The Rain for Rent Seattle branch provides a novel solution to a complex water quality problem.

The Port of Tacoma wanted to swap a section of wetland for a section of an old landfill to make room for a new port development project.  The landfill contained contaminated soil that needed to be removed and replaced with clean fill before construction of several new wetland structures. 

Rain for Rent was asked to supply a solution for stormwater filtration.  Several job walks were performed with the consulting engineers to review the filtration complexities of the project.  Field filter tests provided the required specification data.    

Due to the possible contamination of the stormwater, Rain for Rent employed an innovative filtration equipment solution to produce the required water quality.  

The first step was to change the incoming stormwater pH from 11.0 to 7.0 by adding a   controlled amount of CO2 Gas in the first chamber of two parallel weir tanks. The gas dissolves in water forming carbonic acid, thus lowering the pH slowly. 

Next, to deal with the high turbidity, a pretreatment dose of Chitosan flocculent was used to drop the majority of sediments into the middle sections of the two weir tanks that emptied into a temporary holding pond. An additional Chitosan dose was injected into the piping when the contents of the holding pond were pumped in to a series of three bi-level tanks for final settling.  A DV-200c 8-inch, Power Prime™ Pump pumped the treated water through a water quality monitoring box and a 54-4 sand filter into parallel BF-400s, using one-micron bags.

The final stage was the removal of the dissolved metals using two 48-4 sand filters filled with a special media.  As the flow rate was limited by contact time, two identical systems were set up in parallel to provide a maximum flow rate of 500 gpm.

The system ran without issues during the nine months of operation and met all the water quality regulations. 

Rain for Rent was awarded the equipment rental bid two years after the original contact because of our ability to show the consulting engineering firm that we provide cost-effective solutions and are willing to invest time early in the project's planning stages.