7 Del. Admin. Code § 7103-36.0

Current through Register Vol. 28, No. 3, September 1, 2024

Section 7103-36.0 - Public Health Protection

36.1 Many wastewater land treatment systems have operated successfully for years without public health problems. However, the public must be educated about the effectiveness of these systems in treating wastewater while minimizing public health hazards. Public health protection sometimes becomes the major issue in choosing land treatment over conventional waste treatment which discharges wastewater to rivers or streams. The EPA design manual (7) has a chapter on "Health and Environmental Effects." The possible health effects considered to be the major ones are presented here.

36.2 The main public health concerns that must be considered in designing and managing land treatment sites are:

36.2.1 microorganisms surviving to enter drinking water, transferred by grazing animals or inhaled in aerosols leading to possible infection or disease

36.2.2 trace elements such as cadmium getting into food chain or drinking water leading to possible toxicity levels

36.2.3 trace organics and synthetic organic compounds getting into drinking water or the food chain leading to possible toxicity levels and carcinogenesis nitrate nitrogen additions to drinking water aquifers leading to potential health problems or methemoglobinemia (blood disorder) in infants.

36.3 Low numbers of pathogenic bacteria and viruses and some intestinal parasites may survive the sewage treatment process and be present in wastewater. Bacteria and viruses are greatly reduced by primary and secondary treatment, but as a general policy, active disinfection is required in Delaware as an additional precaution (see Subsection 303 of these regulations). The Department will determine disinfection requirements for irrigation of wastewater on a case-by-case basis. When "active" disinfection is not proposed by the applicant or consulting engineer, adequate justification must be submitted for consideration.

36.4 The EPA has issued general guidelines for pre-irrigation treatment of municipal wastewater (7) which are less stringent than Delaware's requirements. EPA's general guidelines are listed here as a matter of information:

36.4.1 Primary treatment - acceptable for isolated locations with restricted public access and when limited to crops not for direct human consumption.

36.4.2 Biological treatment by ponds or inplant processes plus control of fecal coliform count to less than 1,000 MPN/100 mL - acceptable for controlled agricultural irrigation except for human food crops to be eaten raw.

36.4.3 Biological treatment by ponds or inplant processes with additional BOD or suspended solids control as needed for aesthetics plus disinfection to log mean of 200/100 mL (EPA fecal coliform criteria for bathing waters) - acceptable for application in public access areas such as parks and golf courses.

36.5 Concerning chlorination for disinfection, trace organics (e.g. trihalomethanes) may be produced when wastewaters containing organic material is chlorinated. More research is needed in this area, but chlorination should be used with caution where drinking water supplies are potentially affected.

36.6 Several measures in addition to disinfection can be used to reduce bacterial and viral exposure through aerosols. These measures include:

operating sprinklers during daylight hours increases the number of microorganisms killed by ultraviolet radiation and drying;

36.7 use of downward-directed, low-pressure sprinklers results in fewer aerosols than upward-directed, high-pressure sprinklers;

36.8 buffer zones may be used to separate the spray source and the general public;

36.9 planting vegetation, particularly trees, around the site in the buffer can reduce the aerosols leaving the site by causing vertical dispersion and trapping.

36.10 Growing vegetables or grazing animals on an actively irrigated land treatment site is generally prohibited because of the potential for transfer of pathogens and intestinal worm eggs (see Subsection 308 of these regulations). Other considerations that prohibit grazing are soil compaction by animals, which affects infiltration rates, and the problem of essentially little net removal of nutrients during grazing. If wastewater applications are terminated, the following precautions are recommended when a wastewater with domestic sources is irrigated:

36.11 Grazing by animals (other than lactating dairy cows) whose products are consumed by humans should be prohibited for at least one month after irrigation ceases.

Grazing by lactating dairy cows should be prohibited for at least one year because of the potential of intestinal worms being transferred into milk by udder contamination.

36.12 Growing vegetables and root crops, which are eaten raw, should be prohibited for at least 18 months.

36.13 For pathogen considerations (when the wastewater contains domestic wastes), hay should not be cut for at least four days after application of disinfected secondary effluent. If the wastewater contains appreciable amounts of synthetic organic compounds or cadmium (or other potentially harmful trace elements), then the forage should be monitored for potential toxicity problems to animals or possible food-chain effects, especially in the case of feeding hay to lactating dairy cows.

36.14 EPA requirements for limiting cadmium application to land (Table 2) and design considerations to prevent nitrate pollution of groundwater have been previously discussed in Chapter 4.

7 Del. Admin. Code § 7103-36.0