Section 33.1-18-02-08 - Monitoring well construction materials1. Riser. a. Specifications. The riser for a monitoring well must retain structural integrity for the duration of the monitoring period under actual subsurface conditions. (1) The riser and couplings must be constructed of materials that neither absorb nor leach chemical constituents that could bias representative ground water samples. The riser and couplings must be compatible, resisting corrosion, with anticipated contaminants. Depending upon the intended use of the well, the riser should have a vented cap, except wells constructed in a potential flooding condition or flush-mounted wells must not have a vented cap.(2) The riser must be capable of withstanding installation and development stresses without damage.b. Assembly and installation. (1) The interior and exterior surfaces of the riser and couplings must be thoroughly cleaned in a manner that does not conflict with the monitoring objective prior to assembly and installation.(2) The individual sections of the riser must be joined in a manner that neither absorbs nor leaches chemical constituents that could bias representative ground water samples.(3) The riser must be centered, as practicable, in the borehole.2. Screen. A ground water monitoring well must be constructed with a screen. a. Specifications. (1) A screen and bottom plug must be constructed of material that is nonreactive with constituents in soil and ground water at the monitoring location.(2) The screen must be capable of withstanding installation and well development stresses without damage.(3) The screen must be new, machine slotted or continuous wrapped wire-wound. The screen slots must not be hand-cut or wrapped with filter fabric, unless approved prior to installation by the department.(4) The screen slot size must retain and prevent at least fifty percent of the grain size of the collapsed formation or ninety percent of the filter pack from entering the screen.(5) The screen placement and length must allow for entry of ground water from a predetermined zone appropriate for the collection of representative ground water samples and future fluctuations of the water table.b. Assembly and installation. (1) The screen and bottom plug must be thoroughly cleaned, in a manner which does not conflict with the monitoring objective, prior to assembly and prior to insertion into the borehole.(2) The screen must be permanently joined to the well riser in a manner that neither absorbs nor leaches chemical constituents that could bias representative ground water samples.(3) The screen must be centered, as practicable, in the borehole.3. Filter packs. a. Specifications. When filter packs are used, they must be compatible with the purpose or objective of the monitoring well and have a specific gravity of two and one-half or greater. The filter pack grain size must minimize formation materials from entering the screen. Collapsed formation may be used as filter pack material if it limits passage of at least fifty percent of the formation to the screen.b. Installation. The filter pack should extend upward from the bottom of the screen to at least two feet [0.609 meter] above the top of the screen. Where shallow water tables occur, the required height of filter pack above the top of the screen may be reduced a maximum of one foot [0.304 meter] to allow space for the annulus sealant. In special cases where the potential for a cross-connection or commingling of different water-bearing zones is documented by the monitoring well contractor requiring less than a one-foot [0.304-meter] filter pack above the screen intake, a reduction in the filter pack to less than one foot [0.304 meter] above the top of the screen to meet site specific conditions is allowed.4. Filter pack seal. A ground water monitoring well must be installed with a filter pack seal. a. Specifications. The filter pack seal should extend at least two feet [0.609 meter] upward from the top of the filter pack. Where shallow water tables occur, the filter pack seal may be reduced a maximum of one foot [0.304 meter] to allow for annular space sealant. Sodium bentonite chips of size three-eighths-inch [0.95-centimeter] diameter or smaller should be placed in a manner which avoids bridging of the chips. Sodium bentonite chips or pellets must be used for seals placed below the water table, except in circumstances where the sodium bentonite may bias representative ground water samples.b. Installation. Sodium bentonite pellets, chips, or granules used as filter pack seal above a water table must be hydrated after placement.5. Annulus seal. A ground water monitoring well must be installed with an annulus seal. a. Specifications. (1) The annulus seal should extend from the top of the filter pack seal upward to the ground surface seal, and it should be at least two feet [0.609 meter] in length.(2) Grout material: (a) Should have an equal or lower permeability than the least permeable geologic formation penetrated by the borehole.(b) Should be compatible with formation material, well casing and riser and not capable of contaminating ground water.(c) Should be in a form which can be positively and accurately placed to fill all voids.(d) Should be self-leveling in the annulus and uniform in setup.(e) Should, when setup, assist the structural stability of the riser.(f) Should be capable of bonding to the riser and borehole wall to provide a watertight seal.(3) Acceptable grouts above the water table include neat cement, bentonite chips, high solids bentonite grout, or a cement and bentonite clay mixture not exceeding five pounds [2.27 kilograms] of bentonite clay per ninety-four-pound [42.6-kilograms] sack of cement.(4) Bentonite chips or pellets may be used as a seal material in the annulus of shallow monitoring wells provided it is hydrated after each bag is poured into the annulus.b. Installation. The annulus seal must be placed in a manner so as to ensure the proper placement and distribution of the sealant material.6. Ground surface seal and protective casing. a. A protective casing and locking cap is required when the monitoring well is located in an area where the well needs physical protection or is likely to be tampered with. (1) The protective casing should consist of a metal or polyvinyl chloride assembly at least two inches [5.08 centimeters] larger in diameter than the riser and have a locking cap.(2) The protective casing should extend from the bottom of the ground surface seal, and it should extend above the top of the riser at least one inch [2.54 centimeters] but not more than four inches [10.15 centimeters].(3) The locking cap should be secured and locked at all times when the monitoring well is not in use.b. The ground surface seal should consist of concrete or neat cement. If a protective casing is used, the surface seal should be placed around the protective casing and may not be placed between the protective casing and the riser. The ground surface seal should be sloped to promote drainage away from the riser or protective casing.c. Dry bentonite pellets or chips should be placed in the annular space between the protective casing and the riser up to the level corresponding with the top of the ground surface seal.d. A weep hole or vent should be used in the protective casing, provided it is placed at least six inches [15.2 centimeters] above the surface of the ground surface seal, but in no case should it be above a vent hole in the riser.N.D. Admin Code 33.1-18-02-08
Adopted by Administrative Rules Supplement 370, October 2018, effective 1/1/2019.General Authority: NDCC 43-35-19.2; S.L.2017, ch.199, § 1
Law Implemented: NDCC 43-35-19.2; S.L.2017, ch. 199, § 47