5 Groundwater Protection
Groundwater in Delaware is plentiful, and a majority of the state’s citizens use it as drinking water. Groundwater is the sole source of drinking water for approximately 65% of the state’s population, specifically residents south of the Chesapeake and Delaware Canal in southern New Castle, Kent, and Sussex counties. North of the canal, approximately 30% of public water come from groundwater and the remainder from surface water.
Though plentiful, groundwater in Delaware is a vulnerable resource due to geology: the shallow depth to groundwater (typically less than 10 feet in Delaware) and the permeability of the subsurface material. Because of these characteristics, the Delaware Department of Agriculture’s Pesticide Section began monitoring the state’s shallow groundwater for pesticides in 1995. The department monitors a network of just over 100 dedicated monitoring wells and screens samples for pesticides commonly used in agriculture and the commercial industry. While the majority of the wells have tested negative, some pesticides have been detected above reporting levels. Therefore, preventing leaching and protecting wellheads are important aspects of golf course management that help protect drinking water sources.
5.1 Regulatory Considerations
The Ground Water Protection Branch of the Water Supply Section of DNREC is responsible for the groundwater protection program, the source water assessment and protection program, and the wellhead protection program for the state. Responsibilities include regulatory review, resource assessment, database quality control, and public education. The regulatory authority includes the location, design, installation, use, disinfection, modification, repair, and sealing of all wells and associated pumping equipment as well as prescribing certain requirements for the protection of public and private potable water supply wells under Title 7301 Regulations Governing the Construction and Use of Wells.
The Water Allocation Branch of the Water Supply Section of DNREC regulates water withdrawals in the state under Title 7303 Regulations Governing the Allocation of Water. Permits are required for withdrawals greater than 50,000 gallons per day from any surface or groundwater source. If a withdrawal is in the jurisdiction of the Delaware River Basin Commission (DRBC) and will withdraw more than 100,000 gallons per day, a separate approval from the DRBC is also required. All wells in Delaware must be constructed by a well driller or well driver licensed with DNREC. New irrigation ponds require a permit, which can be obtained with an application for a permit to construct a water impoundment.
Permit holders are required to record and report water usage each year. Golf courses must report monthly production for each water facility (well or intake) and a system summary of total monthly production. Other information such as water transfers and leak-losses are also required to be reported. For more information on reporting requirements, see the Water Supply – Water Allocation Branch web page.
Wellhead protection programs restrict land-use activities within protection areas for public drinking water wells. Local ordinances should be reviewed to determine the location of these protected areas and all relevant regulations should be communicated to staff and followed as required.
5.2 Preventing Leaching
Leaching refers to the loss of water-soluble plant nutrients or chemicals from the soil as water moves through the soil profile and reaches the saturated zone. Some of the factors that can influence leaching potential include the depth to groundwater, soil type and structure (e.g. sandy soils), geology, rate of precipitation, and amount of irrigation. Especially in areas with high recharge rates (most of Delaware), irrigation should only be sufficient to reach the root depth. More information on making irrigation decisions can be found in the “Irrigation” chapter of this document.
When applying fertilizers or pesticides, the rate, timing, and location of applications should be considered to minimize the potential for losses due to leaching. Sandy soils, for example, have a low potential to fix phosphorus and therefore are more likely to leach phosphorus. Nitrogen, in the form of nitrate (NO3-N) presents leaching concerns for groundwater quality. Fertilizers with solubility >30 mg/L (or 30 ppm) can pose a risk for leaching.
The potential for pesticides to leach to groundwater depends on many factors, such as those described above. In addition, pesticide properties, such as solubility, influence leaching potential (Table 2). Because of the increased potential for leaching in Delaware due to the state’s high water table and sandy soils, the Delaware Department of Agriculture (DDA)’s Groundwater Monitoring Program has been monitoring for pesticide contamination in groundwater since 1995.
Table 2. Threshold values indicating potential for groundwater contamination by pesticides
|Chemical or Physical Property||Threshold Value|
|Water solubility||Greater than 30 ppm|
|Henry’s Law Constant||Less than lO-2 atm to m-3 mol|
|Kd||Less than 5, usually less than 1 or 2|
|Koc (Soil Adsorption)||Less than 300 to 500|
|Hydrolysis half-life||More than 25 weeks|
|Photolysis half-life||More than 1 week|
|Field dissipation half-life||More than three weeks|
Source: USEPA, 1986, Pesticides in Groundwater
5.3 Protecting Water Supplies
The Source Water Assessment and Protection Program (SWAPP) delineates the wellhead protection areas for all public wells in Delaware and posts them to FirstMap Delaware. Within wellhead protection areas, land-use activities are restricted that could otherwise adversely affect the quantity or quality of groundwater moving toward the wells or well fields. Superintendents should also be aware of any local ordinances that restrict land-use activities in these areas.
Before installing new wells, DNREC and the local regulatory authority should be contacted to determine permitting and any setback requirements. The Delaware SWAPP will meet with applicants to do a preliminary site review to look at well placement with respect to any identified potential sources of contamination that may be in the area (if requested). New wells should be located up-gradient as far as possible from potential pollutant sources, such as petroleum storage tanks, septic tanks, chemical mixing areas, and fertilizer storage facilities. Most pesticide labels now prohibit mixing/loading pesticides within 50 feet (or other specified setback distances) from any well. Pesticide users are required by federal law to follow all restrictions on the pesticide label; users must read the label to determine what restrictions, if any, are in place regarding mixing/loading and applying pesticides around wellheads. Licensed water-well contractors are needed to drill new wells, which must meet regulatory and code requirements.
5.4 Groundwater Protection Best Management Practices
Preventing Leaching Best Management Practices
- Identify areas on the course that may be prone to leaching (shallow depth to groundwater, sandy soils, etc.)
- Manage irrigation to avoid over-watering.
- Consider the potential for fertilizers or pesticides to leach before applying.
Wellhead Protection Best Management Practices
- Use backflow-prevention devices at the wellhead, on hoses, and at the pesticide mix/load station to prevent contamination of water sources.
- Follow pesticide labels for setback distance requirements (typically a minimum of 50 feet).
- Properly decommission illegal, abandoned, or flowing wells.
- Surround new wells with bollards or a physical barrier to prevent impacts to the wellhead.
- Inspect wellheads and the well casing routinely for leaks or cracks; make repairs as needed.
- Maintain records of new well construction and modifications to existing wells.
- Obtain a copy of the well log for each well to determine the local geology and the well’s depth; these factors will have a bearing on how vulnerable the well is to contamination.
- Develop a written plan that minimizes environmental risk and potential contamination to wellheads.