Rinalta, Siti Dhanty (2026) Analisis Tipe dan Fasies Airtanah Dangkal Serta Karakteristik Litologi Daerah Mengkirau, Kecamatan Tasik Putri Puyu, Kabupaten Kepulauan Meranti, Provinsi Riau. Other thesis, Universitas Islam Riau.

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Abstract

Mengkirau area is a coastal region located near the Asam Strait and is dominated by peat and clay deposits, making it vulnerable to shallow groundwater quality problems. Groundwater in the study area is visually characterized by yellow to reddish-brown coloration. This study aims to analyze the distribution of major ions, the level of seawater intrusion based on major ion composition, shallow groundwater types, groundwater facies, subsurface lithology, and the relationship between seawater intrusion, groundwater types and facies, and subsurface lithology in the study area. The methods used include shallow groundwater sampling, major ion chemical analysis, groundwater type determination using the Stiff diagram, groundwater facies classification using the Piper trilinear diagram, and subsurface lithological observation using the hand auger method. The results show that seawater intrusion levels vary across the study area. Four stations (25%) are classified as not affected by saline water, one station (6%) shows a low level of saline influence, four stations (25%) are moderately affected, six stations (38%) experience a fairly high level of saline influence, and one station (6%) is strongly affected by saline water. Based on the sodium to chloride (Na⁺/Cl⁻) ratio, it is indicated that 69% of chloride originates from anthropogenic activities, while 31% is influenced by seawater intrusion. The dominant groundwater type is Na–Cl (88%), with minor occurrences of Na–HCO₃ (6%) and Na–SO₄ (6%). The identified groundwater facies include Na⁺+K⁺ facies (19%), Cl⁻+SO₄²⁻ facies (25%), and Na⁺(K⁺)–Cl⁻(SO₄²⁻) facies (56%), indicating the combined influence of seawater intrusion, anthropogenic activities, ion exchange processes, and groundwater–rock interaction. Subsurface lithology analysis based on bore log observations shows that the study area consists of two main lithologies, namely clay and peat. Clay is the dominant lithology, occurring at 10 stations (69%), peat is present at 5 stations (25%), and one station (6%) consists of a mixed peat–clay lithology.

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