http://www.chinascreenpipe.com/Water Well Maintenance and Rehabilitation

The purpose of the study to obtained water well screens opening size and gravel packs size, and to access within the groundwater inter through the aquifer to the well screen and prevent running sand from entering the well. The use of properly designed screen and gravels are important and this paper is an important reference for the design of groundwater wells. In this study, the purpose of the circle method is to design water well and the benefits of sand control. The determination of screen slot size and its variation in the opening is often a major aim of hydrogeological studies. However, measurement of hydraulic conductivity (K) at a high spatial resolution in sedimentary aquifers is a challenge. One commonly used approach is to estimate slot size from grain size analysis. The objectives of this study are to compare between curve of grain size analysis, bar graph and circle method used applied different formulas for the determination of slot size from grain-size data and to evaluate how well this method predicts slot size and gravel pack. Correlation between the mechanical analysis curve, bar graph and the circle methods were found for the used applied different formulas. Based on circle results, the applied circle formulas appear to be suitable for an initial assessment of aquifer properties. However, considering the difference in calculated aquifer parameter values, results are smaller significantly and reliable for the high analysis of aquifer materials.

The well screen is the component of a well which provides an opening through which water enters the well casing from the aquifer, as well as stabilizing the material in the “near-well zone” and preventing it from entering the well. Screens may be constructed with a variety of different materials and designs, as appropriate to the design of the well and its aquifers. Typical types of screen are:

Horizontal bridge slot screen, a pipe-based well screen with punch-formed downward facing louver-shaped openings.

Continuous wire wrap screens, manufactured by wrapping shaped wire around an internal array of rods.

Bridge slot screens, produced by rolling and welding perforated steel plates or sheets.

Machine-slotted (milled) screens, manufactured by milling casing with axially oriented precision cutters.

Well casing perforated in place with a mills knife or a hydraulic perforator lowered down the cased borehole.

Different wedge wire screen may by evaluated for a particular well design based on the material, size of perforations, percent of open area, cost, susceptibility to corrosion, and collapse strength. A properly designed screen allows sand-free water to flow into the well with a minimum drawdown.

As a water well ages, the rate at which water may be pumped (commonly referred to as the well yield, flow or performance) tends to decrease, especially in wells that were not properly developed when first drilled. This fact sheet briefly describes common well problems and discusses prevention and rehabilitation measures.

Water Well Maintenance

Water wells require regular maintenance to ensure adequate water flow and continued drinking water safety. To ensure water quality, well water should be tested annually for total coliform bacteria and E. coli bacteria by a state accredited testing laboratory.

Every three years, additional testing is recommended for pH and total dissolved solids as well as tests related to land uses occurring or expected to occur within sight of the well. Additionally, if there are obvious stains, tastes, or odors in water, seek testing that will help identify the source of these symptoms.

Water wells should also be inspected annually for obvious signs of damage or contamination. Be sure the area within 100 feet around the continuous slot screen is clear of debris or items that might pollute the water supply.

Get the well professionally inspected by a water well contractor every ten years. Keep all records related to the water well including:

Water well completion report or log (if you have it) which should include information such as water well depth, date drilled, construction (including casing specifications, grouting and screen), and water well yield or flow rate in gallons per minute (gpm)

Water quality test reports

Past inspection reports

Invoices from work done by water well contractors (including pump replacement)

Water treatment equipment warranties, invoices and manuals

To find some of this information you can check with the Pennsylvania Department of Conservation and Natural Resources (PA DCNR) Pennsylvania Groundwater Information System (PaGWIS) or contact a local well driller.

Well Performance

As a water well ages, the rate at which water may be pumped (commonly referred to as the well yield, flow or performance) tends to decrease, especially in wells that were not properly developed when first drilled. A drop or complete loss of water production from a well can sometimes occur even in relatively new wells due to a lowered water level from persistent drought or over-pumping of the well which can dewater the water-bearing zones. More often, reduced well yield over time can be related to changes in the water well itself including:

Incrustation from mineral deposits

Bio-fouling by the growth of microorganisms

Physical plugging of “aquifer” (the saturated layer of sand, gravel, or rock through which water is transmitted) by sediment

Sand pumping

Well screen or casing corrosion

Pump damage

This fact sheet briefly describes these common problems and discusses alternative prevention and rehabilitation measures.

Water Well Rehabilitation

Measures taken to correct these problems are referred to as well rehabilitation or restoration. A successful well rehabilitation will maximize the flow of water from the well. The chances for successful rehabilitation are dependent on the cause(s) of poor well performance and the degree to which the problem has progressed.

Upon noticing loss of performance in your well have a professional water well contractor inspect your well, preferably with a downhole camera.

A common measure of the delivery of water by a water well is referred to as the “specific capacity” which is defined as the pumping rate (gallons per minute) divided by the drawdown or increased depth to water during pumping (in feet).

Generally, a decrease of 25% or more in well yield indicates that rehabilitation is in order. Delaying rehabilitation procedures can significantly increase costs and in some cases make rehabilitation impossible.

To detect deterioration of well performance, you must have a point of reference. Often this reference is the original well construction and pump test data which are normally supplied to you by the well driller on a well completion report or well log when the well is installed. However, even if you do not have this information, significant changes in your well are also a warning sign.

The principal means used for rehabilitation of chemical incrustation problems involves the use of strong acid solutions to dissolve incrusting materials.

Once loosened or dissolved, the incrusting materials are pumped from the well with the acid solution for disposal.

The type of acid to be used, its form (liquid, granular, pelletized), the procedures used to introduce and agitate the acid solution, and the severity of incrustation all play a part in determining the success of acid treatment. It is common for acid-treated older wells to completely recover or even exceed the original well yield assuming any material dislodged by the acid is removed from the pre-packed well screen.

While acid treatment methods for incrustation removal are very effective, mechanical methods, such as wire brushing or scraping, are often used in conjunction with acid treatment to improve results.

A less common mechanical approach is the use of controlled blasting. Controlled blasting involves the use of explosives, carefully set at specific locations in the well bore, to fracture consolidated rock aquifer and incrusting materials. Experience has shown this technique, when done properly, to be useful for temporary well yield improvement. However, cracks opened by blasting often eventually become incrusted and additional rehabilitation measures are required to maintain well productivity.

Rapid growth of these bacteria can quickly clog well screen pores and render a well virtually useless in a matter of months. Once iron bacteria become established in a well, they are extremely difficult to eradicate.

Treating iron bacteria colonies in water wells is often a perpetual process that seeks to maintain well performance at an acceptable level. In general, chemical means of control are most effective. However, best results are achieved when chemical bactericides are used in conjunction with physical agitation of the well bore water to remove the biological residue.

The chemical of choice for most small diameter wells is chlorine. It has the advantage of being readily available, inexpensive, and is generally accepted by health officials for use in potable water supplies. For general disinfection purposes following routine well and piping construction, repair, or pump installation, a 50 mg/L dose of free chlorine is recommended. For treatment of severe iron bacteria problems concentrations as high as 500 to 2,000 mg/L are used.

However, chlorine treatment of iron bacteria problems may not be effective without subsequent agitation of the well water. Turbulent flow causes greater surface area exposure of slime growths to the chlorine solution and assists in dislodging obstructions.

For more information on how to shock chlorinate a well, consult our fact sheet Shock Chlorination of Wells and Springs or contract with a professional well driller.

Since precipitation of iron in the bacteria biomatting contributes to clogging of flow spaces, rehabilitation results are usually improved when acid treatments are alternated with bactericide treatments.

The most important preventative measure to avoid physical plugging is proper well development. Adequate well development will stabilize the aquifer material so that subsequent pumping from the well will not result in excessive sediment removal. Removal of fine silt and clay particles introduced in some drilling fluids, or which naturally occur in certain kinds of aquifers, can only be accomplished with the use of chemical treatments.

As with other chemical rehabilitation treatments, agitation of the chemical into and out of the aquifer formation is crucial to success of the operation. This agitation may be provided by a surge plunger, compressed air, well pump, or high-velocity jet.

Use of a high-velocity jet is generally recognized as the most effective means of agitation. When water from the well is re-circulated for jetting, sediment should be removed prior to reuse. Continuous removal of dislodged sediment, as done in a re-circulating jet operation, gives the best results as the cleaning solution is able to penetrate more deeply into the aquifer medium.