A The N C L E A Small R O Small I N H G MA FlowsFlows JournalLL A collection of F professional papers on L

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small community Volume 2, Issue 1, Winter 1995 W

wastewater issues. Volume 2, Issue 1, Winter 1996

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C L E E S A U R I N G H O A The N C L E A Small R O Small I N H G MA Flows JournalLL A collection of F professional papers on L the study of onsite and O Contents Volume 2, Issue 1, Winter 1995 ontents small community C W wastewater issues.

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The Small Flows Journal From the Editor ...... 2 Sponsored by: by Cathleen Falvey U.S. Environmental Protection Agency Steve Hogye, Project Officer Municipal Support Division Office of Wastewater RESEARCH Enforcement and Compliance Washington, D.C. Shallow Intermittent Sand Filtration: National Small Flows Clearinghouse West Virginia University Performance Evaluation ...... 3 John L. Mori, Ph.D., Manager, WVU Environmental Services and by Jeannie Darby, Ph.D., P.E. Training Division Patricia Miller, Ph.D., Technical Advisor George Tchobanoglous, Ph.D., P.E. Jill A. Ross, Publications Supervisor Cathleen Falvey, Editor M. Asri Nor Eric Merrill, Graphic Designer David Maciolek International Standard Serial Number 1079-1531

The Small Flows Journal National Small Flows Clearinghouse FEATURE West Virginia University P.O. Box 6064 A Private Market Approach To Onsite Wastewater Morgantown, WV 26506-6064 1-800-624-8301 Treatment System Maintenance ...... 16 by James Herring Reprints For permission to reprint information appearing in The Small Flows Journal, please send a letter of request to Manuscript Guidelines...... 25 the editor.

The Small Flows Journal is funded by the United States Environmental Protection Agency. The contents of this journal do not necessarily reflect the views and policies of the Environmen- tal Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

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1 From the Editor

EditorialT Review Board A

rom the Editor N FFrom the Editor Terry Bounds, P.E. Roseberg, OR

James Converse, Ph.D. BiologicalC Systems Engineering Dept., University of Wisconsin he National Small Flows Brian Cooper, C.E.T. Clearinghouse (NSFC) is Simcoe EngineeringL Group, Ltd., Pickering, Ontario pleased to present this second E issue of The Small Flows Donald Gray, Ph.D. T Professor of Civil Engineering,A West Virginia University Journal. We were overwhelmed by the RI positive response to our first issue, Michael Hines, M.S., P.E N published in the fall of 1994, and we Quantum Engineering Corporation, Knoxville, TN hope to continue to inspire the same level of enthusiasm from you, our Anish Jantrania, Ph.D., P.E. Engineering Consultant, City of Gloucester, MA readers, with each issue to come. Craig Jowett, Ph.D., P. Eng. Many of the comments we received Research Associate Professor praised the articles for being directly relevant to you in your work Waterloo Centre forS GroundwaterM Research,A UniversityL of Waterloo as sanitarians, public health officials, and engineers. We also L L A Jim Kreissl received many compliments on the quality of the information and Environmental Engineer, Center for Environmental Research F the style in which it was presented. U.S. Environmental Protection Agency

George Loomis The two papers presented in this issue were selected with these Research Soil Scientist goals in mind. The first paper, Shallow Intermittent Sand Filtration: Natural Resources Science Dept., University of Rhode Island Performance Evaluation" reports the results of a study by environ- mental engineers at the University of California, Davis on the Roger E. Machmeier, Ph.D., P.E Professor Emeritus, University of Minnesota minimum media depth required to produce high quality effluent from intermittent sand filters. ADD TWO SENTENCES HERE. Karen Mancl, Ph.D. Associate Professor of Agricultural Engineering The second article, A Private Market Approach to Onsite Wastewa- The Ohio State University

ter Treatment System Maintenance" is a feature article proposing a Richard J. Otis, P.E. new strategy for encouraging onsite system maintenance by Vice-President, Ayres and Associates, Madison, WI individual homeowners. This idea could E Michael H. Ogden, P.E. A Southwest Wetlands Group, Santa Fe, NM U We hope that this long-awaited second issue meets or exceeds your R O expectations. While word of the journal is still spreading we have INSherwoodG Reed, P.E. H nearly 5,000 subscribers, unfortunately, enough manuscripts did not Consultant and Principal successfully complete the peer review process in time to publish Environmental Engineering Consultants, Norwich, VT two issues in 1995 as hoped. A.R. Rubin, Ph.D. Extension Specialist and Associate Professor Manuscripts are now being accepted for review for upcoming issues North Carolina State University of the journal If you would like to submit a manuscript, see the manuscript submissions guidelines on page 28. Information cards Jerry Stonebridge President, Stonebridge Construction, Inc., Langley, WA for free subscriptions are also found on page 28.We would very much appreciate it if you would help to continue to spread the word George Tchobanoglous, Ph.D., P.E. about The Small Flows Journal by passing these cards along to your Professor of Civil Engineering, University of California at Davis colleagues. Jerry Tyler, Ph.D. Associate Professor, University of Wisconsin Sincerely, SMA Volume 2, Issue 1, Winter 1996 Volume L

AA.T. Wallace, Ph.D., P.E. Professor, DepartmentN of Civil Engineering, University of Idaho O Ted Walker, R.E.H.S. Cathleen Falvey I Sonoma County Health Department, Sonoma, CA Editor T The Small Flows Journal A

The Small Flows Journal 2 TECHNICAL ShallowShallow IntermittentIntermittent SandSand Filtration:Filtration: PerformancePerformance EvaluationEvaluation

by Jeannie Darby, Ph.D., P.E., George Tchobanoglous, Ph.D., P.E., M. Asri Nor, and David Maciolek

ABSTRACT: Twelve shallow sand filters (0.38 m deep, nominal diameter of 1.2 m) were loaded intermittently with primary effluent to evaluate effects of hydraulic loading rate (HLR), dosing frequency (DF), and filter media characteristics on removal of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) , suspended solids (SS), turbidity, and organic and ammonia nitrogen. Hydraulic loading rates between 0.041 and 0.652 m/d1 were applied during an 85-day

period at DFs between 4 and 24 times/d. Media effective sizes (d10) ranged from 0.29 to 0.93 mm with uniformity coefficients between 1.4 and 4.52. At an HLR of 0.163 m/d and a dosing frequency of 24 times/d, effluent quality was excellent and comparable to effluent from advanced wastewater treatment facilities. Specifically, average removal rates of between 90 and 99 percent for BOD, SS, organic and ammonia nitrogen and turbidity, and at least 81percent for COD, occurred, regard- less of media characteristics.

ntermittent sand filtration is one Pell and Nyberg, 1989a,b,c; Pell et al., of the oldest known methods of 1990; Peeples et al., 1991). wastewater treatment and was I common in the U.S. before 1900 for Early filters, being relatively deep (ap- treating community sewage (EPA, 1980; proximately 2 meters) and lightly loaded, Marshall and Middlebrooks, 1974). were material-intensive and required large Wastewater is applied to granular media land areas. These factors, combined with beds in one or more doses per day such potential for odor production, resulted in that the media drain and reaerate between few such filters being constructed after doses. Excellent detailed descriptions of 1950. However, there is renewed interest the intermittent sand filtration process are in intermittent sand filters as shallower available elsewhere (Andersen et al., media depths and higher loading rates, and 1985; Metcalf and Eddy, 1991). special applications are being explored.

The Small Flows Journal

Many studies of intermittent sand filters Because intermittent sand filters are have been conducted to investigate the capable of producing high quality effluent effects of various parameters on perfor- and have relatively low maintenance mance. Key among these are effects of requirements, they are well-suited to onsite

hydraulic loading rate (HLR), dosing and small municipal applications. How- frequency (DF), and media characteristics ever, for the full potential of intermittent Volume 2, Issue 1, Winter 1996 and depth (Grantham et al., 1949; Furman sand filters to be realized, high quality et al., 1955; Schwartz and Bendixen, effluents need to be obtained reliably with 1970; Marshall and Middlebrooks, 1974; low capital and operating costs. Ideally, EPA, 1980; Siegrist and Boyle, 1981; filters constructed of shallow, locally Anderson et al., 1985; Andreadakis, 1987; available common sand would produce the

3 J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

required effluent quality at a high waste- water loading rate. To move toward this ideal, the minimum media depth for adequate treatment must be determined, as well as the effect of sand characteristics, loading rates, and dosing frequencies on performance.

Little information is available in the literature on the minimum media depth required to achieve adequate treatment. Previous research has indicated shallower media depths (i.e., 0.5 to 1 m versus the typical 2-plus m) may provide adequate treatment especially when dosed at higher frequencies (Grantham et al., 1949; Furman et al., 1955). However, a thorough investigation of filter performance with sand depths shallower than 0.5 m has not been published.

The objective of this research was to investigate the effects of HLR, DF, and filter media characteristics on removal of biochemical oxygen demand (BOD), FIGURE 1 chemical oxygen demand (COD), sus- plan view of experimental pended solids (SS), turbidity, organic- facilities nitrogen (organic–N), and ammonia

nitrogen (NH3–N) in shallow (0.38 m) sand filters loaded intermittently. Primary effluent Plywood cover wrapped with polyethylene sheeting Halved 102 mm PVC pipe cover (typ.)

Experimental Methods 19 mm PVC pipe manifold 76 mm 51 mm Experimental Facilities Washed pea gravel 76 mm

3 mm mesh plastic screen Twelve shallow sand filters were loaded intermittently with effluent from the Sand 381 mm primary settling tank of the University of California, Davis (UCD) wastewater Washed pea gravel treatment plant (WWTP). A plan view of layer 102 mm thick 9-16 mm gravel around drainpipe

the experimental facilities is presented in 102 mm figure 1. 38 mm PVC pipe underdrain 6 mm filed grooves surrounded by 9-16 mm gravel @ 102 mm on center (typ.) The filter units were constructed above Effluent outlet and ground, using galvanized metal stock sampling port water tanks with a depth of 0.61 m. The nominal inside diameter of the tanks was

Volume 2, Issue 1, Winter 1996 Volume

1.2 m with a range of ± 0.07 m. A FIGURE 2 schematic cross-section of a filter is cross-section of filter unit shown in figure 2.

The Small Flows Journal 4 Shallow Intermittent Sand Filtration: Performance Evaluation

99.999 52-mm holes were cut through the plastic 99.99 sheet of each cover to provide aeration to the filters. 99.9

99 The depth of the media in each filter was 381 mm. Two types of sand were used: 95 (1) concrete sand obtained from a local 90 ready-mix concrete company and (2) 80 70 cleaned and kiln-dried filter sand. Before 50 use, the concrete sand was washed to remove clay and silt. The average grain 30 20 size distribution of the washed concrete 10 sand and filter sand is shown in figure 3. 5 The average effective size and uniformity Sand Type d ,mm UC coefficient of the washed concrete sand 1 10 Concrete 0.29 4.52 Percent equal to or less than indicated size were 0.29 mm and 4.52, respectively. .1 Filter 0.93 1.29 Three effective sizes (0.33, 0.54, and 0.93 Filter 0.54 1.32 .01 mm) of filter sand were used. The Filter 0.33 1.42 uniformity coefficients of the filter sand .001 0.1 1 10 were less than 1.5. Size of Mesh Opening, mm

Experimental Design and FIGURE 3 Data Collection filter media particle size Because the filters were intended for distribution (average of frequent dosing, the volume of influent washed samples) applied per dose would be insufficient to Filter Design and Operating Parameters. flood the surface, resulting in uneven Design and operating parameters of the distribution. Thus, an influent distribution filters are summarized in table 1. Four system was provided consisting of a sizes of sand (0.29, 0.33, 0.54, and 0.93 19-mm PVC pipe manifold with 3-mm mm), four uniformity coefficients (1.29, upward facing orifices. Each branch of the 1.32, 1.42, and 4.52), five loading rates manifold was covered with halved, (0.041, 0.081, 0.163, 0.326 and 0.652 m/ 102-mm PVC pipe, and the whole system d), and three DFs (4, 12, and 24 times/d)2 was underlain with 76 mm of washed pea were investigated. These parameters were gravel. A spacing of 130 to 170 mm varied such that the effect of each param- between each orifice resulted in 52 eter could be investigated systematically orifices for each filter unit. The underdrain and independently of the other three of the units consisted of 38-mm diameter parameters. perforated PVC pipe surrounded with washed 10- to 16-mm gravel in a layer of Sampling. Grab samples of the effluent washed pea gravel 102 mm deep. The were collected through 13-mm sample

underdrain perforation was achieved using ports on each filter unit. The effluent was The Small Flows Journal 6-mm filed grooves spaced at 102 mm allowed to flow continuously through the center to center. Ventilation was provided sample ports to avoid settlement of through the open top surface and the suspended solids. To observe the perfor- effluent overflow outlet. mance at system start-up, samples were collected every other day during the first

two weeks of operation. Thereafter,

To prevent the accumulation of falling Volume 2, Issue 1, Winter 1996 debris on the filter surface and reduce sampling was conducted once per week. algae growth in the system, a removable Approximately three liters of effluent plywood cover wrapped with plastic was were collected from each filter unit using provided for each unit. The covers were 1-L plastic sample bottles during each raised 76 mm above the tanks, and four sampling event. Samples of the influent

5 J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

Dosing Hydraulic were obtained each time Filter Effective Uniformity frequency, Loading Application size, mm rate, m/d TABLE 1 effluent sampling occurred. number coefficient, UC times/d rate mm/dose 1 0.29 4.52 0.041 4 10.3 filter sand Sampling continued for 85 characteristics and days. 2 0.29 4.52 0.081 24 3.4 3 0.29 4.52 0.326 24 13.6 applied loading 4 0.29 4.52 0.652 24 27.2 Laboratory Analysis. 5 0.29 4.52 0.163 24 6.8 Samples were analyzed for 6 0.29 4.52 0.163 4 40.8 turbidity, SS, BOD, COD, 7 0.29 4.52 0.163 12 13.6 NH -N, NO -N, and organic- 8 0.33 1.42 0.163 24 6.8 3 3 9 0.54 1.32 0.163 24 6.8 N. Turbidity was measured 100.931.29 0.16324 6.8 with a HACH Model 2100A 11 0.93 1.29 0.163 4 40.8 turbidimeter. Analyses of 12 0.93 1.29 0.163 12 13.6

BOD and SS were conducted Note: To investigate the effect of each parameter independently of others according to Standard the following comparisons were made: Methods (APHA, 1989). Parameter investigated Compare filters: Spectrophotometric analysis Hydraulic loading rate 2, 3, 4, & 5 and 1 & 6 Effective size 8, 9 & 10 for NH3-N, NO3-N, and Dosing frequency 5, 6, & 7 and 10, 11, & 12 organic-N were conducted Uniformity coefficient 5 & 8 using a HACH DR3000 spectrophotometer and HACH methods (HACH DR3000 manual, the study is compared with typical septic 1985). Chemical oxygen demand was Expericmentaltank effluent, also inDesign table 2. and Values Data for analyzed by digestion followed by the primary effluent quality parameters colorimetric determination. Ammonia were generally in the lower one-third of nitrogen was analyzed using the the range that is typical for septic tank nesslerization method. Where interference effluent. was suspected (i.e., turbidity greater than 2 NTU), the nesslerization analysis was Data pertaining to the effect of varied preceded by distillation. Nitrate was parameters on performance of the inter- analyzed using the modified cadmium mittent sand filters are presented and reduction method. Organic nitrogen was discussed in the following sub-sections. analyzed using the nesslerization method Most of the discussion is focused on data preceded by digestion and distillation collected after the filters had been according to Standard Methods. Air operating three weeks and effluent quality temperatures measured at a climatological had stabilized. To determine whether data collection facility 2 km from the filter results from various filters were statisti- TABLE 2 site at the same elevation are representa- cally different, hypothesis tests using quality of wastewater applied tive of those at the filter site and were nonparametric (Wilcoxon signed-rank to filters recorded. The actual temperature of the media and wastewater were not measured

during the study. This study a Septic tank effluentb

Parameter Average Range Average Range Turbidity (NTU) 26.1 18 - 38 - - Experimental Design and COD (mg/L) 143.8 98 - 226 327 25 - 780 BOD (mg/L) 75.1 38 - 105 138 7 - 480 5 Data Collection TSS (mg/L) 29.1 20 - 38 49 10 - 695 NH -N (mg/L - N) 10.6 6.1 - 23.6 31 0.1 - 91 3 Characteristics of the wastewater applied Nitrate + Nitrite (mg/L-N) 0.3 0.0 - 1.1 0.4 0.1 - 7.4 Organic N (mg/L -N) 4.6 3.3 - 6.2 - - Volume 2, Issue 1, Winter 1996 Volume to the filters during the study period are

presented in table 2. Because intermittent a Values, at approximately 10 a.m PST, from startup through day 86 of operation sand filtration is most often used to treat (20 data points) septic tank effluent or similar quality b Adapted from USEPA (1978) wastewater, the primary effluent used in

The Small Flows Journal 6 Shallow Intermittent Sand Filtration: Performance Evaluation

test) and analysis of variance techniques carbon adsorption (Metcalf and Eddy,

(ANOVA) were conducted. When the two 1991). Effluent organic-N and NH3-N, tests produced conflicting results, data under these loading conditions, were distributions were inspected for normality. below levels listed in the same reference For normally distributed data, ANOVA as typical for activated sludge with results were used. Otherwise, results of separate stage nitrification/denitrification. Wilcoxon signed-rank tests were used. When operated as described above, each Confidence levels used in all tests were 95 1.2-m diameter filter unit was able to treat percent. 184 L/d of septic tank or similar quality effluent to tertiary quality Effluent concentration, levels. Percent removal mg/L except NTU for turbidity Parameter Average Minimum Maximum Average Minimum Maximum In this research, removal rates Turbidity 97 91 99 0.7 0.3 1.7 in filters dosed 12 times/d or COD 94 81 >99 8.8 1.042 more, exceeded most removal rates reported in the literature BOD5 99 97 >99 0.7 0.0 2.6 SS 98 94 >99 0.4 0.0 1.8 employing DFs of 1 to 4 times/

NH3-N 99 99 >99 0.04 0.01 0.20 d. The observed removal rates

Organic N 95 90 >99 0.20 0.0 0.5 for BOD, SS, NH3-N, and organic-N compare favorably a Based on data collected from day 23 through day 86 of operation with the results of Furman et (10 measurements per filter for each parameter) al. (1955), where DFs of up to 24 times per day were used. Overall Performance TABLE 3 Most previous research used sand of summary of treatment significantly greater depth than used in achieved for filters loaded A summary of the performance of filters this research; yet effluent quality observed at 0.163 m/d with dosing 5, 7, 8, 9, 10, and 12 (loaded at 0.163 m/d in this research was as good or better than frequency of 12 or 24 and dosed 12 or 24 times/d) is shown in reported in previous research. In the times/daya table 3. Effluent from these filters was of literature reviewed, only Peeples et al. excellent quality and (except for coliform (1991) tested a filter with shallower media levels, which were not measured) would than were used in this study (0.30 m vs. be suitable for most disposal methods or 0.38 m), and the performance reported reclamation. In these filters, average was noticeably worse. Peeples et al. removal rates were 94 percent or better for (1991) used media with a d10 of 0.44 mm all parameters, and removal rates of and a UC = 3.3 and employed a DF of 1 greater than 99 percent were common. time/d at an HLR of 0.255 m/d. The Effluent quality from the filters was improved performance observed in this extremely stable, with only one excursion study, compared to that of Peeples et al. from a very robust performance (one (1991), is probably due to increased DF (4 effluent COD measurement, from one times/d or greater). Higher media tempera- filter, was 42 mg/L; otherwise the maxi-

tures may have been an additional factor. The Small Flows Journal mum would have been 20 mg/L). Filters with lower HLRs had equal or better The average air temperature from June performance, except when dosed at a through August was 22.6 °C, which is frequency of 4 times/d, which sometimes near the high-end of the range in the resulted in worse performance. previous studies that reported temperature.

Due to the filter design and intense solar

Volume 2, Issue 1, Winter 1996 At an HLR of 0.163 m/d and a DF of 12 radiation, the filter media were probably times/d or greater, maximum effluent as warm as or warmer than the average air values of BOD, COD, SS, and turbidity temperature. Previous studies reported (presented in table 3) were below levels increased removal rates at higher tempera- listed as typical for activated sludge tures (Grantham et al., 1949; Pell et al. followed by granular media filtration and 1990; Schwartz and Bendixen, 1970).

7 J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

250 of DFs, from 4 to 24 times/d. It can be Filter DF, times/d seen in figure 4 how 11 4 200 12 12 stable the effluent 10 24 COD values were Influent relative to the influent, especially 150 for filters dosed 12 or 24 times/d after 25 days of filter COD, mg/L 100 operation. As DF increased from 4 to 24 times per day, average COD 50 removal improved FIGURE 5 from 79.3 to 93.3 effect of hydraulic loading rate on COD percent, an effect that removal at 0 0 102030405060708090 is discussed in more (a) DF = 24 times/d and Day of Operation detail below. (b) DF = 4 times/d (d10 = 0.29 mm, UC = 4.52)

FIGURE 4 applied (influent) and 100 effluent COD from (a) DF = 24 times/d three filters 80 (HLR = 0.163 m/d)

60 Grantham et al. (1949) reported that improvements in performance due to air 40 Filter HLR, m/d temperature increases were greater for 2 0.081

coarser sand and for shallower depth and Removal COD Percent 3 0.326 concluded that this was due to greater air 20 4 0.652 circulation with larger media and/or 5 0.163 shallower depths. The higher media temperatures in this study may be a factor 0 in the performance, but no conclusions 100 can be drawn without an explicit focus on the effects of temperature on filter performance. 80 (b) DF = 4 times/d

Influent and effluent COD concentrations for three filters are shown in figure 4 to 60 illustrate overall removal of organic material. Effluent data for filters 10, 11, 40 and 12 are shown because these filters have the same sand effective size of Filter HLR, m/d Percent COD Removal COD Percent 0.93 mm, the same relatively high loading 1 0.041

Volume 2, Issue 1, Winter 1996 Volume 20

rate of 0.163 m/d, and represent the range 6 0.163

0 0102030405060708090 Day of Operation

The Small Flows Journal 8 Shallow Intermittent Sand Filtration: Performance Evaluation

Effect of HLR on average percent removala TABLE 4 (d = 0.29 mm, UC = 4.5) effect of HLR on average 10 percent removala (d = 0.29 10 Dosing = 24 times/day Dosing = 4 times/day mm, UC = 4.5) Filter 2 Filter 5 Filter 3b Filter 4 Filter 1 Filter 6 Parameter 0.081 m/d 0.163 m/d 0.326 m/d 0.652 m/d 0.041 m/d 0.163 m/d

Turbidity 97.0±1.2 97.7±1.1 92.2±1.9 c 96.9±1.3 94.4±1.6 COD 94.9±2.094.3±3.4 71.6±20.7 c 96.3±1.092.1±2.1 BOD5 99.4±0.4 99.5±0.3 76.1±9.5 c 99.4±0.6 98.5±0.6 TSS 98.1±1.2 99.0±0.5 90.7±4.4 c 98.2±0.9 94.7±2.6 NH3-N 99.5±0.2 99.6±0.1 - 5.7±42.7 c 99.7±0.1 99.2±0.3 Organic N 97.4±2.0 96.0±1.8 82.3±3.4 c 99.3±0.7 93.5±2.9

Note: Shading of adjacent columns indicates that results exhibit a statistically significant difference a Based on data collected from day 23 through day 86 of operation (10 measurements for each parameter) b Filter 3 clogged (overflowed) after 70 days in operation c Filter 4 clogged (overflowed) after 20 days in operation

Effect of HLR on Performance 0.326 m/d) than for filters 5 and 6 (loaded at 0.163 m/d). This increased loading also caused filter 3 to clog, as evidenced by The effect of HLR on filter performance effluent overflowing the filter housing was evaluated for concrete sand (d = 0.29 10 after 70 days in operation. When loaded at mm, UC = 4.52) at DFs of both 4 and 24 an HLR of 0.652 m/d, filter 4 clogged times/d. The effect of increasing HLR on after only 20 days in operation, thus no COD removal at both DFs is presented in data comparable to other filters were figure 5. Increasing the HLR from 0.081 collected. to 0.163 m/d had little effect on COD removal at a DF of 24 times/d. At this DF, An HLR between 0.163 m/d and 0.326 m/d HLR increases to 0.326 and 0.652 m/d appears to be the maximum sustainable caused noticeable decreases in COD loading for the concrete sand beyond removal. At a DF of 4 times/d, the COD which clogging occurs in less than three removal in the filter dosed at 0.163 m/d months of operation. Sauer et al. (1976) was slightly, but consistently, less than the reported a similar threshold HLR between filter dosed at 0.041 m/d. 0.2 and 0.57 m/d for a more uniform filter sand (d = 0.45 mm, UC = 3.0) and DF of The response of COD to variation in HLR 10 4 to 13 times/d with media 0.61 deep. At is typical for all parameters studied, as can the higher HLR, Sauer et al. (1976) be discerned from table 4, a summary of reported an operating duration of 45 to 80 the effect of increasing HLR on removal days while at the lower HLR, operating rates for each parameter. Shading of The Small Flows Journal duration exceeded 150 days. Furman et al. results in adjacent columns indicates that a (1955), applied an HLR of up to 0.280 m/d statistically significant difference existed without clogging in over five months of between those results. When dosed 24 operation in filters with media ranging times/d, increasing HLR from 0.081 to from 0.46 to 0.76 m deep, and d ranging 0.163 m/d caused no statistically 10

from 0.46 to 1.04 mm.

significant decrease in removal for any Volume 2, Issue 1, Winter 1996 parameter except turbidity, which had a The early clogging of filter 4 (HLR = very slight, but statistically significant 0.652 m/d, DF = 24 times/d, d = 0.29 lower removal rate at the higher HLR. The 10 mm, UC = 4.52) in this study may be removal rates for all parameters were attributed to the high HLR combined with significantly lower for filter 3 (loaded at

9 J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

the relatively low permeability of the 100 concrete sand. Although permeability was not measured, it can be seen in figure 3 80 (a) d = 0.29 mm, that the concrete sand used in filters 1-7 10 UC = 4.52 had a fairly broad and even size distribu- tion. This size distribution allows the 60 smaller sand particles to fill interstices between large particles, resulting in smaller and more convoluted pore spaces. 40 This condition encourages clogging of Filter DF, times/d remaining void spaces with suspended Removal COD Percent 6 4 solids and biological growth. In previous 20 7 12 studies in which wastewater of similar or 5 24 greater strength was applied at an HLR ≥ 0.163 m/d without clogging, the UC of the 0 media was less than 3.3. EPA (1980) and 100 Metcalf and Eddy (1991) recommend a UC no greater than 4.0. 80 Clogging reduces natural aeration, which can lead to anaerobic conditions within (b) d = 0.93 mm, 10 the filter. When filter 3 was taken out of 60 UC < 1.5 service and the media examined, the top 7.5 cm was found to be black. The blackness was probably due to iron 40 sulfide, which is highly indicative of Filter DF, times/d anaerobic conditions, implying that Removal COD Percent 11 4 20 aeration had ceased due to clogging. The 12 12 same color was observed in the top 2.5 cm 10 24 of sand in filter 4, which clogged after 0 only 20 days in operation at HLR = 0.652 0 102030405060708090 m/d. After resting filter 4 for three weeks, Day of Operation the pea gravel on top of the sand and the top 5.0 cm of sand were replaced. The filter was again loaded at 0.652 m/d with resulted in obvious improvements in COD the DF increased to 48 times/d. After 10 removal in the coarser media and small, FIGURE 6 days, this filter again clogged and over- but noticeable improvements with the effect of dosing frequency on flowed, which may indicate that the media finer sand. At a DF of 12 times/d or COD removal at greater, removal rates were very high for porosity had been permanently reduced, HLR=0.163 m/d (a) d10= either by clogging or compaction. all parameters with all media types. 0.29 mm, UC=4.52 and (b) d10=0.93 mm, UC < 1.5 The excellent performance observed at DFs of 12 times/d or greater may be Effect of Dosing Frequency attributable to the manner of flow through on Performance the media and the resulting hydraulics and diffusion rates. At high DFs, the volume Increasing the DF from 4 to 12 to 24 of wastewater applied in any one dose is times/d generally improved the perfor- small, e.g., 15.3 L at an HLR of 0.163 m/d mance of the filters. The effect of DF on and a DF of 12 times/d. When distributed

Volume 2, Issue 1, Winter 1996 Volume COD removal is illustrated in figure 6. over the surface area of the filter, this

Improvements were more dramatic for the 15.3 L dose translates to an application rate of only 1.36 mL/cm2 or 13.6 mm. If coarse filter sand (d10 = 0.93 mm) than for the application rate does not exceed the the concrete sand (d10 = 0.29 mm). Increasing the DF from 4 to 12 times/d water holding capacity of the media, the

The Small Flows Journal 10 Shallow Intermittent Sand Filtration: Performance Evaluation

Effect of dosing frequency on average percent removala Consistent with the proposed at HLR of 0.163 m/d thin-film flow phenomenon, d = 0.29 mm, UC = 4.52 d = 0.93 mm, UC = 1.29 increasing DF would have a 10 10 greater effect for large media Filter 6, Filter 7 Filter 5 Filter 11 Filter 12 Filter 10 filters than small media Parameter 4 times/d 12 times/d 24 times/d 4 times/d 12 times/d 24 times/d filters due to the difference Turbidity 94.4±1.6 97.3±1.2 97.7±1.1 77.0±4.9 96.0±1.6 97.0±1.8 in water holding capacity. COD 92.1±2.1 95.2±1.7 94.3±3.4 79.3±8.092.6±1.7 93.3±1.5 Coarser media have a lower BOD5 98.5±0.6 98.8±0.8 99.5±0.3 87.0±5.8 98.7±0.4 99.2±0.4 water holding capacity than TSS 94.7±2.7 97.8±1.5 99.0±0.5 77.0±8.5 97.2±0.9 98.6±0.9 fine media, and thus a NH3-N 99.2±0.3 99.7±0.1 99.6±0.1 98.7±1.9 99.4±0.3 99.6±0.1 Organic N 93.5±2.9 95.8±2.5 96.0±1.8 70.1±5.7 92.3±2.2 94.0±2.0 smaller dose volume (higher DF) is required to promote Note: Shading of adjacent columns indicates that results exhibit a statistically significant difference the thin-film flow pattern. In a Average (± 95% confidence interval) of data collected from day 23 through day 86 general, these findings are of operation (10 measurements for each parameter). consistent with those of Furman et al. (1955) who reported that, with an TABLE 5 increase in DF, BOD and SS removal applied water flows over the sand grains in effect of dosing frequency on improved slightly for media of d ≤ 0.31 a thin film allowing maximum oxygen 10 average percent removala at mm, but improved substantially for media diffusion and maximum contact between with d ≥ 0.44 mm. HLR of 0.163 m/d organics in the waste flow and the 10 microbial growth on the media. Thin-film At a DF of 4 times/d, the removal rates in flow allows longer contact time between a the concrete sand were better than the given parcel of applied wastewater and corresponding removal rates for the coarse attached microbes than would occur under filter sand (see table 5). As DF was flow conditions resulting from a large dose increased (for a given HLR), the differ- volume (low DF). ences in removal rates between the two media consistently decreased. These The effect of DF on removal efficiency for results are consistent with the proposed all parameters can be discerned from thin-film flow concept. Concrete sand has table 5, which is a comparison of average a large unit wetted surface area relative to removal in filters containing concrete sand the coarse filter sand. The large surface (d = 0.29 mm) with filters containing 10 area allows thin-film flow conditions to coarse filter sand (d = 0.93 mm). As in 10 occur at higher per-dose application rates, table 4, shading of results in adjacent i.e., relatively low DFs. Increasing DF for columns indicates that a statistically a given HLR decreases the volume significant difference existed between applied per dose and allows thin-film flow those results. For the concrete sand, conditions in the coarser filter sand. Thus, increasing DF from 4 to 12 times/d increasing DF (i.e., reducing the per-dose resulted in a slight, but statistically application rate) may partially compensate significant increase in removal for for lower unit wetted surface area of turbidity, COD, and organic N; increasing The Small Flows Journal coarser media. Coarser media, used with a DF from 12 to 24 times/d did not signifi- high DF, may be advantageous as they are cantly increase the removal efficiency of less likely to clog. any parameter. For the coarse filter sand, increasing the DF from 4 to 12 times/d significantly improved the removal of all

Effect of Media Size on Performance

parameters, and increasing DF from 12 to Volume 2, Issue 1, Winter 1996 24 times/d significantly improved the removal of turbidity, BOD, and ammonia. An attempt was made to isolate the effect For both media types, increasing the DF of media size on filter performance using from 4 to 12 times/d had a greater effect very uniform filter sand (UC< 1.42) of

than increasing it from 12 to 24 times/d. three sizes: d10 = 0.33 , 0.54, and 0.93 mm. A fairly high loading rate of 0.163 m/d

11 J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

and DF of 24 times/d were used. The 100 removal efficiencies for turbidity, SS, (b) SS BOD, and COD for the three media (a) Turbidity sizes are compared in figure 7. 80 Differences between the removal efficiencies in the different media 60 sizes are difficult to discern. Slightly higher turbidity removal in the finest 40 Filter d10

sand was the only statistically Percent Removal 8 0.33 significant difference. 9 0.54 20 10 0.93 Performance effects due to media size appear to be affected by DF as 0 discussed previously. Grantham et al. 100 (1949) and Marshall and (c) BOD Middlebrooks (1974) reported (d) COD increased removal rates with finer 80 sand with DFs of 1 or 2 times/d. Furman et al. (1955) reported much 60 better removal rates for BOD and SS and more nitrogen oxidation with 40 finer media when dosed two times Percent Removal per day. However, when the DF was 20 increased to four times per day, Furman et al. (1955) reported very 0 similar performance for fine and 020406080020406080 coarse media. In this study, effect of Day of Operation Day of Operation media size was compared using a DF of 24 times/d and a moderate HLR; thus only a small volume of wastewater was effect of media uniformity on filter FIGURE 7 applied per dose and effects of media size performance was not explicitly explored. effect of media size on were apparently overshadowed by the Design recommendations call for media removal of (a) turbidity, (b) high overall removal rates. If greater per- UC of less than 4.0 (Anderson et al., SS, (c) BOD, and (d) COD dose application rates had been used 1985; EPA, 1980). This recommendation (UC < 1.5, DF=24 times/d, (same DF but larger HLR), differences in is intended to avoid clogging at higher HLR=0.163 m/d) removal rates between media of different loading rates. The clogging of filters 3 and sizes may have been more apparent. 4 at HLRs equal to or greater than 0.326 m/d was partially attributable to the well- graded nature of the concrete sand (UC = Effect of Uniformity Coefficient 4.52) used as media. on Performance At a lower HLR of 0.163 m/d and DF of 24 times/d, all media had high removal Removal rates for turbidity, SS, BOD, and rates and media uniformity did not appear COD in two filters with sands of similar to have much effect on filter performance.

effective sizes (d10 = 0.29 and 0.33 mm) The lower per-dose application rates but different uniformity coefficients favored thin-film flow conditions and (UC = 1.42 and 4.52) are shown in allowed excellent removal rates regardless figure 8. The same HLR (0.163 m/d) and of media uniformity. As the per-dose

Volume 2, Issue 1, Winter 1996 Volume DF (24 times/d) were used in both filters. application rate increases, media unifor-

The filter with more uniform sand mity apparently becomes more important demonstrated a slight, but statistically because it affects pore geometry and significant increase in turbidity and SS conditions under which thin-film flow removal. In the literature reviewed, the occur.

The Small Flows Journal 12 Shallow Intermittent Sand Filtration: Performance Evaluation

listed as typical (Metcalf and Eddy, Conclusion 1991) for activated sludge followed by granular media filtration and For the conditions studied in this research, carbon adsorption; organic-N and the following conclusions can be drawn: NH3-N were below levels listed in same reference as typical for Intermittent sand filters with a activated sludge with separate stage relatively shallow bed depth (0.38 nitrification/denitrification. Based m) are capable of producing on the above-listed loading and excellent quality effluent at an HLR dosing rates, each 1.2-m diameter of 0.163 m/d when dosed 12 to 24 filter unit was able to treat 184 L/d times/d with wastewater equivalent of septic tank or similar quality to septic tank effluent. The mini- effluent to tertiary treatment levels. mum removal efficiencies observed

for BOD, SS, organic-N, and NH3- The deleterious effects of increases N, are similar to the best removal in HLR, media size, or UC were rates reported in the literature for shown to be mitigated significantly intermittent sand filters of greater in certain situations by increasing FIGURE 8 depth. DF. The effects of DF were found to effect of media uniformity be more significant for higher coefficient on removal of (a) At an HLR of 0.163 m/d, with a DF values of HLR, coarser media, and turbidity, (b) SS, (c) BOD, of 12/d or greater, the maximum less uniform sand. effluent values of BOD, COD, SS, and (d) COD (d10=0.3 mm, DF=24 times/d, HLR=0.163 and turbidity were below levels No single filter design or operating parameter was found to adequately predict the performance of intermit- tent sand filters. The effects of the 100 many parameters are interrelated in (b) SS a complex manner. However, (a) Turbidity 80 research focused on the per-dose application rate and a characteriza- tion of the media pore geometry 60 together may provide insight for the performance variation observed. 40 The excellent performance observed

Percent Removal Filter UC at high DFs is hypothesized to be 5 1.42 the result of per-dose application 20 8 4.52 rates that allow development of thin-film flow through the media 0 and subsequently maximum oxygen 100 diffusion and contact time.

(c) BOD The Small Flows Journal (d) COD 80 Acknowledgements 60

Support for this research was provided 40

by the National Science Foundation Volume 2, Issue 1, Winter 1996 Percent Removal through a Presidential Young Investi- 20 gator Award to J. Darby. The dona- tion of equipment and technical 0 assistance by Harold Ball of Orenco 020406080020406080 Day of Operation Day of Operation Systems, Inc. (Roseburg, Oregon) is gratefully acknowledged. m/d) 13 J. Darby, Ph.D., P.E., G. Tchobanoglous, Ph.D., P.E., M. A. Nor, and D. Maciolek

Notes organic matter and phosphorus. Journal of Environmental Quality 18: 451-457. ______. 1989b. Infiltration of wastewater in 1 2 1 m/d is equivalent to 24.54 gal/ft •d a newly started pilot sand-filter system: 2 1/8 inch orifice with a residual head of Part II. Development and distribution of 8 ft. the bacteria population. Journal of Environmental Quality 18: 457-462. ______. 1989c. Infiltration of wastewater in References a newly started pilot sand-filter system: Part III. Transformation of nitrogen. Journal of Environmental Quality 18: American Public Health Association. 463-467. 1989. Standard methods for the Pell, M., F. Nyberg, and H. Ljungren. 1990. examination of water and wastewater. Microbial numbers and activity during 17th ed., Washington, D.C. infiltration of septic-tank effluent in a Anderson, D. L., R. L. Siegrist, and R. J. subsurface sand filter. Water Research Otis. 1985. Technology assessment of 24, no. 11: 1347-1354. intermittent sand filters. Municipal Sauer, D. K., W. C. Boyle, and R. J. Otis. Environmental Research Laboratory. 1976. Intermittent sand filtration of U.S. Environmental Protection Agency. household wastewater. ASCE Journal of Cincinnati, Ohio. EPA 832/R-85/100. the Environmental Engineering Division Andreadakis, A. D. 1987. Organic matter (August): 789-803. and nitrogen removal by an onsite Schwartz, W. A., T. W. Bendixen, and R. E. sewage treatment and disposal system. Thomas. 1967. Project report of pilot Water Research 21, no. 5: 559-565. studies on the use of soils as waste Furman, T. D., W. T. Calaway, and G. R. treatment media. In-house report Grantham. 1955. Intermittent sand prepared for the Federal Waste Pollution filters—multiple loadings. Sewage and Agency. Cincinnati, OH. Industrial Wastes (March): 260-276. Siegrist, R. L., and W. C. Boyle. 1981. Grantham, G. R., D. L. Emerson, and A. K. Onsite reclamation of residential Henry. 1949. Intermittent sand filter graywater. Proceedings of the Third studies. Sewage Works Journal 21, no. National Symposium on Individual and 6:1002-1015. Small Community Sewage Treatment. Metcalf and Eddy. 1991. Wastewater ASAE:176-186. treatment. 3d. ed. San Francisco: Simons, A. P., and F. R. Magdoff. 1979. McGraw Hill. Laboratory evaluation of design Marshall, G. R., and E. J. Middlebrooks. parameters for mound system disposal of 1974. Intermittent sand filtration to septic tank effluent. Journal of Environ- upgrade existing wastewater treatment mental Quality 8, no. 4: 486-492. facilities. Utah Water Research Labora- Tchobanoglous, G., and E. D. Schroeder. tory, College of Engineering. Utah State 1985. Water quality: characteristics, University at Logan. modeling, and modification. Addison Peeples, J.A., K.M. Mancl, and D.L Widrig. Wesley Pub. pp. 120-121. 1991. An examination of the role of U.S. Environmental Protection Agency sand depth on the treatment efficiency of (EPA). 1978. Management of small pilot scale intermittent sand filters. waste flows. Municipal Environmental Proceedings of the 6th National Sympo- Research Laboratory. Cincinnati, Ohio. sium on Individual and Small Commu- EPA 600/2-78-173. nity Sewage Systems (Chicago, Decem- ______. 1980. Design manual. Onsite ber 16-17). ASAE publication n10-911.

Volume 2, Issue 1, Winter 1996 Volume

wastewater treatment and disposal St. Joseph, MI: ASAE system. Municipal Environmental Pell, M., and F. Nyberg. 1989a. Infiltration Research Laboratory. Cincinnati, Ohio. of wastewater in a newly started pilot EPA 625/1-80-012 sand-filter system: Part I. Reduction of

The Small Flows Journal 14 Shallow Intermittent Sand Filtration: Performance Evaluation L O

W George Tchobanoglous, Ph.D., P.E.

S George Tchobanoglous is a professor emeritus in the depart- ment of civil and environmental engineering at the University of

California at Davis. He has a BSCE from the University of the EPacific (Stockton, CA), Sa M.S.M inA Jeannie Darby, Ph.D., P.E. S sanitary engineeringL from Univer- sity of CaliforniaA at Berkeley, and AJeannie Darby is an associateU a Ph.D. in Ncivil engineering from professor in the departmentO of RI H StanfordO University. He is a civil andN environmentalG engineer- registeredI professional engineer. ing at the University of California T at Davis. She has a BSCE from Rice University (Houston, TX), a A MSCE from Tufts University M. Asri Nor (Medford,MA MA), and a Ph.D. in civil andN SengineeringL from the University of L David Maciolek Texas at Austin. She F is a regis- tered professional engineer.L M.C Asri Nor is an instructor in the O department of civil engineering at W the UniversityL of Technology, If you would like more information Malaysia.E David Maciolek is an engineer at Larry Walker & about this article, write to JeannieS A Associates in Davis, CA. At the Darby, Ph.D., P.E.; Department of Civil R time of this research, bothIN wereGH and Environmental Engineering; graduate students in the depart- University of California at Davis; ment of civil and environmental engineering at the University of The Small Flows Journal 116 Everson Hall; Davis, CA 95616. M California at Davis. L S E A S N

OU O Volume 2, Issue 1, Winter 1996

15 FEATURE AA PrivatePrivate MarketMarket ApproachApproach ToTo OnsiteOnsite WastewaterWastewater TreatmentTreatment SystemSystem MaintenanceMaintenance by John Herring

Malfunctioning or failing onsite wastewater treatment systems (OWTS) are a significant source of pollutants, adversely affecting hundreds of waterbodies nationwide. Currently, system design, siting, and construction are fairly well-managed, with maintenance of existing systems the remaining weak link. In this article, some limitations of traditional regulatory approaches to OWTS management are discussed, and an alternative approach using private-market catastrophic OWTS insurance is proposed and developed. Possible advantages of an OWTS insurance approach include improved water quality, risk reduction for homeowners and lending institutions, increased incentives for additional research regarding OWTS management practices, and reduction in the need for publicly- funded regulatory programs.

n the United States, approximately 25 In response to problems with failing million private residences rely on systems, some communities regulate and onsite wastewater treatment systems control OWTS maintenance through I (OWTS), such as septic tanks with management districts and other commu- leach fields (Bureau of the Census, 1993, nity programs. While these programs can 165, table 12). When properly designed, be very effective, their successful imple- sited, constructed, and maintained, such mentation often depends on widespread systems can provide an excellent, low-cost community support. means of treating waste with little risk to human health or environmental quality. In this article, some of the advantages and However, inadequate system care can limitations of current OWTS management result in system failure, with consequent programs in the U.S. and Canada are environmental and public health risks. discussed, and an idea for an alternative, insurance-based strategy for managing Virtually all jurisdictions in the U.S. have OWTS maintenance is offered. The regulations or programs to assure proper proposed strategy allows for individual

Volume 2, Issue 1, Winter 1996 Volume OWTS siting, design, and construction— participation by homeowners living in

but maintenance, the final step in OWTS communities where management districts management, is much more troublesome are impractical or unpopular. to control and is the most frequent source of system decay and failure.

The Small Flows Journal 16 A Private Market Approach To Onsite Wastewater Treatment System Maintenance

of this extraordinarily valuable resource (KWIC, 1993). Shore- line properties in this watershed are economically critical. For several of the municipalities, shoreline properties constituting only a few percent of total land area contribute over half of all property tax revenues. Keuka Lake OWTS inspections, performed by municipal officers, include verification of adequacy of baffles, checks for holes or cracks, and a determination of whether pumping is needed. Funding for these inspections is provided by fees for services and by municipal support.

Many of the other successful KEUKA LAKE, NEW YORK OWTS management programs discussed Economically critical OWTS Management Programs in the literature were developed precisely shoreline properties on because of real or perceived threats to public health or economic well-being. For Keuka Lake, New York, Regulating Maintenance example, the Stinson Beach Water District are protected by an in Stinson Beach, California is the result intermunicipal OWTS of direct threats to public health in an area maintenance agreement. Typically, state or local health departments promulgate standards for OWTS design heavily dependent on water-based and siting criteria. Sound OWTS construc- recreation (Richardson, 1989). Groundwa- tion is usually achieved through onsite ter sampling and testing of the residences inspection during the construction phase in the Stinson Beach area indicated 10 by health department personnel, local percent of the systems were malfunctioning. building inspectors, watershed inspectors, or some other regulatory authority. In Other examples include the onsite many instances, backfill over a system is management program in Fountain Run, in prohibited until such an inspection occurs. south central Kentucky, where there was greater than a 30 percent failure rate for However, direct regulatory programs existing systems, with many additional aimed at managing OWTS maintenance systems undersized by current standards are rare and usually focus on remediation and “expected to fail in the near future” of a direct threat to public health or (Otis, Robertson, and Kleinschmidt,

property values, or the protection of a 1981). The Westboro, Wisconsin district The Small Flows Journal specific highly-valued waterbody. was developed to deal with a situation in which over 80 percent of all systems An example of a preventive management discharged directly into a small stream program aimed at protecting a highly- (Otis, Robertson, and Kleinschmidt, valued waterbody is an intermunicipal 1981). And in Virginia, the Arlington

County Chesapeake Bay Preservation agreement among six towns and two Volume 2, Issue 1, Winter 1996 villages sharing frontage on Keuka Lake, Ordinance, which requires five-year one of the New York Finger Lakes. The pumping cycles for onsite systems (EPA, agreement requires inspections for 1993, 4.116), clearly bases its legitimacy systems within 200 feet (60.96 meters) of on the issue of protecting the highly the shoreline at least once every five years significant Chesapeake Bay. as a means of protecting the high quality

17 John Herring

Examples of OWTS management Assigning responsibility to existing programs in Nova Scotia show the same agencies, such as watershed inspectors or general trend. Mooers and Waller (1994), local health departments, would simply in their survey of Nova Scotia’s OWTS mean an increase in workload such that management districts, noted only three significant staff additions would be successful districts since the 1982 necessary. It also should be noted that legislation authorizing their formation. In these estimated costs merely focus on each case, significant problems led to inspections, and do not include the formation of the districts. In Port potential costs of remediating inadequate Maitland, problems included failed systems. systems and direct discharge to ditches. In Guysborough, a survey found that only 10 In the absence of significant perceived percent of the systems did not drain to benefits, such a program is unlikely to ditches or surface water. In Woods gain widespread community support, Harbour, many systems were determined especially because its successes (early to be malfunctioning. detection of OWTS problems) imply an additional cost, sometimes substantial, to affected homeowners. Mooers and Waller Limitations of Current Programs (1994) note that in some communities in Nova Scotia, the lack of a public percep- While the aforementioned examples of tion that OWTS problems even exist has managed OWTS maintenance have resulted in the failure to adopt onsite largely been successful, expansion of such management programs. Therefore, while direct regulatory programs to cover all the concept of a district or other public onsite systems is highly unlikely. One utility as a mechanism for onsite system reason is that, in many areas, the immense maintenance has obvious advantages, it is cost associated with such an expansion not a panacea. It appears to be an attrac- would require a significant increase in tive alternative only if at least one of the public funds. following conditions can be met:

New York State, for example, has there is a serious threat to health or approximately 1.5 million residential property values that a district might OWTS, with Suffolk County accounting reduce at less expense than central for over 20 percent of that total (Bureau sewers, of the Census, 1993, 224–230, table 66). Straightforward calculations assuming there is a widespread perception of a four inspections per person per day, or threat to public health or the environ- 1000 per year, mean that New York would ment and a perception that central need 1500 new inspectors if annual sewers would be more expensive, or inspections were implemented. Even inspection on a three-year cycle, as is the area is undergoing significant recommended under the Management new development, so that district Measures Guidance for the Coastal formation is a part of an overall Nonpoint Pollution Control Program development package. (EPA, 1993, 4.114), would require 500 inspectors. Adding salary and benefits to In a few instances, however, it appears that other program costs such as office space, districts can be developed and supported staff support, materials, etc., leads to a by a community in the absence of a real or cost estimate of at least 15 to 20 million perceived immediate threat, given a

Volume 2, Issue 1, Winter 1996 Volume

dollars per year. Whether generated population that is exceptionally commit- through fees for required services, as part ted to minimizing environmental impacts. of a community’s general budget, or through some form of special tax, these costs would be borne by the public.

The Small Flows Journal 18 A Private Market Approach To Onsite Wastewater Treatment System Maintenance

Advantages of Effective to focus on OWTS maintenance only after gross failures occur. OWTS Maintenance Because properly designed and sited Despite the costs and limitations of a systems do not require maintenance often, public management district or utility homeowners are unlikely to incorporate approach, the concept of controlling system maintenance as routine. Also, OWTS maintenance is attractive from when faced with the choice between the both individual and societal perspectives. certainty of spending a small amount of Societally, the pollution avoided through money now versus the possibility of routine inspection and maintenance will having to spend a large amount in the improve water quality in hundreds of future, time preferences for money waterbodies nationwide. In New York reinforce the desire to avoid spending State alone, it is estimated that OWTS money when there is no immediate pollution is the primary cause for over 180 benefit. waterbodies failing to meet designated use standards. OWTS failures are a secondary The fact that OWTS maintenance can cause of pollution for an additional several often be delayed without immediate hundred waterbodies (DEC, 1993). repercussions can also lead to neglect. Also, homeowners are sometimes un- For the individual system owner, routine aware that OWTS maintenance is neces- inspections also can provide significant sary, or even that they rely on onsite benefits. Early detection of many malfunc- treatment. tions, such as loss of in-tank baffles, allows early and inexpensive maintenance. Education programs regarding OWTS In addition, inspection normally includes maintenance are sponsored by some tank pumping, itself an important factor political jurisdictions, educational extending a system’s useful life. associations, and other groups (see Mancl and Magette, 1991). While such programs For a variety reasons, it seems that most can address some of the homeowner homeowners do not perform appropriate maintenance issues discussed previously routine OWTS maintenance despite and are virtually always a component of demonstrated benefits. The author has OWTS management programs, education been unable to locate any formal studies programs are, at best, rarely completely showing voluntary high levels of effective in changing behavior. Education homeowner OWTS maintenance in the and outreach efforts are necessary but are absence of the same preexisting conditions not usually sufficient in preventing listed earlier as being important in neglect, just as the posting of speed limit management district formation. Indeed, in signs does not obviate the need for a survey conducted at the beginning of the enforcement. process leading to the Keuka Lake intermunicipal agreement, a systematic The Small Flows Journal random sample of the records of 839 Preventing OWTS Failure systems in the watershed showed that fewer than 40 percent of systems had been For the reasons above, it is not uncommon inspected in the previous ten years. Nearly for homeowners to focus on OWTS 22 percent of systems in the watershed had maintenance until after gross failures

not been inspected in over 20 years occur. When a system fails noticeably (for Volume 2, Issue 1, Winter 1996 (Powell, Herring, and Anderson, 1988). example, with surface discharge), owner These findings, together with those of inconvenience from such factors as odor Lemley (1995) and information from those is usually sufficient to assure relatively working in the field, lead to the conclusion prompt remediation. Unfortunately, that it is not uncommon for homeowners remediation by owners is often predicated on a clear and inconvenient failure, and

19 John Herring

corrective measures can be significantly policies, that would cover the cost of more expensive than preventive ones. OWTS repair or replacement. Clearly, insurers would have an incentive to The first problem with preventing OWTS develop expertise to assess and reduce failure is related to the difficulty of clearly risks of system failure in order to maxi- defining “failure.” Reliance on owner mize their profits. An obvious approach to action tends to imply a definition based on doing so is to establish minimum mainte- obvious inconvenience, such as odor nance standards that void the policy when problems, surface discharge, etc. Even not met. Systems maintained according to obvious symptoms of incipient failure, these minimums would, in fact, have a such as transient surface ponding directly reduced likelihood of failure, protecting over leach lines, may well be missed or environmental and public health as well as ignored by the homeowner. Symptoms reducing overall costs to homeowners. recognized by the homeowner usually appear well after more subtle symptoms The concept of using insurance programs of failure. Water quality impacts and to reduce pollution potential from private threats to public health can occur well homes is already being considered in New before the more obvious symptoms of York. In response to concern over failure. pollution potential in the New York City watershed system, New York State has Implications of the increased OWTS announced that legislation will be intro- remediation costs include overall in- duced authorizing the creation of “. . . a creased expenses for the homeowner voluntary program of homeowner (public funds for the remediation of insurance for underground home heating failing private onsite systems are small oil tanks. Such insurance would cover the and are likely to remain so) and the cost of necessary soil and groundwater problem that some individuals will not be remediation and thereby encourage able to remediate at all. Regulatory homeowners to investigate and report on officials are thus placed in the position of the conditions of their underground tanks, enforcing against individuals who already and remediate identified problems” (New perceive themselves as victims, and who York State, 1995, 10). The impetus for this cannot afford to remediate. program is concern over public health— the New York City water supply system Given such undesirable alternative provides drinking water to over 9 million solutions as property condemnation, people. Similar logic could be used to regulatory agencies are faced with simply extend the program to address OWTS attempting to meliorate problems. While maintenance issues. the creative use of alternative onsite systems can resolve problems in many Insurers of onsite systems might offer a instances, cases still remain in which the range of options with policies, such as results are unsatisfactory from both varying deductibles. Thus, a very low- environmental and public health perspectives. priced policy with a high deductible would not cover routine costs such as periodic pumping, while a more expensive policy could (for a hypothetical example A Private Market Alternative of OWTS coverage, see table 1). Such policies would be, from the homeowner’s One approach that could offer a workable perspective, analogous to a utility district, OWTS maintenance alternative for allowing the homeowner to trade a lower

Volume 2, Issue 1, Winter 1996 Volume

individual homeowners would be the regular payment for protection from larger development of a private market in unexpected costs. For example, the catastrophic OWTS failure insurance. Georgetown Divide Public Utility in Private insurers could offer policies, California includes inspections for onsite perhaps as riders to existing homeowner systems in a large subdivision among its

The Small Flows Journal 20 A Private Market Approach To Onsite Wastewater Treatment System Maintenance

ing and support for OWTS manage- Policy Services Included Deductible Coverage provided ment is random. In most instances, a Low–Cost none High Repair and replacement relatively small portion of systems costs up to $2,500 constitute the majority of pollution Standard Inspection of System Medium Repair or replacement of potential. This serves to increase the existing system up to $5,000 difference between the two ap- proaches. If we assume that those Deluxe Annual inspection of system none Repair and replacement Annual household plumbing costs up to $10,000. Up to owners most likely to pollute are also and water use audit $1,000 design permitting most likely to oppose required Pumping of tanks needed costs for alternative onsite maintenance (because of the repair or special systems. costs it would impose), the insurance strategy would provide some benefits but not adequately deal with the services. Homeowners are charged $12.50 TABLE 1 highest-risk cases. per month for the management of single- hypothetical example of On the other hand, the district ap- family systems (Dix, 1992). levels of OWTS insurance proach could be expected to have one of two results. If a sufficient majority coverage To compare the private market plan to that of homeowners were interested in of public districts or utilities, first consider required maintenance (i.e., the a situation in which all homeowners proportion of high-risk systems was participate. The systems would have equal low), they could force the creation of a beneficial impacts, in that maintenance program that would address the high- would be uniformly addressed. In each risk situations. If, however, those case, the homeowner would pay a rela- opposing the district were capable of tively low fee in order to avoid the blocking formation, there would be no possibility of a much larger cost should the required maintenance for anyone. In system fail. The only difference under the this sense, the district strategy may be full participation scenario is that the fee seen as a high-risk, high-payoff strategy. would be paid to a private insurer in one case and a public utility in the other. Advantages of OWTS Insurance However, if support for OWTS mainte- nance is not universal, the two systems would differ. With the insurance approach, Following are several points of interest there is a direct correlation between those and possible benefits of the private supporting OWTS maintenance and insurance approach to OWTS mainte- participation. Under the district plan, those nance: supporting maintenance can, if sufficiently numerous and vocal, force a maintenance An insurance plan may allow for program on those reluctant to participate. the application of market forces to The result under the district plan would be minimize the costs associated with high participation, assuming adequate OWTS management.

enforcement of the regulatory program is Just as individuals frequently The Small Flows Journal included. If, however, those supporting compare costs and services for autos OWTS maintenance are not sufficiently or homes, a private market system numerous or well-organized, their desire will offer the opportunity for for a district will be frustrated. In such a competition to improve prices and case, the only maintenance that will occur service to the homeowner. Estimates

of the cost of such insurance are, of is that which can be attained through Volume 2, Issue 1, Winter 1996 voluntary means, such as education. course, heavily dependent on assumptions regarding such issues The above comparison assumes, for both as system life cycle and the exten- options, that each OWTS contributes sion to be expected through routine equally to pollution problems, or that the maintenance, definitions of system relationship between likelihood of pollut- failure, and so on.

21 John Herring

Observed OWTS failure rates usually Insurers might consider site conditions range between one and five percent per such as soil porosity and proximity to year (EPA, 1993, 4.114). Assuming a water supplies (which affect the risk an catastrophic failure rate of one percent individual OWTS poses) in determin- per year with remediation costs ing premium rates, the frequency of averaging $4000, a fee of forty dollars appropriate inspections, and action per year should cover claims. Premi- levels for remediation. Insurers might ums must be higher to allow for elect to require that inspections be overhead costs and profit. In addition, performed by their staff or by indi- at least in the initial stages of such a viduals with specified credentials, such program, a significant margin for error as registered sanitarians. would be needed. This margin would presumably be reduced as expertise Individual insurers would have the accumulated. It thus seems that a burden of determining at what point premium of one hundred dollars per a system can be considered in year, competitive with costs of some failure. existing governmental districts, is One major difficulty facing any feasible. If policies were incorporated traditional OWTS regulatory inspec- as riders on existing homeowner tion program is the determination of policies, administrative costs would be failure, because OWTS failure is most minimized. With 25 million such often a continuum rather than a single systems in the United States, the catastrophic event. This problem potential market is significant. would be much less important under an insurance plan, as individual Private insurers can be expected to insurers might establish their own set maintenance standards for systems of evaluation. Insurers would OWTS policies in order to reduce thus balance the increased protection their costs. from setting high standards (very early Just as an insurer may encourage warning of possible problems) with the proper maintenance for a home in increased costs associated with the risk order to avoid later claims, OWTS reduction. It is to be expected that, insurance would provide an incentive over time, some standardization would for insurers to work with their custom- occur. At a minimum, certain failure ers to improve routine maintenance. “trigger points” would be set so as to Examples of approaches include meet relevant public health and offering differential premiums, environmental standards, so that the distributing educational pamphlets, insurance would actually protect the and establishing minimum mainte- homeowner. Clear trigger points would nance requirements. Again, as with probably include those currently traditional homeowner policies, the applicable in regulation, such as insurer may reject or limit claims if surface discharge, and other possible reasonable and customary maintenance criteria such as the physical integrity is not performed by the owner (e.g., if of tanks and lines (avoiding cracks), the OWTS is never pumped or evidence of solids flow into leach inspected). Both insurer and insured lines, etc. thus have strong incentives to improve maintenance and reduce the likelihood An insurance approach may encour- of failure. age and generate funding for further OWTS research.

Volume 2, Issue 1, Winter 1996 Volume

Private insurance holds the promise Because of the direct economic of allowing tailoring to site-specific implications of setting specific points conditions, always an important of failure, insurers would have a factor in OWTS management. significant incentive to improve

The Small Flows Journal 22 A Private Market Approach To Onsite Wastewater Treatment System Maintenance

knowledge of such factors as efficiency tion. Just as most lending institutions and life span of differing types of require insurance to protect against other systems under differing conditions and value-reducing problems such as fire, they the effectiveness of various best might require OWTS insurance. management practices. As a further parallel to existing insurance mecha- Because OWTS management has not nisms, such information might be historically been a major issue for such generated in many ways. For critical institutions, an education program for questions, insurers might themselves lending institutions would probably be fund research. The Insurance Institute necessary. Such a targeted program might for Property Loss Reduction, for be developed by water quality experts as example, funds research aimed at a long-term means of improving water reducing property losses due to natural quality. Alternatively, private groups, disasters, such as hurricanes and whether they be environmental interest earthquakes (McLean, 1995). In other groups or associations focusing on the instances, research done under other insurance industry, might also assume the auspices could be used. The incentive role of educating lenders. to improve understanding of OWTS operation should improve both the Adoption of OWTS insurance require- insurance market and OWTS mainte- ments by such federal lenders as HUD and nance over time. FHA would both introduce the concept to the private sector and establish a market, Benefits of OWTS failure insurance to the justifying private insurers in taking action environment and insurers are clear. The to develop their offerings. Alternatively, chief advantage for homeowners is in having OWTS insurance might translate terms of risk reduction. As such, accep- into a small rebate on mortgage costs, tance of the plan will depend on reflecting the risk reduction. This possibil- homeowner perceptions of risk. An ity is unlikely, however, unless a similar insurance program would provide addi- reduction were applied to mortgages for tional opportunities for education pro- homes served by public sewerage. grams. Also, because insurance premiums are predictable, there would be an in- A factor affecting lending institution creased recognition that OWTS manage- acceptance of OWTS insurance is the ment is needed and can have direct recent growth of the secondary mortgage economic impact. Therefore, the insurance market. This has led to pressure to strategy should not be considered a standardize mortgage terms and condi- replacement or substitute for educational tions, so that groups of mortgages may programs. Instead, they are complementary. more readily be “bundled” for resale. This will initially act to discourage lender requirements for OWTS insurance. OWTS Mortgage Insurance However, if the insurance provides

adequate risk reduction, some institutions The Small Flows Journal Perceived risk reduction as a driving force are likely to require it. Other factors, such is not limited to the homeowner. Approxi- as proximity to potable water supplies, mately two-thirds of the owner-occupied, may be important in the determination of one-family housing units in the United risk reduction. Once OWTS insurance is States are currently covered by a mortgage required for some mortgages, the same

or other lien (Bureau of the Census, 1993, tendancy toward standardization should Volume 2, Issue 1, Winter 1996 224–230, table 66). Financial institutions act rapidly to increase the number of may be expected to recognize the risk institutions requiring the insurance. reduction potential of such an insurance plan and take steps to encourage participa-

23 John Herring

Keuka Watershed Improvement Cooperative T Conclusion (KWIC). 1993. A draft proposal to A protect and improve the quality of Keuka

N Existing regulations to ensure appropriate Lake. Yates County Planning Office. Penn Yan: New York. OWTS maintenance are inadequate, and Mancl, K. and W. Magette. 1991. Water public support for expansion of regulatory resources 28—maintaining your septic authority through mechanisms such as tank. Cooperative Extension Service. C wastewater management districts or College Park: University of Maryland. utilities is limited except in specialized McLean, Dan D. 1995. Report of the L circumstances. Voluntary programs, such chairman. Remarks made at the Second E as education programs developed by Annual Meeting of the Insurance Institute A cooperative extension offices, cannot be for Property Loss Reduction. (November R completely effective. Voluntary programs 14) Chicago. IN also must overcome inherent disincentives Mooers, Jordan D. and Donald Waller. 1994. for establishing routine maintenance or Wastewater management districts—the John Herring remediating failed systems, because it is Nova Scotia experience. In Proceedings less expensive in the short-term for of wastewater nutrient removal technolo- John Herring is unconcerned system owners to do nothing. gies and onsite management districts currently a coastal conference. Waterloo Centre for Ground- What is needed to ensure OWTS mainte- waterS qualityM Aspecialist nance in areas without community pro- water. (June 6) Waterloo, Ontario: L LL grams, then, is an institutional mechanism University of Waterloo. Awith the New York New York State Department of Environmen- F that internalizes the cost of OWTS State Department of tal Conservation (DEC). Division of maintenance, thus reducing failure rates Water. 1993. Priority water problem list. State’s Division of and consequent public health and environ- Albany: 7–15. Coastal Resources mental problems. New York State Office of the Governor. and Waterfront 1995. Agreement in principle for the New In summary, a private market system for York City water supply. (November 2) Revitalization, and the catastrophic OWTS failure insurance could Albany. coordinator for New provide an alternative approach to improv- Otis, Richard, Marc Robertson, and James York State’s Coastal ing OWTS maintenance, the major Kleinschmidt, 1981. Guide to wastewater problem in overall OWTS management. facilities planning in unsewered areas. Nonpoint Pollution The insurance approach would offer risk Small Scale Waste Management Project. Control Program. He reduction for the homeowner, avoid the Madison: University of Wisconsin. holds BS and Ph.D. Powell, John, John Herring, and Thistle need for a large and expensive governmen- E degrees in natural tal entity, and internalize costs which are Anderson. 1988. Keuka Lake septic A U currently external. This strategy could system survey final report. Yates County resourceR managementO create new incentives for the development Aquatic Vegetation Committee. Penn from ICornellN Univer-H Yan: New York. G and refinement of better OWTS mainte- Richardson, Mark S. 1989. Public manage- sity, and an MS in nance practices, and may also affect siting ment, operation and maintenance of on- environmental health and design practices. Improved environ- site sewage systems. In Proceedings of from the Harvard mental quality and reduced threats to the 6th Northwest on-site wastewater public health are possible benefits of such a treatment short course. (September 18- School of Public system. Risk reduction aspects of the 19) Seattle: University of Washington Health. Previous proposal may also trigger support from U. S. Bureau of the Census. 1993. 1990 professional experi- lending institutions, despite recent pressure Census of housing: detailed housing for standardization of mortgage provisions. characteristics: Prepared by Housing and ence includes coop- Economic Statistics Division, Bureau of erative extension the Census. Washington, D.C. agent, environmental U.S. Environmental Protection Agency SMA consultant, and Volume 2, Issue 1, Winter 1996 Volume References (EPA). 1993. Guidance specifying L

A management measures for sources of collegeN professor in Dix, S.P. 1986. Case study no. 4—Crystal nonpoint pollution in coastal waters. both economics and U.S. EPA Division of Water. Washington, O Lakes, Colorado. National Small Flows environmentalI science. D.C.: 4.114–4.116. Clearinghouse. Morgantown: West T Virginia University. A

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