L.A. Baker, B.C. Asleson, A.J. Erickson, and R.M. Hozalski
Except for visual inspection (level 1), each level of assessment outlined in Developing an Assessment Program requires the collection of samples. After samples have been collected (see Sampling Methods), analysis is required to determine soil or water properties such as soil moisture or pollutant concentration. The goal of this section is to identify specific parameters to be measured and to outline the analytical process that occurs after samples have been collected. A key guide for specific methods for sample collection and analysis of water is Standard Methods (A.P.H.A. 1998) and for analysis of soils is Klute (1986). A compilation of EPA methods is available on the web (Nelson 2003). Finally, the American Society of Testing and Materials (A.S.T.M.) publishes individual methods which are also available online.
Selecting analytical methods
Identification of assessment goals and an assessment approach (see Developing an Assessment Program) and development of a sampling program (see Sampling Methods) lead to general selection of analysis for one or more constituents. There are often several different analysis methods for measuring a given constituent in water or soil. In some cases, regulatory requirements may specify the analysis method and constituent (e.g., total phosphorus at a certified laboratory) but most assessment goals and programs allow for several methods of analyses that could satisfy the assessment goals. The questions below can be used to select an appropriate analysis method:
- Is a specific analysis method required by regulatory or other restrictions? National Pollution Discharge Elimination System (NPDES) permits, Total Maximum Daily Load (TMDL) programs, or other regulatory requirements may require specific analysis methods, analysis by certified laboratories, or both. These restrictions should be listed when developing as assessment program and considered when selecting analytical methods.
- Will analytical results need to be compared with results from other assessment programs? If so, sample collection, preservation, and analytical methods must be as similar as possible to minimize bias. This is particularly important for samples that must be compared to other samples within the same assessment program or at the same location. For accurate and unbiased comparison of several locations within the same assessment program, a consistent quality control program for all analysis methods may be needed.
- What is the quantification range of interest? Often there are several analytical methods available for a given constituent, with varying limits of quantification (smallest concentration that can be measured). It is important to select an analysis method with limits of quantification that include the expected range for the constituent of concern. Also, the potential for contamination increases as the limits of quantification decrease, so additional care may be needed in sampling.
- Will measuring total concentration (dissolved + particulate-bound pollutants) satisfy the assessment goals, or is it necessary to measure both dissolved and particulate forms of a pollutant separately? For example, in assessing phosphorus capture, it may be necessary to analyze both particulate and dissolved forms in order to develop an understanding of the capture and transformation mechanisms.
- Can multiple constituents be measured with a single analytical method? Some analytical methods measure multiple constituents without the need for separate samples or additional analysis. For example, inductively coupled plasma (ICP) emission can measure several different constituents from one analytical injection, and ion chromatography (IC) can measure several different ions from one injection. These methods are often more expensive than analysis of a single constituent, but can be considerably cheaper than analyzing several constituents separately. For many parameters, field test kits are also available and can provide fast, inexpensive analysis without sending samples to an analytical laboratory.
The answers to each of these questions is provided in the discussion and recommendations within the next several sections:
Continue to Constituents in water.