Low Impact Development Manual for Michigan - OSEH - University ...

In ultra-urban areas where land costs are high, however,
underground sand filters can represent significant cost
savings in reduced land consumption. For small ultraurban
areas with no land available, they may be the only
practical option for stormwater quality treatment as they
can be placed under roads or parking lots.
In recent years, various manufacturers have made available
prefabricated units that include precast vaults and
inlets delivered to the site either partially or fully assembled.
These units have generally resulted in decreased
construction costs. Typical significant cost variables
include the location of subsurface utilities, type of lids
and doors, customized casting of weirs, sections, or
holes, and depth of the vault.
The surface sand filter design is a moderately expensive
water quality option to employ (Claytor and Schueler,
1996). However, the cost of installation is strongly
correlated with the nature of the construction employed.
If the filter is installed within an ultra-urban setting, it
is likely that relatively expensive concrete walls will
be used to create the various chambers. This type of
installation will be significantly more expensive than
an earthen-walled design, where relatively inexpensive
excavation and compaction construction techniques
lower the installation cost. However, earthen-wall
designs require a greater land area commitment, which
can offset the reduction in construction costs.
The construction cost of surface sand filters is also related
to economies of scale: the cost per impervious acre
served typically decreases with an increase in the service
area. In 1994, the construction costs for surface sand or
organic media filters were $16,000 per impervious acre
for facilities serving less than two acres (Schueler, 1994).
Once again, these construction cost estimates exclude
real estate, design, and contingency costs.
Designer/Reviewer Checklist for Constructed Filters
Type of constructed filter(s) proposed: _________________________________________________________
Type of filter media proposed: ________________________________________________________________
ITEM YES NO N/A NOTES
Adequate depth of filter media?
Acceptable drawdown time (72 hour max.)?
Pretreatment provided?
Adequate hydraulic head available for filter to operate?
Flow bypass and/or overflow provided?
Permeability of filter media acceptable?
Underdrain provided for non infiltration systems?
Appropriate placement of nonwoven filter fabric?
Gravel layer provided beneath filter media?
Non-erosive inflow condition?
Adequate surface area provided?
Construction timing places installation after site stabilization?
Erosion control provided during construction?
Cleanouts included?
Maintenance accounted for and plan provided?
LID Manual for Michigan – Chapter 7 Page 167