Environmental Engineering Reference
In-Depth Information
chemicals associated with the reservoir. Because many drinking-water reser-
voirs are designed as aboveground, open-air structures, they are potentially
vulnerable to airborne deposition, bird and animal wastes, human activities,
and dissipation of chlorine or other treatment chemicals; however, one of the
most serious potential threats to the system is direct contamination of the
stored water through the dumping of contaminants into the reservoir. Utilities
have taken various measures to mitigate this type of threat, including fencing
off the reservoir, installing cameras to monitor for intruders, and monitoring
for changes in water quality. Another option for enhancing security is cover-
ing the reservoir using some type of manufactured cover to prevent intruders
from gaining physical access to the stored water. Implementing a reservoir
cover may or may not be practical depending on the size of the reservoir;
covers are not typically used on natural reservoirs because they are too large
for the cover to be technically feasible and cost effective. This section focuses
on drinking-water reservoir covers, where and how they are typically imple-
mented, and how they can be used to reduce the threat of contamination of
the stored water. Although covers can enhance the security of a reservoir, it
should be noted that covering a reservoir typically changes the operational
requirements of the reservoir; for example, vents must be installed in the
cover to ensure gas exchange between the stored water and the atmosphere.
A reservoir cover is a structure installed on or over the surface of the res-
ervoir to minimize water quality degradation. The three basic design types
for reservoir covers are
• Floating
• Fixed
• Air-supported
Various materials are used to manufacture a cover, including reinforced
concrete, steel, aluminum, polypropylene, chlorosulfonated polyethylene, or
ethylene interpolymer alloys. Several factors affect the effectiveness of a res-
ervoir cover and thus its ability to protect the stored water, including
• The location, size, and shape of the reservoir
• The ability to lay or support a foundation (e.g., footing, soil, and geo-
technical support conditions)
• The length of time reservoir can be removed from service for cover
installation or maintenance
• Aesthetic considerations
• Economic factors, such as capital and maintenance costs
It may not be practical, for example, to install a fixed cover over a reservoir
if the reservoir is too large or if the local soil conditions cannot support a
foundation. A floating or air-supported cover may be more appropriate for
these types of applications.