O Poço de monitoramento é a melhor maneira de caracterizar uma área?

O estudo de áreas contaminadas no Brasil tem alguns "dogmas" que precisam ser revistos.

Um deles diz respeito ao poço de monitoramento: há algum tempo ele é considerado não a melhor, mas a única forma de se caracterizar uma área. Os diagnósticos e Modelos Conceituais são elaborados quase sempre apoiados em dados que são obtidos durante a sondagem para a instalação do poço de monitoramento e, posteriormente, do próprio poço.

Um debate muito interessante está ocorrendo no Linkedin sobre isso. Para quem participa do Grupo "Groundwater Remediation Search and Destroy Methodologies", vale a pena ler na íntegra .http://www.linkedin.com/groupItem?view=&srchtype=discussedNews&gid=2621693&item=251986034&type=member&trk=eml-anet_dig-b_pd-ttl-cn&fromEmail=&ut=02QAL8Jojv_5M1 

Para quem não participa, transcrevo abaixo as participações que achei mais interessantes. Boa leitura:

Are monitoring wells the best way to characterize a site and then gauge remediation performance and the overall risks posed by the site?

The same question could be asked about current approaches for soils and soil gas?

Eliot

6 dias atrás

Lance Robinson • We were just writing a paper on this subject. I am curious to see the responses. Yes, no, then yes. In short to many geologic and unsteady state changes make gw data a inconsistent way to determine total mass. Anyone whom had calculated total mass (guessed) should tell us that. So judging technologies ot progess that way is way so many sites have long processes to actually get them closed.

5 dias atrás• Gostei

Tom Koester • If direct-sensing technologies are prohibitive then monitoring wells may be the best available strategy. I'm sure there are plenty of MIP operators in this group who have been told by clients that they have some amount of cVOCs in their well only to find that a MIP (or even better an MiHPT) boring show a much higher concentration in a fine-grained zone bracketed by coarser grains. In that particular case which I've personally seen on over a dozen sites the monitoring wells were not the best method but rather they turned out to be quite misleading.

I would also add that UV-based detectors (FFD and uvost) can be highly effective in delineating diesel and fuel oil releases without the costly installation and monitoring of wells.

Parar de seguirMark

Mark Kram, Ph.D. • Great question. This will often depend upon how well the characterization phase was designed and executed. If field analytical methods are used to determine and design optimal long term monitoring points, then those monitoring wells should yield better results than if no field analytical methods were employed during the characterization phase.

EPA has sponsored a few workshops and webinars on what has been referred to as the "single mobilization solution". An example of this would be where MIP could be used for solute plume deliniation, the high resolution piezocone (HRP) is then deployed to characterize the site specific hydraulics (e.g., K field, head field, gradient, velocity and flux, etc.) and specify monitoring well design parameters (e.g., filter pack and slot size), then custom designed monitoring wells (using the Kram/Farrar relationships) can be installed in appropriate locations for long term trend analyses. A variation on this could be where sensors are deployed in these wells following installation to allow for automated reporting of trends related to remediation. All of this can be implemented in a single mobilization/phase with the same talented field crew.

An approach like this has many benefits, and could be useful regardless of remediation approach employed (MNA or something more aggressive). When this type of approach is employed (e.g., coupling field analytical methods with monitoring network design), practitioners should have more confidence in the use of monitoring wells for remediation perfomance assessment

Lynn Sherman • NO. I was first charged in 1981 to place monitoring wells under RCRA to deterime if our 40 year old industrial landfill soon (10 years) to get a license. We moved from one up gradient aquifer well and three down gradient aquifer wells (100 ft deep), then added 10 fifteen foot lacustrine wells and ended up with 111 wells at 100, 60, 15 feet with a 5 foot screen built to RCRA standards. With the exception of one shallow till well placed in or very very near an oil pond that caught fire then was filled with garbage to co-mingle and solidify the oil sludge and it showed part per billion levels of five water soluble oil constituents. We all know that some of the oil ponds and landfills were never lined and never used recompacted clay. There should have been a halo around this site. No contamination was found in monitoring these wells for the selected contaminants and twice they were sampled for Appendix VIII and Appendix IX parameters at $2800 per well. No contamination was found at the SW-846 detection levels.

Add up all the costs and the fact that no contamination has been found and this should be a good case for why wells are not the way to characterize or monitor most if not all sites located in anything less that 10-5 cm/sec soils.

Lynn

1 dia atrás• Gostei

Seguir Bob

Bob Burger • Eliot, I have to chuckle as I read the responses to your question and several other of your recent questions all relating to the "new" High resolution characterization tools and process. Chuckle because over 20 years ago we contracted a CPT company with an electrical piezocone, pushed along traverses perpendicular to the groundwater flow and collected vertical and horizontal stratigraphy.

Also used dissipation testing for approximation of hydraulic permability, immediately reviewed logs and collected discrete depth GW samples at locations of lower perms or potential aquitards using the CPT. Analyzed soil and GW samples onsite using GC and GC/MS system. It worked quite well, saved months and many $ for clients.
I hope we see a real movement to use these tools, and the new systems you have been talking about must be a big technical improvment! Can anyone explain why we have not used the tools and techniques we have had for several decades?

But to the topic at hand, I also have spent many years understanding (or trying to anyway) how best to collect GW samples. GW is one of the three media that is regulated and factors directly into risk assement and drives remediation, it is critical that we collect and analyze as accurately as possible. My experience suggests that we collect too broad of a vertical interval, even a 5 or 10 foot screen probably eclipes the vertical interval of contamination. What I have seen is the composit GW sample from high concentration interval diluted with lesser or low concetration above and/or below. I theorize this may play into inconsistant GW data. Even the the old CPT data indicated this occurence of short vertical intervals of contamination.
I have been an advocate for discrete interval GW products like the Waterloo or Westbay sampler but low cost pvc wells win out. I have studied the low flow sampling process and not convinced it is worth the time and results for more accurate GW analysis. But that another item for discussion. Interested in hearing who is using what technologies!

12 horas atrás• Gostei (desfazer)

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Parar de seguirMark

Mark Kram, Ph.D. • Bob brings up many excellent points. It is true that CPT has been around for some time. I had the great fortune of being part of a team that first started working with LIF (which resulted in UV/LIF, ROST, etc.) in 1993. This technology was an outgrowth of Dr. Steve Lieberman's groundbreaking oceanographic observations coupled to the ACOE's CPT system, and was also based on Dr. Greg Gillespie's (w/Randy St. Germain as a key team member) similar efforts to excite polyaromatics with UV sources and binned fluorescence response processes. Early on, the DoD supported our development and dem/val efforts, and then my team received central funding from the Navy to offer our services for free to all Navy and Marine Corps RPMs (as well as a few other entities, including DOE, Army, and a few energy firms) for 2 years. We successfully demonstrated significant cost savings (e.g., over $1.5M saved at two selected sites where remediation estimates were already negotiated, and then we obtained closure after our field campaigns without the need for these remediation components). It is difficult to know how much we saved the government during those times, but our team was comprise of extremely talented and dedicated engineers and scientists, and our efforts resulted in optimized remediation and/or closure of dozens of sites within that brief window. After the 2 year centrally funded window expired, we had to market our services as internal DoD consultants and eventually transferred the technology to two public works entities (San Diego and Jacksonville). While the transfer was very successful (due to the dedication and skills of key players within those commands), we received a few protests from the private sector that suggested they did not support the competition. I recall that for one of the sites where we documented Navy savings of ~$900K, the lead consulting engineer expressed concerns to me about losing his job. Soon thereafter, the powers-that-be decided to privatize the service in various capacities (e.g., dismantle our team by giving most of the key government operators their walking papers, hire consultants to run the Navy system [some were the same former government employees], etc.). As a result, while the technology has stood the test of time w.r.t. expediency, and has served as a flagship for the Triad concept, we've seen practitioners struggle to gain market share when compared to conventional approaches. In addition, in the early 2000s, we demonstrated that we can locate DNAPL source zones using the same LIF based tooling, but with optimized energy sources. One can debate why entities are not using these tools more frequently. However, I maintain that coupling these proven approaches with monitoring wells (where network designs are based on the hi-res results) remains the best option for cost effective assessment, remediation design and remediation performance evaluation.

With respect to using piezocones for hydraulic assessment, the "new" high-resolution piezocone (also developed by the Navy during those years, and recently commercialized) affords the ability to quantify K for even coarse grained soils. Imagine how one can improve predictive models and remediation designs, and determine flux/discharge with such a tool. Now we can because the technology is finally available to the private sector!

With respect to short screened wells versus traditional long screened wells, my colleagues and I have performed comprehensive tests that confirm what Bob has stated. One must consider, however, that if the screens are too short, and are not placed in the zones of highest concentration or K, conclusions regarding plume status and remediation progress will be considerably impacted. This again cries out for the use of high-resolution approaches (e.g., MIP, LIF, HRP, etc.) BEFORE committing to well design and installation locations.

11 horas atrás• Gostei (desfazer)

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