Human and environmental risk ranking of onsite sewage disposal systems for Oahu

This study evaluated the human health and environmental risk posed by on-site sewage disposal systems (OSDS). Oahu, Hawaii, was chosen as the study area for this project to develop and implement the methodology that will be applied to other islands in the future. The specific objectives of this study were to: • Estimate the quantity and types of OSDS on Oahu; • Estimate the effluent load discharged to the environment by these systems; • Identify which individual critical receptors (drinking water sources, streams and near shore waters) are most impacted by OSDS; • Identify other factors contributing to potential risk of OSDS; • Develop a risk scoring scheme based on various factors to assist regulatory managers in prioritizing inspection efforts for OSDS; and • Assign a risk score to each OSDS.Safe Drinking Water Branch, Department of Health, State of Hawai

Lahaina groundwater tracer study -- Lahaina, Maui, Hawaii

The studies presented in this report provide the positive establishment of hydrologic connections between the municipal wastewater injection from the LWRF and the nearshore region of the Kaanapali coast on the Island of Maui, Hawaii, and provide the results from the study’s principal objectives, which have been to: (1) implement a tracer dye study from the LWRF (Section 3), (2) conduct continuous monitoring for the emergence of the injected tracer dyes at the most probable points of emergence at nearshore sites within the coastal reaches of the LWRF (Section 2), (3) conduct an airborne infrared sea surface temperature mapping survey of coastal zone fronting the LWRF in an effort to detect cool and/or warm temperature anomalies that may be indicative of cool submarine groundwater discharge and warm wastewater effluent (Section 4), (4) complete radon and radium radiochemical surveys to detect the emergence points and flow rates of the naturally occurring submarine groundwater along the coastal zone (Section 5), (5) complete geochemical and stable isotopic analyses of LWRF effluent, upland well waters, terrestrial surface waters, marine waters, and submarine groundwater discharge in an effort to help partition the relative contribution of effluent waters to the ocean (Section 6), and (6) combine complete dye emergence breakthrough curves with which to develop groundwater models to determine the LWRFs effluent flow paths and rates of emergence to the coastal zone (Section 7).U.S. Environmental Protection AgencyDepartment of Health, State of HawaiiU.S. Army Engineer Research and Development Cente

Is it appropriate to apply porous media groundwater circulation models to karstic aquifers?

Written by renowned experts in the field, this book assesses the status of groundwater models and defines models and modeling needs in the 21st century. It reviews the state of the art in model development and application in regional groundwater management, unsaturated flow/multiphase flow and transport, island modeling, biological and virus transport, and fracture flow. Both deterministic and stochastic aspects of unsaturated flow and transport are covered. The book also introduces a unique assessment of models as analysis and management tools for groundwater resources. Topics covered include model vs. data uncertainty, accuracy of the dispersion/convection equation, protocols for model testing and validation, post-audit studies, and applying models to karst aquifers

Is it appropriate to apply porous media groundwater circulation models to karstic aquifers?

Written by renowned experts in the field, this book assesses the status of groundwater models and defines models and modeling needs in the 21st century. It reviews the state of the art in model development and application in regional groundwater management, unsaturated flow/multiphase flow and transport, island modeling, biological and virus transport, and fracture flow. Both deterministic and stochastic aspects of unsaturated flow and transport are covered. The book also introduces a unique assessment of models as analysis and management tools for groundwater resources. Topics covered include model vs. data uncertainty, accuracy of the dispersion/convection equation, protocols for model testing and validation, post-audit studies, and applying models to karst aquifers

Assessment of Nutrient Use and Nitrate Contamination in Central Oahu, Hawaii

Groundwater contamination by agricultural fertilization is a widely recognized problem in the USA and worldwide. Here in Hawaii, agricultural fields have posed a threat to the invaluable basal aquifer. The concentration of nitrate-N in the Pearl Harbor aquifer on Oahu was below 2.3 mg/L in the 1950’s and 1960’s, but has increased in some wells in the Kunia area to a maximum of 7.6 mg/L in 1992 to 1994. The objective of this study is to assess nitrogen use in the agricultural lands and nitrate contamination in the Pearl Harbor aquifer. Nitrate distribution and migration in the subsurface are influenced by many mechanisms. Nitrogen fertilizer undergoes many N transformations and interactions with the soil and the plant after applications. In this study, a field data collection was done and analysis of the samples was completed to understand the leaching process of nitrate in the root zone of three different cropped fields. A detailed discussion is presented to address various factors that control the transport process. Field measurements were evaluated statistically to judge the sampling plan in relation to spatial variations. The study uses an uncertainty index in the analysis, which is the density of samples required for a sample mean to fall within a defined limit of accuracy. To simplify the process of estimating leaching rates to the aquifer, a simple lumped parameter model (LPM) was developed. The model, which is analytical in nature, uses a limited set of input data. Average leaching rates can be estimated in response to agricultural practices, N transformations, and other processes. The model is tested against two detailed numerical models with great success. The model will be made available for interested parties for use in assessing the potential threat to aquifers. Various types of uncertainties affect our ability to predict nitrate fate accurately. Five major sources of uncertainty were identified in this study: (1) uncertainty due to spatial variation, (2) uncertainty related to the accuracy of the input data, (3) uncertainty due to simplifications in the development of the models, (4) uncertainty due to modeling parameters, and (5) uncertainty due to the complexity of the unsaturated zone in Hawaii. The impact of these uncertainties on the simulations of nitrate leaching is evaluated and a sensitivity analysis was done to quantify the uncertainty due to the modeling parameters in a leaching model. The result showed that hydraulic properties, plant uptake, and dispersivity are very important in achieving reliable simulation or prediction. It is recommended that hydraulic conductivity and water retention relationships be measured under field conditions before the use of the model. A historical record of specific plant growth and nutrient assimilation by the plant can provide reasonable data for modeling the plant uptake process. Dispersivity can be obtained by calibration of the model in a specific soil. Although the sensitivity analysis suggests that uncertainty in nitrate adsorption exert a considerable effect on nitrate transport results, anion adsorption is not a principal factor that affects nitrate leaching in the root zone. The relatively high content of organic matter in the root zone may favor a net negative surface charge on soil colloids, which contributes to the leachability of negatively charged nitrate. In contrast however, retardation of nitrate plays a dominant role in nitrate leaching below the root zone in central Oahu. Only a small fraction of the nitrate leaching reaches the groundwater. Although different explanations have been proposed for the sorption process in the thick unsaturated zone in central Oahu, a retardation factor should be considered for interpreting the results of the outflow from the root zone. Nitrate contamination in the Pearl Harbor aquifer was assessed. Quasi three-dimensional models were used to simulate water flow and nitrate transport in the aquifer. The models were calibrated by using available records and used for predictions based on assumed scenarios for water and land use. Future predictions show the likelihood of a nitrate contamination problem. Assumed conservative nitrate concentrations at the water table and a very mild increase in water use resulted in concentrations that exceed the MCL for nitrate of 10 ppm. Nitrate concentration below the agricultural lands is likely to increase with planned land use changes that may require additional fertilizer use. The possibility of changes in the physical or chemical ability of the unsaturated deep formations to store nitrate may also lead to increased leaching rates. A need exists for a better management of fertilizer use, a process that should be possible without sacrificing agricultural productivity. The approaches developed in this study can help in such an endeavor.State of Hawaii Department of Health; City and County of Honolulu Board of Water Supply; University of Hawaii's Water Resources Research Center: U.S. Geological Grant; Governor's Agricultural Coordinating Committee; State of Hawaii Department of Agriculture; Del Monte Company; ICI Seed Company; Amfac/JMB; The Robinson Trus

Modeling Streamflows and Flood Delineation of the 2004 Flood Disaster, Ma¯noa, O‘ahu, Hawai‘i.

v. ill. 23 cm.QuarterlyIn October 2004 a flood caused extensive damage to the University of Hawai‘i (UH) campus and neighboring residential areas in Ma¯noa Valley, O‘ahu, Hawai‘i. This modeling study was aimed at streamflow evaluation and flood delineation for the area impacted by the flood. The study concluded that the HEC-1 model of the U.S. Army Corps of Engineers is suitable for simulating storm runoff response for the study area, considering the nature of small Hawai‘i watersheds, which generate hydrographs with steep rising and falling limbs. The curve-number method of the U.S. Soil Conservation Service is also suitable because it predicts reasonably well the main features of streamflow hydrographs, including runoff duration and time of peaks. To improve on accuracy, however, there is a need for better characterization of spatial rainfall distribution through measurements. A flood delineation model, which treats the flood as a hypothetical dam break, was used to predict the floodwater pathway, flood zone extent, maximum flood depth, and the time to reach that depth. The model predicted an upper value for storm total flow volume that would not cause flooding on the UH campus. Although not fully validated, the developed models can guide data-collection and decision-making processes. For example, the models demonstrated that it is possible to mitigate the flood through streamflow diversion and stream dredging, realignment, and lining. For efficient management, we recommend defining a new subwatershed of the Ala Wai basin (to be called the West Ma¯noa Watershed) that contains the university campus

WRRCTMR No.84 The Cell-Analytical-Numerical Technique for Solving Unsaturated-Flow and Solute-Transport Problems

The cell analytical-numerical (CAN) method was developed and applied for the solution of one dimensional water flow and solute transport problems in the unsaturated zone. The flow equation is characterized by a nonlinear governing equation. The CAN method is similar to other numerical techniques in that it divides the domain into a number of computational elements, each homogeneous in nature. It differs, however, by implementing a local analytical solution within the element. The soil moisture flux (for the flow equation) or solute mass flux (for the transport equation) is applied at the interface between two adjacent elements to define an algebraic relationship between the values of pressure head or concentration, respectively, at three neighboring points. Assembling these three-point equations provides a tridiagonal system of equations that can be solved by the Thomas algorithm. The system describing the flow problem is nonlinear in nature, and is solved iteratively within an implicit linearization scheme. For water flow, the method is applied to a number of soil types and the results are compared to Philip's semi-analytical solution and a numerical solution that is based on the finite-element technique. The results indicate the method's high accuracy over a wide range of soil types. However, an upstream weighting approach is needed for coarser soils, a process that may lead to relatively large mass-balance errors. The high accuracy of the solute transport solutions is demonstrated through comparison against available analytical solutions.U.S. Department of the Interior, Geological Survey Grant/Contract No. 14-08-0001-G1558-0

Human and environmental risk ranking of onsite sewage disposal systems for the Hawaiian islands of Kauai, Molokai, Maui, and Hawaii

Outside of the urban centers and major towns, residences and small businesses dispose of wastewater at the location where it is generated. This on-site disposal of wastewater gives rise to risks to human health and the environment. This study assessed the potential risk posed by on-site sewage disposal systems (OSDS) to human health and critical ecosystems on the islands of Hawaii, Kauai, Maui, and Molokai. To assess this risk, the number and locations of OSDS were estimated based on a search of wastewater and tax databases. The risk posed to critical ecosystems and human health was evaluated based on the volume and water quality characteristics of the effluent discharged and the proximity of OSDS to receiving ecosystems and potential points of human contact. Finally, a cumulative risk severity score was calculated to rank the relative risk posed by each OSDS. Project Goals and Methods The objectives of this study were to: 1. Estimate the quantity, location, and types of OSDS on the islands of Hawaii, Kauai, Maui, and Molokai; 2. Estimate the effluent load added to the environment by these systems; 3. Identify and map the factors influencing the risk posed by OSDS to the environment and to human health; 4. Evaluate the potential risk to the receptors of concern (ROC) that may be impacted by OSDS; 5. Develop a scoring system to map the severity and distribution of OSDS risk factors for each class of ROCs; and 6. Based on the ROC scoring results, compute an overall risk score to rank the severity of the risk posed by individual OSDS. The objectives are met by: • Completing an inventory to estimate the quantity, characteristics, and location of the OSDS (Section 3); • Modeling the impact to the groundwater from the effluent discharged from these OSDS (Section 4); • Using Geographical Information Systems to map the spatial distribution of the hydrologic parameters that affect the vulnerability of the human and environmental receptors to OSDS effluent contamination (Sections 4, 5, 6, and 7); and • Linking the OSDS locations to the OSDS risk factors to compute a relative risk-ranking score for each OSDS parcel. Data developed by this study can be used by planning and regulatory agencies to set policy regarding OSDS, identify areas most suitable for locating OSDS, and delineate those areas where the negative impact from OSDS effluent is most likely to occur. The information can also be used to develop a schedule for OSDS inspections by prioritizing systems based on relative risks.Safe Drinking Water Branch, Department of Health, State of Hawai

Impact of Climate Change on Daily Streamflow and Its Extreme Values in Pacific Island Watersheds

The integration of hydrology and climate is important for understanding the present and future impact of climate on streamflow, which may cause frequent flooding, droughts, and shortage of water supply. In view of this, we assessed the impact of climate change on daily streamflow duration curves as well as extreme peak and low flow values. The objectives were to assess how climate change impacts watershed-wide streamflow and its extreme values and to provide an overview of the impacts of different climate change scenarios (Representative Concentration Pathways (RCP) 4.5 and 8.5) on streamflow and hydrological extremes when compared with the baseline values. We used the Soil and Water Assessment Tool (SWAT) model for daily streamflow and its extreme value modeling of two watersheds located on the Island of Oahu (Hawaii). Following successful calibration and validation of SWAT at three USGS flow gauging stations, we simulated the impact of climate change by the 2050s (2041–2070) and the 2080s (2071–2100). We used climate change perturbation factors and applied the factors to the historical time series data of 1980–2014. SWAT adequately reproduced observed daily streamflow with Nash-Sutcliffe Efficiency (NSE) values of greater than 0.5 and bracketed >80% of observed streamflow data at 95% model prediction uncertainty at all flow gauging stations, indicating the applicability of the model for future daily streamflow prediction. We found that while the considered climate change scenarios generally show considerable negative impacts on daily streamflow and its extreme values, the extreme peak flows are expected to increase by as much as 22% especially under the RCP 8.5 scenario. However, a consistent decrease in extreme low flows by as much as 60% compared to the baseline values is projected. Larger negative changes of low flows are expected in the upstream part of the watersheds where higher groundwater contributions are expected. Consequently, severe problems, such as frequent hydrological droughts (groundwater scarcity), reduction in agricultural crop productivity, and increase in drinking water demand, are significantly expected on Oahu. Furthermore, the extreme values are more sensitive to rainfall change in comparison to temperature and solar radiation changes. Overall, findings generally indicated that climate change impacts will be amplified by the end of this century and may cause earlier occurrence of hydrological droughts when compared to the current hydrological regime, suggesting water resources managers, ecosystem conservationists, and ecologists to implement mitigation measures to climate change in Hawaii and similar Islands