Figure 13. Diagram of wastewater collection and return flow.
The majority of wastewater systems are simple systems consisting of a wastewater-collection system, primary and secondary treatment at a wastewater-treatment plant, and discharge into a surface-water body. Sludge is either transported to a landfill or to a larger wastewater-treatment facility. However, as the population density intensifies, regional wastewater systems may be developed to combine wastewater from several communities. The regional wastewater-treatment facilities, about 20 percent of treatment plants, treat 72 percent of New England wastewater. Therefore accurately collecting and analyzing information from the more complex system, illustrated in figure 13, are required for an accurate view of wastewater disposal activities.
Wastewater data include the rate of: (1) releases from domestic, commercial, and industrial users; (2) deliveries to the wastewater treatment facility; (3) estimated infiltration and inflow; (4) evaporation from long-time natural water treatment; (5) returns to surface water and ground water; and (6) release of reclaimed wastewater.
Lists of wastewater-treatment facilities can be obtained from the
State agency responsible for the program that supports the Clean Water
Act. Some of the geographic, hydrologic, and rate or volume data are
stored in USEPA's PCS data base. Most large wastewater-treatment
facilities meter and automate the volume of water sold to customers
and assume a direct relation to the volume discharged into the sewers.
As the wastewater-treatment facilities decrease in size, metered data
are less available. Data available from State agencies will decrease
as the size of the wastewater-treatment facility decreases--State
agency resources will be used to concentrate on the largest
wastewater-treatment facilities that have the greatest impact on the
water resources. However, the availability of data, even automated
data, does not necessarily mean that the data are immediately usable.
Analysis must be done to ensure that the data are consistent with
project requirements.
The first step in working on wastewater data is to acquire data from
State agencies and evaluate them. This is followed by determining (1)
additional data required and (2) the best method for obtaining
them.
California State University, 1990, Operation of wastewater treatment
plants, a field study training program, 3rd ed.: Sacramento,
California State University, School of Engineers, v. 1, 504 p, v. 2,
667 p.
-----1991, Operation and maintenance of wastewater collection systems,
a field study training program, 3rd ed.: Sacramento, California State
University, School of Engineers, v. 1, 532 p., v. 2, 560 p.
Corbitt, R.A., 1990, Wastewater Disposal. Standard Handbook of
Environmental Engineering: New York, McGraw-Hill.
Nemetz, P.N., and Drechsler, H.D., 1979, Least cost solutions to the
problems of effluent abatement in urban systems: Water Resources
Bulletin, v. 15, no. 5, p. 1374-1384.
U.S. Environmental Protection Agency, 1987, Permit compliance
system--PCS generalized retrieval manual: 282 p.
11.L.2. Sources of wastewater information
Wastewater information is available from the State agency responsible
for compliance to the USEPA's Clean Water Act Program or directly from
the USEPA Permit Compliance System (PCS). The USEPA administers the
Permit Compliance System (PCS) database, which was designed to track
permit, compliance and enforcement status data for the NPDES program
under the Clean Water Act. An NPDES permit is required for all point
discharges into United States waterways. The PCS database contains
descriptive information on wastewater-treatment facilities, their
location, treatment processes, and monthly return flows. The USEPA
also administers the Needs Survey database, which consists of an
inventory of existing and proposed publicly-owned treatment works
(POTW's) which need construction to meet requirements of the Clean
Water Act. Because the Needs Survey file is designed to project
future POTW needs, it contains data on wastewater conveyance and
treatment facilities, including populations served. A third USEPA
database, the Industrial Facilities Discharge (IFD) file, contains a
listing of industries and their SIC codes which are permitted through
the NPDES program to directly or indirectly discharge wastewater to
surface waters in the United States. Individual wastewater-treatment
facilities can also be contacted. 11.L.3. Measurement, estimation, and data-collection methods for
wastewater collection and return flow
The first step in wastewater data collection is to determine required
data elements and level of accuracy, and the available resources.
Although this section provides guidelines in obtaining all the data
listed above, individual projects may require only a subset of the
data. Information on deliveries to the wastewater-treatment facility
and returns to surface water and ground water generally are readily
available, evaporation during long-time natural wastewater treatment
can be estimated, releases from users and infiltration and inflow are
difficult to obtain and are frequently estimated, and reclaimed
wastewater and release information should be available from the
wastewater-treatments plants.
11.L.3.a. Primary data acquisition
Most large wastewater-treatment facilities are metered so measurement
by project staff is unnecessary. It may, however, be reasonable to
measure some of the small wastewater-treatment facilities. 11.L.3.b. Secondary data acquisition
Wastewater-treatment data usually are reported to the State agency
responsible for the Clean Water Act, and the return flow volumes are
entered into the PCS data base. Individual wastewater-treatment
facilities also maintain data on releases from users as well as
facility influent and effluent. In general, data obtained from the
above sources should provide a fairly comprehensive list of automated
identification, geographic, and hydrologic information for
wastewater-treatment facilities, including data on the rate or volume
of return flow to each source. The data need to be checked for
consistency and completeness. Data also may be available on water
released by users into the wastewater-collection system. However,
frequently, these values are not developed from uniform criteria and
will need careful study before being incorporated into the project
data base. Careful analysis of metered water-use data is critical;
the data may be unreliable because of inconsistent record-keeping or
because there is no meter-replacement or meter-calibration program to
ensure meter reliability. 11.L.3.c. Derived data
Although deliveries to the wastewater treatment facility, returns to
surface water and ground water, and releases of reclaimed wastewater
usually are available from either EPA or the wastewater-treatment
facility, releases from domestic, commercial, and industrial users,
infiltration and inflow usually need to be estimated. Metered data
may be available on water delivered to domestic, commercial, and
industrial users, however, adjustments for consumptive use losses are
required in addition to regular analysis done on public water supply
delivery data. Further adjustments need to be made for the
disposition of unaccounted for water. Estimates of inflow and
infiltration can be made for wastewater-collection system that are not
combined with storm drains by carefully examining measurement of
delivery at the wastewater-treatment facility and precipitation data
and separating overland flow from storm events (inflow) from the later
contribution from ground-water flow infiltration. Analyzing return
flow data on a per capita basis also is useful in identifying
wastewater-treatment facilities with significant inflow and
infiltration problems. 11.L.3.d. Quality Assurance
A quality control check between public-supply withdrawals and
wastewater return flow should be made. If the wastewater return flow
is significantly larger than public-supply withdrawals minus
consumptive uses and distribution losses, there may be an interbasin
transfer or self-supplied users on the system. If the flow through
the treatment plant increases significantly during period of
precipitation, as noted by Bertoldi (1973), there may be a combined
sewer and storm water collection system, or the wastewater-collection
lines may be in need of repair. 11.L.4. Wastewater selected references
These references are supplemental to the ones in the General Reference
Section.
Bertoldi, G.L., 1973, Wastewater infiltration near the city of Mount
Shasta, Siskiyou County, California: U.S. Geological Survey
Water-Resources Investigations Report 20-73, 31 p.