California has measures in place to protect groundwater. This requires that no listed pre-emergent stay 100 feet away from wellheads, use “well-safe” herbicides, or ensure that a berm is in place around the wellhead. This is an issue that must be addressed. The Tuolumne County Road Department got cited for violation of this a few years back. So it’s serious. This is not limited to wellheads on your own property. The law is 100 feet, so if your neighbor has a wellhead within 100 feet of where you want us to spray, we need to know that too.

There are some pre-emergent herbicides that are allowed for use near unprotected wellheads:

  • Oxyfluorfen Goal
  • Pendimethalin Pendulum, Prowl
  • Prodiamine Barricide
  • Flumioxazin Chateau, Payload

These are excellent pre-emergent herbicides, but they are not sufficient to always give a high, let alone acceptable, level of control across the wide range of herbicide-resistant weed species we encounter. If these materials are used, we may need to do a followup, chargeable, spray to control any escapes.

That takes us to creating berms. The goal of a berm is to stop runoff water from entering the wellhead. On sloped ground, it’s sufficient to have the berm on the uphill side, only. On level ground, the berm needs to be completely around the wellhead. This image, from a County of Sonoma webpage, is among the best I have seen.

There is no height specifications given, but it should work under all reasonable weather conditions.

We can discuss this issue with you. Please call us if you have questions.

Here are some references.

Pesticides labeled for agricultural, outdoor institutional or outdoor industrial use that contain any of the following chemicals are designated as having the potential to pollute ground water: Groundwater Protection List

6609. Wellhead Protection

(a) Except as provided in subsection (b), the following activities shall be prohibited within 100 feet of a well (including domestic, municipal, agricultural, dry or drainage, monitoring, or abandoned wells)

(1) mixing, loading, and storage of pesticides.
(2) rinsing of spray equipment or pesticide containers.
(3) maintenance of spray equipment that could result in spillage of pesticide residues on the soil.
(4) application of preemergent herbicides. 

(b) Wells shall not be subject to the requirements in (a) if they are:

(1) sited so that runoff water from irrigation or rainfall does not move from the perimeter of the wellhead toward the wellhead and contact or collect around any part of the wellhead including the concrete pad or foundation; or

(2) protected by a berm constructed of any material sufficient to prevents movement of surface runoff water from the perimeter of the wellhead to the wellhead.

(c) Application of preemergent herbicides shall be prohibited between the berm and the wellhead.