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East Roseland QAPP Section B Revision No . _ Date : 11 / 16/04 Page 15 of 22 weighted samples at fifteen - minute intervals . Rainfall data will be collected at the lake with an associated rain gauge and compared against rainfall data obtained from the nearest weather station . However, if the lake depth drops to a predetermined level within four hours after initiating sampling , the samplers will shut off, since this will indicate a non -significant rainfall event . All sampling intake points will be located near the lake ' s influent pipe or effluent weir (within ten to fifteen feet) , as applicable , and approximately mid -depth in the water column . The sample locations are shown on Figure A . 2 Sampling will consist of seven ( 7 ) rainfall events ( composite samples ) . All of the parameters that will be measured are for information . Since this project is a stormwater system retrofit , there is no critical parameter of concern . The purpose of the stormwater sampling is to determine the pollution removal effectiveness of the constructed stormwater management system . B2 . Sampling Methods Requirements B2 . 1 Sample Collection Procedures and Methods Automatic stormwater samplers will collect post-construction composite samples . Each automatic sampler will be equipped with a large plastic sample container that is properly cleaned before each sampling event . The automatic samplers will be programmed to take a flow-weighted sample every fifteen minutes . Once activated , each sampler will draw the flow-weighted sample through a Teflon tube , into its sample container every 15 minutes for approximately six hours or until at least 4 , 800 mL is collected . The composite sample containers will be thermally preserved during the collection process , then the composite jug will be stirred and siphoned into lab-supplied bottles that have been properly chemically preserved , and the samples will be transported to the laboratory on ice in order to ensure proper preservation . At the time of collection of the samples , field measurements (temperature , pH , salinity , dissolved oxygen ) will be performed .