EHST 3370 Wastewater Management Spring 2016 Unit 1:Introduction to On-site Wastewater Treatment and Disposal Systems Septic System Treatment and Disposal Mechanisms 1)Septic Tank- settling tank where wastewater is stratified, liquid effluent exits tank, solids remain 2)Distribution device to convey effluent to trenches 3) Drainfield trench is aerobic environment where wastewater is stored until it infiltrates the soil 4) Soil beneath trench is aerobic, and most pollutant transformation and removal occur 5) Setbacks- required horizontal distance from system to point of interest such as a surface water, well, property line, etc., 1)Septic Tank- settling tank where wastewater is stratified, liquid effluent exits tank, solids remain 2)Distribution device to convey effluent to trenches 3) Drainfield trench is aerobic environment where wastewater is stored until it infiltrates the soil 4) Soil beneath trench is aerobic, and most pollutant transformation and removal occur 5) Setbacks- required horizontal distance from system to point of interest such as a surface water, well, property line, etc., Septic Tank Drainfield Trenches Distribution Box Plan-View of On-Site Wastewater Treatment and Disposal System Plan-View of On-Site Wastewater Treatment and Disposal System Soil On-site Wastewater Treatment and Disposal Systems On-site Wastewater Treatment and Disposal Systems % of US population use On-site systems 50% of NC residents (4.5+ million people) use On-site (2 million systems in NC) 30, ,000 new systems/yr installed in NC ~7,000 repairs each year 60% Coastal NC residents use on-site Pitt County, 460/yr % of US population use On-site systems 50% of NC residents (4.5+ million people) use On-site (2 million systems in NC) 30, ,000 new systems/yr installed in NC ~7,000 repairs each year 60% Coastal NC residents use on-site Pitt County, 460/yr % Septic >40 > 700,000 systems Wastewater, Water-Borne Diseases and Public Health Raw Sewage Characteristics Component Range of Concentrations Typical Concentration Total Suspended Solids, TSS 155 330 mg/L 250 mg/L BOD 286 mg/L 250 mg/L pH Total Coliform Bacteria 10 8 CFU/100mL 10 9 CFU/100mL Fecal Coliform Bacteria 10 6 10 8 CFU/100mL 10 7 CFU/100mL Ammonium-Nitrogen, NH 4 -N mg/L 40 mg/L Nitrate-Nitrogen, NO 3 -N Less than 1 mg/L Total Nitrogen 26 75 mg/L 60 mg/L Total Phosphorus mg/L 10 mg/L mg/L = milligrams per liter s.u. = standard units CFU/100 mL = Colony-Forming Units per 100 milliliters Adapted From: US EPA Onsite Wastewater Treatment Systems Manual, EPA/625/R-00/008, US EPA Office of Water, 2002 NC Design Flow = 60 g/d Water Use Characteristics Microbial Waterborne Disease Prior to the late 19 th century, outbreaks of epidemic waterborne disease claimed heavy tolls in human lives and suffering. As late as the 1880s typhoid killed people per 100,000 population in the US every year. Cholera was also a serious issue in the US in the 19 th century. Contamination of waterways in the developing world continues to persist as the most pressing environmental health problem. Wastewater and Public Health Almost 5,500 people die every day due to fecal contaminated drinking water (developing nations). Wastewater and Public Health Wastewater Pre-treatment Improving Tank Performance Principles of On-site Wastewater Treatment and Disposal I. On-site systems should ensure that the effluent is absorbed by the soil and does not come to the land surface or flow directly into streams, rivers, lakes, the ocean or the groundwater 1)Sewage contains pathogens, if the sewage remains below the surface direct exposure will not occur. If sewage surfaces, there are immediate public health concerns. 2)On-site systems treat and dispose of wastewater, via the septic tank and soil beneath the trenches. For treatment to happen, wastewater must stay in soil beneath the surface and above the water table. Principles of On-site Wastewater Treatment and Disposal II. On-site systems should maximize the aerobic treatment of the sewage. 1) Aerobic treatment occurs in aerated soil beneath the drainfield trenches (unsaturated zone). 2) Aerobic treatment is the fastest and most complete treatment the effluent can receive in the soil. 3) On-site systems should be located where the effluent must travel the farthest distance before reaching the water table or saturated layers. Wastewater Treatment Groundwater Septic Tank Aerated soil Wastewater Treatment 18 12 Group II-IV Soils: Loams, clay loams and clays Group I Soils: Sands Principles of On-site Wastewater Treatment and Disposal III.On-site systems should apply effluent to the soil only in suitable and prepared treatment and disposal field. 1)The treatment and disposal field includes trenches or beds lined with porous media, where effluent is discharged into via pipes with holes. The soil beneath the trenches/bed absorbs the wastewater. 2)Septic system components (tank, distribution devices, pipes, etc.,) should not leak- may cause contamination. 3)Systems should only be installed in areas with suitable soil and site conditions, as determined by trained professionals (EHS). Principles of On-site Wastewater Treatment and Disposal 4) Treatment and disposal field trenches should be designed to maximize the effluent contact with soil, thus improving treatment. 1) Long, narrow trenches provide more wastewater/soil contact area than shorter, wide trenches (Beds). 2 trenches - 50 x 3 x1 1 Bed- 50 x 6 x 1 Contact Areas Trenches = 500ft2 Bed = 400 ft2 Principles of On-site Wastewater Treatment and Disposal 5) Treatment and disposal field trenches should have level bottoms and should be level along their entire length to distribute effluent as evenly as possible. 1) Slanted or sloped trench bottoms will make effluent flow to the lowest area, possibly causing overload and ponding of wastewater to the surface. Biomat Formation Reduces infiltration rate Promotes unsaturated flow Can improve treatment May cause hydraulic failure Indicator Bacteria Conc. Near Septic Systems Cogger et al., 1988 Scandura and Sobsey, 1997 Humphrey et al., 2011 Conn et al., 2011 Harris et al., 2013 Relatively high concentrations adjacent to drainfields, and sandy, shallow soils more prone to bacterial loadings Indicator Bacteria Conc. in Surface Waters Adjacent to Septic Systems Booth et al., 2003 Ahmed et al, 2005 Cahoon et al., 2006 Harris et al., 2013 Previous Septic System Studies North Carolina Environmental Issues Shellfish Waters (SA) Over 1,157 acres of SA waters have closed since 1990 (NC DWQ, 2007) High bacteria concentrations Recreational Waters- swimming advisories due to bacteria concentrations 46 advisories in 2006 due to excessive bacterial concentrations (NC DENR, 2007) More stringent coastal stormwater rules enacted in 2008 Are septic systems efficient at reducing bacteria densities in wastewater before discharge to shallow groundwaters? Previous Septic System Studies Nitrogen Concentrations in Groundwaters Beneath and/or Adjacent to Septic Systems Serving residential areas with shallow, sandy-sandy clay loam soils Carlile et al., 1981 Corbett et al., 2002 Reay et al., 2006* Del Rosario et al., 2014* Serving residential areas with deep, sandy soils Robertson et al., 1991* Postma et al., 1992* Buetow, 2002* Humphrey et al., 2010* All studies showed higher N near systems than background. Some (*) showed higher than water quality standards for NO 3 - (10 mg/L). Nitrogen Concentrations in Groundwaters Beneath and/or Adjacent to Septic Systems Serving residential areas with shallow, sandy-sandy clay loam soils Carlile et al., 1981 Corbett et al., 2002 Reay et al., 2006* Del Rosario et al., 2014* Serving residential areas with deep, sandy soils Robertson et al., 1991* Postma et al., 1992* Buetow, 2002* Humphrey et al., 2010* All studies showed higher N near systems than background. Some (*) showed higher than water quality standards for NO 3 - (10 mg/L). Previous Septic System Studies Phosphorous Concentrations in Groundwaters Beneath and/or Adjacent to Septic Systems Serving residential areas with shallow, sandy soils Corbett et al., 2002* Reay et al., 2006 Humphrey et al., 2014* Serving residential areas with deep, sandy soils Robertson et al., 1998* Postma et al., 1992 Humphrey and ODriscoll, 2011* Elevated P concentrations relative to background conditions (3 or more times higher)Elevated P concentrations relative to background conditions (3 or more times higher) North Carolina Environmental Issues Eutrophic Conditions and Fish Kills in 1990s Neuse River Nutrient Sensitive Waters Management Strategy 30% N loading reduction from baseline implemented in 1998 Tar-Pamlico River Nutrient Sensitive Waters Management Strategy 30% N loading reduction from 1995 baseline implemented in 2000 No increase in P loading from 1995 baseline Lake Jordan Watershed Strategy Neuse, Tar Pamlico and Lake Jordan Rules targeted most point and nonpoint sources of nutrients (agriculture, urban runoff, wastewater treatment plants), but not septic systems) Eutrophic Conditions and Fish Kills in 1990s Neuse River Nutrient Sensitive Waters Management Strategy 30% N loading reduction from baseline implemented in 1998 Tar-Pamlico River Nutrient Sensitive Waters Management Strategy 30% N loading reduction from 1995 baseline implemented in 2000 No increase in P loading from 1995 baseline Lake Jordan Watershed Strategy Neuse, Tar Pamlico and Lake Jordan Rules targeted most point and nonpoint sources of nutrients (agriculture, urban runoff, wastewater treatment plants), but not septic systems) Neuse River Foundation (2009)