Pump Station Considerations for a Simple Duplex Station Discharging into a Combined Regional

Force Main

Rachel Rausch, EIT

Site Location

Bluffton, SC

Project Background

• Private development client

• Development includes two large retail buildings, service station,

bank, and general commercial

• No gravity sewer service in area

Project Background

Unique Design Considerations• Donation of project to Beaufort Jasper Water and Sewer

Authority (BJWSA)

• Little topographical variability on site

• Deep wetwell

• Site pump station will pump into 16” combined regional

force main Unknown conditions in regional force main

Design Solution: Data Collection

• BJWSA Standards

• Force main record drawings

• Force main operating conditions

• Operating pressure

• Flow

Design Solutions: Calculations• Wastewater Flow Estimate

• Site Storage Volume

• Force Main Operating Conditions

• Choosing Pumps

Design Solutions: CalculationsWastewater flow from site:Peaking Factor=4Qpeak=92.4

BJWSA storage volume requirement:

Storage volume in site MH and pipes > 24 hour volume from site

Pump SelectionExisting force main conditions analyzed

• Regional Force Main Pump station on• 1,000 gpm @ 70’ TDH

• Regional Force Main Pump Station CP-67 off

• No flow in regional force main

• Two C factors analyzed for each system curve

System Curve-Pumps On

0 200 400 600 800 1000 12000

50

100

150

200

250System Curve-Regional Force Main Pumps On

TDH C1 MIN [FT] TDH C1 MAX [FT] TDH C2 MIN [FT] TDH C2 MAX [FT] PUMP CURVE #1

PUMP CURVE #2 PUMP CURVE #3 PUMP CURVE #4 PUMP CURVE #5 PUMP CURVE #6

Flowrate (gpm)

TDH

(ft)

Design Point:310 gpm at 102’ TDH

Hazen-Williams C Factors:C1=110C2=130

System Curves-Pumps Off

0 200 400 600 800 1000 12000

50

100

150

200

250

300

350System Curve-Regional Force Main Pumps Off

TDH C1 MIN [FT] TDH C1 MAX [FT] TDH C2 MIN [FT] TDH C2 MAX [FT] PUMP CURVE #1

PUMP CURVE #2 PUMP CURVE #3 PUMP CURVE #4 PUMP CURVE #5 PUMP CURVE #6

Flowrate (gpm)

TDH

(ft)

Design Point:410 gpm at 96’ TDH

Hazen-Williams C Factors:C1=110C2=130

Pump Selection

Other Calculations

• Cycle time

• Buoyancy Calculations

• High groundwater table

• Deep wetwell, approximately 24 feet deep

Final Pump Station Layout

Project Status• BJWSA Approval• Construction Status

Questions?

Lessons Learned