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TMDLs:  A significant Change in Water Quality Regulation Enforcement

Summer 1999

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Fall 1998

New Method Developed To Measure the Vertical Infiltration Capacity of the Soil Using Single Ring Infiltrometers

The UCR technique provides a solution to correct for lateral flow and ring geometry in measurements of infiltration rate by infiltrometers. A value for the vertical infiltration capacity of the soil is derived easily.

Laosheng Wu

Asst. CE Irrigation/Water Management Specialist

Water infiltration into soil from ponded sources is of interest for many scientific and engineering aspects of water management, including irrigation, runoff prediction, and contaminant transport in the vadose zone. Our UCR laboratory has developed a simple method to measure the vertical infiltration capacity of the soil using single ring infiltrometers, based on a knowledge of the soil's hydraulic properties, ring geometry, and boundary conditions. The new technique has many practical applications in water management: For example, the rate at which water can be applied to the soil surface without generating runoff is determined by the one-dimensional (1-D) final vertical infiltration capacity of the soil, which can now be solved easily, as explained herein.

Single-ring (SR) infiltrometers are probably the most widely used device for measuring the infiltration rates of water in the field; however, water flow into soil from a ring infiltrometer represents a three-dimensional (3-D) water flow. Therefore, the total infiltration capacity from the ring can be divided into two components: vertical infiltration capacity and infiltration capacity due to lateral seepage (horizontal flow) driven by matric force. Thus, a generalized relationship between the 1-D vertical infiltration capacity and infiltration rates measured by ring infiltrometers under various infiltrometer configurations, which consist of both vertical and horizontal flow components, has practical applications. When a SR infiltrometer is used, the contribution from lateral flow to the total measured infiltration rate increases as the ring size decreases. The texture and the water content of the test soil also affect the contribution of lateral flow to the total infiltration capacity measured by infiltrometers.

Using numerical simulation and scaling techniques that model water flow in the field, our laboratory has quantified the effects of soil conditions and ring geometry on infiltration rates and developed simple equations to solve for the vertical infiltration capacity of the soil. In the field, it is difficult to evaluate the effects of soil conditions and ring geometry on infiltration measurements because of the spatial variability of the soil and nonequal soil surface disturbances caused by ring installation. Such uncertainties make it impossible to replicate the field measurements that are needed to evaluate the effects of soil conditions and ring geometry on infiltration.

Based on our simulation and scaling techniques, we found that a SR infiltrometer measures the final, stabilized infiltration rate (if) to be f times greater than the 1-D (vertical) infiltration rate, which can be expressed by the following equation, where f is the correction factor:

if = f i1-D    (1)

Thus, the steady-state vertical infiltration capacity of the soil (i1-D) and the infiltration rate measured by a SR infiltrometer (if) differ by a factor of f. f can be calculated independently using the hydraulic properties of the soil, ring geometry, and initial and boundary conditions, as expressed in the following equation:

if f= (H + 1/α)/(d + r/2) + 1      (2)

where H (cm) is the ponding depth; d (cm) is the ring insertion depth; and r (cm) is the ring radius. Typical α values for sand, loam, and clay may be approximated by 0.36, 0.12, and 0.04, respectively (Elrick et al., 1988). It can be seen from Eq. (2) that f approaches unity (f=1) as either d or r approaches infinity (as the radius becomes as large as possible and the insertion depth becomes as deep as possible), which means that the infiltration rate measured by the SR infiltrometer (if) equals the 1-D vertical infiltration (Eq. 1), i.e., no lateral flow.

Table 1 provides an example of applying these concepts. The f values are given for three soil types in Table 1, and a SR infiltrometer of 20 cm diameter, insertion depth (d) of 5 cm, and ponding depth (H) of 5 cm was used to measure infiltration capacity (if). For the Yolo light clay, the SR infiltrometer with a ring diameter of 20 cm measured water flow to be about 3.5 times the 1-D infiltration rate (Table 1). After calculating f according to Eq. (2), the if measured experimentally by the SR infiltrometer is divided by f to give a measure of the 1-D vertical infiltration capacity of the soil (i1-D). The vertical relative infiltration rates of the three soils calculated by Eq. (1) (if /f) were very close to the actual 1-D (vertical) relative infiltration rates (i1-D), Table 1).

If other ring sizes and ponding depths are used, or the infiltration rates of other soil types are being measured, the values of these variables must be substituted into Eq. (2) in order for correct f values to be calculated.

References

Elrick, E.E., W. D. Reynolds, and K. A. Tan. 1988. A new analysis for the constant head well permeameter technique. In Proceedings of validation of flow and transport models for the unsaturated zone. New Mexico, 23-26 May 1988.

Wu, L. and L. Pan. 1997. A generalized solution to infiltration of single-ring infiltrometers. Soil. Sci. Soc. Am. J. 61:1318-1322.

Wu, L. L. Pan, M. J. Roberson, and P. J. Shouse. 1997. Numerical evaluation of ring-infiltrometers under various soil conditions. Soil Sci. 162(1):771-777.

 

Practical Applications

Equations (1) and (2) have practical applications: A person can easily calculate the vertical infiltration capacity (i1-D) of the soil from field measurements of the infiltration rate using an SR infiltrometer. First, by knowing the ring insertion depth, ring radius, ponding depth, and α value of the soil, the value of f can be determined independently using Eq. (2). Second, the value of f from Eq. (2) can be plugged into Eq. (1) along with the experimental value of the infiltration rate measured by the SR infiltrometer (if). The ratio of if /f gives a measurement of the 1-D vertical infiltration rate of the soil (i1-D).

Table 1. The Actual Vertical Relative Infiltration Rate (i1-D) vs. the Calculated Vertical Relative Infiltration Rate (if /f)
Soil texture i1-D ifa f if /f
Berino fine sand 1.00 2.78 2.57 1.08
Sandy clay loam 1.05 1.91 1.87 1.02
Yolo light clay 1.07 3.52 3.29 1.07
aInfiltration measured by SR infiltrometer; diameter of SR infiltrometer=20 cm.

(Editor's Note: Part II. Survival and Fate of Microbial Pathogens on Food and Non-Food Crops Irrigated with Reclaimed Wastewater and Part III. Assessing Microbial Risks will be in the Winter and Spring 1999 issues of Soil Water and Irrigation Management. The series of three articles is adapted from and excerpted in part from a comprehensive chapter authored by Dr. Marylynn V. Yates, Professor of Environmental Microbiology and Extension Groundwater Quality Specialist in the Department of Environmental Sciences at the University of California, Riverside and Dr. Charles P. Gerba, University of Arizona, Tucson. Their 51-page chapter, "Microbial Considerations in Wastewater Reclamation and Reuse," is published in Wastewater Reclamation and Reuse (1998), edited by Takashi Asano, Ph.D., P.E. (Volume 10 of the Water Quality Management Library), Technomic Publishing Co., Inc, Lancaster, PA.)

Microbial Considerations in Wastewater Reclamation and Reuse

Part I: Types and Occurrence of Microbial Pathogens in Wastewater

The major source of pathogenic microorganisms found in domestic wastewater, which may include bacteria, viruses, parasites, fungi, and algal toxins, is the fecal material of infected individuals; however, urine may also be a source of certain pathogenic viruses (Hurst, 1989). The numbers and types of pathogens found in wastewater will vary both spatially and temporally, depending on the disease incidence in the population producing the wastewater, season, water use, economic status of the population, and quality of the potable water (Rose and Carnahan, 1992).

Parasites

Parasites pathogenic to humans found in domestic wastewater can be classified into two groups: the protozoa and the helminths. The resting (cyst) life cycle stage of pathogenic protozoa is generally relatively resistant to inactivation during conventional wastewater treatment processes. Pathogenic protozoa are transmitted primarily by fecally contaminated water and food. The concentration of pathogenic protozoa in the fecal material of infected individuals can be quite high and can persist for extended periods. The reported concentrations of Giardia and Cryptosporidium are 106 and 107 per gram feces (Jakubowski, 1984; Robertson et al, 1992). Excretion of Giardia may persist for up to 6 months (Pickering et al., 1984).

Two pathogenic protozoa, Cryptosporidium and Giardia, are the causative agents for 74.3% and 4.8%, respectively, of the waterborne illnesses reported in the United States from 1971-1994. Although these two protozoa have caused 19.7% of the waterborne outbreaks reported in the 23-year period, they have caused more than 79% of the waterborne illnesses and disease reported, compared to gastroenteritis of unknown etiology, identified as the causal agent in 49.1% of waterborne outbreaks but only 14.4% of waterborne illnesses during the period (Craun, 1991; Herwaldt et al., 1992; Moore et al., 1994; and Kramer et al., 1996).

Bacteria

Human fecal material typically contains up to 1012 bacteria per gram, but the majority are non-pathogenic. The bacteria of most concern in domestic wastewater are the enteric bacteria, those that infect the gastrointestinal tract of man and are shed in fecal material. Bacterial pathogens are transmitted by direct contact with an infected individual or by consumption of contaminated water and food. An infected individual excretes high numbers of pathogenic bacteria. For example, an individual infected with Shigella, which causes bacillary dysentery, may excrete up to 109 organisms per gram of feces (Bitton, 1994). The results of infection with other enteric bacteria range from gastroenteritis (E. coli, Yersinia, Campylobacter) to typhoid and salmonellosis (Salmonella) and cholera (Vibrio), among others. When these organisms are introduced into wastewater and the soil environment, their ability to survive and reproduce tends to be limited by competition with indigenous bacteria for scarce nutrients and by temperature conditions less hospitable than the gastrointestinal tract of man, where the enteric bacteria are highly adapted.

Viruses

Unlike bacteria, viruses typically are not found in human feces. Viruses are present only in the feces of individuals who have been infected either intentionally (e.g., poliovirus vaccination) or inadvertently through contact with an infected individual or contaminated water or food. In these cases, viruses can be excreted in very high numbers and for long periods of time: The concentration of rotaviruses, a common cause of diarrhea, may be as high as 1012 particles per gram feces (Flewett, 1982). Rotavirus excretion usually lasts 1 to 3 weeks, but up to 2 months has been observed (Kapikian and Chanock, 1990). Excretion of enteroviruses (i.e., poliovirus, echoviruses and coxsackie viruses) may persist for 16 weeks (Melnick and Rennick, 1980). More than 140 types of enteric viruses can contaminate wastewater. The results of infection by viral pathogens in wastewater can range from undetectable to diarrhea and vomiting (rotavirus, Norwalk virus), to a variety of diseases including gastroenteritis, respiratory illness, meningitis, encephalitis, hepatitis, paralysis, myocarditis, and conjunctivitis.

References

Bitton, G. 1994. Wastewater Microbiology. Wiley-Liss, New York.

Craun, G.F. 1991. Causes of waterborne outbreaks in the United States. Water Sci. Technol. 24:17-20

Flewett, T.H. 1982. Clinical features of rotavirus infections. In: Virus Infections of the Gastrointestinal Tract. D. J. Tyrell and A. Z. Kapikian, eds. Marcel Dekker, New York.

Herwaldt, B.L., G.F. Craun, S.L. Stokes, and D.D. Juranek. 1992. Outbreaks of waterborne disease in the United States: J. Amer. Water Works Assoc. 84:129-135.

Hurst, C.J. 1989. Fate of viruses during wastewater sludge treatment processes. CRC Crit. Rev. Environ. Contr. 18:317-343.

Jakubowski, W. 1984. Detection of Giardia cysts in drinking water: state of the art. In: Giardia and Giardiasis, Biology, Pathogenesis and Epidemiology. Plenum Press, New York.

Kapikian, A. Z. and R. M. Chanock. 1990. Norwalk group of viruses. In: Virology. B. N. Fields, D. M. Knipe, R. M. Chanock, M. S. Hirsh, J. L. Melnick, T. P. Monath, and B. Roizman, eds. Raven Press, New York.

Kramer. M. H., B. L. Herwaldt, G. F. Craun, R. L. Calderon, and D. D. Juranek. 1996. Waterborne disease: 1993 and 1994. J. Amer. Wat. Works Assoc. 88:66-80.

Melnick, J. L. and V. Rennick. 1980. Infectivity of enterovirus as found in human stools. Med. Virol. 5:205-220.

Moore, A. C., B.L. Herwaldt, G F. Craun, R. L. Calderon, A. K. Highsmith, and D. D. Juranek. 1994. Waterborne disease in the United States, 1991 and 1992. J. Amer. Wat. Works Assoc. 86:87-98.

Pickering, L. K., H. W. Kim, and C. D. Brandt. 1987. Occurrence of Giardia lamblia in children in day care centers. J. Pediatr. 104-522-526.

Robertson, L.J., A.T. Campbell, and H.V. Smith. 1991. Survival of Cryptosporidium parvum oocysts under various environmental pressures. Environ. Mirobiol. 58:3494-3500.

Rose, J.B. and R.P. Carnahan. 1992. Pathogen removal by full scale wastewater treatment. Report to Dept. of Env. Regulation, State of Florida.

Domenigoni Reservoir: An MWD Study to Avert Potential Microbial Contamination

A hotly contested issue recently debated in Riverside County is whether body contact water sports should be permitted at the Domenigoni Reservoir currently under construction in Hemet by the Metropolitan Water District (MWD) of Southern California. Dr. Marylynn Yates, Professor of Environmental Microbiology and Extension Groundwater Quality Specialist in the Department of Environmental Sciences at the University of California, Riverside (UCR) and lead scientist on a study sponsored by the MWD to assess the potential public health risks associated with body-contact recreation on the drinking-water reservoir, says body-contact recreation should not be permitted on the reservoir.

"The study found that disease-causing microorganisms will be added to the water by people engaged in water contact activities, resulting in an increased risk of illness in the community drinking this water unless additional treatment is installed," wrote Yates in The Press-Enterprise Opinion pages on Sunday, October 4, 1998. The annual treatment costs that will be required to reduce microorganisms to acceptable levels are greater than the estimated economic benefit to the local community from body contact-recreational activities, Yates said. Moreover, the potential economic liability to the local community from waterborne illness to recreators in the reservoir or to MWD's water consumers has not been calculated or estimated to date, Yates said.

The Domenigoni Reservoir will hold 196 billion gallons of water, which, nonetheless, could be contaminated to a level that would result in significant public health risk. If one person infected with rotavirus, a common cause of diarrhea, had an accidental fecal release during recreational activities at the reservoir, 1012 (one trillion) virus particles could be released into the water, resulting in a concentration of five virus particles per gallon, if the virus were evenly distributed in the water.

This rotavirus concentration is sufficient to cause illness in one person out of every 100 people who swallow one ounce of the water while recreating. After conventional drinking water treatment, the water would have more than 600 times the virus limit established by the EPA for drinking water, Yates said.

Some local politicians opposed Yates' position, citing the economic benefits of the proposed recreational activities to the region, but on Tuesday, October 13, 1998, the MWD Board of Directors voted not to allow body contact water sports on the drinking water reservoir.