<p>I have a layered aquifer with water that contains high concentrations of calcium and sulfate (~400 mg/L Ca<sup>2+</sup>, ~1300 mg/L SO<sub>4</sub><sup>2-</sup>), at 50 cm below ground surface (bgs), 250 cm bgs and 300 cm bgs. The water level in the aquifer was quite low, due to evaporation and little recharge. I think gypsum formed in the surface and dissolved when it rained, carrying Ca<sup>2+</sup> and SO<sub>4</sub><sup>2-</sup> downwards. I looked at Cl<sup>-</sup> concentrations and they were really low, not even comparable to Ca<sup>2+</sup> and SO<sub>4</sub><sup>2-</sup>, so how can I prove that evaporation was the mechanism that formed gypsum?    </p>

CC BY-SA 3.0
2018-01-13T11:16:05.697Z
Is this a homework question or a real world problem? Where is this aquifer located? Is it connected to the sea somehow? Is the recharge by rain, rivers?
Gimelist
CC BY-SA 3.0
2018-01-13T15:38:30.547Z
This is a real world problem, not a homework question. The aquifer is located in a dry region, only recharge is rain.
Henry
CC BY-SA 4.0
2019-04-02T07:49:59.900Z
Do you mean m bgs, not cm?
haresfur
CC BY-SA 4.0
2019-04-02T08:23:10.110Z
Are you asking about whether the water composition resulted from dissolution of gypsum or about how the (hypothetical?) gypsum formed in the first place? Do you have any idea about the composition of local rainfall? How far is this from the ocean?
haresfur
<geochemistry><hydrology><mineralogy><groundwater>
Chloride and evaporation
Henry
# Chloride and evaporation

(Asked by: username_0 on 2018-01-13)

I have a layered aquifer with water that contains high concentrations of calcium and sulfate (~400 mg/L Ca2+, ~1300 mg/L SO42-), at 50 cm below ground surface (bgs), 250 cm bgs and 300 cm bgs. The water level in the aquifer was quite low, due to evaporation and little recharge. I think gypsum formed in the surface and dissolved when it rained, carrying Ca2+ and SO42- downwards. I looked at Cl- concentrations and they were really low, not even comparable to Ca2+ and SO42-, so how can I prove that evaporation was the mechanism that formed gypsum?

**Tags:** geochemistry, hydrology, mineralogy, groundwater

> **Comments:**
> **username_1**: Is this a homework question or a real world problem? Where is this aquifer located? Is it connected to the sea somehow? Is the recharge by rain, rivers?  
> **username_0**: This is a real world problem, not a homework question. The aquifer is located in a dry region, only recharge is rain.  
> **username_2**: Do you mean m bgs, not cm?  
> **username_2**: Are you asking about whether the water composition resulted from dissolution of gypsum or about how the (hypothetical?) gypsum formed in the first place? Do you have any idea about the composition of local rainfall? How far is this from the ocean?  

---

## 0 answers

