Abstract: A method of removing contaminants from a contaminated soil area in situ comprises the steps of placing a barrier in engagement with the exposed surface of the contaminated soil area, sealing the barrier around the periphery of the contaminated soil area and reducing the pressure beneath the outer layer of the barrier to draw the contaminants out of the soil. The barrier is comprised of an outer fluid impermeable layer and an inner fluid permeable layer. The edges of at least the outer layer of the barrier are sealed by digging a trench in the uncontaminated soil beyond the periphery of the contaminated soil area, inserting the edges of the barrier into the trench, refilling the trench and compacting the fill against the ends of the barrier. A liberating fluid may be injected into the soil beneath the contaminated soil area through a plurality of conduits inserted into the soil at acute angles.

Abstract: A method of transmitting half-sinewave ultrasonic monopulses utilizes a flip-flop (22) to reverse the states of a bridge circuit (Q.sub.1 -Q.sub.4) with each output pulse from a timing pulse generator (20). This reverses the polarity of a dc voltage which stresses a piezoelectric transducer (24) to substantially its limit. Each pulse from the timing generator thus causes one mechanical transition of the transducer and clamps it in its reversed stress condition, thereby producing a half-sinewave ultrasonic output for each timing pulse.

Abstract: A method and apparatus for locating and mapping a pool of a pollutant (12) in a body of water (11) comprising the steps of scanning the bottom of said body of water with ultrasonic energy using a transducer (10) periodically pulsed to project pulse envelopes of acoustic energy downwardly to the bottom (14) of the body of water and receiving echo returns from the bottom preceded by echo returns from a reflective interface (13) with a pool of pollutant, if present. The presence of an echo return from an interface (13) as a precursor to an echo return from the bottom indicates the presence of the pool of pollutant at the navigational position of the transducer as the process of scanning continues. Locating and marking the perimeter of the pool permits rapid clean up operations to be directed.