Long-Term Prediction of Water Quality in Marine Water Areas

Random walk approach is used to develop a model for long-term prediction of water quality in shallow marine waters. The model allows one to simulate variations in hydrological situations, reactive solutes, interaction between solutes and liquid and solid boundaries. The model application is illustrated by calculations for Amur Bay. Calculations using the long-term prediction model has not found a stationary state in the pollution level. The velocities of seaward motion of pollution front and the rates of increase in the concentration of a nonreactive solute are given.     

Acquisition of Representative Ground Water Quality Samples for Metals

R.S. Kerr Environmental Research Laboratory (RSKERL) personnel have evaluated sampling procedures for the collection of representative, accurate, and reproducible ground water quality samples for metals for the past four years. Intensive sampling research at three different field sites has shown that the method by which samples are collected has a greater impact on sample quality, accuracy, and reproducibility than whether the samples are filtered or not. In particular, sample collection practices that induce artificially high levels of turbidity have been shown to have the greatest negative impacts on sample quality. Results indicated the ineffectiveness of bailers for collection of representative metal samples. Inconsistent operator usage together with excessive purging generally resulted in excessive turbidity (>100 NTUs) and large differences in filtered and unfiltered metal samples. The use of low flow rate purging and sampling consistently produced filtered and unfiltered samples that showed no significant differences in concentrations. Turbidity levels were generally less than 5 NTUs, even in fine-textured glacial till. We recommend the use of low flow rates, during both purging and sampling, placement of the sampling intake at the desired sampling point, minimal disturbance of the stagnant water column above the screened interval, monitoring of water quality indicators during purging, minimization of atmospheric contact with samples, and collection of unfiltered samples for metal analyses to estimate total contaminant loading in the system. While additional time is spent due to use of low flow rates, this is compensated for by eliminating the need for filtration, decreased volume of contaminated purge water, and less resampling to address inconsistent data results.     

Statistical Analysis of Secondary Water Quality Impacts from Enhanced Reductive Bioremediation

Enhanced reductive bioremediation (ERB) is effective for treating a broad range of groundwater contaminants, but does result in secondary water quality impacts (SWQIs). Monitoring data from 47 ERB projects were analyzed to gain a better understanding of the formation and extent of SWQIs. The database analysis revealed that SWQIs occur at virtually every site, including reduced levels of background aqueous electron acceptors (O₂, NO₃^?, and SO₄^2?), increases in dissolved‐phase metals (Fe and Mn), and the production of CH₄. However, the SWQI “plume” that is produced is usually confined within the original contaminant plume. As a result, SWQIs from ERB are unlikely to adversely impact potable water supplies. SWQIs do attenuate with distance downgradient, with concentrations often returning to near background levels. The results of the database analysis were combined with previous research to develop a general conceptual model (CM) of SWQI production, mobilization, and attenuation. This CM can assist in identifying conditions where SWQIs may pose a concern. These can include sites with low iron/high sulfate (H₂S mobilization), high groundwater velocity (SWQIs at distances far downgradient), and sites with low CH₄ anaerobic oxidation rates (CH₄ migration).     

The Challenge of Ground Water Quality Monitoring

"Valuable information pertaining to contaminant sources, contaminants, and ground water quality was derived using the state-supplied data."     

Making the Most of Field-Measurable Ground Water Quality Parameters

The primary ground water quality parameters temperature, pH, Eh, electrical conductivity, and dissolved oxygen must be measured in the field, though not necessarily in situ, to avoid errors caused by contamination such as aeration. These measurements, when made during the purging of a well, can be used to verify aquifer-representativeness of a sample, detect abnormalities within an aquifer, check laboratory measurements to detect sample deterioration, and prompt further monitoring actions.
Electronic sensors are available for reliable field measurement of the primary parameters. Measurements should be made continuously in an in-line flow cell that is sealed from the atmosphere. Flow can be provided by a bladder pump dedicated to a single well. Samples for laboratory analysis should be collected when the values of the primary parameters do not vary more than 10 percent per casing volume pumped.     

A Systematic Approach for Evaluating the Quality of Ground Water Monitoring Data

The recognition and assurance of the quality of ground water monitoring data are crucial to the correct assessment of the magnitude and extent of a ground water contamination problem. This article addresses an approach being developed to systematically evaluate the quality of a given set of ground water monitoring data collected during site investigation/ remedial action efforts. The system consists of a checklist of criteria, grouped into four major categories, which can be applied to laboratory or field measurements.
The first category, basis of measurement, considers whether the appropriate sampling, boring and/or analytical methods were chosen to obtain the measurement and the limitations of each method. Secondly, application of the method is assessed. This includes examination of the extent to which procedures were correctly performed, the use of quality control measures and calibration, and possible sources of error in the measurements. Third, evaluation of applied statistical methods is made, with consideration given to which statistics are meaningful in a given context and whether measurements are reproducible. The final category, corroborative information, considers whether independent data or other information are available that add credibility to the values measured.
In this approach, a "high quality" data value is defined as one in which accuracy is supported by meeting the preceding criteria. When accompanied by precision information, high quality data allow for defensible assessments and actions. This evaluation system is useful in developing monitoring programs and in guiding documentation of field and laboratory methods during data collection. It relies heavily on experienced judgment and can be catalyst for the beneficial exchange of knowledge and ideas among ground water professionals.     

Use of a Geo Flowmeter for the Determination of Ground Water Flow Direction

The Geo Flowmeter is manufactured by K.V. Associates of Falmouth, Massachusetts, and is used to determine ground water flow direction and velocity in monitoring wells or open boreholes. It operates by emitting heat pulses and measuring subsequent temperature increases carried by the ground water movement. The meter can be used in wells as small as 2 inches in diameter and only a single well is required for determination of ground water flow direction and rate.
This paper is a case history of the use of the Geo Flowmeter in a complex hydrogeologic setting consisting of a partially above grade landfill located between a navigable waterway and a large storm water impoundment basin. Mounding effects of the landfill, tidal changes in the channel, varying water levels in the impoundment basin and a complex substrate (alternating layers of sand, silt and clay) presented a challenge for ground water interpretation and analysis. The Geo Flowmeter was lowered into existing monitoring wells surrounding the landfill to determine ground water flow direction and rate. Sensitivity of the meter was sufficient to distinguish two separate flow directions in a single well screen. Later investigation involving installation of piezometers, long-term ground water level monitoring and plotting of ground water contours verified initial findings of the meter.
This article presents numerous graphs and pictures to illustrate field use of the instrument and discusses advantages and disadvantages of its use. Actual field data collected is included to provide a basis for evaluating the accuracy of the instrument and identifying situations where it may be used.     

Developing Objectives for the Ground Water Quality Monitoring Network of the Salinas River

This article describes how objectives were developed and applied to design a ground water quality monitoring network for the Salinas River drainage basin in central California. Four agencies worked together: the USGS as network designer, the Central Coast Regional Water Quality Control Board as network manager, and Monterey and San Luis Obispo county agencies as data providers. After investigating the basin's ground water quality problems, a list of objectives was developed. These objectives were written as concise statements. The network designers and managers arranged the objectives in the order of importance and set priorities for them. An ideal network was designed to meet all of the monitoring objectives. In the ideal network exercise, budget and manpower constraints were ignored. Each monitoring location was chosen for a specific objective or group of objectives. The ideal network was compared with the existing network to identify where both more and less monitoring was needed. Then a proposed network was chosen. The ideal and existing networks were composited to produce the proposed network, but budget and manpower were considered. To keep the network at a realistic size, monitoring was only recommended to meet the most important objectives. Existing monitoring sites were retained to meet any of the objectives.     

Sampling Strategies for Estimation of Parameters Related to Ground Water Quality

Multiple theoretical sampling designs are studied to determine whether sampling designs can be identified that will provide for characterization of ground water quality in rural regions of developing nations. Sampling design in this work includes assessing sampling frequency, analytical methods, length of sampling period, and requirements of sampling personnel. The results answer a set of questions regarding whether using innovative sampling designs can allow hydrogeologists to take advantage of a range of characterization technologies, sampling strategies, and available personnel to develop high-value, water-quality data sets. Monte Carlo studies are used to assess different sampling strategies in the estimation of three parameters related to a hypothetical chemical observed in a ground water well: mean concentration (MeanC), maximum concentration (MaxC), and total mass load (TML). Five different scenarios are simulated. These scenarios are then subsampled using multiple simulated sampling instruments, time periods (ranging from 1 to 10 years), and sampling frequencies (ranging from weekly to semiannually to parameter dependent). Results are analyzed via the statistics of the resulting estimates, including mean square error, bias, bias squared, and precision. Results suggest that developing a sampling strategy based on what may be considered lower quality instruments can represent a powerful field research approach for estimating select parameters when applied at high frequency. This result suggests the potential utility of using a combination of lower quality instrument and local populations to obtain high frequency data sets in regions where regular monitoring by technicians is not practical.     

Impacts of a Rural Subdivision on Groundwater Quality: Results of Long-Term Monitoring

A rural subdivision in south central Wisconsin was instrumented with monitoring wells and lysimeters before, during, and after its construction to examine the impacts of the unsewered subdivision on groundwater quality and quantity. Prior to construction, the 78-acre (32 ha) site was farmland. Sixteen homes were constructed beginning in 2003. Initial monitoring from 2002 to 2005 showed that groundwater beneath the site had been impacted by previous agricultural use, with nitrate-N values as high as 30 mg/L and some detections of the herbicide atrazine. Our 12-year study shows that the transition from agricultural to residential land use has changed groundwater quality in both negative and positive ways. Although groundwater elevations showed typical seasonal fluctuations each year, there were no measurable changes in groundwater levels or general flow directions during the 12-year study period. Chloride values increased in many wells, possibly as a result of road salting or water softener discharge. Nitrate concentrations varied spatially and temporally over the study period, with some initial concentrations substantially above the drinking water standard. In some wells, nitrate and atrazine levels have declined substantially since agriculture ceased. However, atrazine was still present at trace concentrations throughout the site in 2014. Wastewater tracers show there are small but detectable impacts from septic effluent on groundwater quality. Particle traces based on a groundwater flow model are consistent with the hypothesis that septic leachate has impacted groundwater quality.