Friday, August 15, 2014

Rainwater Collection System at Grinnell College

The following in an article by Jason Koester explaining Grinnell College's rainwater collection system that has been designed to collect, store, and water the game day football field and more.
Grinnell College completed phase two of an athletics building construction project in late August of 2010. The phase two construction consisted of an Olympic size swimming pool and an indoor field house with athletic offices attached.   Phase one { Darby gym } was completed in 2005 home of record breaking Grinnell College Men's basketball team. A unique aspect of the phase two project included a rain water collection system from the large field house roof and surroundings, which feeds a 20,000 gallon collection tank. Condensate water is also harvested from the air handling system in the field house, which provides a large amount of clean water for the collection tank.   The water collected is used for toilets in the field house and to irrigate the game day football field.  A new main irrigation line, valves, decoder system and controller were installed after the building project was completed.   This system was hooked onto our current infield piping and irrigation heads. We  installed a wireless Solar Sync unit  to help with weather monitoring.  Weather monitoring will help conserve water on the football field.
City water is used for all of our other fields and the water quality is poor.  With high pH, bicarbonates and sodium issues, the potential idea of using natural rain water was quite optimistic. With any unique project we had our reservations but after a full calendar year of having the system in tack it has performed well.
How the collection system works is simple, the rain water is collected from the roof, storm drains, and bleachers from the field house area and funneled by drains into a large concrete 20,000 gal holding tank under the field house. Condensate from chiller and air conditioner units also help feed the storage tank. The collection tank was actually dug, formed and poured with concrete as the field support structure was being constructed. When the tank water level reaches a full level of 91”, the excess water is diverted to the storm sewer system which feeds the Grinnell Country Club ponds. [ Irrigation for golf course is pumped out of these ponds].  When a low point level is reached at 34” the system switches to city water by sensors and electric valves, until the collection tank is recharged by rainfall. As an example, the summer of 2013 was a statewide drought and our system never had to switch over to city water because condensate collection kept up with the watering demand. Ground water seepage and the condensate lines must be adding a lot of water to the tank to keep up with our current water demands and lack of rainfall.
The water from the collection tank is filtered on the way out of the tank before reaching the pumping system, which is a dual variable pump system, is based on flow needs for the restrooms and field irrigation. The variable pump system has been a large upgrade and the coverage of the irrigation heads has increased. The water quality has been relatively good so far, we have been sending in water samples to track the water quality to see if there is much fluctuation in the tank water through the year. One interesting sample I sent in was in early April 2011 at irrigation start up, the water that had sitting for an extended period of time; the test came back very good even after being stagnate.  Water test results have fluctuated some but the tank water has led  to increased turfgrass quality in comparison to prior city water usage.

This water collection system has been a success so far and more systems similar to this will be examined for any future building projects on our campus.  Benefits we are experiencing so far are saving water, spending less money on water resources, slowed the watershed runoff speed from the building and have increased the water quality immensely.

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