Let \( \alpha > 0 \). If \( \displaystyle \int_{0}^{\alpha} \dfrac{x}{\sqrt{x+\alpha} - \sqrt{x}} \, dx = \dfrac{16 + 20\sqrt{2}}{15} \), then \( \alpha \) is equal to:
\( \sqrt{2} \)
\( 2 \)
\( 2\sqrt{2} \)
\( 4 \)