The challenge. Maximising deployable output from a groundwater source that effectively becomes a river intake for approximately 10 % of the time

Transcription

1 Water quality constraints on Deployable Output of a Chalk groundw ater source Simon Wood (Atkins) & Mike Packman (Southern Water ) Groundwater Asset Management September 8 Plan Design Enable September 8 Water quality constraints on Deployable Output of a Chalk groundwater source The challenge Maximising deployable output from a groundwater source that effectively becomes a river intake for approximately % of the time

2 September 8 Water quality constraints on Deployable Output of a Chalk groundwater source The geology N LINE OF SECTION C8/ -LSCSL British Geological Survey NERC. All rights reserved S From: Chalk Rock Ltd September 8 Water quality constraints on Deployable Output of a Chalk groundwater source The problem 8 -minturbidity (NTU) Burp ham + W arningcamp combined ab st raction (Ml/d) Burp ham d aily abstraction (Ml/d) Combined raw water turbidity (NTU ) Average dai ly abstracti on (Ml/d) Filtered Turbidity PC V 8 -Jan-998 -Jan-999 -Jan- -Jan- -Jan- -J an- -J an- -J an- -J an- -J an-

3 September 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The mechanism W Burpham Loop Burpham Borehole No. Burpham Borehole No. E High tide Low tide September 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The pathway ()

4 September 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The pathway () W Burpham Loop Burpham Borehole No. Burpham Borehole No. E High tide Low tide September 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The analysis () 8 Water Level (maod ) Tur bidity (N TU) Jan- -Feb- -Mar- - Apr- -M ay- -Jun- - Ju l- -Aug- -Sep- - Oct- -Nov- 8 -Dec- River water level at Offham Bridge (maod ) ABH groundwater level(maod) ABH groundwater level(maod) ABH groundwater level (maod) ABH Turbidity (NTU ) ABH Turbidity (NTU ) Combined Raw Turbidity (NTU )

5 September 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The analysis () M J Heigh t of r iver water level above ABH g roun dwater lev el (m) ABH not pumping until Feb Sig nifican t incre ases in tur bidity o nly o ccur wh en r iver wa ter level is app rox..m hig her than ABH grou ndwa ter le vel ABH stopped pump ing here and therefo re ABH does not con tribute to recor ded turbidity from this point onwards dur in g. Subsequent p eaks in combined r aw water turbidity caused by turbidity in ABH (not shown here) Tur bidity ( NTU) - -Jan- -Feb- -Mar- -A pr- -May- -Jun- -Jul- - Aug- - Sep- -Oct- - Nov- 8- Dec- Height of Spring level above ABH GW level (maod ) Z ero hydraulic gradient (m) A BH turbidity (NTU ) Hydraulic gradient required for significant influence on turbidity (m) AB H Turbidity ( NTU) C ombined R aw Turbidity (N TU) September 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t o f a C h a lk g r o un d w a ter s o ur c e The analysis () D e s p ite h av in g r e la tive ly lo w flo w s an d s imila r ma g n itu d es o f a q u ife r - r iv e r hy d ra u lic r ev e rs a ls du r in g b o th p e r io ds, ABH p u mp e d tu r b id itie s mu c h h igh e r e nd Se p th a n mid Ma y. Po s s ib le e x p lan a tio n is th e a c cu mu la tio n of turbid w ater in the fissure netw ork over the summer during successive hydraulic reversals >.m T urb idity (NT U) and river flow ( cume cs) Height of r iver wa ter le vel abo ve ABH gr ou ndwater level (m ) -Jan- -Feb- - Mar- -Apr- -May- -Jun- -Jul- -Aug- -S ep- -O ct- - Nov- 8-Dec- Boreh ole No. turbidity (NTU) Boreh ole No. turbidity (NTU) River Arun da ily mean flo w at Pallingham (m /s) Height of Spring above ABH River- ABH head difference above which significant increases in pumped turbidity occur (m) Zero gradient between ABH and river - O f th e Bu r p h a m b o r e h o les o n ly ABH is p u mp in g in N ov ( ABH c o u ld n't b e s ta r te d b e ca u se s u ch h ig h tu r b id ity ) an d th e r e a so n fo r ABH h a v in g su c h h igh tu r b id ity h e r e an d n o t o n th e p r e v io u s sp r in g tid e s mus t b e th a t r iv e r tu r b id itie s a r e h igh d u e to th e h ig h flo w s in th e r iv e r ( tu r b id itie s ar e time s h ig h er th a n d u r in g lo w flo ws )

6 Slide 9 M J Text box RHS - ABH turbidity does appear to be shown on graph. Packman, /9/8

7 September 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t o f a C h a lk g r o un d w a ter s o ur c e The analysis ().... Height of river water level above ABH groundwater level (m) H eight of Spring level above AB H GW level (maod) Hydraulic gradient required for significant influence on turbidity (m) Zero hydraulic gradient (m) AB H Turbidity (NTU ) Combined Raw Turbidity (NTU ) Turbidity sta rt s t o drop ra pidly in ABH as soon as the hy draulic gradient i s aquif er to riv er i.e. when he ight of river above ABH GWL is <m Turbi dit y starts rising in ABH a s soon as the hydraul ic gradient is from river to aquifer i. e. w hen height of river above ABH GWL is >m Turbi dit y rise s rapidly in ABH when hydraulic gra die nt is approximat ely >.m Turbi dit y ( NTU) -. -Ju l- -Ju l- 8-Ju l-. Se pt e mbe r 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The analysis ()

8 Se pt e mbe r 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The solution Height of Burph am L oop river level above ABH gro undwater level ( m) Pump swit ch of f periods Pumped turbiditi es reduc ed if pumps switch off until aqui ferrive r hydra ul ic gra die nt returns positive T urbidity (NTU) 8- Nov- 9- Nov- - Nov- - Nov- - Nov- - Nov- - Nov- - Nov- - Nov- - Nov- 8- Nov- 9- Nov- - Nov- - Dec- Height of Burpham Loop river level above ABH water level ( m) Estimated minimum gradient threshold (m) Filtered water turbidity ABH t urb id ity Combined raw water turbidity Zero hydraulic gradient Warningcamp t urbidity ABH turbidit y ABH tu rbid it y Se pt e mbe r 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The impact of the solution PDO originally. Ml/d and MDO. Ml/d based upon precautionary operation of source. Water quality was a poorly defined constraint. PDO now increased to. Ml/d and MDO to 9. Ml/d due to better understanding of timing and mechanism of turbidity breaches. Turbidity still a constraint but a well defined constraint. Filter replacement costs can be minimised by operation of sources according to new protocols developed

9 Se pt e mbe r 8 W a te r q u a lity c on s tr a in ts on D e p loy a b le O u tp u t The conclusion Improve the hydrogeological understanding of your source it may be a more cost-effective solution to a water quality constraint than treatment 8