Oh Se-hoon names a substitute: Yongsan turns from a veto into a parcel swap

Take the density Seoul Economic Daily quoted and run it backwards. Market estimates of 3,000 to 4,000 homes on the Yongsan Children's Garden's roughly 300,000 square meters ^[7][4] imply 10 to 13.3 homes per 1,000 square meters. Applied to the Tancheon Water Recycling Center's 393,000 square meters ^[3], the same band yields 3,930 to 5,240 homes ^[17]. The "more than 5,000 at most" figure in that report sits at the very top of the band ^[8], and the report itself says the calculation is area and nothing else ^[8]. Tancheon is about 31 percent larger than the Children's Garden ^[16], so on paper it buys the government roughly one extra Children's Garden's worth of nothing.

What eats the difference is listed but not priced: the sewage treatment function has to be kept, the plant may have to go underground and be modernised, and then usable land, the floor area ratio, parks and roads all have to be settled ^[9]. Nowhere in the material is there a cost for putting a working treatment plant below grade. That absent number, not the 393,000, is what the two sides will actually be arguing about.

The move matters because a refusal has no price attached to it. "Not one centimeter" ^[10] left the Land Ministry with a single option, which was to keep the main grounds on its idle-site inventory and press ^[10]. By naming Tancheon and, two days earlier, four scattered plots around the park ^[2][11], the mayor gives the ministry something it can counter-value. That is a different conversation from an ultimatum, and it is one the city can lose on the merits rather than on the politics.

Oh's sharpest argument is procedural rather than preservationist: the main grounds still need the U.S. base returned, contaminated soil remediated and the park development plan revised, which he says makes construction inside this government's term difficult ^[12]. The ministry, meanwhile, needs residential land in central Seoul it can count against supply targets, and the city says it does not oppose more supply as such ^[14]. Those two positions have an overlap, and the overlap is any parcel already in public hands with no base handover attached.

The trade also relocates the objection. Building on Tancheon avoids the charge of tearing down a park to make homes ^[15], but the site currently carries an outdoor performance venue, sports facilities, parking and green area ^[5], sitting beside Daecheong Station on Line 3, the Tancheon stream, the Suseo interchange and Samsung Medical Center ^[6]. A Yongsan fight becomes a Gangnam fight, with better transport arithmetic and a louder set of incumbent users.