Alexander Szabo and Oscar Engle - Svenskt Vatten

Total influent water flow
The total inflow for 5-6 November has been calculated with Eq. 8.5 where the peak-flow during
the rain is included and Eq. 8.6 where the peak-flow during the rain is excluded. The total inflow
for 18-19 November has been calculated with Eq.8.7 where the peak-flow during the rain is
included and Eq. 8.8 where the peak-flow during the rain is excluded. The total inflow for 9-10
January has been calculated with Eq. 8.5 and since there was no precipitation during this
measuring period no rain peaks has been considered. Average inflow quantity to the pond each
day will be based on Q tot with rain from 5-6 November, 18-19 November and Q tot without rain
from 9-10 January. The results can be seen in Table 8.4.
Table 8.4: Calculated total influent waterflow into the pond system for one day. *Partly using
designed values. ** Rainfall peaks excluded (on the 5-6 November designed values are used).
Date
5-6 Nov
Q tot
With rain
(m 3 /day)
6346*
Q tot
Without rain
(m 3 /day)
5428**
Q max
(m 3 /s)
0.190
Q min
(m 3 /s)
0.039
Q Average
With rain
(m 3 /s)
0.073*
Q Average
Without rain
(m 3 /s)
0.058**
18-19 Nov
7527
6617**
0.203
0.059
0.087
0.077**
9-10 Jan
No rainfall
5526
0.085
0.049
No rainfall
0.064
Infiltration
High infiltration of groundwater into the sewer pipes is a common problem. Sewers may leak
waste water out of the pipes or infiltrate groundwater into the sewer pipes, depending on the
water content of the surrounding soil. It has been observed during our measurements that there is
a flow of waste water even in late night or early morning even during vacation periods. The waste
water flow drastically increases during rain events, and the waste water strength is weak (diluted).
This is an evidence of infiltration into the pipes. The extra infiltrating water is mostly unwanted
since it demands bigger tanks, or ponds, and to some degree will make the treatment less
effective. However, one benefit is that since the water is already diluted, it may be easier to meet
the requirements for discharging the water.
Three different approaches have been used to find the amounts of infiltrating water.
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