| City
Services : Water & Utilities : Water : Biosolids Program
| What Are Biosolids?
Biosolids are byproducts of wastewater treatment. They
are organic treated wastewater materials that are suitable for
recycling as a soil amendment. The difference between biosolids
and sewage sludge is that sewage sludge is untreated solids and
in this form cannot be beneficially recycled as a soil amendment.
The EPA regulates and encourages the recycling of biosolids on
crop or range land because they contain nutrients and organic matter
that can improve plant production and enhance soil physical conditions.
Beneficial nutrients in biosolids include nitrogen, phosphorus,
potassium, zinc and iron. The organic matter present in biosolids
improves soil quality by improving water holding capacity and soil
structure. Land application of biosolids can ultimately decrease
topsoil erosion.
What Are the Federal Requirements?
In 1993, the Environmental Protection Agency (EPA)
set forth requirements for management of biosolids. Known as the
503 Rule, it encourages the beneficial reuse of biosolids, as opposed
to disposal in a landfill or incineration, and establishes strict
standards under which wastewater byproducts can and cannot be beneficially
recycled as soil amendments. Central to the rule is EPA's determination
that biosolids are an important resource that can and should be
safely recycled. The safe recycling of biosolids means adherence
to standards that protect public health and the environment. The
503 Rule includes standards for pathogen (disease causing microorganisms)
destruction and for levels of metals. It also governs the stability
of the materials by reducing the attraction of vectors, agricultural
practices, site restrictions, and crop harvesting restrictions.
How Does the City of Laramie Meet the 503 Rule?
The Laramie Wastewater Treatment Plant is permitted
by the EPA to recycle its biosolids via land application. The biosolids
are thereby put to beneficial use as it is used as a soil amendment
to enhance the growth and production of alfalfa and rangeland soils.
Table 1 below outlines the 503 Rule requirements and how the City
of Laramie Biosolids Program meets the requirements:
Table 1
Requirement
|
How
The Requirement Is Met.
|
|
Pathogen
Destruction --
Fecal
coliforms must be
< 2,000,000
colonies/gram |
Sludge
is aerobically digested for 20 days and then dried at a depth
of 9 inches for a minimum of 3 months. Sampling results indicate
the biosolids average 10 - 8000 colonies/gram.
|
|
Metals
Limitations |
The
levels of metals are controlled via the Industrial Pretreatment
Program, which regulates the amounts of metals that can be
discharged by local businesses to the sewer system. Sampling
results indicate that the biosolids are significantly below
the metals limitations. See Table 2 for the metals limitations. |
|
Vector
Reduction |
In
addition to the digestion requirement noted above, the mass
ofvolatile solids is reduced by a minimum of 38% prior to
land application.
|
|
Site
Restrictions |
- Feed
crops are not harvested from the application site for 30
days after application.
- Animals
are not allowed to graze on the application site for 30
days after applications.
- Public
access is restricted for 30 days.
- Biosolids
are not applied to frozen, ice-covered or snow covered
sites where the slope exceeds 6%.
|
Groundwater Restrictions -- Applications must not contaminate
groundwater and therefore must
not exceed the agronomic rate for
available nitrogen of the crops
grown on the site.
|
- Biosolids
are not applied to a site where the high groundwater level
is within 5 feet of the surface.
- Biosolids
are applied at the time of year where vegetation nutrient
uptake is at its greatest.
|
Surface Water Restrictions --
Applications must not cause a
violation of any water quality
standard from the discharge of
surface runoff. Applications
cannot occur within 10 meters
or less of surface waters,
including wetland sites.
|
The
application sites are not in the vicinity of any surface
water except
for a single wetland site near the rangeland application
site. Applications
do not occur within 10 meters or less of this wetland.
|
|
Endangered
Species --
Application
must not adversely affect threatened or endangered species
or critical habitat. |
Application
to land that is subject to normal tillage, cropping and grazing
practices or other activities that turn the soil and impact
vegetation is not considered to adversely affect threatened
or endangered species or critical habitat. |
Table 2
Metals
Limitations
|
Metals
Results
|
|
Pollutant
|
Daily
Max
Mg/kg |
Cumulative
Loading
Kg/Ha |
Daily
Max
Mg/kg |
Cumulative
Loading
Kg/Ha |
|
Total
Arsenic |
75 |
41 |
4.0 |
2.2 |
|
Total
Cadmium |
85 |
39 |
5.4 |
3.4 |
|
Total
Copper |
4300 |
1500 |
794 |
541.6 |
|
Total
Lead |
840 |
300 |
83.0 |
48.2 |
|
Total
Mercury |
57 |
17 |
5.63 |
2.8 |
|
Total
Molybdenum |
75 |
N/A |
18.4 |
9.2 |
|
Total
Nickel |
420 |
420 |
24.0 |
15.2 |
|
Total
Selenium |
100 |
100 |
14.2 |
9.4 |
|
Total
Zinc |
7500 |
2800 |
626 |
425.9 |
How
Much Biosolids Does The City of Laramie Produce, Where Are
They Applied and How Often?
The
Wastewater Treatment Plant generates approximately 450 dry metric
tons of biosolids annually and applies the biosolids to 734 acres
of rangeland located on the city-owned Monolith Ranch. The range
land is located approximately 7 miles south of Laramie, on the
east side of Highway 287. The City's biosolids permit also allows
application on 234 acres of alfalfa cropland, alos on the MOnolith
Ranch, approximately 2 miles south and 3 miles west of Laramie.
The City has not yet applied biosolids to the alfalfa site. Biosolids
are generally applied in late spirng and early fall.
Inspections
and Follow Up of Application Sites
Soil
samples are collected for the top one-foot of soil at the application
sites in order to calculate new agronomic application rates prior
to application. Nitrate movement is monitored annually in order
to plan for future and continued applications. |
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