epidemiological investigations? ___
Sampling or posting recommendations. This section should describe circumstances which indicate the need to post warning notices or close beaches and provide information such as sampling locations, times and frequencies.
8.1.3 Sampling location, time and frequency
The first step in planning a sampling activity is to define clearly the objective; in most cases the objective will be either exploratory (assessment) or monitoring (surveillance). While the former is designed to provide preliminary or “one-off information about a site, the latter is undertaken for regulatory or non-regulatory purposes” (Keith, 1990). For a recreational water use area, both objectives may initially coincide. Exploratory sampling will be required to define subsequent sampling. Special requirements for epidemiological studies will be necessary as highlighted in Chapter 13.
The selection of sampling sites, time and frequency of sample collection should attempt to capture the overall microbiological quality of the water at the recreational water use area. These choices should be based upon the information gathered during the sanitary inspection. The selection of sampling stations and time of sampling should take into consideration, variables known to affect water quality, such as the length of the bathing area, presence and periodicity of point and non-point sources of faecal contamination, influences of local weather, the physical characteristics of the bathing area and the presence of bathers. For example, at bathing areas with no detectable sources of external faecal contamination, samples should be collected at the places with the greatest bather densities. Bathing areas known to be influenced by direct or indirect faecal contamination will require additional sampling sites to help define the degree and extent of pollution. The time of day can be an important source of variation (Brenniman et al., 1981; Fleisher, 1985; Tillett, 1993; PHLS, 1995) especially at beaches with significant tides (Cheung et al., 1991). Consideration should also be given to collecting samples at times when bather densities are greatest for example, afternoons at weekends (Cheung et al., 1991; APHA, 1995). Chapter 9 gives an example of an approach to a sampling programme.
Sampling frequency can also influence the acquisition of reliable information on microbiological pollution in a bathing area (Fleisher, 1990; Tillett, 1993). For those laboratories with limited economic or human resources it is better to direct efforts towards increasing sampling frequency instead of confirming presumptive results for Escherichia coli and faecal streptococci. The sampling frequency adopted in many programmes and assessments is fortnightly during the bathing season. Some authors have advocated more frequent samplings such as weekly or more, especially in the peak season in temperate climates (Figueras et al., 1997) and others maintain lower intensity monitoring (e.g. monthly) outside the bathing season. Evidence suggests that once an understanding of quality behaviour has been developed through relatively intensive monitoring and sanitary surveys, then reduced sampling frequencies may be justifiable and can contribute to reducing the burden of monitoring (Chapter 9). For colder climates where the bathing season is restricted by weather, water sampling should be concentrated in that period where historical data show a higher probability of favourable weather conditions for recreational activities. If abnormal favourable weather conditions