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Catastrophic Mortality, Large Animal Disposal, Trench

State of Connecticut

Definition

Catastrophic Mortality, Large Animal Disposal, Trench is a method of disposing of large volumes of dead animals by placing the carcasses in successive layers in an excavated trench, a long deep hole dug in the ground. The carcasses are spread, compacted, and covered daily with a thin layer of soil that is excavated from the trench. When the trench is full and has reached grade level, a final cover of soil material at least 2 feet thick is placed over the trench area to form a mound.

Summary

This interpretation is a guide for identifying potential disposal sites for burying large volumes of deceased animals in a trench due to disease or catastrophic natural disasters. This guidance applies to all catastrophic animal mortality events that may occur within the state of Connecticut. In the event of an unexpected disaster, the Connecticut NRCS maintains a listing of suitability for Catastrophic Mortality, Large Animal Disposal, Trench by soil component. This list can be accessed through the Soil Data Mart or viewed on a map using the Web Soil Survey at http://soils.usda.gov/.

Ratings

Ratings are based on soil properties and qualities to the depth normally observed during soil mapping which is 200 cm (80 inches). The interpretive rating assigned is the maximum rating indices for one or more of the soil properties that comprise the Catastrophic Mortality, Large Animal Disposal, Trench interpretive rule. The minor restrictive soil properties are identified but are not considered as part of the overall rating process. These restrictive properties could be important factors where the major soil limitations have been overcome through design application.

Soils are placed into interpretive rating classes per their rating indices. These are not limited (rating index <= 0.10), somewhat limited (rating index > 0.10 and < 0.98), or very limited (rating index >= 0.98). If a soil's property within 200 cm of the soil surface has a rating index greater than 0.10, then that soil feature is limiting. Each soil that is mapped in the state will fall into one of the following categories:

  • Not Limited - Soils are expected to be suitable for burial. These soils are preferred areas for locating burial trenches.
  • Somewhat Limited - Soils may be used for burial, as long as limitations shown are addressed. Soils in this category may have slight to moderate limitations. Care should be taken in evaluating a potential burial site on these soils.
  • Very Limited - Soils are generally not suited for burial trenches without overcoming major limitations. These locations are not recommended for burial. Alternative methods of disposal will normally be required if these are the only available soils.
  • Not Rated - Areas labeled Not Rated have characteristics that show extreme variability from one location to another. The work needed to overcome adverse soil properties cannot be estimated. Often these areas are urban land complexes or miscellaneous areas. An on site investigation is required to determine soil conditions present at the site.

The interpretative rating is based on soils in their natural condition and does not consider present land use. A catastrophic mortality burial site should never be selected without a site visit to verify assumptions about the location.

Scope and Use

Soil properties that influence the risk of pollution, ease of excavation, trafficability, and revegetation are major considerations. Soils that flood or have a water table within the depth of excavation present a potential pollution hazard and are difficult to excavate. Slope is an important consideration because it affects the work involved in road construction, the performance of the roads, and the control of surface water around the trench.

The ease with which the trench is dug and with which a soil can be used as daily and final covers is based largely on texture and consistence of the soil. The texture and consistence of a soil determine the degree of workability of the soil both when dry and when wet. Soils that are plastic and sticky when wet are difficult to excavate, grade, or compact and difficult to place as a uniformly thick cover over a layer of carcasses.

The trench should be mounded with a covering of at least two feet of soil, and surface water should be diverted away from the mound. Specifying earth fill compaction is not recommended. Compaction will be very difficult to achieve and could have a negative impact on the natural decay process. As animals begin to decay, it may be necessary to place additional soil material in areas that subside. If a potential exists for nuisance animals such as coyotes, dogs, opossums, etc., to dig into the trench, either use more than the two feet of cover material (recommended) or use an appropriate temporary fence to exclude these animal types.

The uppermost part of the final cover should be soil material that is favorable for the growth of plants and should not be too acid. In comparison with other horizons, the A horizon in most soils has the best workability and the highest content of organic matter.
Thus, it may be desirable to stockpile the surface layer for use in the final blanketing of the burial site which should be vegetated as soon as practical to prevent erosion of the soil cover.

It should be noted that soil interpretations are a preliminary planning tool. They only provide flags for things that need to be considered. Soil interpretations do not provide criteria for trench design or construction. While some general recommendations can be made, onsite evaluation is required before the final site is selected. Improper site selection, design, or installation may cause contamination of ground water, seepage, and contamination of stream systems from surface drainage or floodwater. Potential contamination may be reduced or eliminated by installing systems designed to overcome or reduce the effects of the limiting soil property.

Prior to constructing a disposal trench, consult with CT DEP Bureau of Materials Management and Compliance Assistance to insure the proposed activity is in accordance with CT laws and DEP regulations.

Criteria

The interpretive rating is based on the most limiting of the following restrictive soil properties.

  1. Clay Content: Clayey soils may become sticky when wet and are difficult to spread and compact. Soil feature considered is the weighted average of clay content between 25 and 180cm or above a restrictive layer and taxonomic family mineralogy.

Property Used: CLAY PERCENT IN DEPTH 30-200CM
(Modality - representative value)
Restriction Limits:
Somewhat limiting >27 percent
Not limiting All others
Null clay contents are assigned to the Not rated class.
AND
Property Used: TAXONOMIC MINERALOGY CLASS
(Modality - representative value)
Restriction Limits:
If taxonomic family mineralogy is kaolinitic then
the soil clayey rating is reduced by multiplying by 0.5.
Null taxonomic mineralogy classes are assigned Not Rated.

  1. Flooding: Flooding has the potential to transport waste off the site and pollute surface waters. Flooding also limits building, recreational, and sanitary facility use and management of these soils. Soil feature considered is maximum flooding frequency classes over 12 months.

    Property Used: CT FLOODING FREQUENCY (Maximum Duration)
    (Modality - representative value)
    Restrictive Limits:
    Limiting = "occasional" or "very frequent" or "frequent"
    Somewhat limiting = "very rare" or "rare"
    Not limiting = "none"
    Null frequency is assigned to the Not limiting class.
  1. Organic Matter Content: Soil in Unified class pt, ol, or oh is high in organic materials, has low strength, and is hard to reclaim. Soil feature considered is the rv or first Unified class of the thickest soil layer above a restrictive layer and between 25 and 200cm.

    Property Used: UNIFIED THICKEST LAYER 25-200cm
    (Modality - representative value)
    Restrictive Limits:
    Limiting = pt, ol, or oh
    Not limiting not = pt, ol, or oh
    Null Unified classes are assigned to the Not limiting class.
  1. Content of Large Stones: Large stones impede the workability of the soil and restrict trafficability of heavy machinery and site reclamation. Soil feature considered is the weighted average percentage of rock fragments of size greater than 75mm in the horizons above a restrictive feature or from 0 to 200 cm deep.

    Property Used: FRAGMENTS > 75mm Wt. Ave. 0-200cm
    (Modality - high, low, representative value)
    Restrictive Limits:
    Limiting => 50%
    Somewhat limiting > 25% to < 50%
    Not limiting =< 25%
    Null FRAGMENTS > 75mm are assigned Not rated.
  1. Too Acid: Soils with low pH increase metallic ion availability and restrict plant growth and re-establishing vegetation in disturbed area. Soil feature considered is the minimum (pH) of the soil layers.

    Property Used: SOIL REACTION 1-1 WATER (Minimum)
    (Modality - high, low, representative value)
    Restriction Limits:
    Limiting < 3.5
    Not limiting => 3.5
    Null pH values are assigned to the Not rated class.
  1. Ponding: Ponding is the condition where standing water is on the soil surface for a given period of time. Soil that ponds has restrictions that limit the installation and function of most land use applications. Soil features considered are ponding duration and frequency classes for all months.

    Property Used: PONDING DURATION (Modality - representative value)
    Restrictive Limits:
    Limiting = "very brief" or "brief" or "long" or "very long"
    Not limiting not = "very brief" or "brief" or "long" or "very long"
    Null duration is assigned to the Not limiting class.
    OR
    Property Used: PONDING FREQUENCY (Modality - representative value)
    Restrictive Limits:
    Limiting = "none"
    Not limiting not = "none"
    Null depth is assigned to the Not limiting class.
  1. Too Sandy: Sandy soils may slump and are droughty, making establishments of vegetative cover difficult. Soil feature considered is the sand content, minus clay, of the thickest soil layer between 25 and 200cm or above a cemented restrictive layer.

    Property Used: FRAGMENTS 75mm to 250mm THICKEST LAYER IN DEPTH 0-72 in. (Modality - high, low, and representative value)
    Restrictive Limits:
    Limiting >= 35%
    Somewhat limiting > 0% to < 35%
    Not limiting = 0%
    Null 3 to 10 inch rock fragment data are assigned to the Not rated class.

    Property Used: FRAGMENTS > 250mm THICKEST LAYER IN DEPTH 0-72 in. (Modality - high, low, and representative value)
    Restrictive Limits:
    Limiting >= 35%
    Somewhat limiting > 0% to < 35%
    Not limiting = 0%
    Null > 10 inch rock fragment data are assigned to the Not rated class.

    Property Used: SAND (#4-#200SIEVE) THICKEST LAYER (Modality - representative value)
    Restrictive Limits:
    Limiting >= 95
    Somewhat limiting > 50 and < 95
    Not limiting <= 50
    Null sieves are assigned to the Not rated class.
  1. Seepage: Saturated hydraulic conductivity (Ksat) governs the leaching and seepage potential of the soil. When this rate is high, transmission of fluids through the soil and underlying materials is unimpeded and leaching and seepage may become environmental, health, and performance concern. Soil feature considered is the Ksat of the bottom layer or the layer immediately above bedrock.

    Property Used: CT SEEPAGE (BOTTOM LAYER)
    (Modality - high, low, representative value)
    Restriction Limits:
    Limiting > 720 micrometers/sec
    Somewhat limiting 14.0 to 720 micrometers/sec
    Not limiting < 14.0 micrometers/sec
    Null Ksat values are assigned to the Not rated class.
  1. Depth to Bedrock: Shallow depth to bedrock limits the soil's adsorptive capacity and the thickness of the biologically active zone through which waste materials can percolate. Shallow soils may pose environmental and health risks when agricultural and municipal waste materials are applied. These soils may pose construction limitations or environmental and health risks when trench landfills are installed. Soil feature considered is the top depth of the first restrictive layer where restrictive type is "bedrock (lithic)" or "bedrock (paralithic)." Depth to restrictive feature must be synchronized with the depth to the restrictive feature horizon shown in the horizon table.

    Property Used: DEPTH TO BEDROCK (Modality - representative value)
    Restrictive Limits:
    Limiting < 200cm
    Not limiting => 200cm
    Null depth is assigned to the Not limiting class.
  1. Slope: Steep slopes impede trafficability of heavy machinery and make reclamation more difficult. A trench which is a long deep hole, usually with steep or vertical sides, will limit the use of equipment along steep slopes. Overhead water coming down the steep slope must be diverted away from the burial area. Soil feature considered is the component slope.

    Property Used: SLOPE (Modality - low, high, representative value)
    Restriction Limits:
    Limiting > 15%
    Somewhat limiting >= 8 and <= 15%
    Not limiting < 8%
    Null Slope is assigned Not rated.
  1. Depth to Saturated Zone: Soils with shallow depth to a water table may become waterlogged and boggy during periods of heavy precipitation and are slow to drain. Burials in these soils have the potential to contaminate the ground water which may create health and environmental hazards. Soil feature considered is for a saturated or wet condition within a depth of 180cm (approximately 6 feet) of the soil surface. The water moisture status is examined and those saturated or wet conditions are evaluated for depth.

    Property Used: CT - DEPTH TO HIGH WATER TABLE MINIMUM (Modality - representative value)
    Restrictive Limits:
    Limiting < 180cm
    Not limiting => 180cm
    Null depth is assigned to the Not limiting class.
  1. Rock Outcrop: Areas that have rock outcrop in the vicinity are not likely to have a sufficiently large area of soil for the Animal Disposal excavation. Rock outcrops can interfere with renovation of the leachate from the facility.

    Property Used: PA ROCK OUTCROP 2(Modality - representative value)
    Restrictive Limits:
    Limiting The phrase "rock outcrop" occurs in the map unit name.
    Not limiting The phrase "rock outcrop" does not occur in the map unit name.
    All map units have a name; no null data should be encountered.
  1. Adsorption: Soils having a low cec or ecec may not attenuate biohazardous material from the decay process. It is assumed that the upper 25 cm of the site will be stockpiled for use in revegetating the site. It is also assumed that alternating layers of soil and carcass will be placed in the excavation.

    Property Used: CLAY ACTIVITY IN DEPTH 30-200cm
    (Modality - low, high, representative value)
    Restrictive Limits:
    Limiting Below 0.05 meq/100g
    Somewhat limiting 0.05-0.15 meq/100g
    Not limiting > 0.15 meq/100g
    The fuzzy number is weighted by 0.25, meaning this rule cannot cause the component to be absolutely true that the site is limited for carcass disposal.
  1. Large Fragments on the Surface: Soils having a large proportion of the surface covered by rock fragments are limited because of the need to remove the large fragments.

    Property Used: Fragments >250 mm SURFACE LAYER (Modality - low, high, representative value)
    Restrictive Limits:
    Not limiting Below 5.01 percent cover
    Somewhat limiting 5.01-15.01 percent cover
    Limiting > 15.01 percent cover
    Null surface cover is assigned to non limiting.
  1. Cutbanks Cave: Under certain circumstances, the sides of an excavation may collapse. This can be hazardous to anyone in the trench or near the edge at the time of failure. The sloughed material may need to be removed from the trench, increasing the time needed to excavate. The sides of the trench may need to be made to reflect the angle of repose of the material or be shored.

15a.    Instability of the cutbank can be caused by the coarseness of the soil material.

           Property Used: FRAGMENT PERCENT IN DEPTH 30-200CM
           (Modality - low, high, representative value)
           Restrictive Limits:
           Limiting Above 80 percent by volume
           Somewhat limiting 60-80 percent by volume
           Not limiting Less than 60 percent by volume

           Property Used: SAND PERCENT LESS CLAY IN DEPTH 30-180CM
           Restrictive Limits:
           Limiting Above 185
           Somewhat limiting 170-185
           Not limiting Less than 170
           (The clay content is subtracted from the sand content and 100 added to the difference to keep the numbers
           positive. This number is effective sand content, adjusted for the adhesiveness of clay.)

15b.     High shrink-swell can cause instability of cutbanks.

           Property Used: LEP 25-200cm OR ABOVE RESTRICTIVE LAYER WTD_AVE
           Restrictive Limits:
           Limiting LEP above 9
           Somewhat limiting LEP 6 to 9
           Not limiting LEP less than 6

15c.    Silty material that is not loess can be unstable.

           Property Used: PARENT MATERIAL KIND IS LOESS
           Restrictive Limits:
           Limiting High silt and not loess
           Not limiting High silt and is loess

           Property Used: SILT PERCENT IN DEPTH 30-200CM
           Restrictive Limits:
           Somewhat limiting Greater than 75 percent silt
           Not limiting Less than 75 percent silt
           Silt content is not considered to ever be a severe limitation.

  1. Limestone Bedrock may have numerous solution channels that allow contaminants to enter the groundwater quickly and with no renovation.

    Property Used: LIMESTONE RESIDUUM TEST, NULL SENDS NO
    Restrictive Limits:
    Limiting If the bedrock is limestone, the soil is unsuited.
    Not limiting If the bedrock is not limestone, the soil is suited.
  1. Water Gathering (Concave) Surfaces can concentrate water flow and cause accelerated erosion. Increased costs because of materials and land shaping may be needed to prevent erosion.

    Property Used: WATER GATHERING SURFACE
    Restrictive Limits:
    Somewhat Limiting Concave up-down, concave across surfaces
    Slightly limiting Concave across, linear or convex up- down
    Not limiting All other surface shapes

All of the criteria listed above (1 through 17) are evaluated in this interpretation. Using this interpretation on the Soil Survey of the State of Connecticut, the most restrictive soil properties noted are:

  • Clay content
  • Flooding
  • Organic matter content
  • Ponding
  • Too sandy
  • Seepage
  • Depth to bedrock
  • Slope
  • Depth to saturated zone
  • Rock outcrop
  • Adsorption
  • Cutbanks cave