Aquifer Pollution Vulnerability in the Roccamonfina Volcano Area, Southern Italy*

Groundwater Quality: Remediation and Protection (Proceedings of the GQ'98 Conference held at Tubingen, Germany, September 1998). IAHS Publ. no. 250, 1998. 63

Aquifer pollution vulnerability in the Roccamonfina Volcano area, southern Italy*

ROBERTA ALVINO, ALFONSO CORNIELLO & DANIELA DUCCI Dipartimento di Ingegneria Geotecnica: Sezione di Geologia Applicata, Università degli Studi "Federico II" di Napoli, Piazzale Tecchio 80, 1-80125 Napoli, Italy

Abstract In this paper the aquifer vulnerability map of the Roccamonfina Volcano southern sector (southern Italy) is presented. The study was carried out using a geographic information system (ILWIS) to apply two methods for pollution vulnerability assessment, DRASTIC and SINTACS.

INTRODUCTION

This study represents the first contribution to the definition of aquifer vulnerability in the Roccamonfina area. Two aquifer vulnerability assessment methods, DRASTIC (Aller et al. 1987) and SINTACS (Civita & De Maio, 1997) have been applied to this volcanic area.

GEOLOGICAL AND HYDROGEOLOGICAL SETTING

The Roccamonfina, the oldest Quaternary volcano of the Campania region, is a strato-volcano with a smooth morphology, reaching a maximum height of 1006 m a.m.s.l. and occupying an area of nearly 400 km2 (Fig. 1). The lithology of the western sector is represented by alternating lavas and pyroclastics (first phase of activity); the eastern side, on the contrary, is characterized by wide spread pyroclastic deposits (second phase of activity, mainly explosive). The piezometric setting (1996) shows a basal radial flow that partly feeds the contiguous aquifers by underflows, partly increases the flow of some peripheral streams, and only a small amount of groundwater reaches the numerous springs located on the volcano which are characterized by scanty discharge. The recharge volume of the aquifer, which is only due to rainfall, is nearly 113 x 106 m3 year"1 (Alvino, 1997).

GROUNDWATER POLLUTION VULNERABILITY MAPS

The vulnerability study concerns the southern area of the volcano only, because of the distribution of available drill-hole data. The aquifer is unconfined in the western part and in limited sectors in the eastern part, where it is mainly confined.

* This paper is Publ. no 1850 of the CNR-GNDCI Theme 4 (research project on aquifer vulnerability assessment guided by M. Civita)—Team 4.22 (R. de Riso). 64 Roberta Alvino et al.

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The DRASTIC method and its Italian modification, SINTACS, evaluate the vertical vulnerability of an aquifer, classifying seven parameters which have an impact on pollution potential, into ranges (Table 1). Weight multipliers are then used for each parameter to balance and enhance their importance. DRASTIC provides two weight classifications, for normal or intense agricultural activity conditions; for the Roccamonfina area, the first of these has been selected. However, the SINTACS method includes five weight classifications and it is possible to use different sets of weights in the same map; in the Roccamonfina area the weight strings for a normal impact scenario and for a fissured terrain have been utilized. Input data already available (Alvino, 1997) or collected by the authors included topographic data (maps), lithologie data (geological maps, aerial photos, 46 drill holes), climatic data (rainfall and temperature), hydrological data (200 piezometric measurements, 15 transmissivity measurements). Input preparation and integration modelling required the use of a spreadsheet to handle drill-hole data, and of a geographic information system, ILWIS (ITC, 1997), for spatial data analysis and modelling. The process adopted to construct the seven layers and associated comments are shown in Table 1.

CONCLUSIONS

The vulnerability maps are shown in Figs 2 and 3. The most prevalent vulnerability degree is low for DRASTIC and medium for SINTACS, probably due to the higher sets of weights adopted by SINTACS. Areas with high vulnerability do not appear, except for the southeastern area, where the depth to water is very shallow (the water-

Table 1 The procedures used to construct the seven maps for the contamination vulnerability assess ment, and the corresponding DRASTIC and SINTACS ratings. Parameter Process Comments Predominant ratings: DRASTIC SINTACS Depth to Depth of the: The values range between a 1 1-2 water - piezometric level where the few metres in a very small aquifer is unconfined; sector in the eastern part and - top of the aquifer where the more than 100 m in the aquifer is confined western part Net From the hydrogeological The values range between 8-9 7-8 recharge budget (Alvino, 1997) 150 and 550 mm year"1 Aquifer From the drill-holes applying 6-7 6-7 media the weighted average to the classes of each lithological unit Soil media From Alvino (1997) The most prevalent soil 3 3 class is clay loam (50%) Topography From the digital elevation model The values range generally 3-10 6-10 using ILWIS between 0 and 15%, but there are values > 100% Impact of See aquifer media 4 4 vadose zone hydraulic From the transmissivity map The values range between 3 7 Conductivity divided by the thickness of the 7 x 10"5 and 4 x 10"3 m s' saturated zone 66 Roberta Alvino et al.

"Sp =~~f|fj|B VULNERABILITY VULNERABIUTY DEGREE ajamaREj* |NDEx D 90 low Roccamonfîna jgjl tZ]81 " 105 Hl II 106- 116 medium 128

r CJr [:3 WL 140 \ " "^~ ~^ ^l\ ¥ %ll SM129- 152 high fa A. WÊF Biti • 'IJSr Bi53- 163 =F

0 BOOO ™ Fig. 2 Aquifer pollution vulnerability map computed using the DRASTIC method.

N ^ ~^fT CI •• "••• ••,•• VULNERABILITY VULNERABILITY Caianello, INDEX DEGREE D '; ' •: .-:••• . 1. 91 - 105 low Roccamonfina — | 106- 116 medium ':.'.•/ ' i: 117-128

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Fig. 3 Aquifer pollution vulnerability map computed using the SINTACS method. body feeds the Savone river) and, in SINTACS, for the small area where carbonate rocks outcrop (southwest of Teano, Fig. 1). Even in the western sector, where the aquifer is unconfined, the vulnerability degree is low or medium in most areas because of the high value of the parameter Depth to water ( > 50 m) that strongly influences the vulnerability in both methods because of its large weight multipliers. The main differences between the two maps are due to the parameters hydraulic Conductivity (the value range of each rating is wider in SINTACS than in DRASTIC) and Recharge (the ratings distribution is different: SINTACS assigns low ratings to high values of recharge to represent the effect of contaminant dilution). In conclusion, DRASTIC and SINTACS give comparable results in porous aquifers (see also Corniello et al., 1997), but their output differs greatly where Aquifer pollution vulnerability in the Roccamonfina Volcano area, southern Italy 67 fissured and karstic rocks outcrop, for which SINTACS offers a specific set of weights.

REFERENCES

Alvino, R. (1997,) Idrodinamica sotterranea e bilancio idrogeologico del vulcano di Roccamonfina (Campania) (Hydrogeology and water balance of the Roccamonfina Volcano). PhD Thesis, Perugia University, Italy. Aller, L., Bennet, T., Leber, J. H., Petty, R. J. & Hackett, G. (1987) DRASTIC: a standardized system for evaluating groundwater pollution potential using hydrogeoiogic settings. Environmental Protection Agency EPA-600/2-87-035, USA. Civita, M. & De Maio, M. (1997) Sintacs. Bologna, Pitagora, Italy. Comiello, A., Ducci, D. & Napolitano, P. (1997) Comparison between parametric mediods to evaluate aquifer pollution vulnerability using a GIS. An example in the Piana Campana. In: Engineering Geology and the Environment, 1721-1726. Balkema, Rotterdam, The Netherlands. ITC (1997) ILWIS 2.1 for Windows. User's, Reference and Applications Guides. ILWIS Dept, ICT (International Inst, for Aerospace Survey and Earth Sciences), Enchede, The Netherlands.