近二十年前,当我在一个暴水研发实验室割牙时, 关于最合适的方法测量暴水样本中的固态集中的辩论是前向和中向的。suspended sediment concentration (SSC) deliberation.  Compounding the problem was the fact that TSS represented both a regulatory benchmark and a specific analytical method, of which there are multiple variations (SM 2540D1 or EPA 160.22), for measuring the solids concentration in stormwater samples.  From a regulatory perspective, we need to evaluate and subsequently rate our BMP's ability to capture and retain suspended solids relative to benchmarks, such as 80% annual load reduction.  To prove compliance, we turned to the TSS analytical methods initially established for wastewater to analyze our samples.  Unfortunately, research by USGS3 and others demonstrated that the TSS methods often fail to reliable account for coarse solids in stormwater samples and that the SSC method (ASTM D 3977-974) typically yields more representative results.

接连辩论持续多年,但多半围绕SCC法测量暴水样本悬浮固态比较精确。 快速向今天前行,暴水圈新展开辩论,研究悬浮固态分析并质疑BMP评价

自SSC法生成为阻塞下暴水固态集中度的更精确度量以来,它已被纳入数个BMP监测协议中,并被越来越多的管理机构清单所接受,以此确定TSS减载BMP实现率。新泽西州环境保护局暴水制造处理设备认证程序等受人尊敬的检验程序长期以来都依赖SSC法支持TSS方法。问题解决,对吗?

不幸的是,暴水采样采集分析继续是一个易出错工作,特别是在悬浮固态方面。鉴于暴水径流固体负载动态性质和暴水并非总极混合的事实,获取有代表性样本分析比做容易。分析时误入歧途只会加深问题

Putting sampling concerns aside for the sake of this discussion, analytical error remains a significant problem during suspended solids analysis.  Want proof?  Spike a half dozen samples with a known concentration of solids and send them off to a handful of different labs for analysis.  More often than not, the reported results will underreport the actual concentration.  Our internal research into this issue suggests the problem lies in rinsing, or more specifically, a lack of thorough rinsing.  When a technician fails to thoroughly rinse a sample bottle to remove and account for the solids left inside of it, the reported results are not representative of the actual solids concentrations.  Our experience suggests this issue is common, even at accredited laboratories, unless instruction and, in some cases, training on thorough rinsing is provided.

从积极的方面看,提醒分析设施注意这一问题确实产生更多代表性结果。 一旦技术员意识到问题,加粒样本回收率开始接近100%。 换句话说,用点指令,我们可以消除潜在重大误差源

Despite potential solutions, concerns over our ability to collect representative samples paired with the potential for analytical error have some in the industry calling for an end to sampling.  This is easier said than done, especially in the field, but in a laboratory setting, a modified mass balance approach to BMP monitoring is being championed.  More accurately described as a mass capture method, BMPs are evaluated by injecting a known mass of sediment over time at typical concentrations, and then the mass retained in the unit is recovered and measured to determine BMP removal efficiency.  On the plus side, this approach eliminates the potential to collect non-representative samples and the potential for error during sample analysis.  However, the method is certainly not without its own potential sources of error.  If the captured mass is not fully recovered, BMP performance will be underestimated, and much like sample analysis, the magnitude of this type of error is primarily driven by the care taken during the sediment cleanout/recovery process.  The point being, the potential for significant errors is there.  Proponents argue that its ok since the error works against the technology, so it's more conservative.  I'm all for being conservative, but I'm also for being as accurate as possible when it comes to evaluating BMPs.

The mass capture approach also adds significant time, cost, and complexity to laboratory testing compared to sampling.  While we know that the error associated with sample collection and analysis can be minimized, we do not yet have a handle on how closely the mass capture method gets to actual performance or a credible means of determining if the added cost and time are justified.  This approach also raises the question of comparability.  The majority of our stormwater data comes from the field where sampling remains the norm.  I recognize that field monitoring is ripe with its own sources of error and bias, but I'll save that for another day!  That said, are we justified in moving away from sampling in favor of a method that still may introduce significant error, at added time and cost, and with less potential comparability to other datasets?

My personal opinion is that we need more research into both approaches to quantify the potential error and determine whether it can be eliminated or reasonably minimized.  A true side by side comparison of the methods that hold other variables constant so we can determine whether the added cost and complexity is really worth it.   For now, that doesn't seem to be in the cards.  NJDEP is already in the process of updating their laboratory protocol for hydrodynamic separators and the new version will mandate that only the mass capture approach be utilized moving forward.  This change will trigger a mandatory retest for all of the currently certified HDS technologies.  Assuming most are retested, the total cost will likely exceed a million dollars that could have otherwise been invested in new innovations, all without a quantifiable upside to water quality.  It's not the path I would have chosen, but this is stormwater after all, where we tend to shoot first and seek answers later.

引用 :
开工SM 2540D标准水废水检验方法APHA-WAWA-WPCF,1997年第21版

二叉UPA水和垃圾化学分析方法EPA出版物600/4-79/0201983年3月

3级Gray J.R. Glysson D.G. Turcos M.和Schwarz,E.G.(2000年)地质调查报告00-4191http://water.usgs.gov/osw/pubs/WRIR00-4191.pdf