OAR 690-220-0115: Unhydrated Bentonite and Method of Placement

(1) When abandoning a pre-existing well with unhydrated bentonite the Water Supply Well Constructor shall provide additional notification to the Regional Well Inspector or the Well Construction Program Coordinator in Salem by fax, e-mail or telephone 72 hours prior to starting abandonment work. (a) In case of an emergency, the additional notification is not required; however, the Water Supply Well Constructor shall notify the Department prior to beginning abandonment work as required in OAR 690-205-0200. (2) Unhydrated bentonite used in the abandonment of water supply wells shall meet the following requirements: (a) Specifically designed for use in water supply wells; and (b) Within industry tolerance for dry western sodium bentonite; and (c) Free of polymers that promote bacterial growth; and (d) Manufactured to be 3/8-inch or 3/4-inch; and (e) National Sanitation Foundation (NSF) approved or have a swell index greater than 15 milliliters (ml) per 2 grams (gm). (3) Powdered bentonite, bentonite grout or bentonite slurry shall not be used to abandon water supply wells. (4) Unhydrated bentonite shall only be used to abandon water supply wells when in contact with water having less than 800 parts per million (ppm) total dissolved solids (TDS). (a) Unhydrated bentonite may be used to abandon 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. (b) In all cases, the TDS shall be reported on the Water Supply Well Report as required in OAR 690-205-0210. (5) Water supply wells with casing that is at least four inches in diameter and less than eight inches in diameter may be abandoned with unhydrated bentonite to a maximum well depth of 700 feet, if being placed through water. Unhydrated bentonite may be used deeper with prior Department approval. (6) Water supply wells with casing that is at least four inches in diameter and less than eight inches in diameter may be abandoned with unhydrated bentonite to a maximum well depth of 1000 feet, if being placed through air. Unhydrated bentonite may be used deeper with prior Department approval. (7) Water supply wells with casing that is at least eight inches in diameter may be abandoned with unhydrated bentonite to a maximum well depth of 1200 feet, if being placed through water. Unhydrated bentonite may be used deeper with prior Department approval. (8) Water supply wells with casing that is at least eight inches in diameter may be abandoned with unhydrated bentonite to a maximum well depth of 1500 feet, if being placed through air. Unhydrated bentonite may be used deeper with prior Department approval. (9) Unhydrated bentonite shall be screened across a minimum 1/4-inch mesh screen during placement to minimize the introduction of bentonite dust into the sealing interval. The resulting seal shall be free of voids or bridges. (10) A sounding or tamping tool shall be used in the sealing interval during placement to measure the fill rate and to break up possible bridges or cake formations. (11) Unhydrated bentonite shall be poured at the manufacturers recommended rate in the water- filled portion of the drillhole and shall not be less than two minutes per 50 pound sack. (12) In a dry sealing interval, (above the water level), bentonite shall be hydrated from land surface to a minimum depth of 50 feet below land surface. Unhydrated bentonite shall be hydrated with potable water in maximum ten foot lifts to ensure activation. (13) The estimated and actual volume of sealing material used shall be calculated and reported on the Water Supply Well Report as required by OAR 690-205-0210.