A compact high efficiency combined biological and physical unsaturated wastewater treatment filter configured for periodic backwashing is disclosed. There are provided tear strips and tab members to assist in removing the tear strips which delaminate. A switching circuit selectively couples the preamplifier output to an amplifier output stage and also couples a feedback loop between the selected amplifier output stage and the preamplifier stage. A second coil on the logging tool is pulsed with a carrier signal having this frequency and modulated by a CPMG sequence to obtain spin echo signals.