Locating stormwater treatment facilities underground can free more land for development.
address stormwater management issues at projects' commencements, as
storage and treatment facilities' sizes can alter the amount of
available buildable land. Flood-zone regulations and stormwater
treatment requirements affect the amount of land needed. If the land's
opportunity cost is high, the only reasonable choice may be to locate
the stormwater management facility underground. While this solution can
cost four times or more of an equivalent aboveground facility, it frees
the entire site for development. The following case study illustrates
how underground stormwater treatment facilities can solve development
Going Underground to Save Land
To comply with nitrogen removal requirements for the Neuse River Basin
regulations, developer Wood Partners hired the John R. McAdams Co. to
design a stormwater treatment facility for Station Nine, a midrise,
323-unit multifamily project in Durham, N.C.
encountered several challenges when determining the best stormwater
treatment facility to design. The first challenge involved the small
amount of available land -- approximately five acres -- on which the
entire development was to be located. The amount of nitrogen that
needed to be removed from the site runoff was another concern. The City
of Durham required 40 percent reduction from pre-development nitrogen
loading conditions. Typical stormwater treatment devices would not
work, since all of the available land was required for the proposed
To contend with these
challenges, McAdams determined that an underground sand filtration
system was the best use of the land, although it would cost more than
an aboveground facility.
system comprised three 8-foot by 10-foot concrete vaults that were 110
feet long. The top of each vault was buried two feet to three feet
below the ground's surface.
contained a sand chamber used to filter the nitrogen out of the runoff
water. The stormwater ran through three side-by-side chambers to
effectively solve the required 40 percent nitrogen removal.
underground facility solution benefited the land, the surrounding
community, and communities downstream. Since the project itself was
relatively small, and the density required was high, the development
would not have been feasible had any of the site been used for
stormwater management purposes. Even though the estimated cost of the
sand filters was more than $500,000, it made sense financially because
it allowed full use of all of the developable area of the site. It
fulfilled the Neuse River Basin regulations and dealt with the lack of
available land. This approach allowed Wood Partners to use all the
developable land without having to purchase additional land to provide
stormwater treatment above ground.