Bai mau WQI

1. H THNG V TR LY MU PHC V GIM ST CHT LNG NC MT TI

Trnh t tip cn chng trnh quan trc mi trng phc v nh gi cht lng mi trng c minh ha trong hnh 3.1:i tng nghin cu

La chn v tr o v s lng v tr cn o Phng php ly mu

Cc thng s cn o

Thi gian thc hin o c La chn thit b ly mu v thit b o

Thc hin ly mu

Bo qun v phn tch mu

Ghi chp v x l s liu

Trnh by s liu v vit bo co

Hnh 1: S trnh t tip cn chng trnh quan trc mi trng La chn v tr ly mu + Cc yu cu tng qut i vi vic la chn v tr ly mu - V tr cc im ly mu nc cn chn n nh v phi i din cho mi trng nc mt ni quan trc, c xc nh da vo kh nng t lm sch ca thy vc cn cn nhc n cc yu t lin quan n s phn b, pha long trong khu vc quan trc nh tc , lu lng dng chy, lu vc, thi tit - i vi sng, knh, rch chy qua thnh ph v khu cng nghip th ti thiu phi quan trc ti hai im u vo v u ra khu vc nghin cu. + Cc iu kin c th trong vic la chn v tr quan trc: Trn cc sng ngi, tuyn o th nht (nn) phn b tp trung ti khong cch 1km trc ngun nhim v loi b nh hng ca nc thi vo. Tuyn o th hai c ch nh quan trc s thay i cht lng sng rch gn im thi trong vng nhim. Tuyn o ny c b tr ti v tr trc ni s dng1 Chuyn 1: nh gi hin trng cht lng mi trng nc trn cc tuyn sng rch chnh Huyn Bn Lc nm 2009

nc gn nht 1km. Trong cc thnh ph hay khu dn c ni c nhiu ch nc thi, tuyn o kim tra cn b tr khong cch 0.5 1.0km sau knh dn chnh, hoc knh dn cui cng. Tuyn o th ba c b tr sao cho s liu quan trc i din c cht lng mi trng nc ni chung tc l v tr trn ln (> 80%) nc thi v nc sng. S lng cc i tng (sng/rch) cn quan trc v s im ly mu ti mi i tng cn c xc nh vi cc iu kin c th ca thy vc sao cho i din c ch nhim ca i tng cho. i vi tuyn o nn trn sng/rch, cc mu nc cn ly y cc tng t b mt n tng y. i vi cc tuyn o cn li, mu c ly ti cc tng nc tng ng vi su ca i tng quan trc nh sau: - su < 5m: ly nc ti tng mt - su > 5m v < 10m: ly nc tng mt v tng y - su > 10 m: ly nc tng mt, tng trung gian v tng y Trn c s cc v tr v tn sut ly mu thc hin nm 2008, cc c s khoa hc trong vic xc nh v la chn v tr ly mu, tnh hnh thc t v h thng quan trc cht lng nc mt hin c ti a phng, n nghin cu xut h thng v tr ly mu phc v chng trnh gim st cht lng nc mt hng nm ti. (bt u t nm 2009) nh sau: 1.1. Cc i tng chnh cn tip cn

1.2. H thng ly mu c phn b nh sau V tr quan trc c s: v tr quan trc nhm kim sot ngun nc t bn ngoi a vo a phng: (M16, M17); (M15), (M1). V tr quan trc tc ng: c b tr ti khu vc chu tc ng t hot ng sn xut nng nghip, cng nghip v dn c. Tuyn o nhm quan trc tc ng t hot ng nng nghip c b tr ti (M25), (M24), (M26), (M18, M19), (M2).2 Chuyn 1: nh gi hin trng cht lng mi trng nc trn cc tuyn sng rch chnh Huyn Bn Lc nm 2009

Tuyn o nhm quan trc cc tc ng t hot ng cng nghip v dn c: M14, M3, M6, M4, M5, M11, M8, M9, M10, M18. Cc v tr ly mu ti cc hp lu chnh v cc v tr kim tra: (M25); (M24); (M13); (M23), (M19), (M20), (M21), (M22). V tr quan trc xu hng: V tr quan trc nhm kim sot ngun nc ca huyn Bn Lc trao i vi cc a phng ln cn: (M25), (M24), (M23). Tm li, v tr ly mu nc mt trn cc tuyn sng rch ti .nm 2009 c phn b c th nh sau: Bng 1: V tr ly mu nc mt ti .nm 2009STT i tng tip cn V tr K hiu Ta S lng

Tng cng

26 mu

3

Chuyn 1: nh gi hin trng cht lng mi trng nc trn cc tuyn sng rch chnh Huyn Bn Lc nm 2009

Hnh 2: S v tr cc im ly mu nc mt ..nm 2009 1.3. Tn sut ly mu v thng s quan trc - Tn sut v thi gian ly mu nh sau: Tn sut: 2 ln/ nm (ma kh v ma ma) Thi gian: cui thng 03 v thng 06/2009.

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\- Cc thng s quan trc n thc hin phn tch i vi cc thng s cht lng nc mt c quy nh ti QCVN 08:2008/BTNMT Qui chun k thut Quc Gia v cht lng nc mt (National technical regulation on surface water quality). Bng 2: Cc thng s tin hnh phn tch TT Thng s 1 2 3 4 5 6 7 8 9 10 11 12 pH Oxy ha tan (DO) Tng cht rn l lng (TSS) COD BOD5 (200C) Amoni (NH4+) (tnh theo N) Clorua Florua Nitrit (NO2-) (tnh theo N) Nitrat (NO3-) (tnh theo N) Phosphate (PO43-) (tnh theo P) Xianua (CN-) mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l n v TT Thng s 15 16 17 18 19 20 21 22 23 24 25 26 Ch (Pb) Crom III (Cr3+) Crom VI (Cr6+) ng (Cu) Km (Zn) Niken (Ni) St (Fe) Thy ngn (Hg) Cht hot ng b mt Tng du m Phenol (tng s) Ha cht tr c - 2,4 D - Paraquat 13 14 Arsen (As) Cadimi (Cd) 1.4. mg/l mg/l 27 28 E.Coli ColiformMPN/100ml MPN/100ml

n v mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l g/l g/l

Thit b o c, phng php ly mu, bo qun v phn tch mu

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Thit b o c ti hin trng: My GPS, my TOA o nhanh cc thng s ch th cht lng nc. Phng php ly mu v bo qun mu c tin hnh theo TCVN 5992-1995, TCVN 5993-1995 v TCVN 5996-1995. i vi cc v tr ly mu trn cc i tng sng ln nh: sng Vm C ng, sng Bn Lc, Knh Xng Ln, knh Xng An H thc hin ly mu t hp theo khng gian, tc l ly 3 mu 3 v tr (b tri, b phi, gia dng) em trn ln vi nhau. Cc i tng cn li thc hin ly mu n. Cng tc phn tch mu c tin hnh ti Phng Mi Trng - Phn vin Kh tng Thy vn v Mi trng pha Nam (t chun Vilas 284). 1.5. Cc tiu chun so snh, nh gi i vi cht lng nc mt ti mt s tuyn knh rch quan trc, p dng quy chun so snh: QCVN 08:2008/BTNMT Qui chun k thut Quc Gia v cht lng nc mt (National technical regulation on surface water quality). 2. KT QU PHN TCH MU Kt qu phn tch mu tham kho t S liu phn tch ca phng Mi trng Phn vin Kh tng Thy vn v Mi trng pha Nam, ngy 02/04/2009 v ngy 26/06/2009.

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3. NH GI HIN TRNG CHT LNG NC MT TRN CC TUYN SNG RCH CHNH HUYN BN LC LA CHN TIU CHUN I SNH PH HP VI TNG I TNG GIM ST Bng 3: M t thng tin v ngun thi v mc ch s dng 11 tuyn sng rch STT Tn sng /knh, rch Ngun thi Mc ch s dng

Kt qu o c cht lng nc mt h thng sng rch trn a bn huyn c nh gi v so snh vi QCVN 08:2008/BTNMT: qui chun k thut quc gia v cht lng nc mt. Do hu ht cc sng rch c kho st u dng cho mc ch ti tiu v giao thng ng thy nn cc kt qu phn tch c so snh vi ct B1. n thc hin nh gi kh nng s dng nc mt trn sng vo mc ch lm nc cp sinh hot, cc kt qu phn tch trn sng .. c so snh vi ct A2 ca QCVN 08:2008/BTNMT. Da trn kt qu phn tch ca 52 mu c ly trn 11 tuyn sng rch chnh qua 02 t kho st vo ma kh v ma ma, cht lng mi trng nc mt trn a bn huyn nm 2009 c nhn nh: + pH Tr s pH trong nc l n v o lng cho tnh axit, trung tnh hay kim ca nc, pH l mt yu t ch th tt nht. Bt c s thay i no d rt nh trong nc cng lm thay i pH ca mi trng, c th s nhim do thc n tha, to n hoa, nhng thay i v xy ho tan, hm lng ammonia Trn sng (M16, M18, M19, M20, M21, M22, M23) c gi tr pH dao ng t 3.45 n 5.95, cc kt qu dao ng khng ng k, s chnh lch gi tr gia 2 t kho st l khng ln. Vi kt qu phn tch pH ca 7 v tr trn sng vm C ng u cha t QCVN 08:2008 (ct A2). Ti cc tuyn sng rch cn li, thng s pH c gi tr t 3.45 n 6.30, cc gi tr pH o c a s dao ng t 4 n 6, hu ht u khng p ng (thp hn) QCVN 08:2008 (ct B1). Din bin pH trn h thng sng rch cho thy nc mt ti7 Chuyn 1: nh gi hin trng cht lng mi trng nc trn cc tuyn sng rch chnh Huyn Bn Lc nm 2009

y c tnh acid nh. Mu nc ly ti Knh Xng Ln (M1), Knh Xng An H (M17) trong ma kh c gi tr o thp, c bit ti v tr quan trc ng 3 Rch Vng v sng Vm C ng (M21) vo ma ma cho kt qu o pH thp nht (3.45). Cc sng rch ti Bn Lc c gi tr pH dao ng khng ng k v tng i n nh. (Xem hnh 5) + Oxy ha tan (DO) DO (Dissolve Oxygen) l mt ch s quan trng nh gi s nhim nc ca cc thu vc. DO l lng oxy ho tan trong nc cn thit cho s h hp ca cc sinh vt nc (c, lng th, thu sinh, cn trng v.v...) thng c to ra do s ho tan t kh quyn hoc do quang hp ca to. Nng oxy t do trong nc dao ng mnh ph thuc vo nhit , s phn hu ho cht, s quang hp ca to Nhn chung, gi tr DO o c qua 2 t kho st u khng t QCVN 08:2008, dao ng t 1.43 mg/l n 3.27 mg/l. Hm lng DO o c ti cc v tr ly mu trn sng Vm C ng (M16, M18, M19, M20, M21, M22, M23) c bin dao ng (1.74 3.26 mg/l), v tt c 7 v tr trn sng Vm C ng u khng t QCVN 08:2008 (ct A2). Hm lng DO trn sng Vm C ng tng i cao so vi hm lng DO o c trn cc sng rch khc. Ti mt s v tr nh trn knh T4 (M25), knh T6 (M24), rch B King (M26), ch Tn Bu trn sng Bn Lc (M15), rch Bc Tn (M9), sng Rch Chanh (M12) qua 2 t kho st u cho thy hm lng DO khng p ng QCVN 08:2008 - ct B1 (thp hn rt nhiu). S dao ng v hm lng DO gia 2 ma kh v ma ma khng ng k, v c xu hng tng vo ma ma. Ngoi ra, s thay i ca gi tr DO gia hai t ly mu cng ph thuc vo nhit thi im ly mu, s phn hy ha cht, s quang hp ca to. Hm lng DO thp cho thy nc mt sng rch Bn Lc c du hiu theo chiu hng xu, lu di s nh hng n h sinh thi ti cc thy vc v lm gim kh nng t lm sch ca sng rch. (Xem hnh 6)

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Hnh 3.5: Din bin pH trn h thng sng rch huyn Bn Lc nm 2009

Hnh 3.6: Din bin DO trn h thng sng rch huyn Bn Lc nm 2009

Nhn chung: Cht lng nc mt trn 11 tuyn sng rch kho st ti huyn Bn Lc thay i theo thi gian v chu nhiu nh hng t cc ngun thi. S thay i pH gia cc v tr kho st v gia 2 ln o cho thy cht lng nc trong khu vc khng n nh v thnh phn cc cht lun bin i theo khng gian v thi gian. Kt qu phn tch, nh gi cho thy, hin trng cht lng nc mt huyn Bn Lc a phn t tiu chun cho php phc v cho mc ch ti tiu v giao thng thy li. Vo thi im hin ti, nc mt trong khu vc kho st c biu hin nhim cc cht hu c v ha hc, nhng mc nhim cha tht s nghim trng. Cc thng s ch th nh: pH, DO, COD, BOD, N-NH4, Clorua, st (Fe) du m ca cc v tr kho st a phn cha t c tiu chun cho php, mt s cn vt ngng rt cao nh: hm lng du m. Cht hot ng b mt, phenol, kim loi nng pht hin c tn ti trong mi trng nc ca khu vc nhng hm lng tng i thp hn so vi quy chun cho php. Tuy nhin, cc thng s ny cn c kim tra nh k theo tn sut nht nh trong nm bi c trng v s d tch t trong ng vt v thc vt, i vo chui thc n gy nh hng n sc khe con ngi. Mt vi nhn nh i vi tng tuyn sng rch trn a bn huyn Bn Lc: Kt qu phn tch v nh gi cht lng nc sng Vm C ng cho thy a phn cc thng s u t QCVN 08:2008 (ct A2). Tuy nhin, cn mt s thng s vt quy chun cho php nh: pH, DO, COD, BOD, amoni. Hm lng du m trn sng Vm C ng cho thy s tn ti kh cao, vt ngng cho php. Cc mu th cho thy Sng Vm C ng mang tnh acid nh v c du hiu nhim hu c. Bn cnh , hu ht cc knh rch trn a bn huyn Bn Lc u ra sng Vm C ng. Do , kim sot hiu qu cht lng nc trn sng ny, cn phi kim sot t cc knh rch nhnh. Mt iu ng quan tm l ngun nc sng Vm C ng hin ang c s dng cho mc ch cp nc sinh hot, do vy, vic qun l cht ch cc ngun thi vo lu vc ny l v cng cn thit, cng nh cn quan tm p dng cc cng ngh x l nc cp thch hp trc khi a vo s dng. Mt s sng rch khc trn a bn c du hiu nhim ngun nc mt vi a phn cc thng s ch th khng t quy chun cho php (pH, DO, COD, BOD, clorua, st (Fe) hm lng du m) nh: sng Bn Lc, sng Rch Chanh, rch Thanh Lp, rch9 Chuyn 1: nh gi hin trng cht lng mi trng nc trn cc tuyn sng rch chnh Huyn Bn Lc nm 2009

Bc Tn (pH, DO, COD, NH4, du m),. Nguyn nhn nhim c th do nh hng ca hot ng sn xut cng nghip (KCN Thun o thi nc thi ra sng Rch Chanh, mt s nh my, c s sn xut dc sng Bn Lc,) cng nh cc hot ng dn sinh t cc khu dn c phn b dc theo cc sng ny. Knh Xng Ln, rch B King, rch Cy Trm ang c xu hng b nhim (mt s t thng s ch th cht lng nc cha t quy chun cho php: pH, DO, NH4, du m). Cht lng nc trn knh Xng An H, knh T4, knh T6 vn mc chp nhn c, a phn cc thng s ch th u t QCVN 08:2008 (ct B1). Nh vy, vi hin trng cht lng mi trng nc mt trn a bn huyn Bn Lc c nh gi nh trn, cn ra cc bin php thch hp nhm qun l cht lng nc ca h thng sng rch ny cng nh quan tm ton din n cc khu vc cha c biu hin nhim (ch mt s t thng s khng t tiu chun cho php). Trn thc t, mun nh gi tng i ton din v hin trng cht lng nc mt ti mt lu vc th cn phi c mt chui cc s liu theo thi gian v khng gian. Cc kt qu phn tch trn y trc mt ch a ra hnh nh v hin trng cht lng nc mt ti 11 tuyn sng rch vo thi im kho st, cha th phn nh ton din hin trng cht lng nc mt trn a bn huyn Bn Lc trong c nm. Tuy nhin, nhng nhn xt, nh gi da trn cc kt qu phn tch mu phn no cung cp c s khoa hc quan trng, to tin cho vic hoch nh cc bin php khng ch nhim, bo v ngun nc mt ni ring v bo v mi trng ni chung trn ton a bn.

3.4. BIU DIN CHT LNG NC CC TUYN SNG RCH CHNH HUYN BN LC THNG QUA CH S CHT LNG NC WQI NSF3.4.1. ngha ca vic nh gi hin trng cht lng nc qua ch s cht lng nc

nh gi cht lng nc (CLN), nhim nc sng, knh rch, hin nay Vit Nam v nhiu quc gia trn th gii, ngi ta thng da vo vic phn tch cc thng s CLN ring bit, sau so snh tng thng s vi gi tr gii hn c quy nh trong Tiu chun Quc gia hoc Tiu chun Quc t. Tuy nhin, cch lm truyn thng ny c mt s hn ch nh sau: - Khi nh gi CLN qua nhiu thng s ring bit, s khng th ni ln din bin CLN tng qut ca mt con sng (hay on sng) v do vy, kh so snh CLN tng vng ca mt con sng, so snh CLN sng ny vi sng khc, CLN thi gian ny vi thi gian khc (theo thng, ma), CLN hin ti so vi tng laiV th, s gy kh khn cho cng tc gim st din bin CLN, kh nh gi hiu qu u t bo v ngun nc v kim sot nhim Mt khc, khi nh gi qua cc thng s CLN ring bit, thng thng, ch cc nh khoa hc hoc nh chuyn mn mi hiu c, do kh thng tin v CLN

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cho cng ng v cc c quan qun l Nh nc, cc nh lnh o ra cc quyt nh ph hp v bo v v khai thc ngun nc khc phc kh khn trn, cn phi c mt hoc h thng ch s cho php lng ha c CLN (ngha l biu din CLN theo mt thang im thng nht), c kh nng m t tc ng tng hp ca nng nhiu thnh phn ha l sinh trong ngun nc. Mt trong nhng ch s l Ch s cht lng nc (Water Quality Index WQI). B ch s chun cht lng nc (Water Quality Index - WQI) v c bn l phng tin ton hc tnh ton mt gi tr ring l t kt qu mt s th nghim. Kt qu ch s biu hin cht lng nc (CLN) ca mt lu vc nht nh nh ao h, sng rch... WQI c xut v p dng u tin M vo nhng nm 70 v hin vn ang c p dng rng ri nhiu bang. Hin nay, nhiu m hnh WQI c trin khai nghin cu p dng nhiu quc gia nh n , Canada, Chile, Anh, i Loan, c, Malaysia,v ngay ti Vit Nam trong nhng nm gn y cng c nhng nghin cu v vn ny. Mt trong nhng b ch s WQI ni ting, c p dng ph bin nht trn th gii l b ch s WQI- NSF.3.4.2. Phng php tnh ton Ch s cht lng nc NSF - WQI

Ch s CLN ca Qu v sinh Quc gia M NSF (National Sanitation Foundation -Water Quality Index) l mt trong nhng ch s CLN ni ting v c s dng ph bin nht. NSF WQI l kiu ch s CLN tng qut, chung cho cc mc ch s dng. Do , nhm nghin cu s p dng vic tnh ton CLN theo ch s WQI- NSF tin hnh thnh lp cc bn phn vng cht lng. NSF - WQI c xy dng bng k thut Delphi ca tp on Rand. Mc ch ca phng php ny l thu nhn v tng hp kin ca mt s ng cc chuyn gia khp nc M la chn cc thng s CLN quyt nh (Xi), sau xc lp phn trng lng ng gp ca tng thng s (wi) v tin hnh xy dng cc th chuyn i t cc gi tr xi (gi tr o c ca thng s Xi) sang ch s ph (qi). C 4 giai on c bn xy dng WQI. Qu trnh xy dng WQI c th c m t theo s :

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a) Giai on 1: La chn cc thng s CLN quyt nh (Xi): Mt s t cc thng s quyt nh (hay thng s la chn) c chn ra t nhiu thng s CLN tnh vo WQI. T kt qu cc phiu cu hi iu tra cc chuyn gia, 9 trong 35 thng s CLN c la chn, bao gm : Thng s vt l: Thay i nhit , c, Tng cht rn. Thng s ha hc: pH, BOD5, DO, NO3-, PO43-. Thng s vi sinh: Fecal Coliform. b) Giai on 2: Xc nh phn trng lng ng gp ca mi thng s quyt nh (wi). Phn trng lng ng gp (wi) ca cc thng s quyt nh c biu din di dng s thp phn. Mi thng s c mc ng gp ln, nh vo WQI khc nhau v tng phn trng lng ng gp ca cc thng s bng 1 (wi = 1). Song, cng c mt s loi WQI khng tnh n phn trng lng ng gp. Phn trng lng ng gp (wi) c xc nh theo trnh t: Xc nh im xp hng ca mi thng s quyt nh (mi) :Tng im ca thng s i

Tnh phn trng lng ng gp trung gian ca mi thng s (wi'): chp nhn mi nh nht c wi bng 1,0 tnh wi ca cc thng s khc bng cng thc:wi ' mi (min) mi

Tng s phiu cu hi

mi =

(1)

(2)

Tnh phn trng lng ng gp chnh thc ca mi thng s (wi)12 Chuyn 1: nh gi hin trng cht lng mi trng nc trn cc tuyn sng rch chnh Huyn Bn Lc nm 2009

wi =

wi 'n

(3)

wi '1

c) Giai on 3: Chuyn cc gi tr o ca cc thng s quyt nh (xi) thnh cc ch s ph (qi) quy v mt thang im chung t 1-100. chuyn gi tr o ca cc thng s quyt nh (xi) thnh cc ch s ph (qi), ch yu theo hai cch: s dng cc hm th cn gi l hm n hoc s dng cc hm tuyn tnh / phi tuyn tnh. d) Giai on 4: Tnh ton WQI bng cc cng thc tp hp. Cc cng thc tnh WQI c nhiu dng khc nhau, c th tnh v khng tnh n phn trng lng ng gp, c th l dng tng hoc dng tch hoc dng Solway. Trong s su cng thc bng 3.10 th hai cng thc WQI dng tng v dng tch l hai cng thc c NSF xy dng. Hai cng thc ny c s dng rng ri M cng nh nhiu quc gia trn th gii.

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Bng 3.10. Cc cng thc tp hp tnh WQI Dng tng Khng tnh phn trng lng ng gp C tnh phn lng ng gp trng1 n qi n 1

Dng tch ( qi )1/n1 n

Dng Solway1 1 n 2 ( qi) 100 n 1

(UA-WQI)n

(UM-WQI)n

(US-WQI)1 n 2 ( qiwi ) 100 1

qiwi

qi

wi

(WA-WQI)

(WM-WQI)

(WS-WQI)

Kt qu tnh phn trng lng ng gp (wi) ca 9 thng s quyt nh nh sau: Bng3.11. Phn trng lng ng gp (TLG) (wi) ca 9 thng s quyt nh chnh im xp hng TLG trung gian TLG STT Thng s (wi') thc(wi) thng s(mi) 1 DO 1,4 1,0 0,17 2 Fecal Coliform 1,5 0,9 0,15 3 pH 2,1 0,7 0,12 4 BOD5 2,3 0,6 0,10 5 NO3 2,4 0,6 0,10 36 PO4 2,4 0,6 0,10 7 Nhit 2,4 0,6 0,10 8 c 2,9 0,5 0,08 9 TS 3,2 0,4 0,08 1,00 wi Trn c s WQI tnh c, tin hnh phn loi v nh gi CLN theo thang im WQI theo bng 3.12 Bng 3.12. Phn loi cht lng nc theo NSF WQI Loi I II III IV V WQI 91-100 71- 90 51- 70 26 50 0 25 Gii thch Excellent (Tuyt ho) Good (Tt) Medium (Trung bnh) Bad (Khng Tt) Very Bad (Rt t)

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3.4.3. Xy dng cc bn hin trng nhim cht lng nc mt ti cc sng trn khu vc nghin cu theo ch s WQI NSF

p dng tnh ton cht lng nc theo ch s WQI NSF dng tng trnh by trn cho cc s liu quan trc cht lng nc cc tuyn sng rch chnh Huyn Bn Lc nm 2008 v 2009, nhm nghin cu xy dng mt cch s lc cc bn hin trng nhim cht lng nc mt ti cc sng trn khu vc nghin cu. Qua , din bin cht lng nc sng theo thi gian c th c nhn nhn mt cch n gin, trc quan hn qua cc thang im c th v cc bn . Bng 3.15: Kt qu tnh ton WQI-NFS ca cc mu nc mt Huyn Bn Lc vo ma kh nm 2009Stt 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Mu MK M16 M18 M19 M20 M21 M22 M23 M17 M24 M25 M1 M2 M26 M13 M14 M15 M4 pH 16 26 24 22 9 53 46 9 16 17 9 28 18 42 55 27 31 DO 18 17 26 19 14 29 19 27 13 26 18 24 16 20 35 16 16 BOD 24 61 22 31 23 45 23 17 63 62 16 14 61 21 44 54 19 NNO3 96 96 96 97 96 96 96 96 96 96 96 97 97 96 95 97 97 PPO4 99 99 92 94 99 99 99 100 99 97 99 99 99 99 99 99 99 F.C 62 63 60 67 59 70 54 82 45 67 67 60 63 67 57 62 76 Nhit 93 93 93 93 93 93 93 93 93 93 93 93 90 93 93 93 93 c 66 67 70 67 76 61 61 55 66 66 5 23 42 55 44 59 52 TS 85 86 87 86 84 84 82 85 86 87 85 85 81 80 82 81 85 WQI 57 63 59 60 56 66 59 60 58 64 52 55 59 60 64 61 59 R.Cy Trm R. B King S. Bn Lc K. Xng An H K. T6 K. T4 K.Xng Ln Ghi ch Sng Vm C ng

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18 19 20 21 22 23 24 25 26

M5 M3 M6 M8 M9 M10 M7 M11 M12

27 45 35 55 51 55 35 45 52

16 16 27 17 11 14 16 15 16

34 33 27 25 12 24 57 43 16

93 96 97 96 96 96 96 91 97

99 99 99 98 99 99 99 99 99

59 67 57 54 65 63 76 70 62

93 93 93 91 93 93 93 93 93

69 58 72 80 80 69 57 56 61

83 83 84 86 83 83 84 82 76

59 61 61 61 60 61 64 62 59 S. Rch Chanh R. Bc Tn R. Thanh Lp

Bng 3.16: Kt qu tnh ton WQI-NFS ca cc mu nc mt Huyn Bn Lc vo ma ma 2009Stt 1 2 3 4 5 6 7 8 9 10 11 12 Mu MM M16 M18 M19 M20 M21 M22 M23 M17 M24 M25 M1 M2 pH17 18 34 17 6 18 19 16 20 33 37 49

DO23 30 30 25 33 32 23 22 15 16 25 27

BOD60 58 60 61 66 62 78 27 69 62 66 58

NNO396 96 96 96 96 96 96 96 96 96 96 97

PPO495 99 97 97 56 98 97 88 97 98 97 98

F.C30 54 54 62 52 45 54 43 59 52 43 45

Nhit c93 92 93 92 91 92 93 93 93 93 93 93 52 32 76 51 84 45 53 51 56 55 44 47

TS85 81 83 84 87 81 86 84 84 82 85 84

WQI

Ghi ch

56 Sng Vm C ng 59 65 61 59 59 62 53 K. Xng An H

61 K. T6 60 K. T4 61 K.Xng Ln 62

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13 14 15 16 17 18 19 20 21 22 23 24 25 26

M26 M13 M14 M15 M4 M5 M3 M6 M8 M9 M10 M7 M11 M12

15 27 64 18 20 58 53 27 18 17 63 27 27 20

16 31 21 14 27 18 19 17 16 13 21 30 28 14

65 57 32 17 31 26 20 29 57 52 50 37 57 65

96 96 97 97 97 97 96 96 96 96 96 96 96 96

97 98 67 46 46 65 96 94 99 97 97 99 45 92

45 43 52 34 36 54 43 28 52 58 63 40 60 45

93 93 93 93 93 93 93 93 93 86 93 93 93 93

61 61 60 51 61 67 70 66 66 74 76 61 53 66

85 83 83 81 80 80 83 83 83 85 83 86 85 84

58 R. B King 61 S. Bn Lc 59 45 50 R.Cy Trm 57 58 R. Lp 53 Thanh

59 R. Bc Tn 59 67 Rch 58 S. Chanh 57 58

Hnh 3.32, 3.33, 3.34, 3.35, 3.36, 3.37, 3.38, 3.39, 3.40, 3.41 th hin din bin gi tr WQI NSF ca h thng sng rch Huyn Bn Lc nm 2008, 2009 v ca sng Vm C ng (on chy qua Huyn Bn Lc) vo thng 3 v thng 5 nm 2009.

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Hnh 3.32. th din bin gi tr WQI NSF ca h thng sng rch Huyn Bn Lc nm 2008 v 2009

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Nhn xt: th din bin gi tr WQI NSF ca h thng sng rch Huyn Bn Lc nm 2008 v 2009 (Hnh 3.32) cho thy, cht lng nc ti hu ht cc tuyn sng rch u t mc trung bnh (WQI t 50-70). nm 2008 (15 mu th/t), s chnh lch v cht lng gia 2 t kho st l khng ln do thi im ly mu ri vo cc thng ma ma (thng 9) v chuyn tip t ma ma sang ma kh (thng 11). Cc kt qu phn tch mu v gi tr quy i WQI nm 2009 (26 mu th/ma) cho thy c s dao ng v cht lng nc gia 2 ma kh v ma ti mt s v tr (r rt nht l mu 15). Tuy nhin, din bin cht lng nc gia hai ma cha cho thy xu hng r rng (c mt s mu th cht lng nc vo ma ma tt hn ma kh v ngc li). Nguyn nhn ca hin tng ny c th do cc iu kin mi trng trong thi im ly mu (c hoc khng c s x thi nc thi ca cc CSSX/dn c ti thi im ly mu); hn na, gi tr WQI ph thuc kh nhiu vo cc thng s c la chn tnh ton v quy i. th cn cho thy mt s v tr cn quan tm khi din bin cht lng nc ca 2 nm quan trc u c du hiu tiu cc nh: mu 15 trn sng Bn Lc (vng gip ranh gia Huyn Bn Lc v Huyn Bnh Chnh TpHCM), mu M1, M2 trn knh Xng Ln (gip ranh vi Huyn c Ha). Nhn chung, theo kt qu quan trc nm 2009, cht lng nc mt Huyn Bn Lc ang mc trung bnh. Trong , Cc sng rch khu vc pha Nam - ni tp trung nhiu hot ng cng nghip cng nh dn c - c cht lng nc tng i thp hn so vi khu vc pha Bc. Do vy, cn tp trung qun l v kim sot cht ch cc ngun thi ca khu vc ny nhm hn ch n mc thp nht kh nng tim cn cht lng nc mc xu (WQI t 30-50). i vi khu vc pha Bc, cc s liu quan trc cht lng nc ch mi c xy dng ln u tin (nm 2009), do vy, s l kh sm khi c nhng nh gi lc quan v hin trng mi trng nc khu vc ny. Mc d cc kt qu quy i WQI nm 2009 tng i tim cn cht lng nc mc tt (WQI t 70-90), nhng cn ch ng c nhng bin php qun l chc ch cc ngun thi, c bit trong lnh vc sn xut nng nghip cng nh xu hng cng nghip ha trong tng lai ca mt s x ti y.

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