City Council Upgrading Cochrane Memorial Park’s Natural Water-Purification Process


Cochrane Memorial Park is currently undergoing over $300,000 of improvements for “phase one” of its development plan as budgeted by Yelm City Council in their last cycle.

When Yelm’s water reclamation facility is done reclaiming sewer water, the city pumps it to Cochrane Memorial Park, where it is purified in the series of pools that characterize the park’s landscape, a natural system for cleaning reclaimed water.

“The reclaimed water seeps through the ground and removes any more impurities, so by the time that water returns to the ground, you’re looking at the same quality, or better, as rain water coming in,” said Cody Colt, Yelm Public Works director. “The infiltration that people are literally flushing their toilets with is going back into an aquifer as clean water. It’s keeping that continuous cycle.”

Phase one of the development plan will see the park’s inlet pipe expanded.

“Right now, the inlet pipe to Cochrane Park is 2 inches,” Colt said. “We’re making it 4 inches to accommodate more flow. The inlet pipe goes to the waterfall structure, which you see as a waterfall by the bridge where the reclaimed water comes in when you first walk into the park.”

Right now, the pipe handles 50,000 gallons of water a day. With the upgrade, 250,000 gallons will be able to flow into the park. That flow goes to “pond one,” which is the first pond seen on the right as one enters the park, next to the bridge.

“That pond is being completely cleaned out,” Colt said. “It was overgrown with invasive species, weeds, a bunch of stuff that wasn’t supposed to be in there. That pond’s being completely cleaned out, expanded and dug a little deeper and then a new liner is being put in.”

The liner will be made of bentonite, a clay-like substance that isn’t permeable, instead of the current tarp-like material. The bentonite allows water to stay in the pond instead of seep directly into the ground, to be disseminated through the rest of the park’s purifying pools.

“It’s a natural non-permeable membrane that allows the water to stay on top,” Colt said, adding the bentonite will allow for the 250,000 gallons of flow that will be coming in with the expanded inlet pipe.

New plants will also be put in, as well as a new bridge and a permanent restroom facility that will accommodate two unisex bathrooms.

“The cool thing is the toilets in the restroom will be reclaimed water,” Colt said. “So we’re using reclaimed water for the toilets. It’s a perfect cycle. You don’t have to use potable water for toilets.”

These improvements are being done in anticipation for “phase two” of the upgrades, Colt said, which will transform the back half of the park. The other ponds will be expanded and deepened to allow for more flow and the duck pond will get modifications and upgrades.

“These upgrades have needed to happen for a while as part of our water rights,” Colt said. “It needs to be done in order to get our water rights. So council knew that, and budgeted for it out of the sewer fund.”

Specifically, the utility and capital of the sewer fund will be utilized, Colt said, with monies from ratepayers and new connections to the sewer system paying for the development.

“The idea with this is that we can put more water to the aquifer, recharging it faster and better, allowing for us to pull more water without having any impacts on the aquifer itself,” Colt said.


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