Fully flushed samples

NOTE A sample taken by the consumer cannot be considered a true random daytime sample, as the consumer is likely to take a sample with extreme stagnation time (either a first draw sample or a fully flushed sample). 

Fully flushed sampling (FF) is defined as a sample taken at the consumers tap after flushing the plumbing system for at least three pipe volumes. The 90 % prediction range of FF at a COMP level of 10 ug/l is 12 6 igl. Furthermore FF enables detection of only 45 % of problem properties, whereas it results in 4 % false positives. FF is very cost effective, practical and acceptable to consumers. 

Flushing the tap before use is an effective measme to reduce considerably the lead concentration at the consmner s tap. However, flushing does not guarantee that the lead level will be below 10 This study shows that in 50% of properties where the composite proportional sample exceeded 10 (xg/1, the fully flushed sample was less than 10 (xg/1. For 70 % of properties where lead exceeded 25 (xg/1, the lead concentration after flushing was less than 25 ig . ... 

The main value of a fuUy flushed sample is to confirm the absence of lead in the distribution system prior to contact with domestic pipe-work. Lead residuals should normally be below 1 pg/1 in a fully flushed sample from a consumers tap. If not, there are a number of possible reasons (i) flushing has not been sufficient, particularly with very long lead pipes, (ii) there is lead in the distribution network from a lead water main (rare but possible), or (iii) particulate lead problems are being experienced. Fully flushed samples have no role to play in determining compliance with standards at consumers taps. 

The maximum injection volume depends on the volume of the sample loop in the injection valve. The reproducibility of manual injection depends on the skill of the operator. The use of a small sample loop and an overflow injection of the sample solution so that the loop is fully flushed with sample are basic requirements for quantitative analysis. The highest injection reproducibility can be obtained by an auto-injector with a fixed sample loop. The smallest reasonable injection volume is 1 (A. A nl-scale injection valve can be constructed however, the memory effect at the surface of contact parts affects quantitative analysis compared with the use of a /d-scale injection valve. For a semi-micro system, a low hold-up volume injection valve is desired. The minimum injection volume is 80 nl. For a preparative-scale injection, the sample loop can be easily replaced with a larger-volume loop, such as a 200 jA, instead of the standard 20 /A loop. 

The sampler has to estimate the plumbing system volume. The fully flushed (FF) sample is taken after flushing three pipe volumes or 5 minutes (if the plumbing dimensions are not known) at 5 litres/minute. The sampler eollects a 1-litre sample. 

Measures for individual houses consist of lead pipe replacement and flushing before drawing water for eonsumption. The effect of the first measure ean be established using 30-minute stagnation-time sampling and proportional sampling. To assess the efifeetiveness of flushing, the fully flushed protocol can be applied. 

The first draw one litre samples taken will comprise or include any water stood in non-lead pipe-work, in-situ between a lead service line and the tap outlet, effectively diluting any lead in the water that has stood in the lead service line, again making it easier for comphance with the Action Level for lead to be achieved (it is common practice for pipe-work to be fully flushed just prior to the stagnation period). 

The definition of a random daytime sample is a sample that is taken at a random time of a working day directly from the tap in a property without previous flushing. When the sample is taken the tap should be fully opened or as open as possible without losing sample. The stagnation of water in the domestic distribution system influences the concentration of lead in a random manner. It is common practice to select the sampling points at random and for 1 litre sample volumes to be taken. 

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