ASSESSMENT OF GROUNDWATER VULNERABILITY AND TOTAL ORGANIC CARBON IN THE SHALLOW GROUNDWATER OF WONOSARI CITY AND ITS SURROUNDINGS AREA, GUNUNGKIDUL REGENCY, SPECIAL PROVINCE OF YOGYAKARTA, INDONESIA

Soutsadachan Chandalasouk, Dr.rer.nat, Doni Prakasa Eka Putra, S.T,.M.T ; Dr. Wahyu wilopo,S.T., M.Eng

2021 | Tesis | MAGISTER TEKNIK GEOLOGI

lokasi daerah penelitian secara administratif berada di Kota Wonosari, Kabupaten Gunung Kidul, Provinsi Daerah Istimewa Yogyakarta. Kota Wonosari merupakan wilayah dengan pertumbuhan penduduk yang lebih tinggi dibandingkan dengan wilayah lainnya di Kabupaten Gunung Kidul. Secara geologi, Kota Wonosari berada di dataran tinggi Karst yang tersusun atas litologi batugamping. Kedalaman muka airtanah di kota ini relatif dangkal. Airtanah menjadi sumber air bersih utama di kota ini. Penelitian ini bertujuan untuk melakukan kajian kerentanan airtanah intrinsik, mengidentifikasi konsentrasi TOC pada airtanah, dan menginvestigasi hubungan antara kerentanan airtanah dan konsentrasi TOC pada airtanah. Observasi lapangan dilakukan pada 44 lokasi kemunculan airtanah (sumur gali, sumur bor, dan mata air) untuk menginvestigasi tipe akuifer, litologi permukaan, dan kedalaman muka airtanah. Di sisi lain, 20 sampel airtanah diambil dari sumur gali untuk dianalisis kandungan TOC. Pengumpulan data sekunder dari beberapa peneliti terdahulu juga dilakukan, terutama informasi mengenai litologi bawah permukaan. Metode yang digunakan untuk mengkarakterisasi kerentanan airtanah adalah metode GOD. Korelasi antara kerentanan airtanah dan konsentrasi TOC dalam airtanah dianalisis secara spasial dan statistik menggunakan metode overlay, regresi linear, dan uji Spearman's rho. Hasil analisis menunjukkan bahwa kerentanan airtanah di daerah penelitian didominasi oleh kelas tinggi dan ekstrim dengan persentase 84% dari total luas area daerah penelitian. Konsentrasi TOC di dalam airtanah berkisar antara 3.395 mg/l- 6.849 mg/l yang menunjukkan bahwa adanya beban kontaminan di dalam airtanah. Hasil regresi linear menunjukkan bahwa adanya korelasi positif antara konsentrasi TOC dan kerentanan airtanah dengan nilai R2 = 0.0503. Hasil uji Spearman's rho juga menunjukkan hasil korelasi positif, dimana R = 0.201 dengan p-value = 0.369. Walaupun hasil analisis menunjukkan korelasi rendah, studi ini membuktikan bahwa peta kerentanan airtanah cukup baik untuk merepresentasikan kemampuan kondisi alam dalam proteksi kualitas airtanah berdasarkan kerentanan airtanah.

Wonosari City is the capital of Gunung Kidul regency of Yogyakarta Special Province. The city is located in the karst plateau overlaying a succession of limestone lithologies. The groundwater in this city is shallow, and Wonosari City is an area that has a fast population growth compared to other regions in Gunungkidul Regency. Most of the water needs in this area are still rely on groundwater as the primary source. This study aims to determine the intrinsic groundwater vulnerability, identify the TOC concentrations in groundwater, and investigate the relationship between groundwater vulnerability and TOC concentration in the groundwater. Field observation was conducted on 44 groundwater occurrences ( dug wells, bore wells, and springs) to investigate the aquifer types, overlying lithology, and depth to groundwater. At the same time, 20 groundwater samples were taken from the dug wells and analyzed for the TOC content. Secondary data were also collected from previous researches, especially the information on sub-surface lithology. Groundwater vulnerability was evaluated using the GOD method. The correlation between groundwater vulnerability and TOC in groundwater was analyzed spatially and statistically by using map overlying, linear regression, and Spearman's rho test, respectively. The results showed that the groundwater vulnerability in the city is dominated by high to extreme exposure, which covers about 84% of the study area. The TOC concentration in groundwater ranges between 3.395 mg/l to 6.849 mg/l, which shows that pollution loading occurs. Linear regression shows that the TOC concentration and groundwater vulnerability has a low positive correlation with an R2 value of 0.0503 and Spearman's rho R= 0.201 with a p-value of 0.369. Despite the low correlation, the research proves that the groundwater vulnerability map in this study is good enough to represent the ability of natural conditions in protecting the groundwater quality.

Kata Kunci : Groundwater vulnerability, GOD method, and TOC, Wonosari