Marc Wilkins, Director
North Little Rock Wastewater Utility
P.O. Box 17898
North Little Rock, AR 72117
North Little Rock Sewer Committee retained Crist Engineers to provide planning, design, and construction engineering services to upgrade the Shillcutt Bayou Wastewater Pump Station peak capacity from 11.5 mgd to 17.0 mgd as part of a capital improvement program for compliance with a Consent Administrative Order.
The original pump station was designed by Crist Engineers in 1964 as a dry-pit/wet pit arrangement with deep shaft end suction pumps. The pump station was updated and converted to a dry-pit/wet-pit arrangement with dry-pit submersible pumps in 1996 with a firm capacity of approximately 12.0 mgd. The pump station has two smaller 75 HP, dry-pit pumps that operate at 3,450 gpm each, and two larger 125 HP, dry-pit pumps that operate at 8,000 gpm.
To upgrade the station to 17 mgd, Crist evaluated utilizing the existing wetwell and dry-pit configuration to place new pumps, however the operating capacity parameters of the wetwell and pump selection required six new pump positions; two smaller pumps, 60 HP pumps to convey daily diurnal flows for flows up to 7.2 mgd, and four larger 280 HP pumps to deliver a range of flow from 5.5 mgd to 17.0 mgd. All pumps have variable frequency drives. Since the new pump selection could be accommodated in the existing pump station, the Crist design team constructed a new wetwell for a submersible application, but still utilized the existing screen structure with modification to replace two existing vertical climbing screens and one new vertical climbing screen.