(1) All ground water monitoring wells must be constructed by a licensed monitoring well constructor pursuant to 37-43-302, MCA, to the standards contained in ARM 36.21.801 through 36.21.808, and as required by this section, so as to obtain representative static water level data and ground water samples.   An owner or operator may request from the department a waiver of the requirements listed in this rule for wells already constructed by the date of implementation of this rule.   However, this waiver can only apply to wells previously approved by the department.

(2) Water samples may not be collected from piezometers unless constructed to specifications for standard monitoring wells.

(3) Drilling fluids and water may be used to drill monitoring wells only when there are no reasonable alternatives. If drilling fluids are used, the owner/operator shall document the type of fluids, any additives used and the chemical constituents of the mixture.   If water is used, the source of water shall be identified.

(4) Drill rigs and all downhole equipment must be cleaned in accordance with technically accepted procedures prior to initiation of drilling on site.   If site investigation is conducted at an existing landfill facility, then the rig and all downhole equipment must be decontaminated prior to the first borehole and between each borehole.

(5) When drilling equipment comes into contact with probable contaminants in the borehole or above ground, the driller shall thoroughly decontaminate the equipment prior to any additional drilling.

(6) A hydrogeologist, qualified ground water scientist, or other qualified person shall:

(a) observe and direct the drilling of all borings, the installation and development of all wells and all in-field hydraulic conductivity tests;

(b) demonstrate their competency in hydrogeology by submitting to the department a statement of qualifications before commencing work; and

(c) visually describe and classify all of the geologic samples derived from boring and well cuttings or samples.

(7) All monitoring wells must be constructed:

(a) to minimize the potential for contaminants to enter the ground water or to move from one major soil unit or bedrock formation to another;

(b) with a difference of 3 to 5 inches between the outer diameter of the casing/screen and the inner diameter of the surface of the borehole to facilitate placement of the filter pack, as well as annular sealants; and

(c) with grout or other seal material extended down to within 5 feet of the zone being monitored.

(8) All ground water monitoring wells shall have caps to prevent contaminants from entering the monitoring device.   All monitoring wells shall have protective outer casings and locking lids. The lids shall be kept locked.   The department may require additional protective devices such as rings of brightly colored posts around any monitoring device.

(9) All monitoring wells shall be clearly and permanently labeled and water level measuring points clearly marked.   At a minimum, the label shall include the well name and number.

(10) All ground water monitoring wells must be properly developed to remove fine soil particles, drill cuttings and drilling fluids from the vicinity of the well screen. After development the ground water must be tested for pH, temperature, specific conductance and total suspended solids.   If liquid drilling fluids were used during well construction, a sample must also be tested for chemical oxygen demand. After development, all wells must be repeatedly measured for static water level until stabilized measurements are obtained.

(11) Ground water monitoring well information must be reported on department approved forms. The department will provide forms for reporting ground water monitoring well construction, boring log information, well development, and other ground water monitoring information as required by the department, including:

(a) the type, diameter, length and elevation of the top of the protective casing;

(b) the grout used as a surface seal between the well casing and the protective casing, including the depth and width of surface seal below the land surface, the height and width of the plug above the land surface;

(c) the type of cap and lock mechanism;

(d) the well casing material, length, diameter, schedule, and type of joints;

(e) the screen material, length, diameter, schedule, slot type and size, percent open area, and type of screen bottom;

(f) the distance the filter pack extends above the screen;

(g) the thickness of the filter/gravel pack (i.e. the spacing differential between the outer diameter of the casing/screen and the inner diameter of the surface of the borehole) ;

(h) local datum or mean sea level elevations of the top of casing and land surface to plus or minus 0.05 feet, depth from the land surface to an elevation of the bottom of the borehole, the bottom of the well screen, and top and bottom of all seals; and horizontal well locations identified by the landfill coordinate system to the nearest ten feet;

(i) the filter pack material, including grain size analysis, quantity of packing material used and manufacturer and product name or number;

(j) the drilling fluid including additives or water added during drilling;

(k) the drilling method used, type of drill rig, borehole diameter, inside diameter of the hollow stem auger, if used, cleaning procedures, and the date the well was drilled; and

(l) the date the well was developed, development method, time spent developing the well, volume of water removed and added during development, source of development water, the clarity of water before and after development, presence of sediment at the bottom of the well before and after development, and volume of water purged.

(12) Requirements for drilling are as follows:

(a) In order to create a stable, open, vertical well hole for installation of the well screen and riser, one of the following drilling methods must be utilized, listed in decreasing order of preference:

(i) Drilling with hollow stem augers is the most preferred method.

(ii) Air rotary drilling with an oil filter/trap.

(iii) Cable tool methods and other percussion tool drilling may be attempted in hard, consolidated formations.

(iv) Reverse circulation drilling is preferred to wet rotary drilling.

(v) Wet rotary drilling with clean water only and insertion of temporary flush-joint casing, with consideration being given to the procedures used to prevent mixing of upper zones with lower zones.

(b) Continuous soil sampling or sampling collection at five foot intervals and lithologic changes should be performed.

(c) All materials used in construction must be free of chemicals, paint, coatings, etc., that could leach.   Decontamination of all downhole assemblies must be performed, using steam or an appropriate alternative.

(d) When assembling a well screen, riser, and sampler, there must be a stable borehole.   The order of steps to complete the well must be:

(i) assembly of well screen and riser;

(ii) setting the well screen;

(iii) placement of the filter/gravel pack;

(iv) placement of the seal;

(v) grouting of the annular space;

(vi) well protector;

(vii) installation of the [dedicated] sampler.

(e) Well development must be continued until representative formation water, free of the effects of well construction, is obtained and the specific conductance, temperature, and pH have stabilized.

(13) The department hereby adopts and incorporates by reference ARM 36.21.801 through 36.21.808, which contain standards for construction of water wells.   Copies of ARM 36.21.801 through 36.21.808 are available from the Department of Environmental Quality, PO Box 200901, Helena, MT 59620-0901

[(406)444-1430].