Ground injection agent concentration estimation method

A method of introducing a ground injection agent into groundwater, the method comprising:

• injecting an injection liquid comprising one or more injection agent and one or more marker into the ground through a water injection well;
• measuring a concentration of the one or more marker in the groundwater, using a sensor, at a location spaced apart from the water injection well;
• estimating a concentration of the one or more injection agent in the groundwater from the concentration of the one or more marker in the groundwater, and the ratio between a concentration of the one or more injection agent in the injection liquid and a concentration of the one or more marker in the injection liquid, and a coefficient based on a difference between a first absorption/desorption characteristic of the one or more marker and a second absorption/desorption characteristic of the one or more injection agent;
• and
• adjusting the concentration of the one or more injection agent in the groundwater based on the estimated concentration of the one or more injection agent in the groundwater by controlling, through a controller, the injection of the injection liquid into the groundwater through the water injection well,
• wherein the one or more injection agent and one or more marker both comprise a property that are about the same, and
• wherein the property comprises at least one of viscosity, adsorption characteristics, desorption characteristics.