A water analysis is presented in Table 1 below (values in mg/L, except for pH).

The temperature of the water is 20C. Use appropriate values of K given in question #2 of this problem set. You can assume that activities equal concentrations, i.e. that g = 1 for all species.

For this question you cannot assume that the water is in equilibrium with calcite.

Table 1. Groundwater analysis

pH	SiO2 (aq)	Ca2+	Mg2+	Na+	K+	HCO3-	SO42-	Cl-
	mg/L	mg/L	mg/L	mg/L	mg/L	mg/L	mg/L	mg/L
7.8	10	77	14	64	12	199	68	120

20C 10C

K_CO2 (Henry's Law constant) 10^-1.41 10^-1.27 K_H,CO2 = [H₂CO₃]/P_CO2

K_sp,calcite 10^-8.45 10^-8.41 K_sp,calcite = [Ca²⁺].[CO₃^2-]

K₁(H₂CO₃) 10^-6.38 10^-6.46 K₁ = [H⁺].[HCO₃^-]/[H₂CO₃]

K₂(H₂CO₃) 10^-10.38 10^-10.49 K₂ = [H⁺].[CO₃^2-]/[HCO₃^-]

(a) Calculate P_CO2 in equilibrium with this groundwater analysis. Do you think this water is an open system or a closed system with respect to modern-day air?

(As a reminder, P_CO2 in modern-day air = 10^-3.4 atm)

(b) What are the saturation state and saturation index of calcite for this water?

State whether the water is undersaturated, supersaturated, or in equilibrium with calcite.