You have marginally (excluding other variables except the intercept)
$$
\log \left(\frac{G_t}{G_{t-1}}\right) = \beta \ \cdot \mathrm{Surcharge} + C
$$
meaning

$$
G_t = G_{t-1} \cdot \exp \left(\beta \ \cdot \mathrm{Surcharge}\right) \cdot e^C
$$

Here $e^C$ has the interpretation of a `base rate' of growth. A marginal unit increase in $\mathrm{Surcharge}$ yields a multiplication by $e^\beta$. You can interpret this as a $e^\beta$-percent growth (or decrease, if $e^\beta$ < 1) since the last measured value $G_{t-1}$, after the base rate has been applied. For example, an estimated $\hat{\beta} = .5$ would mean the previous value $G_{t-1}$ is first multiplied by the basal rate $e^C$, and then is additionally multiplied by $e^{\hat{\beta}} \simeq 1.648$, a $165\%$ growth compared to the base-rate growth.