National Handbook of Recommended Methods for Water Data Acquisition

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11.L.1. Description

Wastewater collection and return flow includes wastewater collected from domestic, commercial and industrial users, treated at wastewater-treatment facilities, and returned to the hydrologic system or released for reuse as reclaimed wastewater (fig. 13). Wastewater from industries may be treated and returned to the hydrologic system or may undergo pretreatment before being released into the sewers to ensure that wastewater products do not arrive at the treatment plant that could harm the wastewater-treatment process. Ground water may infiltrate into the sewers or wastewater exfiltrate from the sewers during conveyance from the user to the wastewater-treatment facility. Water from storm events may flow into the sewer system either as inflow through breaches in the pipes or as part of a combined sanitary/storm sewer. If more water than can safely be handled by the wastewater-treatment plant flows into the combined sewers, emergency outlets, Combined Sewer Overflows (CSO's), will discharge the combined wastewater and storm water directly into surface water. This usually, but not exclusively, occurs during storm events. Sludge produced during wastewater treatment is either transported to a landfill, incinerated, or stored on site. Consumptive use in the form of evaporation occurs primarily during treatment and (or) sludge disposal and varies with the type of wastewater treatment. The SIC code for these facilities is 4952. Other wastewater-treatment facilities that treat the wastewater on site and are discussed under the specific category of use.

Figure 13.

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.

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.

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.

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.

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.

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