Feasibility Study of Liquid-Waste Injection into Aquifers Containing Salt Water, Wilmington, North Carolina: ABSTRACT

Abstract

An experimental system to inject liquid industrial waste into deeper sedimentary aquifers containing salt water was installed by Hercules, Inc., at Wilmington, North Carolina, in the spring of 1968, under a permit issued by the State Board of Water and Air Resources. The initial experimental system consisted of 1 injection well and 3 observation wells completed between depths of 850 and 1,050 ft, and 1 observation well completed in the next higher aquifer at a depth of about 700 ft. The injection zone is an aquifer consisting of sand layers and some thin beds of limestone interbedded with silty sand and sandy silt. The aquifer has low permeability and productivity. The water in the aquifer is salty, with a natural artesian head of about 65 ft above land surface. The system was placed in operation in May 1968, injecting the by-product from the manufacture of dimethyl terephthalate (DMT). The liquid, deaerated and filtered through 200-µ mesh screen, consisted of water containing acetic and formic acids with some methanol and having a pH of about 4. The maximum injection rate was about 200 gal/minute. The pressure in the injection and observation wells rose sharply during the first few months of operation. By September 1968, the waste had passed the observation wells which were only 150 ft from the injection well, making the system obsolete for observing the rate and direction of waste movement through the aquifer. By June 1969, the injection well had become plugged with sand, and a new system was designed. A new injection well and a part of the new observation-well system were completed and placed in operation in January 1971. One of the initial observation wells also was used for injection of part of the waste. Additional observation wells were added, and in 1972 the monitor system consisted of 6 wells completed in the injection zone at distances of 1,500-2,000 ft from the points of injection, 3 wells completed in the 700-ft zone, and 1 well completed in the 300-ft zone. The monitor system and data-collection program have provided much useful information on injection of this type of waste in relatively shallow sedimentary rocks. The long-term feasibility of such a system appears doubtful, as the aquifer does not appear to be sufficiently permeable to accept the waste at a continuing rate of 200 gpm. Considerable difficulty also has been encountered in maintaining the injection and observation wells. End_of_Article - Last_Page 1602------------