Water Stewardship

Guidelines for Minimum Standards in Water Well Construction, Province of British Columbia — June 1982

Part 2 — Technical Information Appendices

APPENDIX 3: WELL GROUTING

1. Requirements

1.1 Grouting can be defined as filling a void with an impervious material.

1.2 Grouting is required for:

(a) aquifer protection: to stop ground water movement between aquifers and to maintain ground water quality;

(b) well protection: to stop unwanted water entering from the surface or a subsurface zone;

1.3 It is most important that the annular space between formation materials and outer casing be sealed to a sufficient depth (15 or more feet, depending on conditions) to prevent contamination or pollution by surface waters or shallow subsurface waters where there may be effluent from septic tanks, etc.

1.4 Polluted formations encountered during well construction which are yielding ground water of undesirable quality must be adequately sealed off from underlying (or overlying) water-bearing zones.

2. Grouting Materials

2.1 Cement based materials can be used as grout. Neat cement (cement and water), sand cement, and concrete are generally easily obtained and mixed. Concretes find application where space to be filled is substantial for example, in some dug wells etc.

2.2 Clay should only be used as a sealant in well construction when drying out and washing away cannot occur. Clay is defined in these guidelines as bentonite or equivalent commercial slurry, or puddled, clay. Do not use clay when:

(a) sealant will be in contact with the aquifer;

(b) when strength and stability are required;

(d) when flowing or moving water may break down the sealant;

(e) when cement grout is specified to be used as stated in these guidelines.

2.3 Concrete grout is mixed in the proportion of at least five (5) bags of Portland cement per cubic yard of concrete to not more than six (6) US gallons of clean water per bag (one cu. ft. or 94 lbs.) of cement.

2.4 Sand cement grout is mixed in the proportion of not more than two parts by weight sand to one part of Portland cement with not more than six (6) US gallons of clean water per bag (one cu. ft. or 94 lbs.) of cement.

2.5 Neat cement grout is mixed in the proportion of not more than six (6) US gallons of clean water per bag (one cu. ft. or 94 lbs.) of cement.

2.6 Additional Notes*

Better flow characteristics can be produced by using cement additives, rather than excessive water which may weaken the grout. "A combination of 5% Bentonite and 95% cement establishes a better seal than pure cement, because Bentonite prevents cement from shrinking when it sets. Bentonite improves the flow of cement grout if it is to be pumped. Fly Ash keeps cement grout stable longer. It prevents the cement and water from separating.

Both Bentonite and Fly Ash are-known as "Pozzolans" (things which keep finely divided solids in suspension) and may be used almost interchangeably. Unpolished aluminum powder mixed with cement and water causes the mixture to expand.

Use 1/8 oz. unpolished aluminum powder, 4 or 5% (by weight) of Bentonite or Fly Ash, 41/4, to 6 US gallons of water, all per sack (94 lbs. or one cu. ft.) of cement. Mix the aluminum powder with the dry bentonite first; mix this with the dry cement and then add the water.

Calcium chloride added to cement shortens its setting time. Use 217, by weight. Above 4% will destroy the quality of cement.

"Thoro" Waterplug Cement is designed to set under water and is especially useful for creating impervious bottom plugs in a hole.

"Type 3 Cement" is the name given to "high early" which means high strength with an early set.

Cement does not always set, sometimes a chemical reaction with certain mineral waters prevents it. Bring in fresh clean water to make the grout especially if a "salt" well is to be plugged".

2.7 Cement grouting and Thermoplastic Water Well Casing: When a Portland cement based grout cures, a by-product of the process, the heat of hydration, may subject the thermoplastic water well casing to higher temperatures, which can cause a reduction in strengths of plastic casings. Several steps can be taken to minimize temperature increases during grouting, such as circulation of cool water inside the casing, addition of bentonite to the cement grout etc. When bentonite is added to the grout (say 5% by weight) the curing time is increased. This in turn reduces the rate at which heat is generated during the setting of the cement grout.

*From Manual of Water Well Construction Practices — Oregon Drilling Association Inc.

3. Methods of Installation of Grout

3.1 General Considerations

Positive emplacement of grout by tremie, pumping or pressure is strongly recommended for all wells where the void space is not easily accessible from the ground surface, or where waste disposal wells are being constructed or where the casing has been drawn or where the well has been drilled by jetting or hydraulicing method.

The annular space for positive emplacement methods is to be a minimum of 11/2 inches for sand and cement or neat cement grout.

Before grouting the annular space should be flushed to make sure the void is open and ready for grouting.

Where grouting is to exceed 100 feet in total depth, the collapse strength of the casing should first be checked.

The annular space should be filled in one operation and should be completed before the occurrence of the initial set.

Grouting should always be introduced at the BOTTOM of the space to be grouted so as to avoid segregation or bridging.

Grout placement by dump bailer, or by gravity installation without the aid of a tremie or grout pipe should only be used if the interval to be grouted can be seen clearly and is dry and less than 30 feet in total depth below ground surface to ensure adequate visual observation. Bad subsurface water quality zones should be grouted five feet above and below the zone. The annular space surrounding the casing between grouted zones should be filled with sand.

Grout should only extend to within one foot of a pitless adapter or unit casing connection.

Centralizers are required to maintain a minimum annular space where a complete seal is required. Centralizers should be mandatory at the bottom of an irrigation well. In community water supply wells centralizers should be placed in the bottom of the hole and at other critical points.

3.2 Methods of Drilled Well Construction to Provide an Adequate Grout Seal Around the Well Casing

Drilled wells constructed with a surface seal in overburden it is recommended be constructed by first drilling and installing a surface casing of a diameter 4 inches larger than the finished well. In formations where the hole can be kept open the surface casing may not be necessary and a 4 inch oversized open hole can be drilled instead. The annular space between the surface casing or open hole and the permanent inner casing can then be filled with grout. The surface casing can be withdrawn as the grout is placed.

In cases where there is a possibility for contamination of wells drilled into bedrock or drilled wells penetrating clay, hardpan or other relatively stable unconsolidated material, a cement grout seal is recommended which extends from the surface through these formations and in the case of a bedrock well extends 15 feet down into the bedrock.

This cement grout seal in the bedrock well for example, can be achieved by first drilling and installing an oversized casing 4 inches larger in diameter than the finished well, down to the bedrock. The oversized hole is then continued as an "open hole" into the bedrock below the casing to the minimum 15 foot depth. The permanent inner casing is then installed to the bottom of the oversized open bedrock hole. The annular space between the outer casing or open hole and the permanent inner casing is filled with cement grout. The outer casing can be withdrawn as the grout is placed.

3.3 Methods of Grouting the Annular Space Surrounding a Well Casing*

Grout Pipe Outside Casing

If the annular space is of sufficient size to accommodate a grout pipe of such diameter as is necessary to complete operations in the time available, use of such pipe is satisfactory, in fact perhaps the most fool-proof method of grouting. The pipe should extend to the bottom of the annular space initially and should remain submerged in grout during the entire time that grout is being placed. The pipe may be left in place, or it may be gradually removed. In the event of interruption in the grouting operations, the bottom of the pipe should be raised above the grout level and should not be resubmerged until all air and water have been displaced from the grout pipe. The grout may be pumped into the pipe or applied continuously by gravity, although this method of placing grout is not advocated for depths in excess of 100 ft. or where the grout level cannot be readily determined by sampling or by displacement calculations. A minimum width of 11/2 in. is necessary to accommodate a 1/2 in. coupled minimum size grout pipe.

Grout Pipe Inside Casing

A second method of applying grout employs a pipe installed within the casing. The drill hole is plugged below the bottom of the casing, or the grouting operation is conducted when the drill hole has been completed to the depth at which the casing is to terminate. A suitable packer connection, permitting removal of the grout pipe and preventing grout leakage into the interior of the casing pipe, is provided at the bottom of the casing. The casing is suspended slightly above point of bearing, and the grout is forced upward through the annular space by means of pumps or pneumatic pressure arrangements. When the annular space has been filled to the overflow point, the grout pipe is disconnected and pulled out through the casing pipe. The casing may be held in place or lowered to the point of bearing. In deep settings the casing pipe should be kept full of water. After 72 hr. or longer, work on the well may be resumed by drilling out the grout pipe packer connection and plug. When the well is drilled by the rotary method, the grout may be forced into the annular space in a manner similar to that described above, except that the grout is applied through the hollow drill stem.

Halliburton Method

A third method of grouting is that employed by the Haliburton Oil Well Cementing Co. who hold certain patents thereon. With this method the grout is applied through the casing pipe, being preceded and succeeded by a "spacer" or piston plug." In brief, the first plug is inserted and the casing capped; a measured amount of grout is applied; the second plug is inserted and the casing capped; a measured volume of water is pumped into the casing until the second plug reaches the end thereof. The first plug drops into the drill hole below the casing, which is suspended sufficiently to provide clearance, while the grout moves upward into the annular space. Neat cement grout is normally used with this method.

*From AWWA Standard for Deep Wells See also Sanitary Protection of Wells in Part 1 of these guide-lines.

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