Page 347 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch09_297-332.qxd 8/2/10 9:54 PM Page 307

9.2 Public Health Significance of Cross-Connections 307
Numerous complaints of gray-green and “slippery” water were received by the water
department coming from the same general area of town. A sample brought to the water de-
partment by a customer confirmed the reported problem and preliminary analysis indicated
contamination with what appeared to be a detergent solution. While emergency crews ini-
tiated flushing operations, further investigation within the contaminated area signaled that
the problem was probably caused by a car wash, or laundry, based on the soapy nature of
the contaminant. The source was quickly narrowed down to a car wash, and the proprietor
was extremely cooperative in admitting to the problem and explaining how it had occurred.
The circumstances leading up to the incident were as follows:

• On Saturday, February 10, a high-pressure pump broke down at the car wash. This
pump recycled reclaimed wash and rinse water and pumped it to the initial scrub-
bers of the car wash. No potable plumbing connection is normally made to the car
wash’s scrubber system.
• After the pump broke down, the car wash owner was able to continue operation by
connecting a 2-in. (50-mm) hose section temporarily between the potable supply
within the car wash and the scrubber cycle piping.
• On Monday, February 12, the owner repaired the high-pressure pump and resumed
normal car wash operations. The 2-in. (50-mm) hose connection (cross-connection)
was not removed!
• Because of the cross-connection, the newly repaired high-pressure pump promptly
pumped a large quantity of the reclaimed wash/rinse water out of the car wash and
into a 12-in. (300-mm) water main in the street. This in turn was delivered to the many
residences and commercial establishments connected to the water main (see Fig. 9.9).

Within 24 hours of the incident, the owner of the car wash had installed a 2-in. (50-mm)
reduced pressure principle backflow preventer on his water service and all car wash estab-
lishments in Seattle that used a wash water reclaim system were notified of the state
requirement for backflow prevention.

Wax injectors Soap injectors

Hose connection
made here

Rinse Rinse

Scrubbers
To reclaim tanks

Recommended Recirculating
installation of pump
backflow preventer Reclaim tanks
To restrooms

Potable
water supply

Figure 9.9 Car Wash Water Enters the Street Water Main