On-site water-quality measurements

On-site water-quality measurements are carried out predominantly to monitor effective purging of water at the sampling point before sample collection and to measure unstable parameters that cannot be subsequently reliably determined in the laboratory. On-site measurements can also be used to provide a check on a subsequent laboratory analysis. For example, provided that the on-site SEC is measured accurately, it can be compared with the SEC estimated from the laboratory chemical analysis by one of a number of geochemical programmes. This check can be useful for spotting major errors, such as dilution or typographical errors, as well as systematic errors in analytical methodology. 

Specific electrical conductance is the measure of a solution s ability to conduct or carry an electric current and depends on the presence of charged ion species such as calcium, sodium, magnesium chloride, etc. Conductivity measurements are approximately related to total dissolved solids (TDS) in a sample, but since different ions carry different amounts of charge and move at different speeds, their individual contribution to the overall SEC varies. 

SEC is measured with a conductivity meter, which normally consists of an AC bridge and a conductivity cell or electrodes. The conductance is measured between two electrodes. Two solutions of known conductivity should be used, one to calibrate the metre and the other to check the slope. It is important to correct all data for water temperature, either by calculation or by automatically using the metre s auto-temperature correction mode, since SEC is highly dependent on temperature. SEC increases by about 2% per degree centigrade rise in temperature due principally to an increase in water viscosity. 

Alkalinity is a measure of the acid-neutralising capacity of water and is usually determined by titration against sulphuric acid to the endpoint of the acid—base reaction. In groundwaters, the carbonate species predominate and an endpoint of 

Dissolved oxygen levels in water depend, in part, on the chemical, physical and biochemical activities occurring in the water. Oxygen has a limited solubility in water directly related to atmospheric pressure and inversely related to water temperature and salinity. Low-dissolved oxygen levels can limit the bacterial metabolism of certain organic compounds. 

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This chapter aims to provide a step-by-step guide for practitioners involved in the collection of contaminated samples by reviewing current groundwater sampling techniques and procedures and highlighting the major sources of uncertainty associated with sample collection. On-site water-quality measurements, quality assurance procedures and sample handling techniques designed to maintain the representativeness of the sample from field to laboratory are also discussed. 

Figure 3.2 On-site water quality measurements using a flow-through cell.

Trick J. K., Stuart M., and Reeder S. describe the tools available to the field sampler for the collection of groundwater samples, methods of on-site water quality analysis, and the appropriate preservation and handling ofsamples. The authors discuss the merits of different purge methodologies and show how on-site measurements such as pH, specific electrical conductance (SEC), oxidation—reduction potential (ORP), dissolved oxygen (DO), temperature, and alkalinity can be used to provide a check on subsequent laboratory analyses. Techniques for the preservation and analysis of samples and quality assurance and quality control are also presented. 

The complexity with respect to water quality is reflected in the many types of physical, chemical and biological indicators. Therefore, depending on specific project requirements, information about a wide variation of additional parameters may be required in order to describe the state of and the effect on the water quality. Simple measurements such as temperature, pH, dissolved oxygen, conductivity, conductivity, alkalinity (pH) and ammonia can be made on-site in direct contact with the water source. More complex measurements such as toxic contaminants and the presence of micro organisms may require water sampling followed by an analysis in the laboratory. 

The sampling location is selected in accordance with the measurement objectives. If it is the efficiency of a water treatment plant that is to be determined, the sampling sites should be located above and below the points of water entry to the plant. For studying the effect of effluent discharge on water quality in a river, water samples should be collected upstream and downstream of the outfall. 

Ground-water samples were collected from four wells in the study area. Data for these sites, along with previously collected water-quality data, are given in Table 1 and locations are shown on Fig. 1. Measurements of temperature, pH, and dissolved oxygen were made in a flow-through chamber. Field meters were calibrated using appropriate pH standards (Wilde and Radtke, 1998). Alkalinity was determined on-site by incremental titration of filtered water with sulfuric acid (Wilde and Radtke, 1998). 

WHO also summarized water quality data from various sources and reported that data on nitrobenzene levels in surface water appear to be more extensive than data on levels in air. While levels are variable depending on location and season, generally low levels ( 0.1-1 pgl ) have been measured. One of the highest levels reported was 67 rgl, in the river Danube, Yugoslavia, in 1990. However, nitrobenzene was not detected in any surface water samples collected near a large number of hazardous waste sites in the United States (reported in 1988). Based on limited data, it appears that there may be greater potential for contamination of groundwater than of surface water several sites measured in the United States in the... 

Laboratory-based methods have been developed for field-measurement of the main water quality parameters, and their use can be standardized. They are generally based on the same principles as the equivalent laboratory based methods (e.g. oxidation, colorimetry, photometry) but use simplified procedures in order to overcome the constraints of working in the field. Currently there are numerous commercially available devices for online and on-site use, and these provide efficient tools for surveillance, operational and investigative monitoring in the frame of WFD. These techniques are suitable for such applications as incident detection in water treatment plants, detection of accidental pollution, and measurement of spatial and temporal variation in water... 

This field trial was conducted in the Hardt catchment area in Alsace (France). A number of on-site analytical methods (multiparameter probe, immunoassays test kits, UV spectrophotometer) was evaluated for measuring the impact of anthropogenic pressures on water quality within the context of operational and investigative monitoring within the WFD. However, this section focuses on the use of a portable Pastel UV spectrophometer for the rapid mapping of concentrations of nitrate in a catchment. 

Chlorocarbons are a particular concern owing to their persistence in the environment and the lack of metabolic cleansing pathways in organisms and high fat solubility. Consequently, these substances bioaccumulate in the food chain, with unclear or deleterious effects on health and environmental quality. Chlorocarbons are considered separate from pesticides (see separate discussion) in this discussion and are chlorinated benzenes or phenols and chlorinated alkanes or alkenes. Volatile compounds in water were purged for determination by IMS with a corona discharge (CD) ion source. Chlorobenzene at 3 to 30 mg/L was determined in 5 min, which was considered suitable for on-site measurements at a restoration site. 

Part I. Reproduction and larval rearing The first section of the book deals with new techniques and technologies in hatchery husbandry. In Chapter 1, Odd-Ivar Lekang emphasises the importance of hatchery location in relation to water quality. He gives valuable information on how to measure and maintain suitable water quality with very practical information on the type of equipment required for both delivery and treatment. He predicts that in the future good sites for both freshwater and marine aquaculture will be at a premium and this will force operators to become more and more reliant on recirculation technology. 

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