The UK normally uses a Monte Carlo approach, with a Street-Phelps form of model. You specify the current river quality (lower 5% flow, mean flow, water quality, standard deviation); you specify the discharge parameters (mean, standard deviation, distribution type - usually log Normal) and then an estimate of the river quality from the new discharge is calculated.

You are usually limited to the lesser of: no more than a 10% deterioration OR no change in river status (defined on a scale of 1 - 5).

For more details than this you would need to search the UK Environment Agency website and see if you can find the river permitting software and the technical discussion to go with it.

Hi Nafees,

Tricky question, because it involves environmental science and management. I think the set of criteria for defining the water quality guideline varies according to the philosophy of stakeholders. For instance in U.S. it is the standards are often based on the toxicity to local fauna and flora. So after several studies are performed on the toxicity levels of contaminants and the Environment Agency makes sensibility curves and estimates overall 5 %, 20 % and 50 % of toxicity.

In other countries there is an approach of considering the human use as an important defining of limits. For instance, in Brazil there are water quality classes that consider the main human uses of the water, and the contaminant loads are defined to not compromise water uses. Germany has more of a top-down water management (the stakeholders decide and execute), while France has more participation of the water users in defining the quality goals. Thus the national approach to its water resources surely affect which criteria they think it is needed.

Moreover, in many European countries most of waters are not at the "Good Ecological status", so they have to be permissive with certain pollutants and set a small level of effect (generally the LOEC) as acceptable. Other nations, as many american countries, have the a great part of their water bodies at good state. In those cases, the level of contamination settled as acceptable is the one that causes no effect (NOEC).

On top of this geographic mosaic of management strategies, the set of criteria strongly depends on the contaminant itself. For instance, many states in Canada and U.S. have a standard for dissolved copper that varies for each water body because the individual water chemistry strongly affects the toxicity of this metal.

My point is that the ideal set of criteria to establish a water quality guideline will vary depending in the social, geographic, and geochemical context of the water body. At the best case, I could indicate to you the website of the Water Framework directive that offers some guidance to European countries on how to classify and set goals to their waters; and the website from EPA-US, which offer guidelines to the states on how to set their locally specific water quality.

http://ec.europa.eu/environment/water/water-framework/facts_figures/guidance_docs_en.htm

https://www.epa.gov/wqs-tech

Hope it was useful.

Abel

Drain join in stream /lake is a serious issue. Such water may be polluted in terms of physical, chemical and bacteriological. If water use for domestic/drinking , must be free from contaminant and all the parameters within permissible limits. Most of the countries have their own permissible limits. However ever Guide line of World Health Organisation, US public Health and many others may be practised.

Thank you Virendra Kumar Saxena for your feed back.

Water quality standard is developed for a particular pollutant or all considered parameters based on the following aspects:

• Designated Uses of the water body - protection and propagation of fish, shellfish and wildlife, recreation, public drinking water supply, agricultural, industrial, navigational and other purposes
• Criteria to protect designated uses - numeric -e.g., the maximum pollutant concentration levels permitted in a water body or narrative - e.g., a criteria that describes the desired conditions of a water body being “free from” certain negative conditions
• Antidegradation requirements - a framework for maintaining and protecting water quality that has already been achieved

Regards

In addition to what have been truly stated by Jeremy Dudley and Abel Machado , Virendra kumar and Asit kumar, I intend to add as under:

Your question clearly states that the pollutant via drain is joining river, stream or a lake.

In this case safety of drinking water supplies- protection of public health has to be the primary aim for guideline framework. Failure is likely to create risks of outbreaks of serious diseases. While deciding guideline values of each pollutant should be determined based on risk benefit approach - qualitative and quantitative approach. Guideline values are the concentration of a pollutant that does not result in any significant risk to the health of the consumer. Looking to the circumstances when the guideline values exceed the investigation needs to be made for cause-remedial action.

In general, guideline value are used by each country to set the national standards based on risk hazard analysis in the respective countries depending upon socioeconomic, geographical and conditions affecting potential exposure.

The guideline values are considered for human environment and may not be suitable for aquatic life. For aquatic life bio-essay studies on river water are conducted.

WHO guidelines are considered as Environmental Health Criteria

As above Dr Sheth 's answer is satisfactory

As above Dr Sheth 's answer is satisfactory

As above Dr Sheth 's answer is satisfactory

I totally agree with Dr Sheth. The ultimate use of water is one of the criteria used in setting the acceptable threshold for the pollutant, for instance the limit for water that will be used domestic purposes will be different from a water body that has been dedicated to agricultural uses, however we consider the aquatic life in the water. the extent of treatment required is also a factor to be considered.

Very rich discussion and highly appreciated.

Thank you all for your time and nice inputs.

Thank you Dr K N Sheth for your detail reply. We have approved water quality standards equally applicable to all sort of water body (see attachment). We have small and large rivers. A particular industry discharging it's waste in to a big river will have one impact and the same effluent will have different impact on a small river. Question is how to make change in this standard in such a manner to calculate new safe water standard for another water body. It is worth mentioning that the same standards are applied to ocean also.

Good question, following.

Criteria in terms of the allowable values for different uses from different sources.