Remediation of polluted sites in the typical area of karst underground river based on "Three-Source Model": A case study in the Pingqiao underground river system, Zunyi, China
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摘要: 在分析岩溶地下河系统范围内水源、污染源特性的基础上，建立了双源调查、源汇追踪和源头阻控为主要内容的岩溶地下河污染修复治理模式——三源模式。以遵义市坪桥地下河系统为例，利用三源模式对该地下河污染进行修复治理实践。结果表明：研究区分布有各类水点25处，以钻孔、岩溶泉点、地下河出口为主，特征污染物为以NH$_4^{+}$、${\rm{NO}}_3^{-}$、${\rm{SO}}_4^{2-}$、Mn2+、Se2+为主；分布有各类污染源点15处，以工业废渣堆放场为主，主要分布在地下河系统下游坪桥工业园区一带，特征污染物同样为以NH$_4^{+}$、${\rm{NO}}_3^{-}$、${\rm{SO}}_4^{2-}$、Mn2+、Se2+为主；地下河系统范围内有3条地下水污染通道，均分布在地下河出口与坪桥工业园区Z1（1#、2#）废渣处置场之间；通过对2#废渣处置场排洪竖井－地下河出口这一污染通道上游段进行帷幕工程修复后，地下河出口可减排污水排放量47 244 m3·a−1，NH$_4^{+}$、Mn2+浓度可降低66%~78%，其中NH$_4^{+}$最低削减量为16 250 kg·a−1，Mn2+最低削减量为10 960 kg·a−1。研究结果可为类似地区岩溶地下河系统污染修复治理提供参考。Abstract:
Karst groundwater is an important water resource in karst areas of China and even the world, playing a crucial role in residents' daily life and industrial and agricultural production. The soil layer in karst areas is generally thin, with a double-layer structure between the surface and underground. Pollutants can directly enter the underground aquifer through thin soil layers, sinkholes, skylights, and karst cracks, making the karst groundwater extremely susceptible to pollution. In recent years, human's industrial and agricultural activities and domestic pollution have caused a large number of various types of organic and inorganic pollutants to continuously enter the underground river, posing a huge threat to the safety of drinking water and ecological agriculture development of local residents. Therefore, pollution remediation of underground rivers is of great significance for the protection of karst underground water resources. Focusing on water sources and pollution sources, this study conducts a systematic analysis of the investigation, evaluation, and remediation process of underground river pollution. It establishes a pollution remediation and control model of karst underground rivers—the "Three Source Model". This model mainly includes dual-source investigation, source tracking, and source control. As a typical dendritic underground river in the exposed karst area of Southwest China with a pollution history of nearly 20 years, the Pingqiao underground river in Zunyi City, was selected as the study area for remediation and control of the pollution in the underground river with the use of "Three-Source Model". The results show: (1) There are 25 water points in the study area, mainly boreholes, karst springs and underground river outlets, and the characteristic pollutants are mainly NH$_4^{+}$, ${\rm{NO}}_3^{-}$, ${\rm{SO}}_4^{2-}$, Mn2+, and Se2+. Fifteen types of pollution source points are distributed, mainly including industrial waste disposal sites in the area of Pingqiao Industrial Park downstream of the underground river system. The characteristic pollutants are also mainly NH$_4^{+}$, ${\rm{NO}}_3^{-}$, ${\rm{SO}}_4^{2-}$, Mn2+, and Se2+. (2) There are mainly three groundwater pollution channels within the scope of the underground river system: PQE019 (sinkhole)-PQG025 (skylight)-PQS009 (underground river outlet); the flood discharge shaft of 2# waste residue disposal site-CK8 (borehole)-J02 (monitoring well)-CK6 & CK11 (borehole)-JC04 (monitoring well) & ZK2 (borehole)-PQG025 (skylight)-PQS009 (underground river outlet); 1# waste disposal site-PQG025 (skylight)-PQS009 (underground river outlet). The above pollution channels are distributed between the outlet of the underground river and Z1 waste disposal site in Pingqiao Industrial Park. (3) By curtain engineering, remediation was conducted in the upstream section of the polluted channel from the flood discharge shaft of 2# waste disposal site to the outlet of the underground river, and then the groundwater level upstream of the curtain steadily increased from 815.68 m to 823.35 m, but there was no significant change in the groundwater level downstream of the curtain. The characteristic pollutants in the polluted water extracted from the upstream drainage wells (PWZK1 and PWZK2) of the curtain had a maximum NH$_4^{+}$ content of 469 mg·L−1 (exceeding 938 times of a permitted level) and a maximum Mn2+content of 254 mg·L−1 (exceeding 2,540 times of a permitted level). During the stage when the wells (PWZK1 and PWZK2) were not pumped, NH$_4^{+}$ content at the outlet of the underground river was 76-143.6 mg·L−1, and Mn2+content 14.206-21.31 mg·L−1, with the outlet flow rate of 5.0-295.349 L·s−1. In the stage of intermittent pumping in these two wells, concentrations of NH$_4^{+}$ and Mn2+ at the outlet of the underground river showed a downward trend during the pumping period, while concentrations of NH$_4^{+}$ and Mn2+ at the same place showed a significant upward trend during the cessation of pumping. During the stage of continuous pumping, concentrations of NH$_4^{+}$ and Mn2+ at the outlet of the underground river remained relatively low, with NH$_4^{+}$ content generally ranging from 14.4 to 58.6 mg·L−1 and Mn2+content from 2.38 to 6.39 mg·L−1. Concentrations of NH$_4^{+}$ and Mn2+ decreased by 66% -78%, compared to concentrations in the stage when the wells were not pumped. The calculation results of reducing pollutant emissions in the treatment project show that the underground river outlet can reduce wastewater emissions by 47,244 m3·a−1, with a minimum reduction of 16,250 kg·a−1 for NH$_4^{+}$ and 10,960 kg·a−1 for Mn2+. The research results can provide reference for the remediation of pollution in underground river systems in similar regions. -
Key words:
- underground rivers /
- pollution /
- remediation /
- dual-source /
- near-source interception /
- curtain engineering
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图 1 岩溶地下河污染修复治理“三源模式”概念模型
Figure 1. Conceptual model of the "Three-Source Model" for pollution remediation of karst underground rivers
图 3 研究区水源和污染源分布图
Figure 3. Distribution of water sources and pollution sources in the study area
图 4 研究区丰枯季节地下水Mn2+质量分级图
Figure 4. Quality grading of groundwater Mn2+in the study area during the rainy and dry seasons
图 5 研究区丰枯季节地下水NH$_4^{+}$质量分级图
Figure 5. Quality grading of groundwater NH$_4^{+}$in the study area during the rainy and dry seasons
图 6 研究区双源氮氧同位素分布图
Figure 6. Distribution of dual-source δ15N and δ18O in the study area
图 7 坪桥地下河系统下游污染通道分布示意图
Figure 7. Distribution of downstream pollution channels in the Pingqiao underground river
图 11 地下水帷幕工程剖面图
1-地层代号 2-地层产状 3-灰岩 4-泥灰岩 5地层界线 6-地下水帷幕界线 7-地下水位 8-方向 9-钻孔深度(m) 10-地下水帷幕蓄水区 11-上游注浆孔 12-下游注浆孔
Figure 11. Profile of groundwater curtain engineering
1-stratigraphic code 2-attitude of stratum 3-limestone 4-muddy limestone 5-stratigraphic boundary 6-groundwater curtain limit 7-groundwater level 8-direction 9-drilling depth(m) 10-groundwater curtain reservoir 11-upstream grouting hole 12-downstream grouting hole
图 12 近源截排工程实施前后地下水水位变化剖面图
Figure 12. Profile of groundwater level changes before and after the implementation of the project of near-source interception and drainage
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