Yolo County Municipal Code Art. 10 Standards, Criteria, and Regulations for Wells

All wells regulated by this chapter shall be constructed, reconstructed, repaired, abandoned, or changed in use only in accordance with the standards and criteria set forth in this chapter. (§ 1, Ord. 765, eff. October 7, 1976; as amended by § 3, Ord. 1470, eff. July 14, 2016)

Wells left unattended during or awaiting reconstruction, repair, or abandonment shall be temporarily sealed to prevent the inflow of surface materials or access from the surface. (§ 1, Ord. 765, eff. October 7, 1976; as amended by § 3, Ord. 1470, eff. July 14, 2016)

No person required to be licensed in accordance with the provisions of the Contractors License Law (Chapter 9 of Division 3 of the Business and Professions Code of the State) shall be issued a permit unless he has a valid contractor's license of the proper class issued in accordance with the Contractors License Law. (§ 1, Ord. 765, eff. October 7, 1976; as amended by § 3, Ord. 1470, eff. July 14, 2016)

(a) All water supply wells shall be located a safe distance from potential sources of contamination and pollution.

(b) No water supply well shall be located within the minimum distances from the features specified in Table No. 3 set forth in Section 6-8.1005 of this article.

(c) No irrigation well shall be located within the minimum distances from other wells specified in Table No. 4 set forth in Section 6-8.1005 of this article unless exempt from Table No. 4 as provided in Section 6-8.1005 of this article. The County requires minimum well separation distances for ensuring proposed new irrigation wells or irrigation well alterations are unlikely to interfere with the function and operation of nearby wells. Table No. 4, below, presents these minimum required distances from nearby active wells, excluding wells to be abandoned upon completion of the new replacement well if applicable, according to the proposed well pumping capacity and proposed well location in relation to Valley Floor or Upland areas. The minimum well separation distances in Table No. 4 were developed with consideration of the hydrogeologic and well characteristics within the County.

(d) The location of each water supply well for which an application is made shall be approved by the Enforcement Officer. (§ 1, Ord. 765, eff. October 7, 1976; as amended by § 3, Ord. 1470, eff. July 14, 2016; as amended by § 2, Ord. 1579, eff. December 4, 2025)

(a) Table No. 3, referred to in Section 6-8.1004(b) of this article, is set forth as follows:

TABLE NO. 3

Water Supply Well Spacing (Feet)

(b) Table No. 4, referred to in Section 6-8.1004(c) of this article, is set forth as follows:

TABLE NO. 4

Irrigation Well Spacing (Feet) from Other Wells

Note: For Delineation of Valley Floor Areas and Upland Areas, refer to Graph 1.

Graph 1: Map of Groundwater Subbasins Overlapping Yolo County with Delineation of Valley

[Figure]

For all irrigation wells, as defined in Section 6-8.422(a)(5) of this chapter, but excluding minor modifications to existing irrigation wells, the applicant must submit a map and list of known active wells within a radial distance equal to the minimum separation distance set forth in Table No. 4, plus 500 feet. The map should include the proposed well site with known nearby active domestic, public supply, agricultural/irrigation, industrial, or other groundwater production wells. Active wells include wells recently operated (within last five years) as production wells and equipped with an operational pumping and discharge assembly, or wells in the process of being prepared to be operated. The table listing known nearby wells must include the well type, latitude/longitude coordinates, distance from the proposed well site (in feet), and Assessor’s Parcel Number (APN). Any wells owned by the applicant should be indicated on the map and list of nearby wells. The Enforcement Oficer will review the information on nearby wells provided by the applicant in conjunction with additional review of available well location information from the Division of Environmental Health’s database to confirm the minimum well separation is satisfied. However, it is the responsibility of the permit applicant to investigate and confirm the accuracy and completeness of the list of nearby wells.

(c) Exceptions to Table No. 4 separation distance requirements. For purposes of Table No. 4 , an irrigation well does not include:

(1) Minor modifications. Minor modifications to existing irrigation wells that do not increase the discharge rate for the well or significantly alter the depth interval from which groundwater is extracted with the well. Minor modifications may include activities such as installing casing liners, patches, or other work although such work must not modify the well in a manner that increases the total groundwater pumping capacity.

(2) Common ownership exception. Existing wells owned by the applicant that are located on the same parcel as the proposed well or on a parcel adjacent to the parcel with the proposed irrigation well are exempt from the minimum well separation distance requirements set forth in Table No. 4 .

(3) Irrigation wells supported by a hydrogeologist report as set forth in Section 6-8.1012 of this article.

(§ 1, Ord. 765, eff. October 7, 1976, as amended by § 7, Ord. 1015, eff. August 15, 1985; as amended by § 3, Ord. 1470, eff. July 14, 2016; as amended by § 2, Ord. 1579, eff. December 4, 2025)

(a) Except as otherwise provided in this section, all wells shall be cased using casing materials and installation methods in accordance with Sections 12A and B of California DWR Bulletin 74, Water Well Standards.

(b) The Enforcement Officer may approve, with the recommendation of the Technical Advisory Committee, new casing materials which may be developed in the future using new and improved technology.

(c) The uppermost perforations in casings shall not be above the depths specified in Section 6-8.1008 of this article.

(d) Wells may be constructed with a permanent conductor or outer casing, and, if so, there shall be at least two (2") inches of uniform annular space between the conductor and the hole for wells requiring a suffice seal. The inner, or production, casing may be of any size adequate for design production rates. Perforations may be located in the inner casing or in a liner of smaller diameter and suspended from the casing.

(e) Wells may be constructed with a single, or production, casing, and, if so, there shall be at least two (2") inches of uniform annular space between the casing and the hole for wells requiring a surface seal. Perforations may be located in the casing below the surface seal or in a liner of smaller diameter and hung from the casing. Excepted from this requirement is the cable tool drilling method when the drive shoe annulus is sealed in accordance with Section 6-8.1007 of this article. (§ 1, Ord. 765, eff. October 7, 1976, as amended by § 15, Ord. 811, eff. July 27, 1978; as amended by § 3, Ord. 1470, eff. July 14, 2016)

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The annular space between the drilled hole and the outermost casing shall be sealed to the depths specified in Section 6-8.1008 of this article as follows:

(a) Using neat cement, cement grout, or concrete with an aggregate size not to exceed three-eighths (3/8") inch; or

(b) Using puddled clay mixed with clean materials supplied for preparing clay-base mixtures; or

(c) Using bentonide when drying conditions are not present. When a drilling method does not provide a two (2") inch annulus, the drive shoe annulus shall be maintained full of bentonide slurry during the advancement of the casing through the depth of the required seal. The surface seal shall be maintained through the completion of the well.

(d) Such sealing materials shall be placed in one continuous operation with the displacement from the bottom to the top of the interval to be sealed.

(e) Any well deeper than 1,000 feet and which penetrates two (2) or more distinct aquifers shall have a minimum fifty (50') foot annular seal placed in the confining materials between each two (2) aquifers. The installation of such seals will be based on the interpretation of the well log by the Enforcement Officer and the well driller or owner. (§ 1, Ord. 765, eff. October 7, 1976, as amended by § 16, Ord. 811, eff. July 27, 1978; as amended by § 3, Ord. 1470, eff. July 14, 2016)

All wells regulated by this chapter shall be sealed to the following minimum depths:

Type of Well Depth of Seal (Feet)

Individual domestic 20

Public or community domestic 50

Irrigation 20

Monitoring 20

All other 40

Notwithstanding the table set forth in this section, the Health Officer may alter the required depth of the annular seal when adverse or special conditions warrant. (§ 1, Ord. 765, eff. October 7, 1976, as amended by § 8, Ord. 1015, eff. August 15, 1985; as amended by § 3, Ord. 1470, eff. July 14, 2016)

All wells governed and regulated by this chapter shall be constructed only in accordance with the following standards and criteria:

(a) All wells shall be constructed with a concrete base, at least three (3') feet in diameter or three (3') feet square and six (6") inches in thickness, poured to a finished grade at least three (3") inches above the ground surface, with the top of the casing extending at least one-half (1/2") inch through the concrete base.

(b) Domestic water supply wells shall be constructed with no less than an eighteen (18") inch pump pedestal and a casing vent.

(c) The construction of well pits shall be prohibited.

(d) All openings, other than required vents, at the top of a well shall be capped or equipped with watertight seals.

(e) All vents shall be open, with the opening facing ground level, and screened.

(f) If a pump motor is to be mounted over the well, a watertight seal shall be placed between the pump head and base, or between the pump head and production casing.

(g) If an offset surface pump or submersible pump is used, or if any wires or piping enter the well, watertight seals shall be placed around such openings.

(h) All pumping equipment shall be installed with protective devices to effectively prevent the entrance of foreign matter for back siphonage into the well casing. A properly designed air gap may be considered an acceptable protective device for agricultural wells. No person shall install any equipment or mechanism, or use any water-treating chemical or substance, if it is found that such equipment, mechanism, chemical, or substance may cause pollution or contamination of the groundwater supply. Such equipment or mechanism may be permitted only equipped with an approved backflow prevention device. (§ 1, Ord. 765, eff. October 7, 1976, as amended by § 9, Ord. 1015, eff. August 15, 1985; as amended by § 3, Ord. 1470, eff. July 14, 2016)

The following types of wells shall be disinfected using the conventional and acceptable methods at the time of the construction, reconstruction, or reconditioning and prior to the well being used or placed in service:

(a) Water supply wells, except irrigation wells; and

(b) Recharge and injection wells.

All gravel added to any well shall be adequately disinfected prior to, or during, placement in the well.

Water used for the drilling of domestic water supply wells shall be secured from a potable source or another groundwater well. For irrigation wells, the water used for drilling shall be clean water, not obviously polluted, and shall be of a quality which is adequate to support marine life, especially fish. (§ 1, Ord. 765, eff. October 7, 1976, as amended by § 17, Ord. 811, eff. July 27, 1978; as amended by § 3, Ord. 1470, eff. July 14, 2016)

Abandoned wells shall be destroyed within 120 days after notification by the Enforcement Officer that it has been established that the well is abandoned and directing that the well be destroyed. The destruction shall be done by the owner thereof in the following manner:

(a) The well shall be filled with silt, clay, neat cement, cement grout, or concrete to approximately twenty (20') feet from the surface. For gravel envelope wells, additional measures for sealing may be directed where the commingling of water from the various strata may be a problem.

(b) Neat cement, cement grout, or concrete shall be placed from approximately twenty (20') feet to within ten (10') feet, and not higher than three (3') feet, from the surface.

(c) The top three (3') feet to ten (10') feet of the well shall be cut off and a plate welded or sealed on the stub.

(d) The excavation shall be backfilled with native material. (§ 1, Ord. 765, eff. October 7, 1976, as amended by § 10, Ord. 1015, eff. August 15, 1985; as amended by § 3, Ord. 1470, eff. July 14, 2016)

All wells shall be constructed, reconstructed, repaired, or abandoned in accordance with the standards and criteria set forth in this article and the following exceptions:

(a) Exploratory wells and test holes. Unless the owner or constructor completes or changes in use the exploratory well or test hole to another type of well:

(1) The location or site of the exploratory well shall not be limited.

(2) Casings shall not be required.

(3) Subsurface seals shall not be required.

(4) Exploratory wells and test holes shall be abandoned within fourteen (14) days after the completion of the test work.

(b) Recharge or injection wells. Samples of water shall be taken and compared to the proposed recharge or injection water for compatibility by the Enforcement Officer.

(c) Electrolytic protection wells.

(1) A vent pipe may be substituted for casing.

(2) Failed electrolytic protection wells shall be abandoned within 120 days after notification by the Enforcement Officer that it has been established that the well has failed and directing that the well be abandoned.

(d) Drainage, dewatering, and slope stability wells. Licensed drillers shall not be required for the construction of drainage, dewatering, and slope stability wells.

(e) Irrigation wells supported by hydrogeologist report. Irrigation wells are not required to comply with the well spacing requirements in Table No. 4 set forth in Section 6-8.1005 of this article if the application is supported by a report prepared by a licensed professional geologist or hydrogeologist approved by the Enforcement Officer. Such a report must include a map and list of known wells within the appropriate separation distance demonstrated in the report, plus an additional 500 feet. The report must also include technical analyses and justification for why the proposed separation distance is unlikely to impact the function and operation of nearby wells. (§ 1, Ord. 765, eff. October 7, 1976; as amended by § 3, Ord. 1470, eff. July 14, 2016; as amended by § 2, Ord. 1579, eff. December 4, 2025)

(a) The Groundwater Sustainability Agencies (GSA) within each of the three subbasins in Yolo County are responsible for implementing the groundwater sustainability plans (GSP) covering their jurisdiction and managing groundwater in a manner that is consistent with the GSP. The GSPs have defined sustainable management criteria including minimum thresholds, measurable objectives, and undesirable results for all applicable sustainability indicators. The GSAs in the three subbasins have the authority and responsibility to ensure groundwater management is sustainable in the subbasins and undesirable results are avoided. Accordingly, the Enforcement Officer will submit all irrigation well permit applications to the applicable GSA for review and verification in accordance with the review procedures of the pertinent GSA to determine whether the proposed well is consistent with the adopted GSP. Applicants must comply with all applicable verification requirements of the applicable GSA. Most of the County is within the Yolo Subbasin and well permits in the Yolo Subbasin will be referred to the YSGA for evaluation. If the applicable GSA includes best management or other proposed or recommended conditions for the well as part of its written verification, the Enforcement Office shall include those items as required conditions of the irrigation well permit. No irrigation well shall be approved without written verification from the applicable GSA.

(b) Exceptions. The GSA verification requirements shall only apply to new irrigation wells as defined in Section 6-8.422(a)(5) of this chapter and shall exclude other water supply wells and minor modifications of irrigation wells exempt from the well separation distances set forth in Table No. 4 of Section 6-8.1005 of this article. (§ 2, Ord. 1579, eff. December 4, 2025)