250 R.I. Code R. 250-RICR-150-05-3.22

Current through November 7, 2024

Section 250-RICR-150-05-3.22 - Construction Standards for Monitoring Wells and Abandonment Procedures for Private Drinking Water Wells, Monitoring Wells, Piezometers and Other Subsurface Borings

A. Purpose: Provide minimum standards for the construction of monitoring wells for the procurement of samples representative of groundwater and abandonment procedures for private drinking water wells, monitoring wells, piezometers and other subsurface borings.

B. Applicability:

1. The construction standards apply to monitoring wells installed pursuant to these rules. The construction standards shall not apply to drinking water wells or other subsurface borings that are used for purposes other than monitoring groundwater quality.

2. The abandonment procedures apply to private drinking water wells, monitoring wells, piezometers and other subsurface borings that intersect the seasonal water table at some time of the year.

C. Prevention of Groundwater Pollution: During well construction and abandonment, every appropriate precaution shall be taken to prevent introducing pollutants into the groundwater. This shall include, but not be limited to, steam cleaning and washing of drilling equipment and proper cleaning and storage of well casing. Only unpolluted water shall be used in well construction and abandonment unless otherwise approved by the Director.

D. Deviation from the Standards: The Director may waive the requirements and allow deviation from these procedures where such deviations will result in procurement of representative groundwater samples or, in the case of well abandonment, will not result in a reasonable potential for groundwater pollution.

E. Drilled Wells: Monitoring wells constructed using conventional drilling methods shall be installed in accordance with the requirements below. Monitoring wells completed into bedrock without a well screen (open bore hole) are exempt from the requirements of §§ 3.22(E)(3), (4) and (5)(a) of this Part, but must comply with all other requirements in § 3.22(D) of this Part. Bedrock monitoring wells shall have a well casing extending a minimum of 5 feet into the bedrock.

1. Borehole Diameter: The borehole diameter in the overburden shall be a minimum of 4 inches greater than the diameter of the well casing.

2. Well Casing (or Riser): The well casing shall be constructed of PVC material. Monitoring wells less than 100 feet in depth shall be constructed using a minimum of schedule 40 PVC. Wells greater than 100 feet deep shall be constructed using a minimum of schedule 80 PVC. The Director may allow alternate well casing material if the pollutant concentrations or geologic setting require an alternative construction. Alternative materials include, but are not limited to: Teflon, stainless steel, or uncoated or galvanized steel.

a. Assembly and Installation: All casing shall be constructed of flush threaded joints or threaded coupling joints. All joints shall be fitted with an "O" ring or wrapped with teflon tape. Glued or solvent welded joints are not permissible without prior written permission of the Director.

b. Cap: The well casing shall be fitted with a plug or cap.

3. Well Screen: The well screen slot size shall retain at least 90% of the grain size of the filter pack or at least 90% of the grain size of the collapsed formation when no filter pack is used in accordance with § 3.22(E)(4) of this Part. Well screens shall not exceed the length necessary to collect a representative groundwater sample. Well screens shall be factory slotted or continuous wrapped wire-wound. A bottom cap and sump sediment trap shall be installed.

4. Filter Pack: The filter pack shall be clean, chemically inert, well rounded and well sorted glass beads or silica-based sand or gravel of uniform grain size. The filter pack must minimize the amount of fine material entering the well and shall not inhibit the flow of water or movement of pollutants into the well. The filter pack shall be installed by bottom-up tremie methods. The filter pack shall extend from 6 inches beneath the bottom of the well screen to a distance above the well screen equivalent to 20% of the well screen but not less than 2 feet. A collapsed formation may be used as the filter pack if the well screen retention requirement of § 3.22(E)(3) of this Part is met and a filter pack cannot be installed.

5. Sealing Requirements

a. Filter Pack Seal: All monitoring wells installed with a filter pack shall be constructed with a filter pack seal of bentonite pellets or slurry in a manner that does not disturb the filter pack. The seal shall extend to approximately 3 to 5 feet above the filter pack and shall be properly hydrated and set.

b. Annular Space Seal: All monitoring wells shall be installed with an annular space seal using neat cement, neat cement-bentonite mixture, bentonite slurry or bentonite that is properly hydrated and set. Granular bentonite in dry form or powdered bentonite in dry form shall not be used in the saturated zone. The annular space seal shall extend to the ground surface seal, except where a road box meeting the requirements of § 3.22(E)(7) of this Part is used.

c. Ground Surface Seal: All monitoring wells shall be constructed with a continuous pour concrete ground surface seal. To avoid frost heaving and to anchor the well, the ground surface seal shall extend to a minimum of 40 inches below the land surface, unless the seal would interfere with proper placement or functioning of the well screen or a road box is installed in accordance with § 3.22(E)(7) of this Part. The ground surface seal shall be flared such that the diameter at the top is greater than the diameter at the bottom. The top of the ground surface seal shall be sloped away from the well casing and shall be large enough to allow drainage away from the well.

6. Protective Casing: The protective casing shall consist of a minimum 4 inch diameter metal casing with locking cap. The protective casing shall extend from the bottom of the ground surface seal to a minimum of 24 inches above the land surface, allowing for 4 to 6 inches clearance between the top of the well casing and the cap of the protective casing. A 1/4 inch diameter drain hole shall be drilled into the protective casing 6 inches above the ground level. Dry bentonite pellets, granules or chips shall then be placed in the annular space below ground level within the protective casing. Coarse sand or washed pea gravel or both shall be placed above the dry bentonite to a depth covering the drain hole. A high visibility guard post may be required. The Director may request additional protective devices as necessary.

7. Road Box: Road boxes are acceptable in locations where protective casings installed in accordance with § 3.22(E)(6) of this Part are not suitable. All road boxes shall be secured and water tight and shall prevent easy access to the well. The well casing shall be fitted with a locking, watertight cap. The ground surface seal for the road box shall be competent such that vehicle traffic will not cause it to fail. The annular space seal shall extend upward to 1 foot below the ground surface seal. Permeable material shall be emplaced between the ground surface seal and the annular space seal in order to allow for the drainage of runoff which may leak into the road box from the ground surface. The road box cover plate shall clearly indicate that the well is a groundwater monitoring well.

8. Well Development: Development of all monitoring wells shall be performed no earlier than 24 hours after completion and before the initial water quality samples are taken. Well development shall continue until the water has stable pH, temperature, and specific conductivity readings and has turbidity values less than 5 NTUs (nephelometric turbidity units). If a well does not meet the goal of 5 NTUs, it must be demonstrated to the satisfaction of the Director that proper well completion and well development have been employed. Groundwater sampling shall not occur until at least 24 hours after well development, in order to allow natural groundwater flow to be re-established.

9. Monitoring Well Designation: Each monitoring well shall be clearly and permanently labeled as a monitoring well with the well number using such techniques as etching in the protective casing or in the cement of the ground surface seal.

F. Single Rod Direct Push Wells: Wells installed using single rod direct push methods shall be installed in accordance with the requirements below:

1. Annular space seal -- If the screen and riser are of the same diameter and are advanced such that they remain in contact with the formation during installation (exposed screen wells) no annular space seal is created. If the drive rod is smaller in diameter than the sampler body (protected screen wells) an annular space is created that must be sealed in accordance with § 3.22(E)(5)(b) of this Part above;

2. Ground surface seal shall be constructed in accordance with § 3.22(E)(5)(c) of this Part;

3. Protective casing or road box shall be installed in accordance with §§ 3.22(E)(6) or (7) of this Part, respectively. In order to provide a locking, water-tight cap on a small diameter well casing in a road box as required by § 3.22(E)(7) of this Part, a 2 inch PVC casing can be placed over the well riser extending 3 to 4 feet below grade;

4. Well must be developed in accordance with § 3.22(E)(8) of this Part; and

5. Well shall be properly designated in accordance with § 3.22(E)(8) of this Part.

G. Two-tube Direct Push Wells: Monitoring wells installed using two-tube direct push methods create an annular space the length of the well, thus requiring a filter pack, seals and other provisions similar to conventional drilled wells. Two-tube direct push wells shall be installed in accordance with the requirements below:

1. The outside diameter of the borehole shall be a minimum of 1 inch greater than the outside diameter of the well casing;

2. Well casing (or riser) shall meet the requirements of § 3.22(E)(2) of this Part;

3. Well screen shall meet the requirements of § 3.22(E)(3) of this Part;

4. Filter Pack: The filter pack shall be clean, chemically inert, well rounded and well sorted glass beads or silica-based sand or gravel of uniform grain size. The filter pack must minimize the amount of fine material entering the well and shall not inhibit the flow of water into the well. The filter pack shall be installed by bottom-up tremie methods, or it can be a pre-packed manufactured unit. A collapsed formation may be used as the filter pack if the well screen retention requirement of § 3.22(E)(3) of this Part is met and a filter pack cannot be installed.

5. Grout Barrier: All direct push monitoring wells installed with a filter pack shall be constructed with a grout barrier immediately above the screened interval to prevent annular space sealants from entering the screened interval. The grout barrier shall extend a minimum of 2 feet above the screened interval. The grout barrier may be constructed by gravity or tremie installation of fine sand, or by installation of a modular system. Alternatively, collapse of the natural formation may be used to create a natural barrier when the formation material is of appropriate grain size and cohesion.

6. Filter pack seal shall be constructed in accordance with § 3.22(E)(5)(a) of this Part;

7. The annular space shall be sealed in accordance with § 3.22(E)(5)(b) of this Part or a modular system may be used;

8. Ground surface seal shall be constructed in accordance with § 3.22(E)(5)(c) of this Part;

9. Protective casing or road box shall be installed in accordance with §§ 3.22(E)(6) or 3.22(E)(7) of this Part, respectively;

10. Well must be developed in accordance with § 3.22(E)(8) of this Part; and

11. Well shall be properly designated in accordance with § 3.22(E)(9) of this Part.

H. Abandonment of Private Drinking Water Wells, Monitoring Wells, Piezometers and Other Subsurface Borings

1. Private drinking water wells, monitoring wells, piezometers and other subsurface borings shall be abandoned in accordance with this Rule. or alternate procedures approved in writing by the Director prior to abandonment. Abandonment shall take place within 60 days after use has been terminated or within a timeframe approved by the Director.

2. Abandonment Procedures for Monitoring Wells and Borings Constructed with an Annular Space:

a. The borehole shall be inspected from the land surface through its entire depth before it is sealed, to ensure against the presence of any obstructions that will interfere with sealing operations.

b. The casing shall be removed by pulling or overdrilling. If the casing cannot be removed, the screen and casing shall be suitably perforated from top to bottom allowing for the plugging material (see § 3.22(H)(2)(c) of this Part) to penetrate the annular space and formation. If the casing remains, it shall be cut off at least 4 feet below the ground surface where practicable.

c. The remaining casing or borehole shall be filled with neat cement or neat cement grout applied under pressure.

3. Abandonment Procedures for Monitoring Wells and Borings Constructed without an Annular Space:

a. The borehole shall be inspected from the land surface through its entire depth before it is sealed, to ensure against the presence of any obstructions that will interfere with sealing operations.

b. If the casing is to be removed, the remaining borehole shall be filled with neat cement or neat cement grout applied under pressure.

c. If the casing remains in the ground, it shall be cut off at least 4 feet below the ground surface. The remaining casing shall be filled with neat cement or neat cement grout applied by bottom-up tremie methods.

250 R.I. Code R. 250-RICR-150-05-3.22

Adopted effective 1/9/2019
Amended effective 12/28/2023