#### Abstract

The article considers the method of determining the transmissivity of the artesian confined aquifer by using the results of the flow measurement of the flowing wells that were conducted at two different time intervals. The suggested method is based on the design formula which has been earlier got by the author for the single flowing well. Herein the complexities are overcome which are associated with the monotone reduction of the flows and pressures of such wells over time, and also hydraulic resistances generating in them. The checkup of the suggested method by the data of the field observations has yielded satisfactory results.

**Keywords:** Transmissivity; Flowing Well; Hydraulic Resistance; Artesian Aquifer;
Hydrogeological Parameters

#### Introduction

Currently, the methods of data processing of the experimental pumping from the vertical wells are mainly based on the theory of the unsteady filtration (permeability) mode which for determining hydrogeological parameters of aquifers allows using the data about the groundwater level decline over time in the observation wells, or in the water intake well at its time-constant flow rate [1,2].

#### Materials and Methods

By this well-known enough method, except maybe [3], it is rather difficult to calculate with the necessary accuracy the hydrogeological characteristics of the artesian elastic aquifer by the data of operations of the flowing wells. The latter ones obtain the peculiarity-their flow rate and drawdown simultaneously change over time, and downhole hydraulic resistances play great role at the flow rate formation. At the absence of the observation wells, which is true almost for all flowing wells on the Ararat valley, the solution of the assigned task by the known standard methods becomes more difficult. And the absence of observation (unproductive) wells on the Ararat valley is associated with deep location of artesian confined aquifer at which boring of these wells is very expensive. Currently on the Ararat valley, for water supply and irrigation, there are over 900 operating flowing wells without availability of observation network which provides necessary information about drawdown in the artesian aquifer, the parameters of which shall be often determined for different hydrogeological calculations of water intake structures. In the work [4] the author presents the solution of the problem by the data of single measurement of the flow rate of the well, but this solution at its engineering use causes some difficulties, at the same time being vulnerable regarding fullscale measurement of the flow rate.

In the suggested method these shortcomings are resolved. Herein, the author gives the method of determining the transmissivity of the artesian elastic aquifer based only on the information about its parameters and values of the well flow rates measured at two quite separate points of time.

The method is based on the formula obtained by us for determining the flow rate of the flowing well at any moment of time [4]. These wells have the peculiarity-their flow rate and drawdown simultaneously monotonously reduce over time, and formation of their flow rate is equally influenced either by hydrogeological parameters of the aquifer or parameters of the wells themselves [5].

This formula has the following form:

where Q-flow rate at any time moment, T = km-transmissivity,
k-filtration coefficient of the layer, m-its thickness, H_{p}-initial
positive piezometric head in the layer, α-the coefficient of its
piezoconductivity, r_{o}-well radius, ζ_{imp}-its imperfection coefficient of
well, η-total resistance of the well.

Modification to the equation (1) for determining Ln2.25αt ∕r_{o} ^{2} leads to the view:

By writing the equation (2) for the measurements at two
moments of time: t_{1} and t_{2}, and by subtracting first from the second,
for calculating transmissivity Т of the aquifer, we get the following
dependency:

As our preliminary calculations showed, usually in the prolific
flowing wells, the water moves in the quadratic zone of resistance
where the total hydraulic resistance of the well η can be accepted
with the great accuracy in t_{2} - t_{1} time interval as a constant value
i.e η_{1} = η_{2}. Keeping this in mind, from the formula (3) we get the
formula for calculating T in more convenient form:

Illustration and checkup of the suggested method is done by the
example of the well 121^{b} of the PNIIIS (Production and Research
Institute for Engineering Surveys in Construction), bored on the
area of village Kharatlu-Aghamzalu of the Ararat valley. The initial
data are the following:

Positive head on the wellhead Hp = 18.65 m, the total length of
the well ℓ = 98 m, the length of filter ℓ_{f} = 34 m, well radius r_{o} = 0,
1778 m, total resistance of the well η = 1.242 · 10-8 day2/m5, at t_{1}
= 1 day well flow rate Q_{1} = 582 l/s, and at t_{2} = 7 days: Q_{2} = 550 l/s.

Then, for T by formula (4), we get T = 5594 m^{2} /day.

From the reports of the PNIIIS [6], for the given well the value is
brought k = 133 m/day, and m = 50 m, that is Т = 6665 m^{2} / day, it
means that the deviation makes 16 %, which is quite permissible,
especially if we consider that while determining the filtration
coefficient until now considerable deviations from that have been
accepted.

#### Conclusion

At complicated hydrogeological conditions, for more precise calculations of values of hydrogeological parameters, including conductivity of the artesian aquifer we suggest using developed at that inverse problem.

#### References

- Verigin NN, Vasiliev SV, Sargsyan VS, Sherzhukov BS (1977) Hydrodynamic and physicochemical properties of rocks. Moscow: Subsoil, pp. 271.
- Kruseman GP, Ridder NA (1994) Analysis and evaluation of pumping test data. Second edition (completely revised). Netherland, pp. 377.
- Ghazaryan SM (1988) Water exchange against a background of vertical drainage. Yerevan: Hayastan pp. 270.
- Melikyan NL (1996) About the method of calculating the yield of single flowing wells embedded in the artesian aquifer, Bulletin of NAS and SEI of Armenia (series of technical sciences). XLIX (3a): pp. 165-169.
- Harald Klammler, Leif Layton, Bassel Nemer, Kirk Hatfield, Ana Mohseni (2017) Theoretical aspects for estimating anisotropic saturated hydraulic conductivity from in-well or direct-push probe injection tests in uniform media, Advances in Water Resources 104: 242-254.
- PNIIIS (1966) On the results of groundwater surveys in the central section of the Ararat Basin (vil. Kharatlu-Aghamzalu) of the Armenian SSR. Part 1, pp. 272.