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Keeping Ocean Shores Clean: Coastal Town Relies on Vacuum Sewers

This is an excerpt taken from the article "KEEPING OCEAN SHORES CLEAN: Coastal Town Relies on Vacuum Sewers" published in Informed Infrastructure, September/October 2016. The entire article can be downloaded from this page. The city of Ocean Shores, Washington, offers a valuable test case for vacuum sewer reliability and endurance.

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Challenge

The city’s vacuum system is one of the largest in the world, and it’s also mature; most of its components are more than 20 years old and must function in a challenging operational environment. What makes Ocean Shores even more valuable as a sewer system comparison study is that it also has gravity sewer and grinder pump systems to maintain. Like many seaside communities, Ocean Shores began as a collection of mostly vacation homes and campsites. Located about 50 miles west of Olympia, Wash., the small community incorporated in 1970 with a population of about 900. At the time, lot sizes averaged about 7,600 square feet and nearly all had septic sewer systems to handle wastewater.

Its location on the Pacific Ocean encouraged growth and tourism. Up to 8,000 people were in Ocean Shores on summer weekends by the mid 1970's. Predictably, the high concentration of septic tanks and limited wastewater treatment led to a eutrophication problem that showed up as algae bloomed in the area’s many canals and ponds.

In 1980, a consultant recommended gravity sewers be installed throughout the town, but residents were cool to the idea due to the staggering cost estimate: $80-$90 million.

“That was quite a chunk of change,” notes Miles Beach, who recently retired as the city’s waterworks superintendent. “A lot of that cost was to excavate and then repave the streets for collection lines, and install more than 50 lift and pump stations.”

Solution

“One of the interesting things I learned about vacuum sewers is that they are gravity assisted,” Garri (Alan Garri, P.E., engineer with Greenman-Pederson, Inc.) notes. “The collection lines have a sawtooth profile. Vacuum pressure in the lines assists gravity to help move sewage slugs along to the treatment plant. This type of innovative design allows for the vacuum sewer mains to be installed at a much shallower depth than gravity sewers. The sawtooth profile also allows vacuum pumps to operate more efficiently than traditional force-main or grinder pumps, due to gravity assistance. These characteristics really reduce maintenance costs in the long run.”


Vacuum sewers also presented another significant benefit: they don’t leak. Collection lines maintain constant vacuum pressure, so there’s no infiltration or exfiltration; no sewage escapes into the environment, and no ground- water enters the collection system. If a leak occurs, it can    be quickly located and isolated, and because the lines are in shallow trenches, repairs can be made quickly with no large excavation equipment.


Installation of the vacuum sewers began with the construction of two vacuum stations in residential areas. The stations emit no odors and were designed to blend in architecturally with the surrounding homes. The first of two phases went online about three years ago.


Today, it’s clear that Kings Bay is on the mend. “We are now trending in a positive way with regard to nitrogen,” adds Burnell. “Our waters are now very close to dropping below the nitrogen- impairment level.”


No single solution led to this improvement. Removing hundreds of septic tanks helped, as did relining much of the city’s leaky sewer system and instituting new regulations on fertilizers. The combined effect has been to significantly reduce the amount of nitrogen entering the local water- ways and groundwater. That’s excellent news for local residents, manatees and the entire economy of Crystal River.   

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