INSURING SUSTAINABILITY OF PERFORMANCE IN WELL SUPPLIED SYSTEMS BY LIMITING WITHDRAWALS

We have learned that a Well Manager can supply ten houses using a well many people would say is inadequate for one. SEE MULTIPLE BUILDINGS ON A SINGLE WELL. We also discovered that the 5 gpm well has a daily potential four times that needed to do that job.

People in the well business know that most wells lose yield over time. This may be because there are more homes to share the supply with than there were when your home was built, it may be because you have been over pumping the well for years and the fractures are starting to clog up and it may be the result of bio-fouling or nearby blasting. Whatever the cause, this is expected.

There are also areas where well yield varies throughout the year. Well yield may be great in late winter but in July and August it may not be so great. If you are planning a water supply for a vacation home or a car wash, July and August are the times you need the most water. It is possible to insure that your guests won't run out of water in the middle of a shower or that your car wash won't be closed early during your busiest season.

If you build a supply system that depends on the full yield of a well then performance of that system will degrade as the well yield declines. If you build a supply system based on a portion of the well's capacity then yield will need to decline below the design point before performance will suffer.

Let's use the previous example of 10 houses supplied by the 5 gpm well. We determined that the well capacity was 4 times that needed to supply the homes. If we used that well and designed the Well Manager to supply those houses using 2 ½ gpm of the yield, the well yield would need to diminish by half before system performance would be affected.

Time required to refill storage @ 2.5 gpm = 1600 ÷ 2.5 = 640 minutes or 10.66 hours. In that time there will certainly be additional uses so it may actually be 15 or 16 hours before the system shuts off. The system is not maxed out yet because there are 24 hours in a day.

This means that we have built a system capable of supplying ten homes with 4 people each, using a 2 ½ gpm well that spends a good portion of each day shut down. If you think about that you will realize the well yield can drop below 2 ½ gpm until it gets to the point where 24 hours is not enough time to collect the water needed to supply the homes. Arithmetically this means: 40 people @ 75 gallons per person per day = 3000 gallons ÷ 1440 minutes = 2.08 gpm yield required.

The same thinking works for a vacation home or a car wash where the well yield in July is half that of the yield in January. Designing the system for something less than the poorest yield will assure that there is plenty of water throughout the year.

The added benefit is wells that are treated properly do not lose yield as fast as those that are over pumped so designing using a portion of the yield (restricting the amount of water that can be withdrawn) will not only insure the sustainability of the water supply system's performance but may also insure the sustainability of the water supply itself.