COMPARISON OF LYSIMETER TYPES IN COLLECTING MICROBIAL CONSTITUENTS FROM SEWAGE EFFLUENT

There are no standard methods of determining the impact of septic systems on contamination of groundwater aquifers. Sampling of water for microbiological properties in unsaturated soil is particularly difficult. Successful water sampling devices should collect large amounts of percolating water with minimal change in chemical and biological properties of the water. This laboratory study compared the effectiveness of four types of soil water sampling devices for qualitative sampling of water, using total coliform, fecal coliform, and fecal streptococcus as the primary indicators of water quality. The devices tested were: (i) high-flow ceramic tension lysimeter, (ii) high-flow fritted glass tension lysimeter, (iii) sand-filled lysimeters, and (iv) perforated-tube wells. A constant source of vacuum (0.01 MPa) was applied to all devices to collect water samples. High-flow ceramic tension lysimeters collected adequate volumes of water (an average of 0.340 L after 6 h) but excessive filtering led to underestimation of microbial numbers (only 6% of total coliform, 2.2% of fecal coliform, and no fecal streptococcus were collected). Perforated-tube wells did not collect any water under partially saturated soil conditions; collection occurred only below the water table. Sand-filled lysimeters showed the best combination of volume collection (an average of 0.660 L after 6 h) with good estimation of microbial numbers (90% for total coliform, 83% for fecal coliform, and 45% for fecal streptococcus).