Drought & Well Testing FAQ’s

Interpreting Well Test & Inspection Results

Critical Information:

Sustained flow rated from well

The single most important piece of information from a well test is the sustained yield of the well. This yield value should be compared with the potential needs that will be placed on the well. For example:

 A well is tested, produces 5 Gallons per Minute, and is going to provide water for a 5 bedroom 4 bathroom house with a garden and landscaping. This well wouldn’t be up to the task unless a large storage tank has been installed with a booster pump.  Even with the storage tank, careful consideration should be taken to assure that the water supply were adequate for future needs.  If this same well were to be used to provide for a 1 bathroom, 2 bedroom house with water saving fixtures and almost no landscaping, then it would be adequate, especially with a storage tank.

To evaluate water needs think about how many people will be living on the property and figure they will each use about 150 gallons per day. Consult with a landscaper to determine current/future water needs and minimum flow requirements for the landscaping, and then compare the sustainable flow rates from the well with the established requirements.

A property with insufficient water should be carefully considered before purchasing. While it may be possible to drill another well, there is no guarantee that drilling another well will yield water. Relying on trucked water is not a good option as it can be expensive and unreliable.

If you plan to build or remodel, verify what water supply/septic requirements/restrictions are in order to obtain a building permit.

Well Yield or Pump Yield

It is important to note that the well yield and pump yield are very different. The well test may show a yield of 5 Gallons per minute, but that number may be limited by the size of the pump installed in the well.  Installing a larger pump could potentially give the homeowner access to more water. To determine if the pump is the limiting factor in the well test, it is important to look at a few more pieces of information: pump depth and sustained pumping level. If the water level in the well stays far above the pump during the entire well test, then the well pump is the limiting factor in how much water can be withdrawn from the well. If the water level in the well drops to the level of the well pump, then the well is the limiting factor in the well test.  While removing the existing well pump and installing a larger one to ensure the full well yield capacity testing is possible,  it adds significantly to the cost and is not normally done.

Recovery

Recovery is the period of time after the well pump has been shut down from the sustained yield test. Water level measurements during this time are extremely important and reveal if the water level in the well comes back up to normal levels (the level before the well test started). Water levels that stay low/recover slowly can indicate, limited water availability, a plugged well casing, etc...

 Important information:

Condition of well, pump & tank equipment

Potential buyers should be aware that repair and maintenance of a well pump system are part of the rural homeownership experience.  When purchasing a home with an aged well pump system, an aged system may be a point of negotiation in the purchase process.

The inspection should include a general description of the well pump equipment, its condition and approximate age. The equipment should be functioning (hopefully) and providing water reliably. That equipment, while functional, could be 5, 20 or 50 years old. This is an important consideration when the well pump system is being evaluated for the purpose of a real estate transaction.  It is not possible for a well pump technician to give you an exact time frame before a system will fail. Insulation breakdown, corrosion, burned electrical contacts, worn pump, etc… indicate the system is nearing the end of its useful life, however, we’ve seen old/worn systems continue to work for many years. Potential buyers may want to have the current owner repair leaking valves, faulty/corroded parts, failed pressure tanks, etc… OR they may want to use this as a negotiation point on the price and take care of the issues after the sale is completed.

Water Quality & Effective water treatment

Water tests can show if the water has high levels of minerals that can cause staining/spotting, bacterial contamination or low pH/corrosive water. Frequently, water treatment equipment has been installed to correct the issues identified in the water coming from the well. It is important to determine if this equipment is working properly and what types of ongoing maintenance is associated with keeping the filtration equipment working.

Water pH levels below 7 that have been left untreated can be of particular concern. Low pH water, over time, can dissolve metallic piping (iron, galvanized, copper) and result in pinhole leaks in the metallic piping. If the water test results show water with low pH and the water piping system is comprised of metallic pipe, the pipe should be inspected by a plumber to ascertain if the metallic piping has excessive corrosion. In addition, plans to correct the pH to acceptable levels should be investigated.

Time of Year

A well test performed in the summer or early fall on a well that has been in use will typically give the potential buyer the most accurate results. Well tests done during the winter or spring may give different results since well usage is less due decreased due to lower irrigation demands, rainfall, etc…

Interesting information:

Often the well report will have other information of note. Look at it and think about the implications.

For example, some wells have warm or hot water. The temperature of water in the house for “cold” water could be more like tepid/warm. Sometimes the well is in a difficult to access area, this can increase costs to repair/replace the well pump when necessary.

Wells do use electricity to produce water. Sometimes notes will be made as to the pumping efficiency of the well pump. While a system may be perfectly functional and not show any signs of wear, it may be highly inefficient and use unnecessarily high amounts of power.

Should I have a well test done?

Here are typical reasons for testing a well:

1)    In a real estate transaction it is important to establish that the quantity and quality of water is such that it will enable the potential buyer to develop the property, landscaping, garden or agriculture in the way they see fit. If the property has a well or spring on it, a yield test is to establish what type of flow is available. Water quality analysis can establish if the water is fit for consumption/agriculture or if there are any minerals that might stain plumbing fixtures or cause irrigation systems to plug up.  Planting 10 acres of vineyard to later find out the well will only support 5 is not only a huge disappointment, but a waste of money!  Contaminated water, stained fixtures and glass etched with silica can also be unwelcome surprises avoided by testing the water quality.

2)    Well yield tests are essential for those that rely on a well as their sole source of water and have reason to believe that well production has decreased. Performing well yield tests every 5-10 years can give critical information as to whether the well production is declining, if the well is becoming occluded with minerals if the well is still performing optimally. This type of information helps facility managers & home owners as they plan for future water needs, well maintenance and water supply sustainability.

3)    Well tests help your pump contractor install the right pump for the job. There is no single well pump that fits all situations. By having information on the flow available and depth from which the water must be pumped at that flow rate, the highest efficiency pump that is best suited for the job can be selected. Selecting the correct pump can have significant savings upfront (not buying more pump than your well can support) and long term power savings.

4)    If you are planning on building a new residence, Napa County will require a yield test on the well or spring to demonstrate sufficient water supply for the intended use & issue building permits. Wells producing between 1 & 5 GPM will need to have adequate storage tanks installed in order for the building permit to be approved and wells that produce under 1 Gallon per minute will not meet the requirements to issue a building permit. (Please check here for more information in Sections 13.04.040 and subsequent for details.)

Well driller’s reports often have the information necessary on the flow & drawdown of a given well. These reports are usually good at giving ballpark figures for flow & drawdown on a new well, but often don’t reflect the actual flow rate from the well 10 years down the road or after a new well has been pumped for some period of time.

Is my well dry?

For homeowners that rely on a well as their sole source of water, the possibility of a dry well is akin to a nightmare. In most cases, wells don’t “dry up” overnight. In the industry we refer to a well’s capacity or production decreasing instead of saying it’s just “dried up” because the decrease usually happens over a long period of time on the order of years or perhaps months, typically not days or weeks.

There are several methods to determine if the production of your well is decreasing, however, to ascribe decreased production to a specific cause (drought, over-pumping, plugged up well casing, neighbor drilling a well, confined aquifer, etc…) is not within the scope of this document and often includes complex modeling, research, testing & litigation.

The most simplistic method for evaluating water availability is to measure the depth to water from the surface when the pump is not pumping. This is called measuring the Static Water Level (SWL). A single SWL measurement is almost meaningless; the value in measuring static water level comes from a series of measurements during the same season(s) over a period of years. This ensures that you’re not just measuring seasonal trends, but getting the bigger picture.

SWL is measured with a probe that your pump contractor should have. The probe is inserted in the well and lowered until it touches water, at which point it will beep or light up, etc… In some cases, measuring water level can be difficult when the pipe & wire (which connect to the submersible well pump in the bottom of the well) get in the way of the water level probe decent!

While measuring SWL can give a general idea of changing groundwater level and is relatively simple and inexpensive to perform, it overlooks several key factors:

1)     Overall depth of the well. A deep well that taps multiple aquifers will have more water available than a shallow well that taps a single aquifer.

2)     Types of geology & underground formations that impact water availability. Wells that tap into water bearing gravel/sand formations will produce more water than wells that are mostly clay that tap into very minimal sand/gravel/rock formations.

3)     Condition, type & age of the well. Many older wells were simply a piece of steel pipe driven directly into the ground. The steel corrodes, the sand/gravel around the well casing can plug with minerals, or the casing can collapse in certain sections- reducing the well’s capacity.

In order to fully understand a well’s capacity a “well test” must be performed. A well test involves pumping the well for a period of time and measuring/controlling the water level and rate of flow of water coming from the well. When water is removed from the well at the same rate the water is entering the well the water level in the well stops dropping. This point of equilibrium is important because, by measuring the flow rate we now know the capacity that the well can sustain long term. In general, it is important to perform a well test at a flow rate and length of time representative of typical use. Many homeowners opt for 2 hour well tests as they are an economical option. Unfortunately, the results may be misleading as we find that it often takes more than 2 hours to even reach the equilibrium state in some wells.

Contact Oakville Pump to evaluate your well capacity & develop an effective water management plan!

My well is dry, now what?

A dry well, in most cases, is a misnomer. Wells that go "dry" are not actually without water, often they are simply producing less water than they originally produced which his inadequate for the current demand for water. In addition, the normal pattern over time is that demand for water increases as pools, landscaping, & gardens are added or household additions are made. This can cause a well that was once sufficient to meet lower demands, to be inadequate when increased demands are placed on it.

 Lowered production from the well can be due to several different causes:

1. Sustained periods of drought can cause the water table to drop. There is very little one can do about the aquifer level dropping other than drilling a new well since deepening wells is not practical. It may be possible to install your well pump lower in the well if the well is deep enough to do so.

2. Your well can also have reduced production if it becomes plugged with minerals and scale. A plugged well is indicated by the water level dropping very quickly after pumping and slowly recovering after the pump is shut down. These minerals can be dissolved and flushed out via a professional cleaning or well rehabilitation. OPS has conducted many successful well rehabilitations where yields have been restored to acceptable operating levels.

3. Water storage tanks are a frequent solution to a low yield well. A storage tank and booster pump can be installed so that water can be accumulated over longer periods of time and meet high short term demands. For example, a well that produces 1 GPM would be hard to run a house off of when a single shower head requires 2.5 GPM. That same well can be used to fill 2500 gallon storage tank over several days and a booster pump installed to supply 15 GPM. Since a shower only lasts for 10 minutes, there is plenty of accumulated water for this and other household needs.

4. A combinations of solutions that include cleaning the well, decreasing water usage and increasing water usage efficiency and installation of a storage tank can often change the situation dramatically!

5. In some extreme cases, it is time to look for a well drilling contractor and install a new well!