A REVIEW OF THE EFFECTS OF SEWER LEAKAGE ON GROUNDWATER QUALITY

Exfiltration (of sewage into the ground from faults in ageing sewerage networks) has been recognised for many years but has never been quantified. It was considered that this leakage did not pose a groundwater-contamination threat because it was assumed that pathogens in sewage would either die off or be attenuated before reaching the groundwater level.
This paper identifies why sewers have faults that could allow sewage exfiltration where the sewer is above a groundwater resource. Because of a lack of UK data on sewage exfiltration, research work in Germany is discussed and analogies are made between the sewerage networks of the two countries.
Until recently, it has not been possible to positively identify sewage contamination of groundwater because of other pollutants and potential sources within an urban environment. The development of sewage-fingerprinting techniques has overcome these difficulties and provides conclusive evidence of sewage contamination of shallow and deep groundwater resources in researched areas. Studies of groundwater recharge and total solute loadings allow quantification of sewage exfiltration reaching the groundwater within the Midlands conurbation. The paper concludes that urban aquifers are potentially more vulnerable to microbiological contamination from leaking sewers than has previously been assumed.     

FCKW als Tracer für die Ausbreitung von Altablagerungsemissionen im Grundwasser

Emissions from abandoned waste disposal sites into groundwater are difficult to trace further downstream because of their complexity. Typical tracers, for example, like chloride, boron and sulphate are likely to be influenced by several factors like saline waters, emissions from seepage pits and leaky sewers. These types of components are therefore not suitable to characterise groundwater contamination caused by abandoned waste disposal sites; they will thus not be further discussed in this paper. However, due to their special geochemical properties like negligible absorption and degradation rates, chlorinated fluorocarbons, especially difluoro-dichloromethane (F12), which are frequently emitted from abandoned waste disposal sites, are particularly suitable for the detection of maximum contaminant emissions to groundwater. These elements are crucial for the assessment of groundwater contamination and the employment of natural attenuation as a remediation measure.     

ESTIMATING URBAN LOADS OF NITROGEN TO GROUNDWATER

Urban areas can impose significant loads of nitrogen, as ammonium or nitrate, onto the underlying groundwater. There are many sources of nitrogen pollution, including diffuse sources (parks and gardens), intense point sources (industrial chemical spills), and multi-point sources (leaking sewers). Data on the loadings associated with the various sources are scarce, although an estimate of the overall load is available for Nottingham. For other cities, a total load could be estimated by factoring the Nottingham result, or by considering each component of the load separately. Both approaches are described, and the integrated method is recommended for its simplicity.     

Possible Environmental Impact of the Closure of Two Collieries in County Durham

In County Durham the forthcoming closure of two coastal collieries is, in effect, the final closure of a large hydraulically interconnected coalfield which has been progressively dewatered over three centuries. Groundwater will gradually rise through the previously worked strata after the cessation of coalfield dewatering. Past experience shows that the rising groundwater will develop high acidity and heavy metal loadings as oxidized pyrite remnants are dissolved. Conceptual modelling suggests that this acidic groundwater will ultimately discharge into the River Wear and its tributaries, with serious consequences for the aquatic ecology and human use of the River Wear system. Further environmental impacts may include (a) groundwater pollution in the adjacent Basal Permian Sands aquifer, (b) leaching from landfills intersected by the rising water table, (c) compromised integrity of foundations, (d) increased flows in old sewers below the new rest water level (leading to problems at sewagetreatment works and combined sewer overflows), (e) corrosion of other buried services, (f) surface gas emissions, and (g) long-term subsidence risk from old workings. The prevention of these impacts would involve long-term maintenance of regional dewatering, although local mitigation of most effects could be arranged – albeit at considerable cost. Current legislation fails to place responsibility for the prevention of such environmental impacts in the hands of any one organization; this 'vacuum of responsibility'needs to be addressed urgently if a pragmatic, consensual approach to environmental protection in abandoned coalfields is to be pursued.     

A new development in locating leaks in sanitary sewers

A new method called focused electrode leak location system (FELL-41) was developed in Europe for identifying potential leaks in sanitary sewers (mainline and service connections at the mainline). The chief advantages of the FELL-41 technology include: (1) identifying leaking joints on mainline during dry weather; (2) prioritising leak repairs by intensity of leaks; (3) determining leaks in service lateral mainline connections; (4) an alternative to air-pressure testing for acceptance of new and rehabilitated sanitary sewers. The FELL-41 method measures electrical current flow between a probe that travels in the pipe and a surface electrode. Pipe defects that allow liquids to flow into or out of the pipe cause a spike in the electrical signal, thereby locating the sources of infiltration or exfiltration. The intensity of the measured current can be correlated to the magnitude of the leaks. The purpose of this paper is to discuss this technology as well as its limitations. The results of the FELL-41 technology will be validated through several case studies.     

Microbial risks associated with exposure to pathogens in contaminated urban flood water

Urban flood incidents induced by heavy rainfall in many cases entail flooding of combined sewer systems. These flood waters are likely to be contaminated and may pose potential health risks to citizens exposed to pathogens in these waters. The purpose of this study was to evaluate the microbial risk associated with sewer flooding incidents. Concentrations of Escherichia coli, intestinal enterococci and Campylobacter were measured in samples from 3 sewer flooding incidents. The results indicate faecal contamination: faecal indicator organism concentrations were similar to those found in crude sewage under high-flow conditions and Campylobacter was detected in all samples. Due to infrequent occurrence of such incidents only a small number of samples could be collected; additional data were collected from controlled flooding experiments and analyses of samples from combined sewers. The results were used for a screening-level quantitative microbial risk assessment (QMRA). Calculated annual risks values vary from 5 × 10⁻⁶ for Cryptosporidium assuming a low exposure scenario to 0.03 for Giardia assuming a high exposure scenario. The results of this screening-level risk assessment justify further research and data collection to allow more reliable quantitative assessment of health risks related to contaminated urban flood waters.     

North Tyneside Bathing Waters' Scheme

The North Tyneside bathing waters' scheme reduces the frequency and quality of storm sewage which is discharged inshore from existing interceptor sewers along the coast.
Flow-simulation modelling is applied to the existing system to determine the frequency and volume of interceptor sewer overflow against a range of storm intensity and return periods. The models are extended to an evaluation of new systems of storm-sewage management.
An optimized solution is described in which new storm sewers are utilized for the storage of all storm-sewage overflow discharges prior to screening and pumping of the storm sewage to sea via an outfall.     

Identifying Land Contaminated by Chlorinated Hydrocarbon Solvents

This paper provides a method of identifying land contaminated with chlorinated hydrocarbon solvents by sampling and analysing soil gas. Relationships are presented which enable levels of soil gas contamination to be related to levels of soil and groundwater pollution. Two case studies are presented. Soil gas surveying of an industrial site with severe groundwater pollution demonstrated that standards for contaminated land are insufficient to protect groundwater. Solvent levels in groundwater were one to two orders of magnitude higher than UK permitted concentrations in drinking water, whereas soil contamination values did not reach polluted levels. Surveying of a site occupied by a disused fire station showed significant differences in patterns of soil gas and groundwater pollution. This is explained by direct pollution of groundwater though the well at the site and/or possible flow of polluted groundwater to the site from adjacent areas.     

污染预警综述及对放射性污染预警的启示

在分析目前环境污染中的地下水污染、土壤重金属污染等方面的预警系统和具体模型的基础之上,对污染预警系统产生的效果进行了评价,并以已有的污染预警模型的特点为指导,对放射性污染预警模型的建立提出了合理的建议,期望促进放射性污染预警模型的研究和完善。     

下水道中不明水的调查及防治对策

城市下水道中的实际污水量往往超过汇入的污水与雨水量之和，在地下水位高的地区或雨水充沛的汛期这种现象尤为突出。超出的部分在日本被称为不明水量，其主要来源于地下水和雨水的渗入。不明水不仅会造成检查井溢水，还增加了污水处理厂的负荷和运行成本。通过对日本某市下水道的实地调查，就合流制管道中来源不明的水进行了定量分析，并提出了相应的防治对策。     

Excluding Groundwater Infiltration into New Sewers

Much attention has been focused on the need for sewer renovation and rehabilitation of old sewerage systems, but age is not always the reason for sewer failure. Serious problems of performance have also been encountered on sewerage schemes less than 10 years old. This paper considers the problems of groundwater infiltration into new foul sewers, and suggests that deficiencies might exist in some aspects of modern sewer design and construction.
Infiltration is most frequently observed at sewer joints. Results are presented of laboratory tests which show the ability of flexible fixed-ring joints on clay sewers to withstand both internal and external pressures. Damaged polyester fairings on the spigots of these pipes can act as one-way valves, and massive infiltration may result. The standard site water test is shown to be inadequate in detecting some of these types of defect which may result from damaged pipes or poor workmanship.     

ESTIMATING RECHARGE FOR BRITISH AQUIFERS

This paper reviews methods of estimating recharge for a wide variety of aquifers in Britain. A soil moisture balance technique is used with direct representation of relevant soil and crop properties. Recharge contributions due to rainfall, runoff from impervious areas and leaking water mains and sewers are considered. In many field situations low permeability strata, which overlie the main aquifer, modify the timing and magnitude of the actual recharge. Runoff from less permeable strata can become runoff-recharge at the aquifer outcrop. Reference is made to several case studies.     

Deterioration of a Tunisian coastal aquifer due to agricultural activities and possible approaches for better water management

The purpose of this study is to provide a better understanding of the impact of agricultural activities on groundwater quality in a semi‐arid coastal environment (Korba, Tunisia). Impacts have been assessed through groundwater samples that were analysed for a range of chemical and biological parameters. Results indicate that groundwater overexploitation for irrigation and fertiliser use have affected the quality of the groundwater not only by direct contamination but also seawater intrusion. The implementation of appropriate regulatory and economic instruments to foster sustainable practices in the agricultural sector have been analysed within the framework of the EC (European Community) FP6 (funding program 6) INECO (Institutional and Economic Instruments for Sustainable Water Management in the Mediterranean Region) Project. Through stakeholder involvement processes, the project analysed issues relating to the regulation and control of groundwater abstractions, the promotion of wastewater reuse, efficiency improvements in irrigation water use, as well as instruments to strengthen the socioeconomic and institutional environment towards better managing and conserving available groundwater resources.     

国内外地下水污染研究的现状及发展趋势

分析了国内外地下水污染的研究现状,总结了国内外的研究成果,并归纳了目前研究中存在的问题,指明了地下水污染今后的研究方向,促使研究工作向新的深度和广度发展。     

Finding lost streams and springs captured in combined sewers: a multiple lines of evidence approach

Some streams and springs have been historically and intentionally captured into combined sewer systems. This is a source of clean baseflow to combined sewers and wastewater treatment works that, unlike groundwater, infiltration‐inflow through pipe cracks and defective joints, has not been widely considered by the UK water industry. This study presents the first formal methodology, using multiple lines of evidence, to locate lost streams and springs and identify where they have been captured into the combined sewers. In a UK case study, approximately half the total stream length and over 100 natural springs have been apparently lost and could be flowing into the combined sewers. Evidence has demonstrated the suitability of tests to indicate captured flow in sewers, and has confirmed several streams and springs flowing into combined sewers.     

Sediment bags as an integrator of fecal contamination in aquatic systems

The identification of sources of fecal pollution in urban streams or storm sewers is often difficult since fecal contamination events frequently are episodic and/or have ceased before a survey can be undertaken. As an alternative to sampling the water column and/or natural sediments, sediment bags suspended in the water column can act to integrate water quality data with respect to fecal coliform concentrations. Furthermore, sediment bags retain coliform bacteria after their initial sorption to the sand substrate. As a result, they can identify contaminant sources even though, as is often the case, the sampling survey is carried out after the pollution event.     

Identification of pets and raccoons as sources of bacterial contamination of urban storm sewers using a sequence-based bacterial source tracking method

In urbanized areas, contaminated storm sewers can feed high bacterial levels into free-flowing streams and rivers. Although illicit connections sometimes cause contamination, urban wildlife and free-roaming domesticated or feral pets may be another source. After eliminating illicit connections as sources of high levels of Escherichia coli in two storm sewers tributary to the Huron River in southeast Michigan, the roles of urban wildlife, pets, humans, and birds were investigated using a sequence-based bacterial source tracking technology. After enumeration, E. coli were isolated from water samples collected during spring to fall, 2005. Sequences in the gene beta-glucuronidase of each isolate were compared to sequences of reference strains from humans, raccoons, pets (cats and dogs), and birds. The highest percentage source for six of ten events was pets (ANOVA, p=0.005). Among isolates attributed to pets, strains from cats occurred more frequently on seven of nine events in which pets had a non-zero probability. High raccoon percentages (up to 60%) occurred in late summer and fall, and varied significantly more than in the spring (F-test), possibly reflecting urban raccoon den-site mobility. The sequence-based bacterial source tracking method suggests that feces from pets and raccoons are important contributors to urban storm sewers.     

Integrative quantification and balancing of contaminant fluxes in urban groundwater, case study Darmstadt

The qualitative and quantitative impact of a city on groundwater is presented in the case study of Darmstadt. The impact of land use on groundwater quality in Darmstadt is higher than the impact of background geological processes. The occurrence of Cl, B and Fe is only influenced by land use, while EC, HCO₃ and PO₄ are controlled by geology and land use. An integrative, spatially differentiating quantification of mass fluxes shows that e. g. Cl and B are introduced from urban sources such as leaking sewers and road salting. Input is highest under industrial areas (Cl 317 mg/d?·?m², B 0,6 mg/d?·?m²). For N_tot agricultural input (114 mg/d?·?m²) is more important than urban input with a maximum of 14 mg/d?·?m². Comparing overall urban input with estimated urban input, it can be concluded that there are additional sources for HCO₃, Ca, Mg, SO₄, Na, Cl, B and NO₃, which are not included in the estimated input (e. g. geogenic sources, fill material, industrial sources & degradation processes). PO₄ and N_tot on the other hand are being degraded and COD is consumed. A decrease of concentrations downstream from the city can be ascribed to diving plumes.     

Contamination of the Chalk Aquifer by Chlorinated Solvents: A Case Study of the Luton and Dunstable Area

A detailed investigation of contamination by chlorinated solvents of the Chalk Aquifer underlying the towns of Luton and Dunstable was undertaken to assess the extent, causes and mechanisms of pollution. The research programme incorporated land-use surveys, regional groundwater surveys, monitoring of groundwater abstraction points and aquifer profiling by means of the drilling of observation boreholes, the analysis of the recovered core material and the depth sampling of these and other boreholes.
Low-level solvent contamination of the Chalk Aquifer was found to be widespread with 'hotspots'of higher concentrations. At the drilling sites, both the saturated and unsaturated zones were contaminated with solvents, although free product was not observed. The presence of an additional contaminant, oil, at some sites was noted to influence the distribution of solvents within the aquifer.
Clean-up of the aquifer is not a practical option, and treatment of the groundwater at the abstraction points has been adopted.     

Priority pollutants in urban stormwater: Part 1 – Case of separate storm sewers

Organic and mineral pollutants have become part of today's urban environment. During a rain event, stormwater quality as well as the corresponding contaminant loads is affected by both atmospheric deposition and the various types of impervious surfaces (roads, rooftops, parking lots etc.) on which runoff occurs. This study provides results on stormwater pollution in Paris and its suburbs from three separate storm sewers (n = 20 samples). These results show that the stormwater had been contaminated by 55 chemical substances out of the 88 investigated. A particular attention was given to stormwater particle contamination. Concentrations are provided for: metals, PAHs, PCBs, organotins, alkylphenols, phthalates, pesticides, and VOCs. Our findings are among the first available in the literature since the relevant analyses were all conducted on both the particulate (P) and dissolved (D) phases. For most substances, particles from the three storm sewers were more heavily contaminated than dredged sediments and settleable particles from the Seine River. As a consequence of this finding, the release of untreated stormwater discharges may impact the receiving waters and contribute to sediment contamination.