Illinois redesigns its ambient water quality monitoring network

Water quality monitoring involves sampling a "population," water quality, that is changing over time. Sample statistics (e.g., sample mean) computed from data collected by a monitoring network can be affected by three general factors:(1) random changes due to storms, rainfall, etc.; (2) seasonal changes in temperature, rainfall, etc.; and (3) serial correlation or duplication in information from sample to sample. (Closely spaced samples will tend to give similar information).In general, these effects have been noted, but their specific effects on water quality monitoring network design have not been well defined quantitatively. The purpose of this paper is to examine these effects with a specific data set and draw conclusions relative to sampling frequency determinations in network design.The design criterion adopted for this study of effects due to the above factors is the width of confidence intervals about annual sample geometric means of water quality variables. The data base for the study consisted of a daily record of 5 water quality variables at 9 monitoring stations in lUinois for a period of 1 year.Three general regions of frequencies were identified: ( 1 ) greater than approximately 30 samples per year where serial correlation plays a dominant role; (2) between approximately 10 and 30 samples per year where the effects of seasonal variation and serial correlation tended to cancel each other out; and (3) less than approximately 10 samples per year where seasonal variation plays a dominant role. In region 2, either seasonal variation and serial correlation should both be considered or both ignored. To consider only seasonal variation introduces more error than ignoring it. These results are network averages (over variables and stations) from one network, thus results for individual variables may deviate considerably from the average and from those for other networks.

Section: Statistical Criteriamentioning

confidence: 99%

Water quality monitoring—Some practical sampling frequency considerations

Loftis

Ward

1980

“…Sampling frequency proposed for the primary network followed the BWMP guideline of once per month. That sampling frequency is supported by long-term stream chemistry monitoring data (Lettenmaier 1977, Wallin and Schaeffer 1979, Ward and Loftis 1983. Sampling frequency in lakes did not follow BWMP guidelines.…”

Section: Results Presented By the Doe Management Review Teammentioning

confidence: 99%

The environmental audit. II. Application to stream network design

Perry

Schaeffer

Kerster

et al. 1985

Self Cite

/ The planning and execution of water quality management programs requires careful collection and analysis of data coupled with a systematic review and analysis of programmatic success. The environmental audit is a tool which facilitates improved water quality planning and management, This article demonstrates the utility of the environmental audit by reviewing portions of a comprehensive review of the water quality management program for the state of Idaho. The audit is a tool which forces careful design of a sampling program before data are collected. In the audit approach, program objectives are clearly stated prior to initiation of sampiing. Stated objectives are also evaluated regularly to identify tension points, that is, conflicts between expectations and reality. In the example taken from Idaho, a management review team followed a directive to redesign the water quality monitoring program. We present a summary of the redesign as proposed by that team, to illustrate the results of a typical review of monitoring programs. That summary is followed by an example of how the proposed program would differ if the audit approach had been used. The two approaches offered both coincident and conflicting recommendations. Management review team and audit recommendations for lake sampling programs were similar even though a different process was used to develop the recommendations. The most striking contrast between the two results lies in the review team's approach to the problem. The directives followed, and the team's responses, concentrate on tools, such as increasing biological monitoring or reliance on monthly BWMP stations. In contrast, the audit results stress addressing management questions for which clear objectives have been stated, depending on specific tools only as needed to meet stated objectives. Although the audit does integrate externalities in its structure, it is little affected by economic or political influences. A major strength of the audit approach is its ability to provide defensible data for management decision making.

“…(The costs of purchasing and maintaining an automatic composite sampler, if included, makes grabs even more economically attractive.) Wallin and Schaeffer (1979) report that in changing from an ambient water quality monitoring network based entirely on grab sampling, to one based largely on cross-sectional, depth-integrated composites, that the costs per station increase d 3-5 times, without any quantifiable improvement in data quality.…”

Section: Bsample Variance Was Obtained From the Individual Observatiomentioning

confidence: 97%

Grab versus composite sampling: A primer for the manager and engineer

Schaeffer

Kerster

Janardan

1980

Self Cite

ABSTRACT/Effluent subsamples are usually aggregated into flow or time proportional samples before analysis. Although this provides information on average process conditions, that on process variability is lost by compositing Fisher's information is defined and used to estimate the loss due to compositing. The results of simulations based on parameters derived from actual waste streams support the fact that random grabs serve as well as composite samples for monitoring purposes. These findings favor changes in regulatory practice to allow compliance to be demonstrated by grab sample averages. Reporting requirements based on moving averages are shown to be inferior to those based on averages taken over nonoverlapping time periods.