Embedded Files
An Annotated Bibliography
Stephen G.
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Overview
The discussion in Massoud, Tarhini, and Nasr lends background to an interesting observed "paradox" (2009). In studies involving "industrialized" countries, where centralized wastewater treatment is the norm, the presence of on site wastewater treatment (i.e. septic tanks) is often considered a public health liability which may be contributing to elevated risk. In "industrializing" nations the presence and quality of on site wastewater treatment is typically considered to be a public health benefit as compared to direct discharge to the environment. As a result of this circumstance the socio-political context of the study should be considered in addition to the geological and hydraulic conditions of the region. A number of studies are discussed which develop general GIS enabled models for risk assessment which include on-site wastewater as a potential risk factor. In addition specific studies which seek to assess potential health risk from sanitation practices in specific communities are presented.
Massoud, M. A., Tarhini, A., and Nasr, J. A. 2009. "Decentralized approaches to wastewater treatment and management: Applicability in developing countries." Journal of Environmental Management. Vol. 90. pp. 652-659.
This paper provides a broad overview of the case for decentralized wastewater management in developing countries and introduces various treatment approaches. While it does not specifically address GIS based risk assessment it provides useful background in considering the topic. The authors point out that collection, treatment and disposal are the three core components of wastewater treatment. Decentralized systems dramatically reduce the cost of collection presented by centralized systems. This is a huge factor in developing nations. The authors highlight three levels of centralization: on site wastewater treatment, cluster systems, and conventional centralized systems. On site systems treat and dispose of effluent near the generation point. Cluster systems utilize piping to collect wastewater for a number of homes, particularly in densely populated or topographically challenged areas. Centralized wastewater plants collect wastewater for an entire community (or "large" catchment area) and dispose of treated effluent at a point distant from generation. The paper describes two decentralized primary treatment methods: septic tanks and Imhoff tanks. They also present an excellent summary of secondary treatment methods in table form which is reproduced in Appendix A below. In selecting appropriate technologies it is critical to consider economic, environmental, and socio-cultural factors. The paper concludes by emphasizing the importance of integrated management of on site wastewater treatment facilities to ensure adequate maintenance and ongoing protection of public health.
GIS Use and Models
Chitsazan, M. and Akhtari, Y. 2009. "A GIS-based DRASTIC Model for Assessing Aquifer Vulnerability in Kherran Plain, Khuzestan, Iran." Water Resource Management. Vol. 23. pp. 1137-1155. doi: 10.1007/s11269-008-9319-8.
This study utilizes the DRASTIC method composed of seven parameters to model aquifer vulnerability: "Depth to water <5>, net Recharge <4>, Aquifer media <3>, Soil media <2>, Topography <1>, Impact of vadose zone <5> and hydraulic Conductivity <3> (pg. 1140 see Supplemental Materials Ibe, 2003). Each factor is weighted in the final model and the relative weights have been inserted into the preceding quote as numeric values. Each of these factors was evaluated and coded as a raster layer for analysis in GIS. The pixel values were multiplied by the respective weights to generate a final map representing the vulnerability index value produced by the model. These values were then reclassified into High, Moderate, Low and No Risk ratings to produce the final vulnerability map. Samples were taken to test the model. Nitrates were found to most strongly correlate to two model parameters: depth to water, and vadose zone characteristics.
Luzio, M. D., Srinivasan, R., and Arnold, J. G. 2004. "A GIS-Coupled Hydrological Model System for the Watershed Assessment of Agricultural Nonpoint and Point Sources of Pollution." Transactions in GIS. Vol. 8. No. 1. pp. 113-136.
This lengthy technical note describes the Arc View Soil and Water Assessment Tool (AVSWAT). The purpose of the model is to predict the impact of land management over time with an eye towards water, sediment, and agricultural chemicals. Key model components include weather, hydrology, soil temperature, plant growth, nutrients, pesticides, and land management. Flow and infiltration/recharge factors can be established for surface water, soil water, and shallow aquifers. The three pre processor inputs are watershed delineation (DEM with vector streams integrated), Hydrological Response Unit (HRU) definition (typically land use, soil, and slope) and weather station definition (historical weather data). Step by step instructions on software use are provided. The model output provides data on 42 variables including pesticides, metals, and pathogens over user defined time periods.
Note: It should be noted that the most recent update of ArcSWAT was released on 8/19/2010. The extension is freely available at http://swatmodel.tamu.edu/software/arcswat.
Teague, A., Karthikeyan, R., Babbar-Sebens, M., Srinivasan, R., and Persyn, R. A. 2009. "Spatially Explicit Load Enrichment Calculation Tool To Identify Potential E. Coli Sources in Watersheds." Transactions of the American Society of Agricultural and Biological Engineers. Vol. 52. No. 4. pp. 1109-1120.
This paper details the development of the Spatially Explicit Load Enrichment Calculation Tool (SELECT) which is being developed into a GUI extension for ArcGIS 9.x. This tool models maximum potential E Coli loads due to a variety of point and non-point sources. The article illustrates how the tool can be used to estimate these loads for dogs, onsite wastewater treatment, wastewater treatment plants, cattle, sheep/goats, horses, feral hogs, and deer. The demonstrated purpose of this tool is to develop appropriate recommendations for sub watersheds in order to implement best practices to reduce overall E. Coli loading. A key advantage of this tool is the opportunity to analyze potential E Coli loads from readily available demographic data without having to perform specific sampling in the field.
Werz, H., and Hotzl, H. 2007. "Groundwater risk-intensity mapping in semi-arid regions using optical remote sensing data as an additional tool." Hydrogeology Journal. Vol. 15. pp. 1031-1049. doi: 10.1007/s10040-007-0202-0
Groundwater risk assessment through the utilization of remote sensing data is demonstrated through practical application in Jordan. In this case high resolution digital aerial photographs were utilized to assess geologic and hazard characteristics of the region. This utilization of GIS software with remote sensing data was critical to filling the data gaps required for analysis. The focus of this approach is to map potential rather than simply existing hazards. Of note, remote sensing technologies have been utilized to analyze a number of oceanic and land based environmental factors. Particularly color infrared photographs have been used to identify onsite wastewater soil absorption systems and contamination of groundwater. The study utilized LANDSAT ETM data, topographic maps, pan chromatic aerial maps, digital photographs and field survey to generate data (specific analysis undertaken for training areas). This resulted in a broad land use classification map of the study region. Mixed pixels were a considerable problem with classification (resolution 30x30 meters). Misclassification of land cover was assessed through the detailed evaluation of 48 smaller regions throughout the study area. Black and white aerial photographs were utilized to generate layers in ArcGIS corresponding to land use. A portion of the test site was analyzed utilizing color aerial photographs supplemented with GPS karst contour data to develop rules for classification for the rest of the dataset. Additional data pertinent to the hydrological characteristics of the soil which could not be gained through remote sensing were obtained directly and through the digitization of study area maps for topography and soil. The study utilized a PI model for assessing the vulnerability of karstic formations which assigns values for the protective function of layers between the earth's surface and the water table (P) and infiltration and surface/subsurface flow (I). Potential hazards were specifically mapped by GPS and remote sensing within the following categories: wastewater, municipal waste, fuels, transport/traffic, recreational facilities, and other. Detached houses in the example were assumed to be connected to the sewer system. The model can provide for houses without sewer connections with double the potential hazard. The risk intensity map was generated by running the calculated PI value and the calculated hazard indices for each raster cell through the appropriate equation.
On Site Wastewater Risk Assessment
Exposito, J. L., Esteller, M. V., Paredes, J., Rico, C., and Franco, R. 2010. "Groundwater Protection Using Vulnerability Maps and Wellhead Protection Area (WHPA): A Case Study." Water Resource Management. Vol. 24. pp. 4219-4236. doi: 10.1007/s11269-010-9654-4.
This paper utilizes the GOD method to establish wellhead protection areas (WHPA) around deep water wells. This strategy requires a small number of parameters compared to other available models (see also Ibe, 2003). These parameters are: (1) the degree of hydraulic confinement, (2) characteristics of the overlying strata, and (3) depth to groundwater. The WHPA is divided into three zones: absolute, maximum, and moderate restrictions zones. The absolute zone is established as the area requiring 24 hrs or less for the pollutant to enter the well. The maximum zone is established to prevent microbiological pollution of the well. The moderate restriction zone is designed to protect the well against persistent pollutants. This paper further provides the formulas used to calculate these distances. This paper utilized a social inclusion index to predict the populations which had the lowest percentage of sewer coverage and were most likely to be sources of contamination. Following the GIS mapping of the well head protection area a field survey was undertaken to identify potential contamination sources within each zone. In this survey, septic tanks were identified only in the moderate restriction zone. One well had sewage discharge and animal waste storage activities inside of the maximum protection zone. The report recommends that the well be closed or these activities restricted/moved by local authorities.
(Exposito, 2010 pg. 4233)
Gemitzi, A., Tsihrintzis, V. A., Christou, O., and Petalas, C. 2007. "Use of GIS for siting stabilization pond facilities for domestic wastewater treatment." Journal of Environmental Management. Vol. 82. pp. 155-166.
Stabilization ponds (SP) are discussed as a good alternative for collecting the discharge from on-site wastewater treatment systems in small communities which cannot support municipal sewage treatment units. The development of such an alternative is critical to the effective operation of on site wastewater treatment to avoid the direct discharge of septic tank overflow to the environment. This study documents the evaluation process for siting SP's in northeast Greece. Layers were created to evaluate a number of variables and exclusion criteria were applied to generate a list of potential sites. These were as follows: slope less than 5%, 500 m from major faults, appropriate land use, 500 m from village or city limits, 300 m from highways and railways, 500 m from lakes marshes and major rivers, and areas designated as protected or part of national parks. Temperature and the requirements of municipalities were considered for pond sizing. The available area was then calculated for each municipality and presented along with the required pond size. This study was conducted at the "master plan" level to determine potential sites for SP siting. The authors repeatedly emphasized that more specific surveys needed to be conducted in order to determine final site selection at the local level. This type of siting study is important for developing the capacity of on site wastewater treatment to effectively protect public health without posing undue additional risks.
Kelsey, H., Porter, D. E., Scott, G., Neet, M., and White, D. 2004. "Using geographic information systems and regression analysis to evaluate relationships between land use and fecal coliform bacterial pollution." Journal of Experimental Marine Biology and Ecology. Vol. 298. pp. 197-209.
This article presents a model to evaluate the impact of seasonal factors and land use on fecal coliforms in a Marine Estuary in South Carolina. Human sources of fecal coliforms including on-site wastewater treatment were found to contribute only a small proportion of observed fecal coliforms after the estimated contribution from domestic animals was included. The model was found to have an R squared value of .4401 which was considered very good considering the variability of fecal coliform measurements. Stormwater runoff from urban land use areas was found to be the most considerable contributor of fecal coliforms in this estuary.
Lasut, M. T., Jensen, K. R., Shivakoti, G. 2008. "Analysis of constraints and potentials for wastewater management in the coastal city of Manado North Sulawesi Indonesia." Journal of Environmental Management. Vol. 88. pp. 1141-1150.
In considering the constraints and potentials for wastewater management the authors utilized GIS to analyze land use and geomorphology of the city of Manado. This information was critical in pointing out city planning and topographical challenges to solving wastewater problems. The limited amount of land available for development along the coast has contributed to shifts in economic and political priorities including the transition of an area originally designated as a site for eco tourism to commerce. The author interviewed households in three sub districts selected randomly through stratified random sampling to assess the presence and quality of on site septic tanks in households. It was reported that in the three districts 16.8%, 25.0% and 14.7% did not utilize septic tanks. The condition of the septic tanks was found to be "very poor" or "poor" in 12.5% and 4.6% of the two sub districts reported. "Very poor" condition denotes that the septic tank is leaking to the sewer and "poor" denotes that the facility utilizes an open hole. The authors report exceedences for Biochemical Oxygen Demand, Nitrate, Phosphate, Fecal Coliform and E. Coli. The MPN international standard for Fecal Coliform and E. Coli is 200. All readings for fecal coliforms were in excess of 2400 with most readings for E. Coli following suit. There were two readings of 1100 for E. Coli (of 6). The author recommends the development of decentralized wastewater treatment with improved institutional controls and a system of subsidies for economically disadvantaged households.
Meeroff, D. E., Bloetscher, F., Bocca, T., and Morin F. 2008. "Evaluation of Water Quality Impacts of On-site Treatment and Disposal Systems on Urban Coastal Waters." Water, Air, and Soil Pollution. Vol. 192. pp. 11-24. doi: 10.1007/s11270-008-9630-2.
The introduction to this paper includes a series of sources which make a strong case for the public health impact of malfunctioning on site wastewater treatment facilities. This study sought to evaluate the impact of malfunctioning on site treatment and disposal systems (OSTDS) on public health and receiving water bodies. Two communities near Fr. Lauderdale FL were evaluated one which was connected to the municipal sewer and one which utilized OSTDS. Water was sampled at canals running by both of these communities and results were compared over time. This study documents the impact of on-site wastewater treatment on a number of indicators noting that nutrient, pathogen indicators, and chemical oxygen demand were notably higher during high water table events, but not different during low water table events. For E Coli the levels were 5 times higher in the OSTDS proximate canal. In spite of this, negative marine outcomes were not observed (correlation with the state beach monitoring program).
Stark, S. L., Nuckols, J. R. and Rada, J. 1999. "Using GIS to investigate septic system sites and nitrate pollution potential." Journal of Environmental Health. Vol. 61. No. 8. pg.15+.
The effect of nitrates released from on site septic systems on water quality in Summit County Colorado was assessed in this study. Topographic, land parcel and geologic layers were obtained and combined with database information on well and septic system data. This data was located within the ownership parcel data through common identifier codes. A soil map was hand digitized for the study. Hydrological characteristics were predicted for five mapped geologic types in the study area. Eleven soil types were classified according to permeability, depth to high water table, hydrologic soil group and depth to bedrock. The intersection of these attributes resulted in 39 "hydrogeologic units." This data was then entered into the DRASTIC model as explained above (Chitsazan and Akhtari, 2009). This study found no association between elevated nitrate levels and septic systems in multiple regression analysis. A key disadvantage of the study was the fact that water samples were taken from drinking water wells which were sited to maximize protection from potential contamination. As a result it is difficult to determine whether the negative finding was the result of insignificant pollution or distance from pollution sources. The paper provides a good discussion of the importance of utilizing sampling procedures which are designed specifically to evaluate the hypothesis in question as opposed to existing drinking water data.
Umezawa, Y., Hosono, T., Onodera, S., Siringan, F., Buapeng, S., Delinom, R., Yoshimizu, C., et al. 2008. "Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities." Science of the Total Environment. Vol. 404. pp. 361-376.
This article utilizes GIS to analyze sources of ammonium and nitrate groundwater contamination under the cities of Bankok, Manila, and Jakarta. The article begins with a description of the environmental, geological, and social (eg population density) characteristics of each city. Water samples were collected at the beginning of the rainy season in each city. These samples were taken from ground water, river water and tap water. The later two were taken as likely contributors to groundwater recharge. The average nitrate and nitrite combined level was found to be 240, 126, and 32 (micro)M in Jakarta, Manila and Bankok respectively. The EU and US standards are around 800 (micro)M. The overall levels observed were lower than reviewed cities in south Asia, but slightly higher than Long Island, NY. The study found that at this time there does not appear to be a threat to human health from groundwater consumption at the study sites.
This study is useful for this review because it highlights the possible sources of NH4: landfill, septic tanks, or other sewage disposal plants. This suggests that NH4 may be used to recognize leaking septic tanks in the absence of the other sources (and in the absence of other point sources such as intensive poultry farming or non-point sources like the application of organic fertilizers).
Other Resources
Ibe, K. M., Nwankwor, G. I., Onyekuru, S. O. 2003. "Groundwater pollution vulnerability and groundwater protection strategy for the Owerri area southeastern Nigeria." Water Resources Systems. Water Availability and Global Change Symposium. International Union of Geodysy and Geophysics Conference. Sapporo, Italy.
(Ibe et al., 2003, pg. 188).
Lu, Y., Tang, C., Chen, J., and Sakura, Y. 2008. "Impact of septic systems on local groundwater quality and water supply in the Pearl River Delta, China: case study." Hydrological Processes. Vol. 22. pp. 443-450. doi: 10.1002/hyp.6617.
This paper implicates on site wastewater treatment systems in the nitrate pollution of groundwater sources in a small town in the Pearl River Delta of China. The article provides extensive discussion of the chemical processes of nitrification and denitrification in support of the conclusion that observed pollution resulted from human as opposed to agricultural sources.
Appendix A
(Reproduced from Massoud et al. 2009, pg. 655)
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