Soakaway structures : an alternative way for groundwater recharge

Abstract

Malta’s water problems continue to be under continuous pressure with excessive abstractions which result in the deterioration of groundwater quality. This has been augmented by increased urbanisation and a lowering of permeable areas. Since the 1980’s Malta’s drinking water supply has been mostly dependent on the desalination of sea water. According to a review on water resources conducted in 2006 by the Food and Agricultural Organisation of the United Nations in collaboration with the Malta Resources Authority, the lack of education as well as the lack of interest on this issue has led us to depleat much of the natural fresh water resource. The study shows that most of our main aquifers are being depleted at a rate which is higher than that with which they are being recharged. Hence the need to redress this balance in order to ensure their sustainability. This has led to high levels of chlorides and nitrates being exhibited which are symptomatic of behavioural patterns such as over abstraction and intensive agricultural activity respectively.

The aim of this dissertation is lo asses the potential qualitative and quantitative impact of a soakaway structure constructed at the end of Wied Ghollieqa, Gzira, and to assess whether these structures can positively contribute to recharge our groundwater bodies. The study was commenced on the 5" of September 2013 with the first rainfall event and was stopped on the 15" March. Throughout this period water level variations were measured and stormwater and groundwater samples collected from the soakaway structure and the borehole lying adjacent to the site. Stormwater samples were tested for Nitrates, Chlorides, Lead, Nickel, and Total Petroleum Hydrocarbons while Groundwater samples were tested for Nitrates and Conductivity. The quantity of water recharging the aquifer was found to be approximately 54,367m°. Range of values after testing of stormwater and groundwater samples in relation to treshold levels established by the Groundwater Directive 2006/118 were found to be as follows:

Findings have shown that the soakaway structure being investigated is in fact effective when considering the quantitative aspect of stormwater collection, groundwater recharge or also for flood relief. Qualitative data also provided positive results. In fact most of the parameters tested for have shown compliance to threshold levels provided, indicating a potential for recharge and reuse. Groundwater samples have shown a downward trend for Nitrates and a constant trend for Conductivity indicating that the major contributor to pollution of the aquifer is in fact seawater intrusion.