Report No DWI0665

Jun 1986

The water industry has extensive experience of monitoring sewage sludges and soils as an essential part of their sludge disposal operations. Sampling is required not only to meet environmental quality objectives as laid down in national guidelines and the EC Directive on the use of sludge in agriculture but also to provide performance data on sludge treatment and disposal.

A review of current sampling procedures by panel discussions and individual interviews was undertaken by WRc as part of a DoE funded project in order to ascertain the extent of any problems associated with existing sampling methods and to identify the potential for improving the reliability, accuracy and cost-effectiveness of sampling procedures.

The main conclusions and recommendations were:

1. sludge samples are prone to large variation due to the inherent heterogeneity of the material. This can be exacerbated by inappropriate sludge sampling procedures which reduce the value of field archives for predicting soil concentrations of heavy metals applied. The extent of the problem and methods to improve the quality of monitoring need to be identified;
2. the reliability and cost-effectiveness of soil sampling needs to be examined and where necessary improved. Areas of particular concern are sampling depth, consistency and pattern, all of which may introduce bias or lead to an increased sample variability. Sampling following soil injection requires special examination and appropriate procedures need to be developed. The procedures for soil sample preparation and analysis also need further investigation as current methods, particularly for assessing soil density and stone content, may lead to biased results;
3. this review highlighted the water industry's concern for reliable and cost-effective sludge and soil sampling procedures and emphasised some of the difficulties involved in environmental and performance monitoring of sludge disposal operations. It was clear that procedures and equipment which would improve the quality and efficiency of sample collection would be welcomed. There was general support for the development of rapid field methods for dry solids and nutrient analysis, automated sampling devices and in particular, the production of a Code of Practice which should help ensure standardisation and optimisation of sampling procedures.

Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.