Stofkoncentrationer i regnbetingede udledninger fra fællessystemer

1. Introduction

1.1 Background
1.2 Target of the review
1.3 Information sources

1.1 Background

The Danish National Authorities recommend three standard methods of increasing complexity for the calculation of urban runoff pollution loads, ranging from using area unit pollution loads to using long historical rain series and the SAMBA module in the MOUSE package. Common for these methods is the concept of event mean concentrations (EMC’s), i.e. that the pollutant concentration in the runoff is assumed to be independent of the size and distribution of the rain volume and also independent of the characteristics of the catchment such as size, storage capacity, maintenance etc.

Data from recent measurements question these assumptions (Miljøstyrelsen, 1997). During two summer periods runoff from six catchments has been measured. The preliminary analysis of the data showed significant differences between the hydrograph and the pollutograph, and the calculated event mean concentrations were significantly higher than what was previously observed.

In appendix B of this report the Danish data is processed more closely using modern statistical methods. The purpose of this appendix (A) is to review the available international investigations on the same issue, as basis for assessing the results from analyzing the Danish data. Results from the literature review and the data processing are compared in the main report.

1.2 Target of the review

The core of the literature review is to assess levels of EMC’s in stormwater discharges from combined sewer systems. Of particular importance is the variation of average EMC’s from different sites in different regions and countries, e.g. the variation of site mean concentrations (SMC’s). On top of this comes other issues related to the use of these EMC’s for calculation of urban runoff pollution loads. The purpose can thus be divided into the following tasks

• To review procedures for prediction of pollution loads from knowledge about rainfall, catchment characteristics and SMC’s.
• To review the major international investigations where pollution runoff from combined sewer systems has been measured and where EMC’s have been calculated.
• To review to what extent the variation of EMC’s (between events) and SMC’s (between catchments) can be explained by correlation with characteristics related to the runoff events and catchments.

Focus is on suspended solids (SS), organic matter (COD) and nutrients (N and P) but other pollutants will be included where they are available.

1.3 Information sources

The following two information sources available at DTU through the Technical Knowledge Center were systematically searched for relevant literature:

• The web of Science is the web version of Science Citation Index and indexes about 5.600 journals since 1990 worldwide.
• Cambridge Scientific Abstracts Internet Database Service contains in addition to journal papers also conference proceedings, books and technical reports since 1981.

More than 6000 references were found using the following search profile

(stormwater) or (storm water)
cso* or combined sewer overflow*
urban runoff* or urban run-off*
(first flush) or (first foul flush) or (foul flush)
rain and pollution and (discharge* or load* or emission*)
rain and pollution and (runoff* or run-off*)
wet weather and (discharge* or load* or pollution or emission)
emc or (event mean concentration).

However, only a minor part of these references were relevant to the project. After importing the references in the literature database program Reference Manager 8.0 for Windows 95 they were manipulated in different ways, including visual inspection of on-line abstracts, finally leading forward to a selection of about 90 references of some relevance to the project.

This limited number of references illustrates that technical reports from national and regional sources are not commonly included in such databases and that there was no strong tradition until recently among researchers of urban drainage to publish results in international forums. Some of the major international measurement programs have only been published in national technical reports and these have not generally been available during the project.

To complement the literature search publications collected at DTU and AAU during the past years (books, reports, conference proceedings and journal papers) were added to the material scanned in detail. This increased the information level significantly as far as conference proceedings and technical report goes.

The reference list covers all the references cited in the text but references only to the general subject are not included.