The clock is ticking, and the “numeric target” for Total Maximum Daily Loads (TMDL) for two organophosphate insecticides will be finalized within 10 months. June 30, 2002 may still seem a ways off. But the effort to develop practical mitigation measures or best management practices has been under review by CAFA for more than a year to help growers reduce irrigation runoff and OP levels in natural waterways to comply with the Federal Clean Water Act.

The TMDL issue affects diazinon and for alfalfa the widely used chlorpyrifos (Lorsban, Lock On). The Central Valley Regional Water Quality Control board has identified the Sacramento and Feather Rivers as being “impaired” due to diazinon. The San Joaquin River and the Sacramento-San Joaquin River Delta are identified as being impaired due to both chlorpyrifos and diazinon. It's a complicated issue in view of farm and non-farm organophosphate use.

In June, a Regional Water Quality Control Board workshop in Modesto offered a look at the challenges that lay ahead. Based on current information, the Regional Board revealed that the “acceptable chlorpyrifos level would be somewhere between zero and the target derived by the California Department of Fish and Game: 14 ng/L(nanograms/liter) 4-day average, and 25/ng/L 1-hour average.”

The target will apply to the main stem rivers and main channels of the Delta.

While several factors will be used to decide the final numeric target, the bottom line is that CAFA and growers have a lot of work to do between now and next June to sort out best management practices.

To put things in perspective, the numeric target will boil down to parts per trillion. One part per trillion translates to approximately one drop in about 43-acre feet of water. CAFA Chairman, Tom Ellis of Grimes did the math and had his figures checked through UC Irrigation Specialist Blaine Hanson.

Ellis started by working on the assumption that one drop in 14 gallons of water is equal to one part per million. The final calculation surprised him in that only one drop in 14 million gallons of water (43 acre feet) is the equivalent of one part per trillion. In checking out the math, Hanson agreed that Ellis' conclusion was a realistic figure assuming that a chemical's density is close to the density of water.

Hanson noted that “it doesn't take much of a chemical to result in a detection level.” On the other hand, he offered a positive outlook by saying that runoff can be eliminated if an irrigation system is properly designed and managed.

The effort to supply growers with practical measures for controlling surface water runoff is being spearheaded by CAFA board members, Dan Putnam, UC Extension agronomist, and Jesse Richardson of Dow AgroSciences. Alfalfa growers, UC scientists and industry representatives have contributed to the effort. A wide range of best management practices has been developed to take into account different conditions and grower practices. “Although CAFA wants to be proactive, there is concern about monitoring and how improvement can be demonstrated when so many sources are implicated,” points out Putnam.

When the final list of mitigation measures are released, they'll be disseminated in a variety of ways and published in this column. It's clear, however, that it will take a cooperative effort from growers to help meet the numeric target of Total Maximum Daily Loads for chlorpyrifos. Meeting the goal set by the Regional Water Quality Control Board will avoid having restrictions placed on one of alfalfa's most important insect control tools.