Biosolids Loadings for Preliminary Site Area Determination

Option3

Agricultural Forest

Reclamation Type B

Application Schedule

Annual 5-yr intervals One time Annual

Typical Loading Rate (Mg/ha)b

10 45 100

a See Chapter 9 for a detailed description of options. b Metric tons per hectare (Mg/ha) x 0.4461 = lb/ac.

to determine which processes and sites are technically feasible. A complex screening procedure is not usually required for pond and wetland systems, because close proximity and access to the point of discharge are usually most important in site selection for these systems. For land application systems for wastewater and biosolids, the economics of conveyance to the potential site may compete with the physical and land use factors described in the next section.

2.2.1 Site Screening Procedure

The screening procedure consists of assigning rating factors to each item for each site and then adding up the scores. Those sites with moderate to high scores are candidates for serious consideration, site investigation, and testing. Among the conditions included in the general procedure are site grades, depth of soil, depth to groundwater, and soil permeability (Table 2.6). Conditions for the wastewater treatment concepts include land use (current and future), pumping distance, and elevation (Table 2.7). The relative importance of the various conditions in Table 2.6 and Table 2.7 is reflected in the magnitude of the values assigned, so the largest value indicates the most important characteristic. The ranking for a specific site is obtained by summing the values from Table 2.6 and Table 2.7. The highest ranking site will be the most suitable. The suitability ranking can be determined according to the following ranges:

Low suitability <18

Moderate suitability 18-34

High suitability 34-50

For land application of biosolids, a similar matrix of factors can be arrayed for each potential site using the rating factors shown in Table 2.8. The rating factors for forested sites are presented in Table 2.9 and Table 2.10. The restrictions on liquid biosolids (<7%) in Table 2.8 are intended to control runoff or erosion of

TABLE 2.6

Physical Rating Factors for Land Application of Wastewater

Soil Aquifer

TABLE 2.6

Physical Rating Factors for Land Application of Wastewater

Soil Aquifer

Condition

Slow Rate

Overland Flow

Treatment

Site grade (%)

0-5

8

8

8

5-10

6

5

4

10-15

4

2

NSa

15-20

Forest only, 5

NS

NS

20-30

Forest only, 4

NS

NS

30-35

Forest only, 2

NS

NS

>35

Forest only, 0

NS

NS

Soil depth (m)b

0.3-0.6

0

0

NS

0.6-1.5

3

5

NS

1.5-3.0

8

6

3

>3.0

9

7

8

Depth to groundwater (m)

<1

0

4

NS

1-3

4

5

1

>3

6

6

6

Soil permeability of most restrictive soil layer (cm/hr)

<0.15

1

10

NS

0.15-0.50

3

8

NS

0.50-1.50

5

6

1

1.50-5.10

8

1

6

>5.10

8

NS

b Soil depth to bedrock or impermeable barrier.

Source: Adapted from USEPA, Onsite Wastewater Treatment Systems Manual, EPA/625/R-00/008, CERI, Cincinnati, OH, 2002.

surface-applied biosolids. Injection of liquid biosolids is acceptable on 6 to 12% slopes but is not recommended on higher grades without effective runoff control.

The economical haul distance for a biosolids land application will depend on the solids concentration and other local factors and must be determined on a case-by-case basis. The values in Table 2.8 can be combined with the land use and land cost factors from Table 2.7 (if appropriate) to obtain an overall score for a

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