2. REPORT by technicians who have worked at AVIGDOR

(by HAIM MICHELSON)

The Possibilities to Develop Groundwater in the Avigdor Farm.
Entre Rios, Argentina. 

2.1. INTRODUCTION

Avigdor colony is located about 120 km east of Parana, about 17 km north of Bovril, at an altitude of 60 to 65 mts above Mean Sea Level. The area is almost flat, covered by black soil (composed mainly of montmorilonite). The natural vegetation cover is of Acacia trees, which is presently removed in the farm areas. Corn and wheat are the main agricultural crops of the area.

The farm acquired by Preceptos company and by Mr. Yelin is located at the entrance to Avigdor, about 1 km due south of the colony, on about 250 hectars.

This report is based on a short mission to the area of Bovril and Avigdor (23 - 24/11/99) and on meetings held in Parana and in Santa Fe on 25 - 26/11/99, with the following experts:

Arq. Moreno, Ing. Duarte, Ing. Santi, Ing. Fresler from Secretaria de Hidraulica de Provincia Entre Rios en Parana, Ing. Ofelia Tujchneider and Ing. Mario Fili from the University of the Litoral in Santa Fe, Ing. Paparotti and Lic. Dante Bedendo of Inta in Parana.

In addition we met Ing. Eduardo Diaz of Proinsa company (for drilling) in the field (24/11/99), as well as visited other drilling companies: Diderle in Parana and Camparo in Santo Tome.

It is worth mentioning a few articles that were studied in order to recognize the hydrogeological conditions in the Province of Entre Rios and on which this report is based:

(a) J.C.Bertolini, M.A. Tomas (1989): Inventario del Recurso Aguas Subterraneas en la Provincia de Entre Rios (by the Direccion de Mineria y Recursos Hidricos).

(b) C.C. Tujchneider, M.F. Fili, M.D. Carmen Paris, M.P. D’elia (1994): Investigaciones Geohidroquimicas e Isotopicas en las Aguas Subterraneas de la Provincia de Entre Rios (Republica Argentina).

(c) O.C. Tuchneider y M.F. Fili : Hidrogeologia de la Cuenca del Arroyo Feliciano, Provincia de Entre Rios.

(d) A.E.C. de Rojas, J.H. Saluso (INTA): Informe Climatico de la Provincia de Entre Rios. Pub. Tecnica No. 14.

2.2. CLIMATE CONDITIONS 

The average annual rainfall for the last 20 years in Avigdor (La Lila station) is 1087 mm.

The rainy season is during the months October to May, with the most rainy months : October, November, January, and April. The dry season is during the months June to September.

Climate variations are typical to this area, where the maximal rainy month can be changed from one year to the next year. Moreover, at the present year - 1999, the dry season has continued from August to the end of November with a forecast to be finished at March next year! (the last recorded dry season like this year was at 1933, 66 years ago), while at 1998 the annual rainfall was 1517 mm!, which is about 400 mm above the average.

The average annual evapotranspiration in the Avigdor area is about 925 mm, thus the excess of precipitation in relation to the evapotranspiration is about 160 mm per year. This excess takes place during the less rainy months (March - October), while the deficiency exist during the rainy months of November to February (Report of Recursos Hidricos, 1989).

2.3. GEOLOGY AND STRATIGRAPHY

This report deals with the geological features and with the stratigraphic units (formations) prevailing in the studied area of Avigdor and Bovril (see table No. 1).

Table No. 1: The stratigraphic units (formations) at Avigdor - Bovril area.

2.3.1 Hernandarias Formation

The uppermost cover of the area of Entre Rios Province, 20 - 30 mts thick, is composed of black soils that overlie clays and siltstones of the Hernandarias Formation. In some places, like Alcaraz and Bovril the thickness is about 40 mts, while in valleys along rivers and arroyos, due to the erosion, it is very thin or nonexistent. The lithological profile of the Hernandarias Fm. is grey clays, somewhat sandy, with calcareous concretions in the lower part, brown clays with abundant gypsum layers or lenses (in some places it is quarried on a commercial basis) in its middle part and silty clays with calcareous concretions in the upper 5 to 10 metres.

The Hernandarias Fm. is of fluvial origin, of Pleistocene age. 

The dominant clay mineral is montmorillonite.

The Hernandarias Fm. overlies unconformably all the previous formations.

2.3.2 Ituzaingó Formation

The dominant lithology of the Ituzaing’o Fm. is fine to medium grained yellow sandstones with some thin clay and siltstone layers. The lower part of the Ituzaing’o Fm. commences with gravel beds or conglomerate and some green layers of clay, with fossil plant remains, and continues with fine to medium cross bedded sandstones in its middle and upper parts. The Ituzaing’o Fm. is of fluvial origin and its thickness varies between 20 to 40 mts.

The age is Middle Pliocene to Early Pleistocene.

It overlies the Parana Formation unconformably. The main outcrops of the Ituzaing’o Fm. are located in the cliffs along the Parana river and along some river valleys in the provinces of Corrientes and Entre Rios.

2.3.3 Paraná Formation

The upper part of the Parana Fm. is composed of coarse sandstones, while most of its profile is made of clays, silty and sandy clays. The Parana Fm. is of marine origin.

Its thickness is more than 100 mts.

The Parana Fm. may be divided into 3 members as follows:

- Basal member composed of green clays, green-grey clays with gypsum, of a regional distribution.

- Intermediate member composed predominantly of grey, fine to medium grained sandstones, with intercalations of green clay, somewhat sandy and fossiliferrous.

- Upper member of sandy clay, calcareous and layers of conglomerates.

In some places the upper member is eroded, thus the Ituzaing’o Fm. overlies unconformably the Parana Fm.

The most eastern appearance of the Parana Fm. is at latitude 59 degrees, while the intermediate mb. was detected at Bovril at 17 mts. above M.S.L.

The age of the Parana Fm. is Late Miocene.

The Parana Fm. overlies unconformably the following Formations:

Fary Bentos (Oligocene), Pay Ubre (Upper Cretaceous), Yeruba and Serra Geral (Cretaceous), which are out of the scope of this report and irrelevant to the studied area.

2.4. HYDROGEOLOGY

The main hydrogeological units in the area of Avigdor - Bovril are the following:

2.4.1 Hernandarias Fm. Aquiclude to aquitard

This formation, composed of clay and siltstones, is considered as an aquiclude that overlies the main aquifer of the Ituzaing’o Fm., except the uppermost 5 to 10 mts., where thin fine grained sand layers or lenses may form a local aquitard, that can supply 1 to 2 m3/hour for restricted domestic demands and for animal needs.

Most of the Molinos (wind operated) pump from this phreatic shallow aquitard.

2.4.2 Ituzaing’o Fm. Aquifier

The Ituzaing’o Fm. , composed predominantly of fine to medium grained sandstones, is the main aquifer of the studied area. It is distributed over the whole area of Entre Rios province.

In several locations exists a separation of a clay bed, several meters thick, between the upper fine to medium grained sandy aquifer, and the lower coarse grained sandy aquifer, as for instance at Algarrobo well. This clay bed is not continious over the whole region! The coarse grained aquifer, which in some places contains gravel in its basal part, is supposed to be the upper part of the Parana Fm.

Nevertheless, this sandy unit is considered as one main aquifer, that is overlaying green clays of the Parana Fm.

The Ituzaing’o aquifer is semiconfined with transmissivity (T) values of 540 m2/day 

(Avigdor) to 850 m2/day (Bovril wells). Considering a thickness of 30 to 40 mts. of the aquifer leads to permeability values (k) of 15 - 20 m/day for this aquifer.

2.4.3 Water level and flow direction

The absolute water level at Bovril is about 48 mts (85 - 37) above M.S.L., while in Avigdor it is about 41 mts. (65 - 24) above M.S.L. Considering that the water level near the Parana river is about 12 mts. above M.S.L. (O.C.Tujchneider et al 1994) we get a gradient of 0.3 promil, for the whole region that drains into the Parana river, which is a very smooth gradient. It is supposed that the flow direction of the groundwater is from Avigdor due north - west, towards the Parana river (Tujchneider et al 1994). Since the distance between Bovril and Avigdor is 17 kms, the gradient of the groundwater in this direction is 0.4 promil.

2.4.4 Recharge area

The recharge areas of the Ituzaing’o aquifer are not , so far, agreed between all the geohydrologists that worked in this area. There are several hypotheses concerning the recharge areas as follows:

(a) Direct rainfall through the clayey Hernandarias Fm., which contributes sulfate into the aquifer, by dissolved gypsum, contained in this formation.

(b) Outcrops of the Ituzaing’o Fm. sandstones in northern Corrientes province, as well as along some other river valleys

(c)Direct contact between Uruguay river and Ituzaing’o sandstones, at Concordia, which enables recharge from the river into the aquifer( Paparotti, oral information).

2.5. EXISTING DEEP WELLS IN BOVRIL – AVIGDOR REGION

The following relatively deep wells, of about 80 to 90 mts. depth, exist in the region of Bovril - Avigdor (see table No. 2):

Bovril 4, 5, 6 wells, that supply the potable water of Bovril, where about 6,000 people live (figs.8,9), Avigdor well (4”) that supply the water demand of Avigdor colony of about 200 families, Alcaraz well that supply the water demand of this colony and the non operating well of Algarrobo farm.

The technical and hydrological data are presented in table No. 2.

Table No. 2 - Data of the existing wells in the region of Bovril - Avigdor:

The yield of the wells could not have been measured, since they pump directly into the water supply net. The quantity of the yield have been supplied by the local operator and should be confirmed by field measurements.

Since the wells are not equipped by a non-returning valve, it was impossible to perform in most of the wells pumping tests, except at Bovril 4 and Avigdor 1 wells.

The pumping test data of Alcaraz well were analyzed according to the existing data accepted from the local moncipality.

2.6. WATER QUALITY

Partial chemical analyses of groundwater from the wells of Bovril 4, 5, Avigdor 1 and Alcaraz are presented in table 3. Except Avigdor well, the water are rich with sulfate and chloride, even above the standard of potable water (in Bovril wells - sulfate, in Alcaraz - sulfate and chloride).

The high sulfate content arrives from the gypsum beds and lenses that exist in the Hernandarias Fm. , that overlies the aquifer.

Table No. 3: Chemical analyses of existing wells in the region of Avigdor (in mg/lit.).

In the present study 8 water samples were collected and sent to analysis in the Parana University laboratory, including 2 samples of superficial water taken from the reservoirs of the farms.

The groundwater of Avigdor area (including Greenvald well and Molino Erart) is of the sodium - bicarbonate type, while the groundwater of Bovril wells is of the sodium - chloride or sodium - bicarbonate type.

The outstanding feature of these water is the high sodium content, that may be fourfold than the chloride content at Bovril wells and eightfold at Avigdor and Greenvald wells. This high sodium content, together with the relatively high sulfate and bicarbonate content may be explained by the evaporite deposits that exist in the Hernandarias Fm., that overlie the aquifer. Several minerals that contain sodium, sulfate and water in their structure and appear in association with gypsum and halite (evaporites), can contribute the high sodium and bicarbonate content of the groundwater of this region. Such minerals are:

Trona - Na2Co3.NaHCO3.2H2O.

Natron (Soda) - Na2Co3.10H20.

Borax (Tinkal) - Na2B4O7.10H20.

Glauberite - Na2S04.CaSo4.

The S.A.R. values of the groundwater is defined as good for irrigation purposes, according to Todd (1959, p. 192) where S.A.R < 10 is excellent, 10 - 18 is good,

18 - 26 is fair and > 26 is poor.

The superficial water of both reservoirs are of very low salinity but of high organic matter content. The possibility to mix groundwater with superficial water for irrigation purposes calls for treatment of the superficial water. 

2.7. GROUNDWATER POTENTIAL OF THE FARM AREA

Considering the regional extension of the Ituzaing’o sandy aquifer, it is possible in this stage of reconnaissance to give only a general evaluation of the groundwater potential of the farm area.

(A) Assuming that the recharge arrives through the Hernandarias Fm., then we have an excess of about 160 mm per year. Since the farm area is 2500 dunam (250 hectars), it means a recharge of 400,000 m3 per year.

(B) The volume of groundwater that flows through the region of Avigdor can be estimated by the Dardy formula: Q = B x j x T x t

Where:

Q - is the volume of groundwater that flows through a defined strip (in M.C.M.)

B - is the width of the strip. In the case of Avigdor we estimate it in about 5 kms.

j - is the gradient of the groundwater flow.

T - is the transmissivity of the aquifer (m2/day) in the Avigdor area.

t - is the time considered (days). In our calculation one year is taken.

In the case of Avigdor farm the direction of the groundwater flow is due north - west, towards the Parana river, through a strip of about 5000 mts. that can be influenced by pumpage, with a gradient of 0,5 promil ( between Bovril and Avigdor), during a time unit of a year. The transmissivity value typical to Avigdor area is about 600 m2/day.

Q = 5,000m x 0,5 promil x 600 m2/d x 365 day = 550,000 m3 per year, which means that during a year a volume of about 0,55 M.C.M. flows through this strip.

(C) The one time reserve of the aquifer below the farm is estimated as follows:

2,500,000 m2 x 30 m x 20% = 15 M.C.M., considering the thickness of the aquifer is 30 mts. and the storativity is about 20% (typical for sandstone). It means that during dry years, like this year, pumpage of 0,5 M.C.M. from the one time reserve volume will lower the water level in 1 mt. This deficiency will be replenished in the rainy season most probably.

If we suppose that a successful well will yield about 60 m3/hour during 10 hours per day (600 m3/day), then 5 wells can pump 3,000 m3 per day and 300,000 m3 annually, which is compatible with the evaluated groundwater potential of the area.

The pumped volume will be replenished in the coming rainy season. This evaluation should be confirmed by the first proposed production well in the farm area.

If the results of this well, concerning yield and water quality will be positive, it is suggested to drill additional 4 wells in the farm areas, at least 500 mts. between each of them.

2.8. DESIGN OF THE PROPOSED PRODUCTION WELL 

The first well was designed as a pilot exploration well of 6” diameter, to about 110 mts. depth. It has been located at farm A (point a). The profile of this exploration well should be analyzed by Electric, Resistivity and Gamma Ray logs, as well as by examining its rock samples. The aquifer sand samples should be checked by granulometric analyses, in order to design the final casing and filter of the production well.

The second stage is to widen the pilot well into a production well, equipped with 10” casing and 8” Johnson screen, connected by a reducer, down to the first clay layer at about 80 - 90 mts. depth.

The purpose of drilling the pilot well down to 110 mts. is to examine if additional sand beds exist below the upper clay bed of the Parana Fm.

If such sand bed exist, it will enlarge the groundwater potential of the area.

The technical details of the designed well were sent to three drilling companies:

PROINSA from Santa Fe

CAFARO from Santo Tome

DIDERLE from Parana

The technical demands of the drilling companies concerning this well were the following:

(1) To drill the pilot well of 6” diameter to approximately 110 mts. depth, and collect rock samples every 3 mts. or at every change in lithology. It is forbidden to use bentonite during the drilling, but it is possible to use degradable polymer.

(2) To execute Electric and Resistivity logs, as well as Gamma Ray log at the end of drilling the pilot well. Analyse the logs, by correlation with the cuttings collected, to the aquiferrous units and interpret the salinity of the water.

(3) Widen the pilot well for a production well down to the first clay layer, at about 80 - 90 mts. depth. The borehole should be vertical, according to conventional standards.

(4) Insert 10” Johnson casing in the uppermost 60 - 65 mts.(depends on the profile) connected by a reducer to 8” Johnson filter, about 15 mts. long, with screen of 0,75 mm - 1 mm, according to the granulometric analyses.

(5) The lowermost part of the Johnson filter will be connected to a basket of 2 mts. 8” Johnson pipes, plugged at the bottom.

(6) Insert gravel of 2 - 3 mm grain size into the space between the Johnson filter and the wall of the well. The uppermost 5 mts. will be filled by cement in order to protect the well of contamination.

(7) Develop the well after completion by a compressor until clean water, without sand, are pumped (duration of at least 48 hours).

(8) Introduce a 1” P.V.C. or galvanized pipe down to 65 mts., in order to enable measurement of the static and the dynamic water levels in the future.

2.9. COST OF THE FIRST BOREHOLE

The following prices for drilling the pilot borehole and afterwards the production well were received by Preceptos:

The prices of Cafaro were too expensive. Moreover, they asked for additional payment ( for polymer, pump etc’).

Thus, the selection should be between Proinsa and Diderle companies; both of them

are qualified to do the job.

It is suggested to try to convince Diderle to reduce their prices in 10% to 12% and arrive to 19,000$ - 19,500$, similar to the price of Proinsa.

Anyhow, the cost of drilling the first pilot - production borehole at Avigdor farm is about 19,000$. The cost of a submerssible pump that will yield 65 m3/h from 70 mts. depth is about 6,000$, altogether a cost of about 25,000$.

This cost estimation does not include the cost of connecting the well to the electricity net, neither to the water supply system.

2.10. CONCLUSIONS AND RECOMMENDATIONS

- The Ituzaing’o Fm. is the main regional aquifer in the area of Avigdor - Bovril.

- It is suggested to drill the first pilot - production well to 110 mts. depth in the farm at Avigdor.

- The forecast of the yield of this well is 60 m3/hour.

- If the results of the first borehole will be positive, concerning the yield and water quality, it is suggested to drill 4 additional production wells to approximately 80 - 90 mts. depth.

- The annual pumpage, mainly in the dry season will be, in these circumstances, 3,000 m3 per day and 300,000 m3 during the dry season. During the rainy season the aquifer will be replenished and the only pumpage will be for drinking water.

- The agricultural crops will be planned according to the chemical parameters of the water, accepted after the water analyses.

- In order to protect the farms of inundation during the rainy season, it is recommended that an expert of surface water will estimate the runoff of the arroyos that feed both reservoirs and the earth dams, as well as the drainage system will be planned accordingly.

- The high sodium content of the groundwater of Avigdor area, about eightfold than the chloride content! (normally it is equal), calls for taking precaution means, when these water will be used for irrigation. Although the S.A.R. of the water is about 15 (defined good), the danger of plugging the local heavy soil needs permanent control and examination of the water quality, as well as of the soil.

ACKNOWLEDGMENT

Thanks are due to Preceptos S.A. company for their hospitality and assistance, specially to Gabriel Yelin, Josue Bauerberg, Gabriel Bermann and Sergio Bergman. I would like also to thank all the experts we met during my short mission, at Inta, the direction of Recursos Hidricos in Parana and Profs. Ofelia Tujchneider and Mario Fili of the University of Santa Fe who submitted me important oral and written information.

Finally, I wish to acknowledge Eliezer Levin and Uri Ben Eli of Israel, who sent me to this interesting mission and were interested in all the stages of the work.

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