SECTION IV ESTIMATING WASTEWATER …

1 SECTION IV ESTIMATING WASTEWATER CHARACTERISTICS TABLE OF CONTENTS Sub- SECTION No and Title Page No. A. Introduction 1 B. Residential WASTEWATER Characteristics 2 1. Published Information 2 2. Data from Department Files 2 C. Commercial and Institutional WASTEWATER Characteristics 3 1. General 3 2. Food Processing and Serving Establishments 3 3. Health Care Facilities 7 4. Hotels, Inns and Resorts 7 5. Offices 8 6. Supermarkets 8 7. Shopping Centers and Factory Outlets 8 8.

2 Travel Centers (aka Truck Stops) and Truck Terminals 8 9. Schools 10 10. Power Plants 10 11. Summer Camps 10 12. Roadside Rest Areas, Campgrounds and Marinas 10 13. Ski Resorts 11 D. Sampling for Estimation of WASTEWATER Characteristics 11 E. References 17 TABLES Table No On or Following Page No. 1. Review of Current Literature on Concentrations of BOD5 and TSS in Residential Septic Tank Effluent 13 2. Review of Current Literature on Concentrations of Total Nitrogen and Phosphorus in Residential Septic Tank Effluent 14 3.

3 WASTEWATER Characteristics of Food Processing and Serving Establishments 15 4. WASTEWATER Characteristics of Commercial and Institutional Facilities 16 SECTION IV, Page 1 of 19 SECTION IV ESTIMATING WASTEWATER CHARACTERISTICS A. Introduction This SECTION provides information on WASTEWATER characteristics for residential, commercial and institutional sources obtained from various published sources. In addition, significant information on WASTEWATER characteristics gleaned from the engineering reports and Discharge Monitoring Reports (DMRs) in the files of the Department for large scale on-site WASTEWATER renovation systems (OWRS) is also presented herein.

4 It is important to understand that historical data on WASTEWATER characteristics is accurate for the time and place in which they were obtained. In many cases the historical data is based on statistical analyses of the results obtained from grab samples of relatively small sample sizes. These analyses assume the results can be described by arithmetically normal distributions, which is not necessarily true. Most of the historical OWRS data are based on grab samples of septic tank effluent.

5 The acceptability of characterization of septic tank effluent using grab samples is based on the premise that the septic tank effluent has been homogenized by the physical and biological activity that takes place within the septic tank. This may be a reasonable assumption where the WASTEWATER flow rate is low, no large WASTEWATER flow surges occur, the WASTEWATER characteristics are relatively uniform on a temporal basis, and there is ample detention time in the septic tank.

6 These conditions may be approached most of the time in the case of residential WASTEWATER sampling. However, this is generally not the case for septic tanks receiving commercial, institutional and community WASTEWATER . Some factors that influence the results obtained from sampling of septic tanks include: 1. Configuration of the septic tank(s) sampled, including shape [rectangular or circular cross- SECTION ], volume, length to width ratio, liquid depth, number of compartments, the type and arrangement of baffles, the presence of effluent screens, and actual liquid detention time.

7 2. Frequency of pumping (cleaning) the tank ( too great a depth of solids in the tank adversely effects the pollutant removal efficiency of the tank). 3. Whether the sample(s) were taken shortly after the tank(s) had been pumped. 4. Sampling protocol, including location and depth in which the samples were taken, whether the samples were randomly taken, the preparation and handling of sample containers, and the time elapsed between sampling and testing. 5. Temperature in the septic tank (varies with the seasons).

8 6. Number of samples taken. SECTION IV, Page 2 of 19 7. Method(s) of analyzing test results. 8. Laboratory accuracy. Variations in some or all of these factors may cause the sample results to be biased. While septic tanks serving individual residences typically provide a retention time of 2 to 3 days or more, many septic tanks receiving commercial, institutional and community WASTEWATER have much lower retention times, generally less than 24 hours. For example, the Manual of Septic Tank Practice ( Public Health Service-1972) recommended that, for WASTEWATER flows greater than 1,500 gpd, the minimum effective tank capacity should equal 1,125 gallons plus 75 percent of the daily flow.

9 This recommendation has been widely followed for design of large-scale OWRS. Consider that, for a flow of 5,000 gpd, the recommended volume = 3,750 gal. + 1,125 gal. = 4,875 gal, which would provide a nominal detention time of somewhat less than one day. Thus, if the Manual of Septic Tank Practice recommendation is followed, it can be expected that the percent removal efficiencies for pollutants often discussed for residential septic tanks will not be realized in the case of septic tanks serving commercial, institutional and community facilities.

10 The intent of providing information herein on characteristics of residential and the domestic fraction of commercial and institutional WASTEWATER is to indicate the wide range in values of such characteristics. It is not intended that such information be used directly to prescribe values for design of an OWRS for a particular facility without substantiation by obtaining field samples of WASTEWATER from existing facilities as nearly similar as possible to that for which the OWRS is being proposed, or from the existing facility where a replacement system, or system upgrade, is required.