scope:

A series of simulation experiments were conducted to evaluate how different produced water release and environmental characteristics (model inputs or factors) affect the fate of chloride in the subsurface (model outputs or responses). Model inputs include the hydrological and geological characteristics of the vadose zone and of the aquifer, climate, and characteristics of the release. A total of 11 factors were identified:

1. Texture of the vadose zone (e.g. sand, clay, etc.),

2. Depth to ground water,

3. Natural water content in the vadose zone,

4. Dispersion length of chloride in the vadose zone,

5. Climate,

6. Chloride concentration of the produced water release,

7. Volume of the produced water release,

8. Initial depth of produced water on the land surface (e.g., ponded within a berm or dispersed over a large area),

9. Ground water flux of the aquifer,

10. Background chloride content in the aquifer, and

11. Saturated thickness of the aquifer.

Model outputs from HYDRUS-1D are:

• The maximum chloride concentration entering the aquifer from the vadose zone, and

• The arrival time of the maximum chloride concentration at the aquifer.

Model outputs from the groundwater mixing model are:

• The maximum chloride concentration measured at a monitoring well at the down gradient edge of the surface produced water release, and

• The arrival time of the maximum chloride concentration at a monitoring well at the down gradient edge of the surface produced water release.