Internet for “U.S. sewer bills,” and the first page of results will show
examples of communities where monthly household sewer rates are nearing or
exceeding three figures. For example, in Islamadora, Fla., a headline dated May
30, 2012, reads, “Sewer bill could run $140/month.”
generally, the 2010 report Trends in Local Government Expenditures on Public
Water and Wastewater Services and Infrastructure: Past Present and Future,
released by the U.S. Conference of Mayors (Washington, D.C.), projects that
water and sewer rates will double or quadruple during the next 20 years — with
$0.60 of every dollar going to operations and maintenance (O&M). On the
flip side, residents of Bethel Heights, Ark., are paying $35/mo; residential
customers in the South Alabama Utility District pay $35/mo; and in Yelm, Wash.,
and Victoria on Prince Edward Island, monthly bills are about $43.
these small communities with affordable sewer rates have something in common:
All are served by decentralized effluent sewer systems that use a septic-tank
effluent pump (STEP) configuration. These systems range from 5 to 19 years old
and were designed, equipped, and installed to tight specifications with ongoing
sewer systems are not new. They were first installed in the early 1970s, and
the technology has been optimized during the past 4 decades. Consequently, many
members of the engineering community now acknowledge that decentralized sewer
systems typically are less expensive to purchase and install than conventional
gravity sewer systems — but many still are unaware that decentralized sewers
also are less expensive to operate and maintain.
proposals often overestimate STEP sewer O&M costs by a factor of 2 or more
while greatly underestimating O&M costs for gravity sewers. According to
the 2004 report Replacing and Securing Water Utility Infrastructure by
the National Regulatory Research Institute (Silver Spring, Md.), gravity sewer
O&M costs can approach $328/m ($100/ft) or more. The bottom line is that
many engineers and communities lack accurate life-cycle costswith which
to make decisions.
Some of this is completely understandable. STEP O&M
data can be difficult to obtain. Because STEP sewers need so little O&M in
the first decade, a system has to be in the ground for at least 10 years to
start accumulating useful O&M data. Also, STEP sewers need so little
O&M overall that often there is little consistency in recordkeeping from town
to town and subdivision to subdivision.
However, based on the documented performance data of
thousands of STEP sewer connections collected by one manufacturer, the
operational cost of STEP sewers that have been designed, equipped, and
installed to the manufacturer’s rigorous specifications, at a 4% interest rate,
is about $7.05/mo per residence (see Table 1, p. 66).
O&M costs and intervals
As Table 1 shows, O&M and repair and replacement
(R&R) costs for STEP sewers fall into four main categories.
Table 1. Effluent sewer operations and maintenance and R&R costs
Cost per month per EDU
EDU = equivalent dwelling unit.
R&R = repair and replacement.
About 30% of monthly O&M costs are for preventive
maintenance (PM) and reactive maintenance (RM).For PM, protocols vary
widely among systems. Some are given too little attention, some too much. Both
approaches create problems.
In the March 2009 WE&T article “O&M
Considerations for STEP Systems,” the author, Mike Saunders, concludes that
“[t]he most cost-efficient STEP management approaches balance PM and RM to
achieve the lowest overall costs of O&M.” For nearly 10 years, Saunders
served as the utility engineer for Charlotte County (Fla.) Utilities — one of
the largest STEP systems in the U.S.
A proper PM program requires only a few tasks every 3 to
5 years, consisting of measuring the solids and scum in the on-lot tank,
cleaning the pump and its filter, and verifying the operation of floats and the
control panel. Conservatively estimating 1.5 hours per visit at a rate of
$40/h, PM costs about $60 per visit in 36 months, or about $1.60/mo per
equivalent dwelling unit (EDU).
As for RM, data from 11 systems in four states (totaling
nearly 3100 connections) show that these systems average 1.4 h/mo per 100 EDUs.
Conservatively estimating 1.5 h/mo per 100 EDUs yields a cost of $60 per 100
EDUs (using a business-hour labor rate of $40/h, because on-lot tanks have
enough reserve capacity to enable operators to handle after-hour emergencies
during the next business day). This comes to a monthly RM cost of $0.60 per
The greatest-cost category for STEP systems — about 40%
of the monthly O&M costs — is for equipment R&R. R&R costs are
related directly to equipment quality, especially with regard to pumps. A
high-quality pump for STEP systems provides, on average, more than 20 years of
service. The average R&R costs shown in Table 2 represent actual
costs from several STEP systems.
Table 2. Effluent sewer R&R schedule and costs
Cost per event (materials + labor)
Cost per month per EDU*
|Miscellaneous component R&R
*Amortized at 4% interest.
R&R = repair and replacement.
EDU = equivalent dwelling unit.
Tank pumping is the fourth and final cost category shown
in Table 1. It accounts for nearly 30% of monthly O&M costs and is directly
related to pumping frequency (pump-out intervals). Table 3
reliable pump-out intervals for households with various sizes of tanks and
numbers of occupants derived from an 8-year audit of watertight tanks in Glide,
Ore., and a 5-year audit in Montesano, Wash.
Table 3. Pump-out intervals for 3785-L (1000-gal) tank at 95% confidence level
|Number of occupants
|Pump-out interval, years
Assuming a 3785-L (1000-gal) tank and three occupants in
the household, this chart shows a pump-out interval of about 11 years at a 95%
level of confidence. Estimating a pump-out fee of $300 at an annual interest
rate of 4% and a 10-year frequency, the cost comes to $2.04/mo per connection.
Pacific Northwest example
The community of Yelm, Wash., offers a good case study
of STEP O&M costs. In the early 1990s, Yelm was growing fast and wished to
replace its outdated septic systems with a sewer system that would not burden
residents with high rates or the cost of future growth. A phased system with low
maintenance costs was crucial. So, in 1994, the city installed a STEP system
that now serves nearly 6000 people (1700 STEP connections).
Like other small communities, Yelm was concerned about
two O&M cost categories: periodically pumping and hauling solids from
septic tanks, and replacing in-tank pumps. Yelm’s experience during nearly 2
decades shows that these situations rarely occur, meaning costs are very low.
With regard to pumping, most residential units have
two-compartment, 3785-L (1000-gal) tanks (some of which are shared with another
home) that are pumped out about every 6 years at a cost of $0.06/L ($0.24/gal).
Amortized at 4% interest, this equals about $2.96/mo per EDU. As for pump
replacement, between 1994 and 2009, only 28 pumps were replaced out of 1700
connections. With a pump replacement cost of $600 in labor and materials, the
monthly cost of each household’s pump is only $2.50.
Yelm has been able to keep its base sewer rate to
example comes from the growing community of Bethel Heights in Benton County,
Ark. Bethel Heights installed its STEP system and a packed-bed filter treatment
system in 2003 to accommodate strong interest in new development. The community
now has a population of about 2800 and 470 STEP connections.
To minimize costs for the first several years until
connection fees from new subdivisions started coming in, Bethel Heights’ mayor,
Fred Jack, obtained a Class I operator’s license and operated the STEP and
treatment systems himself. By 2010, the system was regularly maintained by a
staff of 1.5 full-time equivalents.
In a 2010 interview, Jack said, “We focus on preventive
maintenance and repair rather than replacement. ... I can repair a pump for
about $40 instead of buying a new pump. ... We really work to operate in the
black.” Bethel Heights is on course to pay off its 30-year wastewater bond in
only 7 years. Its base sewer rate is $35/mo.
deserve hard data
After 40 years of technology development, ample data
exist to show decentralized sewers save ratepayers in upfront installation
costs and long-term life-cycle costs. We no longer have a failure of data; we
have a failure to communicate — but the fiduciary duty to clients has not
about STEP sewer O&M costs has been an impediment to wider adoption of
affordable, environmentally sustainable effluent sewer systems, causing
financial hardship to residents of small communities and consuming funding
dollars at double the rate necessary. The data are in. It’s time to do a better
job of communicating the message.