Geological Survey Professional Paper Volume 491 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. Excerpt: ...plants in the greasewood tanks, however, did not show any symptoms indicating boron toxicity. The backwashing evidently had not been as effective in the rabbitbrush tanks as in the greasewood tanks, or the greasewood plants had a greater tolerance to boron than rabbitbrush. The latter explanation seems more appropriate. These symptoms of boron toxicity indicated that the rabbitbrush tanks needed to be backwashed a second time. Backwashing of all three tanks was completed in early April 1966. Sampling of the soil in the tanks to determine the reduction of its boron content as leaching progressed was not practicable. Collection of soil samples at depth would have been exceedingly difficult and facilities for analytical determinations were not available at the site. In lieu thereof, the specific conductance (in micromhos at 25C) of the effluent water was used as a measure of the effectiveness of the treatment. The volume of water used for leaching and the rate at which it was added to each tank was measured with water meters. As soon as the soil mass in each tank was saturated, a 5-foot extension was attached to the supply pipe of the tank to provide a head for the upward movement of water through the soil. The rate of flow through the soil was not the same for all tanks of equal surface area; however, an approximately uniform flow through each tank was achieved by a rate of inflow adjusted to maintain a head of about 5 feet above the surface of the tank. The rate of inflow to greasewood tank 1 and rabbitbrush tank 1 in October 1962 was less uniform than the rates for greasewood tank 2 and rabbitbrush tanks 1, 2, and 3 in April 1963 and 1966. The difficulty was due largely to the low temperatures during the night causing ice to form on the surface of the tanks and ...