United States
Environmental Protection
Agency
ju|y
1984
&EPA A Practical
Technology
Hydrograph
Controlled
Release
Lagoons
A Promising
Modification
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Hydrograph Controlled
Introduction
A challenge faced by many communities is the
need to upgrade existing or construct new
wastewater treatment facilities to protect water
quality of receiving streams. Typically, the cost of
meeting this challenge places a large financial
burden upon the community.
Recently, several communities, working with their
engineering consultants and State and Federal
regulatory agencies, have turned to Hydrograph
Controlled Release (HCR) lagoons as an
innovative, cost-effective means of meeting their
wastewater treatment needs. HCR lagoons control
the discharge of wastewater to receiving waters in
accordance with the stream's assimilative capacity.
Potential advantages of HCR lagoons, compared to
mechanical treatment systems, include:
• Adaptability to use with existing treatment works
• Operation and maintenance cost savings
• Reduced energy consumption
• Reduced operational complexity
Description and Operation
Normally, a stream's assimilative capacity is related
to its flow; although other factors, including water
quality and temperature, are important
considerations. The primary function of the HCR
lagoon is to allow the discharge to be restricted
when the flow in the receiving stream is low and
the ability of the stream to accept the discharge is
limited. As stream flow increases, the stream's
capacity to assimilate the discharge increases, and
treatment plant flow previously stored in the HCR
lagoon can be released to the receiving stream.
An example of a discharge hydrograph for a
treatment plant having an average flow of 1 mgd is
shown in Figure 1. In this example, the treatment
plant discharge must be restricted when flows in
the receiving stream are less than approximately 35
cubic feet per second (cfs). As the stream flow
increases above 35 cfs, the stream has a capacity
to accept a discharge greater than the treatment
plant's average flow of 1 mgd. Thus, a portion of
the plant flow previously stored .in the HCR lagoon
could be released to the stream.
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Design Considerations
HCR lagoons will not be a cost effective alternative
to other treatment systems in all cases. Design
considerations which must be evaluated include:
• Site availability
• Receiving stream effluent requirements
• Receiving stream flow pattern
Due to the relatively large area required for
construction of an HCR lagoon, lack of a suitable
site near the treatment plant may not permit cost
effective construction of the HCR lagoon. Receiving
streams which have stringent year round effluent
requirements or low flow patterns in comparison to
the WWTP flow may not permit the variable
discharge characteristic of HCR lagoons to be used
effectively.
In some cases, the State regulatory agency may
not permit the treatment plant discharge to be
varied in accordance with the stream flow.
Therefore, the possibility of obtaining a flow
regulated discharge permit should be discussed
with the agency prior to considering the use of a
system employing an HCR lagoon.
Costs
In general, capital costs for HCR lagoons are
dependent upon the following factors:
• Storage volume required
• Pond liner requirements
• Land costs
The total storage volume required is related to both
the treatment plant flow and the receiving stream
flow pattern. If the receiving stream has a relatively
high flow in comparison to the plant flow, a storage
volume equal to 30 days of the average plant flow
may be adequate. Conversely, a relatively low
stream to plant flow ratio may require a storage
capacity in excess of 120 days.
The pond liner requirements are site specific, and
depend upon the nature of the existing soils,
proximity of ground water, and State requirements
regarding permissible pond leakage. Typical pond
liner materials include clay, plastic liners, and soil
additives such as bentonite. In some cases, asphalt
or concrete liners may also be used. Clay seals or
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soil additives are generally less costly than the
other liners if clay is readily available or the soils
are suitable for use with an additive.
A graph showing typical capital costs versus HCR
lagoon size is presented in Figure 3. The costs
shown are based upon a maximum water depth of
8 feet, use of a clay liner, and a land cost of $1,000
per acre.
25
Lagoon Size - Acres
Figure S.Capital Cost: HCR Lagoon
Operation and maintenance costs for HCR lagoons
are low, generally being similar to the O&M costs
for wastewater stabilization lagoons. The major
O&M costs are for site maintenance, periodic
sampling and analysis, and adjustment of discharge
rates. Energy costs may be encountered if it is
necessary to pump either the lagoon influent or
effluent. However, most systems are designed for
gravity flow, and thus pumping is not required.
Facility
West Monroe, LA
Raleigh, MS
Canton, MS
*7-% discount rate f
Design Flow
(mgd)
5.6 '
0.2
3.6
or20yearsyvit|:
Capital Cost
(x $1,000)
HCR Alternati
System Systen
1,711 6,000
537 427
4,500 5,000
Lassuffie^satvageA
Table 2. Cost Comparisons
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In Table 2, the estimated capital and O&M costs for
three facilities which will use HCR lagoons as a
part of the treatment system are compared to the
cost of alternative treatment systems which were
considered. For the West Monroe, LA facility, the
HCR system is based upon upgrading an existing
lagoon system, while the Raleigh, MS and Canton,
MS facilities involve construction of new lagoon
systems. As shown in Table 2, the capital costs for
some HCR systems, such as Raleigh, are higher
than the capital costs of the alternative systems
considered. This primarily reflects the larger land
area and earthwork quantities associated with the
HCR systems in comparison to the alternative
systems. For the West Monroe facility, the ability to
utilize existing lagoon facilities resulted in a large
capital cost savings. In all three cases, the total
annual O&M costs for the systems which utilize
HCR lagoons are substantially less than the costs
for the alternative systems. The large O&M savings
are due to major reductions in labor requirements,
equipment maintenance, and energy usage. Due to
the lower life cycle cost, the HCR system was
selected as the cost-effective alternative for all
three communities.
Annual O&M Cost
' (x $i,000)
HCR Alternative
System System
94 ", 1,025
47 - J70
140 259
of $0.00 after 20 years!
Life Cycle Cost* ','
(*
HCR
System
" 2,643
1,003
5,887
$1,000)
Alternative
^System
16,158
2,112
7,567
- a J* - # ff
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Mention of trade names or commercial products
does not constitute endorsement.
Prepared by Environmental Resources Management, Inc.
For additional information contact:
EPA-OWPO{WH-547)
401 M Street, SW
Washington, DC 20460
(202)382-7370/7369
EPA Region 1
John F. Kennedy Federal Building
Boston, MA 02203
EPA Region 2
26 Federal Plaza
New York, NY 10278
EPA Region 3
6th & Walnut Streets
Philadelphia, PA 19106
EPA Region 4
345 Courtland Street, NE
Atlanta, GA 30365
EPA Region 5
230 South Dearborn Street
Chicago, IL 60604
EPA-MERL (489)
26 West St. Clair Street
Cincinnati, OH 45268
(513)684-7611
EPA Region 6
1201 Elm Street
Dallas, TX 75270
EPA Region 7
324 East 11th Street
Kansas City, MO 64106
EPA Region 8
1860 Lincoln Street
Denver, CO 80295
EPA Region 9
215 Fremont Street
San Francisco, CA 94105
EPA Region 10
1200 6th Avenue
Seattle, WA 98101
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