SW SAMPLING--Quality control samples for NAWQA microbiology (updated 7/11/03)

Type of sample

Description

Purpose

Frequency of collection

Criteria for acceptance

NWIS data-base information (Questions on coding samples for NWIS can be directed to Jeff Martin)

Comments

Analytical QC--Parameter code 90902, E. coli, modified mTEC MF agar, col/100 mL

Filter blank

(Filter blank is not stored in NWIS as a QC sample)

Sterile buffered water filtered before processing the environmental sample

Determine sterility of equipment and supplies. Measures positive bias in the results for the associated environmental sample.

Every environmental sample

Reject environmental sample results

If target colonies in filter blank are > 20 percent of target colonies in sample OR

If nontarget colonies in filter blank cover the plate, inhibiting growth of target colonies

1. Enter the col/100 mL for the environmental sample into QWDATA. 2. Set the data quality indicator to "Q" (Reviewed and rejected). 3. Set Remark code to "V" (Value affected by contamination). 4. Set Value-qualifier code to "w" (High variability). 5. Enter ONE of these result-level comments: "X Target colonies in filter blank" OR "Nontarget colonies inhibited growth."

Dilution(s) used to calculate col/100 mL are used to determine percentage for qualification. Even though sample results are rejected, they are still stored NWIS. We include remark codes and result-level comments in the event that criteria will be changed later It is, therefore, important to know why QC has failed criteria and by how much.

Qualify environmental sample results

For target colonies, 5 to 20 percent of sample colony count

1. Enter the col/100 mL for the environmental sample into QWDATA. 2. Set Remark code to "V" (Value affected by contamination). 3. Set Value-qualifier code to "w" (High variability). 4. Enter this result-level comment: "X Target colonies in filter blank."

Dilution(s) used to calculate col/100 mL are used to determine percentage for qualification. Sample results are qualified in NWIS. We include remark codes and result-level comments in the event that criteria will be changed later. It is, therefore, important to know why QC has failed criteria and by how much.

Accept environmental sample results

For target colonies, < 5 percent of sample colony count

1. Enter the col/100 mL for the environmental sample into QWDATA. 2. Enter this result-level comment: "X Target colonies in filter blank."

Procedure blank

(Procedure blank is not stored in NWIS as a QC sample)

Sterile buffered water filtered after the sample

Measure the effectiveness of the rinsing technique. Measures negative bias in the results for the previous sample.

One every 10 samples

Same as for filter blank.

Include procedure blanks if analyst is inexperienced in membrane filtration and (or) if water is suspected to have high concentrations of target colonies.

Positive control culture

(Not stored in NWIS as a QC sample)

Pure cultures analyzed in the same manner as the sample

Ensure the procedure is correctly performed and test the integrity of the media. Measures positive or negative bias in the samples plated on this medium.

One per year per analyst

Will develop criteria with study units in 2002 and 2003; Tentative criteria--for positive control, dilution series evident.

Ohio District will email expected results to study units, and study units will email their results to the Ohio District

None at this time. Ohio District will compile a spreadsheet with all results.

Field QC--Parameter code 90902, E. coli, modified mTEC MF agar, col/100 mL

Field blank

(Stored in NWIS)

Sterile buffered water handled in the same manner as a sample

Assess overall contamination of samples by all sources and causes (field and lab).

One every 10 samples, spread out over sample period

Do not qualify individual environmental samples on the basis of field blanks.

Contact Ohio District if contamination is found

Enter colony count of field blank into QADATA--sample medium is "Q", sample type is "2", parameter code 99100 is "70" for sterile buffered water PO₄/MgCl₂ or "60" for sterile saline buffered water (lot number is not required), parameter code 99101 is "80" for Ocala, parameter code 99102 is "100" for field

Field replicates

(Stored in NWIS)

Split sequential grab sample (two bottles are collected and each bottle is plated twice)

Assess sampling and analytical variability

One every 10 samples, spread out over sample period

Do not qualify individual environmental samples on the basis of field replicates. High variability often is caused by incomplete mixing. Collect an additional set of replicates the next sampling trip if variability is greater than 30 percent.

Contact Ohio District if variability of repeated replicate is greater than 30 percent

Enter colony count of 1st sample in QWDATA--sample medium is "9" for SW, sample type is "7" for replicate, parameter code 99111 is "30" for replicate or "100" for more than 1 type of qc sample, parameter code 99105 is "50" for split sequential

Enter colony count of the 2nd to 4th samples in QADATA--sample medium is "R" for SW, sample type is "7" for replicate, parameter code 99105 is "50" for split sequential

Offset sample times so that splits of the same grab sample are closer in time than splits of different grab samples. For example: 1300, 1301, 1305, and 1306 where 1300 is the 1st environmental sample (grab sample 1, split 1), 1301 is the 2nd sample (grab sample 1, split 2), 1305 is the 3rd sample (grab sample 2, split 1) and 1306 is the 4th sample (grab sample 2, split 2).

Ohio District Microbiology