Wastewater disposal option in mundaring: a practical case study

DESALINATION

ELSEVIER Desalination 106 (1996) 361-370

Wastewater disposal option in Mundaring: A practical case study

Eugene Murphy Water Authority of WA, 629 Newcastle Street, Leederville 6007, Western Australia

Tel. +61 (9) 420-2420; Fax +6/ (9) 420-3200

Received 19 May 1995; Accepted 5 August 1995

Abstract

Urban development in the Hills areas of Perth is difficult to provide with local or regional wastewater systems due to the remoteness and isolation as well as the sensitive environment. Development to date has therefore mainly been on the basis of large-sized lots with individual on-site systems. This in turn puts limitations on f&her development or re-development of these areas. In some locations such as Kalamunda, a connection to one of the Authority’s major schemes has recently been possible. In other areas such as Mundaring, a local scheme would be required. This paper describes the development of such a scheme to the concept stage for the development of the Mundaring town centre.

Ke_~word.s: Small community wastewater treatment plant; Health; Environmental and social issues; Economics- user pays; Community consultation; Advanced wastewater treatment

l.Introduction

The Perth region consists of a relatively flat

coastal plain some 20 km wide, extending to the foot of the Darling Scarp. Urban development has occurred in corridors extending outwards from the major central business districts of Perth and Fremantle (see Fig. I).

The Shire of Mundaring covers a number of urban cells in rural settings located in the eastern corridor. The population of the region is some 30,000. The main business area of Mundaring is located approximately 30 km from the city of Perth.

Mundaring is not connected to the Authority’s sewerage system (see Fig. 1), and consequently the whole Shire is served by individual on-site septic tank systems. It has been general government policy that residential lots of 2000 m2 or greater as used in this region, are suitable for on- site systems. These facilities must meet the requirements of the controlling authority, the Health Department of WA.

The Hills Area of the Darling Scarp drains naturally into the Swan and Canning Rivers, which like most river systems in WA, Australia and the world, are sensitive to excessive nutrient loads from urban development and agricultural/

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362 E. Murphy / Desalination 106 (1996) 361-370

~ n INFLL AREAS

--I : i IISEWERED A.AEAS

SCARBOROUGH

FREMANTLE

Garden Island

Fig. 1. Urban development in the Perth area.

E. Murphy /Desalination IO6 {I9961 361-370 363

SURF&E WATER \

CAKHUENT tit3 [EXISTING k flliURE) -_-___ b )

”

CnURCHUAN BROOK-

horticultural activities in the catchment. The principal authorities involved in controlling the condition of these rivers are the Department of Envjronment, the Swan River Trust, the Water- ways Commission and the Health Department.

Additionally, the Hills area east and south of Perth currently provides the bulk of the potable water supply for the Perth region and for the Goldfields and Agricultural Water Supply scheme (see Fig. 2). This water is only chlori- nated and fluoridated prior to supply to the consumer.

Consequently, it has been the policy of the Water Authority to pursue acceptable wastewater schemes for any new development or re-development in this region. This is done to protect present and future surface water supplies. as well as to reduce the impact on the sensitive river systems. Since the mid-1980s the Authority has actively pursued providing a wastewater scheme in this area. This has resulted in the current proposal of a limited wastewater scheme to serve the Mundaring town centre and two primary schools.

This facility is planned for commissioning in 1995/96.

WOOROLCO BROOK

INDIAN OCEAN

n

ROlTN EST FREMANTLE

ISLAND 9

Fig. 2. Sources of potable water supply for the Perth region.

2. Criteria for a wastewater scheme

Any wastewater scheme must be capable of dealing with the flow produced on a continuous basis each day of the year. The system must also meet four essential criteria:

l protection of the health of the community . safeguarding the environment l social (community) needs . economic considerations

These criteria vary to some extent depending on the specific application and location of the scheme, and most importantly, on the type of effluent disposal system, either with or without reuse applications.

For the Mundaring region, due to its remoteness from existing Authority schemes, a local treatment and disposal/reuse scheme is required. The scheme would provide an effluent which ultimately would reach local water courses (Jane Brook) and eventually the Swan River. During the drier months, the effluent could be used for irrigation of ovals or parklands, with storage or the alternative disposal system being provided in


case of non-use or failure of the irrigation plant.

For such a scheme the following aspects need to

be considered with regard to the four criteria.

sources. It was also observed that public health

and protecting the environment are the most

important issues for the community.

2.1. Impact on human health 2.3. Economic considerations

The critical issue here would be to control the

level of pathogens in the effluent to meet the

relevant quality requirement. Disinfection of the

effluent would be essential. For irrigation appli-

cations special conditions need to be adopted,

such as the Guidelines for Use of Re-claimed

Water in Australia produced by NHMRC and

AWRC in 1987, currently under review.

The Authority is a self-funding organization

and operates generally on the “user pays” princi-

ple. Consequently, the overall community served

by any wastewater scheme must bear the cost.

This applies both to the cost of constructing the

facility and to the annual cost of operating and

maintaining the system. These costs are recouped

from the community through the annual sewerage

rating system. Essentially this scheme will ser-

vice developed land which will make the provi-

sion of sewerage uneconomic to the Water Au-

thority.

2.2. Environmenta issues

As previously mentioned, the most important

issue is the residual levels of nutrients (N and P)

in the effluent, and their impact on the receiving

wraters. Conventional wastewater treatment as

practised at the Authority’s three major Perth

plants would not be sufficient. The technology

exists to provide an advanced treatment plant

which produces an effluent with the acceptable

level of nutrients. Such a plant is currently being installed by the Authority for the town of Pem-

berton in the southwest of the State.

2.3. Communify needs

At the present time the Authority is undertak-

ing a major review of its long-term wastewater

treatment and disposal strategy for the Perth-

Bunbury coastal region, known as the Waste-

water 2040 project. This involves a community

consultation program to seek input from the

wider community. The Authority recently pub-

lished its Wastewater 2040 Discussion Papers as

the initial Authority response to the issues and

concerns raised from the community consultation

program to date.

In summary, the community generally has a

strong conviction that wastewater is a valuable

resource and that treated wastewater should be

reused to conserve scarce potable water re-

In summary, a number of authorities and

groups are involved in providing a wastewater

scheme and these are as follows:

9 Dept of Environmental Protection - sets con-

ditions for and issues discharge licences

l WA Health Department - defines public

health standards

l Local Authority - ensures planning by-laws

are met

l Local Community - ensures that it addresses

their needs l Operating Authority (Water Authority) -

must meet all requirements including the

financial implication

3. The proposed scheme

3.1. Development of scheme

Detailed investigations of a wastewater

scheme for Mundaring were commenced by the

Authority in 1986. At that time development

proposals of two remaining large landholdings

were initiated. The Shire of Mundaring, as part of

their review of their town planning scheme, held

a workshop in 1987 on the issues of wastewater

treatment ‘and disposal. This was attended by

E. Murphy / Desalination 106 (1996) 361-370 365

Table 1 Mundaring limited wastewater scheme

Source Equivalent population (EP for WWTP)

Primary school: assume 300 students/staff

Areas as defined by Shire of Mundaring letter of 16/4/l 991: A. Central business area at 5000 m2 and 10 m’!ha!d = 5 m3/d = 25 persons over

8 h day, EP=75 B. 3 x (9 residences + 8 units) = 51 persons plus others, say 19 EP

C. 3 x (16 units -t 7 residences) = 69 persons plus others, say 11 EP

D. 3 x (32 units + 7 residences) = 117 persons plus others, say 63 EP

E. 3 x (10 residences + 24 units) = 102 persons plus others, say 28 EP

F. 3 x (11 residences + 24 units) = 105 persons plus aged hostal = 40 EP plus aged units 0 72 x 2 = 144 persons

Possible future private school - as for above

representatives from Shire of Swan, Health De- partment, EPA, the Waterways Commission and

the Water Authority. In 1988 several development proposals were

given conditional approval by the DEP to pro- ceed without a wastewater scheme in the short term [EPA Bulletins 333 (6/88), 357 (S/85)]. In the longer term, a connection to a “reticulated sewerage service” was recommended.

In 1988 a wastewater scheme for development of the Mundaring town centre was proposed by the Authority and received favourable consider- ation by the Council of the Shire. It was considered that a larger scale regional wastewater scheme could not be economically justified, while lot sizes remain at 2000 m* or larger. A limited scheme for 1000 EP was therefore con- ceived as detailed in Table 1.

In 1990 the Authority commenced studies on a pilot plant employing advanced treatment technology for application to the Mundaring scheme.

100

75

(175) 70

(245)

(3;:) 180

(505) 130

(635) 289

(924)

100

1024 ___. -~ - -.~

The basic processes used were as follows:

Chcmid Feed (aalum, caustic)

I

wastewater ---_, lntetmitent ------> glow -----> Sand ------a Disinfection

extended balancing filtration

aeration ‘“”

I process I

, , 1 Effluent I

Waste sludge

Typical test results from this pilot plant are given in Table 2.

3.2. Current status qf project

Over the last 3 years discussions held with relevant authorities to bring

have been the project

to fruition. The main issues were what treatment/disposal/reuse system was to be provided in what location, and how the project was to be funded. The Shire has held a public meeting on

E. Murphy / Desalination 106 (1996) 361-370

Table 2 Pilot plant test results

pH SS mg/l

SVI” DO BODj COD COD (sol) ml/g mgil mg/lS mgil mg/l

lnfluent 6.7 270 340 710 Mixed liquor 6.5 6400 85 1.2 Effluent 6.9 10 10 Final effluent after Dynasand and UV 7.0 < 5 <5 55 45

(225)

Total N NH,-N NO,-N NO -N 3

Total P Sol P mgil ml/g mglL mg /l mg/l mg/l

Influent 6.7 45 10 4.6 Effluent 6.9 3.0 0.15 0.80 1.2 0.45 Final effluent after Dynasand and UV 7.1 3.1 0.15 0.85 0.80 0.25

% UV transmittance Faecal coliforms at 254 nm no./100 ml

Salmonella

Effluent Final effluent after Dynasand and UV

100,000&450,000 51-55 median iOb

Present Seldom isolated

aBased on nine tests only. Values were within the range ~10 - 420. bUV transmittance of >55% is required for reliable disinfection.

the issue, and petitions for and against this pro- A further major hurdle to overcome was find- ject have been submitted to the Council and the ing an acceptable site for the treatment plant. government.

The estimated cost for stage 1 of the scheme is $2.6 million. Of this $2.0 million will be provided by the Authority under the advanced infill sewerage program announced by the State Gov- ernment earlier this year. Additionally, funding was sought and granted from the Commonwealth Government under the One Nation Program to assist with this scheme. Due to on-going delays with the project, this funding has now been di- verted to the Denmark WWTP. However, assis- tance with funding for the treatment plant has been obtained under the National Landcare Pro- gram ($0.48 million). The Shire of Mundaring will also contribute to the scheme ($0.12 million).

Fig. 3 indicates the alternative sites considered by the Authority in liaison with the Shire and authorities such as the DEP and CALM. It needs to be appreciated that this region covers three different water supply catchment areas, as shown in the Table 3.

On the basis of these and other factors, including a present value cost analysis, the current preferred site was selected. Needless to say, the proposed treatment plant site is not favoured by the community living in close proximity. This is a common problem with such facilities. Although the community needs and desires the benefit of the wastewater service, location of the treatment plant often receives the NIMBY response. The Authority for the current proposal has made the

E. Murphy /Desalination 106 (1996) 361-370 367

FUTURE JANE BROOK CATCHMENT

WATER CATCHMENT BOUNDARY - I - I

ALTERNATIVE EXAMINED WWTP SITES

MUNDARING WEIR CATCl-iMENT AREA

/LOWER HELENA PIPEHEAD DAM I

CATCHMENT AREA

Fig. 3. Water catchment areas and alternative sites for water treatment plant.

Table 3 Water supply catchment areas

Catchment area

Mundaring Weir

Protection objectives ----..._ -.. -I

Priority 1 : Non-degradation by strict limitation on land use

Lower Helena pipehead dam Priority 2: Restrictions on land use to ensure level and risk of pol- lution is not increased

Ian Brook catchment (future) Priority 3 Protection through management with less emphasis on restrictions


ARFA 10 BE SERVED (S IAGt 1)

lii_TIMAT- SCHEMt

W/‘&II WitI t: I’liMI’ l;lA ION

WASTrW.4T’R PRESURE MAlN

Fig. 4. Layout of the treatment plant.

guarantee to the Shire Council that the plant would not exhibit odour nuisance or unacceptable noise levels at 200 m from the facility under normal operating conditions. This buffer distance would be provided by the existing bushland of the current proposal.

3.3. C’oncept design

The current proposal provides for the staged installation of the plant in two 500 EP modules. The possible layout of the plant is shown in Figs. 4 and 5, and the treatment units require an area of 30 m by 2.0 m. The effluent from this plant would flow through a storage/reed bed

system prior to reuse for irrigation or discharge to a creek via a leach drain system for further effluent polishing. It may be necessary in the final design to use the storage/reed bed for flow balancing, and then filter and disinfect the bed effluent. A regular monitoring program would be set up for the performance of the total system. The treatment plant would be designed to pro- duce the following effluent quality:

l Suspended solids - 5 mg/l l BODS - 10 mgil l Total nitrogen - 15 mg/l l Total phosphorus - 1 mg/l l Faecal coliforms - 10 per 100 ml

E. Murphy / Desalination 106 (1996) 361-370 369

EFFLUENT TO REED BEDS-P

AIR COMPRCSSORS A L-DUAL MOUNTED COMPRESSORS

TO UYNASAND FILTER

Fig. 5. Details of the treatment plant.

Table 4 Major activities still to be undertaken

_

Activity

Acceptance by community DEP works approval Statutory approval Funding approvals Design and construct:

Sewerage reticulation Pump station/pressure main Treatment plant Effluent system

Commissioning of system

3.4. Work stiIl to be undertaken

Table 4 summarises the major activities still

to be executed before the scheme is put into

operation.

Government

Comments

WAWA - in liaison with Shire WAWA - under EP Act 1986 WAWA - under WA Act 1984 WAWA - with Commonwealth

Design ~ WAWA; const. - contract Design - WAWA; const. - contract Design and construct contract Design - WAWA; const. - contract WAWA and contractors

4. Conclusions

On the basis of the Authority’s experience

with the development of the limited wastewater scheme for Mundaring, the following conclusions

can be made.


1. The underiying concept of small community plants with local effluent disposal, with or without reuse applications, is generally supported but difficult to implement due to the many aspects that need to be addressed, and due to the different groups involved with their specific interests which have to be considered.

2. The most critical issue to be addressed is the disposal of the effluent from the treatment plant, with or without reuse applications.

3. When a local treatment plant is envisaged, provisions have to be made in the town planning schemes for suitable sites with buffer areas.

4. Cooperation between all groups involved including the community, is essential for the success of the scheme.

5. Discussions between these groups should take place as early as possible in the planning and concept development phases, and this should occur at least 5 years before the system is to be become operational.

6. At the outset an environmental impact as- sessment should be undertaken of both the existing facilities and of the proposed facilities for the future development.

7. There must be an on-going community education process and program.

8. Research into new technology and monitoring of existing similar plants, both here in Australia and elsewhere, should be on-going.

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Wastewater disposal option in mundaring: a practical case study