In Colorado there are approximately 2,100 public water systems ranging from a small gas station with a drinking water well up to Denver Water serving 1.4 million residents. Nearly 1,600 of those 2,100 public water systems serve 500 or less people. Many times, those very small systems consist of a simple groundwater well, hydropneumatic pressure tank (pressure tank), and a small distribution system. Oftentimes the distribution system at the smallest systems is only one building. Other than hand-pumped wells at campgrounds (which operate under a special rule), the remainder of public water systems must continuously chlorinate their source water and provide a chlorine residual throughout distribution greater than 0.2 mg/L.
For some water systems, the appropriate location for the chemical injection point can be a point of confusion. This confusion may be exacerbated by the fact that the Colorado Division of Water Resources rules for well drillers has traditionally defined the scope of the water well supply system as being part of the well driller’s responsibility. Typically this is up to and including the pressure tank if installed. The definition from the well driller’s rule is as follows:
5.2.56 “Water well supply system” includes all components of a groundwater well, pump, drop pipe, pitless adapters or units, other pumping equipment, storage tanks or cisterns, and piping and connections between the well and its point of discharge from the pressure tank, if such a tank is installed.
Based on the above definition, a well driller may install a water well, pressure switch, and a pressure tank. Then, when a system becomes a public water system, it must add chlorine feed. Typical installation of chlorine feed involves linking the feed pump to an existing pressure switch that turns on both the well pump as well as the chlorine injection pump. In some cases, we have discovered that a public water system has installed their chlorine injection point at a location after the hydropneumatic pressure tank.
The main issue with having the injection point after the pressure tank, but the chlorine feed pump linked to the well pump is that the pressure tank can discharge water to the distribution system even when the well pump isn’t running. This means that raw water (unchlorinated well water) would be fed to distribution without a chlorine residual, which may not be safe. Per Sections 11.11 and 11.8 of the Colorado Primary Drinking Water Regulations (Regulation 11), water must be continuously chlorinated at the entry point. Therefore, whenever our field inspectors discover a situation where the pressure tank may be located in the potentially unsafe configuration, the issue is cited as a significant deficiency in the inspection findings and must be repaired.
Fixes to the improper chlorine feed point:
Solution #1: Move the injection point:
Many public water systems choose to simply relocate their chemical injection location to a location prior to the pressure tank. This change will solve the significant deficiency of having unchlorinated water enter the distribution system. A typical schematic after correction is as follows:
*image courtesy of University of Georgia Extension
In the above example, please note that a carbon filter may remove all the chlorine residual, which is not allowed in Colorado because a 0.2 mg/L chlorine level must be maintained throughout the distribution system. Also, the chlorine metering pump can continue to be linked to the well pump on a pressure switch.
Some water systems and water professionals have expressed concerns about the chlorine feed degrading the rubber bladder in the pressure tank and have indicated they prefer to keep the chlorine feed location after the pressure tank. If that is the case, then solution #2 may be a better option.
Solution #2: Install a flow switch to inject chlorine when there is flow
A second solution is to leave the chlorine injection point after the pressure tank and install a flow switch so that the chlorine feed pump is activated when flow is detected rather than when the well pump is turned on. A typical installation of a proportional flow meter or flow switch can be seen in our pre-accepted groundwater disinfection design document and is in the following schematic:
Typically, flow switches can be purchased from a variety of locations including usabluebook, amazon, grainger, omega, and more. The department strongly recommends small water districts employ personnel who have experience working with and installing such components if they choose to configure their system to work with a flow switch and it has been previously plumbed to use a pressure switch. Certified plumbers may also have the expertise necessary to perform the system upgrades. While we do not require design approval to convert from a pressure switch to a flow switch, the department is happy to provide technical assistance if there are questions about the installation.
