Well and Pump vs Tank
Well and Pump vs Tank
(OP)
What are some of the considerations for a water distribition system for 4-13 homes in a rural area. An onsite spring has been measured to provide clean potable water at 60GPM. The two intial designs are (1) pump water from the spring 150 feet up to a possible tank location or (2) use wells do provide water on demand (elev of homes would be approx 75' above spring -exact depth to ground water is unknown at this time). We are a geotech firm and would be subing out the design, however I would like to know a little more about the general design critera and rough costs of the two alternatives.
Thanks in advance
Thanks in advance





RE: Well and Pump vs Tank
My father-in-law used to get his water from a spring and the quality was impeccable. Unfortunately the source was directly across the street from him, and the State decided he couldn't cross the road to get his water. He had to tap his well and now the water is very sulphuric and he had to install a sophisticated (expensive) multi-stage filtration system to get the water to shower/toilet level. He does not drink the water, but buys bottled water instead. The spring and well are at most 500 ft apart.
RE: Well and Pump vs Tank
It may be that we are going to have to use a water tank and common water system due to local fire regs. For the academic sense of the problem however, what are the issues you water guys look at when comparing the costs of different supply systems.
For example the tank alternative may require a disinfectant system. Do smaller tanks have a short enough holding time to not require this?
How does the cost of running and maintaining an on demand well system compare with a water tank system?
How many wells and pumps must be installed before the cost of a single larger pump and tank break even?
I understand that costs vary greatly with location, but I value the wide range of engineers that post here. I plan to talk with civils local to my area, and a little more knowlege before hand certainly cant hurt.
RE: Well and Pump vs Tank
Fireflow and emergency water is another issue to consider. It may be desirable - or required - to provide the following: emergency storage, emergency generator for the pump, standby pump and last but not least, additional storage for fire fighting.
Also, have you performed an analysis of the drawdown on the spring? If you begin pulling 60 gpm to serve 13 homes, will the water level in the well go down? Will this require additional pump head to supply the needed water? will the drawdown affect other nearby wells?
You indicate that you can provide 60 gpm. Will this be enough to provide for peak demand from the future homes? When everyone waters the lawn, turns on the shower and flushes the toilet at 7:00 am each morning, will the total demand exceed 60 gpm? If so, you need to provide sufficient storage in a tank and the pumping system to provide for that.
RE: Well and Pump vs Tank
Sounds like you're at the proposal stage. This would be a good time to select your Civil consultant(s) and ask them to help you put together a good proposal. Also, get more information on both water quantity and quality. The more you know now, the fewer unpleasant surprises you'll need to deal with later.
Good luck
RE: Well and Pump vs Tank
CCG-
Initial water quaility has been tested by others, and has been found to be beautiful!
The spring is currently flowing at a natural rate of no less than 60GPM year round. Becuase the spring will flow at this rate regardless if we use it as a source drawdrown/recharge will not need to be considered at this stage. If the spring was to be used as the sole water source over individual wells per dwelling, a tank is proposed insure the common water supply can meet the max daily demand (and fire (;). The water tank will be locatated at an elev 150 above the spring so a pump will be required to provide flow.
RWF7437-
The project is indeed in a proposal stage, however we are not considering costs for the purpose of future billing, rather trying to estimate the ballpark extent one would need to involve themselves financially. The project consists of 4 single family dwellings. The additional 9 may or may not be built on a neighboring property. For the sake of simplicity lets assume its only the 4 to be built. I believe in the end we will have to provide to fire suppression, however the project is small and in a rural area so we may be below the regulatory threshold. For the sake of simplicity lets assume fire can be neglected from costs.
What are the methodologies you use to estimate costs? For example it is probably too simple to assume # of bores x depth of bores x linear cost to drill. What are some of the additional costs that need to be considered for a home to use a well? A UV system, water softener...
What are some of the costs to consider for a common water supply from a tank. the cost of the tank, pump, pipe...
RE: Well and Pump vs Tank
Good luck
RE: Well and Pump vs Tank
Pumping directly to the homes will also require a tank (or tanks) which are pressurized with air and provide a steady supply of water at a relatively constant pressure without surges and without constant stop and start pumping. For instance, you could install a large hydropneumatic tank at the spring or pump directly to each house and each house would have a small hydro tank in the basement or garage. This may be a cheaper initial cost due to the shorter transmission main and smaller reservoir, plus no need for additional site. But the cost of O&M for the pump system will probably be higher and will have less redundancy.
RE: Well and Pump vs Tank
It is probably not practical to consider a water distribution system for only 4-13 homes.
For such a small system, you probably need storage of about 50 gals. per capita, so the total storage would be only about 600 gals to 2000 gals.
Plus you have the situation regarding fire flows. The fire demands are so much larger than the normal daily flows, the water distribution system would never work properly. You also will have high ratio for peak flows to average daily flows with such a small system.
You will also have all of the headaches that come with managing a water company. Sampling, billing, etc.
Save yourself a headache. You would be better off recommending individual wells for each house. Unless of course, the geology of the site preclude well construction. I think wells go for $4-5K each.
RE: Well and Pump vs Tank
I had not considered that a new water district would likly be formed with a common water supply. That is the type of information I'm kinda poking for.
RWF7437,
I understand that costs vary by location, the dollar amount in your area may not correspond to those here, but would still be interesting to consider. What I'm trying to ask for are what are the componets of which the costs must be considered.
RE: Well and Pump vs Tank
If it is construction costs these must include, at least:
Land cost
Well drilling if necessary
Piping costs for the entire distribution system
Pump costs
Reservoir costs
Controls
Design, survey, inspection, and testing
Interest on borrowed funds
contingencies which at this very early time must be at least 25% of the total
Then there will be the continuing operating costs including:
salaries of the operator and others
chemicals
pumping power
planned replacement ( a sinking fund is often used )
billing
meter reading ?
routine required periodic testing
For this small system these costs will be relatively high per customer.
Are you sure you want to undertake all this without the help of experienced people ?
RE: Well and Pump vs Tank
The water quality may be good; but, what sort of bacteria is or could easily get in the water?
A lot of states don't regulate below 25 connections; however, as an engineer I wouldn't want families to get giardia or crypto because I didn't filter and/or disinfect the spring (ie. surface) water. What keeps the beavers, rats, squirrels, cats, dogs, mice, surface runoff, etc. away from the spring?
This water could possibly work fine for fire flow; but, you will need some form of storage (at the spring or elevated) to provide enough volume. 60 gpm isn't a high enough flow and you need to store enough water to meet your fire flow demands.
If this is rural, a large pond without distribution system may meet the needs. In my area, it is common for the rural fire department to pump water from local ponds to their water trucks or directly to the fire if it is close.
RE: Well and Pump vs Tank
RE: Well and Pump vs Tank
Check with the local fire dept. for their fire flow requirements. Where I worked, the rural fire departments were all volunteer fire departments and they had trucks that they'd fill and pump from the truck. We weren't required to meet fire flow rates or residual pressures on the water mains. If this is a non-municipal water service area, you may not have any fire flow requirements at all. (Which doesn't necessarily mean you shouldn't provide any.)
Wells and perennial springs are waters of the state, so without state approval, it's not possible to tap into either source. In TN, TDEC's Division of Water Supply provides well permits. I'm not sure how using a spring would be regulated (water intake?), but you're right, it is important to consider the downstream impacts of reducing the flow. Wetlands or fish ponds could be severely impacted, particularly if flow is intermittently interrupted during dry spells.
RE: Well and Pump vs Tank