Impact Of Wastewater Quality On The Long-Term Acceptance Rate Of Soils For On-Site ...

102 Pages·2008·5.02 MB·English

REPORT N0.316
by
Aziz Amoomegar
Soil Science Department
Agricultural Research Service
College of Agriculture and Life Sciences
North Carolina State University
July 1998
Copies available from: Water Resources Research Institute
ofTheUniversityofNorth Carolina
North Carolina State University
Box 7912
Raleigh, NC 27695-7912
THE UNIVERSITY OF NORTH CAROLINA is composed of the sixteen public senior insfitutionsi n North Carolina.
UNC-WRRI-98-3 16
IMPACT OF WASTEWATER QUALITY ON THE LONG-TERM ACCEPTANCE RATE
OF SOILS FOR ON-SITE WASTEWATER DISPOSAL SYSTEMS
Aziz Amoozegar
Soil Science Department
Agricultural Research Service
College of Agriculture and Life Sciences
North Carolina State University
Raleigh, North Carolina 27695-7619
The research on which this report is based was financed by the Water Resources Research
Institute of The University of North Carolina.
Contents of this publication do not necessarily reflect the views and policies of the Water
Resources Research Institute, nor does mention of trade names or commercial products constitute
their endorsement or recommendation for use by the Institute or the State of North Carolina.
The use of trade names does not imply endorsement by the North Carolina Agricultural Research
Service or the North Carolina Water Resources Research Institute of the products used or
mentioned nor criticism of similar ones not mentioned.
WRRI Project No. 70140
July 1998
One hundred fifty-five copies of this report were printed at a cost of $1,066.40 or $6.88 per copy.
ACKNOWLEDGMENT
Special recognition is extended to Mr. Christopher Niewoehner, Agricultural Research
Technician, Soil Science Department, for his hard work and dedication to this project. He was
instrumental in setting up the field experiments, training other personnel, completing the
laboratory analyses, managing the data, and preparing graphs for this report. Both Chris and Ms.
Jennifer Engele, a temporary Research Technician, worked long days and visited the research
sites at nights for many weeks during the project. Their efforts, along with the efforts of Alex
Adams, Brett Martin, and Dean Granthem, undergraduate students who conducted various
experiments and analyses, are greatly appreciated. Appreciation is also extended to Mr. Stewart
Starr, Mr. George Clark, and Mr. Ken Schneider, the superintendents of Research Stations at
NCSU, for their cooperation with this project. Other individuals who must be recognized for
assisting with site selection and providing the necessary information about the drip systems are
Mr. A1 Peoples, Franklin County Health Department; Mr. Bob Dewees, Department of Public
Instruction; Mr. Steven Berkowitz, On-Site Wastewater Section of the North Carolina
Department of Environment, and Natural Resources; and Mr. Jack Harmon from Waste Water
Systems of North Carolina. The school administrators and maintenance staff at Edward Middle
School in Franklin County and Vaughn Elementary School in Warren County should also be
recognized for their help with the project. Finally, special thank you to the secretarial and
accounting staff at both the Soil Science Department and Water Resources Research Institute and
to all the faculty and staff in the Soil Science Department who facilitated the efforts of the
research team in this project.
*..
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ABSTRACT
People living in rural areas and around large municipalities with no access to public sewage
systems must dispose oftheir wastewater on-site. The most common type of on-site sewage
management in North Carolina is the conventional septic system, which is composed of a septic
tank (interceptor tank) and a drainfield. It is not uncommon for septic systems to fail. Hydraulic
failure within the drainfield area of a young septic system is generally attributed to faulty design,
installation, and/or misuse of the system. The quality of wastewater, however, can have a major
impact on soil hydraulic properties, particularly on wastewater infiltration from the trenches into
the soil. A reduction in the infiltration rate from the trenches of a septic system into the soil may
result in surface failure of the system. The overall objective of the research presented here was to
assess the effects of various components of domestic wastewater on soil hydraulic properties.
Saturated hydraulic conductivity (LJan d infiltration rate (IR) for tap water, well water, and
four different simulated wastewaters from washing machine, kitchen sink, bathroom sink and
shower (bathroom wastewater without toilet wastes), and a car wash in a clayey soil, a sandy
soil, and one saprolite were measured in situ for five consecutive days using three replications.
Saturated hydraulic conductivity was measured by the constant-head well permeameter method
using 6-cm diameter cylindrical holes. A 15- to 20-cm constant depth of water was maintained
at the bottom of the hole and was calculated using the Glover solution. The IR was
measured under a 5- to 7-cm of constant head using double-cylinder (ring) infiltrometers. After
the measurement phase, soil samples were collected from three depth intervals at three locations
in the area between the outer and inner cylinders of each infiltrometer and from three depth
intervals at three locations around each 6-cm diameter auger hole for laboratory analysis. In
addition, intact core samples (6.5 cm diameter and 10 cm long) were collected from the clayey
Lt
soil and saprolite and analyzed in the laboratory for and water retention using the five
solutions. For selected experiments, a CaC1, solution was applied to the soil and saprolite
following the initial measurement of IR or Gtt o determine if the rate of water flow into the soil
or saprolite could be improved.
kt
In general, and IR of the two soils and saprolite for water did not change substantially with
kt
time. For the simulated wastewaters, however, both and IR decreased for saprolite and sandy
soil. For the clayey soil, mixed results were obtained for most cases. Overall, simulated
wastewater from washing machines (laundry wastewater) had the most negative impact on soil
hydraulic properties. Based on measurement results after addition of CaCl, to the soil and
saprolite, it appears that the adverse effect of wastewater application on soil hydraulic properties
may be reversible using calcium amendments. Based on the Na content and sodium adsorption
ratio (SAR) of the simulated wastewaters, and considering that the adverse impact of
wastewaters on infiltration rate and hydraulic conductivity were reversed with the addition of Ca
to the soil or saprolite, it appears that in the absence of a biological clogging mat, Na (or a
compound containing Na, such as a surfactant in laundry detergent) is the most likely cause for
hydraulic failure of a septic system. Considering the reduction in the rate of flow into and
through different soils for various components of wastewater, wastewater quality should be
considered when determining the loading rates (long-term acceptance rates) for designing septic
systems, particularly for laundry, car wash, and other businesses in rural areas.
V

TABLE OF CONTENTS
...
ACKNOWLEDGMENT .......................................................
111
..................................................................
A8STRACT v
...........................................................
LIST OF FIGURES ix
...
...........................................................
LIST OF TABLES XIII
.............................................
SUMMARYANDCONCLUSIONS xv
RECOMMENDATIONS ...................................................... xix
.............................................................
INTRODUCTION 1
.............................................................
Objectives 7
..................................................
MATERIALS AND METHODS 9
Soil Characteristics ...................................................... 9
Wastewater Characteristics ................................................ 9
.......
Field Measurement of Infiltration Rate and Saturated Hydraulic Conductivity 10
................................................
Laboratory Measurements 16
..............................................
Assessment of Drip Systems 17
.................................................
RESULTS AND DISCUSSION 21
Characteristics of the Soils and Wastewaters ................................. 21
............................................
Variations Among Replications 21
Site 1 .. Saprolite ....................................................... 24
Infiltration Rate .................................................. 24
....................................
Saturated Hydraulic Conductivity 32
..........................................................
Site2.. Sand 37
..................................................
Infiltration Rate 37
....................................
Saturated Hydraulic Conductivity 42
Site 3 .. Bt Horizon ..................................................... 44
..................................................
Infiltration Rate 44
.....................................
Saturated Hydraulic Conductivity 47
.....................................................
Laboratory Analysis 48
Saprolite at Site 1 ................................................. 48
...............................................
Bt Horizon at Site 3 54
Septicsystems ......................................................... 56
Wastewater Quality ............................................... 56
Soil Water Status ................................................. 57
VaughnElementary School ................................... 57
Edward Best Middle School .................................. 57
vii
REFERENCES .............................................................. 63
GLOSSARY ................................................................ 69
..........................................................
Abbreviations 69
Units of Measurement ................................................... 70
............................................
PUBLICATIONS/PRESENTATIONS 71
.................................................................
APPENDIX 73
....
Results for the Three Replications for Each Soil-WaterNastewater Combination 73
...
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