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D.C. Municipal Regulations (Last Updated: September 13, 2017) |
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Title 21. WATER AND SANITATION |
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Chapter 21-18. WELL CONSTRUCTION, MAINTENANCE, AND ABANDONMENT STANDARDS |
Section 21-1818. WELL CONSTRUCTION REQUIREMENTS: WELL GROUTING
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1818.1Except as provided in §§ 1818.2 and 1818.3, a person constructing a well with an annulus shall pressure grout the well in accordance with the grouting standards of this chapter.
1818.2The grouting of a monitoring well, observation well, piezometer, injection well, or recovery well shall not be required if all the following conditions are met:
(a)The un-grouted annulus exists above the anticipated water table;
(b)A low-permeable seal a minimum of two feet (2 ft.) thick is installed atop the filter pack;
(c)The upper terminus of the well is protected in accordance with § 1812.3;
(d)The well is not constructed or maintained in a manner that allows the vertical migration of contaminants in the aquifer;
(e)The well penetrates a single aquifer; and
(f)The well is abandoned within thirty (30) days of well completion in accordance with §§ 1830 and 1831.
1818.3The grouting of a dewatering well shall not be required if all the following conditions are met:
(a)The well is constructed to a maximum depth of twenty feet (20 ft.) below ground surface;
(b)The well penetrates a single aquifer;
(c)The well is constructed and maintained in a manner that does not allow the vertical migration of contaminants in the aquifer; and
(d)The well is abandoned within one-hundred and eighty (180) days of well completion in accordance with §§ 1830 and 1831.
1818.4The annulus of a well to be grouted shall be a minimum of one and one-half inches (1.5 in.) wide, or the diameter of the annulus shall be a minimum of three inches (3 in.) greater than the outside diameter of a well casing.
1818.5A low-permeability seal a minimum of two feet (2 ft.), but no greater than three feet (3 ft.) thick, shall be placed atop the filter pack to prevent surface water from entering the screened interval.
1818.6A sodium-based bentonite slurry grout shall be placed on top of the low-permeability seal and extend towards the ground surface with sufficient space to install the upper well terminus.
1818.7A request may be made to the Department in accordance with §§ 1803.10 and 1803.11 to deviate from the grouting standards of this chapter, provided the deviation does not result in a less protective standards than those set forth in this chapter.
1818.8A well shall be grouted as soon as feasible, but not later than twenty-four (24) hours after the well casing has been set in place, unless otherwise specified in the well construction building permit or well construction work plan authorized in accordance with the requirements of §§ 1803.10 and 1803.11.
1818.9If pressure grouting the annulus is not feasible during the construction of a monitoring well, observation well, or a piezometer, the well shall be grouted by pouring medium-size, sodium-based bentonite chips or pellets down the well annulus in a manner that prevents the bridging of the bentonite chips or pellets.
1818.10A well in which a permanent outer casing is installed shall be grouted in a manner that will allow the grout to set prior to the top of the inner casing being terminated below ground surface.
1818.11The material of a low-permeability seal shall sustain a hydraulic conductivity equal to or less than 1x10-7 centimeters per second (1x10-7 cm/s) and be comprised of:
(a)Sodium-based bentonite slurry:
(1)At a ratio of two (2) pounds of sodium-based bentonite powder to one (1) gallon of potable water; or
(2)At a mix ratio according to the manufacturer’s specifications, provided that the grout results in a low-permeability seal with a hydraulic conductivity equal to or less than 1 x 10-7cm/s;
(b)Sodium-based bentonite-cement at a ratio of one hundred fifty pounds (150 lbs) of bentonite powder to ninety-four pounds (94 lbs) of portland cement hydrated with eighty-two gallons (82 gal) of potable water;
(c)Hydrated, medium-size bentonite chips at a ratio of one (1) gallon of potable water to twelve and one-half pounds (12.5 lbs.) of medium-size, sodium-based bentonite chips or pellets; or
(d)Hydrated, specially-coated, medium-size bentonite pellets which allow a time-delayed reaction at a ratio of one (1) gallon of potable water to twelve and one-half pounds (12.5 lbs.) of medium-size, sodium-based bentonite chips or pellets.
1818.12Standards for grouting shall be as follows:
(a)Well grouting shall be performed to provide a water-tight seal against downward fluid migration along the well annulus into the filter pack, well screen, and surrounding aquifer;
(b)A sodium-based bentonite slurry mixture shall be installed by pumping the slurry mixture through a tremie pipe at least one inch (1 in.) in diameter using a positive placement technique;
(c)If a borehole diameter is not wide enough for a slurry mixture to be emplaced using a tremie pipe, the following sodium-based bentonite chips shall be used:
(1)Uncoated, sodium-based bentonite chips shall be used above the potentiometric surface, with a sufficient amount of potable water added to fully hydrate the chips; or
(2)Specially coated, time-release sodium-based bentonite pellets shall be used when several layers of pellets must be emplaced below the potentiometric surface of the well, with a sufficient amount of potable water shall be added to fully hydrate the pellets if there is insufficient groundwater entering the well;
(d)Sodium-based bentonite chips and pellets shall be sized according to the well diameter to be filled, and the chips or pellets shall be less than one fifth (1/5) the radial thickness of the annulus into which they are to be placed, except that medium or coarse sized chips may be used in well diameters from four inches (4 in.) to ten inches (10 in.);
(e)Sodium-based bentonite chips and pellets shall be placed within the borehole in a manner that prevents the bridging of the bentonite chips or pellets;
(f)Medium-size, sodium-based bentonite chips or pellets shall be used at a ratio of one (1) gallon of potable water to twelve and one-half pounds (12.5 lbs.) of medium-size, sodium-based bentonite chips or pellets as follows:
(1)The chips or pellets shall be pre-screened to remove fragments; and
(2)The chips or pellets shall be hydrated in accordance with the manufacturer’s specifications to ensure that the chips or pellets achieve a low-permeability seal with a hydraulic conductivity equal to or less than 1x10-7 cm/s;
(g)If an outer casing is required for a well penetrating a confined or multi-layer aquifer with the potential for aquifer cross-contamination, the space between the open borehole wall and the outer casing shall be pressure grouted, and the following shall be required:
(1)The annulus between the open borehole wall and the outer casing shall be pressure grouted;
(2)The outer casing shall be installed and pressure grouted a minimum of ten feet into the uppermost confining layer; and
(3)In the event the confining layer is less than ten feet (10 ft.) in thickness, the outer casing shall be pressure grouted entirely through the uppermost confining layer;
(h)All grout materials placed in the borehole shall be free of contaminants;
(i)All sand and gravel placed in the borehole shall be silica based and inert, unless a material other than silica is used in a commercially available product that is inert and meets all other grouting requirements;
(j)Drill cuttings or muds shall not be left in boreholes, or placed in the borehole as fill material and shall not be used as a grouting material; and
(k)All grout inserted into a well annulus for sealing purposes shall not be disturbed until the grout has fully set.
1818.13Grouting materials for unconsolidated formations shall meet the following requirements:
(a)Grout shall be fully hydrated and comprised of sodium-based bentonite, or a sodium-based bentonite-cement mixture comprised of a minimum of five percent (5%) and a maximum of ten percent (10%) sodium-based bentonite, and a minimum of ninety percent (90%) and a maximum of ninety-five percent (95%) cement;
(b)Cement shall be hydrated consistent with § 1818.14(a) of this chapter; and
(c)A sodium-based bentonite clay shall not be used if it may come into contact with groundwater with a known pH below five (5.0) or groundwater having a total dissolved solids content greater than one thousand milligrams per liter (1,000 mg/L).
1818.14Grouting materials for consolidated formations shall consist of the following:
(a)Portland cement or quick-setting cement in a ratio of no greater than six (6) gallons of water per ninety-four pound (94 lb.) sack of cement or as otherwise authorized by the Department in the well construction work plan;
(b)Sodium-based bentonite powder may be added to the cement grout in an amount of five pounds (5 lbs.) for each ninety-four pound (94 lb.) sack of cement; and
(c)When adding sodium-based bentonite clay to neat Portland cement grout, additional water shall be allowed at a rate of one (1) gallon of water to two pounds (2 lb.) of sodium-based bentonite powder.
1818.15The grouting of a closed-loop ground source heat pump well shall meet the following requirements:
(a)Approved sealing and filling materials shall include fully hydrated high solids sodium-based bentonite grout comprised of a minimum twenty percent (20%), but no greater than thirty percent (30%) of solids by weight, or approved high efficiency, thermally-enhanced grouts comprised of a maximum twenty percent (20%) by weight silica sand to powdered sodium-based bentonite;
(b)All grout shall meet the manufacturer’s specifications and the hydraulic conductivity of the low-permeability seal shall be equal to or less than 1 x 10-7 cm/s;
(c)The hydraulic conductivity value shall be derived by using American Society for Testing and Materials (ASTM) D-5084 and verified by an independent testing facility certified by American Association of State Highway & Transportation Officials, Materials Reference Laboratory to perform ASTM D5084 at the time of verification;
(d)The entire length of the borehole shall be grouted from bottom to top with sodium-based bentonite or thermally enhanced grout specifically designed to facilitate heat transfer and provide a low-permeability seal;
(e)Grouting shall be completed immediately after installing the geothermal loop or in case of extenuating field conditions, no later than twenty-four (24) hours after installing the geothermal loop;
(f)Open boreholes shall be protected as necessary to prevent the entry of surface water or pollutants;
(g)Boreholes with temporary casing shall be grouted during or before removal of casing depending on borehole stability;
(h)Boreholes with permanent outer casing shall be grouted and the grout shall be allowed to set before the top of the casing is terminated below ground level;
(i)Boreholes with no casing shall be looped and grouted immediately after drilling;
(j)When voids are encountered, including fractures in bedrock and degraded bedrock, the borehole shall be cased from below the void to the surface; and
(k)Boreholes drilled with a mud rotary drilling system in unconsolidated formations shall be looped and grouted immediately after drilling.
1818.16If the annulus cannot be grouted in accordance with this chapter, the well shall be abandoned in accordance with §§ 1830 and 1831.
1818.17The Department may impose additional requirements pertaining to the grouting of a well in the well construction building permit to ensure the protection of public health and safety and the environment.