Municipal wastewater - KOSTRA, 2014

The figures are published on national and regional (municipal and county) level, in addition to grouped in economically comparable groups.

Key figures are published annually in connection with Municipal-State-Reporting (KOSTRA) on the 15th of Mars (unrevised) and 15th of June (revised).

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The raw data is saved in text-format. Revised data sets are saved in Oracle-databases here with Statistics Norway. The Norwegian Environment Agency also has a copy of the dataset.

KOSTRA started up as a project in 1995 with the intention to provide relevant and up-to-date information about resources spent, priorities and meeting targets in municipalities and counties. The goal is to collect data in a co-ordinated way, and make the information flow a one time delivery per year for all steering-information needed by municipality. The number of municipalities and counties was gradually increased until the reporting year of 2001, then all municipalities were included in the KOSTRA.

KOSTRA provide steering information about municipalities and counties to the different interest groups, inhabitants, media, the municipality itself, different state organs and controlling authorities etc.

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The statistics is also related to other statistics like municipal residential charges , turnover from sewage and refuse activities , sewage and refuse disposal (structural business statistics) , Municipal wastewater treatment and KOSTRA - municipal water supply

Data are collected by Statistics Norway on behalf of the Norwegian Environment Agency with legal basis in the Pollution Control Act (13th Mars, 1981, no. 6). Statistics Norway can make use of the collected data for official statistical purposes with legal basis in the Statistics Act (16th June 1989, no. 54, §2-2).

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All municipalities in Norway are covered, thus it is a complete collection (and not a survey).

The Municipal-State-Reporting system (KOSTRA).

From 2015, the Norwegian Environment Agency also became an information source as they took over part of the electronic forms traditionally collected by KOSTRA.

Data is collected electronically once every year, and the information should submitted to Statistics Norway by 15th of February. The Norwegian Environment Agency apply the same reporting frequency and deadlines as in KOSTRA.

The electronic forms in KOSTRA and by the Norwegian Environment Agency contain built-in consistency checks and logical tests. After arrival data are checked automatically and manually by Statistics Norway.

Unrevised data will be published on 15th of Mars. There is a second deadline on the 15th of April for municipalities to correct possible errors in the figures just published.

Data are being published on different levels, as basic data and key figures. Basic data is generally reported in absolute numbers, and will largely constitute aggregated numbers summed up for a certain period of time or at a time of year. Key figures, on the other hand, are commonly a ratio (made up of different basic data).

Calculation of statistics on country, county and KOSTRA group level (estimations)

Every year there are incidents of non-respondents, and this is visible in the statistics on municipality level as “blank data”. When it comes to figures reported in the plant level - sewage and sludge treatment –Statistics Norway make corrections in order to "neutralise" such deficiencies when calculating figures published on country, county and KOSTRA group level . Normally, this implies direct imputation of figures reported earlier i.e. if it is not reported anything in this year's reporting such missing information is collected from last year or previous years. These earlier reporting thus form the basis for the respective site when you sum up to a country, county or KOSTRA group level. The municipality in question will still come out as missing in the statistics on municipality level in that particular year, since they didn’t reported, but the statistics published for the country, county and KOSTRA group level will be subject to "statistical correction", not directly visible in the published KOSTRA figures. Thus, one can not simply sum up basic figures for all municipalities and expect that total corresponds to published national figures in the statistics. The purpose of such corrections is of course to remedy for non respondents and create more robust and reliable estimates on statistics published by Statistics Norway for the country, counties and KOSTRA groups.

Calculation of load

Due to the fact that only a minority of wastewater facilities undertake direct measures of pollution load, standard factors needs to be incorporated in the calculations. Thus, total load figures of phosphorus are largely based on this set of factors (see below for further details).

The following calculation procedure has been applied to municipal wastewater facilities, capacity of 50 pe or more:

1. If the wastewater facility provides information on load, expressed as kilogram per year, this information will be used directly.

2. If the wastewater facility provides no information, as specified in number point 1 above, but given outflow concentrations and average water quantities, then load is calculated in kilos per year from the following equation:

concentration (mg/l) x average water quantity (m3/day) x 365 / 1000

3. If measurements are not carried out, total load are calculated by multiplying the number of people connected to wastewater facilities with standard factors of average load per person per day (1.6 gram phosphorous per person per day):

number of people connected x 1.8 (g P/ day x person) x 365 / 1000

NB! For the years 2015 and earlier 1.6 g TOT-P/day x person was used as a factor instead of 1.8 as mentioned above, thus here is a “small break in time series".

Calculation of use of sewage sludge

2005 and 2006 data were reported based on gross sewage sludge and its associated percentage dry weight is now included in the reporting. In all other years dry weight of sewage sludge has been asked for. But in order to calculate the dry weight in 2005 and 2006, the information of percentage dry weight was essential, and in cases where percentage dry weight was missing, then the following method was applied to the data:

1. If percentage dry weight of the produced sludge product was reported, but not for the amounts of sludge used, then this percentage was then applied.

2. If percentage dry weight of neither the produced sludge product nor the amounts used was reported, a standard factor of 25 per cent dry weight was applied.

Calculation of age of the municipal wastewater pipelines
Calculations of the age of municipal wastewater pipelines on country level in the article - Todays Statistics - has been adjusted for pipelines of unknown age (not specified time period). Pipelines in these cases has been spread accordingly over the following time periods (1) before 1940, (2) 1940-59, (3) 1960-79 and (4) 1980 with the following percental distribution 50, 20, 20 og 10. In addition, the age presented in the article has in for some municipalities been imputated with data from earlier years if data was not avaliable from last year. These corrections constitute a few small excemptions, while the age figures in Statbank has not been corrected in this way (based solely on last years reporting and on the part of the pipelines which can be pinned down to one spesific time period).

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Key figures on country level and for regions (counties and KOSTRA groups) are up to 2007 based on just average calculations of reported data, while data from 2008 and later constitute statistical calculated estimates which take into consideration non responses in the dataset to a higher degree.

Comparisons over time may be reduced by the fact that some facilities have not been reported the year they first were established, but years later ("delayed reporting"). The statistics are not automatically re-calculated back in time series just because new and updated information become available. This applies primarily to smaller facilities.

Use of sewage sludge has been reported in different ways after KOSTRA took over. The 2004 reporting was carried out on aggregated municipality level, but this was changed back again to reporting on sludge treatment plant level in the 2005 data collection.

The category deposited was not included as a separate use-category in 2003 due to a ban on deposition of wet organic waste, including sewage sludge (Regulation on deposition of waste (Department of Environment 2004). Because it is not totally face out the category was re-introduced again in 2004 in order to cover these amounts in the official statistics. The changes in the reporting, in addition to that the reported data is of various quality, result in some uncertainty in the statistics.

As mentioned under chapter " Collection of data, editing and estimations" a small adjustment in methodology has taken place in the calculation of phosphorous load (TOT-P). In cases where the wastewater facility doesn’t carry out monitoring or analyse its discharges, a theoretical discharge factor of 1.8. gram TOT-P per person and day is applied. This factor however was 1.6 for the years 2015 and earlier, thus here is a small break in the overall time series of the relevant key figures and basic data published on our web sites.