Obayashi/Johnson Bros. JV (OJJV) constructed tunnels at the Minneapolis-St. Paul International Airport for the underground portion of the Metropolitan Council’s Light Rail Transit (LRT) project.

Braun Intertec assisted OJJV with discharge permitting, compliance sampling and chemical analyses, as well as compliance reporting related to the discharge of groundwater on the tunneling project at two locations, the North Portal and North Vent Shaft.

Challenges

Groundwater generated from the cutting face of the tunneling machine, and water that collects in the related excavation, is pumped to the ground surface. Contaminants are present in the generated water.

At the North Portal location, the water is discharged into settling ponds to decrease suspended solids. The water is then pumped from the settling ponds and routed through filters to further remove suspended solids, routed through vessels containing granular-activated carbon to remove dissolved contaminants, and then discharged to either the storm sewer under a National Pollutant Discharge Elimination System/State Disposal System (NPDES/SDS) permit issued by the Minnesota Pollution Control Agency (MPCA) or to the sanitary sewer under a temporary discharge permit.

Solutions

We assisted OJJV in obtaining temporary Metropolitan Council Environmental Services (MCES) sanitary sewer discharge permits for the North Portal and North Vent Shaft construction areas. We collect samples of the discharge on a semi-monthly basis, and chemically analyze the samples on an expedited basis, according to the frequency and parameters dictated by the discharge permits.