NRA T h a m e s 217
-ji
N ational Rivers Authority
Thames Region
A Review of the
Performance of Aldershot STW
and its effect on the River Blackwater
En v i r o n m e n t Ag e n c y
NATIONAL LIBRARY &
INFORMATION SERVICE
THAMES
Kings M£ad6w House, Kings Meadow
(oad, Reading RG1 8DQ
Heed C^jice,
Mark Liddiard MSc
NRA Thames Region
Ladymead
Guildford
December 1992
THE PERFORMANCE OF ALDERSHOT STW AND ITS EFFECTS
ON THE RIVER BLACKWATER
INTRODUCTION
The River Blackwater flows from the north of Famham to Swallowfield, where it joins the
Loddon. The southern half of the course flows through the highly urbanised and industrial
area of Aldershot, Famborough and Camberley. Much of the river flow in dry weather
consists of treated sewage effluent. This, combined with large amounts of urban run-off, has
led to an RQO of 3 being set. During the 1990 survey this level was achieved, but no better.
ALDERSHOT STW
The works catchment is the civilian part of Aldershot to the west of the River Blackwater.
The military town has its own STW which is operated by the MOD. Sewerage to the east
of the river flows into the Ash Vale STW. The consent from 1st October 1991 has been set
at 20/12/3 which takes into account the addition of a new 8 lane A.S. plant. The old filter
works has not been demolished. Recent results have shown the STW to be performing
within this consent, except for a few failures on solids as 22/23 mg/1 which are not
significant. Much better levels of nitrification are now being achieved with the ammoniacal
nitrogen level generally less than 0.5 mg/1. These samples have been taken generally
between 10.00 and 15.00 and little account is taken of any diurnal variation.
The BOD levels and Ammoniacal Nitrogen levels were previously assessed over a 24 hour
period in August 1989 and showed a large diurnal variation. It would be very interesting to
see how this has changed with the modifications to the works. The spot sample results have
much improved since mid 1991.
The consent for the works was reviewed in September 1991. The old works has two
outfalls, the North (PLDE.0002) and the South (PLDE.0003). One consent covers both of
these points. The North outfall is redundant and the grid reference in the consent
(CNTD.0073) refers to the South outfall. However, the reviewed consent has only been
applied to the disused outfall. As a result of this the results have been assessed against the
old summer/winter consent (20/12/6 from the 1st May, 25/20/10 from 1st November).
Virtually no failures have been recorded under the summer/winter consent since 1st October
1991. If the same results are assessed against the correct (20/12/6) consent then 4 solids and
6 ammonia failures have been recorded since 1990. This error has now, hopefully, been
corrected and the proper parameters are being used. A number of failures for the Cadmium
parameter of 0.005 mg/1 have been recorded and a prosecution case was prepared on the
basis of this. This case was subsequently dropped when TWU took action against a trade
effluent discharge.
RIVER BLACKWATER DOWNSTREAM ALDERSHOT STW
The downstream sampling point is at Government Road, Aldershot (NGR: SU 8850 5190).
The URN here is PLDR.0002 and the RQO is currently 3. This point was not used during
the surveys carried out in the summer of 1989 so there is virtually no data for diurnal
variation. The time of travel from Aldershot STW to here is also not known.
If the archive results are assessed against the Class 3 RQO parameters (D.O. > 10% and
B.O.D. <17 mg/1) then only 1 failure for B.O.D. is seen (1990-1991 results).
If the same results are assessed against the Class 2B parameters (D.O. >40% , B.O.D. < 9
mg/1, unionised ammonia <0.021) then 18 failures for D.O., 2 failures on B.O.D. and 3
failures on unionised ammonia are recorded. Since the new STW consent came into force
only 3 D.O. failures have been recorded.
The failures in the RQO have not matched up with poor samples taken from the works.
There are many outfalls into the river between the STW and Government Road and polluting
discharges from the industrial areas are very likely.
CONCLUSION
The recent modification to Aldershot STW hasve resulted in greatly improved effluent
quality. The tightened consent should now see an improvement in the river quality
downstream. The levels of B.O.D., Ammonia and Unionised Ammonia are very low and
for these the river would comply with Class 2A RQO for recent samples. However, low
D .O .’s are being recorded with the improved effluent.
The reasons for this are likely to be either a wide diurnal variation in the effluent or pollution
discharges via surface water outfalls. In order to determine the causes, some continuous
monitoring is necessary and a programme of pollution prevention in the Aldershot Industrial
area needs to be carried out.
Consent No. D.73
W A T E R A C T 1989
CONSENT TO DISCHARGE SEWAGE EFFLUENT INTO THE RIVER BLACKWATER
W H E R E A S :(a ) t h e T h a m e s W a t e r A u t h o r i ty s u b m i t t e d an a p p l i c a t i o n to the
S e c r e t a r y o f S t a t e d a t e d 17 M a r c h 1989, (as s u p p l e m e n t e d o n 25
A u g u s t 1989) in a c c o r d a n c e w i t h s e c t i o n 34 of the C o n t r o l of
P o l l u t i o n A c t 1974, as m o d i f i e d by the C o n t r o l of P o l l u t i o n
( D i s c h a r g e s b y A u t h o r i t i e s ) R e g u l a t i o n s 1984, to d i s c h a r g e s e w a g e
e f f l u e n t i n t o the R i v e r B l a c k w a t e r from A l d e r s h o t T o w n S e w a g e
t r e a t m e n t W o r k s ("the p r o p o s e d discha r g e " ) ;
(b) t h a t a p p l i c a t i o n is d e e m e d by v i r t u e of p a r a g r a p h 25 ( 2 ) (a)
of S c h e d u l e 26 to the W a t e r Act 1989 to have been m a d e b y T h a m e s
W a t e r U t i l i t i e s L i m i t e d ("the Com p a n y " ) to the N a t i o n a l R i v e r s
A u t h o r i t y ("the A u t h o r i t y " ) , and the S e c r e t a r y of S t a t e h a s
d e t e r m i n e d t h a t p a r a g r a p h 25(3) of that S c h e d u l e is to a p p l y to
th a t a p p l i c a t i o n ;
(c) the S e c r e t a r y o f State, in e x e r c i s e of h i s p o w e r s u n d e r
p a r a g r a p h 4(7) a n d 6(4) of S c h e d u l e 12 to the W a t e r A c t 1989, h a s
d i r e c t e d the A u t h o r i t y to i s s u e the f o l l o w i n g c o n s e n t f o r the
p r o p o s e d d i s c h a r g e a n d to r e v o k e all p r e v i o u s c o n s e n t s r e l a t i n g
to t h a t d i s c h a r g e .
N O W T H E R E F O R E the A u t h o r i t y , in e x e r c i s e of its p o w e r s u n d e r
p a r a g r a p h s 2 a n d 6 o f S c h e d u l e 12 to the W a t e r Act 1 9 8 9 : (a)
g r a n t s a c o n s e n t to the p r o p o s e d d i s c h a r g e s u b j e c t to the
c o n d i t i o n s s e t out in the S c h e d u l e hereto; a n d
(b)
r e v o k e s all e x i s t i n g c o n s e n t s r e l a t i n g to the p r o p o s e d
discharge.
T h e p e r i o d d u r i n g w h i c h no n o t i c e by v i r t u e of p a r a g r a p h 6(2) o r
(4)(c) o f S c h e d u l e 12 to the W a t e r Act 1989 s h a l l be s e r v e d in
r e s p e c t o f the c o n s e n t shall be the p e r i o d e n d i n g on the d a t e two
y e a r s f r o m the d a t e o f this consent, o r the d a t e s p e c i f i e d in
p a r a g r a p h C . 1 . i of t h e . S c h e d u l e hereto, w h i c h e v e r shall b e later,
o r s u c h o t h e r d a t e as the p e r s o n who p r o p o s e s to make o r m a k e s
the d i s c h a r g e a g r e e s .
0
S i g n e d o n b e h a l f o/ftfte A u t h o r i t y
. $0. )jl
J. . .1 989
SCHEDULE
CONDITIONS PRESCRIBED FOR THE DISCHARGE OF SEWAGE EFFLUENT FROM
ALDERSHOT TOWN SEWAGE TREATMENT WORKS TO THE RIVER BLACKWATER.
A.
NATURE OF EFFLUENT
1 . T h e d i s c h a r g e s h a l l c o n s i s t of t r e a t e d s e w a g e e f f l u e n t f r o m
an o u t l e t at N a t i o n a l G r i d R e f e r e n c e SU 8 030 'l O G U r*
B.
VOLUME OF EFFLUENT
1.1.
F o r the p e r i o d up to and i n c l u d i n g 30 S e p t e m b e r 1991:
The v o l u m e of treated sewage effluent disc ha rg ed unde r dry
w e a t h e r c o n d i t i o n s s h a l l n o t e x c e e d 7064 c u b i c m e t r e s in a n y
p e r i o d o f 24 h o u r s .
ii. F o r th e p e r i o d f r o m 1 O c t o b e r 1991:
The v o l u m e o f t r e a t e d s e w a g e e f f l u e n t d i s c h a r g e d u n d e r
w e a t h e r c o n d i t i o n s s h a l l n o t e x c e e d 9900 c u b i c m e t r e s in
p e r i o d o f 24 hours.
C.
dry
any
COMPOSITION OF EFFLUENT
1. S u b j e c t t o p a r a g r a p h C . 2 below, no s a m p l e of the t r e a t e d
s e w a g e e f f l u e n t t a k e n by the A u t h o r i t y s h a l l c o n t a i n m o r e than:
I . F o r t h e p e r i o d u p to a n d i n c l u d i n g 30 S e p t e m b e r 1991^ :
i . F o r the, p e r i o d 1 May to 31 October:
(a) 20 m i l l i g r a m s p e r l i t r e of s u s p e n d e d s o l i d s
a f t e r d r y i n g at 105 d e g r e e s Celsius);
(measured
(b ) 12 m i l l i g r a m s p e r li tre of b i o c h e m i c a l o x y g e n d e m a n d
( d e t e r m i n e d in the p r e s e n c e of 0.5 m i l l i g r a m s per l i t r e o f
a l l y l - t h i o u r e a a f t e r 5 d a y s at 20 d e g r e e s Celsius);
(c) 6 m i l l i g r a m s p e r l i t r e of a m m o n i a c a l n i t r o g e n e x p r e s s e d
as n i t r o g e n .
ii. F o r t h e p e r i o d 1 N o v e m b e r to 30 April:
(a) 25 m i l l i g r a m s p e r l i t r e of s u s p e n d e d s o l i d s
a f t e r d r y i n g at 105 d e g r e e s Celsius);
(measured
(b) 20 m i l l i g r a m s p e r l i t r e of b i o c h e m i c a l o x y g e n d e m a n d
(d e t e r m i n e d in the p r e s e n c e of 0.5 m i l l i g r a m s per l i t r e o f
a l l y 1 - t h i o u r e a a f t e r 5 d a y s at 20 d e g r e e s Celsius);
(c) 10 m i l l i g r a m s p e r l i t r e of a m m o n i a c a l n i t r o g e n e x p r e s s e d
as n i t r o g e n .
1 1 . [For 2tHe[£ger x o S ^ f rpm;,1J;Oc tober..i 9 9 i :
(a)
m i l l i g r a m s p e r l i t r e of s u s p e n d e d s o l i d s ( m e a s u r e d
a f t e r d r y i n g at 105 d e g r e e s Celsius);
(b)
m i l l i g r a m s p e r l i t r e of b i o c h e m i c a l o x y g e n d e m a n d
( d e t e r m i n e d in t h e p r e s e n c e of 0.5 m i l l i g r a m s per l i t r e of
a l l y l - t h i o u r e a a f t e r 5 d a y s at 20 d e g r e e s Celsius);
( c ) | 3 f m i l l i g r a m s p e r l i t r e of a m m o n i a c a l n i t r o g e n e x p r e s s e d
as n i t r o g e n .
2.
T h e l i m i t for a n y of the d e t e r m i n a n d s set o u t in p a r a g r a p h
C.1 a b o v e m a y be e x c e e d e d where, in any seri e s of s a m p l e s of
t r e a t e d s e w a g e e f f l u e n t t a k e n ( w h e t h e r b e f o r e or after the g r a n t
of this c o n s e n t ) by t h e A u t h o r i t y in the p e r i o d of twelve m o n t h s
e n d i n g o n the d a t e of the d i sch a r g e , as l i s t e d in col u m n (1) of
the tab l e at A n n e x A to t h i s schedule, no m o r e t h a n the r e l e v a n t
n u m b e r o f s a m p l e s , as l i s t e d in c o l u m n (2) of t h e said table,
e x c e e d s the a p p l i c a b l e l i m i t for that d e t e r m i n a n d at the t i m e
w h e n a s a m p l e is taken, t h a t is in r e s p e c t of s a m p l e s t aken a f t e r
the g r a n t of this c o n s e n t , the limit set o u t in p a r a g r a p h C.1,
and in r e s p e c t o f s a m p l e s t a k e n b e f o r e the gr a n t of this c o n s e n t ,
the c o r r e s p o n d i n g ' ' p r o v i s i o n of the c o n s e n t then in force.
3. N o t w i t h s t a n d i n g p a r a g r a p h s C.1 and C.2 above, for the p e r i o d
up to a n d i n c l u d i n g 30 S e p t e m b e r 1991 no s a m p l e o f the t r e a t e d
s e w a g e e f f l u e n t s h a l l c o n t a i n m o r e than:
IS' 'z- t
i . F o r the p e r i o d 1 M a v ^ o * ^ ^ O c t o b e r : / ^ / /
(a) 60 m i l l i g r a m s p e r l i t r e of s u s p e n d e d s o l i d s
a f t e r d r y i n g at 105 d e g r e e s C e l s i u s ) ;
(measured
(b) 24 m i l l i g r a m s p e r l i t r e of b i o c h e m i c a l o x y g e n d e m a n d
( d e t e r m i n e d in the p r e s e n c e of 0.5 m i l l i g r a m s per l i t r e of
a l l y l - t h i o u r e a a f t e r 5 d a y s at 20 d e g r e e s Celsius);
(c) 12 m i l l i g r a m s p e r l i t r e of a m m o n i a c a l n i t r o g e n e x p r e s s e d
as nitrogen.
ii
.
F o r the p e r i o d 1 N o v e m b e r to 30 April:
(a) 75 m i l l i g r a m s p e r l i t r e of s u s p e n d e d s o l i d s
a f t e r d r y i n g at 105 d e g r e e s Celsius);
(measured
i
(b) 60 m i l l i g r a m s p e r litre of b i o c h e m i c a l o x y g e n d e m a n d
( d e t e r m i n e d in t h e p r e s e n c e of 0.5 m i l l i g r a m s per l i t r e of
a l l y l - t h i o u r e a a f t e r 5 da ys at 20 d e g r e e s C e l s ius);
(c ) 20 m i l l i g r a m s p e r litre o f a m m o n i a c a l n i t r o g e n e x p r e s s e d
as n i t r o g e n .
4. A t all t i m e s n o s a m p l e o f the t r e a t e d s e w a g e e f f l u e n t s h a l l
c o n t a i n m o r e than:
(a) 5 m i c r o g r a m s p e r l i t r e o f total C admium.
_
5. The p r o d u c t of the c o n c e n t r a t i o n of the t r e a t e d s e w a g e
e f f l u e n t a n d t h e f l o w of the d i s c h a r g e at the t i m e of s a m p l i n g
( e x p r e s s e d in t e r m s o f the q u a n t i t y of m a t t e r d i s c h a r g e d o v e r a
24 ho u r p e r i o d ) s h a l l at n o time b e ' g r e a t e r than:
(a)
D.
35 g r a m m e s o f t o tal C a d m i u m .
TAKIN G OF S A M P L E S
1.
F a c i l i t i e s s h a l l be p r o v i d e d to the A u t h o r i t y ' s a u t h o r i s e d
r e p r e s e n t a t i v e s so as to e n a b l e s a m p l e s of the e f f l u e n t to be
conveniently obtained.
2. A m e a s u r e m e n t w i l l be taken of the r a t e of flow o f the
d i s c h a r g e at t h e t i m e of sampling, a n d r e c o r d s t h e r e o f k e p t for
i n s p e c t i o n by t h e A u t h o r i t y ' s a u t h o r i s e d r e p r e s e n t a t i v e s .
Aldershot STW.Diagram
Outfall
Outfall
.... A...
t
Storm Overflow Area
Secondary Tanks
Intake Works
Primary Tanks
o
Storm Tanks
Sludge Digestors
Eight Lane A.S.Plant
Archive Results For Aldershot STW and Downstream
BOD mg/1
30
25
20
15
Consent Max.l2mg/1
10
Jl
I
J
0
]
J
J
I
J
i
fiL
1991
1990
Time/Date
Govt.Rd.
Aldershot
STW
m lm m
1992
I_II
Effect of Aldershot STW on River D.O.
D. 0 .% sat.
140
120
RQO 3=>10X
Same Day Sampling
•f r r f r r r r f r f 1 1 f f 11 f t r «
100
»Pf ff
80
f M f f ff ff M f f
f M r r f f f f f f r r t t f f t r tt
60
■ I
j
40
20
L
0
1990
Time/Date
Upstream STW |
Downstream STW
Archive Results For Aldershot STW and Downstream
Amm.N.mg/1
30
25
20
15
j
10
Consent
||
0
1990
L
i
X ^1 !■mil in 1 ■■J
Govt.Rd.
-JLL k h
1991
T ime/date
Aldershot STW
1992
M a x . 3 mg / 1