In Search of Potable Groundwater

Oct. 28, 2009

About the author: Heather Petrig is technical writer for Myron L Co. Petrig can be reached at 760.438.2021 or by e-mail at [email protected].

Related search terms from groundwater, testing

The task of providing safe drinking water to the inhabitants of rural Ghana is a daunting one. Though Ghana has achieved government stability and fostered economic development over the past decade, just 71% of the rural population has access to improved water for drinking and sanitation, and groundwater demand is projected to increase by 69% by the year 2020.

In rural areas, groundwater is plentiful, but natural geographic contamination by inorganic contaminants like iron, manganese and fluoride render government-sponsored boreholes useless. Fluoride in the upper-east, upper-west and northern regions of Ghana often exceeds the general World Health Organization recommended limit of 1.5 mg/L.

The effects of excess fluoride consumption are serious. Mottling of tooth enamel in children progresses to structural damage to teeth. As daily fluoride intake increases, skeletal fluorosis, weight-loss, thyroid dysfunction, kidney failure and eventually death result; therefore, hand pumps in contaminated locations are capped or abandoned. This comes at a high cost to the community members and government sponsors.

Impoverished rural communities cannot afford to waste effort and funding on further drilling of boreholes contaminated by fluorides, but they do not have the resources to determine the extent and location of the contamination. Testing and mapping is needed to guide future efforts. It is this need that inspired Katherine Alfredo, a graduate student at the University of Texas at Austin, to propose a project for a Fulbright Fellowship.

Mapping Fluoride

The purpose of the fellowship was to map the extent of the fluoride concentration in the Bongo District of the Upper Eastern Region for use by local authorities and eventually use the data collected in the development of a cost-effective defluoridation filter for existing capped wells.

Alfredo began her research by observing and recording local water usage habits. She conducted borehole water usage counts on centrally and noncentrally located borehole sites tracking the quantity of water collected daily. Coupling this data with familial compound water usage surveys, Alfredo was able to begin understanding the volumetric demand placed on each borehole daily and how that volume translates to the household level.

Along with the quantity studies, 286 boreholes throughout the Bongo District were visited between January and March 2009 with the help of local guides using a bicycle for transportation.

At each borehole, GPS data and borehole identity information were collected. When no borehole identity number was present, the identity number of the pump was recorded; if that was unavailable, an identity was created for logging purposes. A 1-L sample of water was retrieved for testing and used for all of the water quality tests.

An aliquot of the sample water was placed in an Ultrameter II 6P donated by Myron L Co. to measure pH, ORP, conductivity, total dissolved solids (TDS) and temperature.

Alfredo found the Ultrameter II to be an ideal tool for her work. “I was so impressed with the Ultrameter II and its ability to hold a calibration,” she said. “This one fact not only made my sampling progression quicker, but it also saved me from carrying more than 100 mL of each calibration fluid with me on any given day, given the fact that I performed all of my sampling via bicycle, carrying all the equipment on the bicycle as well, was something of extreme importance to me.”

The Ultrameter II utilizes a KCl gel-filled pH sensor for accurate electrometric pH readings within ±0.01 pH. The pH levels of the water were of specific importance to Alfredo’s research of adsorbing fluoride on aluminum-based adsorbents. This is because the amount of fluoride an adsorbent is able to absorb is directly related to the pH of the water. The ideal pH for removal of fluoride by activated alumina from raw water, for example, is 5.5.

Conductivity readings from the Ultrameter II were within ±0.01 mV achieved through an advanced design 4-electrode conductivity cell. These readings will be used to simulate influent water containing excessive levels of fluoride in Alfredo’s laboratory. Using Bongo as a design test case, she plans to adjust the ionic strength of her synthetic influent to reflect that seen in the Bongo District.

Solution temperature measured by means of thermistor was logged automatically by the Ultrameter II with each parameter measured. Fluctuations in temperature will be studied to see how temperature affects fluoride removal.

TDS readings were used as a quality indicator of water as it is dispensed from a borehole. The amount of all dissolved solids is important in determining the potential for interference and competition for adsorption sites on the aluminum adsorbents. Preventing any ions from competing for active sites on alumina surfaces will greatly increase the efficiency of filtration. ORP readings gave a good indication of the general biological activity in the water.

Additional testing was performed using two 2-mL tubes filled with sample water to measure nitrate/nitrite and ammonia using test strips. In another 2-mL tube, a 1:1 dilution of the sample was created using distilled water to measure alkalinity using test strips. Using a 0.45-micron filter, a 30- or 60-mL sterile plastic bottle was completely filled for fluoride concentration testing later in the laboratory and was labeled with a sample ID number that was later used to correlate borehole data with water quality information.

Finally, sample time, the date and basic notes on the state of the borehole construction and surroundings were logged in the logbook. Fluoride concentrations were measured using an ion selective electrode typically within 72 hours of collection.

Each capped borehole, new borehole or nonfunctional borehole that was visited had its corresponding borehole identity (actual or created) recorded in a handheld GPS device. After each governance was covered, eight capped boreholes (due to elevated fluoride levels—not broken parts) were chosen for water quality testing to be compared to the nearby functional boreholes. For each capped borehole, additional information corresponding to the total depth of the borehole and depth to the water surface were collected.

An undisturbed sample was retrieved using a point source bailer 15 ft from the bottom of the borehole under the assumption that at this level the aquifer would be flowing through the screened interval. Water quality information and the samples were collected using the same methodology as that for functional boreholes.

Using GIS, a base map of the Bongo District was created and the sample identity number, borehole identity, latitude, longitude, measured fluoride concentration (mg/L) and pH were uploaded for each borehole tested. Using the interpolation tools in GIS, an inverse distance weighted interpolation was performed on the fluoride concentration borehole data to approximate the concentrations throughout the aquifer. This data will be correlated to the geologic and drainage information for the area during the next phase of research.

At the time of Alfredo’s departure, she had reported the pH and fluoride concentration of each well to the two water and sanitation government agencies in the Bongo area—the Community Water and Sanitation Agency and the Bongo District Assembly Water and Sanitation Team.

Alfredo continues to analyze data recorded in Ghana and experiment with cost-effective solutions for fluoride removal in rural communities.

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About the Author

Heather Petrig

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