Lab Science News

A recent United States Geological Survey (USGS) study of public drinking water wells in California, Connecticut, Nebraska and Florida found that some were contaminated, but in amounts so minimal, human health was unlikely to be affected. The USGS tracked the movement of contaminants in groundwater and public-supply wells in four different aquifers.

According to the USGS, wells are not equally vulnerable to contamination because of differences in three factors: the general chemistry of the aquifer, groundwater age, and direct paths within aquifer systems that allow water and contaminants to reach a well. The importance of each factor differs among the various aquifer settings, depending upon natural geology and local aquifer conditions, as well as human activities related to land use and well construction and operation. However, the USGS feels that the study of the four different aquifer systems can be applied to similar aquifers and wells throughout the nation.

Examples of specific chemical findings from the USGS study:

• In the Central Valley Aquifer near Modesto, Calif., the USGS found that agricultural and urban development have enabled uranium to move from sediments to water in the upper part of the aquifer. This water can drain down the well when it is not pumping and enter the lower aquifer. When pumping resumes, contaminant concentrations can be temporarily elevated in water pumped from the well.
• In the Glacial Aquifer in Woodbury, Conn., it was found that the young age of the water throughout the aquifer makes it vulnerable to contamination from man-made compounds. The USGS also found that dry wells used in Woodbury to capture stormwater runoff reroute the potentially contaminated water directly into the aquifer used as a drinking water source. This direct transfer prevents soil and unsaturated sediments near the land surface from filtering out some of the contaminants.
• In the High Plains Aquifer near York, Neb., the USGS found some contaminants in a public-supply well that seems protected by overlying clay. Nearby irrigation wells have allowed water containing nitrate and volatile organic compounds to leak down from an overlying shallow aquifer into the aquifer that serves as the drinking water source for the public-supply well.
• In the Floridan Aquifer near Tampa, Fla., it was found that a large percentage of young water and contaminants from a shallow sand aquifer travels quickly along natural conduits until it reaches a supply well in a lower rock aquifer that serves as a drinking water source. Because of these natural conduits, the supply well is vulnerable to the man-made contaminants in the upper aquifer, and the mixing of waters from the two aquifers has caused arsenic concentrations to increase in water reaching the supply well.

The study of public-supply well vulnerability to contamination is one of five national priority topics being addressed by the USGS with their National Water-Quality Assessment (NAWQA) Program. The study began in 2001 with the following general objectives:

1. Identify the dominant contaminants and sources of those contaminants in public-supply wells in representative water-supply aquifers across the Nation;
2. Assess the effects of natural processes (such as degradation) and human activities (such as irrigation) on the occurrence of contaminants in public-supply wells in representative aquifers;
3. Identify the factors that are most important to incorporate into public-supply well vulnerability assessments in different settings and at different spatial scales;
4. Develop simple methods and models for screening public-supply wells for vulnerability to contamination in unstudied areas and from newly emerging contaminants; and
5. Increase understanding of the potential effects of water-resource development and management decisions on the quality of water from public-supply wells.

Approximately 35% of the U.S. population receives their drinking water from public groundwater systems. Public drinking water systems are considered public when 25 or more people are connected to the well or there are at least 15 service connections for a minimum 60 days per year.

 
Reference:
http://oh.water.usgs.gov/tanc/NAWQATANC.htm

Introduction: Historical mining practices in the Coeur d’Alene River Basin (Idaho) have resulted in heavy metal contamination of soil, sediment, surface water, and groundwater. Canyon Creek, located in the upper basin, has elevated levels of dissolved zinc (average concentration ~ 3,000 μg/L), dissolved cadmium (average concentration ~ 22 μg/ L), and total lead (average concentration ~ 174 μg/L). Heavy metal loading near the mouth of Canyon Creek is influenced by surface water/groundwater interactions. Dissolved zinc concentrations in the groundwater have been detected in the 100,000 μg/L range while dissolved cadmium and lead have been detected in the hundreds to thousands μg/L ranges, respectively.

EPA’s consultant, URS Corporation (URS), developed a multi-phase treatability study to obtain quantitative information on a treatment process to effectively remove metals from the water of Canyon Creek. The treatment process incorporated different combinations of pH adjustment, chemical coagulation and coprecipitation, polymer flocculent additions, and additions of ballasted micro-sand to improve sludge settling. The results of the study will be used to help evaluate potential treatment technologies for surface water and/or groundwater at Canyon Creek. These data will also be used to help develop the pilotscale treatability study for Phase II of the study.

URS contracted Columbia Analytical Services, Inc.’s (CAS) Redding Lab to perform an in-depth, bench-scale treatability study. CAS performed the study in accordance with the procedure described in Canyon Creek Treatability Study Plan, Coeur d’Alene Basin, RAC, EPA Region 10, April 2004 and its Appendix A, Laboratory Scope of Work (SOW).

Treatability Study: The study involved performing a seven step process (see Table 1) involving sixteen jar and nineteen settling rate tests. Varying combinations of lime stabilization (adjusting the pH up to 11) with a calcium hydroxide slurry and coagulation / coprecipitation with ferric chloride followed by polymer flocculation (anion, cationic, and nonionic forms) and micro-sand additions (used as a flocculation aid) were used. The jar and settling rate tests were performed using a 6-place paddle stirrer or jar tester.

The bulk surface water feedstock collected for the treatability study was slightly acidic with a pH of 5.0 and low in conductivity (80 umhos/cm) and hardness (20 mg/L as CaCO3). The bulk sample was received in a Teflon lined 55-gallon drum by over-night courier. To help maintain sample stability the bulk sample was stored in a large walk-in cooler at 4°C for the duration of the study. Sub-samples (each approximately 8-L in volume) were taken for each jar or settling test by mixing the contents of the bulk sample using an acid washed, plastic paddle and then filling a 20-L cubitainer with the sample using an allplastic siphon pump. In addition to the treatability study, CAS analyzed 9 surface water and 4 groundwater samples for ICPMS and ICP metals, general chemistry, physical analyses, and neutralization curve analyses to evaluate site characteristics at the time of feedstock water collection.

Over two hundred samples were generated by the treatment study. CAS immediately analyzed the samples for pH, conductivity, turbidity, and zinc by the Zincon colorimetric procedure. The Zincon method was used so CAS and URS could quickly determine which combination of reagents provided the best reduction in zinc in order to quickly select the optimum combination of reagents for the next jar test. Selected samples were also analyzed for cadmium, lead, and zinc by ICPMS, calcium and magnesium by ICP, and a variety of general chemistry and physical measurements. After Step 3, all zinc analyses were performed by ICPMS because the treatment process was reducing the zinc concentration to below the Zincon detection limit of 20 μg/L.

Study Results: Overall the project was very complicated as each jar test required different combinations of lime, ferric chloride, and different types of flocculating agents depending on the results from the previous jar test. Due to the unknown stability of the water matrix CAS personnel worked through the initial weekend. The testing was completed over a period of 14 days. The bulk sample proved to be stable over this period based on daily analyses of dissolved metals concentrations and conventional parameters.

URS and CAS personnel worked closely with daily communications to insure a smooth progression and successful project outcome. Frequent communications between URS and CAS were essential, as minor modifications to the work-plan were required as the study progressed.

The first phase of the Canyon Creek Treatability Study provided quantitative information on the effectiveness of a variety of treatment approaches for removing dissolved metals from surface water collected from the mouth of Canyon Creek. The treatment process, using the optimum combinations of reagents, resulted in significant reduction of metals plus the formation of a sludge that has very good settling rates and ease of filtering (see Table 2).

- - -

Learn more about testing for mines…

- - -