The county landfill in the diagram was monitored to verify that toxic compounds were not leaching into the local water supply. Wells drilled at 21 locations were monitored over a year and pollutants were observed only at sites\(8,11,12\), and 13 . Monitoring all 21 sites each month is very expensive. Suggest a strategy to use composite samples (Box 0-1) made from more than one well at a time to reduce the cost of routine monitoring. How will your scheme affect the minimum detectable level for pollutants at a particular site?

A collection of individual samples (grab samples) taken over a specific time period (e.g., 24 hours for a daily composite). The water characteristics in a composite sample represent the conditions in the sampled flow during that time period. Subsamples can be collected at regular intervals to produce time-weighted composites, or their volume and timing can be varied to produce flowweighted composites.

In this task we will suggest a strategy to use composite samples (Box 0-1) made from more than one well at a time in order to reduce the cost of routine monitoring. Also, explain how would our scheme affect the minimum detectable level for pollutants at a particular site.

One of the possible schemes would be to monitor the wells \(8,11,12\) and 13 individually, but we would pool from other sites samples

A composite sample can be made with same volumes from wells\((1,2,3,4)\), whereas other composite samples could be made from \((5,6,7);(9,10);(14,15,16,17);(18,19,20,21)\)

(1) If there is no warning level of analyte found in composites, we could say that each well in those composites contains no analyte.

(2) If we find that analyte is present in composites, then we would separately analyze each contributor to the composite sample.

The main disadvantage of pooling samples from different \(n\) wells is that the sensitivity of analysis in each well would be reduced by \(1/n\).

How the scheme affects the minimum detectable level for pollutants at a particular site is explained above clearly.