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Now 4 . Total Phosphorus 5 . Orthophosphorus 6 , Biological Oxygen Demand ( BOD ) 7 . Total Suspended Solids (TSS ) 8 . Oil and Grease 9 , Hardness 10 , Zinc 11 . Copper 12 , Cadmium 13 , Chromium Sample Locations and Other Pertinent Sampling Information : Sample locations are shown on the attached figure . Composite samples will be taken by automatic stormwater samplers . Each automatic sampler will take flow-weighted composite samples ( Le , the amount of sample collected is proportional to the flow rate ) . The composite sample containers will be thermally preserved during the collection process , the composite jug will be stirred and siphoned into lab- supplied bottles ( in the field ) that have been properly chemically preserved , and the samples will be transported to the laboratory on ice in order to ensure proper preservation . Each automatic sampler will be activated based on a rise in water depth in the lake . Once activated , the samplers will take flow-weighted samples at fifteen minute intervals for approximately six hours or until at least 4 , 800 mL is collected . However, if the lake depth drops to a predetermined level within four hours after initiating sampling , the sampler will shut off, since this will indicate a non - significant rainfall event . The sample suction points are located near the influent pipe or effluent weir (within ten to fifteen feet) , as applicable , and are approximately mid -depth in the water column . Field samples (Temperature , pH , Salinity , and Dissolved Oxygen ) will be taken in the vicinity of each sample suction point. Proposed field instruments are : ( 1 ) YSI Environmental 4 YSI 63 pH/Salinity/Conductivity/Temperature Instrument , and (2 ) YSI Environmental 4 YSI 55 Dissolved Oxygen Instrument . 3 F:\Public Works\KeithM\Stormwater Projects\Roseland\QAPP - Quality Assurance Project Plan\East Roseland Stormwater Sampling Plan - Revised July 23, 2004 .doc