From: Andy Peters
Sent: Mon Apr 02 09:04:54 2018
To: Jake Ehredt; James Clifton
Cc: 'Bob Dillard'; Gerald Fisher
Subject: Final DO
Importance: Normal
Okay Gents, the story on the test from 3/22 that had DMS final DO results of less than 1.0 mg/L:
In Standard Methods (23rd edition) 6.a on page 5-9 it states: Only bottles (including seed controls) whose DO depletion is >= 2.0 mg/L and residual DO is >= 1.0 mg/L after 5 d incubation are considered to produce valid data, because >= 2.0 mg oxygen uptake /L is require to give a meaningful measure of oxygen uptake and >= 1.0 mg/L must remain to ensure that waste constituents’ oxidation rates were not limited by insufficient DO. According to 7. B on page 5-10 when you report, you only average results for bottles that meet those minimums, but we must record and report tests that fail QC and indicate the type of failure. There are 5 types of failure, and in this case it’s “all dilutions result in a residual DO < 1.0mg/L [5210B.7a3]]”. I’ll do this on the DMR today and send to Bob for review.
Andy Peters
City of Molalla
Public Works Operations Supervisor
(503) 829-6855 x220
Cell: 503-793-0507
117 N Molalla Ave
Molalla, OR 97038