Grey Water

First Grey Water Irrigation System: Lessons

WEDNESDAY, DECEMBER 2, 2009 AT 3:17PM
Gray Water Irrigation System


In order to accommodate Abode Communities request to explore water saving measures for landscape irrigation, Khalifeh & Associates Inc. set out to design the first gray water system approved by the County of Los Angeles.

At a time when Los Angeles is facing water shortages, Abode Communities (a non-profit developer specializing in sustainable low-income housing projects) was committed to invest the necessary resources for designing and installing an environmentally sound system that would reduce water consumption in their 70 unit senior housing project.

Khalifeh & Associates explored different ways to meet this challenge and found that the best way to reduce consumption would be to retain, filter, and reuse the discharged water from the project’s onsite laundry facility. The effluent released from the washing machines would be captured in a 750 gallon underground storage tank located nearby the Laundry room. Contractors bid this system to have an installed cost of $60,000 and project that landscape water consumption to be reduced by 90%, giving the system a 25 year payback. The water factors of standard front load clothes washers are 31.5 gallons per cycle, 1 hour cycle time, and there are a total of 7 washers installed onsite. The laundry facility operates 12 hours per day, making its’ water usage 2,646 gallons/day.

31.5 gallons per wash x 1hr cycle x 7 washing machines x 12 hour occupancy = 2,646 gallons per day

100% of the effluent released by the washing machines will be captured in an underground storage tank equipped with a small irrigation pump. The effluent from the washing machines require sufficient filtration and treatment before landscape application is done. Dependant on the type of soil, local codes require respective minimum square footage of irrigation area per 100 gallons of estimated daily gray water dispersal. The Soil sample taken by a Geotechnical engineer proved the soil to be in a category requiring 100ft² of landscape area per 100 gallons of gray water. This made the total required area 2,646ft².

2,646 gallons x 100ft² ÷ 100gallons = 2,646ft² of required landscape area

The actual total irrigation field onsite is just less than 10,000ft² which is considerably larger than the minimum required area per code. With this information along with plumbing system design drawings and additional calculations, Khalifeh & Associates sought to have their water saving system approved by the Los Angeles County Building and Safety plancheck department. Such a system had never been approved and thus review of the Khalifeh & Associates proposal was extremely thorough. The county wanted to know, without a doubt, that the system would function properly and that well thought out safety measures would be incorporated to address the possibility of system failure.

After several attempts to obtain the county’s approval, the engineers at Khalifeh & Associates were able to convince the plancheck department that all of the county’s stringent requirements would be satisfied. Their approval makes the team at Khalifeh & Associates the first consulting engineers to design an approved gray water system in the county of Los Angeles for reducing water consumption and improving the environment.

Jack Khalifeh is president of Khalifeh & Associates Inc. Consulting Engineers, P.E., a multidisciplined, professional engineering firm specializing in mechanical, electrical, plumbing, fire protection, lighting, sustainable design, commissioning and energy audit services. Jack is a LEED-accredited professional and a member of the U.S. Green Building Council. Visit www.khalifehassociates.com tel:(310)-305-1555