Using s::can probes to get real-time water quality data Martin Davis SOP – Adv. Field Methods in Hydrology

1. Using s::can probes to get real-time water quality dataMartin DavisSOP – Adv. Field Methods in Hydrology

2. Why monitor in the field? • Allows capture of data as notable events occur • No need to transport samples back to the laboratory • Fewer concerns with contamination risk • Gives ability to more easily characterize changes and trends • Provides mobility for assessors without fixed locations • Allows for continuous monitoring of remote locations • Gives the ability to share data in real-time with collaborators • Provides rapid response ability for water contamination events

3. Who is using this technology? • USGS: Tracking Nitrate in the Mississippi River • Vienna Waterworks: Drinking water QC • Arizona Dairy Industry: Reducing plant waste • Indian Government: Monitoring contamination in the Ganges river during Kumbh Mela festival • Virginia Tech: BSE department using it to track micronutrient levels in local streams

4. A brief primer on spectroscopy

5. Protocols: Part 1 – Site Selection Select an appropriate site: Factors to consider for site selection include: SITE CHARACTERISTICS • Potential for water-quality measurements at the site to be representative of the monitored system. • Cross-section variation and vertical stratification. • Unique constraints of channel configuration. • Range of stream stage (from low flow to flood) that can be expected over the measurement interval • Presence of existing monitoring or surveillance. • Water velocity. • Presence of turbulence. • Conditions that may enhance the rate of fouling, such as excessive fine sediments or algaeThis is particularly important for spectroscopy. • Range of values for water-quality field parameters. • Need for protection from debris damage. • Need for protection from vandalism. MONITOR INSTALLATION • Type of state or local permits required • Safety hazards relevant to monitor construction • Optimal type and design of installation. • Consideration of installation challenges/costs. LOGISTICS (MAINTENANCE REQUIREMENTS) • Accessibility of site. • Safe and adequate maintenance space. • Presence of conditions that increase the frequency of servicing intervals needed to meet data-quality. • For stream sites, proximity to an adequate location for making cross-section measurements. • Accessibility and safety of the site during extreme events (for example, floods or high winds). • Availability of electrical power or telephone service. • Need for real-time reporting.

6. Protocols: Part 2 – Instrument Choice • S::can instruments have many probes. • All interface with a central control unit. • Choice depends on things like cost & desired monitoring. • Spectrometer is the most robust, but the most difficult to configure & costly.

7. Protocols: Part 3 – Installation Types • Pipes are convenient when there are existing monitoring stations in place at a survey site. • Cages are easily transportable and inexpensive. They can provide some instrument protection, though not as much as fixed installations.

8. Protocols: Part 3 – Installation Types • Fixed-site pumped deployment is ideal if there is already a long-term installation available. It provides the maximum access control, and sensor protection. Costly. • Buoys are mobile like cages and are more robust, but can be pushed off course if anchors break away.

9. Protocols: Part 4 – Port Access For this type of monitoring to work, sensors must be clean & exposed: Mounting Options and Requirements • Water must pass evenly through the instrument gap to be accurately measured by spectroscopy. • Horizontal orientation decreases bubbles and sediment in the probe. • Secure installation prevents sensors from knocking into objects. • Vertical orientation is easier to put into place but cables must besecured against damage. Cleaning and Anti-Fouling Options • Screens may be used to prevent larger particles from entering the sensor. Certain metals such as copper also exhibit anti-fouling properties to prevent algal growth. • Polymer coats can inhibit deposition and microbial growth. • Wipers or brushes can be very effective at removing stubborn deposits but require power and maintenance. • Air blasts are easily automated and often have built in ports on the instruments. • Pumping water through a flow chamber at a gage house is ideal for controlling fouling and cleaning, but it is costly.

10. Protocols: Part 5 – Power & Cables Issues in controlling power to a field spectroscopy system • Power cable length, thickness, and quality of insulation are essential in achieving a steady input voltage necessary for continuous operation of the instruments. • Degradation of battery terminals and sensor connectors is a common problem. • Solar cells can provide a means to recharge a battery, but they are not perfect. • In permanent installations, wired power systems are an option. • Depending on the probe, output can be either analog or digital. Considerations like cable shielding are necessary for long cables with analog output. Left: An example of corroded battery terminals. Corrosion like this will impact instrument function. Periodic cleaning of contacts is necessary in the field, especially in sites with saltwater.

11. Protocols: Part 6 – Communications Collecting and sending data from a field unit to a central repository Data from the probes is stored on a monitoring unit in one of two configurations: con::cube • One box solution for data logging and instrument monitoring. Mini-PC with many I/O options. • Touch screen interface with plug and play options for s::can peripherals. • Data output via built-in USB, WIFI, Ethernet, or cellular modem (with SIM card and data plan). • Can interface with third party sensors through expansion ports in industrial settings con::nect • Allows use of a standalone computer to control the instrumentation and data collection. Allows flexibility in fixed installations and eliminates the need to transfer data to a PC for processing. Both the con::cube and the con::nect use the moni::tool software, either running on the user’s PC or cube. An online demonstration of the moni::tool web interface is available at: http://monitool.s-can.at/index.x.

12. Protocols: Part 7 – Data Quality Ensuring that data is useful and filtering out noise and interference Interference from dissolved constituents • Dissolved constituents which absorb light at similar wavelengths to the desired analyte can disrupt measurements obtained through spectroscopy. Their presence will increase absorptivity. • In nitrate, for example, dissolved organic carbon, bromide, hydrogen sulfide, and other types of compounds can produce this type of interference. Advantages of using an s::can spectrometer over a conventional single or dual wavelength sensor allows for more complex spectral filtering. Interference from suspended particles • Suspended particles will scatter light and can result in overestimating absorbance. • This scattering can vary and change both magnitude and shape of a curve. • High turbidity values can prevent an instrument from functioning beyond a certain threshold.

13. Protocols: Part 7 – Data Quality Ensuring that data is useful, and filtering out noise and other undesirable effects Interference from dissolved constituents Interference from suspended particles (Both actual nitrate concentrations are in 1mg/L as Nitrogen)

14. Protocols: Part 7 – Data Quality Reading a spectral fingerprint and compensating for background values • This figure presents a spectral fingerprint example with both filtered and non-filtered spectra. • Compensating is typically done at the hardware level on most control units. • Algorithms are dependent on the contents of the water and must be updated for new sites. • In the Easton Lab, our work originally used calibrations for wastewater effluent which had to be adjusted by the company to function properly in a stream.

15. Protocols: Part 7 – Data Quality Other items worthy of consideration when processing field data Sampling Interval vs. Reporting Interval • How often do you want the instrument to take each measurement? • Additionally, when reporting this data, do you want instantaneous values or a mean over a short measurement interval (to account for moment-to-moment fluctuations in absorption values) Understanding detection limitations for various instruments, algorithms, and media • Bias can occur as discussed before due to turbidity or dissolved solids. It can also occur due to wear on the instrument, a dirty aperture, and a lamp which no longer provides enough light. • Bias can be accounted for with correction algorithms. • For the S::CAN spectro::lyser probe, the maximum error for bias correction is: ±6% of reading plus 3/optical path length (in mm; mg/L). Ranges of data validity Turbidity: 0–50 NTU, precision 0.05 NTU Nitrite (NO2-N): 0–7 mg/L, precision 0.005 mg/L abs/m DOC: 0–6 mg/L, precision 0.003 mg/L Ozone: 0 –10 mg/L, precision 0.005 mg/L Nitrate (NO3-N): 0–7 mg/L, precision 0.005 mg/L TOC: 0–8 mg/L, precision 0.005 mg/L Spectral Absorption (SAC254): 0–25 abs/m, precision 0.015 Color: 0–250 Hazen, precision 0.1 Hazen

16. Protocols: Part 9 – Troubleshooting From the USGS guide to optical techniques for determination of nitrate in situ. These guidelines are applicable in many cases to a variety of target analytes when using s::can units.

17. Protocols: Part 8 – Maintenance Performing diagnostics and maintaining quality data collection Remote Access • Regular review of data collected by the instrument. • Regular checking of sensor indicators (lamp hours, noise levels, power, internal temperature). • Regular checking of system indicators (storage remaining, data transmission). • Flagging abnormal data for review. • Modifying the data collection and processing parameters as necessary. Field Access • Inspections for damage, fouling, and corrosion on instrument and all connections. • Cleaning and servicing sensors as needed. • Checking the battery, solar panels, inverters, or other power components. • Downloading data and diagnostic information as necessary. • Manual sample collection for comparison to ensure data validity.

18. References • Pellerin, B.A., Bergamaschi, B.A., Downing, B.D., Saraceno, J.F., Garrett, J.A., and Olsen, L.D., 2013, Optical techniques for the determination of nitrate in environmental waters: Guidelines for instrument selection, operation, deployment, maintenance, quality assurance, and data reporting: U.S. Geological Survey Techniques and Methods 1–D5, 37 p. • Lane, S.L., and Fay, R.G., 1997, Safety in field activities: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A9, October 1997, accessed Nov. 1, 2013, at http://pubs.water.usgs.gov/twri9A9/. • Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, B.A., 2006, Guidelines and standard procedures for continuous water-quality monitors—Station operation, record computation, and data reporting: U.S. Geological Survey Techniques and Methods 1–D3, 51 p. • Langergraber, G., N. Fleischmann, F. Hofstaedter, and A. Weingartner. 2004. Monitoring of a paper mill wastewater treatment plant using UV/VIS spectroscopy. Water science and technology : A journal of the International Association on Water Pollution Research 49(1):9. • U.S. EPA. Technology Evaluation Report, s::can Measuring Systems Spectro::lyser. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-12/065, 2012.