DESIGN AND CONSTRUCTION OF SAND-BENTONITE LINER FOR EFFLUENT TREATMENT LAGOON, MARATHON, ONTARIO

A case history of the design and construction of the sand-bentonite li ner for an effluent treatment lagoon located in Marathon, Ontario, is presented. The results of hydraulic conductivity tests which were carr ied out on a series of trial mixes to measure the effects of varying t he proportions of silt supplement used as a void filler to the local s and material, and the proportion of bentonite are described. Laborator y hydraulic conductivity tests were carried out at a low effective str ess. After initial hydration of the mix with tap water, pulp mill effl uent was used as permeant fluid for a duration of 1 year to measure th e long-term stability of the trial mixes. In a few of the trial mixes, an increase in hydraulic conductivity with increasing passage of perm eant fluid was experienced. It was found that application of a small i ncrease in effective stress was sufficient to stabilize the performanc e of these test specimens and lower the hydraulic conductivity to a sa tisfactory value. A comprehensive testing program was carried out duri ng Liner construction to establish conformance to project requirements . This work included performance of single-stage borehole tests to est imate the in situ hydraulic conductivity of the constructed line, meth ylene blue tests to measure bentonite contents, and conventional compa ction-control testing. The results of the single-stage borehole test c onfirm its usefulness in assessing the performance standards of a rela tively thin (300 mm) sand-bentonite liner.