1:45 PM - 3:15 PM
[O11-P80] Analysis of sewage contamination diffusion and flow in basin-shaped subsurface structures and new tank model validation
Keywords:Tank model, groundwater, environment
Analysis of Sewage Contamination Diffusion and Flow in Basin-Shaped Subsurface Structures and Validation of a New Tank Model
Validation Using CarbAMtazepine and Well Water Level Variation Observations
This study aims to estimate groundwater flow and the contamination status from sewage using well water from Otomeyama Park in Shinjuku. Based on groundwater level data, a new tank model is proposed to test the hypothesis that the subsurface beneath the park is a basin-like structure surrounded on three sides by elevated terrain. CarbAMtazepine, a recalcitrant compound, is used as an indicator, with concentration and water level variations observed before and after rainfall.
The highland aquifer consists of a loam layer, a tuffaceous clay layer, and the Musashino gravel layer, whereas the well taps only the Musashino gravel layer. The bottom of the well is set at a Tokyo Bay intermediate tide level (T.P.) of 18.35 m, the Musashino gravel ranges from T.P. 18 to 23 m, and the ground is at T.P. 21 m. Once water is released from pressure, backflow toward the higher pressure zone is assumed not to occur. Both the CarbAMtazepine concentration measurements and the groundwater level observations were conducted using the Keisya well within the park.
The surrounding topography is basin-like, enclosed on three sides by highlands and connected to the Musashino gravel layer on the escarpment. When water levels in the highland gravel exceed a threshold, contaminated water is likely to infiltrate the subsurface, raising CarbAMtazepine levels. Due to the sloping geology, the outflow coefficient is high, and excess water is swiftly discharged.
Groundwater levels were measured every 30 minutes using a HOBO logger from March 7 onward, and the average values were used for evaluation. CarbAMtazepine concentrations were determined by sampling the Keisya well every three days from January to March and analyzing them via LS/MS/MS. The total rainfall over the previous four days was then plotted against the measured concentrations.
A tank model was constructed instead of a full physical or machine learning model because of data constraints and the need for scalability. The model approximates groundwater flow in the basin-like setting by assuming:
An upper-level tank representing the highland loam layer,
Lower-level tank 1 for the highland Musashino gravel layer, and
Lower-level tank 2 for the park subsurface.
Parameters for the two highland tanks (outflow coefficient, threshold, and storage coefficient) were adopted from Shimogawabe (2022). Since the park subsurface shares the same Musashino gravel layer as the highland lower-level tank, parameters b2 and S2 were not re-identified. In addition, water flowing from lower-level tank 2 that exceeds a threshold h3 is discharged further after being multiplied by a base outflow coefficient a4. In this study, h3 and a4 were identified by minimizing errors between observed and modeled groundwater levels. Using Excel Solver s evolutionary algorithm (3000 iterations) followed by manual adjustment, the identified parameters were a3 = 8.0e-1 and h3 = 35.8 mm.
The results suggest that CarbAMtazepine infiltrates from the surface or shallow layers in the upper section and is then transported to lower sections within the groundwater. Although the concentration typically remains around 2.75 ng/L, it rises by approximately 0.1 to 0.5 ng/L following rainfall. The model s performance, evaluated using the Nash coefficient (0.63), indicates high accuracy. Furthermore, spring water directly from the highland lower tank showed a CarbAMtazepine concentration of 8.3 ng/L. While the high outflow coefficient fits the sloping terrain, the model may underestimate water level declines, suggesting that either the discharge coefficient should be higher or the threshold lower.
These findings demonstrate that in basin-like terrains contaminated from surrounding highlands, contaminants tend to accumulate following rainfall. The innovative combination of contaminant transport mechanisms and a basin-like tank model provides versatile insights applicable to similar settings beyond Otomeyama Park.
Acknowledgments: Professor Takeshi Murahashi, Japanese Pharmaceutical University Advisors: Naoki Yamada, Masaru Iwade Also, thanks to Mikio Asami, Yuichiro Tsukahara, Yoshinari Kato, Kaname Morita, and Akihisa Matsuoka.
References:
Ryosuke Sato, "Investigation of Park Spring Water and the Effectiveness of Infiltration Facilities at Otomeyama, Shinjuku" (2012)
Taichi Shimogawabe, "Numerical Modeling of Groundwater Surrounding Spring Water: A Case Study Around Otomeyama Park, Shinjuku" (2022)
Validation Using CarbAMtazepine and Well Water Level Variation Observations
This study aims to estimate groundwater flow and the contamination status from sewage using well water from Otomeyama Park in Shinjuku. Based on groundwater level data, a new tank model is proposed to test the hypothesis that the subsurface beneath the park is a basin-like structure surrounded on three sides by elevated terrain. CarbAMtazepine, a recalcitrant compound, is used as an indicator, with concentration and water level variations observed before and after rainfall.
The highland aquifer consists of a loam layer, a tuffaceous clay layer, and the Musashino gravel layer, whereas the well taps only the Musashino gravel layer. The bottom of the well is set at a Tokyo Bay intermediate tide level (T.P.) of 18.35 m, the Musashino gravel ranges from T.P. 18 to 23 m, and the ground is at T.P. 21 m. Once water is released from pressure, backflow toward the higher pressure zone is assumed not to occur. Both the CarbAMtazepine concentration measurements and the groundwater level observations were conducted using the Keisya well within the park.
The surrounding topography is basin-like, enclosed on three sides by highlands and connected to the Musashino gravel layer on the escarpment. When water levels in the highland gravel exceed a threshold, contaminated water is likely to infiltrate the subsurface, raising CarbAMtazepine levels. Due to the sloping geology, the outflow coefficient is high, and excess water is swiftly discharged.
Groundwater levels were measured every 30 minutes using a HOBO logger from March 7 onward, and the average values were used for evaluation. CarbAMtazepine concentrations were determined by sampling the Keisya well every three days from January to March and analyzing them via LS/MS/MS. The total rainfall over the previous four days was then plotted against the measured concentrations.
A tank model was constructed instead of a full physical or machine learning model because of data constraints and the need for scalability. The model approximates groundwater flow in the basin-like setting by assuming:
An upper-level tank representing the highland loam layer,
Lower-level tank 1 for the highland Musashino gravel layer, and
Lower-level tank 2 for the park subsurface.
Parameters for the two highland tanks (outflow coefficient, threshold, and storage coefficient) were adopted from Shimogawabe (2022). Since the park subsurface shares the same Musashino gravel layer as the highland lower-level tank, parameters b2 and S2 were not re-identified. In addition, water flowing from lower-level tank 2 that exceeds a threshold h3 is discharged further after being multiplied by a base outflow coefficient a4. In this study, h3 and a4 were identified by minimizing errors between observed and modeled groundwater levels. Using Excel Solver s evolutionary algorithm (3000 iterations) followed by manual adjustment, the identified parameters were a3 = 8.0e-1 and h3 = 35.8 mm.
The results suggest that CarbAMtazepine infiltrates from the surface or shallow layers in the upper section and is then transported to lower sections within the groundwater. Although the concentration typically remains around 2.75 ng/L, it rises by approximately 0.1 to 0.5 ng/L following rainfall. The model s performance, evaluated using the Nash coefficient (0.63), indicates high accuracy. Furthermore, spring water directly from the highland lower tank showed a CarbAMtazepine concentration of 8.3 ng/L. While the high outflow coefficient fits the sloping terrain, the model may underestimate water level declines, suggesting that either the discharge coefficient should be higher or the threshold lower.
These findings demonstrate that in basin-like terrains contaminated from surrounding highlands, contaminants tend to accumulate following rainfall. The innovative combination of contaminant transport mechanisms and a basin-like tank model provides versatile insights applicable to similar settings beyond Otomeyama Park.
Acknowledgments: Professor Takeshi Murahashi, Japanese Pharmaceutical University Advisors: Naoki Yamada, Masaru Iwade Also, thanks to Mikio Asami, Yuichiro Tsukahara, Yoshinari Kato, Kaname Morita, and Akihisa Matsuoka.
References:
Ryosuke Sato, "Investigation of Park Spring Water and the Effectiveness of Infiltration Facilities at Otomeyama, Shinjuku" (2012)
Taichi Shimogawabe, "Numerical Modeling of Groundwater Surrounding Spring Water: A Case Study Around Otomeyama Park, Shinjuku" (2022)