Design Criteria And Construction Standards

Design Criteria And Construction Standards. The Licensee shall be responsible for compliance with all applicable state and federal statutes and regulations. A. Water Wells and Boreholes Penetrating Aquifers In General Use For Domestic and Public Water Supply – The standards contained herein are the minimum construction standards considered necessary for the protection of the state’s high-quality groundwater resources. Other regulatory programs may be applicable and additional standards may be required for certain types of facilities, such as Mississippi State Department of Health regulations governing public supply wells. If a water well contractor encounters geologic formations or unusual circumstances that appear to dictate a deviation from the standards, the contractor shall consult with MDEQ staff regarding proposed construction procedures for the water well or borehole in question. (1) Construction Standards – The following construction standards apply to wells and boreholes penetrating water bearing strata including but not limited to, potable water wells, irrigation wells, monitoring wells, observation wells, underground discharge wells, dewatering wells, saline or brackish water withdrawal wells, contaminant recovery wells, heat pump water supply holes and vertical closed- loop system holes, industrial supply wells, cathodic protection wells, rig supply wells and geotechnical boreholes: (a) All water wells and boreholes covered under this section shall be constructed by a licensed water well contractor unless specifically exempted by statute. (b) Well casing shall terminate not less than twelve (12) inches above natural ground elevation or, where practicable, above the 100-year flood elevation. However, if flood levels around the well routinely exceed a reasonable height for an extended casing above the twelve (12) inch minimum, then the well shall be fully sealed with a Braden Casing Head, or approved equivalent, to prevent the flow of flood waters into the casing. The casing head shall contain a screw-in plug with a minimum diameter of one-half (1/2) inch to provide access for water level measurements. If the casing is not covered with a recorder box or pump housing, then it must have a locked, overlapping cover or other suitable cover capable of preventing unauthorized access to the casing head and access plug. (c) Public water supply wells shall have the top of the well casing set at least one (1) foot above the 100-year flood level. (d) All wells shall have a check valve installed in the discharge line to prevent the intentional or accidental introduction of contaminants into the well. All new unmetered wells larger than six (6) inches in diameter shall have a minimum of four (4) feet of straight pipe installed between the casing head and the check valve, and all other equipment, valves, pressure relief valves, vacuum breakers, and distribution systems shall be connected on the discharge side of the check valve. (e) All wells, except approved underground discharge wells as specified in paragraph o. below, shall be constructed in such a manner that the finished ground elevations around the casing are sloped to drain away from the casing. Equipment such as engines, pressure tanks, or fuel tanks to be installed shall be placed on pre-cast concrete blocks or pads to prevent differential settlement that could result in damage to the pump and the well. (f) The annular space on all wells covered by this section of the regulation shall be grouted from a depth of at least ten (10) feet below the surface to the surface, except as specified in paragraphs g, i, j, k, l, m, o, and p below. (g) Wells located within one hundred (100) feet of a potential source of pollution such as sewers, septic tanks, landfills, and waste and raw material piles shall be grouted from a depth of at least fifty (50) feet below the land surface to the surface, except as specified in paragraphs h, i, j, k, l, n, and o below. (h) Potable water wells shall not be constructed within 100 feet of any potential source of pollution. (i) Wells located within one-quarter mile of a known existing area of contaminated aquifer shall be grouted from the top of the water bearing stratum to the ground surface, or the top of the casing for underground discharge wells. (j) Outer casing for wells serving public water supply systems shall be grouted from the top of the target water bearing stratum to the ground surface. (k) monitoring wells shall be grouted from the top of the seal or filter pack to the ground surface, unless a more stringent requirement is mandated by other applicable regulatory programs. Specifics of monitoring well construction shall follow the most stringent requirements of the applicable regulatory programs. (l) Cathodic protection wells shall be grouted from a depth of fifty (50) feet below ground surface to the ground surface. Wells constructed with granular material such as gravel from the top of the anodes to near the surface are prohibited. If wells are no longer used, the vent pipe, casing or other non-grouted openings shall be grouted from a depth of at least ten (10) feet below the ground surface to the ground surface. (m) For continuous lengths of grout not separated by multiple screens, grout shall be introduced in one continuous operation from the top of the water rearing stratum to the ground surface. (n) Grout for all holes covered under this section shall consist of either neat cement, cement grout, cement-bentonite mixture (5-8% bentonite), or bentonite. Bentonite pellets or bentonite chips may be added under free-fall conditions for depths not exceeding twenty-five (25) feet. Free-fall addition of any other type grout from the surface is prohibited. Granulated or pelletized bentonite may be placed to greater depths only if introduced through a tremie pipe. (o) All wells, regardless of size, which are drilled through or into aquifers containing chloride concentrations in excess of 250 milligrams per liter (mg/l) and/or total dissolved solids (TDS) concentrations in excess of 1000 milligrams per liter (mg/l), must be completed using metal casing. Furthermore, all such wells shall be completed using only the casing method of grouting (Halliburton method) to grout thoroughly the annular space from the bottom of the casing to ground surface or to the top of the casing for underground discharge wells. (p) Outer casing for underground discharge domestic wells shall be grouted from a depth of at least ten (10) feet below the top of the casing at the underground discharge head, or pitless adapter, to the top of the casing. (q) Public water supply wells shall be constructed in such a manner that any column/casing vents and blowoff valves are properly screened. (2) Disinfection (a) All water used in the drilling or construction process and in well development shall be clean and free of impurities that could contaminate water bearing sands penetrated by the well or borehole. For construction and development of a potable water well, water shall be obtained from a groundwater source of proven quality such as a domestic well or a public water supply system. If the water is obtained from a local public water supply distribution system, it need not have additional chlorine added during the drilling and/or construction process; otherwise, the water shall be chlorinated. A residual of free chlorine of not less than 5 parts per million (ppm) shall be maintained in any water used for well development. (b) Gravel to be placed in potable water wells shall be disinfected with a solution of at least 50 mg/l free chlorine. (Clean pre-packaged gravel is exempt from this requirement.) (c) Upon completion of drilling potable water wells, the well and adjacent aquifer shall be disinfected using a solution of at least 50 mg/l free chlorine applied for at least 24 hours. The procedure shall meet or exceed the American Water Works Association (AWWA) Standard current at the time of the activity. (d) After disinfection, the potable water well shall be pumped until a chlorine free sample is collected from the well. The sample also must be free of coliform bacteria. Samples shall be collected, submitted, and analyzed in accordance with applicable Mississippi State Department of Health requirements. B. Water Wells and Boreholes Constructed in the Mississippi River Valley Alluvial Aquifer (MRVA) – The MRVA is a uniquely situated shallow aquifer used almost exclusively for agricultural irrigation with very little potential of increased demand for domestic or public water supply. Because of the unconsolidated nature of the material and the predominant agricultural water use, the drilling technique in general use for large diameter irrigation wells in the MRVA is reverse circulation rotary drilling. Consequently the standards for construction and disinfection have been modified slightly to reflect the water usage and drilling practices in the MRVA. If a water well contractor encounters geologic formations or unusual circumstances that appear to dictate a deviation from the standards, the contractor shall consult with MDEQ staff regarding proposed construction procedures for the water well or borehole in question. (1) Construction Standards – The following construction standards apply to irrigation wells screened and completed in the MRVA and to boreholes that do not penetrate the base of the MRVA, including but not limited to, irrigation wells, monitoring wells, observation wells, and geotechnical boreholes: (a) All water wells and boreholes covered under this section shall be constructed by a licensed water well contractor unless specifically exempted by statute. (b) Well casing shall terminate not less than twelve (12) inches above natural ground elevation or, where practicable, above the 100-year flood elevation. However, if flood levels around the well routinely exceed a reasonable height for an extended casing above the twelve (12) inch minimum, then the well shall be fully sealed with a Braden Casing Head, or approved equivalent, to prevent the flow of flood waters into the casing. The casing head shall contain a screw-in plug with a minimum diameter of one-half (1/2) inch to provide access for water level measurements. If the casing is not covered with a recorder box or pump housing, then it must have a locked, overlapping cover or other suitable cover capable of preventing unauthorized access to the casing head and access plug. (c) All wells shall have a check valve installed in the discharge line to prevent the intentional or accidental introduction of contaminants into the well. All new unmetered wells larger than six (6) inches in diameter shall have a minimum of four (4) feet of straight pipe installed between the casing head and the check valve, and all other equipment, valves, pressure relief valves, vacuum breakers, and distribution systems shall be connected on the discharge side of the check valve. (d) All wells, except approved underground discharge wells, shall be constructed in such a manner that the finished ground elevations around the casing are sloped to drain away from the casing. Equipment such as engines, pressure tanks, or fuel tanks to be installed shall be placed on pre-cast concrete blocks or pads to prevent differential settlement that could result in damage to the pump and the well. (e) The annular space on all wells covered by this section of the regulation shall be grouted or sealed with bentonite from the lowest level of disturbed earth immediately adjacent to the casing down to a depth of at least ten (10) feet below that level, except as specified in paragraphs of. and g. below. (f) Wells located within one hundred (100) feet of a potential source of pollution such as sewers, septic tanks, landfills, and waste and raw material piles shall be grouted from the lowest level of disturbed earth immediately adjacent to the casing down to a depth of at least fifty (50) feet below that level, except as specified in paragraph g. below. (g) Wells located within one-quarter mile of a known existing area of contaminated aquifer shall be grouted from the lowest level of disturbed earth immediately adjacent to the casing to the top of the water bearing stratum. (h) Grout for all holes covered under this section shall consist of either neat cement, cement grout, cement-bentonite mixture (5-8% bentonite), or bentonite. Bentonite pellets or bentonite chips may be added under free-fall conditions for depths not exceeding twenty-five (25) feet. Freefall addition of any other type grout from the surface is prohibited. Granulated or pelletized bentonite may be placed to greater depths only if introduced through a tremie pipe. (2) Drilling Fluids and Disinfection (a) All water used in the drilling or construction process and in well development for non-potable water wells in the MRVA shall be dosed to a minimum concentration of fifty parts per million (50 ppm) of chlorine, i.e., two (2) gallons of sodium hypochlorite (laundry bleach, approximately five percent (5%) available chlorine) per one thousand (1000) gallons of drilling water. (b) The licensee shall denote on the driller’s log portion of the State Well Report the location of the source of any surface water used as well as the method of dosing and the volume of chlorine used in the drilling and development of a non-potable water well in the MRVA. (c) Equipment used in the transport, storage, or circulation of surface water during the drilling and development of a non-potable water well in the MRVA shall not be used thereafter in the drilling and development of a potable water well without having first been disinfected with a solution of at least fifty parts per million (50 ppm) free chlorine for a minimum contact time of twenty-four (24) hours.