The Cost of Surface Inflow
Wet weather inflow and infiltration create sanitary systems capacity problems and result in unnecessary treatment costs that get passed on to the user. Sanitary systems all over are looking to reduce I&I. Surface inflow can be a significant contributor to I&I problems.
A large manhole casting company conducted a study of the inflow through an average 24” manhole with concealed pick holes and found the following:
1/8” of Standing Water = 637 GPH Inflow per Manhole
1” of Standing Water = 1008 GPH Inflow per Manhole
Calculate Annual System (Manhole)
Inflow Treatment Costs
Obviously, every system will have different surface inflow rates. But the following calculations help to begin putting a value to controlling surface inflow.
Example:$1.01 x $2.50 Actual Treatment Costs per 1000 Gallons x 1000 Affected Manholes x
100 Annual Hours of Inflow = $252,500 Unnecessary Annual system Manhole Inflow Treatment Costs
Potential Treatment Costs of Uncontrolled Surface (Manhole) Inflow
Annual System Treatment Costs Based on 100 Hours of Inflow and Varying Number of Manholes
Standing Water on Average 24" Manhole (Concealed Pick Holes) |
Inflow (GPH) |
Treatment Costs Per 1000 Gallons |
Treatment Costs Per Hour Per Manhole |
|
100 |
250 |
500 |
1000 |
5000 |
10,000 |
1/8" |
637 |
$1.00 |
$0.64 |
$6,400 |
$16,000 |
$32,000 |
$64,000 |
$320,000 |
$640,000 |
|
|
$1.50 |
$0.96 |
|
$24,000 |
$48,000 |
$96,000 |
$480,000 |
$960,000 |
|
|
$2.00 |
$1.28 |
|
$32,000 |
$64,000 |
$128,000 |
$640,000 |
$1,280,000 |
|
|
$2.50 |
$1.60 |
|
$40,000 |
$80,000 |
$160,000 |
$800,000 |
$1,600,000 |
|
|
$3.00 |
$1.92 |
|
$48,000 |
$96,000 |
$192,000 |
$960,000 |
$1,920,000 |
|
|
|
|
|
|
|
|
|
|
1" |
1008 |
$1.00 |
$1.01 |
|
$25,250 |
$50,500 |
$101,000 |
$505,000 |
$1,010,000 |
|
|
$1.50 |
$1.52 |
|
$38,000 |
$76,000 |
$152,000 |
$760,000 |
$1,520,000 |
|
|
$2.00 |
$2.02 |
|
$50,500 |
$101,000 |
$202,000 |
$1,010,000 |
$2,020,000 |
|
|
$2.50 |
$2.53 |
|
$63,250 |
$126,500 |
$253,000 |
$1,265,000 |
$2,530,000 |
|
|
$3.00 |
$3.03 |
$30,300 |
$75,750 |
$151,500 |
$303,000 |
$1,515,000 |
$3,030,000 |
Controlling Surface (Manhole) Inflow:
The Manhole Insert
Manhole inserts are the simplest way to control surface inflow. They can be installed in minutes, and inserts offer a quick payback on treatment costs and establish a front line of defense against over-capacity problems during significant wet weather events.
Not all manhole inserts are equal, however. The Man Pan manufactures manhole inserts of exceptional strength and rigidity. Their patented designs maximize inflow prevention and minimize the chances of collapsing into the collection system. The Man Pan inserts have also been designed with the field staff in mind, especially The Man Pan Classic, with patented lifting lugs to save backs and fishing around in the dark muck for breakable straps.
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