11.L.1. Description

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.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

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.