Costs of Arsenic Treatment for Potable Water in California and Comparison to U.S. Environmental Protection Agency Affordability Metrics1

Hilkert Colby, Elizabeth J., Thomas M. Young, Peter G. Green, and Jeannie L. Darby, 2010. Costs of Arsenic Treatment for Potable Water in California and Comparison to U.S. Environmental Protection Agency Affordability Metrics. Journal of the American Water Resources Association (JAWRA) 46(6):1238–1254. DOI: 10.1111/j.1752-1688.2010.00488.x Abstract: The United States (U.S.) federal standard for arsenic in potable water systems is only the second water quality standard in which the U.S. Environmental Protection Agency (USEPA) administrator used “discretionary authority to establish a less stringent standard” based on the results of cost-benefit analyses. Based on the findings that a “standard of 3 μg/l would be feasible but not justified,” the revised maximum contaminant level (MCL) lowered the allowable arsenic concentration from 50 to 10 μg/l in 2002. In 2009, approximately 145 systems in California were out of compliance. The objectives were to gather performance and cost data from arsenic treatment systems in California to compare with data from the USEPA demonstration sites as well as with the USEPA affordability metrics for drinking water. The median cost of compliance with the revised arsenic MCL for the 36 surveyed systems was $1.95/1,000 gallons (2008 dollars), which is 69% of the average cost of delivered tap water in the U.S. in 2008 ($2.81/1,000 gallons). Additionally, 22% of the surveyed systems in California paid more than the maximum predicted cost of compliance with the revised arsenic MCL ($5.05/1,000 gallons). The largest variation in cost was seen in the systems that treated <500 gpm. For the systems utilizing adsorption, systems obtained between 20 and 80% of the expected bed volumes prior to breakthrough, indicating the need for better prediction of performance.     

Occurrence of Volatile Organic Compounds in Aquifers of the United States1

Abstract: Samples of ambient ground water were collected during 1985‐2002 from 3,498 wells in 98 aquifer studies throughout the United States. None of the sampled wells were selected because of prior knowledge of nearby contamination. Most of these samples were analyzed for 55 volatile organic compounds (VOCs) to characterize their national occurrence. Volatile organic compounds were found in samples collected from 90 of the 98 aquifer studies. Occurrence frequencies of one or more VOCs for the 98 aquifer studies ranged from 0 to about 77% at an assessment level of 0.2 microgram per liter (μg/l). The aquifer studies with the largest occurrence frequencies were in southern Florida, southern New York, southern California, New Jersey, and Nevada. Trihalomethanes and solvents were the most frequently occurring VOC groups. Of the 55 VOCs included in this assessment, 42 occurred in at least one sample at an assessment level of 0.2 μg/l. Chloroform, perchloroethene, and methyl tert‐butyl ether were the most frequently occurring VOCs. Many factors, such as the hydrogeology of the aquifer, use of VOCs, land use, and the transport and fate properties of VOCs, affect the occurrence of VOCs in ground water.     

Finding Water for Growth: New Sources,New Tools,New Challenges1

Abstract: Rapidly growing regions such as the western United States face difficult challenges in mobilizing new water supplies to meet new demands. Environmental concerns have curtailed the scope for large new surface storage projects, and widespread basin overdraft has limited ground water’s potential as a source of expansion. Drawing on the California experience, this article explores modern water planning approaches, which focus on a portfolio of options including nontraditional sources (recycling, desalination, underground storage) and more efficient use of existing supplies (conservation and water marketing). It reviews the advantages and drawbacks of the elements of the portfolio, provides examples of innovative planning approaches, and assesses the role for supportive government policies.     

WESTERN WATER RESOURCES: THE DESERT IS BLOOMING,BUT WILL IT CONTINUE?1

ABSTRACT: The arid Southwest of the United States is confronted with increasing water demands and a limited resource. Past efforts to meet water demand have been directed toward development of scarce water resources. While development programs have been successful in stretching available supply, few feasible development options remain. Furthermore, heavy water utilization has affected water quality within drainage basins. It seems likely that water management will play a much more significant role in water resource allocation in the future. This paper will examine water development activity in the Southwest to date. Attention will be given to several of the problems that have arisen. The paper will then examine water management options. Particular attention will be given to water management options being implemented in the State of Arizona.     

Variability and Trends in Runoff Efficiency in the Conterminous United States

Variability and trends in water‐year runoff efficiency (RE) — computed as the ratio of water‐year runoff (streamflow per unit area) to water‐year precipitation — in the conterminous United States (CONUS) are examined for the 1951 through 2012 period. Changes in RE are analyzed using runoff and precipitation data aggregated to United States Geological Survey 8‐digit hydrologic cataloging units (HUs). Results indicate increases in RE for some regions in the north‐central CONUS and large decreases in RE for the south‐central CONUS. The increases in RE in the north‐central CONUS are explained by trends in climate, whereas the large decreases in RE in the south‐central CONUS likely are related to groundwater withdrawals from the Ogallala aquifer to support irrigated agriculture.     

OCCURRENCE OF TOTAL DISSOLVED PHOSPHORUS IN UNCONSOLIDATED AQUIFERS AND AQUITARDS IN IOWA1

ABSTRACT: Seven sets of ground water samples from 103 observation wells were analyzed for total dissolved phosphorus (TDP) in four areas and five materials including loess and loess derived alluvium in the Deep Loess Hills of western Iowa, outwash and fractured till adjacent to Clear Lake in north central Iowa, fractured till in central Iowa, and a sand and gravel aquifer in northwest Iowa. Land use in ground water recharge zones in all four areas is dominated by crop or animal production or both. Concentrations of TDP exceeding the minimum laboratory detection limit of 20 μg/l as P were found in all areas and in all materials sampled. Samples from the outwash deposits associated with Clear Lake contained significantly larger concentrations than all other areas and materials with a median of 160 μg/l. Water from fractured till in three areas produced the smallest range of concentrations with a median of 40 μg/l. The mean value of TDP in all sample sets exceeded 50 μg/l, an important ecological threshold that causes increased productivity in lakes and perennial streams and one being considered as a surface water nutrient standard by regulatory agencies. These results clearly show that ground water in essentially all near‐surface aquifers and aquitards discharging to Iowa's streams and lakes is capable of sustaining P concentrations of 50 to 100 μg/l in streams, lakes, and reservoirs. Consequently, even if point discharges and sediment sources of P are substantially reduced, ground‐water discharge to surface water may exceed critical thresholds under most conditions.     

DISSOLVED HEAVY METALS IN SHALLOW GROUND WATER IN A SOUTHEASTERN MICHIGAN URBAN WATERSHED1

ABSTRACT: The occurrence of dissolved heavy metal concentrations in shallow ground water were measured at 126 sites within an urban watershed in southeastern Michigan. A total of 1,140 samples were collected from the first saturated zone, and the mean concentrations of 11 heavy metals (arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, and zinc) were obtained and compared to their corresponding mean concentrations within surface soil. The results suggest that former and current land use processes have resulted in significant adverse impacts on the study region. Levels of Cr 20 to 30 times the maximum contaminant level (MCL) have been detected in the ground water beneath industrial sites. In addition, Cd and Pb have been found at levels exceeding their MCLs where surface soils are clay‐rich, and in sandy soils at more than 10 times their MCLs. The high levels of Cr in ground water strongly suggest that the chromium is in a hexavalent form, and this likelihood is supported by current studies. Given the hydraulic connection between the watershed's surface waters and the Great Lakes, these findings raise significant ecological and public health concerns.     

MEETING FUTURE PUBLIC WATER SUPPLY NEEDS: A SOUTHWEST PERSPECTIVE1

ABSTRACT: Most southwestern cities were founded along rivers or in areas having springs or readily available ground water. Because of the generally sparse precipitation, the renewable fresh water supply in the Southwest is smaller than most other areas of the United States. Despite the arid climate, water use has increased rapidly, first in the form of irrigation, and more recently the use in cities. This has caused extensive development of local water resources and overdraft of ground water basins in some areas. It is difficult to implement new local supplies and importation projects due to a myriad of environmental and legal constraints and a general shortage of public funds. Various opportunities and plans for water management, both on the demand and supply sides, are discussed. Evolving water strategies in four metropolitan areas - El Paso, Albuquerque, Las Vegas, and Phoenix - and issues regarding the Central Arizona Project are presented.     

The Water‐Year Water Balance of the Colorado River Basin

Model‐estimated monthly water balance components (i.e., potential evapotranspiration, actual evapotranspiration, and runoff (R)) for 146 United States (U.S.) Geological Survey 8‐digit hydrologic units located in the Colorado River Basin (CRB) are used to examine the temporal and spatial variability of the CRB water balance for water years 1901 through 2014 (a water year is the period from October 1 of one year through September 30 of the following year). Results indicate that the CRB can be divided into six subregions with similar temporal variability in monthly R. The water balance analyses indicated that approximately 75% of total water‐year R is generated by just one CRB subregion and that most of the R in the basin is derived from surplus (S) water generated during the months of October through April. Furthermore, the analyses show that temporal variability in S is largely controlled by the occurrence of negative atmospheric pressure anomalies over the northwestern conterminous U.S. (CONUS) and positive atmospheric pressure anomalies over the southeastern CONUS. This combination of atmospheric pressure anomalies results in an anomalous flow of moist air from the North Pacific Ocean into the CRB, particularly the Upper CRB. Additionally, the occurrence of extreme dry and wet periods in the CRB appears to be related to variability of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation.     

PESTICIDES IN GROUND WATER: DO ATRAZINE METABOLITES MATTER?1

ABSTRACT: Atrazine and atrazine-residue (atrazine + two metabolites - deethylatrazine and deisopropylatrazine) concentrations were examined to determine if consideration of these atrazine metabolites substantially adds to our understanding of the distribution of this pesticide in groundwater of the midcontinental United States. The mean of atrazine.residue concentrations was 53 percent greater than that of atrazine alone for those observations above the detection limit (> 0.05 μg/l). Furthermore, a censored regression analysis using atrazine-residue concentrations revealed significant factors not identified when only atrazine concentrations were used. Thus, knowledge of concentrations of these atrazine metabolites is required to obtain a true estimation of risk of using these aquifers as sources for drinking water, and such knowledge also provides information that ultimately may be important for future management policies designed to reduce atrazine concentrations in ground water.     

GROUND WATER/SURFACE WATER RESPONSES TO GLOBAL CLIMATE SIMULATIONS,SANTA CLARA‐CALLEGUAS BASIN,VENTURA, CALIFORNIA1

ABSTRACT: Climate variations can play an important, if not always crucial, role in successful conjunctive management of ground water and surface water resources. This will require accurate accounting of the links between variations in climate, recharge, and withdrawal from the resource systems, accurate projection or predictions of the climate variations, and accurate simulation of the responses of the resource systems. To assess linkages and predictability of climate influences on conjunctive management, global climate model (GCM) simulated precipitation rates were used to estimate inflows and outflows from a regional ground water model (RGWM) of the coastal aquifers of the Santa Clara‐Calleguas Basin at Ventura, California, for 1950 to 1993. Interannual to interdecadal time scales of the El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) climate variations are imparted to simulated precipitation variations in the Southern California area and are realistically imparted to the simulated ground water level variations through the climate‐driven recharge (and discharge) variations. For example, the simulated average ground water level response at a key observation well in the basin to ENSO variations of tropical Pacific sea surface temperatures is 1.2 m/°C, compared to 0.9 m/°C in observations. This close agreement shows that the GCM‐RGWM combination can translate global scale climate variations into realistic local ground water responses. Probability distributions of simulated ground water level excursions above a local water level threshold for potential seawater intrusion compare well to the corresponding distributions from observations and historical RGWM simulations, demonstrating the combination's potential usefulness for water management and planning. Thus the GCM‐RGWM combination could be used for planning purposes and — when the GCM forecast skills are adequate — for near term predictions.     

EMERGENCY WATER SUPPLIES FROM GROUND WATER IN HUMID REGIONS1

ABSTRACT: This paper focuses on the development and testing of a mathematical model of an emergency ground water supply operated principally during periods of low streamflow. The process of ground water withdrawal and recharge is simulated taking account of streamflow, water demand, evapotranspiration, natural and artificial recharge and increased evapotranspiration due to artificial recharge, ground water pumpage, and streamflow contribution to pumped water. The model determines whether natural recharge is possible in less time than the return period of drought and also whether artificial recharge is needed. By simulating operation over a long period of time, the model can examine different droughts of short and long duration and can test the operating rules for ground water storage development in an area. Submodels analyze the components of the operating process including ground water flow into the stream, seepage losses, stream portion of well discharge due to induced infiltration and recharge from rainfall or water spreading. The model has been tested for areas in the humid northeastern United States.     

USE OF THE KRIGING METHOD FOR STUDYING CHARACTERISTICS OF GROUND WATER DROUGHTS1

round water drought events were derived by taking a truncation level through the time series of daily ground water depth that are recorded elevation differences between the water table and land surface at a well site. Droughts of various truncation levels at 70, 80, 90, and 95 percent, were obtained, where a 70 percent truncation level means that 70 percent of ground water depth data are less than or equal to the truncated value. The conditional probability that a drought occurring at a certain truncation level will prolong and advance to that of the next higher level was estimated. The regionalization analysis was conducted assuming that conditional probabilities estimated at selected wells are regionalized variables. Contour lines of conditional probabilities for each truncation level were constructed to express their spatial variability in the region. Estimation errors associated with the regionalization were reasonably small.     

Operational Evapotranspiration Mapping Using Remote Sensing and Weather Datasets: A New Parameterization for the SSEB Approach

The increasing availability of multi‐scale remotely sensed data and global weather datasets is allowing the estimation of evapotranspiration (ET) at multiple scales. We present a simple but robust method that uses remotely sensed thermal data and model‐assimilated weather fields to produce ET for the contiguous United States (CONUS) at monthly and seasonal time scales. The method is based on the Simplified Surface Energy Balance (SSEB) model, which is now parameterized for operational applications, renamed as SSEBop. The innovative aspect of the SSEBop is that it uses predefined boundary conditions that are unique to each pixel for the “hot” and “cold” reference conditions. The SSEBop model was used for computing ET for 12 years (2000‐2011) using the MODIS and Global Data Assimilation System (GDAS) data streams. SSEBop ET results compared reasonably well with monthly eddy covariance ET data explaining 64% of the observed variability across diverse ecosystems in the CONUS during 2005. Twelve annual ET anomalies (2000‐2011) depicted the spatial extent and severity of the commonly known drought years in the CONUS. More research is required to improve the representation of the predefined boundary conditions in complex terrain at small spatial scales. SSEBop model was found to be a promising approach to conduct water use studies in the CONUS, with a similar opportunity in other parts of the world. The approach can also be applied with other thermal sensors such as Landsat.     

Modeling Summer Month Hydrological Drought Probabilities in the United States Using Antecedent Flow Conditions

Climate change raises concern that risks of hydrological drought may be increasing. We estimate hydrological drought probabilities for rivers and streams in the United States (U.S.) using maximum likelihood logistic regression (MLLR). Streamflow data from winter months are used to estimate the chance of hydrological drought during summer months. Daily streamflow data collected from 9,144 stream gages from January 1, 1884 through January 9, 2014 provide hydrological drought streamflow probabilities for July, August, and September as functions of streamflows during October, November, December, January, and February, estimating outcomes 5‐11 months ahead of their occurrence. Few drought prediction methods exploit temporal links among streamflows. We find MLLR modeling of drought streamflow probabilities exploits the explanatory power of temporally linked water flows. MLLR models with strong correct classification rates were produced for streams throughout the U.S. One ad hoc test of correct prediction rates of September 2013 hydrological droughts exceeded 90% correct classification. Some of the best‐performing models coincide with areas of high concern including the West, the Midwest, Texas, the Southeast, and the Mid‐Atlantic. Using hydrological drought MLLR probability estimates in a water management context can inform understanding of drought streamflow conditions, provide warning of future drought conditions, and aid water management decision making.     

Hydrologic Model Framework for Water Resources Planning in the Santa Cruz River,Southern Arizona1

Abstract: The authors develop a model framework that includes a set of hydrologic modules as a water resources management and planning tool for the upper Santa Cruz River near the Mexican border, Southern Arizona. The modules consist of: (1) stochastic generation of hourly precipitation scenarios that maintain the characteristics and variability of a 45‐year hourly precipitation record from a nearby rain gauge; (2) conceptual transformation of generated precipitation into daily streamflow using varied infiltration rates and estimates of the basin antecedent moisture conditions; and (3) surface‐water to ground‐water interaction for four downstream microbasins that accounts for alluvial ground‐water recharge, and ET and pumping losses. To maintain the large inter‐annual variability of streamflow as prevails in Southern Arizona, the model framework is constructed to produce three types of seasonal winter and summer categories of streamflow (i.e., wet, medium, or dry). Long‐term (i.e., 100 years) realizations (ensembles) are generated by the above described model framework that reflects two different regimes of inter annual variability. The first regime is that of the historic streamflow gauge record. The second regime is that of the tree ring reconstructed precipitation, which was derived for the study location. Generated flow ensembles for these two regimes are used to evaluate the risk that the regional four ground‐water microbasins decline below a preset storage threshold under different operational water utilization scenarios.     

Implications of Upstream Flow Availability for Watershed Surface Water Supply across the Conterminous United States

Although it is well established that the availability of upstream flow (AUF) affects downstream water supply, its significance has not been rigorously categorized and quantified at fine resolutions. This study aims to fill this gap by providing a nationwide inventory of AUF and local water resource, and assessing their roles in securing water supply across the 2,099 8‐digit hydrologic unit code watersheds in the conterminous United States (CONUS). We investigated the effects of river hydraulic connectivity, climate variability, and water withdrawal, and consumption on water availability and water stress (ratio of demand to supply) in the past three decades (i.e., 1981–2010). The results show that 12% of the CONUS land relied on AUF for adequate freshwater supply, while local water alone was sufficient to meet the demand in another 74% of the area. The remaining 14% highly stressed area was mostly found in headwater areas or watersheds that were isolated from other basins, where stress levels were more sensitive to climate variability. Although the constantly changing water demand was the primary cause of escalating/diminishing stress, AUF variation could be an important driver in the arid south and southwest. This research contributes to better understanding of the significance of upstream–downstream water nexus in regional water availability, and this becomes more crucial under a changing climate and with intensified human activities.     

ENHANCEMENTS OF NONPOINT SOURCE MONITORING OF VOLATILE ORGANIC COMPOUNDS IN GROUND WATER1

ABSTRACT: The U.S. Geological Survey (USGS) has compiled a national retrospective data set of analyses of volatile organic compounds (VOCs) in ground water of the United States. The data are from Federal, State, and local nonpoint‐source monitoring programs, collected between 1985–95. This data set is being used to augment data collected by the USGS National Water‐Quality Assessment (NAWQA) Program to ascertain the occurrence of VOCs in ground water nationwide. Eleven attributes of the retrospective data set were evaluated to determine the suitability of the data to augment NAWQA data in answering occurrence questions of varying complexity. These 11 attributes are the VOC analyte list and the associated reporting levels for each VOC, well type, well‐casing material, type of openings in the interval (screened interval or open hole), well depth, depth to the top and bottom of the open interval(s), depth to water level in the well, aquifer type (confined or unconfined), and aquifer lithology. VOCs frequently analyzed included solvents, industrial reagents, and refrigerants, but other VOCs of current interest were not frequently analyzed. About 70 percent of the sampled wells have the type of well documented in the data set, and about 74 percent have well depth documented. However, the data set generally lacks documentation of other characteristics, such as well‐casing material, information about the screened or open interval(s), depth to water level in the well, and aquifer type and lithology. For example, only about 20 percent of the wells include information on depth to water level in the well and only about 14 percent of the wells include information about aquifer type. The three most important enhancements to VOC data collected in nonpoint‐source monitoring programs for use in a national assessment of VOC occurrence in ground water would be an expanded VOC analyte list, recording the reporting level for each analyte for every analysis, and recording key ancillary information about each well. These enhancements would greatly increase the usefulness of VOC data in addressing complex occurrence questions, such as those that seek to explain the reasons for VOC occurrence and nonoccurrence in ground water of the United States.     

STATE WATER CONSERVATION STRATEGIES AND ACTIVITIES1

States have the potential to play a major role in moving water conservation from conferences and reports that identify its advantages to actual practice. The research identifies four generic “strategies” that categorize the states' approaches toward conservation and reports on the states' current conservation activities. The four strategies are: reliance on agricultural advisors, leverage incentives, performance standards, and mandatory actions. Four levels of state conservation activity exist. California and Florida maintain the most extensive programs; Arizona, Massachusetts, New Jersey, North Carolina, and Oklahoma also have numerous programs but significantly lower staff commitments; eight additional states maintain more modest conservation effotts. Elsewhere, state directed conservation actions remain minimal and limited to those provided as agricultural advice. The study found support for water conservation the norm among water supply planners.     

222RN IN THE WATER DISTRIBUTION SYSTEM OF TUCSON,ARIZONA1

ABSTRACT: A study of ²²²Rn concentrations in the water distribution system of Tucson, Arizona, revealed levels of 60 to 1260 pCi/L in domestic waters. These measurements are comparable to levels of between 80 and 1400 pCi/l for ²²²Rn found in ground water samples in the North-Central Tucson basin (Kahn et al., 1994). Estimated loss of ²²²Rn due to radioactive decay during travel from the well head to the home ranges from 8 to 50 percent.