SU0003307 - Laserfiche WebLink

Home Browse Search

GROUNDWATER SALINITY IMPACTS FROM IRRIGATION WITH CANNERY WASTEWATER The impact of dissolved solids on groundwater result from the inorganic fraction of the dissolved constituents. A significant fraction of the total dissolved solids as measured by standard laboratory procedures can be attributed to organic components (8) . In land treatment of cannery wastewater the organic fraction of the dissolved solids (organic acids, etc.) will be metabolized by soil microorganisms and incorporated into the soil humus. For this reason it is preferable to consider only the fixed dissolved solids in estimating the impact of wastewater on groundwater quality. The concentration of fixed dissolved solids has been estimated in this analysis on the basis of sample specific conductance. Fixed dissolved solids can be calculated on the basis of specific conductance to an accuracy of ± 10% (9) . To convert from conductivity to fixed dissolved solids the following formula was used: conductivity umhos/cm = 1.55 fixed solids (mg/1 ) . QAP's wastewater disposal system involves dilution of wastewater with fresh water prior to application by either surface or sprinkler irrigation. Salts are present in the fresh water which is blended with wastewater. The wastewater contains a higher concentration of salts. Since the fresh water is a large proportion of the total water applied the fresh water accounts for a significant amount of total salt applied. In order for the land to remain productive the applied salt (fixed dissolved solids) must be carried past the root zone by excess water applied for leaching and infiltration of rainwater during the winter months. In order to estimate the impact of wastewater disposal operations on groundwater quality an estimate of the quantity and average salt concentration of the infiltrate was determined. The quantity of water percolating past the root zone was calculated for two different regimens. During the growing season considered from April to September inclusive a leaching fraction of 0.3 times the evapotranspiration demand was considered to be the percolate. During the winter months the percolate was estimated the difference between average rainfall (10) and evapotranspiration. Calculation of applied salt was based on an irrigation water requirement of 1.3 x evapotranspiration demand during the growing season. Volume of wastewater was subtracted from the total irrigation water requirement to give the volume of fresh water used for irrigation. Applied salt was then calculated based on salt concentration data for the fresh water and wastewater. Salt Application Rate The salt application rate is lower on the Bozzano field due to its irrigation schedule and relatively larger area. Total wastewater volume from QAP is 1-11 RP033-L