Wenyong Wu

Groundwater Vulnerability Assessment and Feasibility Mapping Under Reclaimed Water Irrigation by a Modified DRASTIC Model

Increasing water shortages promote reclaimed water irrigation (RWI), which potentially causes additional contaminants in groundwater. The DRASTIC model has become an important tool to assess specific groundwater vulnerability. In this study, five parameters of the model were kept to calculated intrinsic vulnerability index (IVI). Aquifer media rating is calculated using the weighted average of ratings for all mediums instead of using the major medium rating, and the rating of the impact of vadose zone is adjusted for the clayey soils on the basis of their thickness. Subsequently, a single parameter sensitivity analysis is used to compute the effective weights of those five parameters. The Pearson’s correlation coefficient between IVI and Nemerow’s synthetical pollution Index (NI) of groundwater quality is significantly improved from 0.185 to 0.775 after four steps of revision. The RWI factor, Rrr, is introduced to assess specific vulnerability index (SVI) under RWI. The SVI decreases from east to west with the increases in depth to water, clayey soil thickness, and other factors. To manage contamination risk, the study area is divided into preferential zones, feasible zones and unfeasible zones for RWI planning and operation with suggested engineering measures.

Spatial distribution and migration of nonylphenol in groundwater following long-term wastewater irrigation.

Seen as a solution to water shortages, wastewater reuse for crop irrigation does however poses a risk owing to the potential release of organic contaminants into soil and water. The frequency of detection (FOD), concentration, and migration of nonylphenol (NP) isomers in reclaimed water (FODRW), surface water (FODSW), and groundwater (FODGW) were investigated in a long-term wastewater irrigation area in Beijing. The FODRW, FODSW and FODGW of any or all of 12 NP isomers were 66.7% to 100%, 76.9% to 100% and 13.3% to 60%, respectively. The mean (±standard deviation) NP concentrations of the reclaimed water, surface water, and groundwater (NPRW, NPSW, NPGW, repectively) were 469.4±73.4 ng L(-1), 694.6±248.7 ng(-1) and 244.4±230.8 ng(-1), respectively. The existence of external pollution sources during water transmission and distribution resulted in NPSW exceeding NPRW. NP distribution in groundwater was related to the duration and quantity of wastewater irrigation, the sources of aquifer recharge, and was seen to decrease with increasing aquifer depth. Higher riverside infiltration rate nearby leads to higher FODGW values. The migration rate of NP isomers was classified as high, moderate or low.

Geostatistical analyses of spatial distribution and origin of soil nutrients in long-term wastewater-irrigated area in Beijing, China

The purpose of this study was to investigate the current status of soil fertility in the long-term wastewater-irrigated agricultural areas of Beiyechang District in the suburb of Beijing. A total of 103 soil samples from the top 20 cm of soil layer were collected and analyzed for macro- and micronutrient elements. The mean values of these elements were: total nitrogen (TN), 0.08 ± 0.02%; available nitrogen (AN), 60.34 ± 10.08 mg/kg; available phosphorus (AP), 19.59 ± 9.75 mg/kg; available potassium (AK), 84.22 ± 19.66 mg/kg; and availabilities of trace elements (B, Cu, Fe, Mn, Mo, and Zn), 0.29 ± 0.12, 1.44 ± 0.34, 8.97 ± 2.05, 5.44 ± 0.95, 0.27 ± 0.16, 1.16 ± 0.42 mg/kg, respectively. Compared with other similar areas, the overall soil nutrient content in the study area was still at a low level after nearly 30 years of wastewater irrigation. The organic matter content of wastewater-irrigated soils has significant impact on the accumulation of nutrient elements in these soils. Geostatistical analyses suggested that the spatial distribution of TN and AP was on account of agricultural practices, such as wastewater irrigation and fertilizer use. The availability of P, Mo, Cu and Zn may be due to the joint effect of soil parent material and wastewater irrigation. The availability of K, Fe and Mn was attributed to soil parent material. A significant availability of some elements occurred around sewage outfalls in the irrigation area and water canals, where the wastewater could be easily lifted. The knowledge of spatial distribution and sources of soil nutrients in such areas is the basis for undertaking appropriate farming and irrigation activities with rationalized utilization of treated wastewater.

The impact of river infiltration on the chemistry of shallow groundwater in a reclaimed water irrigation area

Reclaimed water reuse is an effective method of alleviating agricultural water shortages, which entails some potential risks for groundwater. In this study, the impacts of wastewater reuse on groundwater were evaluated by combination of groundwater chemistry and isotopes. In reclaimed water infiltration, salt composition was affected not only by ion exchange and dissolution equilibrium but also by carbonic acid equilibrium. The dissolution and precipitation of calcites and dolomites as well as exchange and adsorption between Na and Ca/Mg were simultaneous, leading to significant changes in Na/Cl, (Ca+Mg)/Cl, electrical conductivity (EC) and sodium adsorption ratio (SAR). The reclaimed water was of the Na-Mg-Ca-HCO3-Cl type, and groundwater recharged by reclaimed water was of the Na-Mg-HCO3 and Mg-Na-HCO3 types. The hydrogeological conditions characterized by sand-clay alternation led to both total nitrogen (TN) and total phosphorus (TP) removal efficiencies >95%, and there was no significant difference in those contents between aquifers recharged by precipitation and reclamation water. >40years of long-term infiltration and recharge from sewage and reclaimed water did not cause groundwater contamination by nitrogen, phosphorus and heavy metals. These results indicate that characteristics of the study area, such as the lithologic structure with sand-clay alternation, relatively thick clay layer, and relatively large groundwater depth have a significant role in the high vulnerability.

Migration and health risks of nonylphenol and bisphenol a in soil-winter wheat systems with long-term reclaimed water irrigation

Reclaimed water reuse has become an important means of alleviating agricultural water shortage worldwide. However, the presence of endocrine disrupters has roused up considerable attention. Barrel test in farmland was conducted to investigate the migration of nonylphenol (NP) and bisphenol A (BPA) in soil-winter wheat system simulating reclaimed water irrigation. Additionally, the health risks on humans were assessed based on US EPA risk assessment model. The migration of NP and BPA decreased from the soil to the winter wheat; the biological concentration factors (BCFs) of NP and BPA in roots, stems, leaves, and grains all decreased with their added concentrations in soils. The BCFs of NP and BPA in roots were greatest (0.60-5.80 and 0.063-1.45, respectively). The average BCFs of NP and BPA in winter wheat showed negative exponential relations to their concentrations in soil. The amounts of NP and BPA in soil-winter wheat system accounted for 8.99-28.24% and 2.35-4.95%, respectively, of the initial amounts added into the soils. The hazard quotient (HQ) for children and adults ranged between 10-6 and 1, so carcinogenic risks could be induced by ingesting winter wheat grains under long-term reclaimed water irrigation.