Pittsfield Township Underground Stormwater Retention System

Beztak Land Company needed a solution to control stormwater runoff coming from their new apartment units located on 15-acres in Pittsfield Township, Michigan.

The site which borders regulated wetlands, was not large enough to construct a typical retention pond, so Delta Precast was contracted by Northern Concrete Pipe to design two underground stormwater retention systems, installed below the 482 parking spaces above, and discharging into the adjacent wetlands.

The system was designed to ASTM C1577 Standards and support loads according to LRFD HL-93. The purpose is to capture water from impervious surfaces during large rain events and detain stormwater until it can be slowly released into the soils and wetlands.

The first system included 44 box sections of twin-cell boxes. Each cell has an outside width of 24 feet by 10 inches. During rain events, it is designed to fill evenly throughout the entire system before releasing stormwater to the outlet control structure. The storage capacity is 21,610.85 cubic feet.

The second system includes 98 sections of twin-cell boxes. Each cell has an outside width of 24 feet 10 inches. It was designed to fill evenly throughout the entire system as it releases stormwater to the outlet control structure. The storage capacity is 48,140 cubic feet.
Each box was set on 4 to 6 inches of stone which eliminated the need to pour a concrete base. With the ability to set 14 box sections per day, the contractor was able to meet the project deadlines and provide a stormwater retention system that will service this area now and in the future.