Over Pumping Well Water Causes Problems – Low Yield Well – Can your water well be over-pumped?
Over Pumping Well Water Causes Problems – Low Yield Well – Can your water well be over-pumped?
By Mr. Brian Oram, Professional Geologist
The simple and direct answer is Yes. A water well can be over-pumped and when this occurs the actions can cause premature failure of pumps and motors, damage the wellbore integrity, decrease the wellbore yield, impact produced water quality, and ultimately decrease rate of production.
In most cases when a new well is drilled, the well driller reports the blown yield of the well. This is typically the amount of water the driller can physically blow out the top of the well over a short period of time or in a very few cases this may be the rate they were able to pump from the well for a short time period. This period of time is multiple hours, but more likely at most 1 hour. This is not the long-term sustainable yield from the well and in many cases, this is all the water that was in the well.
The Know Your H20 program is based in Northeastern Pennsylvania and we have worked on a number of cases where the actual well yield of the well was significantly less than the blown yield for the well over the last 30 years. One example: (look for the red flags)
Well Case 1- Pocono Vacation Home (2nd Home)
This well is used intermittently during the year and used mostly over long weekends during the summer and ski season. The well was drilled by a licensed well driller, but the pump/motor was installed by the home builder. The well was 150 feet deep and reportedly the well had a blown yield of 10 gpm. The well was serving 1 single family home (3 bedrooms) and the peak water usage should be equivalent to about 400 gpd.
We (Keystone Clean Water Team) were called out because the homeowner was getting very dirty water that contained a lot of “gas” and at sometimes no water. We looked at the available well log for the well and drillers notes and we found the following:
- Primary water bearing zone was at 100 feet, static water level at 45 feet top of casing (toc), and a blown yield (15 minutes) of 10 gpm. We searched and found the actual drillers log in the PAGWIS Database.
- Pump was set at 120 feet or 20 feet off the bottom of the well. Note: Is not a good idea to install a pump below the primary water bearing zone. We got to review the actual plumbers bill and notes on the pressure tank.
- The pump that was installed was rate at 10 gpm, but from the pump curve this rate would apply to a dynamic water level of 120 feet and not the more likely dynamic water level of about 80 feet or 20 foot above the water bearing zone. Therefore, the pump would initially pump at a rate greater than 10 gpm for some period of time.
These observations suggested that one of the problems was the well was being over-pumped. After we investigated, this is what we found:
- The actual static water level in the well was not 45 feet top of casing, but 80 feet top of casing. We used a sonic water level sensor.
- We camera surveyed the well and tested the water and found that a bioslime layer and scale coated the fractured zone.
- We filled the borehole with water to 45 feet toc and turned on the pump and discovered that the pump was actually pumping at a rate of 15 gpm and not 10 gpm and if permitted the dynamic water level would drop to 130 feet toc. This means that the dynamic or pumping water level was below the point that groundwater would enter the borehole. This means that the aquifer was no longer acting like a confined aquifer under pressure, but the aquifer was being drained. We confirmed the well was being over-pumped.
We were correct the well is being over-pumped and the well also has a problem with bioslime/ scale formation. Our first action item was to clean out the well and do some basic well development to increase the well conductivity and yield. After cleaning out the wellbore and fractured zone using a combination of chemical cleaning and surging, the static water level was about 50 feet toc. We then conducted a step pumping test that lasted a total of 4 hours and estimated that the “safe yield” of the well was more like 5 gpm and not 10 gpm. We recommended that the pump be changed and the pump be set at a depth that could not draw the water below the water bearing zone.
Summary : Therefore, what we really had was a low producing well that was not properly identified originally and then the pump installer (not the well driller) installed a pump with an excessive pumping rate at a depth that did not protect the aquifer.
Because this article is really about low producing water wells, we went looking for solutions and found “EPP Well Solutions” – https://eppwellsolutions.com/well-health and their article on “Well Health”. A few quotes from this article that we found most helpful:
“Over pumping is a common factor with the low water well. A well is over-pumped if the water is withdrawn at a faster rate than the well was designed for or the aquifer is able to produce. Over-pumping is the most common well problem that leads to premature well failure. Over-pumping not only depletes the groundwater aquifer (or source), but it rapidly increases the rate of corrosion, incrustation, and biofouling related problems. Over-pumping also increases the rate of sediment particles moving toward the well, causing plugging of the perforated area where water flows into the well. It can also cause the aquifer to settle and compact which further restricts water flow to the well.”
In the article, they highlighted the problems that might occur with over-pumping a well, which were perforation plugging (slotted casing), mineral incrustation, and biofouling. One that was not mentioned was natural decrease in aquifer porosity and conductivity. In the case of our example, the aquifer was a confined aquifer under artesian pressure, which means that the pressure of the water in the formation were helping to keep the fractures open along the borehole walls. When the well was over-pumped and the water was permitted to cascade into the well, this means that the weight of the earth and rock above the fracture could cause the fracture to partially close.
The typically solution to a problem with low yield wells are as follows:
- Drill more than one well or attempt to modify the well by drilling deeper or hydrofracturing the well.
- Installing some internal storage within the system, i.e., a storage tank and then using a second set of pumps to re-pressurize the system.
- Supplementing the system capacity with surface water or a rainwater harvesting system.
EPP Well Solutions have developed a hybrid option using the Water Harvester System. “The Well Harvester automatically harvests the water in the well while preventing the well from over-pumping itself. The harvested water is then pumped from their system into the house. Their system is compact and can fit in most garages or well houses and is able to harvest and store 215 gallons (or more with additional tanks) for use throughout the day. “
If you suspect you have this problem, we would recommend you review EPP WELL Solutions educational videos. In addition, the company has a really interesting Emergency Well Hand Pump System.
Brochure on the Well Harvester System – https://static1.squarespace.com/static/5f064f110a5809607307b409/t/651720188163296aa76c4151/1696014361571/Well+Harvester+Brochure+2023.pdf
Recommended Links
Well Harvester System – https://eppwellsolutions.com/well-water-system
Emergency Well Hand Pumps – https://pump.eppwellsolutions.com/
Rain Water Capture and Harvesting
WellSeal™ Gives Well Owners and Well Drillers Peace of Mind About Groundwater and Drinking Water Safety.
Secure the Water First, Buy the Land Second – groundwater location services
Water Testing and Contamination
The Top Drinking Water Contaminants in Well Water and City Water
Lead Service Lines – City Drinking Water
National Water Testing Kits – Well Water
National Water Testing Kits – City Water
Other Educational links
Groundwater and the Water Cycle
https://news.stanford.edu/2018/06/05/overpumping-groundwater-increases-contamination-risk/
https://wellwater.oregonstate.edu/groundwater/understanding-groundwater/groundwater-and-wells
https://www.usgs.gov/media/images/cone-depression-pumping-a-well-can-cause-water-level-lowering