Performance of Vadose Zone Monitoring Equipment for Land Treatment Facilities.

Soil pore-liquid monitoring is required beneath landfills and hazardous waste treatment facilities to identify hazardous constituents.  However, similar monitoring is requested beneath food processing land application facilities for nutrients.   Monitoring objectives for land application facilities with crops should focus on mass balance of water, nutrient and salt loading onto land.  Comparing pore-liquid samples from the vadose zone to groundwater protection standards (e.g. MCLs) is not appropriate. 

This work summarizes the difficulties in obtaining and interpreting pore-liquid data from pressure vacuum lysimeters in an active food processing land application facility in the southern San Joaquin Valley over a two year period.  Hourly soil moisture data collected from two and four feet below ground surface (bgs) over a continuous 16 month period is presented.  Soil moisture content approached but did not exceed field capacity moisture content and steadily declined throughout the monitoring period because improved control of irrigation was achieved by installing and optimizing a center pivot sprinkler system. 

Water balances completed throughout the monitoring period suggest that applied water plus rainfall matched the bermudagrass crop evapotranspiration throughout the two-year monitoring period with few exceptions.  Perimeter groundwater monitoring well samples suggest a decline in salt and nutrient concentrations that correlate with the decline in soil moisture content over the same two year monitoring period.  This study supports that the most reliable vadose monitoring programs focus on crop health, yield, water and nutrient management.  Obtaining soil pore-liquid data from pressure-vacuum lysimeters was less reliable than soil moisture monitoring, conventional soil sampling and analysis and groundwater monitoring.