Publication Details

EVALUATING EFFECTIVENESS OF BANK INFILTRATION PROCESS IN JENDERAM HILIR, SELANGOR, MALAYSIA

This study was inspired by the Klang Valley water crisis, for which Bank Infiltration (BI) is considered a potential solution. Higher incidents of pollution to rivers in Malaysia could lead to decrease in resources for drinking water. Many developing countries, like Malaysia, are faced with a big challenge to provide safe drinking water to an ever-increasing population. Currently, treatment of river water is using chemicals to reduce several contaminants due to pollution. The chemical contents could give long term effects to the health of consumers. But now there is hope in a more effective but low-cost technology known as Bank Infiltration (BI) or Riverbank Filtration (RBF). BI is natural process using natural soil (aquifer) to treating river water and at same time utilized groundwater. Because of its ability to remove even the most persistent contaminants and microbes, BI can support other treatment steps in a water treatment scheme especially in conventional water treatment. BI is a method that has long been known but still new and not being practiced in Malaysia. However, BI is site specific and requires site investigations to assess its feasibility basing on local site characteristics. The study area is located in the southwest state of Selangor within the Langat Basin, Peninsula Malaysia and covers an area of 10 km2. Three major tributaries, namely, the main Langat River, Semenyih River, and Jenderam Hilir River, drain the study area. In this study was specifically conducted to explore the possibility of using BI systems to source the polluted surface water in conjunction with groundwater. Three major factors were considered for evaluation: (i) investigation on the contribution of surface water through BI (ii) input of local groundwater, and (iii) water quality characteristics of water supply. Initially, the geophysical method was employed to define the subsurface geology and hydrogeology of the area. Isotope techniques were performed to identify the source of groundwater recharge and interaction between surface water and groundwater.A total of 25 monitoring wells and 2 test wells were constructed to define the BI system. The physicochemical and microbiological parameters of the local surface water bodies and groundwater were analyzed before and during water abstraction. Abstraction water revealed a 5%–98% decrease in turbidity, as well as HCO3-, SO4-, NO3-, Al, As, and Ca concentration reduction compared with those of Langat river water. However, water samples from test wells during pumping show high concentrations of Fe2+ and Mn2+. In addition, amounts of E. coli, total coliform and Giardia were significantly reduced (99.9%). Pumping test results indicate that the two wells (DW1 and DW2) were able to sustain yields of 15.9 and 128 m3/hr, respectively. BI method is a surface water and groundwater interaction. Next, the water quality interaction was assessed through multivariate statistical analysis based on analytical quantitative data. Multivariate statistical analysis were used, including discriminant analysis (DA) and principal component analysis (PCA), based on 36 water quality parameters from rivers, lakes, and groundwater sites in Jenderam Hilir and were collected from 2009 to 2011 (56 observations). The DA identified six significant parameters (pH, NO2, NO3, F, Fe, and Mn) from 36 variables to distinguish between river, lake, and groundwater groups (classification accuracy = 98%).The PCA confirmed and identified ten possible causes of the variation in groundwater quality with an eigenvalue greater than 1 explained 82.931% of the total variance in the water quality data set: hydrochemistry; redox conditions; groundwater flow; surface runoff; groundwater contact with rock or weathered rock (Kenny Hills formations); river water and groundwater interaction, as well as discharge of untreated sewage and industrial waste into the river; interaction between the river, lake, and groundwater; heavy metal pollution from past mining activities; and industrial pollution such as from dyeing or paint operations. To evaluates the effects of groundwater pumping and BI operation on the installation of wells as well as determines the effect of pumping rate on flow paths, travel time, the size of the pumping and capture zone delineation, and groundwater mixing in a pumping well numerical modeling simulation using MODFLOW and MODPATH were use. The simulation involved trying different scenarios by changing variables to perform infiltration safely and achieves the ideal pumping rate. Results indicate that the migration of river water into the aquifer is generally slow and depends on the pumping rate and distance from pumping well to the river. Most water arrives at the well by the end of a pumping period of 1 to 5 days at 3072 m3/day for test wells DW1 and DW2, and during simultaneous pumping for DW2 and PW1 for a well located 40m and 20m, respectively, from the river. During the 9.7-day pumping period, 33% of the water pumped from the DW1 well was river water, and 38% percent of the water pumped from DW2 throughout 4.6 days was river water. The models provide necessary information for water operators in the design and construction of pumping and sampling schedules of BI practices. Detailed field investigations program obtain from this study can be use for preliminary BI system design and pilot construction by stakeholders, water operator or related agencies in Malaysia which provide a good method and the investigation (geophysical, isotope, grain size analysis, colloidal borescope systems, water quality analysis), statistical method and numerical method technique to study the BI may also used in other area of similar hydrological characteristics and climate change conditions.