Extending Water Main in Rural Community 3

[gwater12]

We are required to extend City water service to approximately 50 homes north of the City limits. The existing distribution system will need to be extended approximately 3 miles to pick up these home. There is no feasible way to loop this main extension into other parts of the system due to the rural nature of the community. The current end point of the distribution is a 12" pipe and has static pressure around 50 psi.
We are looking at using automatic flushing valves on the end of the main and I assume we will try to minimize our pipe size to increase water turnover in the main.
Is it feasible to extend service this far to pick up so few customers? Any other thoughts/suggestions?
Thanks in advance for your suggestions.

 

[bimr]

Are you responsible for supplying water for the fire district?

Is this the same utility or are you selling water?

Does the subdivision have an existing distribution system?

 

[RWF7437]

In addition to BIMR's questions....

Are you in the U.S.?
Does the City have a water system master plan?
If so, does it show your 50 houses to be within its ultimate service area?
Has the City approved this extension?
What is the topography ?
Are these house higher or lower than the existing City main ?
Are these houses existing or proposed?

If minimum fire flow is 1500 gpm @ 20 psi for two hours a 12-inch pipe will not be large enough if existing static pressure is 50 psi. 33 psi ( 75 feet of head ) will be needed to deliver 1500 gpm @ 20 psi in a 12-inch pipe. But you only have 30 psi available.

Pipe size will be governed by fire demand, not by some need to "turnover" water. Similarly, looping is practiced to improve reliability not, primarily to improve water quality through frequent "turnover".

Who will be responsible for water quality; the City or the owners of these 50 houses ?

good luck

 

[bpattengale]

I'd suggest you look up or contact the local rural water supplier. As you said this is a rural community and rural water supply systems are not designed for the same flows or standards as the urban systems.

or as previously stated look at the master plan that the city has to see what its ultimate developement will be.

 

[cvg]

sounds like you may need a booster pump station and perhaps a tank to assist with water supply for fire fighting and emergency use. Technically you can do it, but economically - it might be cheaper to drill a well.

 

[coloeng]

Yes it is feasible to extend this far to serve those customers. A few questions that need to be answered first are:

1) Is fire protection required? If it is, then as previous responders have pointed out, you will probably need larger mains and possibly a tank and pump station. If these homes are in rural setting and not close together in a subdivision, the fire flows can be as low as 500 gpm according to ISO;

2) Will there be future growth in that area that you anticipate serving? If so you need to size the lines to serve that expected growth, or size the line just to serve the existing and plan on replacing the line in the future.

3) What type of disinfection is used? Depending on the size of line that is extended and the method of disinfection, disinfection byproducts (DBPs) can be a huge issue. We have a system that extends 50 miles from our treatment plant to the end of the farthest main. We had to switch from Chlorine to chloramines for disinfectin due to the DBPs.

4) What do the elevations do from the end of the existing main? The main size may be dictated by not only the demand, but also by any headlosses or gains from changes in elevation.

Hope this helps.

 

[gwater12]

Bimr:

Are you responsible for supplying water for the fire district?

As a preliminary assumption the main doesn't need to supply fire protection

Is this the same utility or are you selling water?

This is the same utility. The City needs to extend service because the private wells have been contaminated.

Does the subdivision have an existing distribution system?

There is no existing distribution system or sewer system. The 41 homes are in a rural setting spread out over approximately 3-4 miles.

RWF7437

Are you in the U.S.? Yes
Does the City have a water system master plan? No
If so, does it show your 50 houses to be within its ultimate service area? No, the main is being extended due to private well issues.
Has the City approved this extension? The City will ultimately approve the project but it is still in the planning stages.
Topography? Relatively flat. Existing main end point is 39 feet lower than proposed end point.
Are these house higher or lower than the existing City main ? The homes to be connected are typically higher than the existing main end point.
Are these houses existing or proposed? All homes are existing. There is limited belief that service area will grow in the foreseeable future.

If minimum fire flow is 1500 gpm @ 20 psi for two hours a 12-inch pipe will not be large enough if existing static pressure is 50 psi. 33 psi ( 75 feet of head ) will be needed to deliver 1500 gpm @ 20 psi in a 12-inch pipe. But you only have 30 psi available.


Who will be responsible for water quality; the City or the owners of these 50 houses ? The City will be responsible for maintaining the water line that why I am concerned about avoiding stagnant water and being able to maintain disinfection residual.

 

[coloeng]

One thought, since they all currently have wells, would be to install a cistern for each house that they could then pump out of and then install a smaller line that doesn't have to meet the peak flows, but would just need to top off the cisterns. They would probably need new pumps and the total system might be more expensive than one large water line, but it may alleviate the quality concerns.

 

[RWF7437]

The short answer to your original question, which was:
"Is it feasible to extend service this far to pick up so few customers?" is:

It is possible but very expensive and will require the review and approval of many regulatory agencies including probably; your State Health Department, the City, possibly the EPA, and perhaps others. This is what an old boss of mine used to call a "spaghetti system"; miles and miles of small lines serving widely separated homes and providing little or no storage for emergencies. Very expensive and very unreliable. Also, such systems are often underfunded even with high water rates.

Just to begin, because the City has no master plan you, and they, have no guidance as to the line sizes needed. The City will, I think, view this as a highly undesirable main extension and would not likely willingly approve it. Also the City will be even more worried than you are about maintaining water quality at the end of this long, dead end main.

Because the highest home to be served is some 39 feet above the end of the City main water will have to be pumped. If the City decides that a tank or reservoir is needed that pump station will probably have to have at least two pumps, each capable of pumping the maximum day demand to the tank. An emergency generator may also be required at the pump station.

The tank will probably have to be sized to provide storage for the difference between the max day demand and the peak hour demand PLUS enough water to supply these homes for the duration of any anticipated power outage or other interruption of service. At a minimum, my best guess would be a couple thousand gallons.

The tank will probably also have to have an overflow elevation at least 92 to 100 feet above the highest house to provide at least 40 psi even when the tank level is low. For health reasons, an absolute minimum pressure of 20 psi is required in some States. Given your "relatively flat" topography this will be an elevated tank.

As Coloeng points out, it will be difficult to maintain water quality 3 miles from the City system. This could require re-chlorination at the tank or other kinds of disinfection. Frequent flushing will also waste water.

As to the "limited belief" that the area is unlikely to grow, history suggests that once a good water supply is available, whether adequate or not, there will be increased pressure from landowners and developers to build more homes. Everyone wants their 20 acre ranch but few are willing to pay what such sprawl costs. In addition to the water service costs fire protection insurance rates will be high with such a system.

It sounds as though the City may be forced, for public health reasons, to actually provide this water service but they will be very unwilling to undertake the continuing maintenance and public health responsibilities that entails. They will also, it seems likely to me, to be very conservative in their design criteria.

good luck

 

[cvg]

rather than a booster and an elevated water tower, a hydropneumatic system could be designed near the new community. This would be probably be cheaper than a booster and water tower. Fire protection rates will not change from before as there is currently no city water supply / fire hydrants. However, to provide those hydrants will require additional storage and a fire pump to do it. However, I generally agree with everything else RWF has said.

 

[bimr]

I agree with RWF7437's comments.

You probably would be best served with a 20,000 gallon tank at the end of the pipeline. That tank would hold about one days water volume.

You are talking about a $1.5 million dollar project to service 50 homes.

Have you considered just installing a new well and distribution system? It would proabably make more sense.

 

[vodokanal]

I think you need to carry out a feasibility study - to make a cost analysis for different water sources. Maybe it is more feasible to drill a new well nearby the homes. Also, the operational costs should be considered (pumping, possible treatment, etc). Hopefully, you will find a better local water source with high quality potable water.