STATUS Total Maximum Daily Load Progress Report Chollas Creek Watershed Diazinon TMDL

Total Maximum Daily Load Progress Report
Regional Water Board
San Diego, Region 9
Beneficial uses affected:
Pollutant(s) addressed:
Implemented through:
Approval date:
WARM, WILD
Diazinon
NPDES Permit, MS4 Permits
November 3, 2003
Chollas Creek Watershed Diazinon TMDL
 Conditions Improving
STATUS
 Data Inconclusive
 Improvement Needed
 TMDL Achieved/Waterbody Delisted
TMDL Summary
Storm water in Chollas Creek at station SD8(1) showed sublethal toxicity on water fleas (87%) and fathead minnows
(67%) in biological toxicity tests. Toxicity identification
evaluation (TIE) results indicated that the insecticide
diazinon had caused the toxicity to the water flea. The
Chollas Creek Watershed TMDL for Diazinon was adopted
by the San Diego Regional Water Board on August 14, 2002
and approved by the U.S. EPA in November 2003.
The TMDL is implemented through the municipal storm
water permit, which requires actions to be taken to reduce
diazinon entering the creek. U.S. EPA banned the sale of
diazinon for non-agricultural outdoor uses effective
December 31, 2004. Diazinon levels in Chollas Creek have
declined markedly.
Chollas Creek Watershed
TMDL Waste Load Allocations/Load Allocations
Water Quality Outcomes
 Water quality data show significant reductions in
diazinon loading from San Diego’s municipal storm water
conveyance system.
Both WLAs and LAs for point and nonpoint sources are
concentration-based, equal to 90% of the Numeric Target*
value after applying 10% of Margin of Safety:
Acute WLA/LA = 0.072 μg/L ; Chronic WLA/LA = 0.045 μg/L
*For the Chollas Creek diazinon TMDL the Regional Board has set the
numeric targets equal to the California Department of Fish and
Game (CDFG) Water Quality Criteria for the protection of freshwater
aquatic organisms from diazinon (Menconi and Cox 1994). The
acute Water Quality Criterion protects aquatic life from short-term
exposure to diazinon, while the chronic criterion protects aquatic
life from long-term diazinon exposure.
 Diazinon concentrations at monitoring station SD8 (1)
have been meeting the WLA/LA since December 2007
(8 consecutive sampling events).
 Diazinon concentrations at station DPR2, on the south
fork of the creek, have been meeting the WLA/LA since
February 2005 (17 consecutive sampling events).
 Continue monitoring for TMDL achievement/delisting.
1.2
1
0.8
0.6
0.4
0.2
0
Diazinon WQO and Acute WLA
(0.08 and 0.072 ug/l)
Diazinon Chronic WLA
(0.045 ug/l)
Retail Sales for indoor use ends
(12/2002)
Diazinon manufacturing stops;
retail sales for lawn/garden care
ends (8/2003)
Diazinon is no longer available
for purchase (1/2005)
11/8/1998
1/25/1999
3/15/1999
2/12/2000
2/21/2000
3/5/2000
10/27/2000
1/8/2001
2/13/2001
2/23/2001
11/12/2001
11/29/2001
2/17/2002
3/8/2002
11/8/2002
2/11/2003
2/25/2003
2/3/2004
2/18/2004
3/2/2004
10/17/2004
2/11/2005
2/18/2005
10/18/2005
1/2/2006
2/19/2006
10/14/2006
12/10/2006
2/19/2007
11/30/2007
12/7/2007
2/3/2008
10/5/2008
11/4//2008
2/6/2008
11/4/2008
12/7/2009
2/6/2010
Diazinon Concentration (ug/L)
Chollas Creek Water Quality at Chollas Creek Site SD8 (1)
Updated September 2011