I'm having a well put in in the foothills just east of the Sierran
Nevada mountains. The area is rocky (decomposed granite) and other
homeowners in the area have wells ranging from 150 to about 300 feet
with good flow rates. One neighbor just put in a well (same driller)
and gets 20 gal/minute. My well digger went down to 390 feet without
finding any significant water, but he thought there might be some
higher up based on the hole filling overnight. So he removed the "mud"
from the hole but found only about 7 gal/minute (which seems inadequate
for a 3700 sq ft house). He says the only other (than 7 gal/minute)
option at this point would be to go deeper. This would be deeper than
any of my neighbors, most of whom are at slightly higher elevations
1) Would it make sense to drill elsewhere on my 2 acre lot? It seems
like perhaps the water table varies since my neighbors have good wells.
Starting over is an expensive proposition but may be the only option if
water isn't found deeper.
2) What other choices are there if more water is not found in the
present hole. Can large storage tanks be used to "buffer" the
3) What is a minimum reasonable flow rate? We'd hoped to use a new
variable speed pump that can handle up to 30 gal/minute.
Serious advice is welcome.
In a previous post email@example.com wrote...
7 gallons per minute is a pretty good flow rate. If you are concerned
about loss of water then use a larger than normal pressure tank. It would
be very unlikely that you are going to use more than 7 gpm for any
extended period of time, unless you plan to do a lot of irrigation.
Remember, most toilets are only 1.5 gallons/flush. Showers and other
constant flow devices typically use 3 gpm.
I have a 5 gpm well that works just fine. My pressure tank may be a tad
small if we are doing a lot of laundry plus a lot of showers, but if we
spread the load out a bit, there is no problem.
Bob Morrison, PE, SE
R L Morrison Engineering Co
Bob's recommendations are good... we have 7 gpm, but only use it for our
heat pump. The one thing that we did was go with a larger than normal
pressure tank (sized one up from what was calculated -- it as actually $30
cheaper for some odd reason). The larger size prevents short cycling. You
should be fine.
My concern in that area would be the source and the reliability over
long term. How long a test was the 3 gpm rate test?
I'd talk to somebody local who knows the aquifer for more data prior to
making a final decision...of course, the driller wants to either finish
this or move on _real soon now_, so you've got a tough decision to make.
Are you high? You expected 30 gpm in a residential well? What do YOU
What's considered "normal" expectation around here is 5 gpm and
anything from 3 gpm up is accepted by the local authorities and the
mortgage companies. Below that and you need a storage tank.
A normal residence uses in the neighborhood of 250 to 400 gallons a
day. If there is something more unusual about yours (3,700 s.f. is no
big deal - usually the rating is by number of bedrooms not by their
size) maybe you'd need a tank. Do you plan to irrigate a large yard
or something? Now, THAT takes some water.
Do you also have a septic system going in? Who designed that?
Usually the daily flow it is designed for will be stated right on the
plans, but go ahead and ask that engineer how many gallons per day.
See how few minutes of pumping that is. Ask that engineer what a
reasonable rate would be.
I would be VERY surprised if 7 gpm was thought inadequate - unless you
are irrigating, or plan to fill the pool out of that well.
Reply to NG only - this e.mail address goes to a kill file.
Sounds like "Well Envy". Unless you are seriously irrigating, or have an
industrial need, 7GPM is plenty especially since you must deplete any
storage tank before that limitation would be a factor. Give it a year,
Given your location, the flow rate may in fact change with the seasonal
runoff rate, not that you'll notice any change using only what you need.
Seems like late October/ early Novenber would be the lowest time of the year
for water in the Sierras, it only started raining a couple of weeks ago.
When did your neighbors drill and measure flow rate, May (flood season in
Yosemite)? If you need more water, it will be apparent within a year. No
need to make a quick descision since you already paid for the hole and it
On 15 Nov 2005 07:57:33 -0800, " firstname.lastname@example.org"
Just went through a similar situation.
I'm in OH. The well driller told me these guidelines:
20 gpm is good for unrestricted use for 4 or more people in a large
house on a large lot (2+ acres of lawn). Unrestricted use includes
frequent lawn watering, garden irregation, laundry, washing cars, etc.
10 gpm is good for all of the above with some restrictions. Not
trying to wash the car while doing laundry and the lawn sprinklers are
on, for example.
5 gpm: will be ok to water the garden and shrubs; forget about
frequent lawn watering, such as a sprinkler system, unless it's a very
Below 5: Aux. storage recommended, from 300 to 1000 or more gallons
down at the 2-3 gpm level.
Having said that, he then said that if you are willing to forgo any
significant irrigation of lawn or garden, and you don't mind being
careful to sequence things, such as spreading laundry over several
days, you can manage on a few gpm.
The numbers may sound high to some, but flows do tend to decrease a
bit over time and vary seasonally, and can also be greatly affected by
load on the acquifer from more building in the area.
The problem with low flows and no aux storage (he told me) is that if
you aren't careful, and you keep drawing the well down a lot, or
worse, running it dry, the water washing up and down the sides of the
well tends to loosen sand and grit, which gunks up the water supply
and leads to early pump failure.
FWIW, in our case, we drilled two wells, neither went above 2 gpm
although there were some 20 gpm wells within a thousand yards or so.
We walked away from the deal (it was contingent on getting a good
Unrealistic flow rate aside/addressed by other respondents very well.
Drilling water wells is hit and miss. They are usually pockets of water,
not a continuous body of water likening an underground major lake. Whether
they hold out during some minor drought periods depends on many factors. A
holding tank like a 1.5/2K gallon versions are a good idea for a number of
reasons, but adds substantial cost to the water supply.
Beware the rule quoters, the corp mindset, the Borg
1 gallon per minute is over 1400 gallons per day... thats more
than enough for normal household use on a DAILY basis. The problem
is that water USAGE isn't evenly distributed. The solution
for that is a low-volume pump and a big-ass storage tank.
If you're irrigating, either crops or lawn, then you
should check with local authorities about how much water
you're likely to need, but at that point, I'd be looking
at annual rainfall, because if you use more water than
falls, then eventually you're likely to run out.
Other posters have covered it pretty well (no pun intended), but I'd
like to add, having just sold a house in NY state: the federal HUD
guideline states that 5gpm sustained flow over a 4 hour period is
adequate for a 1 or 2 family dwelling.
Jim also had a good point with the pockets of water. Our well had a
lot of dissolved iron and other hard minerals, while the neighbors did
not. All were drilled. One other neighbor drilled 3 wells and hit
salt water pockets in every one (this was near Syracuse, nowhere near
any saltwater bodies). My point is that there is a lot of variation in
the water table and the surrounding geological conditions.
That's precisely the point--in most of the west the underground aquifers
are not dependent on surface precipitation. That doesn't _necessarily_
mean it is an unreliable source, just that it isn't surface replenished.
WATER TABLE FOR SALE: Ours has been above the ground for almost
two years now, or at least it seems that way: take it, it's
: >Unrealistic flow rate aside/addressed by other respondents
: >Drilling water wells is hit and miss. They are usually
pockets of water,
: >not a continuous body of water likening an underground major
: >they hold out during some minor drought periods depends on
many factors. A
: >holding tank like a 1.5/2K gallon versions are a good idea for
a number of
: >reasons, but adds substantial cost to the water supply.
: 1 gallon per minute is over 1400 gallons per day... thats
: than enough for normal household use on a DAILY basis. The
: is that water USAGE isn't evenly distributed. The solution
: for that is a low-volume pump and a big-ass storage tank.
: If you're irrigating, either crops or lawn, then you
: should check with local authorities about how much water
: you're likely to need, but at that point, I'd be looking
: at annual rainfall, because if you use more water than
: falls, then eventually you're likely to run out.
Depends on the source of the water. Local rainfall may mean nothing in
regards to the well's water supply. An example would be a pocket as part of
a large aquifer. On the side of mountain, most likely local precipitation
dependent if not very deep in relation to the mountain's hieght and well
If the source of water is interconnected to other's water supply, their
usage may affect anothers water availability. Another holding tank bennie.
Beware the rule quoters, the corp mindset, the Borg
It does seem odd though that a neighbor is pulling down 20 (!) gal/min,
and your neighbors are pulling more at higher elevations.
Theoretically, you'll have a greater pressure head and a shallower
water table at a lower elevation, so theoretically you should be able
to pull more than your neighbor.
When you say decomposed granite, I don't know whether you just mean
heavily fractured and partially metamorphosed granite, or something
like a saprolite. Usually if you have a basement of fractured igneous
rock, you pull less water and have a greater recharge rate than if you
have a very permeable rock. However, what can happen is that over
short distances, you can have a fault in the bedrock that allows water
to permeate deep fast, essentially being a drain in the local water
table. If this is the case, you could go lower and potentially find
However, I don't know the geology of that area, and it could just be
speculation. However, faults are common over here in the appalachians,
and can cause some of the local differences in the water table that you
are talking about. You may want to consult a geological map and see if
any faults are marked in your immediate area.
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