Lagrangian Sampling for Emerging Contaminants Through an Urban Stream Corridor in Colorado1

Abstract: Recent national concerns regarding the environmental occurrence of emerging contaminants (ECs) have catalyzed a series of recent studies. Many ECs are released into the environment through discharges from wastewater treatment plants (WWTPs) and other sources. In 2005, the U.S. Geological Survey and the City of Longmont initiated an investigation of selected ECs in a 13.8‐km reach of St. Vrain Creek, Colorado. Seven sites were sampled for ECs following a Lagrangian design; sites were located upstream, downstream, and in the outfall of the Longmont WWTP, and at the mouths of two tributaries, Left Hand Creek and Boulder Creek (which is influenced by multiple WWTP outfalls). Samples for 61 ECs in 16 chemical use categories were analyzed and 36 were detected in one or more samples. Of these, 16 have known or suspected endocrine‐disrupting potential. At and downstream from the WWTP outfall, detergent metabolites, fire retardants, and steroids were detected at the highest concentrations, which commonly exceeded 1 μg/l in 2005 and 2 μg/l in 2006. Most individual ECs were measured at concentrations less than 2 μg/l. The results indicate that outfalls from WWTPs are the largest but may not be the sole source of ECs in St. Vrain Creek. In 2005, high discharge was associated with fewer EC detections, lower total EC concentrations, and smaller EC loads in St. Vrain Creek and its tributaries as compared with 2006. EC behavior differed by individual compound, and some differences between sites could be attributed to analytical variability or to other factors such as physical or chemical characteristics or distance from contributing sources. Loads of some ECs, such as diethoxynonylphenol, accumulated or attenuated depending on location, discharge, and distance downstream from the WWTP, whereas others, such as bisphenol A, were largely conservative. The extent to which ECs in St. Vrain Creek affect native fish species and macroinvertebrate communities is unknown, but recent studies have shown that fish respond to very low concentrations of ECs, and further study on the fate and transport of these contaminants in the aquatic environment is warranted.     

软件滤波在土体自振柱试验中的应用

自振柱试验是测量土样动剪切模量和阻尼比的常用方法,但由于噪声等环境因素的影响,土样扭剪自由振动的衰减波曲线有时会因高频干扰出现不平滑现象,难以得到合理的测试结果。软件数字滤波是解决这类问题的有效方法。本文通过多种软件数字滤波方法优缺点的对比,认为平均滤波法和惯性滤波法能有效解决试验数据中的高频干扰问题,并分别选择适当的滤波参数,得到了平滑的自振衰减波曲线;最后,采用平均滤波法处理了两组自振柱试验数据。结果表明,软件滤波法确能有效消除不合理数据,得到符合一般规律的土体动剪切模量和阻尼比试验结果,从而验证了其在土体自振柱试验中的应用价值。     

Factors affecting nitrate distribution in shallow groundwater under a beef farm in South Eastern Ireland

Groundwater contamination was characterised using a methodology which combines shallow groundwater geochemistry data from 17 piezometers over a 2 yr period in a statistical framework and hydrogeological techniques. Nitrate–N (NO₃-N) contaminant mass flux was calculated across three control planes (rows of piezometers) in six isolated plots. Results showed natural attenuation occurs on site although the method does not directly differentiate between dilution and denitrification. It was further investigated whether NO₃-N concentration in shallow groundwater (<5 m below ground level) generated from an agricultural point source on a 4.2 ha site on a beef farm in SE Ireland could be predicted from saturated hydraulic conductivity (K_sat) measurements, ground elevation (m Above Ordnance Datum), elevation of groundwater sampling (screen opening interval) (m AOD) and distance from a dirty water point pollution source. Tobit regression, using a background concentration threshold of 2.6 mg NO₃-N L⁻¹ showed, when assessed individually in a step wise procedure, K_sat was significantly related to groundwater NO₃-N concentration. Distance of the point dirty water pollution source becomes significant when included with K_sat in the model. The model relationships show areas with higher K_sat values have less time for denitrification to occur, whereas lower K_sat values allow denitrification to occur. Areas with higher permeability transport greater NO₃-N fluxes to ground and surface waters. When the distribution of Cl⁻ was examined by the model, K_sat and ground elevation had the most explanatory power but K_sat was not significant pointing to dilution having an effect. Areas with low NO₃ concentration and unaffected Cl⁻ concentration points to denitrification, low NO₃ concentration and low Cl⁻ chloride concentration points to dilution and combining these findings allows areas of denitrification and dilution to be inferred. The effect of denitrification is further supported as mean groundwater NO₃-N was significantly (P < 0.05) related to groundwater N₂/Ar ratio, redox potential (Eh), dissolved O₂ and N₂ and was close to being significant with N₂O (P = 0.08). Calculating contaminant mass flux across more than one control plane is a useful tool to monitor natural attenuation. This tool allows the identification of hot spot areas where intervention other than natural attenuation may be needed to protect receptors.     

Modelling of iron cycling and its impact on the electron balance at a petroleum hydrocarbon contaminated site in Hnevice, Czech Republic

Over a period of several decades multiple leaks of large volumes from storage facilities located near Hnevice (Czech Republic) have caused the underlying Quaternary aquifer to be severely contaminated with nonaqueous phase liquid (NAPL) petroleum hydrocarbons. Beginning in the late 1980's the NAPL plume started to shrink as a consequence of NAPL dissolution exceeding replenishment and due to active remediation. The subsurface was classified geochemically into four different zones, (i) a contaminant-free zone never occupied by NAPL or dissolved contaminants, (ii) a re-oxidation zone formerly occupied by NAPL, (iii) a zone currently occupied by NAPL, and (iv) a lower fringe zone between the overlying NAPL and the deeper underlying contaminant-free zone. The study investigated the spatial and temporal variability of the redox zonation at the Hnevice site and quantified the influence of iron-cycling on the overall electron balance. As a first step inverse geochemical modelling was carried out to identify possible reaction models and mass transfer processes. In a subsequent step, two-dimensional (forward) multi-component reactive transport modelling was performed to evaluate and quantify the major processes that control the geochemical evolution at the site. The study explains the observed enrichment of the lower fringe zone with ferrihydrite as a result of the re-oxidation of ferrous iron. It suggests that once the NAPL zone started to shrink the dissolution of previously formed siderite and FeS by oxygen and nitrate consumed a significant part of the oxidation capacity for a considerable time period and therefore limited the penetration of electron acceptors into the NAPL contaminated zone.     

Evaluation of the potential for the natural attenuation of hexavalent chromium within a sub-wetland ground water

In this work, the potential for natural attenuation (NA) of Cr(VI) is evaluated for sub-wetland ground water at a chromium-contaminated site in Connecticut, incorporating the experimental findings of previous work at the site. Experimental data is assessed through long-term attenuation capacity calculations and modeling, which incorporates statistical uncertainty of parametric values. The NA evaluation yielded the following results: (1) Significant increases in Cr(VI) concentration and extremely long chromium source dissolution timeframes are required to exceed the attenuation capacity of the sub-wetland region soils studied in this work; and (2) Based on the 1-D transport modeling and incorporating input parameter uncertainty, there is an approximately 92% and 98% probability that the applicable regulatory criteria will not be exceeded at Point C, near a river which serves as the receptor, for the cases of (1) sorption of Cr(VI) only and (2) pseudo first order disappearance of Cr(VI) from the aqueous phase only, respectively.     

基于城市火灾风险的消防站分级覆盖选址模型——以济南市区为例

为更科学规划消防站选址,实现有限资源下应急资源的合理配置,提高消防站联动效率,根据“不同火灾风险等级的需求点应得到主管消防站和不同数量增援消防站服务”的原则,提出1种消防站分级覆盖选址模型,同时使用覆盖衰减函数表示消防站对需求点的覆盖度;基于遗传算法设计消防站分级覆盖选址模型的求解流程;以济南市区为例,基于POI和火灾数据,使用核密度分析法进行城市火灾风险分级,进而对选址模型进行验证。结果表明:以覆盖火灾风险值为评价指标,分级覆盖选址模型的选址结果优于现状消防站、广义最大覆盖模型、P-中位模型和P-中心模型。     

典型农药污染场地地下水中苯系物监控自然衰减研究

通过对某农药污染场地地下水中苯系物（BTEX）4年的长期监测数据进行分析,识别了该场地地下水中BTEX浓度的空间分布规律,并研究了场地地下水中BTEX的自然衰减规律.结果表明,地下水BTEX污染程度较重,浓度为0.001～180.52 mg·L-1,平均浓度为13.30 mg·L-1;BTEX浓度和污染羽面积随时间出现波动式变化,但整体仍呈逐渐减小的趋势,表明地下水中BTEX发生了自然衰减;地下水中氧化还原电位（ORP）与BTEX浓度呈显著负相关,说明研究区中BTEX高浓度区域在发生生物降解;研究区BTEX的衰减速率较小,半衰期较长,说明该场地单纯依靠监控自然衰减的修复时间将较长,需要与化学刺激等其他主动修复技术相结合以提高自然衰减效率.     

Assessment of aerobic biodegradation of lower-chlorinated benzenes in contaminated groundwater using field-derived microcosms and compound-specific carbon isotope fractionation

Biodegradation of lower chlorinated benzenes (tri-, di- and monochlorobenzene) was assessed at a coastal aquifer contaminated with multiple chlorinated aromatic hydrocarbons. Field-derived microcosms, established with groundwater from the source zone and amended with a mixture of lower chlorinated benzenes, evidenced biodegradation of monochlorobenzene (MCB) and 1,4-dichlorobenzene (1,4-DCB) in aerobic microcosms, whereas the addition of lactate in anaerobic microcosms did not enhance anaerobic reductive dechlorination. Aerobic microcosms established with groundwater from the plume consumed several doses of MCB and concomitantly degraded the three isomers of dichlorobenzene with no observable inhibitory effect. In the light of these results, we assessed the applicability of compound stable isotope analysis to monitor a potential aerobic remediation treatment of MCB and 1,4-DCB in this site. The carbon isotopic fractionation factors (ε) obtained from field-derived microcosms were -0.7‰ ± 0.1 ‰ and -1.0‰ ± 0.2 ‰ for MCB and 1,4-DCB, respectively. For 1,4-DCB, the carbon isotope fractionation during aerobic biodegradation was reported for the first time. The weak carbon isotope fractionation values for the aerobic pathway would only allow tracing of in situ degradation in aquifer parts with high extent of biodegradation. However, based on the carbon isotope effects measured in this and previous studies, relatively high carbon isotope shifts (i.e., ∆δ¹³C > 4.0 ‰) of MCB or 1,4-DCB in contaminated groundwater would suggest that their biodegradation is controlled by anaerobic reductive dechlorination.     

两种不同构型b射线颗粒物分析仪线性关系的有效性评价

为评价导流锥式同时采样-测量β射线颗粒物分析仪的测量准确度,以分步采样-测量β射线颗粒物分析仪采样分析作为参比方法,使用2类构型的仪器对环境空气中可吸入颗粒物PM₁₀和细颗粒物PM_2.5进行长期平行比对监测.本文依据EN 16450标准对比对数据线性关系进行有效性评价,建立了修正的线性方程,导出了方法间不确定度评价式,结果表明导流锥式同时采样-测量结构和分步采样-测量结构的β射线颗粒物分析仪之间存在有效的线性关系.通过仪器内置修正参数浓度斜率、浓度截距修正后,在较宽浓度跨度范围（0~250μg/m³）内和足够多的比对数据（n>100）条件下,两种不同结构的仪器监测PM₁₀和PM_2.5的比对斜率、截距和相关系数（参比方法作为X轴）均能满足EPA CFR 40part53的要求.     

悬浮泥沙对蓝藻光合及细胞化学计量的影响

选取水华微囊藻Microcystis flos-aquae为实验材料,在含不同浓度的悬浮泥沙中培养,测定其光合特性和胞内营养元素含量.结果显示,除低浓度悬浮泥沙组外,水华微囊藻比生长速率和chla浓度均低于对照组,且随着时间的延长,含泥沙组水华微囊藻的光合活性F_v/F_m显著下降.水华微囊藻的最大放氧速率P_m和光饱和点I_k随着泥沙浓度的增加而减小,而暗呼吸速率R_d和光抑制作用β显著升高.此外,随着泥沙浓度的升高,水华微囊藻单位细胞C和P含量显著降低,而单位细胞N含量略微升高;由于胞内P含量变化较大,导致N/P比和C/P比显著升高,而C/chla比值随泥沙浓度的增加呈下降的趋势.由此可见,悬浮泥沙虽然因光衰减效应减少了水华微囊藻胞内C含量以及能量供给,但微囊藻通过调节自身生理机能和代谢策略,优先补给C和提高N的合成,节约P合成的能量,通过调节胞内C：N：P储存的优化分配,以适应含悬浮泥沙的外界环境维持生长.