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Ref. No. [UMCES] CBL 2017-050
ACT VS17-05
6
The instrument is a bypass design that pulls a sample from a pressurized source or open
channel to the sensor inside a cabinet for measurement. The cabinet provides easy access to the
sensor for visual inspection and routine maintenance. The bypass design also allows for the sample
to be diluted with Real Tech’s proprietary dilution system to achieve a greater measurement range.
Another advantageous feature specific to the cabinet design is the ability to clean the measurement
cell with chemicals. All optical sensors are prone to fouling over time which will impact the
accuracy of measurement. Mechanical methods, such as the use of wipers or brushes, tend to wear
down and are often ineffective for many fouling agents. Chemical cleaning provides the flexibility
to use a chemical that is ideal for removing the site-specific fouling agents. Depending on the site-
specific requirements, used cleaning chemicals can be diverted and stored in a container for future
disposal.
Multiple product configurations are available for nitrate monitoring applications. The
monitoring systems are designed for and most commonly used at groundwater blending stations,
municipal drinking water plants, and municipal and industrial wastewater treatment facilities.
PERFORMANCE EVALUTION TEST PLAN
These Test Protocols are based on consensus recommendations of the ACT Technical
Advisory Committee, ACT staff, and participating Manufacturers. In summary, the test:
•
utilized standard, approved laboratory analytical methods to provide best possible measure
of the ‘true’ nutrient concentration from reference samples, which served as performance
standards against which instrument estimations were compared internally by the individual
developer;
•
conducted all reference sample analysis at the state certified Nutrient Analytical Services
Laboratory (NASL) of the Chesapeake Biological Laboratory (CBL), Solomons, MD to
determine true nutrient concentrations using USEPA approved methodologies (see details
below);
•
included a laboratory evaluation of instrument performance;
•
included three moored/dock-based field trials under a wide range of environmental
conditions including freshwater, estuarine and marine ecosystems with varying nutrient
concentrations and water quality characteristics (e.g. turbidity).
All ACT personnel involved in the Nutrient Sensor Verification were trained on
standardized water sample collection, storage and shipping methods. ACT staff was available to
assist in the physical deployment and recovery of all submitted test instruments and were
responsible for the data management of test instrument results. Challenge participants were
responsible for initial set-up and calibration of their instrument. If requested, ACT provided the
chemicals and nutrient standards needed for instrument set-up and calibration. All laboratory
nutrient analyses of the independent reference samples were conducted at the CBL NASL using
standardized automated wet chemistry. All numerical data were recorded to three significant
decimals where appropriate and nutrient concentrations reported in elemental mass units as mgN/L
or mgP/L for nitrate+nitrite (NO
23
), nitrate (NO
3
-
) or phosphate (PO
4
3-
), respectively.
Laboratory Tests
Laboratory tests of accuracy, precision, and range were conducted at the University of
Maryland’s Chesapeake Biological Laboratory (CBL) in Solomons, MD. A series of five tests