Work Sample: OWW Water Quality Report

OWW Water Quality Program

Water Sample Analysis and Interpretation

Jim [-----------]

Carate, Costa Rica

March 31, 2001

Osa Water Works, S.A.

Puerto Jimenez, Costa Rica

7, 2001

1.0 Introduction

This hydrochemical and water-quality characterization was prepared on the basis of a single analysis of a well-water sample collected on March 20, 2001 from a hand-dug well used for domestic water supply by Jim [----------] in Carate, Costa Rica. The purpose of this water quality investigation was to evaluate the well's viability as a potable water supply for domestic consumption.

2.0 Field Information

2.1 Sampling Locations

The sampled well is located on property owned by Jim [----------] adjacent to Playa Carate, on the western side of the Osa Peninsula, Costa Rica. The well is located about 10 meters from the back of his house and is enclosed by a pump house.

2.2 Well Description

The hand dug well penetrates coastal alluvium and extends to a depth of nine meters. At the time of sampling, there was insufficient water in the well to operate the submersible pump. Ground water in this unconfined aquifer flows through intergranular porosity in the beach sand and terrestrial alluvium beds.

2.3 Sampling Methods

Since there was insufficient water to operate a pump, it was necessary to collect the samples using a bailer. Three sample bottles were filled directly from the well overflow. Two sample bottles were left unpreserved for analysis of bacteriology, alkalinity, chloride, nutrients, and sulfate, and one bottle was preserved to a pH beneath 2.0 with ultra-pure nitric acid for metal analyses. Samples were packed in ice and transported to San Jose on March 21 for analysis by Laboratorios Aqylasa, S.A.

3.0 Analytical and Interpretive Methods, Results, and Data Validation

Analytical results are reported in Table 1. An Ion balance was performed on the raw data, yielding an error of 11.9% which is just outside of the +/- 10% error range conventionally accepted for high ionic strength water samples. Possible explanations include the following: 1) one or more of the cations was measured in a quantity somewhat greater than were actually present; 2) one or more of the anions was under-measured; or 3) there is an anion present in the ground water that was not measured that is an important constituent of the ionic matrix. Fluoride is such an anion that could conceivably be present and not measured. Other possibilities include a variety of ionized organic acids. All analytical work is performed in duplicate, some species in triplicate, so the probability of laboratory error is low. At any rate, the error, 1.9% beyond that accepted for scientific interpretation, is not that great, and a complete interpretation of the water quality follows. Laboratory methods for analysis are described in Standard Methods (1995) with the Method number listed in Table 1 for each analyte.

Hydrochemical software including Aquachem Version 3.7 (Waterloo Hydrogeologic) and Phreeqe (US Geological Survey) was used to calculate additional hydrochemical parameters that are discussed in subsequent sections. A summary of all the calculated and modeled hydrochemical values reported are shown in Table 2.

Table 1. Analytical results, showing analytical methods, units, and method detection limits and precision. Analyses performed by Laboratorios Aqylasa, S.A.

Parameter	Method	Units	Detection Limit	Precision (+/-)	Results
Ambient Temperature		^o C	N/A	0.1
Water Temperature		^o C	N/A	0.1	24
PH	4500 - H	SU	N/A	0.01	7.34
Total Coliform	Standard Methods	Colonies/100 ml	1	1	9
Fecal Coliform	Standard Methods	Colonies/100 ml	2	2	>2400
Calcium	2340 - C	Mg/L	0.2	0.2	28
Magnesium	2340- C	Mg/L	0.2	0.2	10
Sodium	4500.Na	Mg/L	0.02	0.02	17.7
Potassium	4500.K	Mg/L	0.1	0.1	10
Iron	3500.Fe	Mg/L	0.02	0.01	0.44
Manganese	4500.Mn	Mg/L	0.02	0.01	0.068
Alkalinity	2320 - B	Mg/L	1	0.3	110.5
Chloride	4500 - Cl	Mg/L	0.1	0.1	15.8
Sulfate	2340 - C 329	Mg/L	0.2	0.2	9.3
Nitrate	4500.NO₃.D	Mg/L	0.02	0.02	7.5
Phosphate	4500.P.C	Mg/L	0.5	0.1	1.0

Table 2. Calculated and modeled hydrochemical parameters, determined using the hydrochemical interpretation software Aquachem and PHREEQE.

Parameter	Unit	Results
Ionic Balance	%	11.9
Total Dissolved Solids	Mg/l	209.3
Temporary hardness	Mg/L as CaCO3	90.6
Permanent hardness	Mg/L as CaCO3	20.4
Total hardness	Mg/L as CaCO3	111.0
Sodium Adsorption Ratio	Unitless	0.73
Exchangeable Sodium Ratio	Unitless	0.35
Magnesium Hazard	Unitless	37.06

4.0 Water Characterization

4.1 Major Ion Distribution

The ionic matrix of a water can be visualized by a variety of graphical means. Three are presented here, the pie (Figure 1), Stiff (Figure 2), and radial (Figure 3) diagrams shown below. Examination of the three graphical tools below reveals that the primary ions in solution include co-equal amounts of the cations sodium (Na⁺), calcium (Ca⁺⁺), and magnesium (Mg⁺⁺), with the vastly predominant anion being bicarbonate alkalinity (HCO₃^-). At a total dissolved solids concentration of 209.3 mg/L, this ground water is classified as a high ionic strength sodium-magnesium-calcium-bicarbonate type of water.

The relative abundance in bicarbonate alkalinity relative to the other major anions (negatively charged ions) is an indication of good mineral water quality controlled by the dissolution of earth materials and not impacted by sulfur, iron, or manganese oxidation/reduction processes. The relatively low content of chloride (Cl^-) and sulfate (SO₄^2-) precludes subjacent sources of poor water quality that might be produced due to proximity to the ocean or biologic influences. As the Ludwig-Langelier diagram reveals (Figure 4), the well water has a higher combined relative sodium and potassium content than all other water quality samples in the OWW database, except for one. The fact that chloride and sulfate levels are not elevated suggests that the sodium and potassium is derived from dissolution of silicate minerals in the alluvial aquifer and NOT due to the influence of marine brines. The same trend is shown in the Piper diagram (Figure 5), illustrating the higher proportion of sodium in the well water matrix relative to other Costa Rican samples that have been collected.

Dissolved iron (Fe²⁺) and manganese (Mn²⁺) are nuisance contaminants common in ground water sources that are anoxic or anaerobic (devoid of dissolved oxygen). Neither metal is toxic to human health in any concentration. Indeed, both iron and manganese are micronutrients required for most forms of life. Nevertheless, even small concentrations of either Fe or Mn have unpleasant effects in drinking water supplies. Both iron and manganese can be tasted at concentrations of less that 0.5 ppm. At this and higher concentrations, the splash from running water causes iron and manganese hydroxides to precipitate from solution and stain porcelain fixtures. The EPA has established maximum contaminant levels of 0.2 mg/L for iron and 0.05 mg/L for manganese to safeguard against these nuisance effects.

Both iron and manganese concentrations were above recommended levels, though this may be a function of water stagnation under low flow conditions. Once the rains comes it is possible that the water remains sufficiently oxygenated that the concentration of these metals

may drop to beneath detection. Though neither is harmful to health, at the measured levels, these nuisance metals impart a stringent, undesirable taste to water and will definitely stain fixtures and promote iron and manganese oxide scale in piping and house fixtures. It is further possible that by deepening the well, the concentration of these nuisance metals may be reduced even during dry season owing to increased ground water flow inside the alantarilla casing. Alternately, it is possible that the concentration of iron and manganese is unusually high and cannot be circumvented without water softening, ion exchange filtration, or alternative post-pumping treatment methods.

Nitrate (NO₃^-) and phosphate (PO₄^3-) are important indicators of domestic, agricultural, industrial, and urban pollution. Very few earth materials are made of nitrate and phosphate minerals, and as a result, the presence of either of these anions in water usually indicates pollution from either non-point (agrochemicals and urban runoff) or point sources (wastewater treatment effluent). Although natural life processes do introduce nitrate and phosphate to the environment (through bacterial nitrogen fixation, or the decay of proteinaceous organic material, for instance) this input is balanced in healthy aquatic environments by the natural demand of the ecosystem and the uptake of nutrients by algae and plants. Both nitrate and phosphate promote algal and other vegetable growth. When nutrients are at natural levels, algae growth in waterways is kept at a minimum but sufficient to contribute toward oxygenation and other natural processes (such as the diurnal aquatic pH cycle) vital for aquatic health. Introduction of non-natural levels of nutrients disrupts the natural biotic balance of aquatic ecosystems like ponds, lakes, rivers, and bays. The nutrients promote the exaggerated growth of algae and plants and results in an adverse, irreversible geomorphic process known as eutrophication, whereby aquatic environments are gradually converted to terrestrial ones.

As an additional concern, the nitrate molecule, when ingested in large quantities over a period of time, can cause a condition in humans known as blue-baby disease (methimoglobinemia). Since nitrate is an electron acceptor only somewhat less energetic than oxygen, the oxygenation of the blood is affected when high nitrate concentrations are in the body, resulting in blue skin coloration. For this reason, the EPA regulates domestic American water supplies with a maximum contaminant level for nitrate in drinking water of 10 mg/L.

Phosphate was detected at a concentration of 1.0 mg/L and nitrate was detected at 7.5 mg/L. Both measurements, while not high enough to be a health concern are considerably above expected background levels and represent levels worthy of concern. While the US EPA maximum contaminant level for nitrate is 10 mg/L, it is unlikely that this concentration of nitrate can be attributed completely to natural causes. Anthropogenic sources of nitrate contamination could include detergents, fertilizers, or septic tank contamination.

Coliform bacteria are a family of micro-organisms that exist in the intestines of all cold- and warm-blooded animals, where they participate in the digestion of food. Fecal coliform bacteria are a subset of the coliform family that exist only in the intestinal tract of warm-blooded animals (mammals and birds). Fecal coliform concentrations in natural waters have historically been used for this reason to determine if a natural water has been contaminated by human or animal waste. Coliform bacteria are normally not disease-causing (Escherichia coli, a member of the fecal coliform group, is a notable exception), but they are very common and have come to have universal use as indicator organisms for pathogenic organisms (viral, bacterial, and amoebic) that spread diseases through contact with the fecal waste of both humans and animals, including: gastroenteritis, cholera, typhoid fever, typhus, hepatitis A, giardiasis, shigellosis, and many others.

The detection of total coliform bacteria in natural waters is not necessarily an indication of poor water quality, since these organisms are ubiquitous in the surface and near-surface environment. However, the confirmed detection of fecal coliform bacteria in any concentration above the detection limit is an indication that the water is contaminated with either human or animal waste and should not be ingested without boiling. Confirmatory tests are always required in the event of a fecal coliform hit to ensure that fecal coliform detection is not the result of sampling or laboratory contamination. In cases of confirmed fecal coliform contamination, additional sampling and engineering measures may be required to eliminate the source or avenue of fecal coliform contamination. In cases of highly contaminated water sources, water treatment (by filtration or membrane processes, UV sterilization, chlorination, or ozonation or a combination of unit operations and processes) is often the only alternative to ensure the exclusion of potential microbial pathogens from the water supply.

The detection of 9 colonies/100 ml of fecal coliform bacteria in the well water sample is an indication that the ground water supply is impacted by fecal contamination from either warm-blooded animals or humans. Commonly, water supplies impacted by fecal coliform contain very high total coliform levels, and the detection of over 2400 colonies per 100 ml supports this probability. Follow-up confirmatory testing should possibly be preceded by extending the depth of the well, cleansing of the well with bleach, and careful sealing of the well head to ensure the exclusion of rodents, frogs, and bats.

If additional coliform hits are registered, then it may be worthwhile to evaluate the possible sources of coliform bacteria to determine if remediation is possible or if well-relocation or water filtration and UV disinfection are viable alternatives.

Water quality standards promulgated for public water supply by the United States Environmental Protection Agency (US EPA) are listed alongside the corresponding analyses of the [----------] well water samples in Table 3.

Table 3. Comparison of the [----------] ground water analyses with US EPA maximum contaminant levels and recommended composition ranges for domestic water supplies. Borderline analyses and exceedances are highlighted in grey.

Due to fecal coliform contamination of the well, this water should not be considered for use as a domestic water supply without some form of water treatment. If it is to be used for drinking water, it should be boiled or filtered through a 0.45 micron filter for removal of potential biologic pathogens.

Additionally, this water is above the Maximum Contaminant Level for potassium, iron, manganese, and very near the MCL for nitrate. The high iron and manganese concentrations gives a definite taste to the water and will stain household fixtures. The relatively high potassium (K⁺) and sodium concentrations in the well water are likely the result of the dissolution of a potassium- and sodium-bearing silicate mineral in the aquifer material. Potassium does not pose a deleterious impact on human health and in fact is a micro-nutrient that minimizes existential angst in the human being. Its impact on irrigation purposes is not known and may warrant additional research. Sodium is an undesirable ion for irrigation purposes due to its propensity to flood electrostatic sites on soil particles an

Figure 4. Ludwig-Langelier Diagram: Finca Alemania samples shown in red. Other sample points are from the OWW Costa Rican Water Quality database.	Figure 5. Piper Diagram: Finca Alemania samples shown in red. Other sample points are from the OWW Costa Rican Water Quality database.

Parameter	Units	Recommended Range	Max. Cont Level	Results
PH	Standard Units	6.5-8.5	9.5	7.34
Fecal Coliform	Colonies/100 mL	0	0	9
Calcium	Mg/L	<100	-	28
Magnesium	Mg/L	<30	-	10
Sodium	Mg/L	<20	200	17.7
Potassium	Mg/L	<10	12	10
Iron	Mg/L	<0.05	0.02	0.44
Manganese	Mg/L	<0.02	0.05	0.068
Chloride	Mg/L	<25	-	15.8
Sulfate	Mg/L	<25	250	9.3
Nitrate	Mg/L	<5	<10	7.5