Page 371 - 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 331

Problems/Questions 331
The surveys should be conducted by personnel experienced in commercial and indus-
trial processes. The owners or owners’ representatives should be questioned as to what the
water is being used for in the facility and what hazards the operations may present to the
water system (both within the facility and to the water distribution system) in the event that
a backsiphonage or backpressure condition were to exist concurrent with a nonprotected
cross-connection. In the event that experienced survey personnel are not available within
the water authority to conduct the survey, consideration should be given to having a con-
sulting firm perform the survey on behalf of the water department.

PROBLEMS/QUESTIONS

9.1 What is the definition of a cross-connection? 9.8 How frequently should backflow preventers be tested to
9.2 Why do we have cross-connections? ensure their proper functioning? Who is qualified to perform
backflow preventer testing? Consult with your local govern-
9.3 How many types of cross-connections are there?
ment for the local rules and regulations.
9.4 What is the difference between backpressure and back-
9.9 In addition to the many cross-connections that may exist
siphonage?
on the premises of a water system’s customers, the water sys-
9.5 What types of devices that can be used to correct cross- tem itself may own or control cross-connections. These poten-
connections? tial cross-connections should be subject to the same scrutiny as
9.6 Successful control of cross-connection hazards depends those that are privately owned. Examples of cross-connections
not only on inspection for cross-connections by the water system that can pose a risk to water quality and public health can be
and by water users, but also on an enforceable cross-connection found in water treatment plants, pumping stations, or in the dis-
control program. If a community subscribes to a modern plumb- tribution system. During a sanitary survey for a water treatment
ing code, such as the National Plumbing Code, its provisions system, what are the potential cross-connections that should be
will govern backflow and cross-connections. However, the water identified by an inspector?
system must obtain authority to conduct a community inspection 9.10 Figure 9.30 shows a chlorine feed system at a water treat-
program through an ordinance or other means and carry out a ment plant. What is required between the chlorine feeding cylin-
comprehensive program. Please outline the major components ders and the chlorine feed points? The same figure also shows
of a water system’s cross-connection control program. that one chlorine cylinder feeds chlorine to the influent water be-
9.7 Protection against sanitary deficiencies from cross- fore chemical flocculation, and another chlorine cylinder feeds
connections is an important engineering consideration in water chlorine to the effluent from the filter. What are the technical
and sewer system design. Visit the website www.10statesstandards terms of this chlorination system for cross-connection control?
.com to learn about the latest government regulations regarding Can one chlorine cylinder be used to feed both the influent to the
the separation distance of drinking water mains crossing sewers. flocculation influent and the filter effluent? Please explain.
Figure 9.30 for Problem 9.10
Filter
Flocculation

Clearwell

Static
mixer