OAR 690-210-0340
Method of Placement of Unhydrated Bentonite


(1)

An upper oversize drillhole, four inches greater than the nominal inside diameter of the permanent well casing, shall be constructed to a minimum depth of 18 feet below land surface. The use of unhydrated bentonite as a casing seal shall not be allowed deeper than 200 feet below land surface. In the event that the materials penetrated by the oversize drillhole cave, or tend to cave, an outer temporary surface casing shall be used to case out the caving materials during construction of the oversize drillhole. The outer temporary surface casing shall be removed during seal installation and before completion of the well.

(2)

In the event groundwater is encountered during the construction of the oversize drillhole, only unhydrated bentonite chips manufactured to be 38 inch to 34 inch, pellets or tablets shall be allowed in the water-filled portion of the annulus. A maximum of 50 feet of water may be present in the sealing interval. Unhydrated bentonite shall be screened across a minimum 14 inch mesh screen prior to being placed in the water-filled portion of the annulus to minimize the introduction of bentonite dust into the seal interval. Unhydrated bentonite shall not be used:

(a)

In the water-filled portion of a temporary casing; or

(b)

If there is any uphole flow in the annular seal interval.

(3)

Unhydrated bentonite may only be used as an annular seal material below the water level in a well when the groundwater it comes in contact with does not exceed 800 parts per million (ppm) total dissolved solids (TDS).

(a)

Unhydrated bentonite may be used as an annular seal material in water supply wells exceeding 800 ppm TDS if the bentonite manufacturer provides documentation that their product can be used in water that exceeds 800 ppm TDS.

(A)

Prior Department approval is required before placement.

(B)

The bentonite manufacturer’s documentation and Department approval shall be submitted with the Water Supply Well Report as required in OAR 690-205-0210 (Well Report Required (Water Supply Well Log)).

(b)

In all cases, the TDS shall be reported on the Water Supply Well Report as required in OAR 690-205-0210 (Well Report Required (Water Supply Well Log)).

(c)

Regardless of the reported TDS, the quality of the water in the well shall not interfere with the proper hydration of bentonite.

(4)

After placement of the permanent casing, the annular space shall be filled to land surface with bentonite. The annular space shall be kept full of bentonite to land surface while drilling or driving casing. A calibrated sounding tape with weight shall be used continuously in the sealing interval during bentonite placement to measure fill rate and to check for and break up possible bridges.

(5)

Placement of bentonite shall conform to the manufacturer’s specifications and result in a seal that is free of voids or bridges. Care shall be taken to minimize the introduction of bentonite dust into the sealing interval.

(6)

The volume of sealing material required shall be calculated prior to seal installation. The calculated volume and actual volume used shall be reported on the water supply well report.

(7)

Unhydrated bentonite chip, pellet or tablet annular seals shall be hydrated from land surface with potable water prior to removing the drilling machine from the well site. The hydration shall begin once all of the bentonite annular seal material has been placed and shall end when the annular seal interval refuses to take more water or after at least one annular space volume of water has been placed.

(8)

Granular bentonite may only be used as an annular seal material in a dry annular space above the interval where water was first encountered. Granular bentonite shall not be screened or hydrated during placement.

(9)

Pour rate shall be two minutes or slower per 50 pound sack in the water-filled portion of the annulus.

Source: Rule 690-210-0340 — Method of Placement of Unhydrated Bentonite, https://secure.­sos.­state.­or.­us/oard/view.­action?ruleNumber=690-210-0340.

690‑210‑0005
Standards Apply to all Methods of Well Construction
690‑210‑0030
Placement of Water Supply Wells
690‑210‑0060
Explosives
690‑210‑0065
Hydrofracturing
690‑210‑0070
Injection Wells
690‑210‑0100
Mineralized or Contaminated Groundwater
690‑210‑0130
Sealing of Wells in Unconsolidated Formations Without Significant Clay Beds
690‑210‑0140
Sealing of Water Supply Wells in Unconsolidated Formations with Significant Clay Beds
690‑210‑0150
Sealing of Water Supply Wells in Consolidated Formations
690‑210‑0155
Additional Standards for Artesian Water Supply Wells
690‑210‑0160
Additional Standards for Filter Pack Wells with Surface Casing
690‑210‑0170
Additional Standards for Filter Pack Wells without Surface Casing
690‑210‑0180
Additional Standards for Driven or Jetted Wells
690‑210‑0190
Steel Casing
690‑210‑0200
Steel Casing Joints
690‑210‑0210
Plastic Casing
690‑210‑0220
Plastic Casing Joints
690‑210‑0230
Inner Casing
690‑210‑0240
Casing Shall be Centered
690‑210‑0250
Top Terminal Height
690‑210‑0260
Openings in the Casing
690‑210‑0270
Pitless Well Adapters and Units
690‑210‑0280
Access Ports, Dedicated Measuring Tubes and Airlines
690‑210‑0290
Liner Pipe
690‑210‑0300
Drill Cuttings or Chips
690‑210‑0310
Cement Grout
690‑210‑0315
Concrete
690‑210‑0320
Methods of Placement of Cement Grout or Concrete
690‑210‑0330
Unhydrated Bentonite
690‑210‑0340
Method of Placement of Unhydrated Bentonite
690‑210‑0350
Resumption of Construction Following Placement of Cement Grout
690‑210‑0360
Movement of Casing after Cement Grouting
690‑210‑0370
Well Test
690‑210‑0380
Disinfection of a Well
690‑210‑0390
Completion of Wells
690‑210‑0400
Construction of Dug Wells
690‑210‑0410
Buried Slab Construction
690‑210‑0420
Surface Curbing
Last Updated

Jun. 8, 2021

Rule 690-210-0340’s source at or​.us