2.2 Where, What, and When to Sample
27
likely be used in permitting or litigation demands perhaps the highest level of
intensity. Thus, there is not a one-size-fits-all approach to establishing watersampling protocols.
The ability to determine the existence of a statistically significant trend
in water quality over time is influenced by (1) the magnitude of change that
actually occurs in the parameter and water body of interest, (2) the temporal
variability that occurs in that water quality parameter and water body, and
(3) the number and temporal distribution of samples collected. Thus, to design
a monitoring plan to detect the existence of a statistically significant change in
lake ANC, one must consider the level of change that one wishes to be able to
detect in conjunction with the known or expected temporal variability in ANC
in that lake or stream. Prior to initiating a monitoring effort that is intended to
evaluate change over time (trends detection), it is helpful to (1) consult with a
statistician (or person knowledgeable about statistics) or with the person who
will be responsible for the eventual statistical analysis of the resulting monitoring data and (2) conduct a pilot study to determine the temporal variability
that occurs in the parameters of interest in that water body (or, at a minimum,
in a water body thought to be similar in its chemistry).
The overall data quality objectives (DQOs) for a water quality sampling
project are to implement quality control (QC) procedures and requirements
for field sampling and laboratory analysis that will provide data that can be
used to achieve the program objectives and to follow procedures that will
provide data of known quality in terms of precision, accuracy, completeness,
representativeness, and comparability. QA/QC issues are covered in detail in
the QA/QC protocol section of this book. It is important to note, however, that
certain aspects of the QA/QC protocols that are adopted for a particular study
will affect choices that need to be made in designing the sampling program
for that study. In particular, it is important to determine, in advance of initiating fieldwork, what the DQOs will be with respect to the selected targets for
analytical detection limits, precision, accuracy, and completeness. In addition,
decisions need to be made concerning how many, and which ones, of the field
samples to be collected will be replicated in the field and whether there will be
field blanks carried into the field. Note that some sampling programs replicate
all samples in the field.
2.2.1 Where to Sample
2.2.1.1 Selection of Sampling Locations
Selection of sites for water quality sampling should be based on systematic and documented criteria. One of the most important criteria is having a well-defined population of interest. The criteria should be chosen
with consideration of watershed factors. These can include representation
27
likely be used in permitting or litigation demands perhaps the highest level of
intensity. Thus, there is not a one-size-fits-all approach to establishing watersampling protocols.
The ability to determine the existence of a statistically significant trend
in water quality over time is influenced by (1) the magnitude of change that
actually occurs in the parameter and water body of interest, (2) the temporal
variability that occurs in that water quality parameter and water body, and
(3) the number and temporal distribution of samples collected. Thus, to design
a monitoring plan to detect the existence of a statistically significant change in
lake ANC, one must consider the level of change that one wishes to be able to
detect in conjunction with the known or expected temporal variability in ANC
in that lake or stream. Prior to initiating a monitoring effort that is intended to
evaluate change over time (trends detection), it is helpful to (1) consult with a
statistician (or person knowledgeable about statistics) or with the person who
will be responsible for the eventual statistical analysis of the resulting monitoring data and (2) conduct a pilot study to determine the temporal variability
that occurs in the parameters of interest in that water body (or, at a minimum,
in a water body thought to be similar in its chemistry).
The overall data quality objectives (DQOs) for a water quality sampling
project are to implement quality control (QC) procedures and requirements
for field sampling and laboratory analysis that will provide data that can be
used to achieve the program objectives and to follow procedures that will
provide data of known quality in terms of precision, accuracy, completeness,
representativeness, and comparability. QA/QC issues are covered in detail in
the QA/QC protocol section of this book. It is important to note, however, that
certain aspects of the QA/QC protocols that are adopted for a particular study
will affect choices that need to be made in designing the sampling program
for that study. In particular, it is important to determine, in advance of initiating fieldwork, what the DQOs will be with respect to the selected targets for
analytical detection limits, precision, accuracy, and completeness. In addition,
decisions need to be made concerning how many, and which ones, of the field
samples to be collected will be replicated in the field and whether there will be
field blanks carried into the field. Note that some sampling programs replicate
all samples in the field.
2.2.1 Where to Sample
2.2.1.1 Selection of Sampling Locations
Selection of sites for water quality sampling should be based on systematic and documented criteria. One of the most important criteria is having a well-defined population of interest. The criteria should be chosen
with consideration of watershed factors. These can include representation