3 Sampling of water and waste water

J.S. Laura

4.1 Introduction

The suitability of water for particular use depends on its quality. The management of water is also linked to its quality. The water standards are also based on the water quality. Hence water quality monitoring is one of the first steps in the rational development and management of water resources. The monitoring comprises all activities to obtain information about the water system. The first and most important step of any monitoring activities is sample collection (sampling).

4.2 Sampling

The objective of sampling is the collection of representative portion of material, from an environment (water, air, sediment or biota), small enough in volume to be conveniently transported and handled in the laboratory. This means, the relative concentration of the components of interest should be the same in the samples, when they are analysed, as they were originally present in the environment. The results of any chemical or biological analysis depend on the samples offered to the analytical laboratory. So the samples are handled and, if necessary, treated in such a way that no significant changes in composition occur that may interfere with proper analysis. So various control procedure set for the sampling should be followed.

4.3 Purpose of sampling

There may be different purposes and objectives for the water sampling program. The purpose of sampling maybe for Planning, Research, Process control and Regulation.

Planning- The planning purpose of sampling include establishment of baseline water quality conditions, to determine the effects of particular project, determination of assimilative capacities of streams and waste load allocation, and to project future water characteristics etc.

Research- Some specific research objectives of sampling includes determination of treatment efficiency of treatment system, determination of effect of change in process control variables on effluent characteristics, and to ascertain health effects of drinking water, effluents etc.

Process control- Process control objective of sampling includes improvement of quality of effluents and determination of interfering substances etc.

Regulation- Regulatory goals of sampling are verification, compliance and enforcement. For example, sampling is conducted to examine compliance with water quality standards.

4.4 General considerations for sampling

The following points should be considered during sampling planning.

1. Sampling location

While sampling convenience, accessibility and practicability are important aspects. The composition of water changes horizontally as well as verticaly in space and it also changes with time hence the following are some important considerations to take into account as they will have a bearing on the quality of the sample.

Homogeneity of the water or wastewater-The nature and extent of spatial heterogeneity can vary with time, and can also differ markedly between systems of the same type, for example, a zone where fresh and saline waters are mixing. Turbulence and good mixing enhance the homogeneity or the uniform distribution of the constituents in the water body. Hydraulic jump, spring and fall turnovers of a lake mix the water.

Non-homogeneity of the water or wastewater:  Non  homogeneity  of  water/wastewater  is

caused by poor mixing of water, so are not good representative of water body. Non homogeneity

occurs due to:

Stratification in lakes River downstream of a waste discharge Different densities of the constituents, such as floating oils or settling suspended solids Chemical or biological factors, such as growth of algae in upper layers of the body of water Concidering the above points suitable sites for a river

• 1) Upstrem of the industrial and domestic discharge points.
• 2) Immediately downstrem of industrial and domestic discharge points.
• 3) At a place of abstraction for industrial use and public water supply.
• 4) Base line stations where water is available in natural state.

2. Samples types

Samples can be collected differently according to the need, the types of samples include

1. Grab or catch samples , also known as spot or snap samples.
2. Composite samples.
3. Integrated samples.

Grab/spot/catch samples: When one sample is taken at a time, at a given location, is called spot sample. It shows only the prevailing conditions at the time of sampling and does not represent the average conditions.

• 1) When a source is known to be constant over a considerable time period , in that case a single grab sample should be considered as representative.
• 2) If the source are known to varz with time, grab sample should be collected at suitable intervals of time and analyzed separately.
• 3) The result can be documented in terms of mean, standard deciation, frequency, and duration of variations. When the source composition varies in space, collect samples from appropriate locations.

Composite samples: When spot samples collected at the same sampling site at different times are mixed, is called composite sample. This method of collection reduces the analytical effort. It is a useful technique when daily variations occur and seasonal variations are the objective of the study. A composite sample of 24 period is considered standard for most of the determination. Sometimes a composite sample representing one shift or a shorter time period or a complete cycle of a period operation may be preferable.A composite sample provides more meaningful data than the grab samples.

Integrated samples: Sometimes samples are collected at the same location but, due to horizontal or vertical variation in the composition of the river (or in water flow) or lake, they come from different points in the cross-section that are regarded with a different relative importance. To evaluate the average composition, total load or mass balance, integrated samples are collected, often in proportion to the river flow of the areas of sample collection.

3. Sampling Frequency

The sampling frequency is governed by the level of variation in water quality of a water body. If variations are large in a short duration of time, a higher frequency is required to cover such variations. On the other hand, if there is no significant variation in water quality, frequent collection of sample is not required. Water sample should be collected at intervals so that no change in water quality could pass unnotice. It depends on the type of data required, purpose of monitoring availability of funds and personnel. The following frequencies may be adopted provisionally.

-Once in a year. Generally applicable for long-term ecological evaluation of biological water quality. The time and place should be the same. Sometimes also used to know the year trends, usually as a result of increased human activities in the watershed.

-Four times in a year for stuying seasonal variation in water quality. Sometimes three samples are taken in a year like, pre-monsoon, monsoon and post-monsoons period.

Sampling will also be dependent on type of data and the parameters to be analysed. Selection of parameters depend on the purpose of sampling. Generally on routine basis, a combination of general parameters, nutrients, oxygen consuming substances and major ions are analyzed. A list of parameters to be considered for analysis and frequency of sampling is provided in the “Protocol for Water Quality Monitoring” notified by Govt. of India.

4. Sampling devices

Sampling devices are devices used for sample collection. Some important sampling devices are the following:

Bottle– The same bottle used for storage is used for collection. Only (sub) surface samples can be collected. The sampling bottle may be made of either glass or plastic, usually polzethylene. It must be capable of being tightly sealed either by stopper or cap.

Sampler– These are for deep water sampling and operated on a line or wire. They are advantageous as several samplers can be mounted together on one wire. They are available in different sizes and for specific purposes e.g. sampling for bacteria (thus sterile), sampling for trace metals (metal free), sampling for pesticides (no plastic).

Different type of water samples are available and many of them are designed for specific purposes. Two most commonly used water samplers are described here.

1. Dissolved oxygen (DO) sampler

A DO sampler is a metal tube about 10 cm diameter and 30 cm length. One end is sealed and other end is fixed with a removable cap.

. Depth sampler

The depth sampler, sometimes called a grab sampler, is designed in such way that it can retrieve a sample from any predetermined depth.

Pump sampler- Automatic sampling devices, using pumping systems are also available. They can be preset to desired volume and/or time of sampling. In these, depending on the collection bottles installed, series of spot samples or composite sample can be collected. For sediment sampling one may use one of the following techniques:

.

Coring– A PVC or perspex tube is used to extract relatively undisturbed sediment.

Grabbing– A larger volume of sediments (disturbed or undisturbed) are collected by grabbing.

Organisms can also be collected by grabbing.

Others- Special types of sediment samplers are also available, e.g. for use in the deep sea (piston corers), for use in sandy sediments (vibro-corers), for large sections of the sediment (box-corers).

5. Cleaning procedures

Improper cleaning of lab-ware used in sampling may give false results. The cleaning of samplers, sampling bottles and other lab-ware that comes into contact with the sample is important step. Cleaning procedure depends on the parameter for which sample is taken. Few of them are given below.

For heavy metals: Rinsing of glassware with 1:1 diluted Nitric acid (supra pure quality) for 1 week is needed, followed by three times washing with double distilled water.

For trace organic compounds: Bottles for trace organic (chlorinated) compounds, like pesticides, should be cleaned with the solvent used for extraction (also of high purity quality). For general sampling: Samples for the general physical-chemical characterization allow less vigorous methods. Thorough cleaning with water to remove particulates and two times rinsing with distilled water will usually are sufficient. However the following is recommended for better results- the bottles should be soaked with 10% HCL for 24 h and then thoroughly cleaned and rinsed with distilled water.

All bottles should arrive at the sampling site in a fully cleaned state, protected from accidental contamination. The last cleaning step is in most cases is to rinsing 2-3 times with the water to be sampled. (NOT all: not for the trace organics, in case a solvent is already present in the bottle and not for microbiological samples) This cleaning should be done, one bottle at the time, at the sampling point and both bottle and cap should be cleaned: fill the bottle (1/3), put on the cap, shake and empty. Repeat this procedure 2 times.

4.5 In-situ measurements

Some parameters are expected to change sooner with time. In such cases the expected changes are so large, that it is impossible to store the sampled material for a correct analysis of these parameters at a later moment. These parameters should be analyzed at the sampling site or, in-situ.Some important parameters that should be analyzed in situ are the pH, dissolved oxygen, temperature, conductivity, turbidity etc For such measurements special portable measuring devices are available. The estimation on numbers and diversity of organisms is also to be considered as in situ analysis.

4.6 Sample Labeling

Sample container is labeled properly. Sample container can be labeled directly with a water-proof marker or by attaching an appropriately inscribed tag or label. Information on the sample label should include:

• ü Sample code number (identifying location)
• ü Date and time of sampling
• ü Source and type of sample
• ü Pre-treatment or preservation carried out on the sample
• ü Any special notes for the analyst
• ü Sampler’s name

4.7 Sample Preservation and Transport

Preservation of collected samples is necessary for some parameters because some parameters are more prone to change in environment and time. Samples for BOD and bacteriological analyses should be stored at a temperature below 4°C and in the dark as soon as possible after sampling. In the field this can be done by placing them in an insulated cool box together with ice or cold packs. Once in the laboratory, samples should be transferred as soon as possible to a refrigerator. If samples collected for chemical oxygen demand (COD) analysis cannot be analyzed on the day of collection, they should be preserved below pH 2 by addition of concentrated sulphuric acid. This procedure should also be followed for samples for ammoniacal nitrogen, total oxidized nitrogen and phenol analysis.

Samples, which are to be analyzed for the presence of metals, should be acidified to below pH 2 with concentrated nitric acid. Such samples can then be kept up to six months before they need to be analyzed; however mercury determinations should be carried out within five weeks.

Transportation: After labeling and preservation, the samples should be placed in an insulated ice box for transportation. Samples should be transported to concerned laboratory as soon as possible, preferably within 48 hours. Analysis of bacteriological samples should be started and analyzed within 24 hours of collection. If samples are being brought to the laboratory they should be transported in less than 24 hours.

4.8 Sampling of waters from different source

1. Rivers, streams and canals – Samples should be collected as far as possible, from midstream at mid depths. Sampling too near the bank provides fictitious results. Sites should be selected preferably where marked quality changes occur and where there are important river uses such as confluences, major river discharges or abstractions. Sampling locations can be fixed by reference to significant features. In this connection use of reference maps may be helpful. The site should be reasonably accessible all the year round. Taking of samples from over the bridges is appropriate. Samples can also be taken from boats wherever feasible for rivers and lakes. Sampling by wading, where the rivers are shallow, care being taken to collect samples upstream of the wader, who can disturb the bottom sediments. When it is intended to monitor the effects of a discharge, both upstream and downstream sampling is necessary. Mixing of discharge with receiving water is important. A sample from 100 meters down stream of the discharge point is considered representative in case of small streams. In rivers many kilometers will be necessary. Therefore, in case of longer rivers there should be three fixed sampling locations through cross-section- left, middle and right. Ideally, sample should be taken from a turbulent point. The general considerations for rivers and streams also supply to canals. Flow and stratification are important factors. The rate of flow in canals changes depending on their use. Stratification is pronounced under quiescent conditions. The water body can be thermally stratified and very significant quality differences can develop at different depths Passage of boats also have marked short-term effect on the quality especially on suspended solids, oil and qreese which may be contributed as a result of spills from boats, etc. Sampling should be carried out at all draw-off points and draw-off depths, in addition to the point of inputs.

2. Ground water – Whenever possible, sample should be collected after pumping the well or bore hole for a period of at least an hour or two. This ensures drawl of new water from aquifer. Depth below ground level or reference level at which the sample is taken, should be

recorded. Samples for groundwater quality monitoring would be collected from one of the following three types of wells:

Open dug wells in use for domestic or irrigation water supply, Tube wells fitted with a hand pump

Power-driven pump for domestic water supply or irrigation General points to be kept in mind for ground water sampling-

Piezometers should be used for recording of water level and water quality monitoring. Open dug wells, which are not in use or have been abandoned, should not be considered as water quality monitoring station. However, such wells could be considered for water level monitoring.

Weighted sample bottle should be used to collect the sample from an open well about 30 cm below the surface of the water. Do not use a plastic bucket, which is likely to skim the surface layer only.

Samples from the production tube wells should be collected after running the well for about 5 minutes.

Non-production well should be purged using a submersible pump. The purged water volume should be equal to 4 to 5 times the standing water volume, before sample is collected.

For bacteriological samples, when collected from tubewells/hand pump, the spout/outlet of the pump should be sterilized under flame by spirit lamp before collection of sample in container.

3. Drinking water supply – The sampling point should be located at a place where all the reactions of the disinfecting agent are completed and also some residual disinfectant is present. The usual sampling position is a tap on a pipe connected directly to the pumping main, as close as possible to the reservoir. Many service reservoirs fill and empty through the same main. Sampling should be made when reservoir is being emptied.

4. Sewage effluents – Samples may be required when sewage enters a treatment plant, after various stages of treatment and the treated effluent. Crude sewages samples are taken after preliminary treatment process (grit removal and screening) to exclude large particles. In case of sewers and narrow effluent channels. Samples should be drawn from a point which is at one-third water depths from the top without skimming the top or scrapping the bottom. In any

   event, velocity of flow at the sampling point should be sufficient to prevent deposition of solids. Sample should be drawn” gently without causing aeration or liberation of dissolved gases. In most cases sewage flows are intermittent and collection of sample every hour may be necessary.

   • 5 Trade effluent – Sampling of industrial effluents must be considered in relation to the nature and location of each Individual effluent. When effluents from a variety of processes discharge into a common drain, adequate mixing is required. Sample should be collected keeping this in mind. In some cases this may require construction of a manhole chamber within the factory before the final outfall. Samples should be drawn from the manhole without entering it. Samples from deep manholes should be drawn with the help of specially designed equipment. There is a possibility of domestic sewage getting mixed into industrial waste. Sampling site should be chosen to exclude such wastes. The general principles for collection of sewages and sewage effluents are applicable in case of trade effluent.
   • 6 Sampling municipal wastewaters Municipal wastewaters are collected and treated by chemical, physical, and/or biological means prior to discharge to surface waters. Up to three stages, primary, secondary and tertiary, are commonly used at municipal treatment plants. The wastewater characteristics vary with the size and habits of the community, the type of collection system (combined or separate), the amount of infiltration and the volume and type of industrial discharges entering the system.
   • 7 Sampling agricultural discharges Agricultural discharges can be separated into three types: concentrated animal waste or manure from a confined feedlot, run-off from an agricultural watershed, and irrigation return flow. These three types of run-off differ mainly in the concentration of pollutants. Field run-off from rainfall, irrigation and snowmelt is characteristically the least polluted, while feedlot run-off is the most concentrated waste. The concentrations of pollutants from field run-off and irrigation return flow vary with the amount and intensity of rainfall or snowmelt, irrigation practices, land use, topography, soil type and use of manure or fertilizer.

   If any of these steps are carried out with insufficient care, the final result (e.g. the concentration of a given compound) will be a an error figure without relation to the actual situation in the environment and the entire operation will be a waste of energy, time and money. Table (4.1) gives the volume needed, preservation if required, and type of container that should be used for sampling for some common parameters.

4.9 Check list for the field visit

Planned route, Timings, Area map, Sampling site location map Personnel and sample transport arrangement Icebox filled with ice or icepacks or ice Weighted bottle sampler, BOD bottles

Special sample containers: bacteriological, heavy metals, etc. Sample containers, Sample preservatives (e.g. acid solutions) Thermometer, Tissue paper, Other field measurement kit, as required Sample identification forms Labels for sample containers

Field notebook, Pen / pencil / marker

Soap and towel, Match box, Spirit lamp, Torch, Rope, Drinking water, Knife, First-aid box, Gloves and eye protection Dump sampler to check well conditions Submersible pump and accessories

References

1. U.S. Geological Survey, Techniques of water- Resources Investigations, 2006. Handbooks for water Resources Investigations. U.S. Geological Survey TWRI. Book 9, Version. 2.0,9/2006. https://water.usgs.gov/owq/FieldManual/chapter4/pdf/Chap4_v2.pdf
2. Central Pollution Control Board (CPCB). Guide Manual: Water and Waste water Analysis. http://cpcb.nic.in/upload/NewItems/NewItem_171_guidemanualw&wwanalysis.pdf
3. American Public Health Association (APHA), American water works association, Water Environment Federation, 1999. Standard Methods for the examination of water and waste water.
4. World Health Organization (WHO). Guidelines for drinking- Water quality- Water Sampling and Analysis.. http://www.who.int/water_sanitation_health/dwq/2edvol3d.pdf