Development of Localized Assessment of Municipal Wastewater Disposal Risks

A means to develop a comparative assessment of the risks of available wastewater effluent disposal options on a local scale needs to be developed to help local decision-makers make decisions on options such as direct or indirect potable reuse options. These options have garnered more interest as a result of water supply limitations in many urban areas. This risk assessment was developed from a risk assessment developed at the University of Miami in 2001 and Florida Atlantic University (FAU) in 2023. Direct potable reuse and injection wells were deemed to have the lowest risk in the most recent study by FAU. However, the injection well option may not be available everywhere. As a result, a more local means to assess exposure risk is needed. This paper outlines the process to evaluate the public health risks associated with available disposal alternatives which may be very limited in some areas. The development of exposure pathways can help local decision-makers define the challenges, and support later expert level analysis upon which public health decisions are based.

Effectiveness of Wastewater-Based Epidemiology as an Early Warning Tool to Detect SARS-CoV-2 (COVID-19)

Medical diagnostic tests to detect Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) for individuals in the United States were initially limited to people who were traveling or symptomatic to track disease incidence due to the cost of providing testing for all people in a community on a routine basis. As an alternative to randomly sampling large groups of people to track disease incidence at significant cost, wastewater-based epidemiology (WBE) is a well-established and cost-effective technique to passively measure the prevalence of disease in communities without requiring invasive testing. WBE can also be used as a forecasting tool since the virus is shed in individuals prior to developing symptoms that might otherwise prompt testing. This study applied the WBE approach to understand its effectiveness as a possible forecasting tool by monitoring the SARS-CoV-2 levels in raw wastewater sampled from sewer lift stations at a large public university campus setting including dormitories, academic buildings, and athletic facilities. The WBE analysis was conducted by sampling from building-specific lift stations and enumerating target viral copies using RT-qPCR analysis. The WBE results were compared with the 7-day rolling averages of confirmed infected individuals for the following week after the wastewater sample analysis. In most cases, changes in the WBE outcomes were followed by similar trends in the clinical data. The positive predictive value of the applied WBE approach was 86% for the following week of the sample collection. In contrast, positive correlations between the two data with Spearmen correlation (rs) ranged from 0.16 to 0.36. A stronger correlation (rs = 0.18 to 0.51) was observed when WBE results were compared with COVID-19 cases identified on the next day of the sampling events. The P value of 0.007 for Dorm A suggests high significance, while moderate significance was observed for the other dormitories (B, C, and D). The outcomes of this investigation demonstrate that WBE can be a valuable tool to track the progression of diseases like COVID-19 seven days before diagnostic cases are confirmed, allowing authorities to take necessary measures in advance and also enable authorities to decide to reopen a facility after a quarantine.

Water System Condition and Asset Replacement Prioritization

The goal of asset management is to identify and track the maintenance and replacement of assets that have reached their useful life. For that reason, gathering data and collecting information is a critical step when developing an asset management plan. Such data gathering includes physical and operational properties of the assets as well as collecting and tracking important events during the lifespan of the asset (i.e., pipe breaks, replacement year, maintenance performed, etc.). Critical factors in the asset management plan may be overlooked when there is no data or poor quality data. However, many utilities lack the resources for examining buried infrastructure and lack good quality work order data, so other methods of data collection are needed. The concept for this paper was to develop a means to acquire data on the assets for a condition assessment to identify pipes that were most likely to break and those with the highest consequences for same. Three utilities were used as examples. It was found that for buried infrastructure, much more information was known than anticipated but the actual predictions relied on only a few factors related to pipe type. However, there is a need to track the consequences, in this case breaks, which would indicate a failure. The latter would be useful for predicting future maintenance needs and the most at-risk assets, but is often missing in utility systems as many utilities do not adequately track breaks sufficiently. In this case two utilities were analyzed and predication on a third was developed.

Assessing the Impacts of Sea Level Rise Using Existing Data

Local communities want to know the cost of improvements needed to their drainage system based on projected sea level rise. Prior research demonstrates that in coastal areas, groundwater will rise with sea level. As a result the combination of groundwater levels and tidal data must be used to predict local impacts of sea level rise on the drainage system. However, it would appear to complicate the situation if the amount of data available for making sea level rise projections with groundwater is limited. The objectives of this task were to identify available data in a data limited community, compare the available data, assess the impact of sea level rise on the community, and its impact on the stormwater system, identify vulnerable areas in the City, provide an estimate of long-term costs for improvements, and provide a toolbox of strategies to employ at the appropriate time. The project was conducted using ArcGIS tools to import tidal, groundwater, topographic LiDAR and infrastructure improvements into GIS software and performing analysis based on current data. The cost of improvements was based on applying actual 2015 construction costs in the subject comments across a larger vulnerable area. It was found that the data sources provided similar results, despite different timelines and dates so did not interfere with the subsequent analysis. The data revealed that over $400 million in current dollars might be needed to address stormwater issues arising from sea level rise before 2100.

A Framework for a Subwatershed-Scale Screening Tool to Support Development of Resiliency Solutions and Flood Protection Priority Areas in a Low-Lying Coastal Community

Flood risk analysis is the instrument for local officials to create a sound strategy and adaptation plans for the impacts of inundation due to heavy rains, climate change and sea level rise. Hence, cities with aging infrastructure are retrofitting their stormwater management systems to mitigate the impacts. However determining the most at risk areas and the options for corrections is more challenging. As a result, there is an urgent need to develop a screening tool to analyze watersheds and identify the most at-risk areas. High-quality, open source data and sophisticated spatial analysis techniques allow engineers to create innovative ways to conduct watershed wide inundation analysis. In this study, the investigators developed a screening tool to identify at-risk properties by combining readily available data on topography, groundwater, surface water, tidal information for coastal communities, soils, open space, and rainfall data. Once the screening tool is developed, the means to identify and prioritize improvements to be funded with scarce capital funds is the next step. A tool box of solutions was developed to address flood risk and vulnerability. Testing of the screening tool was conducted in Broward County, Florida and shows encouraging results. Comparison with FEMA Flood maps and repetitive loss mapping indicates that the process works in a coastal community. The framework appears to be viable across cities that may be inundated with water due to sea-level rise, rainfall, runoff upstream, and other natural events.

Lessons Learned from Aquifer Storage and Recovery (ASR) Systems in the United States

This paper is the result of a survey and analyses of available data from 204 Aquifer Storage and Recovery (ASR) sites in the United States. This ASR site survey included all active and inactive sites and collected both operational and construction details. The inactive sites are of particular interest here because these are the projects from which valuable lessons can often be learned. The intent of this paper is to examine the reasons for those projects that are terminated. Statistical analyses indicated that there were factors associated with terminated ASR projects: general geographic location (e.g., region), operational issue, storage cycle, casing material, and injection formation. The injection formation involves local geology and aquifer characteristics (i.e., whether the aquifer is leaky and/or unconfined, and if water can be displaced to surface water bodies or adjacent aquifers). Operational problems associated with inactive projects include well clogging, metals mobilization, a low percentage of recovery for injected water, and disinfection byproducts in the recovered water.

Characterization of Biofilms and Mineralogical Scale in Underground Injection Well Disposal of Landfill Leachate and Industrial Wastewater Streams

Deep-well injection is a cost-effective alternative for industrial wastewater disposal, given the appropriate geology. Fouling of injection well tubing by biofilm or scale is common and reduces the effective diameter of the pipe, which results in increased wellhead pressure and lower injectivity. A detailed microbiological composition of biofilms and abiotic fingerprints use of mineral scale from an injection well has not been reported before. Therefore, biofilm and mineral scale samples from three depth intervals within a deep injection well (surface zone, D1= 0 - 61 m;intermediate zone, D2 = 62 - 457 m;and above the injection zone, D3 = 458 - 884 m) with recurrent biofilm development were collected to characterize the mineral composition and microbial community DNA. X-ray diffraction (XRD) analysis of the solids confirms the composition of the solids collected was mostly calcium carbonate (CaCO3) with minor contributions from common mineral salts. Microbiological fingerprinting suggests that methanogenic archaea and sulfate-reducing bacteria both of which are anaerobic biofilm producers were the most prevalent members of the prokaryotic community at all sampled depths. Methanosarcinae spp. increased with increasing depths, unlike other archaea. A non-pathogenic biofilm-producing Entamoeba dispar was the most prevalent member of the microbial domain (>30%) in all samples but was highest at the middle depth. The Chao alpha diversity indices for bacteria, viruses, and protozoans were highest at the shallow depth and gradually declined with increasing depth. The prevalent species above the injection zone depth are not barophilic organisms that thrive at high pressures, rather they are sulfate-reducing bacteria involved in anaerobic dissimilatory sulfate metabolism.

The Use of SF₆and GIS to Study Farfield Modeling of Ocean Outfall Plumes in Florida

In June, 2004 and February, 2007, in field tracer studies were conducted on the Hollywood and South Central outfalls, using sulfur hexafluoride (SF6) as a tracer. The objective of these studies was to determine if the tracer could be detected in the farfield at significant distance, and if so, could this data be used to construct a model of the farfield plume. Prior models for farfield plume movement do not appear to comport well with the conditions in southeast Florida. Extensive research was conducted in southeast Florida on 4 outfalls, which led to the development of nearfield dilution equations for same. However farfield modeling of outfall plumes was difficult to accomplish because the tracers used are not detectable for significant distances. The SF6 resolved that problem and as a result the Hollywood outfall was used to construct a model. Two methods were investigated for modeling the plume, 1) the Eureqa formulation method and 2) the Gamma-Curve method. The concentrations in the x-y plane were first found by using the Eureqa formulation to calculate the concentration at each grid point given its depth and the concentration of the centerline at the same latitude. The plume models were generated using MATLAB that matched with the results actually seen in the field.

Analyses of Physical Data to Evaluate the Potential to Identify Class I Injection Well Fluid Migration Risk

Injection wells have been used for disposal of fluids for nearly 100 years. Design of injection well systems has advanced over the years, but environmental concerns due to the potential for migration of injected fluids remain. Fluids range from hazardous materials, to mining waste to treated wastewater. This paper presents an evaluation of wells injecting treated wastewater to assess which create the greatest risk to migration potential. Prior studies have looked at the risks of Class I injection wells for wastewater disposal, but limited data were available at that time. This research involved collecting data and evaluating the differences as a means to predict the potential for fluid migration in the wells. There were four issues that might portend migration: well depth-shallower wells tended to have more migration;the tightness of the confining unit immediately above the injection zone;well age;and the use of tubing and packers. Florida is moving away from tubing and packer wells which may be an indicative of this issue. The results provide a pathway to investigate injection wells in other states.

Assessing Risk of Injection of Reclaimed Water into the Biscayne Aquifer for Aquifer Recharge Purposes

The recharge of non-potable water into a drinking water aquifer is one means to overcome decreasing groundwater supplies and maintain availability of these resources for current and future generations. However, health concerns exist regarding the use of waters of “impaired quality” such as reclaimed wastewater for aquifer recharge. The objective of this study is to evaluate the potential risk to drinking water from the use of reclaimed water for recharge purposes using computational modeling with MODFLOW and MT3D groundwater transport simulation based on an actual situation using rotavirus as a surrogate. The results from the simulation showed that after seven months, the risk of contamination based on concentration contours from the injection well to the production wells was stabilized below 10-6.

Algal Control in Warm Weather Pond Using EMOH Device

Nuisance algal blooms have been a topic of discussion in Florida as a result of highly visible adverse impacts to coastal waters, but algae is hardly a new concern for warm weather communities. The typical treatment is with copper sulfate. However, copper has been identified by regulatory agencies as a contaminant of concern in coastal waters and has been targeted for stricter regulations, potentially limiting its use in the future for algae control. The EMOH device was proposed as a means to test whether a “green” solution could be found to this algae concern. EMOH creates high volume oxidation in concert with activated organisms. The initial treatment effort covered one year (2016). During treatment, water quality was monitored with periodic measurements of the benthic detrital layer, which is a precursor to algal blooms in these ponds. Photographs of the extent of algal coverage on the surface, water quality in the pond and thickness measurements of the detrital layer defined success. Through the hot summer, despite regular influx of nutrients and rain, the amount of algae declined, and the detrital layer decreased in thickness from 22 - 24 inches to 7 - 8 inches. The decrease of the detrital layer means that over time, the benthic source of nutrient availability can be more controlled. The authors concluded that the EMOH process was successful and that physically removing the detrital layer may be an important step in long-term algal reductions.

Risk and Economic Development in the Provision of Public Infrastructure

A public water and sewer utility is created to develop safe, reliable and financially self-supporting potable water and sanitary sewage systems which will meet the water and sewerage needs of the areas served by the utility;to ensure that existing and future utility facilities are constructed, operated and managed at the least possible cost to the users without outside subsidies;and to develop a system that is compatible with the area’s future growth. To gain efficiencies in operation, these new facilities must be developed in accordance with the latest technical and professional standards to protect the health, safety, and welfare of the citizens served now or in the future. Hence a utility must construct new pipelines, pump stations and other infrastructure, whether that infrastructure is for growth, to improve existing service, or to replace infrastructure that has reached the end of its useful, economic, and/or physical life. In established or stable communities, the replacement of existing infrastructure, where it is no longer economical to operate, is deteriorated to a point where replacement is more cost effective than repairs due to wear, neglect or environmental conditions, or where the infrastructure no longer serves its intended purpose or meets regulatory standards, must be pursued. As a result, many established utilities have capital plans that contain many such replacement projects. The question is how much investment should be made. The intent of this paper is to evaluate investment in infrastructure made by public water and sewer utility systems. What was found among the utilities in Florida that were evaluated was that more than half are underinvesting in their infrastructure. Some are not investing at all although more research is needed because it appears that many utilities make large investments periodically as opposed to using pay-as-you-go methods. Large scale investments like bond issues impact rates. Economies-of-scale remain for large utilities. Smaller utilities compete with larger ones to control rates. The data gathered indicates that utilities are underfunded, and under-invested. To reduce potential health risks, this needs to change. At the same time, trends appear to be a key to assess the potential for at risk utilities. Hence a future project would review data for the past 15 - 20 years for trends, identify patterns of altered investments and denote how the 2008 financial crisis changed the utility finances. A road to recapture lost revenues and make the infrastructure more resilient can then be accomplished.

Analysis of Inflow Solutions among Eleven Sewer Systems

This paper was undertaken to compare eleven utilities where part or all of the utility was tested for infiltration and inflow with the intention of determining the value of data gathered from midnight investigations, comparing potential costs (in 2020 dollars), and understanding whether statistical methods can be used to predict potential problems on the system. Inflow and infiltration amounts can be identified on a utility system without significant effort. Inflow correction is robust and easy to implement (though often overlooked). After inflow is addressed, the results indicated that a midnight investigation could quickly identify portions of the sewer system in need of attention. Maps of leaky pipe sections can be identified, and commonalities in the system may become apparent. Statistical methods were used to identify high groundwater levels and lateral issues as critical issues on these systems. The methods can be utilized at other utilities to help guide them to addressing the critical issues first as opposed to focusing only on the traditional pipe lining solutions that often ignore the lateral and inflow issues that plague utility managers.

Public Infrastructure Asset Assessment with Limited Data

When creating an asset management plan, missing data is perceived to be a huge problem, especially when the event data (breaks in water distribution pipes as an example) are not tracked. The lack of tracking makes it difficult to determine which factors are the critical ones. Many utilities lack the resources for examining buried infrastructure, so other methods of data collection are needed. The concept for this paper was to develop a means to acquire data on the assets for a condition assessment (buried pipe is not visible and in most cases, cannot really be assessed). What was found was that for buried infrastructure, much more information was known than anticipated. Knowing exact information is not really necessary. However, there was a need to track event-breaks, flooding etc.—what would indicate a “failure”.?The latter would be useful for predicting future maintenance needs and the most at-risk assets.