Guidelines for Minimum Standards in Water Well Construction, Province of British Columbia — June 1982
Part 1
2. General Guidelines for Water Well Construction
2.1 Preamble
Before deciding on a procedure to follow in constructing a water well, two factors should first be considered (i) the type of well desired and (ii) the method of well construction to be used.
Water Wells can be broadly classified into five main types:
(a) Dug or Pit Wells
(b) Radial Collector Wells
(c) Naturally Developed Screened Wells
(d) Artificial Filter Pack Wells
(e) Open Hole — Partially Cased Wells
To help determine the type of well needed to obtain the amount of water required it is helpful to have information on subsurface conditions at a given site, including the character and the depth of water producing zones and of overlying formations and on the proximity of existing or possible future sources of pollution. This knowledge together with information on relative construction costs will assist in determining the best construction method to use.
Well construction methods are many and varied and range from simple digging with hand tools to the use of high speed sophisticated drilling equipment. The most common construction methods are listed below:
(a) Digging
(b) Boring
(c) Driving
(d) Jetting and Hydraulicing
(e) Cable Tool
(f) Conventional Fluid Rotary Drilling
(g) Reverse Circulation Drilling
(h) Air Rotary Drilling
(i) Down Hole Hammer
(j) Top Drive Air Rotary with Casing Hammer
Further details on types of wells and well construction methods are given in Appendix No. 9.
For those readers who are not conversant with well construction, and ground water development, there is a publication available which gives a brief introduction to the subject entitled Practical Information on Ground Water Development. Single copies can be obtained from the Ministry of Environment, Victoria, British Columbia.
2.2 Well Site Locations
A well should be located on higher ground so that the well head can be protected from normal flooding and surface drainage. Shallow wells should be located away from surface drainage ditches. The distance a well should be located from a possible source of contamination such as a title, field, septic tank, refuse dump, land fill, cemetery, effluent discharge, drainage ditch, etc., will depend on a number of factors. These factors include the nature and the source of contamination, the topography, topographic gradient, the hydrogeological conditions at the site area, nature of the aquifer (bedrock fractures, overburden, etc.), thickness of overlying impermeable beds if any, nature of the ground water flow system, the potential for dilution of the contaminant, the point in the ground water flow system where the well is to be located, i.e., is it in a ground water discharge zone or a recharge zone, is the well a flowing artesian, non-flowing artesian or water table well, etc.
In view of these factors which may vary from site to site, the selection of an arbitrary "standard" minimum distance at which a well should be located from a possible source of pollution, will not necessarily provide the required protection from well contamination.
Information about effluent disposal sites n a specific area can be obtained from the local Public Health Inspector. Specified "minimum distances" can be found in Sanitary Regulations and Sewage Disposal Regulations under the British Columbia Health Act.
Although Sanitary Regulation No. 421 under the British Columbia Health Act relates to minimum distances between a well and potential sources of contamination, of necessity this distance may be often unnecessarily conservative and therefore the drilling contractor should consult the local Public Health Inspector in the interpretation thereof where special circumstances prevail.
2.3 Sanitary Protection of Wells
All dug wells should have an effective seal with grout to a depth of 15 feet or within 3 feet of the bottom of wells less than 18 feet deep. The seat should be at least 4 inches thick around the upper steel or cement well casing. The well head construction must insure that no contaminant can enter the well. See also Section 11 of these guidelines.
All jetted or driven wells should have an effective surface seal of grout, however due to the method of well construction it may not be possible to provide an effective seal to a depth of 15 feet. Special care must therefore be taken in the siting of such wells constructed by these methods. Drilled well completions in general should follow the AWWA standard for deep wells to ensure contamination does not enter the well.The AWWA publication lists eleven types of drilled wells and gives details for construction and scaling to be employed for different conditions encountered.
As a general guide-line it is recommended that all drilled wells be constructed with a surface grout seal to a minimum depth of 15 feet. However, for any specific case the grout seal depth must be deep enough to prevent the entrance of surface water or undesirable subsurface waters into the well.
In cases where there is a possibility for contamination of wells drilled into bedrock or for drilled wells penetrating clay, hardpan or other relatively stable unconsolidated material, a cement grout seal is recommended which extends from surface through these formations and in the case of a bedrock well, extending 15 feet down into the bedrock.
For further information see Appendix No. 3 — 2. Grouting Materials and 3. Methods of Installation of Grout.
2.4 Artesian Conditions
Where flowing artesian conditions are known or expected within the drilling depth, a method of construction using casing should be adopted to the depth of the impermeable layer overlying the artesian aquifer. The casing should be adequately scaled in the impermeable layer so as to prevent surface and subsurface leakage from the artesian aquifer. The flowing well must be equipped with a valve to control the flow.
2.5 Water Well Drillers Report
The drilling contractor should obtain and record all information possible including the depth, the thickness, type of material and water yielding potential of formations encountered in drilling the well. A well log should be completed for all wells and test wells drilled in the Province on the approved Ministry of Environment well record form. Contractors are requested to submit copies of logs of all holes to the Ministry as soon as possible, together with any supplementary information obtained which, in the opinion of the contractor, should be considered in managing the ground water resource.
2.6 Drilling Fluids
Fresh non-polluted water must be used for all drilling fluid preparations. Drilling fluid additives should comply with industry standards and practices and should be applied and used as recommended by the manufacturer. No toxic or dangerous substances are to be added to the drilling fluid at any time. The quality of the drilling fluid should be maintained by the contractor to protect water-bearing and potential water-bearing formations penetrated in the bore hole. All water used in construction of the well or admitted to the well should contain a minimum 50 ppm (mg/L) chlorine.
2.7 Temporary Capping
Wells that will not be placed immediately into service or which will be left uncompleted for any period or which will be removed from service temporarily, should be capped with a water-tight welded locked or threaded cap or equipped with some other type of "vandal-proof" cover. Casing should be terminated not less than one foot above the surrounding ground surface and the well had should be constructed in such a manner to insure that no potential contaminant can drain back toward the well.
*Sanitary regulation No. 42 stipulates among other things that a well must be located at least 100 feet from any probable source of contamination. Readers are referred to this regulation or to the Health District for further details.
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