In establishing a monitoring programme and data collection schedule, the following points will need addressing. This is not a comprehensive list for every eventuality, but most monitoring programmes will need to consider this list as a minimum:
• The equipment, skills, storage and transportation facilities (and, if required, power to the site):
о Sampling, transport and storage protocols should be obtained or prepared to promote good practice and consequently to yield reliability of readings obtained from tests.
о A responsible person should be identified for sample collection and instrument readings and made available over the life of the programme. о Health and safety plans are required for personnel engaged in the sampling.
• Timing of sample collection:
о Sometimes a frequency that reduces over time will be satisfactory if adequate behaviour is demonstrated by early analysis, especially where some new material or construction is being tried or where a singular event has occurred (such as a cargo spillage). Otherwise regular sampling will usually be preferred. There are some cases where only a single sample or one “before” and one “after” sample are necessary at any particular point. о Sampling needs to take account of the weather conditions in which the media will be sampled / measured (rain, wind, heat, etc.). Sometimes collection should be at a fixed time of day, a certain temperature or in a certain season when, otherwise, there wouldn’t be (or would be doubts about) comparability between specimens.
о Sometimes samples are to be collected from a discrete, sometimes from a continuous, source. In some low flow situations, sampling may exhaust the source until slow seepage provides the next specimen. This may have an influence on sampling frequency and/or volume.
• Location of sampling:
о There is usually a conflict between the desired number of points to be sampled and the budget available. As far as possible, the locations should aim to ensure spatial reliability and representativeness. In particular the design should give confidence that all “hot-spots” will be located and that invalid and unreliable readings can be easily distinguished from genuine extreme values. о Vertical and horizontal positions in the ground should be chosen depending on the expected source and route of contaminant flow and the receiving media. For example, where traffic factors are thought to be influential, closeness to the wheel path may be important; where runoff is important, measurements in the verge may be important; where a developing pollutant front is to be detected (or refuted) then positions laterally and beneath the source point may be required. There are similar issues for water bodies — at what depth(s)
and water velocity(ies) should specimens be collected? In the context of road construction, such a question will be irrelevant if water is collected from seepages.
о Consideration should be given to the accessibility of sampling locations once the road is open to traffic. Access through the carriageway will often require lane closures that are expensive or difficult to arrange. The access point may also be difficult to keep sealed under traffic loading thereby compromising the quality of specimens collected.
• Protection:
о Sample collection points and instruments should be designed to be replaceable if they become damaged or aged. Appropriate protection of collection points and instruments against vandalism, traffic over-run, grass-cutting and other maintenance/rehabilitation will often be needed.
• Materials to be sampled:
о The sampling programme needs to assess all relevant material, i. e., groundwater, surface water, soils and aggregates as well as these media in their reference condition(s).
о Adjacent surface water bodies may need assessment if an affect by polluted water from the road is suspected.
о Soil or construction material may need monitoring as well as groundwater. If the subgrade or a construction material will (or may) transport or sorb contaminants, it may need to be sampled from time-to-time to check for any alteration (e. g. permeability value or sorbed contaminant level). Similarly, if construction material, in-place, is thought to be a source of ongoing contamination, the plan should consider sampling it and testing its leachability as use continues.
о While water samples are only tested for their chemical properties, soil specimens may need testing for total solids make-up, organic content, mineralogy, particle size distribution and specific surface area. The last two are important in understanding sorption behaviour. Water can also be extracted from soil samples, e. g. by using a centrifuge.
• Selecting parameters for analysis:
о It is expensive to analyse for all species all of the time. Therefore, it may be necessary to identify key analytes that may act as indicators of change in the seepage/transport process, and to concentrate monitoring on these.
о Often, a regular frequency of assessment can be maintained at modest cost if full chemical analysis is sometimes replaced by surrogates, e. g. pH, Eh, electrical conductivity, etc. by electrical means.
о Where “trigger” values have been set for some intervention, the concentrations of the “trigger” species will require specific, ongoing, analysis.
о It can be a false economy only to analyse collected specimens for the analytes of known concern. A record of the contamination of other species may yield important information on an underlying chemical process (e. g. ion exchange) or may give rise to unexpected values that will lead to the identification of some unexpected problem or benefit.
о The water or soil should be sampled in amounts large enough to permit all the desired testing to be performed on it.
Some duplicated sampling will be needed, usually from the same location. The aims are:
• to ensure evidence of a reading’s representativeness;
• to adequately define statistical scatter in readings;
• to monitor genuine fluctuations in source concentration (e. g. as a consequence of flow levels, season, traffic, etc.);
• to ensure that both mean and “worst-case” values are available; and
• to allow repeated analyses in case of dispute.
To ensure best practice in this area most environmental regulatory authorities issue guidance on sampling (see reference list at end of Section 7.4.1).
