Drexel, Missouri – Summary of Notification and Response to Safe Drinking 

Water Act (SDWA) Atrazine Sample Result from Finished Water Sample 

Collected May 26, 2010

Sample Collection and Reporting

A routine finished water sample taken for SDWA compliance was collected at the Drexel, MO 

CWS on May 26, 2010. The result of the analysis (31.2 ppb atrazine) was reported to MO Department of 

Natural Resources (MO DNR) about 1 PM CST on July 23, 2010. Shortly thereafter, the MO DNR notified 

the Missouri Department of Health and Senior Services (MO DHSS) of this finding. In response, a MO 

DNR public notice was issued about 6:30 PM CST reporting this detection. This notice also included the 

following text: “The Department of Health and Senior Services does not expect to see any significant 

acute health effects as a result of this monitoring spike. The Missouri Department of Health and Senior 

Services recommends neither using the water for drinking nor using it to cook, wash dishes or make 

ice.” Syngenta first became aware of this detection through this public notice the evening of June 23.

Syngenta Follow-Up with MO DNR and MO DHSS

On Thursday, June 24, Syngenta contacted the MO DNR for additional information regarding the 

atrazine detection. We were told that MO DNR had sent someone to Drexel to collect additional 

compliance samples on June 23 and June 24. In addition, the CWS was also provided with sample kits 

for each day the week beginning June 28. The results from the June 24 test were expected to be 

available as soon as Friday (June 25). We also learned the “do not drink” recommendation from MO 

DHSS was taken from an Agency for Toxic Substances and Disease Registry (ATSDR) Environmental 

Media Evaluation Guide (EMEG) value of 30 ppb atrazine based on a child’s body weight and water 

consumption. This value is more than three times lower than the 100 ppb EPA Office of Water (EPAOW) one-day and ten-day Health Advisory Level (HAL) for atrazine, which is also based on a child’s body 

weight and water consumption. The ATSDR EMEG is approximately 10 fold lower than the 298 ppb 

DWLOC published by EPA Office of Pesticide Programs. From a review of the ATSDR Minimum Risk 

Levels (MRL) worksheets, the difference is due to an extra three-fold uncertainty factor that has been 

applied in the derivation of the 30 ppb ATSDR intermediate term exposure value from the EPA-OW HAL 

of 100 ppb (both use a 1 mg/kg/day reference dose). This is the first instance we are aware of in which 

these ATSDR value has been used by a CWS. In Appendix A of the ATSDR Toxicological Profile for 

Atrazine, the following disclaimer is given: “It is important to note that MRLs are not intended to define 

clean-up or action levels.” Therefore, this value of 30 ppb should not have been used by the Drexel 

CWS.

On Friday, June 25, Syngenta contacted the MO DHSS to discuss the atrazine detection and 

health advisory notice for the city of Drexel. Prior to the meeting we had provided to MO DNR and MO 

DHSS copies of the EPA-OW documents and Syngenta summaries, of atrazine HALs and Maximum 

Contaminant Level (MCL) for atrazine in drinking water. We explained that the monitoring result did not 

show that any EPA-OW HALs had been exceeded for children or adults. Since the EPA short-term HAL 

had not been exceeded, a recommendation to not use the water for drinking, cooking, dishwashing or 
ice-making was not justified. Syngenta requested, and has since received, the atrazine ATSDR

documentation from MO DHSS. 

MO DNR Confirmatory and Atrazine Monitoring Program (AMP) Results for Drexel CWS

On Friday afternoon (June 25, 7 PM CST) the results of the confirmatory sample taken and the 

Drexel CWS on June 24 were reported as 0.36 ppb atrazine in finished water. Within a couple of hours 

MO DNR issued a public notice with these results and that the water use restrictions had been lifted. 

This notice also reiterated the following: “The department has been working with the Drexel Public 

Water Supply on compliance issues for several years. The Drexel water system is currently constructing 

a connection to the Tri-County Water Authority in Independence. The water system has signed an 

agreement to begin purchasing water from Tri-County by the end of the year.” Based on our own 

conversations with MO DNR, historic compliance issues include high turbidity and non-compliance with 

Total Trihalomethanes (TTHMs), a disinfection byproduct. 

The 2010 results from Syngenta’s Atrazine Monitoring Program (AMP) available to date are

shown below:

Sample Collection 

Date

Raw Water 

Atrazine (ppb)

Finished Water 

Atrazine (ppb)

SDWA Finished Water 

Atrazine (ppb)

11-Jan-10 0.80 0.70 ---

9-Feb-10 0.56 0.55 ---

22-Feb-10 0.37 0.46 ---

8-Mar-10 0.41 0.42 ---

22-Mar-10 0.49 0.39 ---

7-Apr-10 0.28 0.26 ---

10-Apr-10 0.27 0.28 ---

28-Apr-10 29.72 23.57 ---

3-May-10 28.88 26.81 ---

10-May-10 30.99 29.57 ---

17-May-10 30.67 29.57 ---

24-May-10 23.10 27.44 ---

26-May-10 --- --- 31.2

1-Jun-10 0.13 0.67 ---

24-Jun-10 --- --- 0.36

Historical Monitoring and Current Investigation

The Drexel CWS has been participating in the AMP since April 2006 and also participated in the 

Syngenta Voluntary Monitoring Program (VMP) from February 1995 to December 1991. From April 

2006 through April 10, 2010, no individual sample (AMP) had exceeded 3.04 ppb in raw water or 2.77 

ppb in finished water, until April 28 of this year. In the VMP program, the highest single sample values 

occurred in May 1998, with atrazine concentrations of 14 ppb and 12 ppb, in raw and finished water 

respectively. The next highest VMP atrazine concentrations were 4.32 ppb (raw) and 3.40 ppb 
(finished). Therefore, the recent measurements are extremely uncharacteristic of this CWS and 

watershed. Through phone calls and personal visits, Syngenta is currently engaged with the CWS, local 

officials, a local chemical retailer and growers in the watershed to further investigate this unusual result.

The raw water source for the Drexel CWS is Drexel Lake. This approximately 40-45 acre lake has

a watershed area of 534 acres. At full pool storage, this lake holds 345.1 acre-feet of water. The 

average water use by the CWS is approximately 102,000 gallons/day. As stated earlier, the Drexel CWS 

is slated to be decommissioned and the city will begin purchasing finished water from Tri-County Water 

Authority in Independence by the end of this year or early 2011.