Blank correction omission for Kjeldahl nitrogen and phosphorus tests on samples sent to the National Water Quality Laboratory
 

Date: Wed, 17 Nov 1999 11:48:31 -0700
From: Leona Treloar 
To: "E  - All WRD Employees"
Subject: Blank correction omission

MEMORANDUM


                                                     November 17, 1999


To:       Distribution "e"

From:     Merle Shockey, Acting Chief, NWQL

Subject:  Blank correction omission for Kjeldahl nitrogen and phosphorus
          tests on samples sent to the National Water Quality Laboratory


This notice is to inform the division that during the period from April
20, 1999 until October 4, 1999, samples analyzed at the National Water
Quality Laboratory (NQWL) for Kjeldahl nitrogen (lab codes 1985, 1986,
and 1994) and Kjeldahl phosphorus (lab codes 1983, 1984, and 1992) were
not blank corrected.  On April 20, the blank correction function on both
lines was inadvertently omitted when a new low standard was added to the
calibration curves for both nitrogen and phosphorus.  On October 4,
1999, the problem was identified and the blank correction was restored.

Between the dates of 4/20/99 and 10/04/99, results reported for these
tests are biased high by about 0.05 mg/L for nitrogen and 0.01 mg/L for
phosphorus based on the average rise in blind blank values for each
line.  Readers are reminded that the laboratory reporting level (LRL)
for the nitrogen lab codes is 0.1 mg/L and 0.05 mg/L for the phosphorus
lab codes.

Samples at or near the LRL for nitrogen and phosphorus are most affected
by this problem.  The NWQL is currently analyzing the data to determine
the best course of action.  Guidance on corrections will be issued as
soon as possible so that changes can be made for the annual data
reports.  If you have questions concerning this message, please contact
Gary Cottrell (COTTRELL), Nutrient unit supervisor at (303) 236-3490 or
Harold Ardourel (ARDOUREL) at (303) 236-3151.