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Attachment C Page 5 of 8 <br /> SIGMA CIRCUITS Inc . , STOCKTON DIVISION <br /> FIELD SITE <br /> TREATMENT UNIT OPERATION <br /> UNIT 1 (Continued ) <br /> D) The decantate from the FST, containing some floc , flows <br /> by gravity to the Decant Receiver Tank where slow mixing <br /> and final flocking of the precipitate takes place . <br /> Additional flocculent is added if necessary. <br /> E) From the Decant Receiver Tank , the slurry then flows to <br /> the first clarifier where the preliminary settling of the <br /> metal-bearing sludges occurs. Residence time in this <br /> clarifier is very long (over 3 hours at the normal flow) . <br /> F ) The supernate from the top of the first clarifier then <br /> flows by gravity to the second clarifier , where final <br /> settling takes place . Retention time is greater than 1 <br /> hour. <br /> G) From the second clarifier , the treated water passes <br /> through a series of filter socks and is pumped to the <br /> accumulation tanks. These tanks are plumbed to be used <br /> in alternate fashion ( i . e . , one is filling while the <br /> other is holding water for sampling and analysis prior to <br /> discharge) . <br /> H ) The contents of the accumulation tanks are sampled while <br /> filling and also when full . When one accumulation tank <br /> is full , the flow is switched over to the other tank and <br /> the first one is sampled and analyzed for metals . The <br /> process is reversed when the other tank is full . <br /> I ) If the metals are below discharge limits , the contents of <br /> the full accumulation tank are pumped to the FRDT ( see <br /> Unit Block Diagram, Attachment C-1 , Sheet 1 ) . If the <br /> metal concentration in the tank is too high , the contents <br /> are pumped back to the WRT for re-treatment . <br />