The Collaborative International Dictionary
Impermeably
Impermeable \Im*per"me*a*ble\, a. [Pref. im- not + permeable: cf. F. imperm['e]able, L. impermeabilis.] Not permeable; not permitting passage, as of a fluid. through its substance; impervious; impenetrable; as, India rubber is impermeable to water and to air. -- Im*per"me*a*ble*ness, n. -- Im*per"me*a*bly, adv.
Wiktionary
impermeably
adv. In an impermeable manner.