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<br /> City of Everett, Public Works Department, Water Pollution Control Facility <br /> <br />Page 7 of 13 <br />Biosolids Sampling for Required Biosolids Characterization <br />The City of Everett removes approximately 2,000 dry tons of biosolids annually in a bulk dredging event <br />and does not operate a continuous biosolids dewatering facility. To comply with the requirements of <br />WAC 173-308-150, analyses for pollutant metals, nutrients, and pathogens are done on at least six <br />distinct samples of dewatered biosolids. VAR analysis will be completed on one composited sample <br />consisting of at least six samples of in-situ solids before each dredging event and a lab duplicate. <br />Vector Attraction Reduction (VAR) analysis is completed on in-situ lagoon solids in the area that is <br />scheduled to be dredged. This sampling is done at most 30 days prior to the start of dredging to ensure <br />the sample is representative of the area to be dredged and the final dewatered biosolids product. The <br />VAR sample is collected as a composite of several samples in the area to be dredged, and that composite <br />is duplicated in the lab. The VAR analysis is done on that composite sample and its duplicate. <br />Pollutant metals, nutrients, and fecal coliform analyses are completed on dewatered biosolids. <br />Sampling of the dewatered solids will either be done in several events as solids are being dredged or in a <br />single event throughout the dewatered biosolids stockpile once the dredging project has concluded. <br />If dewatered biosolids are being collected concurrent with the dredging and dewatering project, then a <br />minimum of six discrete grab samples will be collected at even intervals throughout the project. For <br />example, if 2,000 dry tons are to be dredged, then one grab sample will be collected from the <br />dewatered solids every 330 dry tons produced, making six discrete grab samples collected for analysis. <br />If dewatered biosolids are being collected from the stockpile after the dredging project is over, then the <br />stockpile will be split into six distinct areas. Samples will be collected from each area as a composite of <br />several samples throughout the area, making six discrete composite samples collected for analysis. <br />Biosolids Sampling for Internal Monitoring <br />In order to monitor historical metal pollutants and to track changes in metals concentrations, the City of <br />Everett will monitor in-situ solids in the regularly dredged lagoon areas twice per year. These regularly <br />dredged lagoon areas (Aeration Cell #2, Oxidation Pond, and Recirculation Channel) are subdivided for <br />sampling purposes and to trend changes in solids over time. <br />Hydrographic surveys of the lagoons created by City staff assist in tracking the quantity and distribution <br />of biosolids prior to and after contract dredging. Plant operations staff use a Garmin device to take <br />depth data and a sludge judge to take density samples from a boat on the lagoons. The CAD division <br />then uses that data to produce hydrographic survey maps. Surveys of the AC2, Oxidation Pond, and <br />Recirculation Channel are taken in September of each year, and after an area is dredged. <br />In 2021, a small area of AC2 was found to have a lower pond bottom than what was designed. To track <br />any potential changes to the pond bottom, a pond bottom survey is also completed after dredging <br />projects. Pond bottom surveys are conducted by City Staff using a Garmin device to mark GPS <br />coordinates and to take depth data using a rigid, incremented pole. The manual depth measurements <br />and Garmin coordinates are compiled by City Staff and forwarded to the CAD division to produce <br />bottom surveys similar to the hydrographic surveys. Changes in this liner survey would prompt further <br />liner sampling, and, if necessary, notice to Ecology.