Well DesignSince geological conditions are inconsistent from aquifer to aquifer and, within individual aquifers, well designs need to be dealt with on an individual basis to achieve maximum extraction of water a well. We have a process we go through when we come out to your property to evaluate what is required to satisfy your ground water needs. Once the required Gallons per Minute (GPM) are defined and the ground water potential of your property has been researched we need to design a well that has the capabilities of extracting the required amount of water, is large enough in diameter to house a pump that will lift the water, will operate with minimal maintenance and will produce sand free water.The graphic below illustrates a generic design of most wells drilled in the Fraser Valley. Note that surface seal, depth, diameter, screen length, and screen slot opening size are a few of the design features that will change from well to well.
FLOW TESTINGOnce the well installation is completed its yielding capability needs to be assessed. This is done by Flow Testing the well where, often, a temporary pump is set in well and run. The length of pumping time needed can vary from an hour or so to a couple of days or so where conditions are extreme. Data gained while monitoring the water level during the test will accurately determine the well and aquifers yielding capabilities.
In cases where the driller knows a lot about the aquifer the temporary test pump may not be needed and a suitable pump may be installed and used to perform a quick test to attain an accurate Pumping Level and other Base Marks. Correctly sizing the pump will save installation, maintenance and electrical costs. Caution is needed when sizing permanent pumps for wells drilled into aquifers where little is known about their capacities to store and yield water. Often, the Flow Test costs are easily seen in returns from the costs saved by correctly sizing the pump. It is unadvisable to guess at sizing a pump for a well that is drilled into an aquifer that there is little known about and has not been Flow Tested.BASE MARKS
What are “Base Marks”? Base Marks are the original points, levels, elevations etc. that need to be recorded when a well is new. They play a vital role on how we track changing conditions in a well, pump and aquifer. Data provided from ongoing monitoring is compared to the original Base Marks to track changes in the well, aquifer and pumping system. Monitoring will reveal trouble coming, often long before it is a severe problem.The following lists most of the base Marks that need to be recorded on a new well.
- Hole depth
- Top of screen
- Static Water Level
- Pumping level
- Available Draw Down
- Initial Flow Rate through pumping system.
- Pump set level
- Pump amperage draw
- Pump house volts
- Water pressure at well head
- Water analysis lab report.
- Specific Capacity
When the pump starts up in a well the water level begins to drop from the Static Level and will eventually stabilize at is what is known to be the Pumping Level. The water level won’t move from the Pumping Level, or so we think. There are a number of factors that will cause the Pumping Level to fluctuate;
- Seasonal fluctuations of the water table in the aquifer will cause the pumping level to creep up and down,
- Interference from a nearby well/s
- A pump beginning to show signs of wear will pump less water causing the pumping level to rise,
- A leak in the water distribution system will create a pressure drop the pump to move more water will see the pumping level drop,
- Mineral and bio adversities within some aquifers can start to build up on the well screen impeding the passage of water moving through the screen will cause the Pumping Level to begin to creep downward.
MONITORINGAs we delve further into How a Well Works we have discussed Well Design, Flow Testing, Base Marks and Pumping Level. Knowing and understanding these characters of a well is required to track a number of important functions pertaining to your well and aquifer. A simple monitoring program will always keep you up to date of changes, some subtle and some aggressive that maybe be occurring in your well, pumping system and aquifer. Knowing as much as you can about your well will often allow you to see trouble manifesting long before it becomes a serious problem, where in many cases, the owner can schedule necessary maintenance in the near future but before there is a catastrophic breakdown at the most inconvenient time. Tracking water levels and water quality in an aquifer is most important since the aquifer is the very entity that keeps everything going.
WELL MAINTENANCEMost wells will need some form of Maintenance in their life span. Properly designed wells that are drilled into aquifers that have ideal conditions may not need to be serviced for 30 or more years while wells drilled into unfavorable aquifers may need servicing within their first year of operation. The most concerning well problem in the Fraser Valley that occurs is “Biofouling” which is most often related to “Iron Bacteria” that is present in some aquifers. Iron Bacteria begins to slowly build up on the well screen, blocking the slot openings which begins to impede the flow of water as it moves into the well screen. A downward creeping Pumping Level is a tell tail sign of Biofouling that often occurs in wells that are completed in iron laden aquifers. If an Iron Bacteria problem is not dealt with in a timely matter an actual “Bio Mass” begins to form working its way back into the aquifer creating severe problems.To remedy this problem, a service rig is often used to redevelop the well on a rehabilitation program where mechanical surging and, often, chemicals are used to break down the Biofouling to restore the water passage way through the screen. If left to long without servicing a Bio-foul Mass will grow beyond the screen area and back into the aquifer where eventually the energy produced by the redevelopment equipment will be unable to reach all of the Bio Mass. Wells that are prone to Biofouling conditions that are frequently serviced will outlive wells that are left too long between services. The Pumping Level will continue to creep downward and not return to original level in neglected wells that the service work has not been able to remove all of the bio-foul. There is no exact time on how long it takes for a well to Bio-foul. In rare occasions, a well can Bio-foul in a year or so to where many iron laden wells take several to many years before servicing is necessary. Wells completed in ideal aquifer conditions may never need servicing for Biofouling problems. Monitoring the Pumping Level will soon reveal problems that may or may not be occurring in their well.
SPECIFIC CAPACITY“Specific Capacity” is a number attained by dividing the “Pumping Rate” x the Drawdown in a well. For example, a well being pumped at 100 GPM and achieves 50’ of “Drawdown has an S.C. of 2. This value relates to Gallons per Foot of Drawdown at a fixed pumping rate. The S.C. is the key that “Well Specialists” use to track well performance over time. Note that as the Pumping Rate changes so will the Specific Capacity. An increased flow rate will see the pumping level drop and the S.C value drop while as decreased pumping rate will see the Pumping level rise and the S.C. value increase. The drop in the Specific Capacities values are due to inefficiencies in the ability for water to move through the aquifer and well screen. Like any filter the efficiency drops as the velocity increases. This shows up in a Flow Test where the pump is run at various rates. The S.C. will change with the Pumping Rate.
We often perform what is known as a Step Flow Test where a well is pumped at about four different rates of about 30 - 60 minutes each. The Pumping Rates of the four Steps are usually aimed to achieve 20-40-60-80 percent of the Available Drawdown. The pump is started and runs continuously as the Steps increase. The S.C is calculated after each Step then the four values are plotted out. Each value will be less than the previous. The graph will reveal how the aquifer will perform at various Pumping Rates. This plays a large part in determining what level the permanent pump may be set along with a number of other functions of the well and aquifer. A wells current S. C. is compared to the well’s Base Marks to observe changes in well performance and final outcome of Well Rehabilitation work.SOUNDING TUBE
A well must be set up with Sounding Tube which is usually a 1” PVC pipe that is set during the pump installation. The tube is crucial to make way for monitoring equipment to make its way up and down the well.This is where the importance of Base Marks come into play. Newly downloaded monitoring data can be compared with the original data revealing changes that may have occurred in the well, pumping system and aquifer. The information from the new data will allow contractors to make informed decisions on how to deal with problems that may be occurring in the well. An early diagnoses will allow service work to be scheduled to a time when the well is scheduled to be down.
CONCLUSIONThe simple installation of a PVC sounding tube, recording the original Base Marks along with periodically monitoring a well will keep the owner informed of his/her well and aquifer performance while allowing the owner to see trouble coming and predict maintenance rather than wait for the system to stop working.