RBF_Cover (for eps) - National Water Research Institute

Cost-Evaluation of Riverbank Filtration
The capital cost of a RBF system depends on many factors, including aquifer characteristics, type
of well-screen installation (vertical or horizontal), aesthetic considerations in facility design, and
distance to the population served. The operational costs vary as a function of water quality and
required treatment, lift required in pumping, and pump and well-screen maintenance costs. The
ability of a stream to support a given well-field capacity can be calculated as the yield per unit
length of riverbank. This capacity is influenced by the composition of the riverbed, riverbed
scouring characteristics, stream-water quality, and width of the river.
Large river systems situated in glacial sands and gravels (such as the Ohio, Mississippi, and Rhine
rivers) can sustain yields up to 8 million gallons per day (MGD) per 1,000 feet (ft) of riverbank.
Typical installations in these aquifers include 1.5-MGD vertical wells spaced on 200-ft centers, or
15-MGD horizontal collector wells spaced at 2,000-ft centers.
The 20-MGD horizontal collector well system constructed in Louisville in 1999 cost $5 million.
The system included:
• Seven laterals that are 200 to 240 ft in length.
• A 21-ft diameter, 100-ft deep caisson.
• A pump house and controls with one constant speed and one variable speed pump
(both 10 MGD).
• Two thousand feet of 42-inch discharge piping to the plant.
The pump house was designed to include architectural features complimentary to surrounding
residential neighborhoods. This system can peak at over 20 MGD in warm weather and is operated
year-round at 17 MGD.
When this system was being considered, alternative treatment techniques for surface-water treatment
were also evaluated. Critical treatment functions included efficiency in removing Giardia and
Cryptosporidium, ability to remove 2-methylisoborneol and Geosmin, and DBP reduction. Suitable
alternatives were determined from the matrix and evaluated for cost. This process was repeated
twice, by two separate consultants: once in the initial planning stages of the 20-MGD project
(1995), and again just before a contract was let to design a 45-MGD expansion of the system
(2002).
The surface-water treatment process selected in the final cost analysis as providing comparable
benefits to the overall benefits of RBF included: conventional treatment, ozone and biological
treatment in GAC-capped filters, and UV/chlorine/chloramine disinfection. Treatment costs,
however, were also estimated for separate elements of this treatment scheme (as was the cost of
membranes) for the 180-MGD treatment plant at Crescent Hill.
The results of this cost comparison are included in Table 2. The capital costs were amortized over
20 years in this analysis, and the operation and maintenance (O&M) costs include the treatment
costs to reduce hardness from 220 to 160 milligrams per liter (mg/L). Based on this analysis, the
decision was made to proceed with the development of RBF for the entire capacity of the 60-MGD
B.E. Payne Water Treatment Plant, and to continue considering RBF for the larger 180-MGD
capacity Crescent Hill Treatment Plant.
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