3. Notes on the analysis and evaluation of environmental impacts

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3.1 Introductory remarks

To gain a full understanding of a wastewater disposal project is it vital to determine the underlying conditions and constraints of the project, against the background of its ecological and economic effects. The project description may be based on the following criteria:

- previous history of the plan.
- water legislation and standards.
- current wastewater situation (wastewater volume, existing works and their function).
- actual condition of the receiving bodies of water (discharge, quality, self-purification capacity, uses etc.).
- target condition of the receiving bodies of water (management aims: ecological function, uses, expansion requirements etc.; quality targets: characteristics, limits).
- previously established wastewater objectives e.g. based on existing general sewerage plans or other evidence of demand.
- incorporation into regional, national and countryside planning objectives and also the regional/supraregional disposal system.
- reasons for choice of planned works and its main components (pumping stations, storm basins, storm overflows, wastewater treatment plant(s), sludge polders etc.).
- alternatives (e.g. sewerage processes such as dual/combined system, wastewater pumping, sludge recycling/storage, extension or expansion of existing works) as well as baseline state.

Further components of the environmental impact assessment of a wastewater disposal project are descriptions of

- the location-finding process for relevant alternatives, including any necessary socio-economic analyses of sex- and group-specific questions of the population settled in the surrounding area or area covered by the wastewater treatment works in question.
- the location comparison and results.
- the relevant works and their failure risks.
- factors of the project adverse to the environment and those plants or plant components which should eventually form the object of an environmental impact survey.

Major environmental impacts result from the construction and operation of the sewage treatment plants referred to below with minimum size/capacity as follows:

- pumping stations, output Qp > 4 500 m3/2h1)
- rainwater basins (rainwater retention basins, rainwater overflow basins etc.), dry weather discharge Qt > 1 500 m3/2h in the sewer before the rainwater basin system
- rainwater overflows, dry weather discharge in the sewer before the overflow Qt > 1 500 m3/2h
- wastewater treatment plants, which are designed for (see (1)):

Qin > 1 500 m3/2h1) (intake) or

Bd,x > 3 000 kg/d BOD5 (org. daily load in intake) or

Pc > 50 000 PE (connected load in population equivalents with a sewage load per inhabitant of 0.060 kg/d)

The above values should be regarded as guideline figures; in addition, the scope of the assessment must be decided on a case-to-case basis, depending on the environmental relevance of the plant components. This applies particularly, for example, to rainwater retention basins which are installed underground and so are "invisible".

Domestic sewage mainly comprises:

- lavatory wastewater
- kitchen wastewater
- wastewater from baths/showers
- cleaning wastewater (from house cleaning).

It therefore has a varied structure, but as a rule its quality is not such that the existence, operation and safety of the sewage plants or the health of the operating personnel could be endangered. Moreover it lacks properties which could result in adverse changes to the environment, provided the sewage works are designed correctly, the bodies of water managed appropriately and the sewage sludges produced disposed of and recycled properly.

However, here one should note that special attention should be paid to the correct operation of "domestic" sewage plants and hence water conservation, if the volume of wastewater is subject to large variations (sudden loads or temporary and sometimes complete absence of wastewater). This applies particularly to hotels, highway service areas, campsites, convalescent homes and similar installations with individual drainage. Special planning and operating methods are required here to prevent avoidable pollution of bodies of water (33), (34).

The following Sections 3.2 to 3.4 therefore deal only with the analysis and evaluation of the environmental impact of commercial or industrial wastewater, primarily as a component of municipal wastewater (indirect discharges) rather than in terms of discharges from commercial and industrial establishments (direct discharges). For guidance, refer to the German regulations.

3.2 Wastewater collection and removal area

The direct discharge of commercial or industrial wastewater is safe if as a result

a) the health of the staff employed in public sewage works is not adversely affected,

b) the state and operation of public sewage works are not adversely affected,

c) the bodies of water which take the wastewater from the public sewage works cannot be polluted beyond the permitted level or otherwise adversely affected,

d) no lasting odour nuisance occurs at the sewage works and

e) the sludge treatment, sludge recycling and sludge disposal are not seriously hindered.

If adverse effects of the type described above are anticipated, then the discharge of the wastewater into a public sewage works should be conditional on pre-treatment at the point of production or other suitable measures (see German ATV Arbeitsblatt A 115 (35)).

Safety is generally assured if the figures given in Annex I of (35) for the composition and constituents of wastewater are not exceeded. Permissible concentrations of substances not listed in Annex I must be decided on a case-to-case basis.

Substances which block the sewerage network, form poisonous, foul-smelling or explosive vapours and gases or attack buildings and building materials to a significant degree must not be discharged into a public sewage works.

The German ATV Arbeitsblatt A 115 does not yet contain any specific regulations for indirect discharge of hazardous materials within the meaning of 7a WHG (German Federal Water Act (11)), e.g. of certain chlorinated hydrocarbons such as hexachlorobenzene, pentachlorophenol, trichloroethene etc. Basically, 7a WHG and the relevant follow-up regulations of the Federal States required that the state-of-the-art be assessed in order to determine the permissibility of indirect discharge of such substances.

In Germany, the wastewater in question must be monitored and analysed in accordance with the relevant DIN standards (DIN 38400 ff.) (36).

3.3 Wastewater treatment area

In the Federal Republic of Germany, under 7a WHG (11), binding emission standards for the discharge of wastewater into surface waters are given in the appendices to the "Allgemeine Rahmenverwaltungsvorschrift über Mindestanforderungen an das Einleiten von Abwasser in Gewässer" (General Administrative Framework Regulation on Minimum Requirements for the Discharge of Wastewater into Waters) (12). A summary of the relevant administrative regulations is given in (37).

For discharges from municipal sewage works, the standards are defined in appendix 1 of (12). According to this document, the following limit values apply for different size classes of sewage works in Germany in accordance with the generally recognised rules of the art:

Table 2 - Minimum standards for discharges from municipal sewage works

Size class1)

BOD5 (mg/l)

COD (mg/l)

NH4-N (mg/l)


1 (< 60)
2 (> 60 < 300)
3 (> 300 < 1200)
4 (> 1200 < 6000)
5 (> 6000)





1) Figures in brackets: intake values BOD5 (raw) [kg/d]

With increasing plant size (connected load), the standards become more stringent as a result of the greater operational reliability of the sewage works.

Here too, the monitoring analysis is based on the relevant assessment procedures according to the German DIN standard 38400 (36). The same applies to analysis of wastewater from commercial and industrial establishments. The method and scope of sampling also very largely depend on the relevant administrative regulations.

If it is apparent in a particular case that despite the application of relevant emission standards, an unacceptable burden may be imposed on the bodies of water (insufficient capacity of the receiving water), it may be necessary to lay down stricter standards for the condition of the wastewater to be discharged, if other measures, such as transfer of part of the volume into another river basin, are not possible. As regards discharge monitoring (analysis), the same regulations are to be applied as already mentioned above.

3.4 Sludge disposal area

The environmental implications of (municipal) sewage sludge are primarily in relation to its disposal in the form of agricultural fertiliser. Important criteria have been defined in Germany under the Klärschlamm-Verordnung (sewage sludge ordinance) (16) which establishes permitted values for the concentrations of selected heavy metals in the soil and in the sewage sludge itself; in addition, restrictions are imposed on the quantities which may be applied. See Table 3 below.

Table 3 - Permitted concentrations of heavy metals in accordance with the Klärschlamm-Verordnung (sewage sludge ordinance)

Heavy metals(HM)

Generally permitted concentrations in sewage sludge

Quantity permitted to be applied

Maximum permitted heavy metal concentration upon application of sewage sludge









1) related to dry sludge residue

At least in temperate zones, if the regulations contained in the sewage sludge ordinance are complied with, no long-term harm will be inflicted on soil, plants, animals or humans through the use of sewage sludge in agriculture; moreover, in particular, the health of people or animals will not be harmed by consumption of foodstuffs or fodder produced on land to which the sludge is applied (15).

When actually constructing a sewerage system, it may be advisable to determine the heavy metal concentrations which a sewer network may discharge to the central sewage works so as to ensure that the permissible heavy metal concentrations of the sewage sludge can be maintained in accordance with the sewage sludge ordinance. Suitable procedures are indicated in publication (38).

For the sewage sludge analysis, reference should again be made to the relevant regulations in accordance with DIN 38400 ff. (36).


4. Interaction with other sectors

Because of their geographical and physical impact, supply and disposal projects must stand in a clear and plausible relationship with other environmental and geographical areas. This is particularly true of wastewater disposal (WWD) projects, bearing in mind the potential danger posed by the domestic, commercial and industrial wastewater to be disposed of.

Areas which may be affected by WWD projects, such that this may lead to conflicts of use and interactive effects include, in particular, the following:

- bodies of water (surface water, groundwater); water resources management, hydraulic engineering
- soil; agriculture and forestry
- air
- water production, water supply
- waste management, waste disposal
- nature conservation, countryside preservation, recreational resources
- urban/community planning, industrial development
- monuments and heritage
- traffic planning (roads, railways, waterways, flight paths)
- existing/future regional planning, land-use and development planning; activity planning
- distance problems in existing and planned residential areas
- availability of land and soil.

If conflicts of use occur, the options must be weighed up. The standard against which these are judged is not the status quo, i.e. the structures and services existing prior to execution of the wastewater disposal project, but rather the development potential of the area in question. The criterion is thus the capacity and not the present performance (39). This approach also stresses the importance of identifying and assessing the soil potential, the biotope potentials and the hydrogeological potentials (in terms of both quantity and quality). Adjustment, alleviation and compensatory measures may provide crucial help in arriving at the environmentally ideal overall solution.


5. Summary assessment of environmental relevance

To sum up, the following may be said with regard to the environmental relevance of wastewater disposal projects:

The plants of such a project must be planned, built and operated in accordance with the generally accepted rules of the art or wastewater technology and, if hazardous substances are to be eliminated in treating wastewater, in accordance with the state of the art. One must take into account the immission situation (burden), other uses and the hydrological and biological capacity of the receiving body of water.

If the capacity of the receiving body of water in question is not sufficient to absorb the wastewater treated in accordance with the rules of the art, then for the sake of water quality, further requirements must be laid down for the treatment efficiency of the sewage works or the wastewater discharge. A management plan may then be necessary to ensure that the receiving body of water serves the good of the general public, in harmony with the benefit of individuals, and prevent any avoidable adverse effects (§ 1a WHG (11)).

As a general rule, every area must be appropriately treated before the drinking water can be used; this is especially true when wastewater discharges are situated above the point where water is drawn off.

As a general rule, to relieve pressure on wastewater disposal systems, the volume of wastewater should be minimised, both in the domestic and in the industrial and commercial sectors.

Other non-water related effects of a wastewater disposal project, such as occupation of land, noise and odour emissions, flue gas emissions etc. are normally of lesser importance in assessing the environmental relevance. This is because the plant components are mainly installed underground and because few installations affecting air purity, such as sludge incineration plants, are ever built.


6. References

(1) Law implementing the council directive of June 27.1985 on the assessment of the effects of certain public and private projects on the environment (85/337/EEC) February 12, 1990; Article 1: Law on the assessment of the effects on the environment.

(2) Abwasserabgabengesetz - AbwAG of 5 March 1987 (Promulgation of new version); BGBl. (Federal Law Gazette) 1987, Teil I, p. 880.

(3) Friesecke, G.: Die allgemein anerkannten Regeln der Technik beim wasserrechtlichen Vollzug, Wasser und Boden, 5/1985; Verlag Paul Parey, Hamburg.

(4) Gesetz zum Schutz vor schädlichen Umwelteinwirkungen durch Luftver-unreinigungen, Geräusche, Erschütterungen und ähnliche Vorgänge (Bun-desImmissionsschutzgesetz - BImSchG) 22 May 1990, BGBl. (Federal Law Gazette), p. 881.

(5) Bretschneider, H. (Ed.): Taschenbuch der Wasserwirtschaft, 6. Aufl.; Paul Parey Verlag, Hamburg, Berlin; 1982

(6) DIN 4045: Abwassertechnik, Begriffe; Beuth Verlag GmbH, Berlin.

(7) Abwassertechnische Vereinigung e.V. (Ed.): Lehr- und Handbuch der Abwassertechnik, Bd. I bis VII; 3. Aufl.; Verlag W. Ernst & Sohn, Berlin, Munich, Düsseldorf; 1982/1986.

(8) Imhoff, Karl and Naus R.: Taschenbuch der Stadtentwässerung, 27. Aufl.; Oldenbourg Verlag, Munich, Vienna; 1990.

(9) Pöpel, F. (Ed.): Lehrbuch für Abwassertechnik und Gewässerschutz (may be supplemented); Deutscher Fachschriftenverlag, Wiesbaden.

(10) GTZ (Kloss): Stand, Potentiale und Bedeutung der Biogastechnologie auf dem Gebiet der anaeroben Reinigung von dünnflüssigen Abwässern sowie Maßnahmen zur Einführung dieser Technologie in den ländlichen Regionen der Dritten Welt; Report, 1990.

(11) Gesetz zur Ordnung des Wasserhaushalts (Wasserhaushaltsgesetz WHG) in the version promulgated on 23 September 1986, BGBl. (Federal Law Gazette) I, p. 1529.

(12) Allgemeine Rahmen-Verwaltungsvorschrift über Mindestanforderungen an das Einleiten von Abwasser in Gewässer - Rahmen-AbwasserVwV - of 8 Sep. 1989 (GMBl. (joint ministerial circular) p. 518), amended on 19 Dec. 1989 (GMBl. p. 798) and appendices 1 ff., p. 521.

(13) The World Bank, Washington D.C.: Environmental Guidelines, 09/1988.

(14) Meinck, F., Stoof, H., Kohlschlütter, H.: Industrie-Abwässer; Gustav Fischer Verlag, Stuttgart, 1968; new edition in preparation.

(15) Hösel G.; Schenkel, W.; Schnurer, H.: Müll-Handbuch (may be supplemented), 3356 ff., Landwirtschaftliche Klärschlammverwertung; Erich Schmidt Verlag, Berlin.

(16) Klärschlammverordnung - AbKlärV of 25 June 1982; BGBl. (Federal Law Gazette) I, p. 734.

(17) LAWA / ZfA; Merkblatt 7: Die Behandlung und Beseitigung von Klär-schlamm unter Berücksichtigung ihrer seuchenhygienisch unbedenklichen Verwertung im Landbau; May 1972; reprinted in (18), Lfg. 1972.

(18) Hösel, G., Schenkel, W., Schnurer, H.: Müll-Handbuch (may be supplemented); Erich Schmidt Verlag, Berlin.

(19) Merkblatt 10, Qualitätskriterien und Anwendungsempfehlungen für Kompost aus Müll und Müll/Klärschlamm; LAGA, Umweltbundesamt [German Federal Environmental Agency]; reprinted in (18).

(20) Deutsches Institut für Normung e.V.: DIN 4261: Kleinkläranlagen, Teil 1 (Oct. 1983), Teil 2 (June 1984), Teil 3 (Oct. 1983), Teil 4 (June 1984), Beuth Verlag, Berlin.

(21) The World Bank, Washington D.C.: Water-borne Sanitation; Information and Training for Low-Cost Water Supply and Sanitation, 1985.

(22) Wolf, p. (Ed.): Stand der Technik bei der Vermeidung gefährlicher Stoffe in der Abwasserbeseitigung; Schriftenreihe des Fachgebietes Sied-lungswasserwirtschaft Universitität/Gesamthochschule Kassel, 1989.

(23) ATV: Planung von Entwässerungsanlagen, Arbeitsblatt A 101, Jan. 1992; GFA, St. Augustin.

(24) Parker, C.D.: Hydrobiological Aspects of Lagoon Treatment; Journal Water Pollution Central Federation, J.W.P.C.F., vol. 34, pg. 149; 1962.

(25) WBTP 7: Arthur, J.P.: Notes on the Design and Operation of Waste Stabilization Ponds in Warm Climates of Developing Countries; 1983.

(26) Yánez, Fabián: Lagunas de Establización, Centro Panamericano de Ingenieria, Lima, Peru, 1977.

(27) Arthur, J.P.: The Development of Design Equations for the Facultative Waste Stabilization Ponds in Semi-Arid Areas; Proceedings of the Institution of Civil Engineers, vol. 71, part 2; 1981.

(28) Gloyna, E.F.: Waste Stabilization Ponds; WHO, Geneva, 1971.

(29) World Bank Technical Paper (WBTP) 49: Gunnerson, Charles G.; Stuckey, David C.: Anaerobic Digestion, Principles and Practices for Biogas Systems; 1986.

(30) WBTP 51: Shuval, Hillel J.; Adin, Avner; Fattal, Badri; Rawitz, Eliyahu; Yekutiel, Perez: Wastewater Irrigation in Developing Countries; 1986.

(31) The World Bank, Washington D.C.: Aquaculture with Treated Wastewater, A Status Report on Studies conducted in Lima; 1987.

(32) WBTP 36: Edwards, P.: Aquaculture: A Component of Low Cost Sanitation Technology; 1985.

(33) ATV: Richtlinien für den Anschluß von Autobahnnebenbetrieben an Kläranlagen, Arbeitsblatt A 109, Jan. 1983; GFA, St. Augustin.

(34) ATV: Abwasserbeseitigung aus Erholungs- und Fremdenverkehrseinrichtungen, Arbeitsblatt A 129, May 1979; GFA, St. Augustin.

(35) ATV: Hinweise für das Einleiten von Abwasser in eine öffentliche Abwasseranlage, Arbeitsblatt A 115, Jan. 1983; GFA, St. Augustin.

(36) DIN 38400 ff.: Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung, Beuth Verlag GmbH, Berlin.

(37) Lohaus, J.: Übersicht über die geltenden Verwaltungsvorschriften zu 7a WHG, Korrespondenz Abwasser, 37, 1900, Nr. 6; GFA, St. Augustin.

(38) Friesecke, G.: Auswirkungen der Klärschlammverordnung auf abwasser-und abfalltechnische Fragen, Wasser und Boden, 11/1983; Verlag Paul Parey Hamburg.

(39) Gassner, E.: Die medien- und verfahrensübergreifende Umweltverträglichkeitsprüfung, Umwelt- und Planungsrecht 1990/10; Kommunalschriftenverlag Jehle, Munich.

(40) EC Directive: Assessment of the effects of certain public and private projects on the environment; 85/337/EEC-Official Journal No. L175/40 of July 5, 1985.

(41) Schemel, H.-J.: Die Umweltverträglichkeitsprüfung von Großprojekten; Erich Schmidt Verlag, Berlin; 1985 new edition in preparation.

(42) Storm, P.-C. (Ed.): Handbuch der Umweltverträglichkeitsprüfung (HdUVP), may be supplemented, Erich Schmidt Verlag, Berlin.

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