The labor intensive cadmium reduction method requires that careful attention be paid to analyte concentration so that cadmium columns do not become plugged up or run dry. |
Recently, lab staff evaluated several methods for monitoring and reporting of nitrate in drinking water samples and selected a new USEPA approved method from Hach Co. that achieved a major breakthrough in the utility's effort to find a way to run its lab more efficiently.
Manteca's compliance laboratory is located at the city's 6.5 mgd wastewater plant and is responsible for monitoring and reporting parameters listed on the facility's NPDES permit. The lab also runs samples for the utility's drinking water system that serves a population of approximately 70,000 people.
The plant produces water from ground water sources that is also blended with purchased surface water to reduce high levels of nitrate and arsenic present in the ground water source. High levels of nitrate are present due to agricultural runoff in the fertile central valley of California. The plant has found that blending with surface water helps reduce the amount of treatment required for optimized nitrate removal.
The lab typically runs 2-4 nitrate sample batches per week for process control and monitoring in addition to those required for compliance reporting. In total, the lab runs an average of 7-8 nitrate samples per week and 5-6 required QC samples using the traditional cadmium reduction method (SM4500-NO3 E) per nitrate sample batch.
New infrastructure demands, declining revenue, and increasing regulatory compliance requirements are key factors contributing to budgetary pressures faced by water utilities across the country. The City of Manteca is facing these budgetary pressures and is responding in part by finding ways to run their lab more efficiently.
Complex, time consuming analytical methods were a significant drain on the lab's time and on individual analyst efficiency. The commonly used Standard Method (4500-NO3 E) for measuring nitrate was one such method. The Standard Method requires several sample preparation and dilution steps while careful attention must be paid to analyte concentration so that cadmium columns do not become plugged up or run dry, which can slow down analysis time.
In total, the method commonly takes 90 minutes or more per sample, or quality control (QC) sample. The method completely occupies the lab technician's time during this period because it is labor intensive and technique-sensitive. For utilities that run 10 or more samples per week where nitrates in source water are common, this can equate to more than 25% of the total work hours for a lab.