Heterotrphic plate count - HPC

[Nofears67]

A recent water test from my well came back absent for TC and E. Coli but had an HPC of 340 CFU.

Should I be concerned?

 

[Bob999]

The MCL for heterotrophic plate count is a Treatment Technique. Under U.S. EPA's Surface Water Treatment Rule, systems using surface water or groundwater under the direct influence of surface water must achieve a heterotrophic plate count (HPC) no greater than 500 bacterial colonies per milliliter (67 FR 1811; U.S. EPA, 2002).

 

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[Nofears67]

I have a 150' deep private well that is located about 40 feet from a nearby creek. The creek only flows in the winter time. I wouldn't say my well in under "direct" influence of surface water but I'm sure my well "benefits" from the flows in the creek when it is running.

I took another sample about 6 months ago and will post the HPC from that test when I get home and look at the results.

I'm honestly not that concerned but wanted to run this by the experts here.

Thanks

 

[Gary Slusser]

I don't know if anything with Coliform testing has changed since I stopped doing the testing the end of 2004 but, usually that test would be marked TNC (too numerous to count) and no Coliform or other result would have been given and a retest would have been required. IIRC, TNC was 200 or more CFUs (colony forming units) @ 50x.

So if this were my well or a customer's I would not rely on any or the results. I would shock the well properly and then wait 7-9 days after the smell of chlorine is out of the water and retest.

 

[Nofears67]

California does not have a MCLG for HPC but has a recommendation of < 500 CFU. The first test I took back in 6/2009 had 190 CFU. During our initial video log there was a small lizard floating on the top of the water, but this was before the well was brushed and bailed. Then it sat for a couple months until we recently had the pump installed.

I poured 1 gallon of 10% liquid chlorine into the well before they installed the pump and then about 3 hours later we started the pump. All of the CL2 was pumped out very quickly as the pump broke suction after running wide open for about an hour.

The recent water sample was taken after running the well @ 10 gpm for 24 hours.

Should I pour more CL2 down the well and let it sit in the water column for a while in an attempt to eliminate/lower the HPC?

Thanks

 

[Gary Slusser]

I think you missed my point about TNC.

The chlorine probably laid in the bottom of the well; it's heavier than water.

You should have mixed it in like 10 gallons of water and then followed it with water from a hose with water from the well pump but... I'm not sure that a gallon was enough for the 8" well, ti depends on how much water is to be treated and how much demand there is for chlorine.

 

[Nofears67]

It's a 12" casing that is 160 feet deep. The standing water level is at ~30-35 feet. I will be chlorinating the well per the recommendations in the sticky on this forum.

Thanks.

 

[Gary Slusser]

They ought to Open the sticky and let me correct the 1 gallon treats 500 gallons comment by 99K.

He didn't know the demand for chlorine, how much bacteria (you can never know that) or the demand due to iron or manganese etc. so he can't say how much chlorine is sufficient. That's why I say pick a volume and go with it but then check for a strong smell of chlorine and add more if needed. That's especially true with your 12" well.

 

[Nofears67]

I will start with 4 gals of 10% liquid CL2 and circulate the water back into the well per the sticky and probably let it sit for 24 hours.

I spoke to the lab that tested the water and they said not to worry about the HPC being 340 and that it's not a concern until it becomes > 500 cfu.

I'm still going to shock the well regardless...

 

[Ballvalve]

Interesting conversation. Indeed my lab test of California water showed non-coliform bacteria [CFU's] of 900. This gave a "pink " flag as over 500 was of interest. The lab said 900 was not out of line. Then I called my pal the head of the health dept, - wells and septic - he said he wouldnt bother to worry until much over 1000.

I'll probably do a proper chlorine flush one day, and I know how much work is involved to do it RIGHT, but until then, what do you guys think of the enviro engineer saying 1000 CFU's is okay? No one here is spending extra time on the Toto.

 

[Gary Slusser]

With the membrane filtration/petri dish type Coliform bacteria test, you can't read Coliform with 200 or more CFUs of HPC bacteria present. To test for Coliform bacteria you would have to use a Presence/Absence type Coliform bacteria test.

Personally I would not want 200 or more CFUs of HPC in my well water. I've seen up to 200 CFUs in petri dishes and the growth is substantial, looks like various colored spider webs and large black and brown etc. colored spots all over the graph paper in the dish in just 24+ hours in an incubator.

 

[Ballvalve]

Is HPC the same as CFU? Coliform came up as absent or 0, The "Colony forming units" as 900. Neither the lab or the health dept suggest that any action need be taken.

The lab would make money on a retest, and the health dept is usually over cautious. Seems like their advice is solid [?]

I can do a chlorine flush, but with a mile of pipe and several pressure tanks and a 3000g tank with several 3 way valves to swap systems, Its a huge job to do right.

Possibly a retest from the wellhead rather than at the kitchen sink?

 

[Gary Slusser]

Is HPC the same as CFU? Coliform came up as absent or 0, The "Colony forming units" as 900. Neither the lab or the health dept suggest that any action need be taken.

The lab would make money on a retest, and the health dept is usually over cautious. Seems like their advice is solid [?]

I can do a chlorine flush, but with a mile of pipe and several pressure tanks and a 3000g tank with several 3 way valves to swap systems, Its a huge job to do right.

Possibly a retest from the wellhead rather than at the kitchen sink?

HPC interferes with membrane filtration methodology bacteria test results for Coliform and E-Coli.

A search for "Hetrophillic plate count" came up with this;

http://aem.asm.org/cgi/reprint/73/11/3755.pdf

and this; Successfully sanitised water should have Heterophillic Plate Count of <100cfu/ml. Processing Facilities.