Laserfiche WebLink
<br />i <br />I <br />I <br />! <br />i <br />I <br />I <br />I <br />-I <br /> <br />. <br /> <br />. <br /> <br />June 10, 1992 <br />}'fr. John Pritchard, Town M.n"ger <br />Town of Gr.:.nby <br />Page 2 <br /> <br />The problem s"..ems from the fact that the backwash "'-ater from the filters and s1"';~e <br />from the tDbe settlers is dL.-e::ted directly back into the raw water pond which supplies <br />the plmt with w-..ter. In other words, the turbidity ",.hiciJ. the plcnt is designed to remove <br />"ia. the :lilte..~ and c!at.Jier is recycled back to the head of the plcnt which degr..rles the <br />IaW water quality. The inter-relationship or the backwash pond, Ia.W wate.r pond and <br />Fraser RIver Ia.W W'4ter in~ wm require tbt improveme.'1t$ be done to all t.i.~ <br />. components. <br /> <br />Enclosed is a. schematic plan .'iew of the Town's "'-ater treatment pl2r.t wbi~h shows the <br />major components. <br /> <br />Water that is used to remove the ro..."'bidity and s-.....Hme.'1t bcl1dup in the filt::::s (cali=! <br />bacl.-wash warer) is cii=''',,; to two smc.11 bacl..~-ash ponds.' These ponds also receive <br />",'ate.r from the c!.r.fi.er or tube $.'"ttler basin. 'Whe.:l!h~ baSins 2re dr.Jned, the sludge <br />buildup in. the bottom oi the bas'LIlS is removed and cfue=td to the ponds. The bac1.-wash <br />'water and c!ar'..ner d..."";'" w~ is direc:ed to a d.lvc..-sion m.anhole. The diye=sloo. <br />=hole splits the flow to ponds No.1 and 2. <br /> <br />War: .uom the ?Onds is C2.tltl,lte:l irl. an effl=t piDe and is a..c:-ain cili"ec..:e to the S"Me <br />- - ... - , - , <br />;"''''1le:J.t dive.-sicn st!''Jct'Jre. Water then pro~~s .uom the diversion str"..:;.'U:e cili:~dy <br />into the intake re....,';on oond. Sey~.J. soeciB:c problems have bee::L identiJled wi;:h the <br />back\1..-..sh ponds. The mos:: severe probl~m is t~"t t.l-)e effe:::ti:ve volume of the ponds is <br />reduccl because of high groundVr'atel'. Groundv.'ater rises above the bottom of the ponds <br />which effectively redu= the detention time in the ponds. <br /> <br />According to as-built information, the ponds ~ only four feet d~. The hig.it <br />groundwater in. the pond also does not allow the al= sludge buildup to de=''''''. The <br />COllvenno!l2l. =000 of d.ev..a!er~g alum sludge for s....11 water tt""r-"ent pls.ts is to <br />isolate or,e of the backwash ponds and dr..in the de::::mt water. Tne coagulz-<t sludges ~e <br />then aIlowed to dr;y throu"h the=al coIlvec::iCIl or fr--7~Jthaw cycles b. ;:he ;:,mter time. <br />o . <br />~l1se of the high groundwater, tie To';.-n has not bee.n zble to de;:''a~r tie coagul<.!lt <br />sludge. As a res-..Jlt, the sludge has built up :01. the bottom of the ponds which, ag--..in, <br />:reduces the yol=e and detention time. <br /> <br />:Be-""l1se or the short dete:liion times 1.1. tl-te baek",;'ash ponds, the wa:er does not have <br />enough time to se:-J.e out me o.::rbic.ity and. s.---:; me::.:S that a..-e prese.":.t L,4 t..1e bac1.-;;:ash <br />W~'~r This ""'''':''l'd ,,--~~ u'-e;" ;s .;'""",.",.; ";~ec':v :-'0 .1-.. ;,..-l-e T'.....~.:cn po""'; ''';'':ei, <br />~ .. ~......u n.::.I..OW.;.: .;. ..,.. ~.......~ ~ ..... ~_ \..i...l.... _.~'\, .._.11.,1... ,....... "".lJ. "J. <br />supplies the pla.::tt ....i:.l-j raw wate:'. <br /> <br />sc~~.~'':E.S=-=: ~CR:CN :.~~;?.. :NC. <br /> <br />I <br />I <br />I <br />I <br />, <br />; <br />i <br />i <br />i <br />, <br />1 <br />I <br />I <br />i <br />I <br />1 <br />