Summary and Conclusion:::::::::::::::::::::::::::

The characteristics of other sewage system discharges to receiving waterways, including STP effluent and dry weather sewer overflows, differ from wet weather sewer overflows. As a result, environmental and public health impacts are also likely to be different. For this reason, a review of the research literature on these topics has not been included.

In many countries, stormwater run-off and sanitary sewage are conveyed together in combined sewer systems (CSSs) and impacts on receiving waters from combined sewer overflows (CSOs) have been widely researched. Sanitary sewer systems (SSSs), on the other hand, convey only sanitary sewage and stormwater run-off is carried in a separate pipe network. During wet weather there is some unintentional stormwater inflow and infiltration into the SSS. The

difference in the design of these two systems, particularly in relation to larger stormwater run-off or wet weather flows in the CSSs, may result in different impacts from CSO and sanitary sewer overflow (SSO). It is not clear if the differences in impacts are significant and may be a result of the individual characteristics of the site and sewer system under investigation. Therefore, whilst the review focused on SSOs which are most pertinent to the present research, as there have been few international studies on aquatic life impacts from SSOs, some CSO studies were reviewed.

Two key Australian studies in Brisbane and Sydney investigated the impacts of wet weather sewer overflow from SSSs on receiving waterways. The findings revealed that whilst sewer overflow contributes to ecological risks in some instances, stormwater is the main stressor of ecological health. Studies of CSSs show varying degrees of impacts on aquatic life from CSO. In some of these studies, other pollution sources including stormwater run-off are considered to be potentially more of a threat than CSOs. The significance of the contribution of pollution sources other than sewer overflow to the impacts on waterways has also been pointed out in other research. These findings indicate the importance of accounting for other pollution sources when investigating sewer overflow, and in particular stormwater run-off, which is a major contributor of wet weather pollution.

Unlike ecological health, the Brisbane study shows that sewer overflow is a greater risk driver for microbiological hazards than stormwater run-off. The use of human sterol bio-markers in the Brisbane study to assess public health risks from SSO is novel and contributes significantly to our understanding of the public health risks from these events. The USEPA report studies also confirm that SSOs pose a public health threat as they contribute to gastrointestinal illness in recreational users and are also linked to a disease outbreak which caused 4 deaths. They also affect recreational amenity through beach closures. These studies highlight the importance of including microbiological contaminants in investigations of sewer overflow impacts.

The studies reviewed contribute greatly to existing knowledge of the ecological and health impacts of wet weather sewer overflows and in the wider context of wet weather discharges.

However, impacts from wet weather SSOs have not been widely researched to date. Therefore, research in this area would be of significant benefit and would add to existing knowledge.

Furthermore, the variability in impacts for the various studies reviewed indicates that the study site under investigation in this thesis will add its own unique information. Studies show that the variability in impacts between overflow sites is linked to certain factors including the duration, frequency and strength of the discharge, load of contaminants, receiving waterway

characteristics, waterway usage and in-sewer processes such as sediment accumulation. The potential for impacts from sewer overflow to vary so much between sites indicates that the findings of current studies may not represent impacts from all sewer overflows. Hence, decisions in relation to the management of local sewer overflows based on this information are difficult.

Furthermore, the findings of key studies were often based on broad or very specific characteristics making it more difficult to apply the findings to a specific site or catchment. In part, the research in the present thesis aims to account for this variability and allow different scenarios to be explored through the use of risk analysis. A Bayesian network (BN) risk model is used, which is a novel approach to the investigation of risks from sewer overflow. The BN will be of benefit in this research through its ability to account for uncertainty in systems through the use of probabilities, examine different scenarios through probabilistic inference and incorporate both qualitative and quantitative data.

CHAPTER 3

WATER QUALITY AND RAW SEWAGE SAMPLING- DESIGN AND METHODS

3.1 Introduction

A primary objective of the research and an important first step in the analysis of risks associated with wet weather sewer overflows was to determine the impact on the water quality of receiving waterways following these events. The literature review in Chapter 2 showed that a typical urban waterway such as the study site is impacted by a range of pollution sources. Therefore, it is imperative that the water quality in receiving waterways resulting from wet weather sewer overflows is not considered in isolation. In particular, it is important that this study distinguish the impact of sewer overflows from stormwater discharge, which is one of the other major contributors of wet weather pollution.

With this in mind it was necessary to determine the water quality in receiving waters for the following conditions:

• Ambient dry weather conditions –during times of low flow when no rainfall or overflow occurs.

• Wet weather without sewer overflow –during a rainfall event of a size as close as possible to that which would normally cause a sewer overflow to occur. This event is indicative of pollution from stormwater run-off without any contribution from sewer overflow.

• Wet weather with sewer overflow - due to the drought conditions at the time of the study a wet weather sewer overflow event did not occur during the study period. As a substitution, raw sewage samples from the sewerage system were collected with the intention of applying hydrological dilutions to the raw sewage concentration data to predict receiving waterway concentrations following sewer overflow (refer to Chapters 5 and 6 for information on the simulation of in-stream concentrations from sewer overflow).

Ambient sampling will allow changes in water quality to be detected following wet weather sewer overflow and also stormwater run-off, thus highlighting any subsequent increase in contaminant levels and hence potential impacts. A comparison between water quality, following wet weather

with and without a sewer overflow enables conclusions to be drawn on the relative contribution of sewer overflows and stormwater run-off on the impacts to water quality in receiving waters.

This chapter discusses the study design and sampling methods for these three situations;

ambient, wet weather without overflow and raw sewage which is ultimately used to predict concentrations from the wet weather sewer overflow event. The chapter includes determining an appropriate study site, selecting measurement parameters, sampling methods, laboratory analysis and quality assurance.

3.2 Study Area

3.2.1 Overview of wet weather sewer overflows

City West Water (CWW) has approximately 25 operational emergency relief structures (ERS) located on pipelines and approximately 30 ERSs located at or close to sewerage pump stations and detention tanks (City West Water, 2005a). Overflows from this infrastructure are classed as occurring in “wet weather” and “extreme wet weather”. Overflows in extreme wet weather are considered compliant with the State Environment Protection Policy (Waters of Victoria) 2003 (SEPP (WoV, 2003), as they occur in rainfall events with an average recurrence interval (ARI) greater than 5 years. All other wet weather overflows are considered non-compliant, occurring in storms with ARIs of less than or equal to 5 years. Figure 3.1 below shows a graph of wet weather sewer overflows that have occurred from CWW assets from 2003 to mid 2009. The figure includes overflows that are considered compliant resulting from extreme wet weather and non-compliant resulting from hydraulic deficiency in the sewer system. Some of these overflows may involve assets other than ERSs such as sewer manholes. A large storm with an ARI of 50 years occurred early in 2005 which is why such a large number of extreme wet weather overflows occurred in the 2004/2005 period. Following this event, however, drought conditions worsened and there were only two overflow events between 2006 and 2009.

Prior to the commencement of this study, CWW had identified those assets which were not complying with the SEPP (WoV, 2003) requirement to contain flows generated by a rainfall event associated with at least a 5 year ARI. This was part of a hydraulic improvement program established by the water retailer, which involved initial investigation of hydraulic performance of sewerage catchments including modelling and monitoring of overflows (City West Water, 2004).

Upon non-compliant assets being indentified capital works projects such as pipeline augmentation/construction, detention tank construction and inflow/infiltration reduction works are

implemented to bring the sewerage system up to compliance with the 1 in 5 year requirement.

Prior to commencing this study, eight sewerage catchments were identified as being non-compliant. Pipeline construction works in three of these sewerage catchments had recently been completed to address non-complaint overflows. Of the five remaining sewerage catchments identified, non-compliant overflows were occurring from six ERSs, five manholes, and one pumping station.

Figure 3.1 Annual number of wet weather sewer overflows for the last five years from CWW assets

3.2.2 Determining the study catchment

Of the non-compliant sewerage catchments, the Five Mile Creek (FMC) catchment, which has three non-compliant ERSs (given the asset identifications: ERS 97, 98 and 151), was chosen for the study (shown in Figure 3.2). It was considered the most appropriate site for the following reasons:

• It was expected that impacts will be easier to detect in waterways where sewer overflows are more frequent and the FMC catchment ERSs are among those that overflow most frequently. All three structures overflow in storm events with an ARI of 1 to 2 years (City West Water, 2004). CWW have gained an understanding of the estimated return period of overflow from performance indicators such as ERS, rainfall and flow monitoring data, in conjunction with hydraulic modelling of the sewerage catchment (City West Water, 2004).

0 5 10 15 20 25 30

2003/2004 2004/2005 2005/2006 2006/2007 2008/2009

Number of overflows

Year

Hydraulic deficiency Extreme wet weather

• ERS 97, 98 and 151 discharge into the Moonee Ponds Creek (MPC) from the same stormwater drain generating a greater sewage overflow volume and frequency.

• Improvement works for some of the other non-compliant assets had commenced and would interfere with the study.

• Access was available to suitable sampling sites both upstream and downstream of the impact site, whereas access at some other catchments was more difficult.

• The FMC Catchment is a good representation of a typical non-compliant sewerage catchment in the CWW area. This includes both the demographics of the catchment which is primarily residential, and the nature of the receiving waterway, which is a typical degraded urban stream.

Figure 3.2 Map of the study site; Five Mile Creek Sewerage Catchment

The FMC sewerage catchment is located in a predominantly low-density residential urban area of the western suburbs of Melbourne. Three ERSs overflow into the FMC stormwater drain,

which discharges into the lower section of the MPC. The FMC stormwater drain regains its natural state as an open unlined creek for a few hundred meters before it flows into MPC. The FMC stormwater drain is referred throughout the thesis as either the FMC or FMC stormwater drain. The ERSs including ERS 97, 98 and 151, along with the FMC and MPC are shown in the map of the study site in Figure 3.2.

Based on CWW billing data, 95 % of sewer connections in this area are from residential land use (City West Water, 2005b). There are no major trade waste licences in the catchment, with the non-residential sewer connections either from schools or light commercial premises (City West Water, 2005b). Therefore, this study relates to impacts or risks associated with sewer overflows in domestic catchments only. As industrial premises potentially discharge different wastewater to the sewer than residential premises, sewer overflows from industrial catchments may have other issues not identified in this study. For instance, studies in the literature review (Hall et al., 1998;

Marsalek et al., 1999) found a greater impact on receiving waters from sewer overflow in areas where industrial wastewater was discharged to the sewer as opposed to overflows in residential areas. There was in fact no opportunity to look at overflows in predominantly industrial catchments, as all ERSs in the CWW catchment are located in areas which receive primarily domestic-type wastewater.

The compliant and non-compliant overflows from the FMC catchment from 2003 to 2009 are shown in Table 3.1 below. As already mentioned, those overflows associated with storm events with an ARI of less than or equal to 5 years are non-compliant. The overflow volume and duration and also associated average recurrence interval (ARI) of the storm event is also provided in Table 3.1. For the study site the number of overflows during the 2004/2005 period highlighted the potential for data collection at this site including water quality data from non-compliant sewer overflows. Unfortunately, after early 2006 due to lack of rainfall in Melbourne there were no overflow events at this site for the period recorded until mid-2009. Sampling had not commenced prior to this date, which as already mentioned is why the alternative methodology of predicting in-stream concentrations was adopted.

3.3 Contaminants

3.3.1 Selection of measurement parameters

Water quality rather than biological indicators was chosen to assess the impact from wet weather sewer overflow in this study. As shown in the literature review, Walsh (2000) highlighted

that localised impacts on stream biota (in this case benthic communities) are impossible to detect given the typically widely degraded nature of urban waterways. Furthermore, aquatic macro-invertebrate specialists from Monash Water Studies Centre and Melbourne Water (personal communication, Eddie Tsyrlin) have indicated that impacts from sewer overflows on macro-invertebrates will be difficult to detect in urban streams due to the existing poor condition of aquatic life. A study in Sydney, Australia (Bickford et al., 1999) also found the impacts on aquatic organisms from sewer overflow to be inconclusive due to impacts occurring both upstream and downstream of the sewer overflow sites.

Table 3.1 Wet weather overflow data for the ERSs in FMC sewerage catchment study site from 2003 to 2009 considered a good representation of potential pollution from stormwater and sewer overflow within the allocated resources. Furthermore, all contaminants in Table 3.2 including metals are commonly used to assess the health of aquatic environments (ANZECC and ARMCANZ,

2000b). Basic wastewater characteristics such as nutrients and faecal indicators are considered integral in determining the risks from sewer overflows. Faecal indicators were considered particularly important in light of other studies which have highlighted microbiological hazards as potential public health hazards from sewer overflow (D.A. Lord & Associates Pty Ltd., 1997;

Pollard et al., 2005). Similarly, heavy metals such as silver (Bickford et al., 1999) have been identified as a potential risk from sewer overflow and were also included. Heavy metals from domestic sources have been reported (Connor and Wilkie, 1995; McCormick, 1991) and a study of heavy metals and organics in domestic wastewater found that loads of copper, aluminium and zinc to treatment works were primarily from domestic sources (Lock, 1994).

The findings in this study relate only to contaminants listed in Table 3.2. There are many other contaminants in sewage which may also impact on receiving waterways as a result of sewer overflow. However, they are beyond the scope of the present study. For example, an investigation by Environment Victoria into Melbourne’s raw sewage composition found that there are around 200 contaminants of concern known to be in Melbourne’s sewage (Environment Victoria, 1994). The Environment Victoria report further stated that of the total contaminants two were nutrients, twenty-two were metals and approximately 180 fell under the general category of organic chemicals (Environment Victoria, 1994: p 21). There are also key studies in relation to contaminants in domestic sewage (Connor and Wilkie, 1995; McCormick, 1991) which list a wide range of chemicals, including mainly metals and organic chemicals. Organic chemicals include such contaminants as polynuclear aromatic hydrocarbons, chlorinated hydrocarbons, phthalate esters, amines, ethers and phenols.

Hormones, drugs and personal care products have more recently been identified as substances of concern in sewage (Chapman and Leusch, 2006). To date, the focus of chemical pollution has mainly been on the well-known priority pollutants. As a result, there is limited available data for emerging contaminants such as hormones, drugs and personal care products (Chapman and Leusch, 2006). Chapman and Leusch (2006) however reported a study (Leusch et al., 2005) on the estrogenic and androgenic activity in raw sewage, which found both to be relatively high.

Furthermore, a Brisbane study into the impacts of sewer overflows (Pollard et al., 2005) found that the level of estrogenic hormones in sewage following dilution in the waterway could still be in a range that is biologically active.

Table 3.2 Contaminants investigated in the study

Microbiological Metals Ecosystem Health

E.coli Aluminium Ammonia

Enterococci Antimony Nitrite

Arsenic Nitrate

Beryllium Electrical conductivity

Boron Total phosphorous

Cadmium Orthophosphate

Chromium Total nitrogen

Cobalt pH

Copper Total suspended solids

Iron Lead Manganese

Mercury Molybdenum

Nickel Selenium

Silver Thallium

Tin Vanadium

Zinc

3.3.2 Overview of contaminants and potential effects

Escherichia coli and enterococci

Stormwater run-off and sewer overflows containing faecal matter can carry pathogens or disease-causing organisms. This may include bacteria, helminths (intestinal worms), protozoa and viruses (NRMMC et al., 2006). The diseases caused by pathogens are numerous and may

include such things as ear and eye infections, mild to severe gastroenteritis, respiratory illness, typhoid, cholera, hepatitis, dysentery, and meningitis.

Escherichica coli (E.coli) and enterococci, which may be derived from animal or human faecal sources, can be used to indicate faecal pollution and associated infectious microorganisms.

These organisms are not disease-causing agents, but rather appear to behave similarly to faecally-derived pathogens and infer their presence, thus indicating the potential for disease.

Both E.coli and enterococci may also have pathogenic strains (NHMRC and NRMMC, 2004) but this is irrelevant to the indicator function.

E.coli has long been used to describe water quality for both fresh and marine waters impacted by faecal pollution. The Australian Drinking Water Guidelines (ADWG) recommend E.coli (or thermotolerant coliforms) as the most suitable indicator organism for the presence of pathogens in drinking water (NHMRC and NRMMC, 2004). The ADWG suggest that of the thermotolerant bacteria, E.coli is the most suitable as it is the most common in faeces. E.coli is also used to monitor the safety of recreational waters for human users, with safe levels outlined in the SEPP (WoV, 2003), and Australian New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC and ARMCANZ, 2000a). Furthermore, the Australian Guidelines for Water Recycling use E.coli as an indicator organism to verify that sufficient pathogen reduction has occurred to enable safe use of the recycled water (NRMMC et al., 2006).

Enterococci is also identified as an important faecal indicator. In particular, enterococci is used as a faecal indicator in the World Health Organisation (WHO) and Australian Recreational Water Guidelines (NHMRC, 2008; WHO, 2003a) as epidemiological studies have shown that it provides the strongest dose-response relationship with gastroenteritis in swimmers (Kay et al., 1994). Based on a key study (Kay et al., 1994), safe enterococci levels for recreational users have been established which should not result in bather illness. Hence, both E.coli and enterococci were considered important microbiological indicators in the study.

E.coli, which comes from the family Enterobacteriaceae, is described by the ADWG (2004) as

E.coli, which comes from the family Enterobacteriaceae, is described by the ADWG (2004) as