Automated Sequential Composite Sampling
A New Technique for Water Pollution Study and Control
MARTHA I. BEACH, Vice President
JOHN S. BEACH, JR., President
N-CON Systems Company, Inc.
Larchmont, New York
INTRODUCTION
The collection of representative samples is essential to any pollution study or control
program. Agricultural runoff, and storm flows in urban and suburban areas are being
scrutinized to determine their pollutant contributions to receiving waters or treatment
plants. Metering and sampling of municipal and industrial effluents is being used as the
basis for sewer service charges in more and more areas. And, of course, regulatory agencies
are collecting samples for evidence in the prosecution of polluters. For industries, in
particular, many economic benefits may be derived from a well thought out and
conscientiously followed sampling and analysis program. When samples of liquid wastes
within and leaving the plant are analyzed the results can be used to:
1.Reduce product losses by means of process changes, more careful handling, reduction of water use, or recycling of water.
2.Reclaim product, by-product, or other valuable materials for inplant use or resale.
3.Establish the feasibility of sewer separation or of on-site treatment in order to adjust pH or to reduce hydraulic load, BOD, and suspended solids. These are the criteria which generally determine the size and type of treatment facilities needed or
the sewer service charge.
Whether the samples are collected manually or mechanically the sampling techniques
and type of sample collected should be selected after consideration of a number of factors.
These include:
1. the types of waste to be sampled
2. the hydraulics of the site
3. the analysis to be made
4. the proposed applications of the results of the study
The generally recognized types of samples are the "grab" or discrete sample, the simple
composite, and the flow-proportioned composite. The new type of sample described in this
paper, the sequential composite, combines the best features of grab and composite samples.
It broadens the statistical base of the final sample and it minimizes the chance of missing a
significant event of short duration. At the same time it retains the individuality of sampling
periods within the over-all sampling time.
REVIEW OF TYPES OF SAMPLE
777<? "grab" or discrete sample is equivalent to one collected by a man using a fixed
volume dipper or can on a stick. The sample is placed in a suitable container and carried to
the laboratory for analysis. There are several automatic samplers available which provide a
series of "grab" samples and retain each sample separately. A grab sample represents the
condition of the waste at a particular time and a specific place.
The simple composite is made up of a series of constant volume samples collected at
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