

39

55

Average (A) To1al nitroge n N

=

(C)

(B)

p

N

13 µg L-' , 101al ph osp horus P

=

p

55

A comprehensive monitoring programme has been conducted since the outlet was commissioned in June 1984. The results show that the effluent discharge is generally b ehaving as predicted and that no adverse environmental effects have been detected. It can be concluded that the site selected is satisfactory and that the Environment Review and Management Plan ( 1982) has been successful. •

10 µg L-•,

(8) T otal nitrogen N and total phosphoru s P set equal to minimum va lue measured during the survey on each date.

(C) Total nitrogen N = µg V1, tota l phosph oru s P

=

15 µg L· 1

*

*

*

*

*

LETTERS The Editor, In reference to F . W . Bishop's paper 'Water Engineering in Asia - Problems and Solutions', 'Water', March 1986. Case 2 - Central and South Kedah Water Supply - showed a 'Lovo' type sedimentation tank as part of a treatment process achieving the desirable aims of simplicity and suitability for operation and maintenance by less skilled local technicians and labour. With considerable experience in Malaysian water engineering we agree that treatment plant in the provinces must meet the aims listed by Mr. Bishop. However we do not agree that the 'Lovo' tank is the appropriate solution. It has two handicaps: • The flocculated water is out of sight during the main part of the sedimentation process . The operators, therefore, have no visual contact with the process at its most critical moment and are not able to relate to the dosing operation to its effect. Learning how to balance dosing against a variable water quality is made that much more difficult. • The heaviest sludge deposits are found in the darkest end of the lower compartment which tends to discourage labourers from doing a proper job in completing the manual desludging operation. For the above reasons we usually recommend the single direction horizontal

flow sedimentation tank which is more appropriate to the task and the situation, provided land is not scarce. Yours faithfully, SYED MUHAMMAD SHAHABUDI!" S.H.M.B. Sdn. Bhd . Consulting Engineers Kuala Lumpur, Malaysia

AUTHOR'S REPLY I read with interest the letter of July 22, 1986, from Tuan Syed of S.H.M.B . Sdn. Bhd. relative to Water Engineering in Asia, ' Water', March 1986. The experience of S.H.M .B. in Malaysia is well known and the views expressed noted . In response to the views expressed , the Scott & Furphy Group take a somewhat different approach . The importance of ensuring that correct coagulant dosage, rapid mixing and tapered flocculation is achieved for a given raw water quality, temperature and flow cannot be over emphasized . Thus it is necessary to achieve a rapid settling floe at the end of the hydraulic· flocculator unit before it enters the sedimentation unit. In some plants where flocculation is incomplete the final flocculation is completed in the sedimentation tank, but this does not a\ter our viewpoint that the success of the sedimentation process is deter-

mined by laboratory jar testing, correct coagulant dosage and monitoring the results of flocculation at the outlet from the hydraulic flocculator. The 'Lovo' tank with its intermediate horizontal floor has better stability, particularly under conditions encouraging density currents, than the horizontal flow tanks which are frequently installed with diffusion baffles that are less than optimum . The ' Lovo' tank is a simple version of the T. R. Camp multiple tray sedimentation tank, and the later G. Culp's plate settlers with the floe settling velocities being enhanced with the intermediate tray and giving a more effective surface rating and therefore settling velocity than the tank plan area . It is agreed that sludge removal by manual methods using pressure hosing and squeegeeing is not a pleasant task, particularly in the confined space of the lower compartment. Frequently desludging is exacerbated by undersized sludge pockets and draw-off pipes which reduce the rate of sludge removal during cleaning operations. Yours sincerely, F . R. BISHOP Managing Director Camp Scott Furphy Pty . Ltd. Melbourne WATER September, 1986

25


Swampy Odour i~ the Drinking Water of

Perth, Western Australia J.E. Wajon, B. V. Kavanagh, R. I. Kagi, R. S. Rosich, R. Alexander and B. J. Fleay ABSTRACT Between 1980 and 1985, a number of consumers in Perth, Western Australia, received drinking water with an ephemeral, unpleasant, swampy, cooked-vegetable odour. The swampy smelling constituent was identified as dimethyl trisulphide using instrumental analysis combined with odour and taste assessment. The odour threshold concentration of dimethyl trisulphide was 5 to 10 µ.g m- 3 and it was found in swampy smelling samples at concentrations between 10 and 250 µ.g m- 3 (parts in 10 12) . The odour was associated with treated groundwater, but only developed in ·the water mains following treatment. The odour intensity increased in the water mains with increasing distance from the treatment plant, the most intense odours being found at the extremities of the distribution system where chlorine was absent. Extra chlorine added at the outlet of the treatment plant was effective in limiting the occurrence of the odour .

J.E. Wajon

B. V. Kavanagh

R. S. Rosich

R. Alexander

R. I. Kagi

INTRODUCTION The drinking water of Perth, a city of one million people, is provided from a combination of surface and groundwater sources. Surface water supplies between 60 and 70% of the 180 million cubic metres of water used annually and comes from reservoirs and dams on forested catchments in the Darling Ranges to the east and south east of the city (see Figure 1). The water is of high quality and is only chlorinated and fluoridated before distribution. Groundwater supplies come from shallow, unconfined (up to 70 m), sub-artesian (150 to 250 m) and deep artesian (1000 m) aquifers distributed throughout the coastal plain north and south of the city. A large portion of the groundwater is treated in four treatment plants located at Wanneroo, Mirrabooka, Gwelup and Jandakot (see Figure 1) by aeration, chlorination, coagulation and filtration to reduce the levels of sulphide, iron, turbidity and colour. Until recently, odours and tastes were not a major problem in drinking water in Perth, the majority of consumer complaints (more than 80%) being due to coloured or highly turbid water. Complaints of odours and tastes were largely of a chlorinous nature, caused primarily by the need for chlorination at the outl~t of unroofed service reservoirs. Such complaints have decreased m recent years with the implementation of a programme to roof these reservoirs. In the early 1980s, however, complaints of an unpleasant, swampy, cooked vegetable-type odour in water supplied to various parts of the metropolitan area began to occur . The problem was associated with treated groundwater and while the odour was intermittent and transient, it generated considerable community concern about the quality of water. As a result, an investigation was begun in 1981 to address the problem . Specific objectives of the investigation were: (i) to identify the compound(s) responsible for the swampy odour; (ii) to elucidate the mechanism of formation of the swampy odour and (iii) to develop effective measures to prevent or control the occurrence of swampy odours in the water supply system. Objectionable odours have been reported in the drinking water of many countries around the world (Persson 1983). Indeed, complaints of offensive odour and taste have been the most common complaint from consumers in the United States, the United Kingdom and the Netherlands dissatisfied with their water quality (Sigworth 1957 , Rosen 1975, AWWA 1976, Zoeteman et al 1977). Many odours and tastes are caused by the growth of microorganisms in water supplies (A WW A 1976, Lin 1977) with one of the most common complaints being of an earthy/musty nature. These are most commonly caused by one or both of two organic compounds, geosmin and methylisoborneol (Gerber 28

WATER September, 1986

B. J. Fleay

Dr Johannes (Eddy) Wajon, B.Sc.(Hon:) W.A., Ph.D., is a Research Fellow in the School of Applied Chemistry at WAIT. For the past five years, he has been investigating odour and taste problems in drinking water in Western Australia. His interests are in the field of organic water qualitytanalysis and advanced water treatment processes. Dr Robert Alexander, B.Sc.(Hon.) W.A., Dip.Ed., Ph.D., is a graduate of the University of Western Australia. He is currently a Principal Lecturer in the Western Australian Institute of Technology where he heads the Petroleum Geochemistry Group which conducts research, training and consulting in exploration petroleum geochemistry. Dr Robert Kagi, B.Sc.(Hon.) W.A ., Ph.D., M .B.A. is a Principal Lecturer in the Schoo l of Applied Chemistry at the Western Australian Institute of Technology, where his professional interests include studies in petroleum geochemistry and environmental studies commissioned by industry and government bodies. Dr Ron Rosich, B.Sc. W.A. , Ph .D., returned to Perth to take up his present position with the Water Authority of Western Australia in June 1983, after 23 years research, consulting and University lecturing overseas (Canada, USA and Switzerland) and in Australia. He presently manages the Water Supply Laboratory of the Authority with major responsibilities in the quality of potable water and in water resources management. Brian Fleay, B.Eng., M.Eng.Sc., M.I.E.Aust., is Principal Engineer Source Operations, Water Supply Branch of the Water Authority of W.A . He is responsible for the production of water for Perth from surface and groundwater sources together with the field side of catchment management. Dr Brian Kavanagh, Ph.D.(U. W.A.) is the Chief Chemist, Water Authority of Western Australia having joined the Water Authority in 1980from CSIRO, Division of Food Research where he worked on aspects of industrial waste treatment and pollution control. Drs Wajon, Kagi and A lexander are with the School of Applied Chemistry, Western Australian Institute of Technology. Drs Alexander and Rosich and Brian Fleay are with the Water Authority of Western Australia.


DESCRIPTION OF GROUND WATtR TREATMENT PLANTS The swampy odour was associated principally with water from Wanneroo Groundwater Treatment Plant, but also occasionally with water supplied from ot~er groundwater treatment plants. The investigation therefore initially concentrated on an examination of the water supply system associated with Wanneroo Treatment Plant, and later was extended to include the area supplied by Jandakot Treatment Plant. These plants treat water from the unconfined aquifer of the coastal plain and from the sub-artesian aquifers of the Leederville Formation. Water from the subartesian aquifer contains small amounts of hydrogen sulphide, turbidity and colour, whilst water from the unconfined acquifer contains substantially larger amounts of these components (see Table 1). Water at Wanneroo Treatment Plant is first aerated to reduce levels of hydrogen sulphide and carbon dioxide, and to partially oxidise soluble iron. Chlorine, alum and a polymeric flocculant aid is added and the floes produced removed in an upflow clarifier. Lime is used for pH adjustment prior to filtration in sand and anthracite dual media filters. Finally, chlorine is added for disinfection, and the water is stored in a clearwater tank with a detention time of less than one hour before being pumped into the distribution system. Some variations to this sequence occur at the other treatment plants. At Mirrabooka, hydrogen sulphide is removed by chlorination prior to aeration and lime is dosed prior to alum. Caustic soda is used at Jandakot in place of lime. At Gwelup, chlorine is also added prior to aeration to remove hydrogen sulphide . Water from Wanneroo Treatment Plant is pumped to Wanneroo Reservior , an unroofed service reservoir 4 kilometres from the treatment plant. The detention time in the reservoir ranges from 1 to 3 days . Water leaving the reservoir is rechlorinated to a 1 g m-3 free chlorine concentration before being pumped into the distribution system . Water from Jandakot Treatment Plant is mixed with surface water from the Darling Ranges in a trunk main near the plant. The proportion of groundwater in the mixture ranges from O to 60%. Most of the water is fed into an unroofed reservoir several kilometres frum the plant, but a small proportion is fed directly into the distribution system; it was in this area where complaints of swampy odours occurred.

ewanneroo

( -Mirra book a

-

A

Mundaring Weir

-Canning Dam

WJandakot 9wongong -

-

Dam

' Serpentine 'Dam

~

South Dandalup Dam

\

'

10 5 0 10km Figure 1. Location of surface water supplies and groundwater treatment plants near Perth, Western Australia.

1968, Rosen et at 1970), which are produced by many actinomycetes, cyanobacteria (blue-green algae) and fungi (Gerber and Lechevalier 1965, Izaguirre et al 1982, Persson 1983, Wood et al 1983) . Other odours and tastes are due to industrial chemicals which have contaminated surface or ground waters (Kolle et al 1970, Zoeteman and Piet 1974, A WWA 1976, Hrubec and Kruijf 1983) . Odours and tastes may also be produced during water treatement. For example, reaction between chlorine and ammonia or phenolic compounds produces chlorinated compounds which have objectionable odour and taste at extremeley low concentrations (White 1972) . Nevertheless, in many reports in the literature of objectionable odour and taste, the compound(s) responsible have not been identified. In particular, at the commencement of the study there were no reports of previous experience with a swampy odour in drinking water . This paper provides an account of the outcome of the investigation (Wajon et al 1985a), particularly the identification of the odorous compound and the development of a successful management strategy for control of the problem.

THE CAUSE AND NATURE OF THE SWAMPY ODOUR Identification of the Swampy Smelling Constituent

The swampy smelling constituent was identified by a combination of instrumental analysis and odour and taste assessment. Instrumental analysis was used to determine the identity and concentration of volatile organic compounds present in water samples, while complementary odour and taste assessment was used to determine the type and intensity of odour and taste. Water samples were co llected in 2500 cm 3 (2.5 litre) brown glass bottles with Teflon-PTFE lined plastic screw caps. All bottles were cleaned with detergent, rinsed twice with tap water, once with dilute nitric acid and three times with carbon-filtered tap water before being heated at 200°C for 8 hours. Samples were collected by rinsing the bottle twice with the sample to be taken and then filling the bottle slowly a nd to overflowing. Samples were analysed as soo n as possible after collection. Samples not analysed within 24 hours were stored for up to 4 weeks at 4°C before analysis.

TABLE 1. QUALITY OF RAW AND TREATED WATER AT GROUNDWATER TREATMENT PLANTS Wanneroo Treatment Plant Parameter•

Before Treatment Shallow SubArtesian

Capacity ('OOOs m') pH Total dissolved so lids Hardness (as Ca Co,) Colour (HU) Turbidity (NTU) Iron Hydrogen Sulphide • In g m· 3 unl ess indicated.

5.4-6.7 125-330 25-165 20-400 1-600 0.3-2.0 0.1-1.3

t

N.D.

=

6.5 175-400 85- 140 2-10 0.2-3 .7 1.3-10 0.02

After Treatment 95 6.5 230-280 90-110 2.5-7.5 0. 1-2 < 0.1 < 0.1 -0.1

Mirrabooka Treatment Plant Before Treatment Shallow SubArtesian 6.3-7.0 5.3.6.8 130-470 300-900 28-250 80- 140 4-12 9- 125 0.4-12 0.2-4 0.3-6.8 2.2- 17 <0.0 1-1. 2 < 0.01 -0.04

After Treatment 65 6.5 350-450 120- 130 1-5 0.1 - 1 < 0.1 N.D.t

Gwelup Treatment Plant Before Treatment Shallow SubA rtesian 6.0-6.9 300-580 100-380 4-80 0.3 -4 2.9-9.8 N.D.t

6.6-6.9 350-660 120-140 2- 11 0.2-1 5- 14 N.D.t

After Treatment 50 7.0 325-450 120- 150 1-5 0.1-0. 5 <0. 1 N.D.t

Jandakot Treatment Plant Before Treatmen Shallow SubArtesian

After Treatment

28 5.8-7.5 180-750 60-280 6-125 0.5-80 0.1 -2 .4 < 0.01 -0.9

6.7 930 180 7 0.2 4.6 0.02

6.5-6.7 500-650 160-200 5- 10 0.1-0. 5 <0. 1 N.D.t

Not determined.

WATER September, 1986

29


Volatile organic co mpounds present in water samples were analysed us- . (i) it had to be present in all samples with the swampy odour, ing the closed loop stripping technique (Grob I 973, Grob and Zurcher and either absent or present at relatively low concentration in 1976, Krasner et al 1981, McGuire et al 19°81). Recirculating air was passall other samples; ed through a 2000 cm 3 (2 litre) water sample kept at 30°C for 2 hours and (ii) it had to be present in swampy smelling samples at concentrathe volatile organic compounds present in the sample were absorbed onto tions greater than its odour threshold concentration (the 1.5 mg of finely divided activated carbon (Bender and Hobein, Zurich, lowest concentration at which an odour is detectable) and Switzerland). The compounds were eluted from the carbon with 3 x 8 (iii) its odour in water had to be similar in character to that of mm 3 (3 x 8 micro litre) portions of dichloromethane (Nanograde, swampy smelling samples. Mallinckrodt, USA) and analysed using at Hew lett Packard 5880A gas The compound which most closely satisfied these criteria was chromatograph (Hew lett Packard , Palo, Alto, California) with fl a me dimethyl trisulphide (CH,SSSCH ). It was found in 900Jo of 3 ionization detection (GC/FID) and a Hewlett Packard 5895B gas samples with a swampy odour at concentrations ranging from 5 to chromatograph/ mass spectrometer (GC/ MS). 250 µ,g m-3 • The odour threshold concentration of dimethyl Two cubic millimetres (two microlitres) of the total 20 mm 3 (20 trisulphide was determined by the panel to be between 5 and 10 µ,g microlitre) dichloromethane eluate co llected was introduced into a 0.22 3 3 mm I.D . x 50 m fused silica capillary column using an on-column injec- m- , very similar to the value of 10 g m/ - determined by Buttery et al (1976). In addition, the odour of dimethyl trisulphide in tor (OCI-3, Scientific Glass Engineering, Ringwood, Australia). Under these conditions, there was no decomposition or disproportionation of water closely resembled that of swampy smelling water samples. It was therefore concluded that dimethyl trisulphide was the comdimethyl polysulphides, such as that associated with the use of hot pound primarily responsible for the swampy odour. vapourizing injectors (Wajon et al 1985b). The capillary columns were However, dimethyl trisulphide was absent from several samples coated with either OV-1 (Hewlett Packard), cross-linked methyl sili cone (HP) or BP- I (SOE). Gas chromatography was most commonly carried with strong swampy odours. In addition, it was present in a out with the following temperature program: initial temperature 30° C number of samples at concentrations lower than expected based held for I minute , followed by a I ° C/ min ri se to 50° C and then to 250°C on the perceived odour intensity of the sample (Rosen et al 1962 at 10°C/ min. Hydrogen was used as the carrier gas at a flow rate of 40 Krasner et al 1983, Wajon et al 1985c). The compound(s) causing, cm/ min, and nitrogen at 20 cm' / min was used as make-up gas for or contributing to, the swampy odour in these samples have yet to GC/ FID. be identified . The efficiency of the closed loop stripping system was determined 3 regularly by adding 50 to 100 µg m- of a mixture of 1-chlorohexane, VARIATION OF SWAMPY ODOUR IN THE 1-chlorooctane, 1-chlorodecane, 1-chlorotetradecane and 1-chlorohexaW ANNEROO WATER SUPPLY SYSTEM decane (Merck , Darmstad , FRO) and 20 to 100 µg m-' dimethyl trisulphide (prepared according to Milligan et al 1963) to car bon filtered Swampy odours occurred in the Wanneroo water supply system water. Recoveries of the chloralk anes ranged from 60 to 90% for when water from the shallow, unconfined aquifer was being used . chlorohexane and from 40 to 60% for ch lorohexadecane. The recovery of In contrast, no problems were encountered when only water from dimethyl trisulphide ranged from 30 to 60%. the sub-artesian aquifer was being used. Dimethyl trisulphide was Water samples were assessed for odour and taste by panels of I to 6 found in only one of thirty samples of water from the unconfined persons. Any ch lorine present was removed before the assessment by adaquifer and it was not found in any water samples from the subding a sli ght excess of sodium thiosulphate . Panellists were given :warm artesian aquifer. Water leaving the treatment plant also did not (40° C) samples in warmed 200 cm 3 conical fla sks which were 'rinsed contain dimethyl trisulphide, although it did have a sulphurous several times with the sample to be examined. This removed a woody odour similar to that described by Monscvitz and Ainsworth odour which was present in dry flasks even after thorough cleaning and (1974) and Wake and Ward (1982) . heating at 500°C. Panellists were chosen on their ability to consistently Slight swampy odours and low concentrations of dimethyl rank samples containing geosmin at concentrations between 7 and 500 µg trisulphide were occasionally present in water leaving Wanneroo m-' in order of increasing concentration based so lely on the intensity of Reservoir or in trunk mains leading from the reservoir. Data their odour.

Panellists were asked to describe the odour of the samples and to rate the perceived intensity on a six point scale from O(none) to 5 (very strong). The odour intensity was also determined by the dilution to threshold method in which the dilution factor required to render the odour in the sample just perceptible was recorded as the Threshold Odour Number (APHA 1981) .

presented in Figure 3 indicated that the swampy odour intensity 250

• 0

200

,,

Threshold Odour Number 12/7 / 82 Thre shold Odour Number 3/11/82

A,

Dim ethyl Tri sulphid e

6

Threshold Od our Numb er

X

Dim e thyl Trisulphide 19 / 10 / 83

} 15 / 8 / 83 64

z

10,

X

2. w

~

·~

C J:

]

0

150

16

:::>

...I

z

Cl)

IX.

:::>

I

'

6

15

I-

'

20

30

Tim e {minutes)

Figure 2 . Gas chromatogram or intensely swa mpy smelling sa mple. Analytical conditions: 2 mm' (2 microlitres) injected at 30°C (on-column) onto 0.3 mm x SO m OV-1. Initial temperature 30° C held for I min followed by 1°C/ min rise to S0°C, then to 250°C at 10°C/min. Peak Xis dimethyl trisulphide.

Large numbers of volatile organic compounds were detected and identified in swampy smelling water samples by GC/FID and GC/MS. A typical chromatogram is shown in Figure 2. In assessing the results of the instrumental and sensory analyses, the pattern of occurrence of various compounds in water samples was compared with the type and intensity of the odour of the sample. The compound(s) responsible for the swampy odour had to satisfy the following three criteria: 30

WATER September, 1986

:::> 0

a: _,.

al

::!!:

CL

JlLJ_~

!::.. a: w

...I

4

100

>-

C

0 C

J: I-

...I

w

0

i:i

Cl)

J:

::!!:

w a:

50

J:

I-

DISTANCE FROM RESERVOIR (km) Figure 3. Variation of swampy odour intensity and dimethyl trisulphide concentration with distance along a trunk main leading from Wanneroo Reservoir.


I •• 0.7

I I

0.6

,;- 0.5 E

~

DIMETHYL TR ISULPHIDE DDDUR THRESHOLD CONCFNTRATION

I

£!

~ 0.4 ~

a: 0

...J

:c 0.3 (.)

r . .I .. I

•I

UJ UJ

::: 0.2 I

.

II 0.1

~I

I•••

0 0

~ 50

00

-

200 150 100 DIMETHYL TRISULPH ID E (uglm')

-

-

250

Figure 4. Free chlorine concentration and dimethyl trisulphide concentration in water samp les from the water supply system.

and dimethyl trisulphide concentration in water in the trunk mains increased with increasing distance from the reservoir. This occurred as the chlorine concentration in the water progressively decreased. As the data in Figure 4 show, the highest concentrations of dimethyl trisulphide were found in samples where free chlorine was absent or present at concentrations less than 0.1 g m· 3 • Samples with the greatest swampy odour intensity and dimethyl trisulphide concentration were usually found at the extremities of the water supply system, i.e. in reticulation mains or at residences, but the odour intensity and dimethyl trisulphide concentration in the distribution/ reticulation system were extremely variable, and at many locations were much lower than that in the trunk mains. These data indicated that production of dimethyl trisulphide and the swampy odour occurred in the water mains in the presence of chlorine, but mostly at the extremities of the water supply system where the free chlorine concentration was low.

CONTROL OF SW AMPY ODOUR Treatment

Addition of 2 g m· 3 or more chlorine in the laboratory to water having a strong swampy odour completely removed the odour within one hour. Addition of lesser amounts of chlorine only partially removed the odour. This was probably due to the oxidation of dimethyl trisulphide to the relatively non-odorous methylsulphonyl chloride (Padma et al 1971) according to the equation below . CHJSSSCHJ + 8 HOC! = 2 CHJSO,Cl + H,so. + 6 HCI In California, objectionable odours due to dimethyl trisulphide and other dimethyl polysulphides in water leading from main and service reservoirs and from treatment plants have recently been successfully controlled by the addition of chlorine (Krasner 1986). However, adding chlorine to water in the mains in all those areas of the distribution system in Perth affected by swampy odours was impractical. Instead, when complaints of swampy odours were received, the water in the affected areas, which contained little or no chlorine, was discarded by opening hydrants and flushing the water from the pipes. This had the effect of drawing in water with a higher chlorine concentration. By virtue of the inverse relationship between chlorine concentration and dimethyl trisulphide concentration, the incoming water also had a lower dimethyl trisulphide concentration. Flushing, besides being a visible sign of positive action to consumers, was, therefore, very effective in reducing the intensity of the swampy odour and in eliminating complaints. Prevention

Chlorine added at the outlet of the treatment plants was found to greatly influence the subsequent formation of dimethyl trisulphide and swampy odour in the water supply mains. In particular, swampy odours occurred when the chlorine dose was insufficient to meet the full chlorine demand of the treated water. On several occasions when a swampy odour episode occurred in

the Wanneroo water supply system, the clborine dose at Wanneroo Treatment Plant was increased by 2 to 4 g m· 3 • On each occasion, the number of complaints of swampy odours dropped quickly though complaints usually did not cease completely. The concentration of dimethyl trisulphide in the distribution system also decreased, but not always to zero. The concentration of dimethyl trisulphide measured in the Wanneroo water supply system as a function of the free chlorine concentration at the outlet of Wanneroo Reservoir is shown in Figure 5. The data indicated that the concentration of dimethyl trisulphide in the water supply system was less than the odour threshold concentration when the free chlorine concentration at the outlet of Wanneroo Reservoir was greater than or equal to 0.35 g m· 3 , Since 1984 the goal has been to prevent swampy odours occurring by adding sufficient chlorine at the outlet of Wanneroo Treatment Plant to maintain the concentration of free chlorine at the outlet of Wanneroo Reservoir greater than 0.35 g m· 3 , In 1982 and 1983, the chlorine dose at the treatment plant was frequently less than 7 g m· 3 , insufficient to maintain the free chlorine concentration at 0.35 g m· 3 , and there were 300 complaints annually of swampy odour. in 1984 and 1985, when the chlorine dose was maintained between 7 and 10 g m·3, there were approximately 30 complaints of swampy odour annually. These occurred when the free chlorine concentration at the outlet of Wanneroo Reservoir temporarily fell below 0.35 g m· 3 • 0.7

0.6 I

.,..

0.5

i

w 0.4

..

~

z ii:

DIMETHYL TRISULPHIOE ODOUR THRESHOLD CONCENTRATION

0 ~ 0.3 0

8

w w

If

I

I

0.2

0.1 I

0

0

.-- •. .

50

.

'

..

• 100

150

200

250

.,.

DIMETHYL TRISULPH I OE (uglm')

Figure 5 . Variation of dimethyl trisulphide concentration in the water supply system with free chlorine concentration at the outlet at Wanneroo Reservoir. Samples in the water supply system were taken 24 hours after those at Wanneroo Reservoir to compensate for time of travel.

A similar picture emerged from investigations of the Jandakot Treatment Plant. Swampy odours developed when insufficient chlorine was added at the outlet of the treatment plant to meet the chlorine demand. It was found that to avoid swampy odour problems, it was necessary to maintain the free chlorine concentration in the distribution system, at a point before the water reached consumers, greater than 0.2 g m· 3 • The first set of complaints from the Jandakot area occurred in late 1984 when the chlorine dose was reduced from 10 to 8 g m· 3 and the free chlorine concentration at the sample point was less than 0.2 g m· 3 • In 1985, the chlorine dose was maintained near 12 g m· 3 and there were only a few complaints. These occurred when the chlorine concentration at the sample point temporarily fell below 0 .2 g m· 3 • The reason for the effectiveness of increased chlorine doses at groundwater treatment plants in preventing formation of dimethyl trisulphide in the mains is unclear. Increased chlorine doses at the treatment plant increased the chlorine concentration in water leaving the treatment plant and in trunk mains, but not at the extremities of the distribution system where the majority of the dimethyl trisulphide was produced. A problem with sulphur-type odours in Cincinnati, Ohio, which was believed to be due to bacterial growth in the mains, was eliminated by maintaining a free chlorine concentration in the mains (A WW A 1976) . It is currently believed that microorganisms are also responsible for the production of dimethyl trisulphide in the distribution system in Perth. Increased chlorine doses at the treatment plant probably either greatly reduced the number of microorganisms,, capable of producing dimethyl trisulphide , or removed a sulphu r-containing compound used by the microorganisms to produce dimethyl trisulphide. We are currently examining these possibilities. WATER September, 1986

31


CONCLUSIONS 1. The swampy odour was associated with groundwater. 2. The swampy odour was caused primarily by dimethyl trisulphide. It was formed in the water mains, particularly at the extremities of the distribution system where free chlorine was absent, by a yet unknown mechanism. 3. Addition of 2 g m- 3 or more chlorine eliminated the odour from samples of water with an intense swampy odour. 4. Flushing of mains in areas affected by swampy odours greatly reduced complaints of objectionable odours. 5. Addition of an extra 2 to 4 g m-3 chlorine at the outlet of groundwater treatment plants (to give total doses of 7 to 12 g m-3) prevented the formation of swampy odours in the water supply system. 6. Complaints of swampy odours have decreased markedly since large doses of chlorine have been added at the treatment plants . ACKNOWLEDGEMENTS

This project was funded by the Water Authority of Western Australia.

REFERENCES APHA (1981). 'Standard Methods for the Examination of Water and Wastewater ' . 15th Edition. (American Public Health Association, Washington, D.C.). AWWA (1976) . 'Handbood of Taste a nd Odour Control Experiences in the US and Canada'. (American Water Works Association, Denver, Colorado). BUTTERY, R. G. , GUADAGNI, D. G., LING, L. C., SEIFERT, R. M. and LIPTON, W. (1976) . Additional volatile components of cabbage, broccoli, and cauliflower. J. Agri. Food Chem., 24: 829. GERBER, N. N. (1968). Geosmin, from microorganisms, is trans- I , 10-dimethyltrans-9-decalol. Tetrahedron Lellers, 25: 2971. GERBER, N. N. and LECHEVALIER, H. A. (1965). Geosmin, an earthy-smelling substance isolated from actinomycetes. Applied Microbiology, 3: 395. GROB, K. (1973) . Organic substances in potable water and in its precursor. Part I. Methods for their determination by gas-liquid chromatography. J. Chrom., 84: 255 . GROB, K. and ZURCHER, F. (1976). Stripping of trace organic substances from water: equipment and procedure . J. Chrom., 177: 285-294. HRUBEC , J . and DE KRUIJF, H. A. M . (1983) . Treatment methods for the removal of off-flavours from heavily polluted riover water in the Netherlands A Review . Water Sci. Tech., 15: 301. IZAGUIRRE , G., HWANG, C. J., KRASNER, S. W. and McGUIRE, M. J . (1982). Geosmin and 2-methylisoborneol from cyanobacteria in three water supply systems . Appl. Environ. Microbiol., 43: 708. KOLLE, W., KOPPE, P. and SONTHEIMER, H. (1970) . Taste and odour problems with the river Rhine. Water Treatment Exam., 19: 120 KRASNER, S. W. (1986). Organic su lphur compounds in drinking water: taste and odour implications. Paper presented at the seminar Gouts et Odours dans les Eaux Potables, Maisons-Laffitte, France.

*

BOOK REVIEW REVIEW OF AUSTRALIAN ASSISTANCE TO THE INDONESIAN WATER SUPPLY AND SANITATION SECTOR BY THE AUSTRALIAN INSTITUTE OF URBAN STUDIES From A.I.U.S., Box 809, G.P.O Canberra, A.C.T. 2601. Cost: $16 (Aust.) incl. mailing. This ¡ report was prepared by the Australian Institute of Urban Studies (A.I.U.S.) for the Australian Development Assistance Bureau (A.D.A.B.), and comprises some 338 pages. The object of the Report is to evaluate the achievements to date by the Australian Government in the Indonesian Water Supply and Sanitation Sector, to assess future needs and to identify how Australia may best direct future assistance to the sector. A.D.A.B. administers a total aid budget to Indonesia in which about 10% has been allocated to the water and sanitation sector in the form of grants. The report sets out the Government of Indonesia's (G .O.I.) National P lanning, 32

WATER September, 1986

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KRASNER, S. W ., HWANG, C. J. and McGUIRE, M.'!. (1981). Development of a closed loop stripping technique for the analysis of taste-and-odour-causing substances in drinking water. In Advances in the Identification and Analysis of Organic Pollutants in Water, 2. L. H . Keith, e.d., p. 689. (Arbor Science Publishers Inc., Ann Arbor, Michigan) . KRASNER, S. W., McGUIRE , M. J . and FERGUSON, V. B. (1983) . Application of the flavour profile method for taste and odour problems in d rinking water. Presented at the American Water Works Association Water Quality Technology Conference, Norfolk, Virginia, USA . LIN, S. D. (1977). Tastes and odours in water supplies - A Review, N. T.I.S. PUB PB 273 142. McGUIRE, M. J., KRASNER, S. W. , HWANG, C. J . and IZAGU IRRE, G. (198 1). Closed-loop stripping analysis as a tool for solving taste and odour problems. J . Amer. Water Works Assoc., 73: 530. MILLIGAN, B., SAVILLE, B. and SWAN , J. M. (1963). Trisulphides and tetrasulphides from Bunte salts. J. Chem. Soc., 3608. MONSCVITZ, J. T . and AINSWORTH, L. D. (1974). Treatment for hydroge n polysulfide. J. Amer. Water Works Assoc., 66 : 537. PADMA, D . K., SHAW, R. A., VASUDEVA MURTH Y, A. R . and WOODS, M. (1971) . Chloramine-T. Part I. The oxidation of some acyclic organic sulphur compounds. Int. J. Sulphur Chem ., lA: 243. PERSSON, P. E. (1983). Off-flavours in aq uatic ecosystems - an introduction. Wat. Sci. Tech., 15: I. ROSEN , A. A. (1975). Health significance of odour and taste research. Presented at American Water works Association Seminar on Taste and Odour, Minneapolis, Minnesota. ROSEN, A. A., PETER, J.B. a nd MIDDLETON, F. M. (1962) . Odour thresholds of mixed organic chemicals. J. Water Poll. Control Fed., 34: 7. ROSEN, A. A., MASHNI, C. I. and SAFFERMAN, R . S. (1970). Recent developments in the chemistry of o dour in water: The cause of earthy/musty odour. Water Treatment Exam ., 19: 106. SIGWORTH, E. A. (1957). Control of odour and taste in water supplies. J. Amer. Water Works Assoc., 49: 1507. WAJON, J . E., KAGI , R. I. and ALEXANDER, R. (1985a). The occurrence and control of swampy odour in the water supply of Perth, Western Australia. A report submitted to the Water Authority of Western Australia. WAJON, J. E., ALEXANDER, R. and KAGI, R. I. (1985b). Determination of trace levels of dimethyl polysulphides by capillary gas chromatography . J. Chrom., 319: 187. WAJON, J.E., ALEXANDER, R., KAGI, R . I. and KAVANAGH, B. (1985c). Dimethyl trisulphide and objectiona ble odours in potable water. Chemosphere, 14: 85. WAKE, E. H ., and WARD , R. A. (1982). The analysis of sulphur in drinking water, in 'Advances in Thin Layer Chromatography'. J. C. Touchstone, (Ed.), pp. 413-424, (John Wiley and Sons, N.Y., N .Y.). WHITE, G. C . (1972). 'Handbook of Chlorination'. (Van Nostrand Reinhold Co., New York). WOOD, S., WILLIAMS, S. T . and WHITE, W.R. (1983). Microbes as a source of earthy flavours in potable water - A review. International Biodeterioration Bulletin, 19: 83. ZOETEMAN , B. C. J . and PIET, G. J . (1974),.,.Cause and identification of taste and odour compounds in water. Sci. Total Environ., 3: 103 . ZOETMAN, B. C. J., PIET, G. J. and MORRA, C . F. H. (1977). Sensorily perceptible organic pollutants in drinking water. In 'Aquatic Pollutants: Transformation and Biological Effects'. 0. Hutzinger, I. H. Van Lelyveld and B. C. J. Zoetman, (Eds.), pp . 359-368. (Pergamon Press, Oxford).

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goals and specific targets in the rolling five year plans (Repelita). Soon after the start of the U. N. Water Decade, the G.O.I. concentrated on its policies and planning to meet specific needs in the water and sanitation sector. Recognition of availability of resources lead the G.O.I. to set 'basic needs' levels with urban communities categorized into various categories and with rural communities, improvement in shallow ground water. In the sanitation sector realizable targets were projects such as community facilities, solid waste disposal and drainage systems. The achievement of set goals depended on limited financial resources, with US$2,000 million required for Repelita IV from G.O .I. funds, loans and 21 OJo from foreign aid. The report discusses the water supply projects undertaken by A.D.A.B. since 1969 and current and future programmes. It goes on to cover the features of the Australian Aid Programme, and proposes that attention should be focused on project selection and definition and apprecia-

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tion of longer term benefits of projects with joint integration of technical and financial resources in sector projects with Indonesia . It also gives guidelines for future project selection, examining geographical location, technical sphere, project size, with a discussion on goods versus services as part of Australian Aid. The authors consider changes to A.D.A.B. in procurement, project management and a longer view taken on appropriate technology and past project assistance . The report considers the need for integration of sector activities with community involvement and in project training being contributed by A.D.A.B . The conclusion of the authors is that Australia has made a valuable contribution to the Indonesian Water Supply and Sanitation Sector. The Report gives a comprehensive coverage of the G.O.I. policies and achievements in the sector and Australia's contribution is presented in a succinct and readable manner. F. P. BISHOP


WATER HAMMER ALLEVIATION A WESTERN AUSTRALIAN CASE STUDY Y. H. Ng and A. J. Gale -

ABSTRACT A 225 mm diameter asbestos cement pipeline, 3.7 km in length, transfers flyash slurry from the State Energy Commission's Kwinana Power Station to a disused lime-stone quarry for disposal. Since upgrading the system to convey a higher flow of 56 Lps, the flyash pipeline has suffered a number of breaks due to excessive surge pressures caused by pump shutdown. This paper describes the pipeline systems, the surge phenomena experienced by the pipeline and the water · hammer identification, analysis and alleviation measures employed to return the pipleline system to a safe and reliable service.

1. INTRODUCTION 1.1. Aim

The aim of this paper is to present a practical application of identification, analysis and alleviation techniques for elimination of surges in pipelines due to water hammer. A case study of the flyash slurry pipeline at the State Energy Commission's (SECWA) Kwinana Power Station is presented . 1.2 General Theory of Water Hammer

It is not intended to repeat in detail the theory of water hammer in this paper as there are many excellent references available covering the subject (Ref. I to 4). Water hammer is generally referred to as the disturbance in the form of a pressure variation, caused by a rapid change in velocity of flow of liquid in a closed conduit. The disturbance travels along the pipeline at a speed corresponding to the speed of sound in the pipeline. Two theories can be used to analyse a system: • Rigid water column theory - for slow or small changes in flow rate . - assumes that pipe walls are rigid and the water is incompressible. • Elastic water column theory - for rapid changes in flow rate and for long pipelines. - assumes that water and pipe are elastic. In the rigid column theory, the basic equation relating the head change caused by velocity change derived from Newton's second law of motion is expressed as: L dv h

gdt

where h

= head difference between

the ends of the water column (m) L = pipeline length (m) dv = rate of change in velocity dt (m i s) g = gravitational acceleration (m l sis )

Allen J. Gale

Y.H.Ng

Allen J. Gale is an Associate Director of Binnie & Partners Pty. Ltd. and is State Manager for Western Australia. He is a Dip/ornate (Civil Engineering) of the Caulfield Institute of Technology (1968) and has specialised in the water management field for the last 15 years, working in most states of Australia, Asia and the USA. Y. H. Ng, Graduated B.Sc. with honours from Middlesex Polytechnic, UK in 1977. Previously with C. H. Dobbie & Partners in London, he has worked on several flood alleviation schemes in England. He is currently a Senior Engineer with Binnie & Partners Pty Ltd and has experience in water supply and waste disposal projects including pumping stations, pipelines, water hammer analysis, flood studies, computer and mathematical models. For better estimates of water hammer pressures caused by more rapid change in flow rate, the elastic column theory should be used. The elastic column theory according to Joukousky's Law relates the amplitude of the pressure head change at the wave front, which is created as a result of a disturbance, with the change in velocity by the following: h

where h

.!!.Y....

g

= rise in potential, or head

over a length of the wave (m) corresponding change in v velocity over the same length (m i s) a celerity of the wave (m i s) g gravitational acceleration (m l sis) Water hammer estimates can be obtained by graphical methods or by numerical methods using computer . Pipeline systems are often complex and to be able to evaluate and identify the best protection for the system, a basic understanding of water hammer phenomena is necessary. With the trend now towards easy access to a powerful micro computer, solution by computer appears to be gaining favour. 1.3 Causes and Solutions

Common causes of water hammer are:

valve opening and closure pump start up and shutdown improper locations of valves in the system Solutions for overcoming water hammer include: - control on rate of starting and shutdown of pump - control on rate of opening and closing of valves - pump bypass system - feed tanks - air vessel - flywheels on pump shafts - pressure relief valves - surge tower - air release valves The costs of control devices vary widely. Selection of an appropriate protection measure will depend on the degree of protection and reliability required, the pipeline system and the cause(s) of the water hammer.

2. KWINANA POWER STATION FLY ASH PIPELINE SYSTEM 2.1 System Description

General The conversion to. coal firing of power generating units at Kwinana Power Station located south of Fremantle, Western Australia has led to the requirement for off-site disp.isal of flyash. The flyash is disposed of as a slurry through a 225 mm asbestos cement pipeline to a disused limestone quarry, approximately 3.7 km from the power station. To prevent leaching of liquid and dissolved salts into the aquifer surrounding the quarry, a water recovery system consisting of a series of bores, a pumping system and a second pipeline of similar specification, returns water from recovery bores to the power station for reuse. The system schematic is shown in Figure I. The pipelines have generally performed well, but after increasing the original design flow from 44 Lps to 56 Lps in the coal conversion project the flyash slurry pipeline suffered a number of breaks. The breaks were mainly due to surge pressures which occurred as a result of pump shutdown and insufficient restraint and support at bends . Both the flyash and the effluent recovery pipelines are 225 mm Class D asbestos cement except for about 70 rii of 200 mm steel pipe within the power station. The pipeline is laid above ground except for sections in culverts. The asbestos cement pipes have rubber V-ring joints and the steel pipework has flanged and victaulic joints . Gibault joints are used for items requiring periodic removal, ·such as bends, or sections (?f asbestos cement pipeline required to .be rotated (to permit even wear from th e' abrasive flyash slurry). WATER September, 1986

35


partly responsible fo~ some pipe failures. An intensive rehabilitation programme was carried out to upgrade the thrust anchorage requirement to withstand the new duty which was set a 900 kPa working head, with thrust blocks to be designed for a factor of safety of 1.8 at this figure.

FLYASH SLURRY PIPELINE OFF SITE DISPOSAL

WATER RECOVERY PIPELINE RECOVERY~,// BORE ::;.....----PERRON - - QUARRY

Excessive Surge Pressures

OVERFLOW ON-SITE DISPOSAL SALT / FRESH / WATER / INTERFACE/

I

Figure I. Flyash and water recovery flow system.

Plyash Slurry Pipeline Flyash is first mixed into the slurry in a swirl pit with recovered water. The swirl pit acts as a sump for duty and standby centrifugal slurry pumps . The selected duty slurry pump starts automatically on swirl pit high level, empties the pit and stops at low level. Each pump discharges through a 200 mm knife gate valve which can be pneumatically or manually operated. Downstream of the valve is a magnetic flow meter. The asbestos cement pipeline is above ground for most of its length (3,768 m total) to the discharge point at Peron Quarry. At the discharge point, there is a further magnetic flow meter located in the pipeline. The pipeline is generally undulating (Figure 2), the highest point being the discharge end at 26.0 m AHD, while the lowest point is at the pump (0.32 m AHD). There are numerous high points in the pipeline, the highest being at chainage 1150 m at 18.87 m AHD. All the high points are fitted with single or double orifice air valves.

Water Recovery Pipeline This pipeline system returns water from recovery bores around the disposal quarry vi<> ;i nipeline grading down to the power statio;. With the advantage of the static elevation available and also pumping at a lesser now of 40 Lps, the pumping duty is not as severe as for the flyash slurry pipeline. Consequently, there was less evidence of , tress on the water recovery pipeline and surge was not a problem.

testing, it was found that restraint at certain bends, particularly at the vertical 45 degree bends, had been inadequate to resist the thrust pressures due to surge . Whilst the maximum allowable working head of the asbestos cement pipe is 122 m , the pipe size was originally selected anticipating abrasive wear due to the flyash slurry . It was installed as an aboveground flexibly jointed pipeline with provision for rotating pipes as invert wear developed. The original working head envisaged however, was only some 60 m and although the pressure rating of the pipe was well over the strength required, the thrust anchorage at bends was designed for 600 kPa pressure at a factor of safety of 2. The pumping requirement was raised and the pumping system modified in the coal conversion project (managed by consultants for the Commission) but the design of thrust restraints was not upgraded accordingly. This reduced the factor of safety on the thrust anchorages and was INITIAL HYDRAULIC GRADIENT 56 lps

80

z

0

_J

i==

z

I

BELOW INITIAL HYDRAULIC GRADIENT

30

w _J w oil <(

INITIAL HYDRAULIC GRADIENT 56 lps

-----MAXIMUM SURGE POTENTIALS

.§

~ :;,;

MINIMUM SURGE POTENTIALS 4m3 AIR VESS~ f!:2":.2 6_!.es _'.!I~ ~L'1 Q.Oj\.lR1._ - ~ : : _::-

20 - - - 3 AIR VESSEL fLOvi _ -

w f0

SURE NO~VE CLO

>6- 1P'-

t.m

0...

T__:.8 ~

Inadequacy of thrust anr:horage From a review of past failures and observations of the pipelines during

~ _::::----=. ~.::;: _:::-__:--

~g___ - ~ AIR '-¡ - VALVE -

225m ASBESTOS CEMENT PIPELIN E

m

10 AIR VESSEL ' - - - ~ r

2.2 Failures and Causes

Pressure traces obtained from a pressure recorder located at the upstream end of the pipeline showed that rapid valve operating times and pump trip situations had been largely responsible for the high surge pressures occurring in the pipeline. Surge pres re spikes of more than 1400 kPa were recorded and occurred at pump stoppage on completion of the water flushing cycle. The valve was automatically set to close the instant pump stop was initiated, to prevent back flow and emptying of the line to the swirl pit. The knife gate isolating valve was pneumatically controlled and closing and opening time was 5 seconds. During testing it was established that this valve failed to close completely when operated manually and also failed to close automatically on pump stoppage. Surge phenomena involving column separation and recombination is complex and the solution is often to negate the occurence of various conditions. For this flyash pipeline, the following was hypothesised: Pump stoppage caused a rapid deceleration of the water column in the water mass just downstream of the pump creating a negative pressure shock wave along the pipeline . Due to the magnitude of the change in velocity of the water / ash slurry column the _pressure dropped to the vapour pressure of the liquid being pumped. At the high points at chainage 1147 and 1830, if air entry into the pipeline through the double orifice air valves was not possible, vaporisation of water caused the water column to separate during the subnormal pressure surge . At the point where separation occurs, waves were set up in each column of water. Reflection of the negative shock wave at each water column boundary, such as an air space, or at the pump, produced a reflected positive wave. The process of reflections at the pump , air space or at

APPROX PIPELINE PROFILE

j/

KWINANA POWER O d PUMP 10 31m EI 0 lJ STATION O 500

~ 1000

1500 2000 CHAINAGE (ml

2500

3000

FIGURE 2: KWINANA FLYASH SLURRY PIPELINE 36

WATER September, 1986

3500


outlet continued until, at a particular time the water columns rejoined, giving rise to a high surge overpressure. The locations where the. surge pressures, due to recombination of water columns, were likely to occur were where separations first occurred, ie. at the section of the pipeline downstream of the high points and where air pockets were trapped by sharp vertical bends . The locations of past pipe failures in the flyash disposal pipelines confirmed this likely surge phenomenon. Surge pressure due to pump start is normally not a problem unless a positive shock wave, due to rapid acceleration of the water column caused by starting a pump, meets a barrier such as a closed valve located at the downstream end of the pipeline . In this case the magnitude of the reflected pressure wave would be added to the magnitude of the wave arriving . at the barrier so that its effect upon returning to the pump would be doubled. Since there were no valves or dead ends in the flyash delivery pipeline, surge pressures greater than shut off head of the pump would most likely be caused by air in the pipeline during start up.

3.

TESTING AND ANALYSIS PROGRAMME

Field tests were carried out to determine the effect of a different valve operation on the surge pressures in the pipeline. Previously, the pump discharge knife gate valve opened and closed simultaneously with pump start and stop. Tests were conducted with the pump starting against a closed valve first and opening the valve slowly once the pump had built up speed and pressure. Opening and closing time for a valve is critical over the last 10% of valve travel (Lupton 1953). The first three quarters of the gate travel is negligible from the point of view of surge . The tests indicated that pressure surges were reduced as a result of the increases in valve operating time. However, the tests also indicated that the knife gate malfunctioned with flyash slurry, failing to initiate closure in one instance and fai ling to close completely in another. Surge control by slow operation of the valve, although effective, was not reliable and therefore was not recommended. Investigation into other surge alleviation measures indicated the air vessel to be the best overall solution for pressure surge relief. Analysis of surge with an air vessel installed was carried out using the 'BUNTING' programme developed by Binnie and Partners. The programme is a numeric representation of the graphical Schnyder method of surge analysis. The system to be analysed is divided into groups of components within which a balance of potentials and flows is assumed to occur instantaneously. Groups are connected by lines along which surge waves travel with the acoustic velocity so that there is a suitable time delay between a: change in condition in one group and the response to that change in any other group. Complex pipe networks have been analysed using this programme. Under normal operating conditions, the air vessel contains a certain amount of

water and compressed air. On cessation of pumping, water flows out of the vessel into the pipe behind the low pressure wave by means of the compressed air in the vessel. The pressure in the vessel gradually decreases as water is released until the pressure in the vessel equals that in the pipeline. By providing a replacement volume into the void created by sudden stoppage of the water column moving downstream, the vacuum condition is avoided . Having eliminated the chance of column separation in the pipeline, subsequent reduced positive surges are suppressed and dampened as liquid is forced back into the air vessel. It was found that maximum surge pressure with an air vessel installed would be below the steady state pumping hydraulic gradient. Minimum surge would be above the level of the pipeline (See Figure 2).

4. ALLEVIATION SOLUTION An air vessel located in the pump discharge line was found to be the most cost-effective and reliable solution for pressure surge relief in the flyash slurry pipeline . It provides protection against maximum and minimum pressure surges produced by normal operation of the pump and also in the event of a power failure.

2. 3.

4. 5.

6.

7.

in pipe network~ particularly in long pressure mains with low static head compared to dynamic head. Water hammer is often poorly understood and detailed analysis may be complex. The potential for water hammer in a pipe system can be minimised by proper allowances being made in the initial design. Development of computer techniques permits more rigorous analysis. For existing pipelines, integrated testing and analysis to determine causes and magnitude of surges are cost-effective compared to ad-hoc modifications. The particular case study of the Power Station flyash slurry pipeline illustrates the damage which can result from raising the duty of a pumping system without investigating the need for additional surge protection . The investment required for the flyash slurry pipeline was small compared to the capital investment protected and the previous disruption caused by pipe failures.

ACKNOWLEDGEMENTS The authors wish to thank the State Energy Commission of Western Australia for permission to publish this paper and acknowledge the assistance of staff engineers in conducting field tests of the pipeline .

REFERJ;:NCES LUPTON, H. R. ( 1953) , Graphical analysis of pressure surge in pumping systems. J. Inst. Water Eng., 7. STEPHENSON , -,-0. (1976), 'Pipeline design for water engineers', Elsevier Scientific Publ. Co. PARMAKIAN , J. (1955), 'Waterhammer Analysis', Dover Publ. Inc., New York. WEBB, T . H. (1981), 'Waterhammer control in pipelines'. BINNIE & PARTNERS PTY LTD (1984), Flyas h disposal and effluent recovery pipeline. Design audit and testing report for State Energy Comm ission, Perth .

CHANGING YOUR ADDRESS? The air vessel is 4 m 3 in volume with a diameter of 1.52 m x 2.64 m height. Sight gauges are installed to view the working and static water levels (see photo) . The required air quantity in the air vessel is maintained by level sensing devices controlling a solenoid valve which allows air to flow into the vessel from an air supply line . High and low water level alarms are a lso installed to indicate any malfunction of the air feed line and dangerous operating water level in the vessel. The cost of the vessel including associated valves and piping was A$13,000.

5. CONCLUSIONS

HELP US TO HELP YOU

PLEASE LET US KNOW! FAILURE TO ADVISE COSTS TIME AND ~ONEY INFORM YOUR BRANCH SECRETARY (see page 1) OR THE EDITOR ¡¡t

1. Water hammer is a common problem WATER September, 1986

31

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Water Journal September 1986  

Water Journal September 1986