A record of water and salt for PVID since 1951 shows that for most years the return flow carried about 10 percent more salt to the river than was diverted from the river.  Because the drainage flow is so large (about 500 cubic feet per second), no alternative beneficial use for the water has been apparent.  Consequently, investigations have focused on ways to minimize the increment of salt load that the drainage carries in excess of the salt load diverted with the irrigation water.

The most recent land brought into production is in the southern end of Palo Verde Valley and drains there collect water with the highest salinity concentrations.  This land has been under irrigation for only 20 to 30 years, a relatively short time in comparison to the irrigation history of the valley which began about 1880. 

In 1984, an 18-month study was initiated to determine the salinity mechanism responsible for salt loading at PVID.  Analysis of the data collected during the study showed that salt loading is due to flushing of saline water from the southern portion of the district.  There was no indication of saline water entering the district from either the Palo Verde Mesa to the west or from the underlying Bouse Formation.  Neither salt beds nor salt laden materials were found.

Analysis of water samples taken from the outfall drain show a downward trend in salinity concentration since 1966.  This indicates that salts are being gradually flushed from the aquifer.  This trend and the high cost of measures to control salinity led Reclamation to conclude that salinity control would not be cost effective.  Therefore, in January 1988, Reclamation terminated the planning investigation for the PVID Unit. 

Reclamation is continuing to monitor salinity levels to ensure that trends are continuing.  Each year, water samples are collected from the main outfall drains and analyzed.  Results are provided to the Colorado River Basin Salinity Control Forum and the irrigation district.