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From: Jerry Avins on 13 Jul 2010 21:29
On 7/13/2010 8:28 PM, Fred Marshall wrote:
> Jerry Avins wrote:
>
>>
>> Other things being equal, clustering should follow a Poisson
>> distribution. If you measure flow -- a quantity that can be heavily
>> influenced by rainfall -- only twice a week, how do you bill equitably?
>>
>> Jerry
>
> Jerry,
>
> I don't imagine that we bill entirely "equitably" - more like "agreeably".
>
> We measure flow continuously to get the volume and concentration once or
> twice a week.
>
> The concentration is assumed to apply for the entire measured volume
> between concentration samples. So, one may say that we sample loading in
> that fashion.
>
> I think I answered my own question to the point where I can deal with it:
>
> We have the weekly or twice-weekly samples and have computer monthly
> averages - as the latter have some regulatory importance.
> You might consider these monthly averages to be lowpassed versions of
> the samples.
> Then, one can compute the distribution of outcomes and infer(?) the
> amount of loading.
>
> My "backwards" sort of reasoning goes like this:
> We take a set of samples.
> We determine the distribution of those sample values over a suitably
> long time such that daily and even annual variations are included in the
> distribution.
> The caution here is that trends get wiped out - so a suitable time frame
> or set of them needs to be selected that has some meaning where gross
> trends are concerned.
> If we assume that the distribution represents a reasonable estimate of
> ground truth, then we can infer in quantitative terms what's happening -
> such as over-loading (i.e. loading that's above some determined threshold).
> It's surely not "perfect" but it's better than nothing ... I think.

If your samples are taken at times of unusually high I&I, the dilution
can make the measured concentrations uncharacteristically low.

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
From: Fred Marshall on 14 Jul 2010 01:25
Jerry Avins wrote:

> If your samples are taken at times of unusually high I&I, the dilution
> can make the measured concentrations uncharacteristically low.
>
> Jerry

Yes, I know but the sample times are set for a number of reasons.
Actually, our concern right now is why the concentrations are so darned
high! So, in these parts where there's nearly 100 inches of rain each
year, we're used to seeing and fixing I&I. Right now it's not a big
concern.

Fred


From: Greg Heath on 14 Jul 2010 05:55
On Jul 13, 9:29 pm, Jerry Avins <j...(a)ieee.org> wrote:
> On 7/13/2010 8:28 PM, Fred Marshall wrote:
>
>
>
>
>
> > Jerry Avins wrote:
>
> >> Other things being equal, clustering should follow a Poisson
> >> distribution. If you measure flow -- a quantity that can be heavily
> >> influenced by rainfall -- only twice a week, how do you bill equitably?
>
> >> Jerry
>
> > Jerry,
>
> > I don't imagine that we bill entirely "equitably" - more like "agreeably".
>
> > We measure flow continuously to get the volume and concentration once or
> > twice a week.
>
> > The concentration is assumed to apply for the entire measured volume
> > between concentration samples. So, one may say that we sample loading in
> > that fashion.
>
> > I think I answered my own question to the point where I can deal with it:
>
> > We have the weekly or twice-weekly samples and have computer monthly
> > averages - as the latter have some regulatory importance.
> > You might consider these monthly averages to be lowpassed versions of
> > the samples.
> > Then, one can compute the distribution of outcomes and infer(?) the
> > amount of loading.
>
> > My "backwards" sort of reasoning goes like this:
> > We take a set of samples.
> > We determine the distribution of those sample values over a suitably
> > long time such that daily and even annual variations are included in the
> > distribution.
> > The caution here is that trends get wiped out - so a suitable time frame
> > or set of them needs to be selected that has some meaning where gross
> > trends are concerned.
> > If we assume that the distribution represents a reasonable estimate of
> > ground truth, then we can infer in quantitative terms what's happening -
> > such as over-loading (i.e. loading that's above some determined threshold).
> > It's surely not "perfect" but it's better than nothing ... I think.
>
> If your samples are taken at times of unusually high I&I, the dilution
> can make the measured concentrations uncharacteristically low.

Duh, what's, I & I?

Greg
From: Jerry Avins on 14 Jul 2010 06:28
On 7/14/2010 5:55 AM, Greg Heath wrote:

> ... what's, I& I?

Infiltration and inflow, which force sewage plants to process rainwater.
Infiltration occurs when leaky mains are lower that the water table.
Inflow is often illegal pump connections to the sanitary sewer. When
streets become submerged, rainwater can pour in through manhole covers.

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
From: Jerry Avins on 14 Jul 2010 06:34
On 7/14/2010 5:55 AM, Greg Heath wrote:

> ... what's, I& I?

Infiltration and inflow, which force sewage plants to process rainwater.
Infiltration occurs when leaky mains are lower than the water table.
Inflow is often illegal pump connections to the sanitary sewer. When
streets become submerged, rainwater can pour in through manhole covers.

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
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