FGD Wastewater Sample Selection Criteria

for Methods Development Study

To the extent possible, selection of FGD wastewater samples for use in an EPA CRCICP-MS methods development study should satisfy the following criteria:

Criterion #1 – Analytical Interferences

Several characteristics of FGD wastewater make them analytically challenging using the 

“standard” implementation of plasma methods in most commercial laboratories. To 

insure that the samples selected are representative of the analytical difficulties typically

encountered, the following criteria should be met by any sample selected. Sample 

characteristics (criteria) are listed more or less in the order of priority but the samples 

selected should meet as many of the criteria as possible:

1. Total dissolved solids (TDS) ranging from 15,000 mg/L up to a maximum, which 

should be in the 40,000 to 60,000 mg/L range. It is important to select samples 

representative of the range of TDS that can be expected in FGD wastewaters.

2. Calcium (Ca) concentrations ranging from 1,000 up to an expected maximum of 

6,000 mg/L or more.

3. Sulfate (SO4) concentrations ranging from 1,000 up to an expected maximum of 

4,000 mg/L or more.

4. Chloride (Cl) concentrations ranging from 2,000 up to an expected maximum of 

20,000 mg/L or more.

5. Magnesium (Mg) concentrations ranging from 1,000 up to an expected maximum 

of 5,000 mg/L or more.

6. Sodium (Na) concentrations ranging from 300 up to an expected maximum of 

2,000 mg/L or more.

Criterion #2 – Elemental Concentrations

All criteria #1 characteristics being equal, the samples selected should exhibit low 

concentrations of the elements of interest to provide the most realistic information 

regarding actual method detection limits (MDL) and reporting limits (RL) achievable 

using CRC-ICP-MS for FGD wastewater analyses. For example, selenium 

concentrations should be low in the range of < 100-300 μg/L (ppb). This criterion is 

more easily satisfied for many other elements (e.g., Ag, As, Cd, Cr, Cu, Ni, Pb, Sb, Tl, V, 

Zn) whose typical concentrations in FGD wastewaters are low (i.e., < 50 ppb).
Criterion #3 – Addressing FGD Wastewater Variability

To the extent possible, the major sources of variability in trace metals concentrations in 

FGD wastewaters should be addressed during sample selection to allow an evaluation of 

the range of possible interferences during this methods development study. Two 

important factors to be considered are as follows:

1. Coal source being used at a given facility. The most important coal sources used 

by the steam electric industry in the U.S. are eastern bituminous, western 

bituminous, and subbituminous coals (e.g., Powder River Basin). The 

characteristics of these coal types are very different and will impact the 

characteristics of FGD wastewater. 

2. Additives to enhance air pollution controls. Various additives can be used in a

coal-fired power plant to enhance the removal of air pollutants, such as SO2 and 

mercury. These additives include, but are not limited to, DBA, formic acid, and 

bromine. Other factors being equal, FGD wastewater samples should be selected 

that involve the use of as many additives as possible. This approach will increase 

the number of potential interferences that can be evaluated during the study.

It is recommended that as many of the criterion #1 parameters be determined in all 

candidate samples to facilitate an informed decision on sample selection. Depending on 

the number of samples to be used in the study, it may not be possible to address all 

criteria. In this case, samples with the highest concentrations of criteria #1 parameters, 

lowest metals levels (criteria #2) and most additives should be selected.

Other Potential Issues to Consider

UWAG would be happy to review and comment on a proposed Statement of Work 

(SOW) for EPA’s CRC-ICP-MS methods development study. UWAG has specific 

experience in dealing with analytical issues related to FGD wastewaters and could share 

lessons learned and approaches that could help the EPA conduct a successful methods 

development study.

UWAG would appreciate the opportunity to participate in EPA’s methods development 

study. For example, if agreeable with the membership, UWAG would be willing to 

provide an independent analysis, such as HR-ICP-MS and HGAFS (for arsenic and 

selenium), on splits of all the study samples. These additional analyses would provide 

confirming analyses that would assist EPA in evaluating the protocols developed for 

CRC-ICP-MS. 

EPA should also consider conducting a methods development study using EPA Method 

200.7. Experience gained with the analysis of split samples collected during the EPA 

sampling events has shown that a robust implementation of Method 200.7 optimized for 

FGD wastewater analysis can produce accurate, quantified data for many potential 

elements of interest. It is likely that a majority of compliance monitoring of FGD 
effluent wastewaters could be effectively handled by Method 200.7 using an optimized 

method. The sampling study also demonstrated that the standard implementation of 

Method 200.7 by many commercial laboratories did not perform well for the analysis of 

FGD wastewaters. If a version of Method 200.7, optimized for FGD wastewaters could 

be developed, the number of commercial and in-house laboratories able to generate 

acceptably accurate data would be significantly increased.