I have a particular scenario that has been created for TTHM modeling in an existing system. Care has been exerted to model as close to field data as possible. Field data was used for initial amount at sole water source and modeled to conform to data extracted at field test locations.
In trying to lower initial amount at sole source to estimate what actions would be necessary at source to lower concentrations in the system, I have been unable to lower enough to overcome all system occurances of concentrations above the MCL. In fact, I have run the scenario with an applied BRR and concentration limit, but with no system concentrations of any kind (0.0 mg/L) and I am still seeing substantial constituent growth throughout the system. (here is my logic question) How is it possible to have growth that even reaches the concentration limit when there are no actual concentrations present in the system?
Also, I have modeled BRR's as 1st order equations as per majority of literature on the subject - would like to know if anyone has attempted otherwise? - and if so, on what basis of reasoning?
Thank you for any advice,
Eugene
Its great to see the Water Software being used for these advanced purposes. It sounds like you have done quite a bit of fiel calibration work with you model.
Here are a few suggestions that may help - If you provide the model with a growth rate and set up the EPS model for a 48 hour period it will model the constituent in growth over that time. In that case the model is doing what you told it to given the constraints you set = growing to some threshold based on a rate. Keep in mind that this growth is governed by the 1st order growth rate to equilibrium that you determined in the lab or through your literature(the latter may or may not be close to your actual field conditions). Also the growth rate is depenenent on the modeled concentrations that you set at your boundaries, for instance any Tanks in the system. A few suggestions – verify you are using the correct constituent in the alternative, verify that you are using an adequate growth rate for your actual field case, and verify you are using realistic starting conditions for your Tanks.
EPA's Stage 2 Disinfection By Product Rule (DBP) did encourage the use of modeling to identify DBP monitoring locations in IDSE (Initial Distribution System Evaluation) studies. However, because of the difficulty in calibrating DBP models, they used water age a surrogate for locations that are likely to experience high DBP concentations.
Now, as we move into later stages of the rule, I think utilities will be using the models they developed for the IDSE studies to analyze methods for reducing DBP concentrations. As a result of sampling done in Stage 2, they will now have the data they need to calibrate the models. It sounds as if you are well on your way to doing this.
And here you might think that a "private" forum like BE Communities might have been immune to spam....
Reported it, in case anyone else was thinking of doing the same.