Oklahoma Administrative Code
Title 785 - Oklahoma Water Resources Board
Chapter 35 - Well Driller and Pump Installer Licensing
Subchapter 7 - Minimum Standards for Construction of Wells
Section 785:35-7-2 - Minimum standards for construction of monitoring wells and geotechnical borings

(A) Drilling equipment. Drilling equipment shall be decontaminated if contamination is encountered in the well or borehole.

(B) Drilling procedures. Drilling procedures shall be carried out in such a manner that will prevent or minimize contamination.

(C) Construction material. All construction material shall be in a condition that will prevent or minimize contamination.

(A) The diameter of boreholes for monitoring wells, with the exception of boreholes for unsaturated zone monitoring wells, shall be at least three inches greater than the nominal diameter of the well casing and screen for the entire length of the casing.

(B) The diameter of boreholes for unsaturated zone monitoring wells shall be at least one and one-half (1 1/2") inches greater than the nominal diameter of the well casing for the entire length of the casing.

(A) All wells shall be cased. Casing material shall be selected according to groundwater geochemistry, anticipated lifetime of monitoring program, well depth, parameters to be monitored and other site specific considerations.

(B) When PVC casing is used, the casing shall meet or exceed the standard dimension ratio (SDR) of twenty-one (21).

(C) The minimum diameter for monitoring well casing shall be a nominal two (2) inches, with the exception of casing for unsaturated zone monitoring wells. The minimum diameter for unsaturated zone monitoring well casing shall be a nominal one-half inch. Methane gas probes at solid waste management sites shall be exempt from minimum casing diameter requirements.

(D) The casing shall be connected by flush threaded joints or have the ability to be connected by another mechanical method that does not introduce pollutants into the well. Glued joint casing shall not be used when monitoring organics.

(E) The casing joints shall be made water tight by a method that does not introduce pollutants into the well (e.g. wrapping the casing joint with Teflon tape or placing an o-ring or gasket in the joint).

(A) All wells shall be screened and screen material shall be selected according to groundwater geochemistry, anticipated lifetime of monitoring program, well depth, parameters to be monitored and other site specific considerations, provided that the minimum screen depth shall be two and one-half feet (2 1/2') below the land surface, provided further that the minimum screen depth shall be two feet (2') below land surface for tank pit monitoring wells at tank locations regulated by the Oklahoma Corporation Commission.

(B) The well screen shall be factory wire wrapped or factory slotted. Well screens shall not be field slotted.

(C) Slot size shall be selected to prevent or minimize infiltration of the filter pack through the well screen.

(D) Screens shall be of sufficient length to detect, monitor or otherwise describe the contaminant plume according to site specific conditions (e.g. seasonal water level fluctuations). Screen length shall be determined so that commingling of fluids from separate groundwater zones does not occur.

(E) Screen joints shall be placed in the well in such a manner as not to interfere with the accurate investigation of the groundwater quality.

(A) All wells shall be have a filter pack and aggregates used for filter pack shall consist of uncontaminated quartz sand, silica or other material that will not affect the groundwater quality.

(B) Filter pack shall be selected to prevent or minimize infiltration of the geologic formation (e.g. fines migration or sand buildup).

(C) Filter pack shall extend two (2) feet above the top of the screen unless such extension would allow vertical communication of pollution through the filter pack.

(D) Filter pack shall be placed in the annulus of the well in such a manner that bridging of the filter pack material will not occur.

(E) When water or vapor levels being monitored are encountered within five (5) feet of the land surface, the filter pack shall extend a minimum of 0.5 feet above the top of the screen.

(A) Sealing material. All sealing materials shall be compatible with ambient geological, hydrogeological and climatic conditions, as well as any man-induced conditions anticipated to occur during the life of the monitoring well. Any cement used as a sealant shall be equivalent to or have the same properties as ASTM C-150 cement types I-V (commonly known as Portland cement).

(B) Filter pack seal. A minimum of two (2) feet of sodium bentonite pellets, chips or granules of no less than 0.25 inches and no more than 0.75 inches in size shall be placed immediately over the filter pack in each site assessment observation well or monitoring well and properly hydrated.

(C) Annular seal. The annular space above the filter pack seal shall be filled with a cement grout, bentonite grout, bentonite chips or a cement/bentonite grout mixture to within two (2) feet of the surface. The cement grout shall have a mix ratio of one 94 pound sack of cement to a maximum of six U.S. gallons of water. The cement and water must be mixed to the proper consistency as recommended by the cement manufacturer before the mixture is installed around the casing. A maximum of twenty percent (20%) bentonite by dry weight may be added to the cement grout to form the cement/bentonite grout mixture. The bentonite shall be prehydrated to the manufacturer's recommended consistency. The bentonite grout shall be a high solids bentonite grout with at least twenty percent (20%) bentonite by dry weight. The bentonite shall be mixed according to the manufacturer's recommended consistency.

(D) Surface seal. A concrete or cement grout surface seal shall be placed around the casing immediately above the annular seal from a depth of two (2) feet to land surface.

(E) Tremie requirements for grout. When the placement of grout will exceed twenty (20) feet, the grout shall be placed in the annulus of the well through a tremie pipe and filled or pumped from the bottom upward.

(F) Multiple cased or screened wells. No adjacent or collinear casings in the same borehole shall be allowed. No multiple screened intervals in the same casing shall be allowed. Wells shall be drilled with sufficient distances between them so as to prevent the commingling of aquifer zones.

(G) Special annular, filter pack, and surface seal conditions. When water or vapor levels being monitored are encountered within five (5) feet of the land surface, the required depths set forth in C and D above for the filter pack and annular seals shall be reduced to fill the annular space from the top of the filter pack materials to the bottom of the cement surface seal, provided that the minimum screen depth shall be two and one-half feet (2 1/2') below the land surface, provided further that the minimum screen depth shall be two feet (2') below land surface for tank pit monitoring wells at tank locations regulated by the Oklahoma Corporation Commission. The surface seal shall extend a minimum of one (1) foot below land surface.

(A) A concrete or cement surface pad shall be installed around the casing at the surface with minimum dimensions of 3 feet in diameter by 3.5 inches thick.

(B) The surface pad shall be sloped so to insure that all surface water flows away from the well.

(C) The surface pad is not required if the well is completed in competent concrete or asphalt paving, or if the well is an unsaturated zone monitoring well or a site assessment well that is located in a proposed solid waste disposal site and neither is used for a period exceeding one (1) year.

(A) A threaded or flange cap or compression seal shall be installed upon completion of the well to prevent unauthorized use of the well (e.g. tampering with the well or the entrance of foreign material into the well).

(B) The cap or seal shall have the capability of being locked if the well is flush mounted and the well protector is not capable of being locked.

(A) An aluminum or steel surface casing shall be set a minimum of 12 inches through the cement or concrete surface pad and shall extend a minimum of 24 inches above the pad or ground. The top of the protective casing shall be fitted with a locking cap and shall be marked to clearly identify the well as a monitoring well or site assessment observation well; or

(B) If flush mounting is required, then the well shall be completed with a well protector that is capable of supporting vehicular traffic, provided that flush mounting of the casing of monitoring wells installed at concentrated animal feeding operations after July 1, 2006, shall be prohibited. The well protector shall be raised a minimum of one-half (1/2) inch above the surface pad or paving and shall be clearly marked to identify the well as a monitoring well or site assessment observation well. The surface seal shall be sloped so that surface water flows away from the well protector and the bond between the well protector and the removable cover shall be made watertight.

(A) Monitoring wells and piezometers that are installed using direct push (DP) technology shall comply with the applicable standards in 785:35-7-2 for reporting, casing, screening, filter pack, filter pack placement, filter pack seal, development, decontamination, surface seal, cleaning, protection, marking, and completion.

(B) DP monitoring wells and piezometers shall be authorized as applicable at the discretion of the state or federal agency having jurisdiction over a specific site.

(C) DP monitoring wells and piezometers shall also comply with the following additional standards: