Trade Waste Bylaw 2002 - Schedule 1E

Home : Policies and Plans : Bylaws : Bylaws Part 18: Trade Waste Bylaw 2002 : Schedule 1E

SCHEDULE 1E SAMPLING PROCEDURE

1E.1 Sampling Equipment

1E.1.1 Sample Containers

1E.1.1.1

The laboratory responsible for analysing the samples should be consulted about the type of container that should be used for sample collection and subsequent sample storage and transportation.

1E.1.1.2

Desirable factors to be considered when selecting sample containers are:

(a) High resistance to breakage;

(b) Good sealing efficiency;

(c) Ease of reopening;

(d) Good resistance to temperature extremes;

(e) Practical size, shape and mass;

(f) Good potential for cleaning and re-use;

(g) Availability and cost;

(h) Ability to be clearly labelled.

1E.1.1.3

The sample container needs to prevent losses due to evaporation, adsorption, volatilisation and contamination by foreign substances.

1E.1.1.4

Plastic containers are recommended for most characteristics. Some exceptions exist where glass containers only should be used, when for example any of the following analyses are to be made:

(a) Oil and grease;

(b) Hydrocarbons;

(c) Detergents;

(d) Pesticides.

1E.1.2 Apparatus

1E.1.2.1

The sampling procedures set out in this Schedule assumes the use of manual sampling equipment. The simplest equipment used for taking effluent samples consists of a bucket, ladle, or wide-mouthed container that may be mounted on a handle of a suitable length. The sample volume should not be less than 100ml. Where manual samples are to be used for the preparation of composite samples, the volume of the bucket, ladle or container should be well defined and known to a precision of within ±5 %. Manual samples can also be taken with a Ruttner or Kemmerer sampler, consisting of a 1 litre to 3 litre volume tube with a hinged lid at each end of the tube, or other samplers operating on a similar principle.

1E.1.2.2

Manual sampling equipment should be made of an inert material that does not influence the analyses that will be carried out on the samples later.

1E.1.2.3

Before starting sampling, the equipment should be cleaned with detergent and water, or as directed by the equipment manufacturer, and finally rinsed with clean water. The sampling equipment may be washed before use in the wastewater stream from which the sample is taken in order to minimise the risk of contamination. Special attention should be paid to rinsing after cleaning, if the analyses under study are detergents. The sampling equipment cannot be washed in the waste stream where this will influence the analysis carried out later (e.g. analysis of oil and grease, and microbiological analysis).

1E.2 Sampling Location

1E.2.1 Safety Precautions

In all cases when selecting sampling locations health and safety precautions shall be observed.

1E.2.2

The sampling location shall be the first manhole or other access point upstream of the point of discharge, unless, because of poor mixing or some other reason, a location giving more representative samples can be found.

1E.2.3

The sampling location should be kept clean by removing scale, sludge, bacterial film etc. from the walls.

1E.2.4

If turbulent flow conditions do not exist at the sampling location they shall be induced by restricting the flow, for example with a baffle or weir. The restriction should be made in such a way that sedimentation upstream of the restriction does not occur.

The sampling intake point should always be located downstream of the restriction. The inlet of the sampling equipment should preferably face the direction of flow, but may face downstream if too many blockages result.

If mixing is good just upstream of the obstacle, then the intake can be located there, taking care that sediment is not sampled and ensuring that the intake remains below liquid level.

1E.2.5

As a general rule, the sampling point should be one-third of the wastewater depth below the surface.

1E.2.6

It may be necessary to sample the surface by skimming, in order that qualitative information about emulsified and floating material can be obtained. Guidance on the choice of suitable containers for this sampling technique should be sought from the receiving laboratory.

1E.3 Choice of Sampling Method

1E.3.1 Types of Sample

It is common to distinguish between 2 sample types:

(a) Spot (or grab) samples;

(b) Composite samples.

1E.3.2 Spot Sample

1E.3.2.1

A spot sample is defined as a discrete sample taken randomly (with regard to time and/or location) from the trade waste.

1E.3.2.2

In a spot sample, the whole sample volume is taken at one time. Spot samples are useful for determining the wastewater composition at a certain time. In cases with small variations in the volume and composition of the waste stream, a spot sample can be representative of the composition during a longer period.

1E.3.2.3

For certain determinations, spot samples only can be used. For example, this is the case with oil and grease, dissolved oxygen, chlorine and sulphide. Here the result will differ if the analyses are not carried out (or started) immediately after collection of the sample, and if the whole sample volume is not used at a time.

1E.3.3 Composite Sample

1E.3.3.1

A composite sample is defined as 2 or more samples or sub-samples, mixed together in appropriate known proportions (either discretely or continuously), from which the average result of a desired characteristic may be obtained. The proportions are usually based on time for flow measurements.

1E.3.3.2

Composite samples are prepared by mixing a number of spot samples or by collection of a continuous fraction of the waste stream.

1E.3.3.3

In sampling, each of the spot samples should be greater than 50 ml in volume. Often it is advisable that spot samples are 200 ml to 300 ml in volume, in order to be able to collect representative samples.

1E.3.4 Instantaneous Composite Sample

1E.3.4.1

An instantaneous sample is a composite sample taken using the following method.

1E.3.4.2

Three spot samples of the discharge shall be taken at intervals of not less than 1 minute nor more than 5 minutes. The 3 spot samples must be combined using equal volumes of all 3 samples to obtain the instantaneous sample.

1E.3.4.3

An instantaneous sample shall be used for all routine compliance monitoring unless otherwise specified.

1E.3.5 Four Hour Average Composite Sample

A 4 hour average sample is a composite sample taken using the following method:

(a) No less than 12 spot samples shall be taken from the discharge at reasonably even intervals over the whole period. The intervals between the samples must not be less than 5 minutes nor more than 30 minutes. The samples shall be mixed using equal volumes of all samples to obtain the 4 hour average sample.

(b) The 4 hour flow period used when taking a 4 hour average sample shall be a continuous period of 4 hours during which the discharge is occurring and:

(i) Shall as far as practical be representative of the discharge occurring on a typical working day, and

(ii) Shall exclude periods of decreased discharge prior to or after the day’s operations.

1E.3.6 Twenty Four Hour Flow Proportionate Sample

A 24 hour flow proportionate sample is obtained using the following method:

(a) Spot samples shall be taken from the discharge over a continuous 24 hour period. The samples shall be taken at reasonably even intervals over the whole period. The intervals between the samples must not be less than 15 minutes nor more than 60 minutes. Whenever more than one sample is taken within a 60 minute period the samples must be of equal quantity and may be stored with other samples taken during that 60 minute period in a common container.

(b) If the discharge usually flows for a period less than 24 hours then no less than 18 spot samples shall be taken as described in 1E.3.6(a) to represent the nominated 24 hour period.

(c) The 24 hour flow proportionate sample is then obtained by taking a part of the contents of each container and mixing all such samples together. The size of the part of each container sample that is used shall be in direct proportion to the volume of discharge that occurred from the time a sample was first placed in the particular container to the time a sample was first placed in the next container.

1E.4 Frequency, Number and Timing for Samples

1E.4.1 Frequency and Number of Samples

Analyses shall be based on samples taken at regular intervals during each month (the control period).

The samples should be composite samples, unless the determinations to be carried out prohibit the use of a composite sample. The choice of the necessary number of samples taken during each control period should be decided on the basis of statistical techniques (see BS 6068:Section 6:10 : 1992) but shall not be less than once per month when sampling and analysis is required.

1E.4.2 Sampling Programme

1E.4.2.1

The objective of a sampling programme often dictates when and how a sample is collected.

When sampling trade waste, allowance should be made for the following sources of variation in quality:

(a) Diurnal variations (i.e. within-day variability);

(b) Variations between days of the week;

(c) Variations between seasonal discharges (if applicable).

1E.4.2.2

If the identification of the nature and magnitude of peak load are important, sampling should be restricted to those periods when peak loads are known to occur.

1E.4.2.3

The most appropriate type of sampling method (grab or composite) may be dependant on the magnitude of the variation in quality.

1E.4.2.4

Relating the times of sampling to the particular process being monitored may be very important when considering discharges that are either seasonal or operated on a batch basis. In either case, the discharge will not be continuous and the sampling programme will need to take this fact into account.

1E.4.2.5

If taking more than one sample, the samples should normally be taken at fixed intervals during the whole control period. The control period shall normally be one month.

1E.4.2.6

The following formula indicates the working day number during which sampling should take place:

where

WD is the number of working days for the premises in the month

n is the number of samples per month

A is a random number in the interval between (–WD/n) and 0.

After determining the intervals and the working day number, it is necessary to ensure that the sampling does not lead to any risk of systematic error, for example by always taking samples on one particular day, or by systematically omitting particular working days.

1E.4.3 Sampling Period

1E.4.3.1

The overall sampling period may vary from a few hours, where tracing studies on volatile organics are being monitored, to several days, where stable inorganic species are being monitored.

1E.4.3.2

This subclause deals with the selection of the period over which a composite sample has to be taken. When selecting the period, the following 2 factors should be considered:

(a) The objective of the sampling. For example, it may be necessary to assess the average organic load in a flow over several 24 hour periods, in which case diurnal flow proportional composite samples will be adequate.

(b) The stability of the sample. In the example given in (a), it would not necessarily be practical to extend the compositing period for longer than 24 hours, since the organic component in the sample under study may deteriorate.

1E.4.3.3

The stability of the sample may often limit the duration of the sampling period. In such cases, reference should be made to the specific analytical techniques to be employed and the receiving laboratory should be consulted, in order that correct preservative measures can be used.

1E.5 Sample Preservation, Transportation and Storage

1E.5.1

The most common way of preserving wastewater samples is to cool to a temperature between 0o C and 4o C. When cooled to this temperature and stored in the dark, most samples are normally stable for up to 24 hours. For some determinants, long-term stability may be obtained by deep freezing (below –18o C).

1E.5.2

When collecting composite samples during extended periods, preservation should be an integral part of the sampling operation.

1E.5.3

It may be necessary to use more than one sampling device, to allow both preserved and unpreserved samples to be taken.

1E.5.4

The laboratory responsible for analysing the samples should always be consulted with regard to the selection of the preservation method and subsequent transport and storage.

1E.6 Sample identification and records

A printed form for the sampling report should as a minimum include at least the following information:

(a) Name of the trade premises;

(b) Trade waste consent number;

(c) Sampling point;

(d) Date, start and stop of sampling;

(e) Time, start and stop of sampling;

(f) Duration of the sampling period;

(g) Details of the sampling method;

(h) Preservation method;

(i) Details of any field tests;

(j) Name of the person who carried out the sampling.

Multiple Outlets

In premises having multiple connections to the reticulation system, individual outlets need to comply with the Bylaw (i.e. sample each individual outlet separately for compliance). In terms of charging, for each outlet measurements are made on each outlet and charged separately, and no allowance is made for combining of flows.