Water Journal February 2002 by australianwater

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Volume 29 No 1 February 2002 Journal of the Austra lian Water Associ ation

Editorial Board F R Bishop, Chairm an B N Anderson, R Considine, W J Du lfer, G Fi n ke, G Finlayson, G A H o lder, B Labza, M M u ntisov, P Nadebaum , J D Parker,] R issm an, F Roddick, G Ryan, S Gray

~ Water is a refereed journal. This symbol indicates that a paper has been refereed.

CONTENTS

Submissions Su bmissions should be made to E A (Bob) Swinton, Tech nical Editor (sec below for details).

FROM THE FEDERAL PRESIDENT: Our Industry Matures

FROM THE EXECUTIVE DIRECTOR: Rio+ 10 - Australia's Role?

FROM THE TECHNICAL DIRECTOR: How do you like your Water?

Email: bswinton@bigpond.net.au

Crosscurrent Editor

INTERNATIONAL AFFILIATES: ASingle Strategic Council WEF Report

Managing Editor Peter Stirling

Technical Editor E A (Bob) Swinton 4 Pleasant View Cres, Wheelers Hill Vic 3150 Tel/Fax (03) 9560 4752

W (Bill) R ees PO Box 388, Artannon, NSW 1570 Tel +61 2 9413 1288 Fax: (02) 9413 1047 Email: brees@awa .asn.au

Water Production H allmark Editions PO Box 84, Hampton, Vic 3188 Level I, 99 Bay Street, B righton, Vic 3186 T el (03) 9530 8900 Fax (03) 9530 8911 E mail: h allmark@halledit.com.au

Graphic design: Mitz i Mann

MY POINT OF VIEW: Research in the Water Industry - Why do we do it?

CONFERENCE REPORTS

CROSSCURRENT: Water News Around the Nation

Dr Tony Pries tley

FEATURE: CRC FOR WATER QUALITY AND TREATMENT OVERVIEW 20 New programs for the 'second round'

Water Advertising National Sales Manager: Brian Rault Tel (03) 9530 8900 Fax (03) 9530 891 1 Mobile 0411 354 050 Email: brault@halledit.corn.au

Professor Don Bursill

EDUCATION AND TRAINING OF FUTURE LEADERS 22 Combining studies with real experience Ka trin a Ni tschk e

Water (ISSN 0310 · 0367) is publish ed eight times a year in the months of Feb rua ry, March, May, June, August, September , November and December.

REMOVING TASTES AND ODOURS: IS YOUR CHEAP PAC COSTING YOU TOO MUCH? Guidelines on how to choose the most economic PAC

G Newcom be a nd D Coo ke

Australian Water Association PO Box 388, Artarmon, NSW 1570 Tel +61 2 9413 1288 Fax : (02) 9413 I047 Email: info@awa.asn .au

AWA

ABN 78 096 035 773

Federal President

SURFACE MIXING FOR DESTRATIFICATION: SIMULATING THE IMPACT 27 Modeling validated against field data D M Lewis, J D Brookes, J P An ten ucci, M F Lam bert

ASSESSING MICROBIAL RISKS FROM DRINKING WATER: TWO STUDIES 30 Melbourne's water does not benefit from point-of-use filtration:

Barry Norm a n

Crypto is not a drinking water issue

Executive Director

AUSTRALIAN WATER AS SOC IATION

Chris Davis

Australian Water Association (AWA) assu mes no responsibility for opinio ns or statements of facts expressed by contributors or advertisers. Editorials do not necessarily represent official AW A policy. Advertisements are included as an infonnation service co readers and are reviewed before publication co ensure relevance to the water environment and objectives of A WA. All material in Waler is copyright and should not be reproduced wholly or in part without th e written permission of the General Editor.

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ENVIRONMENT 33

ff·,! DESIGNING A MONITORING PROGRAM FOR ENVIRONMENTAL REGULATION: PART II - MELBOURNE WATER CASE STUDY 100% compliance with a licence limit means designing for half that value W Pau l and N T Diam ond

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OUR COVER: Drinking Water Q uality. So Jar, //,e majority of A 11stralia11s are able to drink wa ter direct from the tap safely, thougl, tastes and odours so111etimes present aesthetic challenges . H owever, as pressure on resources increases, more and more technological efforts will be necessary to maintain this security, at an econo111ic cost. Tl,e CR C f or Water Quality and Treatment, ivith its 29 Parties, has developed a prag1·natic research program to assist tl,e 1,vater industry of the fu ture . Photo courtesy of the C RC WQ T .

FROM

THE

PRESIDENT

OUR INDUSTRY MATURES In my time as a water industry practitioner I have seen things change, first imperceptibly, then gradually and now almost precipitously. Management literature abo und s with descript ions o f t h e inevitability, pace and acceleration of change, but its impact on our own lives is always much mo re te lli ng t h an the academic analyses. My own organisation has just joined a large, multinational business, so profound change is suddenly very real for me. Having taken this quantum leap, I can now reflect on the way the Australian water .industry has matured in some respects. Although I hav e always worked for a private consulting fi rm, Barry Norman the water indust1y used to be dominated by public institutions: a mixture of large state agencies and smaller local authorities or water authorities. Time was when the heads of state water authorities held Premiers in their thrall . An apoc1yphal sto1ies about a Premier waiting, hat in hand, while the great water authority chief finished reading his newspaper, feet on desk, created marvellous myths about the old days. The truth is, of course, that the old water utilities were huge, cumbersome organisations, employing thousands oflabourers to build dams, pipelines and treatment plants. Consultants supplemented in-house teams, and equ ipment suppliers provided the proprietary gear that made things work, but the public sector called the shots and did much of the work. Cost was not a problem and designs could be luxuriously engineered to wonderfully high standards. By the 80s, though, things were beginning to change, water authorities slipped down the scale and state premiers began to call the shots. Engineers were replaced by economists and accountants and, worse still, there was talk of contracting o ut more work to the private sector. In 1989 the English water companies were privatised by Margaret Thatcher in one fell swoop, placing ten, new, aggressive players in the field of water around the world. They added their efforts to those of the two, longestablished French private water companies in pursuit of work. A fu1ious debate erupted over the merits of public versus private and 2

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the spectre of privatising Australian water utilities loomed. The pendulum never stands still, though, and one serious attempt to p1ivatise a water utility (in the ACT) failed, effectively closing the door on that phase of evolution. Even in England, the feroc ious regulatory climate, coupled with the diminishing returns from cost cutting have given t h e water compa ni es pause there is talk of a return to at least partial public owne rsh ip. In this climate, the debate about public vs private has become mo r e balanced - p eople acknowledge that there is no real gulf between them and that the two strands should co- exist. This evolution has been reflected in the contracts let around Australia. First, a few large, complicated BOO(T) contracts, let to international players only, with grumbling am ong Australian firms, who were caught unawares. Then, many designbuild projects, and the more interesting alliance contract (Sydney's Northside Tunnel, Perth's Woodman Point plant) and now, not the largest, the Bega Valley Sewerage project in NSW. In a departure from previous practice, where ve1y central decisions were taken about the nature of contracts, Bega Valley Shire Council produced a community discussion paper about the nature of the contract proposed and posted it on the Web for comment. Sadly, this drew unfair criticism from an idealogue, who branded the process as 'privatisation by stealth'. This is doubly unfair, since the move represented the most democratic approach yet seen in Australia fo r a large water- infrastructure contract. It seems to me that we have now arrived at a situation where the public and private sectors are working together more effectively, calling on their respective strengths, collaborating across institutional and national bounda1ies and, most interesting, consulting their stakeholders abou t the nature of contractual arrangements. This is a refreshing sign of maturity and I hope the industry will continue to evolve in that direction. Barry Norman

Aquaphemera In the September edition of Watershed, Professor Peter Cullen of the CRC for Freshwater Ecology outlines ten simple strategies to improve our rivers: 1. Efficiency D ividends - return 3% of aJI water used for environmental flows; 2. C lawback o f Water in Overallocated Rivers - where more than 1/3 of the median flow is extracted; 3 . Burden of Proof - on those who w ish to extract water, studies for 5 years at least w here required; 4. M onitoring of River H ealth audits, SoE's, etc; 5. Protection of Undamaged Rivers; 6. Protecting Important Wetlands; 7. Better Technical Advice to Governments - exp ert bodies and conrnrnnity; 8. Putting the Bits Together integrated catchment management; 9. R egional Science - fo r local issues and to deliver to local communities; and 10. Large Scale Catchment Research. These ten strategies encapsulate a range of actions which can provide the short term improvements to our rivers which are long overdue, as well as the long tenn activities which will improve our knowledge of our rivers and our ability to manage them more effectively. Following the above is an article on cold water pollution - releasing cold water from the bottom of reservoirs which in some cases can take up to several h undred kilometres in the river to return to normal river temperature. Cold water pollution can have significant effects on the river's ecology and native species in particular. Many dams have variable offtakes, but are not usually used for convenience sake . This is a great opportu ni ty in many cases to provide a major improvement to our rivers with very little effort or cost. A very sobering presentation was made by ANU PhD student Stuart Denis at the ACT branch meeting in November on environmental oestrogens. Not only was it enlightening regarding the extent of oestrogens in so much of o ur daily lives, but the possible impact they may have on our health and the woefully inadequate research effort in this area only reinforced the need for adherence to Professor Cullen 's 10 strategies. Ross Knee

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THE CRC FOR WATER QUALITY AND TREATMENT: A NATIONAL DRINKING WATER RESEARCH CENTRE Prof Don Bursill

-;-.

;:f

••,

C RC for Water Quality and Treatment

The Cooperative Research Centre (CRC) for Water Quality and Treatment was established in 1995 with a seven year grant from the Federal Government's Cooperative Research Centres Program. In January this year, the

Research Programs

Government announced that It would provide a further

To determine the best structure fo r the new CRC, researchers , government and industry representatives from across the coun try w ere consulted extensively to identify the water industry's most critical issues. Once these priority areas had been determined, the CRC established three separate programs - two research programs and a stakeholder involvement p rogram - that would give it the capability of supporting the industry effectively. These three programs are the 'Health and Aesthetics Program', the 'Catchment to Customer Program' and the 'Policy, R egulation and Stakeholder Involvement Program' . T h e Health and Ae s thet i cs Program, led by Professor J ohn McNeil of Monash Univ ersity, focuses on pathogens, disinfection by-products, micropollutants, algal toxins, aesthetic quality and customer acceptance. It aims to understand the link between human health and drinking water quality and is also investigating the factors that affect community perceptions of drinking water quality and safety. The Catchment to C u stomer Program is jointly .Jed by Dr Daniel Dee r e of the Sydney Catc hm.ent Authority and Mary D ri kas of th e Australian Water Quality Centre. T his program foc uses on the contaminants that have the greatest implications for urban water supply systems. The program is developing integrated management and treatment options to ensure high quality water from the catchment through the treatment pro cess and reticulation system to the consumer. It investigates holistic water quality management (the catchment to customer concept) , sustainability of

seven years funding and, on July 1 , the 'new' CRC for Water Quality and Treatment was born.

Meeting Industry Needs T he 'second' CRC is a different organisa tion to the 'first' CR C. N ow having 29 Parties from across the Australian water industry, major universities, CSIRO, and local and State governments, it also has new research programs and an increased emphas is on stakeholder involvement. Despite these changes, the 'new' CR C maintains the same commitment to assisting the Australian water industry that

was seen 111 the first CRC, and it will continue to deliver an essential research and knowledge management capability to the industry. One of the most significant things the first C R C achieved was the establishment of a culture of cooperation within the Australian water industry. The networks developed over its six years, and the scientific ou tcomes from the collaborative teams, have shown how much there is to learn from each other.

•

Dr Chris Chow is part of a CRC team that is developing new water treatment methods and enhancing existing processes.

Strengthen ing these links, and expanding them, will be a major focus for the new CRC.

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Th e third p r og r a m , Policy, Regul a tion a nd Stakeholder Involvement, is led by one of the CR.C's two D epu ty Chief Executive O fficers, Dr Tony Priestley o f CSIR.O M o lecular Scie nce (th e o th er D eput y Chie f Execu tive is Dr D ennis Steffensen of the Australian Water Q uality Centre) . This program is looking at water quality guid elin es, standards, and codes of practice. le is also investigating the needs of small commu nity systems, the water quality issues that affe ct indigeno us health, and water quality m anagem ent in tropi cal regions. This program also enco mpasses the C R.C's educa tion and trainin g, commun ication and commercialisa tion activiti es .

CRC researchers like Sandy Brinkmann, of the Australian Water Quality Centre, are helping the Australian water industry provide high quality water at an affordable price.

The Future

water sources, salinity, poi nt of entry/ use systems, disinfection and other treatment, distri butio n system management and n1ai n tenan ce, risk ma nagem e nt and process monitoring.

Th e new C R.C for Water Quality and Treatment will bu ild on the success o f the first CR.C . l e will produ ce research that will help the Australian water industry provide high quality water, affordably.

Prof Do11 B11rsill is Chief Exewti11e Officer of the CR C f or Water Q uality a11d Treatme111. For more i1,for111atio11, ,,isit the CRC 111eb site at 111111111. 111aterq11ality.crc.org.a11 or email do11 . b11rsill@sa111ater.co111 . a11 .

It will help Austra li a's water regulators produ ce guidelines that suit Au stralian conditions and benefi t the Australian commun ity. Most importantly, it w ill continue to foster the cooperative linkages that benefi t th e entire industry.

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EDUCATION AND TRAINING OF FUTURE LEADERS K Nitschke T he Education and Training Program of the CRC for Water Quality and Treatment enables students to combine their academic studies in water science and technology with real experience in the Australian water industry. Students graduating from th e CR C's program will help increase the level of skill available within the Australian water industry and sustain critical linkages be tween the water industry and researchers. The CRC's Education and Training Program consists of • Summer Research Scholarships • Honours Scholarships • Masters research projects • PhD research projects • Coursework postgradu ate acti vity • In volvement of re sea r c hers 111 coursework postgraduate and undergraduate lectures

Industry Focused Education Students within the CRC work closely with industry participants, as well as with unive rs ity res earc hers , dev eloping advanced technical skills along with their academ.ic foundation. Twenty-eight of the forty postgraduate students within the program are supervised jointly by industry and un iversity researchers, with many students spending n1.ost of the time at industry-based laboratories. Graduates of the CR C program are already applying their expertise within the Australian water industry, at places like Melbourne Water, the Department of Human Services Victoria and ECOWISE. The industry-focused natu re of the CRC's education program provid es benefits that a pu rely university-based education does not. Two former studen ts who show the advantages of a CRC postgraduate degree are Robert Considine and Dr D eclan Page. Both agree that a major plus of working withi n the CRC was the development of a network of other water industty professionals. Robert, a former CRC student at CS IRO Molecular Science and the University of South Australia currently awaiting confirmation of his PhD, is now 22

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Graduate Employment Action Group

Each year, the CRC offers ten-week summer projects to third or fourth year students, giving them experience of research life. At the end of the projects, the students present their results at a one-day conference. The 2001 summer students are shown here with the Chair of the CRC's Education and Training Steering Committee, Prof Felicity Roddick (bottom row, far left), the Chairman of the CRC , Emeritus Prof Nancy Millis (bottom row, second from right) , and the Program Leader of the Education and Training Program, Assoc Prof Dennis Mulcahy (bottom row, far right) .

Senior Water Quality Scientist in the Planning Group of M.elbourne Water Corpo rat io n. Robe rt says that his exposure to a variety of h ealth, engineering and scientific professionals during his studies with the CRC has been of real benefit in his current work at Melbo urne Water, where he is involved i n working on a wide range of water quality issues. Declan, who gained his PhD through the Australian Water Quality Centre and the University of South Australia, is now Princ ipal Sc ientist at ECOW ISE E nvironmental Pty Ltd. He also agrees that the industty-based nature of CRC study has provided benefits for him and for his employer, particularly through the establishment of a professional network. H e says that participation in the CRC postgraduate program allowed a seamless transition from postgraduate education to an indusny environment and recommends it to others considering working within the Australian water industry.

As well as helping students develop job-related skills, the Edu cation and T raining Program within the CRC also provides a m e ntor ing proc ess for graduates, helping them find employment in th e Australian water industry. A recently established initiative called the Graduate Employment Action Group (GEAP), chaired by D r Alan Wade of A ct ew/ AGL, provides support for students looking for career positions within the industry. The GEAP program helps industry participants identify future employees with the specific skills they need.

Students Projects To Help Industry Postgraduate students within the CR C work on projects that will show real benefit for the wa ter i11dustry. The Genetic Basis for Algal Toxins Production: Melanie Kaebernick, CRC for Water Quality and Treatment and the University of New South Wales

Melanie Kaebernick, a CRC PhD student at th e University of New South Wales, is part of a team that looks at both long and short term measu res for alleviating the problem of potentially toxic cyanobacterial blooms in freshwate r systems. M elanie's research has focused on discovering the environmental factors that induce toxin production, as well as nying to establish the function of the toxin to the organism that produces it. The answers to these questions wo uld allow us to understand the fundamental reason for toxin production and should allow managerial measures to deal with the problem from the source, opposed to short term strategi es cu rrently in place. The regulatory work of Melanie's PhD was carried out at the genetic level and lead to the discovety of increased toxin gene transcription under conditions of high light, as well as hypotheses on toxin export from i\1icrocystis cells under this condition. Indications of regulation by vatiations in the level of nitrogen and iron are also suggested but require further work.

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Melissa Todd, a PhD student at the CRC, is investigating symbionts of amoeba that could have significant implications for drinking water treatment. Amoeba, Potential Trojan Horses of the Water Treatment Process: Melissa Todd, CRC for Water Quality and Treatment and Australian Water Quality Centre

Melissa Todd, a CRC PhD student based at the Australian Water Quality Centre, provides another example of the strong significance of C R C students' work to the Au stralian water ind u stry. M elissa is investigating bacteria l symbiosis in amoebae to see whether amoebae could act as 'Trojan horses', allowing hum an pathogens into po table w ater supplies. One an,o eba genus that M elissa is lo oking at , Acan.thamoeba, is of particular interest to the water indu stry because o f its ability to harbour bacterial symbionts. Since A canthamoeba forms cysts able to survive chlorination processes, any bacteria carried by this amoeba are highly releva nt to water treatment plant ope rators. Artificial Mixing to Control Algal Blooms: David Lewis, CRC for Water Quality and Treatment and the University of Adelaide

Work by a C R C PhD student at the University of Adelaide, D avid Lewis, has made it possible to model the effect o f surface mixers on reservoir behaviour. U sing surface mixers for destratification and control of algal growth in water supply rese rvoirs is becoming more common, but little resea rch has been done to find our how effective and efficient they are c01npared to more established ways o f achieving destrati fication, such as b ubble plume aerators. U sing the results of his work on raft- mounted surface mixers installed at two reservoirs in South Australia, David has added a ne w feature to an existing well- used and pro ven numerical model of reservoir behaviour. DYRESM is a numerical model o f r eservo ir behavio ur developed at the C entre for W ater Research at the University o f Western Australia and refined ove r the past 20 years. Now, th e effects of surface mixers on controlling w ater quality problems associated with summer stra tification can be compared to other methods of destracification and other managem ent strategies can be investigated with DYRESM, increasing the options available for reservoir managem ent in respo nse to specific wa ter quafoy problems.

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The Author Katrina Nitschke is C ommu nication Manager for the CRC for W ater Quality and Treatment. For more information, visit www.waterquality .crc.org.au or email katr:ina.nitschke@ sawater. com .au .

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REMOVING TASTES AND ODOURS: IS YOUR CHEAP PAC COSTING YOU TOO MUCH? G Newcombe and D Cook Abstract

provide tools to help the • C1 water supplier minimise the 1.0 Powd e r e d a ctivated e C2 amount of PAC used while carbon (PAC) can be a 0 .9 still e nsuring satisfactory A C3 cost- e ffec tiv e way of o, 0 .8 quality. In this article, wa ter 'Y C4 removing offensive tastes C: those tools are used t o .£: 0.7 and odours from drinking ct1 und erta k e c ost - benefit E 0.6 water. To obtain the most ~ analyses related to the applieffective and efficient en 0.5 cation of PAC under practical treatment, w ater supply ~ water treatment conditions, 0.4 C: managers should choose .2 and other fac tors influencing the appropriate typ e of u 0.3 PAC doses, and therefore ~ carbon for their water, use IL 0 .2 costs, are identified. the correct dose of PAC 0 .1 and consider the various Choosing the Right 0.0 factors that influence PAC PAC and the Correct 0 50 100 150 200 250 dose (for instance, appliDoses Time (min) c ation of alu 1n The most important factor simultaneously with PAC). Figure 1. Fraction of MIB rema ining vs. contact t ime for four in the application of PAC fo r If moderate PAC doses activated carbons. Myponga Reservoir water. the removal of MIB and will not fix the problem, an geosmin is the removal of the estimate of the carbon doses treatment of affected water. The advanco mpounds at contact times required, and knowledge of the common tages are tha t PAC: of tw o hou rs or less. Figure 1 shows the time frame over which the taste and odour fraction of M IB remaining against time, • Can be applied only when required compounds will be present, will allow a for four activated carbons (designated Cl, • Is relatively inexpensive cost-benefit analysis of PAC application C2, C3, and C4) in Myp onga R eservoir versus more advanced treatment processes. • C an be retrofitted to existing plants water. Starting concentration of MIB was The major disadvantage of PAC appli Introduction 100 ngL- 1, carbon dose was 20 mgL- 1• cation is that prolonged use may lead to Figure 1 shows that the most efficient 2-methylisoborneol (MIB) and geosmin signifi cant costs, and this is exacerbated by activated carbon for the removal of MIB are earthy/musty o dou r compounds the lack of knowledge regarding correct in a water treatment plant will depend produced as secondary metabolites by doses for the production of water of approstrongly on the contact time available for some cyanobacteria and actinomycetes. priate quality. Dosing at levels greater than adsorption. The choice of an activated They can cause significant problems for necessary can result in very high costs to drinking water suppliers as they are carbon clearly depends on cost, in addition the water supplier and, conversely, underp erceived by most consumers as an to performance. In Table 1, the costs dosing leads to consumer complaints and unpleasant odour and taste in water at very associated with using the four carbons is an inefficient use of the adsorbent. low concentrations (around 5-10 ng L-1) . shown in Figure 1 are given. The calcuR ecently Cook et al. (2001) reported the The c ompounds, aliph ati c, t ertiary lations were based on carbon dose application of the homogenous surface alcohols, are not easily oxidised by predictio ns (obtained using the H SDM diffusion adsorption model (H SDM) for chlo rine or ozone (Lalezaty et al. 1986), model, see Cook et al. 2001 for details) predicting activated carbon doses required consequently activated carbon is currently for a 50% removal of MIB (eg from 20 at fo ur water treatment plants supplying considered the best technology for the to 10 ngL- 1) at a 50 ML per day flow, over the city of Adelaide. The work aimed to a period of 10 days. Although C3 is relatively effective at Table 1. Doses required for the removal of MIB from 20 to 10 ngL·1 for four short contact times, it would probably not activated carbons, and costs associated with dosing at a 50 ML per day flow for be used for taste and odour removal due 10 days. Myponga Reservoir water. to the high costs involved. As a low C1 activation coconut-based product, C4 is C3 C2 C4 PAC dose (mgL·1) expensive per tonne than the high less 16 31 26 38 activation carbon, C 2; however, there is PAC required for 10 days dosing (tonne) 8.0 15.5 13.0 19.0 no cost benefit associated with its use, as Cost for 10 days dosing (AUS$) 28 000 24800 41600 28 500 the doses required are higher. Although 24

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been shown to have an the cost of dosing with C 1 35000 effect on Rive r Murray is higher than that for C2, larg e PAC particle water. H owever, so fa r no the advantage of handling -t-_____• __s_m_a_l_l _P_A_C~ p_a_rt..:. ic_le_ _ ____,,, . ~- - 30000 other water has demonand storing smaller amounts ~ strated a decreased taste and of C1 may be more ~ 25000 1-- - - - - - - - - - -----:::;~ oe::,__ _ _ _ _ _ __ odour removal in chloriimportant for some water 0) nated water in the absence of suppliers. The use of similar C a residual. It has been :g 20000 dose predictions can allow -0 reported that the application auth orities to weigh up the 0 15000 -t-- - - ---:-#=---- --=-"""'= - - - - - - - - - - - of PAC at the point of advantages and disadvanci, addition of alum or other 0 tages and make informed () 10000 -t-- ---::l~ ~ !!:__ _ _ _ _ _ _ _ _ _ __ __ __ coagula nts re du ces the decisions regarding PAC adsorption efficiency (Najm application. 5000+- ----!:.__ _ _ __ __ _ _ _ _ _ _ _ _ _ _ __ et al. 1991). T he adsorption P AC particle size also of MIB and geosrnin are not plays an important role in 100 70 80 90 10 20 30 40 50 60 affected by high turbidity the adsorption of M IB and Geos m in inle t co nc entration (ngL"') levels alone. H owever, in a geosmin. Figure 2 shows the jar test where the PAC was cos t benefit associated with Figure 2. Cost advantage associated with t he smaller particle size added during alum floccuUS ING a particle size of (10 days dosing, 50 ML flow). lation, the turbidity of the 10 µ m co mp a r ed w ith water had a significant effect 23µ m, as a fu nction of required for taste and odour removal. In on the alum dose and also the removal of geosmin inlet concentratio n (dosing in a contrast, dissolved organic carbon (DOC) geosrnin and M IB (Cook et al. 2001). This 50 M L per day plant over 10 days). concentration and character both strongly reduction of removal efficiency is attributed affect the adsorptio n of M IB (Newcombe Clearly there is a parti cle size limi t to the binding of the PAC in the floe. T he et al . 1997; Coo k et al . 2001). below w hich ease of handling of the PAC effective contact between the water and the H OWEVER, Geosmin removal, and becomes an issue . A very small particle size PAC will depend o n the size and density therefore PAC doses, are not strongly may also result in removal diffic ulties using of the resultant floe; for example, more affected by DOC. To date, no clear con ventional methods, and possible breakefficient contact could be expected from relationship has been identified between thro ugh into the distribution system. T he a small floe with loosely bound particles, D OC concentration and PAC doses. As 10 µm median particle size has proven to than a large dense floe. The size and a general rule, an increase in DOC be optimum for the water treatment plants structure of the floe will be dependent on concentration ( or UV absorbance) will sup p lying Adelaide, using both conventurbidity, DOC, and alum dose. resu l t in an increased P AC dose tiona l an d di sso lved ai r flo t atio n requirement fo r MIB removal. Research tech nology. Conclusions into this aspect is continuing, with the aim P AC dose predictions can also be used T he first consideration for water of producing a "DOC facto r", which can to determin e when PAC application suppliers using activated carbon to control be used to modify PAC dose predictions. wou ld no longer be cost effective, and taste and odou r episodes caused by M IB Some water treatment processes affect oth e r, more advanced, techniques should and/ or geosrnin is choosing the most the ren1oval of taste and odour compounds be considered. Figure 3 shows cost effective adsorbent. In general, good using PAC. The presence of a chlorine estimates fo r dosing a high activation quality microporous carbons, such as residual has been shown to reduce the coconut carbon (C2) fo r MIB or geosrnin cocon ut or coal based, will be superior, adsorption of both MIB and geosmin fo r a prolonged period at one Adelaide although at shorter available contact (Gillogly et al. 1998; Lalezary-Craig et al. water treatment plant. T he diffic ulty of times the chemically-activated wood 1988: Newcombe unpublished data). Prerem.oving MIB compared with geosmin carbons may provide better adsorption chlorination where there is no residual is reflected in the cost of PAC dosing. ki netics, particularly fo r geosmin. present at the point of PAC application has If high concentrations of MIB were expected for several months each year, the Geosm in MIB wa t er authority could take a decision regarding other treatment options based on this type of analysis.

•

t---------:,--~-----~=------

When Will We Need To Change Our PAC Doses?

'....1 0)

.s C

O nce the appropriate PAC doses have bee n determined for a particular water source, the question to be answered is " H ow will changes in raw water quality and treatment processes affect PAC doses?". Alkalinity, hardness and pH do not appear to affect the adsorption of MIB and geosmin over the ranges generally encounte r e d in d ri nki ng wate r treat me nt, therefore changes to these water quality parameters will not affect the PAC doses

Cl)

u C

]i E

$120K-$1 40K $100K-$120K $90K-$100K $80K-$90K $60K-$80K $40K-$60K $30K-$40K $20K-$30K $10K-$20K $5K-$10K < $5K

20 6

Days

Figure 3 . Cost estimates for prolonged PAC dosing.

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Recommendations at a glance: Step 1 . Choose the right PAC, then determine appropriate doses for your water treatment plant PAC testing

i) Test a range of PACs, under conditions related to the individual treatment plant

ii) Use computer aids to determine the doses you need

Cost benefit analysis

i) Weigh up t he advant ages of lower dose against higher cost

ii) Decide whether an alternative treatment (such as GAC) wou ld be more cost effective over prolonged T & O episodes

In water treatment plan ts w here taste and odou r episodes are common, the homogenous su rface diffusion model (H SD M) ca n b e used to estimate powdered activated carbon dose requirements under a range of cond itions including inlet concen tration and plant fl ow rates (controlling PAC contact time). This information allows water suppliers to make informed decisions regarding treatment options, and in most cases a goo d quality PAC may be sufficient fo r th e mitigation o f the problem. It may also aid in the often diffic ult decision, "How m uch more will the cheaper activated carbon cost in the long run?". In cases of p rolonged episodes, and high inlet levels, an estimate o f the carbon doses requi red, and knowledge of the comm on tim e fram e over w hi ch t h e taste and odo u r compounds w ill be present, wiU allow a cost-benefit analysis of PAC application com pared to more advanced treatment processes. T his is information that most water authorities currently do not have. When PAC is the desired option, the H SDM p redictions can be ro utinely used for estimates of the required doses w hen the operators have knowledge of approximate inlet concentrati ons and available contact times. H owever, the PAC dose predictions must be used in combi nation with knowledge of the effect that water quality changes and w ater treatm ent chemicals have on the rem oval.

In general, an increase in D OC, often reflected in an increase of UV absorbance, a parameter more routinely analysed , w ill resul t in an i ncre ased ca rbon dose requi rement fo r M IB removal. Geosmin is less sensitive to changes in DOC quantity and quality, and no adj ustment in the dose may be required. For example, in Adela ide the major compou nd of concern is geosm in, and PAC dose predictions have been validated under conditions of a 100% increase in DOC concen tration. Pre-chlo rina tion is not recommended in situations where PAC is used for taste and odour mi tigatio n. Evid ence is clear that a chlorine residual can redu ce the adsorption of M IB and geosmin, and in at least one case, the effect on the natu ral organic material can lead to increased adsorption co mpetiti on , and reduced MIB adsorption. Again, geosmin is not affected by the variation in N O M character brought about by chlo rination . The application of PAC simultaneously with alum or other coagulants, a common practice, can result in a decrease in th e removal of both MIB and geosm in, and therefore an increased dose requirement. The magnitude of the effect w ill depend on the size and structure of the floe formed containing the PAC particles, w hich in turn is dependent on alum dose, turbidity, D OC concen tration, and colou r, if this is one of the criteria fo r alum dosing. In general terms, a higher alum dose, driven by an increase in turbidity, will probably

Recommendations at a glance: Step 2 . Know how PAC doses may change with the situation. (i- increase, NE - no effect) PAC dose geosmin

PAC dose MIB

i) PAC applied to 30 min prior to coagulation

ii) PAC applied simultaneously with increased coagulant dose

DOC/ UV absorbance Turbidity

Pre-chlorination

i) chlorine res idual present

ii) no chlorine residual present

WATER FEBRUARY 2002

lead to a h igher PAC dose requirem ent than predicted by the HSDM. In sum1nary, there is significant scope for the more cost-effective utilisation of powdered activated ca rb on for the m itigation of taste and odou rs, as well as a wider range of other micro-contaminants, using tools such as the homogenous surface d iffusion model (H DSM ), in co nj u nction with knowledge o f th e effects of water q uality and wate r treatment processes.

Acknowle dgements T he authors gratefully acknowledge the generous assistance given by Professor Vernon Snoeyink and D r Tom Gillogly in the application of the H SDM and the implementation of the radio-label method fo r M IB analysis. T he authors also thank P ICA Activated Carbon, and Lorn1ar Pacific for activated carbon samples and info r matio n , a n d Unite d Wa t e r In ternational fo r funding the research project during wh ich some of this inform ation was ob ta ined . Also Katri na Nitschke for much apprec iated editorial advice.

The Aut hors Gayle Newcombe and David Cook are research scientists at the Australia n Water Q uality Centre, a partner in the CR.C for Water Quality and T reatment, PMB 3, Salisbury, South Australia 5108, Australia, e-mail - gayle.newcombe@ sawater.sa.gov .au

References Cook D ., Newcombe G. & Sztajnbok P. (2001) The app lication of powdered activated carbon fo r MIB and geosm in removal: predicting PAC doses in fou r raw waters. W ater Research 3 5(5), 1325- 1333. G illogly TET., Snoeyink VL , H olthouse A ., Wilson CM. & Royal EP. (1998) E ffect of chlorine on PAC's ab il ity co adsorb M IB . Jo11r11al A111erica11 Water Works Association. 90(2), 107-114. Laleza,y S., Pirbazari M., & McGuire M. J. (1986) Oxidation of Five Earthy-M usty Taste and Odor Compounds. J. Am. Water Works Ass. 78(3), 62-69. Lalezary-Craig S., Pirbazari M ., Dale M ., T anaka T. & M cGu ire M . (1988) Opt imising the removal of geosmin and 2-methylisoborneol by powdered activated carbon. J. A111. Water f,1/orks Assoc. 80(3), 73-80. Najm I. , Snoeyink V., Galvin T. & Richard Y. (l 991) Control of O rganic Compounds w ith Powdered Activated Carbon. AWWA R F Report No. 90581. A WW A Research Foundation, D enver, Co. Newcombe G ., D rikas M . & H ayes R . (1997) The influence of charactetised natural organic material on activated carbon adsorption : ll Effect on po re volume d istribut ion and adsorpt ion o f M IB. Water Research 31(5), 1065-1073.

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SURFACE MIXING FOR DESTRATI Fl CATION: SIMULATING THE IMPACT D M Lewis, JD Brookes, JP Antenucci, M F Lambert Abstract An algorithm describing th e flo w fo r a pl ane plume was incorporated into the DYRESM one-dimensional lake and reservoir simulation model to simulate the action of raft-mounted mechanical surface mixers with draft tube diffusers (hereafter referred to as surface mixers). T h e algorithm was validated against extensive physical fi eld data collected at an artificially mixed South Australian water supply reservoir. The use of surface mixers for destratification and control of alga l growth is becoming increasingly popular, however, minimal research has been undertaken to determine the effectiveness and efficiency of such systems compared to more established methods such as bubble plume aerators.

Introduction Individual water bodies have unique seasonal populations of cyanobacteria and eukaryotic micro-algae, dependent o n meteorological and geochemical conditions. Excessive algal growth is likely to recur annually in those water bodies that have a history of algal blooms if there are minimal changes in the physical and chemical conditions (Sivonen & J ones 1999). To control the abundance of sc um-for min g cyanobacte ria and improve water quafoy, the physical and geochernical conditions within the water column can be altered. Thus, artificial destratification is often used to improve water quality (Schladow & Fisher 1995, Brookes et al. 2000), and has been shown to r educe the growth of scum-forming cyan obacteria in reservoirs and lakes (Steinb erg 1983; Visser et al. 1995; Steel & Duncan 1999). The CRC for Water Quality and Treatment, in conjunction with SA Water, is evaluating a novel technique to control the growth of cyanobacteria

.... ....

13 m

Figure 1 . Schematic diagram of the surface mixers, arrows indicate the direction of flow .

in drinking water supply reservoirs. The technique incorporates reservoir mixing using surface mixers in combination with an aerator (Bu rch et al., 2000, Kirke 2000). Surface mixers have been installed at H appy Valley and M yp onga Reservoirs, South Australia, complementing the ex isting aerators, for destratification and control of cyanobacterial growth. T he use of mechanical mixers for destratification is becoming increasingly popular; however, minimal

research has been undertaken t o determine the efficiency and impact of mechanical mixers. The obvious benefits include the range and flexibility of mixers available and eco nomic savings. To destratify reservoirs large quantities of water need to be circulated, subsequently physically large surface mixers have been manufactured for Myponga and H appy Valley Reservoirs. T he surface mixers were designed and supplied by an Australian Company, Water Engineering and R esearch Solutions (WEARS Pty Ltd. ). The surface mixers (Figure 1) are driven by 4 kW motors pumping the top 1-2 m of surface water, down through a draft tube (diameter 4.9 m, length 13 m), via an 8-blade impeller with a diameter of 4.9 m . The blades have a pitch angle of 15° and the impeller rotates at 10 rpm. The flow through each su rface mixer is approximately 3.5 m 3s1

The chosen site for the analysis was Myponga reservoir (S 35° 24', E 138° 25'), Figure 2, situated -70 km so uth of Adelaide, on the Fleurieu Peninsula, South Australia. M yponga reservoir is a highly managed water body with regular chemical (CuSO 4) dosing to manage cyanobacteria growth, and prolonged artificial mixing. T he surface mixers and aerator at Myponga reservoir are required to be operated continuously during the summer months. Therefore to fully analyse the effectiveness of the surface mixers, numerical modelling has been undertaken.

Surface Mixer Algorithm

Soult1t1m Ocean

Figure 2. Location of Myponga Reservoir.

T h e algorithm representing the behaviour of the surface mixers was incorporated into DYRESM . The algorithm is based on a buoyant plane plume, with the line geometry correWATER FEBRUARY 2002

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Obsenrcd temperature

Aern.tor and surface mixers 24

30 22

22 25

,;;,

18 \::.

.!I

t •s

16 20

...t

'.§:Zo

18 \::.

-r £,

..l

...

30 09/01/99

12101/99

03/01/00

0 5/31/00

08/31/00

12101/99

Time (mm/dd/yy)

Figure 3. Observed temperature profile from Sep 1999 to Sep 2000.

spending to the base of the draft tube. The surface mixer draws water from the top 1-2 m of the water body, which emerges as a radial plume at the base of the draft tube. T he density of the inflow to the surface mixer is assumed to be less than or equal to the ambient water at the exit of the draft tu be. As the plume rises through the water column it entrains water from the surrounding environment, thus increasing the density of the plume. As the density increases the plume velocity decreases until the point of neutral buoyancy is reached where horizontal insertion occu rs. The algorithm uses the following assumptions: No initial momentum exists in the surface water entering the surface mixer.

03/01/00 Time (mm/dd/yy)

0 5/31/00

08/30/00

Figure 4 . Simulated temperature profile from Sep 1999 to Sep 2000. The surface mixer and aerator algorithms were operated between Oct 1999 to Apr 2000.

The available impeller energy is always able to pump the surface water down to the outlet of the draft tube. • The flow exiting the draft tube has no jet characteristics The attributes of the internal draft tube flow are the same as the surface water.

Simulation Results Myponga reservoir was simulated with DYRESM, using the surface mixer and aerator algorithms, from September 1999 to September 2000 using hourly averaged meteorologica l data generating a daily ou tput at midday. The observed and simulated temperatu re profiles are shown in Figures 3 and 4 respectively.

No aerator or surface mJxtn

With the successful validation of the surface mixer algorithm (Lewis et al. 200 1) the different combinations of aerator/surface mixer operation could be investigated. Figures 5 and 6 show the results from the following operational strategies: 1. N o artificial m ixing 2. Two surface mixers Under no artifi cial mixing excessive surface heating and permanent stratification occurred during the summer months. These conditions would be ideal fo r buoyant cyanobacterial growth. When the two surface mixers were implemented in the code deepening of the surface mixed layer is evident. The use of the surface mixers is to impact the surface mixed layer directly and remove

Surface mixers

30 22

22 25

,;;-

12/01/99

03/01/00 Time (mm/dd/)')')

05/31/00

08/30/00

Figure 5. Simu lated tempe rature profile with no artificial mixing.

WATER FEBRUARY 2002

,;;,

-,.=~

,.-a= 18 \::. i

18 \::,

...

12101/99

03/01/00

05/31/00

...

08/30/00

Time (mm/dd/yy)

Figure 6. Simulated temperature profile using two surface mixers operated between Oct 1999 and Apr 2000.

WATER buoyant cya nobacteria from the light. Figure 6 shows that th e use of the two surfa ce mixers does impact the su rface mixed layer, deepening it significa ntly.

Conclusions T he surface mixer algorithm has been successfully incorporated into DYRESM an d validated against Myponga reservoir fi eld data. This study has shown that artificial mixing via surface mixers has a significant effect upon the thermal structure of a water body. The two su rface mixers at Myponga do have an impact of the surface mixed layer, as is their intention. Numeri cal simulation of the physical response of reservoirs to artificial mixing can be used as an effectiv e tool with re se rvoi r management. T he combined use of aeracors and surface mixers to manage water quality has great potential and deserves furth er investigation. Each water body is unique and numerica l modellin g can greatly assist in the planning and design of an appropriate destratification system. T he investigation of the surface mixer impact on cyanobacteria growth has not been disc ussed here in any detail but is currently be in g inves tigated with mm1erical modelling using DYRESMCAEDYM and field observati ons.

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Ki.rke, B.K. (2000) C irculation, destratification, mix ing and aeration: w hy and how? f,llater 27(4) 24-30. Lewis, D. M. , Antenucci,) P., Brookes, ). D., Lamb ert, M. F. (2001) Numerical simulation of surface mixers used for destrat ification of reservoirs, fotematio11al

Co11gress 011 Modelling a11d Si11111/atio11, MODSIM 2001, 311-317. Schladow, S. G . & Fisher, I. H. (1995) The physical response of temperate lakes to artificial descratificacion. Li111110/ogy and Ocea11ograph y. 40(2), 359-373. Sivonen, K. and Jones G. (1999) Cyanobaccerial Toxins. In: Toxic Cya11obacteria i11 Water (eds I. Chorus & J. Bartram), 41 - 111 , E & F. N. Spoon , London, . Steel, J. A. and Duncan , A. (1999) Modelling the ecological aspects ofbankside reservoirs and impli ca ti ons fo r m a na geme nt , 1-lydrobiologia 395/396 , 133-147. Steinberg, C. (1983) Effects of artificial destracification o n phytoplankton populations in a small lake, Jo11mal of Pla11kto11 R esearc/1 5, 855-864. Visser, P. M., Ketelaars, H. A. M. and Luuc, R.. M. (1995) R educed grow th of the cyanobacterium Microcystis in an artificially

mixed lake and reservoir, Water Scie11ce a11d Tecl,110/ogy 32 , 53-54.

Authors David Lewis is a CRC Water Quality and Treatment PhD student based at the University of Adelaide, Department of En v ir o nm enta l Engineering. Ph (08) 8303 5033, e-mail dl ewis@c iv e ng.adelaid e .e du. au. Dr Justin Brookes is research scientist with the C R C for Water Quality and Treatment, PMB 3, Salisbu ry, SA, 5108. Ph. (08) 8259 0222, e-mail justin.brookes@sawater. sa.gov .au. Dr Jason Antenucci is an Environmental Engineer and Limnologist at the Centre fo r Water R esearch, U niversity of W estern Australia. Ph. (08) 9380 2048, e-mail antenu cc@cwr.uwa.edu.au . Dr Martin Lambert is a Senior Lecturer at th e Univers i t y of Adelaid e, D e partm e n t o f Environmental Engineering. Ph (08) 8303 5838, e-mail mlambert@civeng.adelaide.edu.au

Acknowledgements The authors w ish to thank the Ce ntre fo r Water Research, University of W estern Australia, for all owing the u se of DYRESM-CAEDYM for research purposes, and in particular Prof. Jorg Jmberger fo r useful discussion and Mr A lan lmerito fo r coding the surface ,nixer algorithm. W e also thank Dr John Vitkovsky and Mr Rudi R egel for field assistance, and Dr D ennis Steffensen and Mr Mike Burch from the Cooperative R esearch Centre for Water Quality and T reatment with the 'Artificial Mixing fo r D es cratifi ca t io n and Control of Cyan obacteria Growth in R eservoirs' proj ect 2.5.1. And last but not least we acknowledge the innovative surface m ixer design by Stephe n E lli ott, WEARS Pty Ltd.

References Brookes, J. D., Burch, M. D. , T arrant, P. (2000) Artificial dest ratificat ion: evidence for improved water quality, Water, 27(4) 18-22. Burc h , M . D. , Brookes, J. D ., Tarrant, P., D eUaverde, P. (2000) Mixing in up with Blue-Green algae, Water, 27(2) 2 1-22 .

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ASSESSING MICROBIAL RISKS FROM DRINKING WATER: TWO STUDIES M I Sinclair P11blic health researchers i11 the CRC for liVater Quality a11d Treatment recently completed the second of two major projects assessing health risks from microbial pathoge11s in drinki11g water. The co-authors involved were: lvlE Hellard, B Robertson, CK Fairley, AB Forbes,] Willis, MCK Veitch, MD Kirk and D Cunliffe. This article provides an overview of the research findings and their i1nplicatio11s for the water industry.

1. The Water Quality Study The reasons for the study

The fi rst project, the Water Quality Study, was designed to assess whether microorganisms in Melbourne's chlorinated but unfiltered surface water supply were a significant cause of gastroenteritis in the community (Hellard et al. 2001). The proj ect was prompted in part by a Canadian study published a few years before format ion of the C R C for Water Quality and Treatment. ln this study, gastroente ritis rates were compared between families randomly allocated a point-of-use reverse osmosis (R O) filter and families drinking plain tap water from a supply that met conventional microbiological quality standards. They found that the gastroenteritis rate was signifi cantly lower in families receiving RO filtered water, and suggested that up to 34% of conununity gastroenteritis was attributable to microorganisms in the treated water supply (Payment et al. 1991) . T his conclusion was quest ioned however, because of the "unblinded" design of the study where participants knew whether they had received the water treatment intervention. A number of health studies have shown that the "placebo effect" of a sham treatment (such as a pill which does not contain an active ingredient) can produce a subjective improvement in up to 60% of patients with conditions as diverse as postoperative pain, seasic kn ess and the common cold. T h us the participants' awareness of the water treatment intervention in the Canadian study may have differentially influenced the reporting of gastroenteritis in the two groups. Around the same time, concerns were also being raised abou t an increasing number of waterborne disease outbreaks from Cryptosporidi11n1and Ciardia, culmi-

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nating in the l arge Milwaukee Cryptosporidium outbreak in 1993 . Such events prompted some commentators to propose that filtration of all surface water supplies was necessary to reduce risks from these protozoa! pathogens. The characteristics of the Melbourne water supply are unlike most large cities in that the catchment area is protected from human influence, so that raw water microbiological quality is very good. Nevertheless, as Cryptosporidium species potentially infective to humans were believed to be carried by virtually all mammals, there was a possibil ity of waterborne disease transmission. While most cases of gastro enteritis are mild and of short duration , some infections are more severe and may lead to serious health consequences and rarely death. Gastroenteritis has a signifi cant economic cost both in terms of medical care and loss of productivity from absent ee ism. If a significant fraction of gastroenteritis were due to drinking water, this would represent a substantial burden of avoidable illness and cost to the community. Thus the CRC believed a ri gorous epid emiological study was needed to address this issue . The study design

The Melbourne stu dy u sed an improved design incorporating double blinding so that neither the researchers nor the participants were aware of the water treatment intervention. This design minimises the potential for bias in data reporting or recording. Six hundred Melbourne families (2811 people) participated in the study for an 18 month period from September 1997 to February 1999. The fa milies were recruited by advertising through primary schools, local newspapers and direct mailing to households. Each family was randomly allocated a real or sham water trea tment unit (WTU ), which was installed th e kitchen of their home and supplied water through a separate tap. The real WTUs consisted of a 1 micron absolute depth filter to remove protozoa (99.95% removal) and an ult ravio let unit to kill bacteria (99.9999%) and viruses (99.99%). Sham WTUs were identical in appearance but were internally modified so that they had

no nucrobiocidal effect. The families were asked to use water from the WTU for drinking, making ice cu bes and cold drinks, and was hing foods which would be eaten w ithout cooking. During the study, participants were asked to record any gastroe n teritis symptoms in a Health Diary, and to collect stool specimens for analysis if they experienced gas tr oenterit i s . Questionnaires on water consumption from the WTU and other sources were also administered on three occasions. At the end of the study, the success of blinding was assessed by aski ng participants whether they believed their water treatment units were real, sham or whether they did not know the type. The results

The compliance of participan ts w ith the study requirements was very high, w ith on ly 41 of the 600 families failing to complete the study. The majority of dropouts were due to people moving house out of the area, and most importantly, the number of dropouts in the real and sham groups was not significantly different (20 and 2 1 respectively) . Over 90% of H ealth Diaries were returned by participants. Blinding to WTU status was successful with 40.6% of participants saying they did not know which WTU type they had been assigned, 33.8% no minating the correct WTU type and 25.6% nonunating the incorrect WTU type. Since there were equal numbers of WTUs of each type, one would expect an equal number of correct and incorrect guesses. Correct guesses were slightly more common in the real WTU group; this may have been due to chance or may suggest that a minority of people became unblinded in tlus group. Water consumption from the WTUs was the same in both groups, with 85% of unboiled water being consumed from the WTU tap. Participants collected 795 stool specimens during episodes o f gastroenteritis, and the rate of isolation of pathogens was not signifi ca ntl y different between the two groups. Comparison of gastroenteritis rates showed no significant difference between the two groups (rate ratio 0.99, equivalent to 1% difference in gastroenteritis rates), and there was also no difference

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in the duration of ill ness episodes, or in the p ercentage of people seeking medical treatment fo r gastroenteritis. Conclusions

Th e results indicate th at microorganisms in drinking water are not a significant cause of gastroenteriti s in M elbourne, since removing them by point-of-use trea tment does not affect illness rates. This result is likely to apply to other water supplies with similar characteristics. The successful co mpletion of t h e study w ith a low withdrawal rate and successful blindi ng demonstrates that stringent epidem iological methods can be successfully appli ed to m easure the relationship between water quality and health.

2. Case-control studies of cryptosporidiosis The reasons for the studies

Wh ile th e Water Quality Study showed that there was no differe nce in overa ll rates of gastro enteritis comparin g no rmal tap water with highly treated water, it did not have adequate statistica l power to test whether water was a significa nt source of any si ngle pathogen. T he highl y chlorine resistant protozoa C ryp tosporidiu,11 par1111111 is probably the most important pathogen to co nsider for unfiltered wa ter supplies, and t hi s o rganism may pass through fil tratio n plants if o perating conditions are suboptimal. Among the 795 gastroenteritis stool specimens exam ined during the W a ter Quality Study, onl y 13 cases of cryptosporidiosis w e re de t ected. T h e refore to accumul ate a suffi cient number of cryptosporidiosis cases to test for a di fference in risk in a randomised trial, about 120,000 fa milies would need to b e enrolled. As this is clearly not feasible, a different kind of epidemiological study is needed. Methods

The ap p ropriate epid em iological design to address this question is a caseco ntrol study. In such a study, people with the disease of interest (cases) are co mpared to p eople without the disease randoml y sel ected from the sa me population (controls). Both groups of people are asked about exposure to risk fac tors w hich may be relevant to developing the disease. If an exposure is truly associated with the disease, it should be significantly m ore common in cases than controls. Two separate case-control studies were carried o ut; one in M elbo urne and o ne in Adelaide (Robertson et al. 2002) . These two cities were chosen to represent

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the opposite ends of the water quality and tre atm ent spect rum of Australian metropolitan water suppli es; M elbourne has h igh quality source water with minimal treatment (chlorination only), Adelaide has poor quali ty source water from unprotected catchments and has full conventio nal water treatment (coagulatio n , sedime ntation , filtration and chlo rination). O ther maj or population centres in Australia have drinkin g water su ppli es between these extremes. Cases (people with Cryprosporidii,1111 dete cted in stool speci m en s) w ere identi fied from pathology laboratory reports to the D epartments of Human Serv ices in Victoria and South Australia, and age-gend er matched con trols were recruited from the general population usin g th e electro n ic White Pages telepho ne direcco ry. Cases comp leted a telephon e qu estionn aire covering the two-week incubati on pe riod b efo re symptom onset, and matched contro ls completed the sa me questionnai re fo r an equivalent tim e period. T o increase th e statisticaJ power of the study, 4 controls were matched to eac h case. Th e questionnaire assessed associations between illness and the type and quantity of water consumed , consumption of

selected foods, travel, recreational water activities, gardening activities, contact w ith other people with gastroenteritis, work with young children or disabled people, and contact with sewage, domestic and farm animals. Results

In Melbourne 271 cases were reported over 35 months (June 1998 - M ay 2001), and 239 were interviewed. Of these, 201 were included in the analysis, 24 were excluded as they formed disease clusters w ith one of the included cases, 14 were excluded as they were interviewed more than 8 weeks after symptom onset. Disease clusters were defined as cases with onset dates within 14 days of a primary case and who resid ed in the sa me hou se h o ld, or a tte nded the sa m e swimmin g pool, or atten ded th e same childcare ce ntre. In Adelaide 173 cases w e re r e ported o ve r 31 m onths (November 1998 - M ay 200 1), and 161 were interviewed. Of these, 134 were included in the analysis, 22 were excluded as th ey formed disease clusters and 5 were excluded as they were interviewed more than 8 weeks after symptom onset. Both citi es repo rted highe r ~ase numbers in late summ er co autumn each

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WATER

QUALITY

year. The median age of cases was 11 years in M elbourne (range 0-81 years) and 10 years in Adelaide (range 0-83 years). T he age distribution was bimodal with peaks in the under 5 years and 20-39 year age ranges. Cases were equally distributed between the sexes. Cryptosporidiosis was no t significan tly associated with the consumpti on of plain tap wa ter in either M elbo u rne or Adelaide . Similarly, there was no significant dose-response relationship between the amount of water consumed and th e risk of i!Jness for either city. For Melbourne, statistically significant ri sk fac t o rs id e nti fied we re swimming in public pools, household con tact with people with diarrhoea, and calf co n tact away fro m home. For Ad elaide, statistically significant risk fac to rs were hou sehold contact with people with diarrhoea, calf contact away from home, and the consumption of unboiled water fro m a rural river, lake or dam within Australia.

Conclusions These are among the first case-control stu dies to examine risk facto rs fo r cryptosporid iosis in an industri alised counny. The results indicate that dLinking

AND

water is unlikely to be a major cause of c r yptos poridio sis in the major m etropolitan centres of Australia. W e fo u nd that the risk factors for infection were generally similar for both Melbourne and Adelaide despite vastly different water supplies. These included Lisk factors commonly associated w ith outbreaks of disease, most importantly, swimming in public pools and person-to-person transm1ss1on. The cases included in this study represen t o nly a min o rity of all cryptosporidiosis cases in the community, since only peopl e with relatively severe symptom s are likely to seek m edical attentio n and have a stool specimen examined . Ho weve r, th e selec ti ve recruitment of people with severe illness is unlikely to affec t the findi ngs on risk factors since current evidence in dicates that each individual strain of C. parvum may produce symptoms ranging from mild to severe gastroen teritis. Therefore we have no reason to suppose that risk factors for m oderate to mild cases are di fferent from those for severe cases.

Summary Both of these studies have contributed to a better u nderstanding of waterborne

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TREATMENT

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disease risks in developed nations. T he Water Q uality Study team were awarded the Victorian Dept of Human Services 2000 Award for Excell ence fo r Public H ealth R esearch for their work on the study. M embers of the team are ac ting as advisors to a U S research group wh ich is presently undertaking a study of similar design in the city of D avenport, Iowa. T he raw water supply to D avenport is of lower quality but is subj ected to conventional w ater treatment and filtration in addition to chlorination. The Davenport study has been fund ed by the US E PA as part of a program to assess the m agnitude of w aterborne disease in the US.

References Payment, P., L. Richardson, Siemiatycki, J. , D ewar, R. , Edwardes, M ., and Franco, E . (1991). A randomized ttial to evaluate the tisk of gastrointestinal disease due to consumptio n o f drinking water meeting current microbiological standards. A 111erica11 Jo11mal of P11blic Health 81 (6) : 703-8 . H ellard, M. E ., M. I. Sinclair, Forbes, A. B. , and Fairley, C. K. (2001). A rando mized, blinded, controlled trial investigating the gastrointestinal health affects of drinking water quality. E11viro11111e11ral I-lea/ti, Perspectives 109(8): 7738. This pape r can be downloaded from the Publications section of the C R.C w ebsite: www.waterquali ty.crc.org.au R obertson B., Sinclair M .I., Forbes A.B. , Veitch M .G .K., Kirk M .D., Cunliffe D. , Willis J., and Fairley C. K. (in press). Casecontrol studies of sporadic c1y ptosporidiosis in Melbourne and Adelaide, Australia .

Epide111iology a11d !1ifectio11.

Acknowledgements This research was suppo rted by the Cooperative R esearch Centre for Water Quality and Treatment, the Water Services Asso ciation of Australia, the D epartment of Hu man Services Victoria, M elbourne W ater C orporation, City West Water Limited, South E ast Water Limited and Yarra Va!Jey Water Limited.

The Authors Martha Sinclair, Margaret Hellard, Andrew Forbes, Brent Robertson and Jessika Willis are researchers from the CRC in the Depa rt men t of Epidemiology and Preventive Medicine at Monash University. Christopher Fairley (formerly of M onash U n iversity) is now located in th e D epartment of Public H ealth, University of Melbourne. Martyn Kirk (form erly of the D epartment of Human Services Vi ctoria) is now at the Australia N ew Z ealand Food Authority. Mark Veitch is at the Microbiological Diagnostic Unit, University of Melbourne and David Cunliffe is at the D epartment of Human Services So uth Australia. Email m artha .sin cla ir@ med.monas h. edu. au

ENVIRONMENT

DESIGNING A MONITORING PROGRAM FOR ENVIRONMENTAL REGULATION: PART II MELBOURNE WATER CASE STUDY W Paul, N T Diamond Abstract W hile we'd like to chink that decisions regarding co mpliance w ith a standard are blac k and white , they can in fact be incorrect owing co the inevitable presence of sampling error. T he risks (i. e., probabilities) associated with decision errors can be as high as 50%, which would surprise mo st p eople given the p otential consequences of such errors. T hese risks, however, can be managed through the tho ughtful design of the monitoring program, treatment process, and perhaps the regulation . In this second part of a two - part seri es, a case study from M elbourne Water's W estern Trea tment Plant will be d iscussed.

Introduction P art I of this two-part series, which was pu blished in the O ctober 2001 issue of Water, described the nature of decision errors in c ompliance assessment and the statistical th eory underlying the operating

characteristic curve (OC curve), which is a tool that can be used to evaluate different strategies fo r controlling the risks of decisio n errors. Part II of this seri es discusses a case study fro m Melbourne W ater's W estern T reatment Plant. W estern T rea tment Plant (W T P) discharges treated effluent to Port Phillip Bay via four EPA licensed o utlets. T he EPA licence specifies limits and sampling frequ encies for a range of environmental indica tors, but th e decisio n error ri sks associated with assessing com plian ce had not been evaluated fo r the prescribed monitoring programs. A study was carried out to exa mine the effect of sa mpling fre qu e n cy on th e prob ab il it y o f co mp liance with current and fut ure EPA limits for ammon ia- nitrogen (N H r N ) (similar studies have been carried out fo r BOD 5 , C BOD 5 and SS ), and to determine the design effl uent quality fo r plant augmentations that w ere to be und ertaken. Interestin gly, M elbo urne

W ater has a corporate target of 100% complia nce with EPA Li cence li nties (i. e., the risk of a type I error must be extremely small) and th is can have considerable co nsequ en ces for th e cost of their monitoring programs and , perhaps mo re imp o rtantly , fo r the des ign effl ue nt quality of th eir lagoons th at are to be retrofitted with supplementary activated sludge plants. T he operating characteristic curve (O C curve) was used to exami ne the probability of compliance for a range of operating levels (i. e., N H 3-N population medians) and to study the effect of various decisio n rules, with different sampling freq uencies and critical values. T he obj ective was to develop a nu mber of options for controlling the risks o f decision errors. As discussed in Part I, the interpretatio n of the regulato r's standard can make quite a difference to the magnitudes of decisio n erro r risks. This paper begins with the assum ption that th e

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ENVIRONMENT

.sz

35 25

~ ---------- --- -------- ---- --- --- -~

"" 5 z

-5 1/07/80

1/10/80

1/01/81

1/04/81

1/07/81

Figure 1. NH 3-N time series for the financial year 1980-81 with the interpolated 1-d values shown as a solid line.

standard is expressed as a critical value and then considers the effect on decision errors when the standard is interpreted as a parameter value. The method used to develop the OC curves is empirical and is based on the bootstrap si111Hlatio11: a theoretical approach, like that taken in Part I, is not possible in this case because th ere is currently no statisti cal theory dealing with serially correlated data and standards that are expressed in terms of a median and maximum rather th an a mean. A limitation to the emp irical approach, however, is: How do we evaluate a sampling frequency of once per day when we only have weekly data? To address this problem, we devised a method, based on theo1y of time series models, to interpolate daily observations from the weekly data. The operating characteristic curve is based on the logic of hypothesis testing, which was developed in the early part of the last centuty as a means of inferring from samples to populations. In the water industry, assess ing compl iance with standards always involves sampling and should , therefor e, be approached in the manner of a statistical hypoth esis test, whic h accou nts for the uncertainty caused by sa mpling variation. The risks associated w ith decision errors in hypothesis testing are real and shou ld be acco unted for w h en designing a monitoring program, effluent quality, or environmental regulation.

Statistical Methodology Bootstrap simulation

Bootstrap simulation comes from an area of statistics known as "Computerlntensive Statistics", so named because of the ma ssive compu tations required . Co mputer-i ntensive m ethods replace inferential methods that require the need for certain unverifiable assumptions to be made regarding th e distribution of the parent population. A more complete discussion of bootstrap simu lation is beyond the scope of this paper and the 34

WATER FEBRUARY 2002

reader is referred to Diaconis & Efron (1983) for an explanation of the basic bootstrap procedure and to H esterberg (1997) for a discussion on bootstrapping long memory processes. For this analysis, 20 years of weekly data were available (1980-81 to 1999-00). The data, which were measurements of NHrN made on grab samples taken at roughly the sam e time each week, appeared lognormally distributed and were serially co rrelated at sh ort lags and seaso nal lags (w ith a p eriod of 12 months). Further, th e data were reasonably consistent from year to year, indi cating that the pro cess was approximately in a state of statistical control, so it can be assumed that each sample (i.e., each year's worth of data) came from an identical population. T he weekly data for the 20-year period X = {X;, 1 ~ i ~ 1040} were divided into 80 blocks B1, ... ,Bso each covering 13 consecutive weekly observations (i.e. 3 months), where B; = {X;1, ... , X;13} is a block oflength 13 and X;; is the/' observation in block i. The blocks were then ranked according to th e one-step-ahead predictio ns from the end of each block (based on a seasonal AR.IMA model fi tted to the 20 year data set) , which quite reasonably reproduced the seasonality in the process. A simulated tim e series of length 1000 years was then built using an algorithm given by Hesterberg (1997) for rank- matching blocks. The block indices (i. e. block numbers, 1 to 80) that comprised the simulated series were uniformly distributed, indicating that all blocks had an equal chance of being selected. Producing a monthly time series from weekly data

A time series of monthl y observations was obtained by selecting every fourth observation from the weekly data. Interpolating daily results from weekly data

To investigate the effect of a shorter sampl in g interval when only weekly data

were avai labl e, a method was developed to interpolate daily observations from the observed data: • The S-Plus function st/ (S-PLUS 2000 Programmer's Guide) was used to decompose the NHrN series into its seasonal and remainder components . The st! fun ction decomposes a time series into freq uency components of variation by a seq u ence of local regression smoothings. • The r emain d er co mp one n t w as modell ed as an ARIMA (AutoRegressive Integrated Moving Average) process. An ARIMA(0,1,1), or IMA(l,1), mode] was identified and fitted to the data. From theo1y on IMA processes, the model coeffi cients and residu al variance can be obtained for any sampling interval longer than th e observed interval (Box & J enkins, 1976, p. 486-491) . If it is assumed that the remainder components also follow an !MA process at sampling intervals shorter than the observed interval, then the reverse is possible. Th is assumption was reasonable in this case beca use th e hydraulic residence times in the lagoons were in the order of 60-90 days, and the weekly cycle in influent flowrate, fo r example, is not detectable at the ou tlets because of mixing and attenuation within the lagoons. Therefore, the coeffi cients and residual variance for a sampling interval of 1 day were calculated from the coefficients and residual variance for the 7-day interval. A robust estimate of the residual variance for the 7-d interval was used, wh ich was obtained by tri1111n ing 2.5% from each tail of the distribution. (Th e value of 5% for the trimming percentage seemed appropriate given the presence of a few large deviations.) The new model was used to simulate the remainder component for a sampling interval of 1 day, while retaining the original remai nder component. • Daily values for the seasonal component were obtained with the linear interpolation function approx in S-Plus. • The daily seasonal and remainder components were then combined to fom1 the NHrN series w ith a 1-d sampling interval. This procedure retained exactly the original observations made at 7-d intervals. Some of the interpolated values were negative in sign, bu t these can be interpreted as non-detects (i.e., " less thans"). To ill ustrate the outcome of this procedure, Figure 1 shows one year of the NHrN series with both the observed 7d values and the values interpolated at 1-d intervals.

ENVIRONMENT

Operating characteristic curves OC cu rves give the probability of compliance that could be expected if the process leve l (i.e., median NHrN concentration) were shifted up o r down to n ew operating, or median, levels. Calculati ng the probability of compliance at n ew median levels (for each of the I, 7, and 28 day data sets) was achieved by transforming the simu lated data: by mulciplying them by the new median level and dividing by the actual median level. T his approach assumed that the eilluent data are lognormally distributed and, therefore, that they exhibit heterogenous var ian ce on the unlogged scale. Lognormality and heterogenous variance are comm on features of environmental data (Berthouex et al. 1978). Finally, for eac h new median level, the percentage of data complyi ng with the critical valu es (i. e., med ian and maximum) was determi n ed and plotted on the OC curve.

0.08

0.02 0 00 +-J___'-r'L-1-+--L-'-,r'--'--+-.1.......J4-'-

-l

ooo+-~-"'~:::t;:L..J..+J...J.,-L.L.+J....i.,.L.L.4--l

Table 1. Current and future EPA limits for NH 3-N (all units are mg/L) Median

Maximum

25 10

40 30

5 w ~ ~ ~ ~ ~ ~ NH,-N Annual Maximum (mg/I.) . 28 d nmpllng lnwrval

0.12

006

f.!l o.08

.!lo 04

0 00 +-.C:l.,--L.l-,1.-1....JL,....L....L.,l-J___l:!==>--I o 6 w m ~ ~ ~

0.00

NH,-N Annual Median (mg/l)- 7 d sampling l!Urval

008

foo6

0.00

s o

5 w ~ ~ ~ ~ ~ ~ NH,·N Annua l Maximum (mg.\.) . 7 d umpllng lnltrval

0.06

I-

0.02

008

.!l 0.04

0.04

0.02

0. 10

T he current and futur e EPA limits for N H rN are given in Table 1. T he E PA Licence also speci6es a sampling frequency of weekly. Histogram s of an nual statistics fo r N H r N , derived from the simu lated data, are shown in Figure 2 for samp ling intervals of 1 clay, 7 days, and 28 days. It is apparent i n Figure 2 that there is a narrowing of the samp li ng distribution of medians as sample size increases (or sampling freq uency in creases). T his is to be expected, according to the centra l li mit theorem, but it was not entirely expected that the difference would be so slight. Diamond (1998) notes that sample size has a mu ch less pronounced effec t on the variance of the sampling distribution when the data are highly autocorrelated. Th e samplin g distribution of annual ma ximums (Figure 2), on the other hand, behaves quite differently from the annual m ed ians in that it becom es much heavier in the upper tail (i. e., left skewed), and thi s mea ns tha t the probability of co mpli ance wi ll initially drop more sha rply at higher sam.pling freq uenc ies. Furthermore, the 'popu lation' maximum (i .e., the maximum of the entire 20 year data record) is near th e EPA limit, so the

Current Limits

6 ~ ~ ~ NH,-N Annual Median (mg/LJ- 28 d samplng lnltrv11

008

Results and Discussion

Future Limits

012

.!lo.04 ~

0 .02

n ~

0.00 ~

NH,•N Annual Median (mg/l) • 1 d u mpllng kUIYII

..,..[ o

w m ro

NH,·N Annual Maximum (mg.\.). 1 d umpbng lnltrval

Figure 2. Histograms of NH 3 -N annual medians and maximums for sampling intervals of 1 d, 7 d, and 28 d. The dashed vertical lines indicate the 'population ' values, i.e., the median or maximum obtained for financial years 1981-2000. Th e solid vertical lines indicate the current EPA limit.

sa m pling distribution of maximums w ill dom inate the shape of the OC curves in the vic inity of the EPA limit. OC curves fo r the c urrent and future EPA limits and sampling periods of 28 d, 7 d, and 1 d, are shown in Figure 3 and Figure 4. These cu rves are more complicated than those show n in Part I of this article: the curves below are based on two limits (median and maximum) rather than one. This makes the curves a littl e more difficult to interpret, because even though the popu latio n m edian may comply, the maximum may not . From the OC curves shown in Figure 3, if it is assumed that the population median for the effl uent N H rN is equa l to the median of the 20-year data set (from the la w of large numbers), the probability of compliance is almost l 00% and the type I error risk is almost 0% for the c urrent EPA limits. In thi s case, the sa mplin g fre quency cou ld be reduced to monthly

witho ut affecting the compliance rate; though , the effect on the EPAs risk (i. e ., the type I I error risk) and on other monito ring objectives such as process monitorin g an d p l ant-cap a c i ty m a n age m ent would need to b e conside red. W ith respect to the fu ture limits for N H rN (Figure 4), the current process would clearly be noncomplia nt. From Figure 4 it can be seen that the future treatment process would need to achieve an N H rN median level of about 5 mg/L to ensure a probabihty of compliance close to 100% (assuming, of co urse, that the new process folJows a similar model to the current process). Furthermore, increasing the sampling fr equency wo uld have little effect on the probability of complian ce: there is very little d iffe rence between th e OC curves obtained at d ifferent sampling frequ encies, and this is probably due to the smaller pro cess va riance at lower WATER FEBRUARY 2002

ENVIRONMENT

median levels and the high degree of serial correlation in the data . T he OC curves in Figure 3 and Figure 4 assume that the EPA Licence limits are expressed as critical values. If the limits were instead interpreted as parameter values, the type I error risk would be reduced . To demonstrate this, two decision rules have been proposed (i. e ., proposed by the au thors and not by M elbo urne Water), which differ in terms of sampling frequency. Both rules assume an effect siz e of 5 mg/L for both the median and maximum criteria, and both use critical values of 12 mg/L for the median and 32 mg/ L for the maximum. OC cu rves for these decision rules are given in Figure 5. The first thing to note is that when the null hypothesis is true (i.e., the effiuent complies with the 10 mg/L standa rd for t h e m ed ian ) th e maximum type I error risk (i.e., the risk that the effiuent will be deemed to be in breach of the standard) has been reduced from 55% (in Figure 4) co 30% (in Figure 5). The maximum type II erro r risk (i.e., the risk that a noncomplianc effiuent will be judged to be compliant), which occurs at an NHr N concentration of 7 mg/L is about 20%. The other thing to note from Figure 5 is that sampling frequency has little effect on the shape of the OC curve. This means chat the only options fo r reducing the type I error risk are to increase the critical values - and , therefore, increase the type II error risk - or upgrade the plant, which would lower both risks. If the plant were to be upgraded it would n eed to achieve an operating level of about 7 mg/L to ensure a probability of compliance close to 100%.

Conclusion

100 -1d

~ 90

- - 7d -28 d

80 ~ 70 1l. 60

8 50

'o 40

:ZS

20 10 0

Pc,pulatlon NH3-N median ("'!jll.)

Figure 3 . OC curves for NH 3-N at various sampling intervals and current EPA licence limits of 25 mg/ L median and 40 mg/L maximum. The solid line indicates the NH 3-N median for fi nancial years 1981-2000. 100 -1 d 7d -28d

~ 90 ';' 80 C .!! 70 '!5. 60

8 50

'o ]; 40

References

:is 30

20 10 0

10 15 20 25 30 35 40 Pc,pulatlon NH 3-N median ("'!jll.)

Figure 4. OC curves for NH3-N at various sampling intervals and future EPA licence limits of 10 mg/ L median and 30 mg/ L maximum. The solid line indicates the NH 3-N median for financial years 1981-2000. -

100

1 d, 12 mg/l median & 32 mg/L max 7 d, 12 mg/l median & 32 mg/l max

.,, 90 ~

80 70

'!5. 60

8 50 .

]; 40 'ls 30

perhaps some scope for designing a decision rule that gives acceptable decision error risks to alJ sta keholders. T he options for deriving a new decision rule, however, are limited by the fact that reducing the sampling period fro m 7 days to 1 day had little effect on the shape of the OC curve. High er samplin g freq uencies via o n-line measurement may produce a better resul t, and this c ould b e in vest igate d from a theoretical perspective. Sampling always carries uncertainty and there is no guarantee that a decisio n made regarding compliance with a standard is correct. This paper has shown, however, that the risks of a decision being in error can be managed through the thoughtful design of the mo nitoring program, treatment process, and perhaps the regulation.

20 10 0

10 15 20 25 30 35 40 Pc,pulatlon NH 3- N median ("'!jll.)

Berthouex PM, H unter W G and Pallesen L 1978, 'Monitori ng sewage treatment planes: some quality control aspects',J o11rnal of Quality Teclmology, 10, no. 4, pp. 139149. Box G E P and Jenkins G M 1973, TIME SER.JES A NALYSIS f orecasting and control, Prentice-Hall, N ew Jersey. Diaconis P and Efron B 1983, 'Computerlntensive Methods in Statistics', Scientific A merican, vol. 245, pp. 96-108. Diamond N 1998, Statistical A nalysis of BOD a11d SS Compliance rates and Licence Limits at ETP a11d WTP, Melbourne Water technical report. H esterberg T 1997, Ma tched-Block Bootstrap f or Long Memory Processes [Online] . Available: http://www.splus.mathsoft.com/splus/ whitepapers/ S-PLUS 2000 Programmer's Guide, Data Analysis Products D ivision , Mathsoft, Seattle, WA.

Acknowledgements

As alluded to earlier, Melbo urne Figure 5. NH 3ÂˇN OC curves for decision ru les This work was commissioned by Water has a corporate policy of 100% based on sampling periods of 7 d and 1 d, and Melbourne W ater and thanks are compliance with EPA licences. This critical values for the median and maximum of offered fo r allowing it to be published. is an admirable target, but it means 12 mg/ L and 32 mg/ L, respectively. The The Authors that the risk of a type I error should desired population median is shown as a solid be close co zero, and this has implivertica l line. Dr Warren Paul is Managing cations for the design effiuent quality Director of Environmental Science 10 mg/ L standard. Pocential1y this means of its treatment plants. In fact, it has impliand Statistics P I L; he is also a sessional doubling the size o f plant augmentations cations for the size and cost of plant l ec tur e r in th e Departments of or halving the load of ammonia in the upgrades, the cost of monitoring, and the Communications & Informatics and Life influent. loads discharged by retail water businesses Sciences & T ec hnology at Victoria and trade waste customers. In the case If the EPA limits were intended as University of Technology. Dr Neil study above, an effluent ammonia concenparameter values - i.e., if they represent the Diamond is a senior lecturer in the tration of about 5 mg/ L N H r N needs values obtained from an assessment of the Department of Communi cations and co be achieved in order to have a nearmaximum acceptable risk to environI nformati cs at VUT . Email: 100% probability of compliance with the mental and public health - then there is warren.paul@bigpond.com.

WATER FEBRUARY 2002