Session 3C - Simple Methods of Water Quality & Quantity Determination
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Session 3C - Simple Methods of Water Quality & Quantity Determination - Jodi Sangster
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Session 3C - Simple Methods of Water Quality & Quantity Determination
- 1. Fundamentals of Environmental Sampling Jodi Sangster
- 2. Operator • Knowledge • Experience Equipment • Detection limits • Size • Power needs On-Site • Difficulty of sampling • Time There are no absolutes. Each project is different. Data Quality Objectives (DQO) Amount and Quality of Data
- 3. Develop a sampling plan based on what you are testing for Representative Sample Plan and organize so that least contaminated site is sampled first Avoid disturbance at the sampling site Avoid contamination Clean and dry collection / testing equipment Use new or clean containers Wear gloves
- 4. Types of Samples A Composite Sample is a mixture of grab samples taken at different times or locations and pooled together to provide one sample. A Grab Sample is a snap shot of the quality of the water at the exact time and place the sample was taken.
- 5. Grab Samples
- 7. What Now? Interactions with air Oxidation Out gassing Chemical reactions during storage or transport Filtering and cold storage Acid preservation Prompt analysis Evaporation Cap tightly pH and carbonates are sensitive to CO2 out gassing and CaCO3 precipitation. Dissolved oxygen is sensitive to gain from air and loss due to microbial. Reduced compounds are susceptible to oxygen increases from air.
- 8. Equipment Calibration Thermometers – annual check Manufacturers User Manual Calibrate DO, pH, on daily or before use basis. Full pH check should be done weekly Conductivity/Salinity checked on daily/before use basis (Std. @ 20oC) Use a QC check standard on daily or before use basis Record data on Calibration Sheet or Field Sheet Know the limitations and interferences for each test!!!
- 9. Quality Assurance and Control Quality control refers to activities used to monitor and minimize error QC Samples – blanks, spikes, duplicates Quality control = error control Quality assurance is the QC management system
- 10. Blank deionized water processed like any of the samples and used to "zero" the instrument Calibration Blank Can be rechecked often to make sure equipment is not showing signs of drift or losing calibration.
- 11. Type How prepared? What does it tell you? Field (ambient) blank Container filled with “analyte-free” water in the field Transport, storage, and field handling Rinsate or equipment blank Container filled with “analyte-free water which has been passed through sample collection equipment Contaminated equipment Trip blank (volatiles only) Container filled at laboratory sent out in the field and returned with samples Contamination during transport Common Blanks
- 12. 0 2 4 6 8 10 12 14 16 18 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 More Frequency Nitrate – N (ppm) Example Data – Field Reagent Blanks Method Detection Limit
- 13. Duplication Field duplicates or replicates FD1 and FD2 Permit calculation of error due to heterogeneity, sampling method, and analytical method Precision expressed as relative percent difference (RPD) or range (R) 𝑅𝑃𝐷 = 𝐷1−𝐷2 𝑎𝑣𝑔 (𝐷1+𝐷2) X 100
- 14. Spikes Checking “known” samples Reinforced Blank Reinforced Duplicate
- 15. Varies depending on DQO Typically depends on the type of project and how the data will be used Most common Field QC samples (frequency) Blanks (1/20, 1/10, or once per day) Field Duplicates (1/20, 1/10, or once per day) Spikes (1/10 or once per day) Frequency of Field QC Samples
- 16. Every sample collected increases project cost Must balance cost of collection with data quality requirements Additional samples do not always insure that the data will be of high quality Cost of Field QC
Editor's Notes
- For most of your projects it is up to each of you to determine your data quality objectives. These data quality objectives will be different with each of your projects. As such, I really can’t give you absolute answers to what needs to be done. Things that work for us, may not be necessary or feasible for another project. But I can give you some things to think about. With most of these projects, we have a lot of limitations including operator collecting and processing samples, challenging sites with limited time, and limits to the equipment or test we can run. All this is affected by expense. Expense to travel can limit man power or time to run tests and also affects the equipment and number of tests we can run. All this has to be balanced with what quality and type of data we need. What is the goal of water quality sampling?
- Remember to plan and organize the sampling so that least contaminated is sampled first. If filling container directly, make sure that water is representative (undisturbed). For some sites, this will be very easy, but for others quite difficult.
- Grab sampling is the most common form of sampling flowing water because it is reliable and easy to do. The primary advantage of grab samples is that sometimes very little equipment is required for sample collection and there is flexibility in sampling location selection. Remember to plan and organize the sampling so that least contaminated is sampled first. If filling container directly, make sure that water is representative (undisturbed). For some sites, this will be very easy, but for others quite difficult.
- The advantage of composite sampling is that it gives you an idea of the average condition of a water body over time, (samples taken at different times and mixed together) or space, (samples taken at different locations within the water body). This is particularly useful in water bodies that have a lot of chemical variability either over space or over short time periods. Composite samples are often used to reduce the cost of analyzing a large number of samples.
- So, we have our sample what now? Do we process it in the field or do we get all our samples and process it one shot? Honestly, this depends on what tests you are running. How do you know? Standard methods, EPA guidelines, or professionals… We have our sample it is processed. So How do we know if it is reliable?
- Quality control is the collection of activities used to monitor and minimize the amount of error produced. Quality Control = Error Control. In manufacturing, quality control refers to all the measurements or observations that are made to ensure an item is correctly made every time. You may have pulled a slip of paper out of the pockets of a new pair of jeans that said “Inspected by 8”. Someone was responsible for checking that pair of jeans to see if it met a set of minimum requirements defined in the quality assurance program for the jean factory. Field quality assurance are the procedures and documentation needed to minimize and quantify the amount of error that is generated during your sampling activities. Your QA plan will specify what additional samples are collected and how they will be treated to measure and document the amount of error that occurred during sampling. Common names used for these samples include “blanks”, “spikes”, and “dups”. In this presentation, we are going to look at each individual type of quality control sample to learn how it is collected or prepared and what we can do with the results.
- blanks are “clean” samples used to measure the sources of contamination at different collection and measurement stages. The purpose of individual blanks prepared at different collection and measurement stages is specific to the stage where it is prepared or analyzed. What’s important for you to know (and document) is what type of blanks you will need and how to prepare them for the analysis the samples will be collected for. The type and frequency of preparation for different blanks will depend on the chemicals you are testing for and the requirements of the project. Remember that every extra sample you collect will add more time, expense, and complexity to the project so it’s important to weigh the information you can potentially obtain from the extra samples before planning to collect them. Field (ambient) blanks are the most commonly-used type of blank in field quality control. You prepare a Field Blank by filling an extra sample bottle with “analyte-free” purified water, and adding preservative if you are using any in the field. The purpose of Field Blanks is to demonstrate that you are not accidentally contaminating a sample through filling a bottle in the field. You can probably imagine this is very important at sites that are heavily contaminated with volatile organic compounds. Your book asserts that Field (ambient) Blanks are not very useful for monitoring air-borne contamination except in cases where the method provides extremely low detection limits and the site is heavily contaminated. I would argue that the Field Blank still provides a good indication of the potential for sample contamination during collection. This is especially true if you are adding a preservative such as acid in the field. Rinsate or equipment blanks help show that your decontamination procedures are working. If you are using a pump and have to reuse the tubing between wells, you have to have a decontamination procedure. The only way to show your “decon” procedure is working is by running some clean water through the tubing and pump after it has been used to first pump contaminated water and then cleaned. The amount of clean water run through the pump and tubing before collecting an equipment blank is usually determined beforehand. Trip blanks are a generally only used for volatiles and can take the place of a Field Blank. The only difference between a Trip and a Field Blank is where the bottle is filled.
- This slide shows some actual data for a group of 35 field reagent blank samples collected and analyzed for nitrate-N. The laboratory method detection limit was determined to be 0.03 ppm. Approximately 85% of the concentrations measured fall at or below this concentration. Do you think there is a problem with the other 15% of the samples? In this case the “action level” is well above the levels detected in the blank, so detection of nitrate at 0.10 ppm or less was not a problem. Still it may be surprising to see that the field blanks may have had traces of the chemical that was sampled for. It may be useful to go back to field records and see if the samples with concentrations higher than the MDL were handled differently than the others for future reference.
- Another type of Field QC sample is the duplicate. Field duplicates or replicates are two separate samples collected from the same sampling point at the same time from a relatively homogenous source. These samples are individually labeled and treated as separate samples throughout the entire sample handling and analysis process. What is key here is that you ensure the medium you are sampling from is well mixed before collection. This is fairly easy when you are pumping a high capacity well at a steady flow rate, but much more difficult when sampling a chemical plume and the well you are pumping is right at the boundary of the plume. Sometimes its useful to use a “Y” connector or splitter to divide flow from your sampling pump. Another approach is to alternate back and forth between filling the 2 duplicate samples. A third option is to fill a larger container first, mix the large contained and then fill your smaller duplicates from the “homogenized” sample. Remember, however, anytime you use additional equipment, such as a splitter or homogenizer bottle, these items must be decontaminated and their cleanliness demonstrated through collection of equipment blanks.
- How often should Field QC samples be collected depends on the data quality objectives – how is the data going to be used? Generally, field blanks are collected at least 1 time per day of sampling, and may be collected as often as ever 10 samples. The same is true of duplicates, though you may have to increase the duplicates from a particular location if you are trying to show that the variability (error) in the sample collection and analysis is less than a certain level in order to meet specific monitoring or clean-up regulations. Equipment blanks show that the equipment (pump, tubing, fittings, etc) you are using does not significantly change the concentration of the chemical you are measuring. Some projects allow you to demonstrate this one time and then there is no longer any requirement to collect them. Other projects would require an equipment blanks after every site or well is sampled. Trip blanks are only needed for volatile organic compound (VOC) samples and will be provided by the laboratory runnig your samples.
- Remember also that collection of additional samples adds to overall cost and must be figured in the project budget – both in terms of laboratory analysis and time in the field. Some QC samples are relatively easy to collect, but others such as an equipment blank can add significantly to the time required to sample a site. Think about the time and effort required to collect each and every sample BEFORE it is collected and analyzed. What are you going to do with the results? Random collection of 10 additional samples for a project can easily add hundreds or thousands of dollars to a project and, if not carefully planned, may not provide any addition level of data quality to the results.