Below is the bus schedule between Izumi JR station and Aquamarine Fukushima and the frequency doesn't look that bad. 平日 is for weekdays; 土曜日祝日 is for weekends and holidays
Bus leaves Izumi station south exit泉駅前（南口）and takes 12 min, get off at Sisyoiliguchi bus stop “支所入口” and walk 10 min. One way bus fare is 270 yen. Aquamarine Fukushima isアクアマリンふくしま.
…fks.ed.jp/english/info/pdf/bus_route2013.pdf (English map for bus stops)
marine.fks.ed.jp/info/pdf/bus_route2010.pdf (Japanese map for bus stops)
Thanks for filling the gaps comprehensively.
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