SINKHOLE AND SINKHOLE AREA

TREATMENT (Acre)

Standard (Interim)

1. Land use.

PA 370-1

Definition

A method of treating sinkholes and sinkhole areas toreduce contamination of ground water resources. (Asinkhole is a circular and funnel-shaped surfacedepression occurring in soluble bedrock areas andcommonly develops as a result of surface soil movingdownward into open bedrock fractures and solutioncavities.)

Purpose

The primary purpose is to treat a source of groundwater pollution by reducing the amount ofcontaminates or contaminated surface water enteringsinkholes. A secondary benefit is improved farmsafety with the closing of sinkhole entries.

Effect On Water Quality And Quantity

Improve ground water quality by removingcontaminated materials from sinkholes andreplacing direct inflow of contaminated surfacewater into sinkholes with land treatment methodsthat improve filtration and infiltration of surfacewater. Improved filtration and infiltration mayprovide some increase in soil moisture.

Conditions Where Practice Applies

On any land surface or existing practice wheregeologic conditions resulted in the development ofsinkholes and where contaminated surface water andother contaminated material have the opportunity toenter sinkholes and pollute the ground waterresource.

Planning Considerations

This practice includes the systems approach forsolving the problem by treating both the sinkholedirectly, and its drainage area (i.e. when possible,the practice should work in conjunction with thebeneficial effects of existing or plannedconservation cropping systems, pest and nutrient

PATG Section IV Standards/Specifications

management and practices that control sheet, rilland gully erosion).

This treatment should be planned withconsideration given to the following:

2. Existing and planned land treatment.

3 Sinkhole drainage area.

4. Dimensions of sinkhole opening.

5. Safe outlet for diverted surface water.

6. Environmentally safe disposal site forsinkhole "clean out" material.

7. Availability and quality of inverted filtermaterial.

8. Safety of equipment operators and laborersduring practice installation.

Design Criteria

The type of treatment selected is based upon the sizeof the sinkhole drainage area and could include bothdirect sinkhole treatment alol1lg with surface watercontrol measures and filter strips. The sinkholetreatment should not result in surface water pondingor high soil moisture conditions over an extendedperiod of time. However, since percolation rates varyamong different soils, ponding and soil moistureconditions may also vary.

The design for this treatment applies to sinkholeswith excavated depths between 5 and 25 feet andwith drainage areas up to 15 acres. (Most sink-holes can be excavated to 5 feet to allow for filterinstallation.) For sinkholes requiring excavateddepths greater than 25 feet or uncontrolleddrainage areas greater than 15 acres, adjustmentsto the inverted filter and/or surface water control

Pennsylvania July 1990

PA 370-2

measure(s) may be required. In this case, geologicand engineering assistance must be requested and asite specific design prepared.

1. Treatment for sinkholes with drainageareas less than 5 acres

a. Treat sinkhole using Inverted Filter 1specification and Figure 1.

(1) Inspection of the treatment should bemade after periods of heavy runoff,since some material may run further intosinkhole voids causing a surfacedepression. In this case, maintenancewill include adding soil material at thesurface.

(2) The existing (or planned) land use orpractice may exist over the treatedsinkhole as long as the treatment ismaintained

2. Treatment for sinkholes with drainage areas greaterthan 5 acres and using with a safe outlet forsurface water control measure(s)

a. neat sinkhole using Inverted Filter 1specification and Figure 1.

(1) Inspection of the treatment should bemade after periods of heavy runoff,since some material may run further intosinkhole voids causing a surfacedepression. In this case, maintenancewill include adding soil material at thesurface.

(2) The existing (or planned) land use orpractice may exist over the treatedsinkhole as long as the treatment ismaintained.

b. Install a surface water control measure to divertrunoff away from the sinkhole to a safe outlet. *

(1) The measure should be located toreduce the internal drainage areaaround the sinkhole to less than 5acres.

(2) The selected measure is based uponspecific site conditions and therespective standard and specificationsshould be followed.

*A safe outlet is one which does not: erode, divertsurface water to another sinkhole, or cause flooddamage to crops, property or buildings.

3. Treatment for sinkholes with drainage areasbetween 5 and 15 acres and no safe outletavailable for surface water control measure(s)

a. Treat sinkhole using Inverted Filter 2specification and Figure 2.

(1) Inspection of the treatment should bemade after periods of heavy runoff, sincesome material may run further intosinkhole voids causing a surfacedepression. In this case, maintenancewill include adding filter material at thesurface.

(2) The treated sinkhole will remain asunused land

b. Install a filter strip around the sinkholeusing orchard grass, bromegrass, reedcanary grass or any other grassdetermined to have equivalent filteringand adsorption qualities.

(1) The filter strip is installed within thesinkhole drainage area and begins at thetreated sinkhole. Its width (in feet) isdetermined by multiplying the sinkholedrainage area (acres) by seven.*

Since surface runoff may be temporarily stored behindthe treated sinkhole, this width should providebeneficial filtering to exist for some distance outsidethe pool. This width determination is not consistentwith Filter Strip Standard and Specification (393).

(2) For other installation and maintenanceinformation, Filter Strip Standard andSpecification (393) should be followed.

PATG Section IV Standards/Specifications Pennsylvania July 1990

SINKHOLE AND SINKHOLE AREA

TREATMENT (Acre)

Design and Check Data Requirements (Interim)

PA 370-3

Basic Data

1. Drainage area of sinkhole.

2. Availability of safe outlet for surface water, ifapplicable.

3. Estimated depth and volume of sinkhole.

Design

1. Plan view showing sinkhole and, if applicable,any associated surface water control measure(s)and filter strip.

PATG Section IV Standards/Specifications

2. Drawing of inverted filter showing thickness ofeach filter material.

3. Determine the quantity of each filtermaterial selected

Check Data

1. Seeding performed

2. Maintenance required after periods of heavyrunoff.

Pennsylvania July 1990

SINKHOLE AND SINKHOLE AREA

TREATMENT (Acre)

References (Interim)

PA 370-4

1. Estimating Runoff and Peak Discharges, USDA-SCS, Engineering Field Manual, Chapter 2,August, 1987.

2. Urban Hydrology for Small Watersheds, USDA-SCS, Technical Release 55, June 1986.

3. Graded Riprap Stone, Quarried Stone for Erosionand Sediment Control, National Crushed StoneAssociation, June, 1978.

4. Specifications, Section 703--Aggregates,Publication 408, Department of Transportation,Commonwealth of Pennsylvania, 1987.

PATG Section IV Standards/Specifications

5. Koerner, R.M., Designing With Geosynthetics,Prentice-Hall, Englewood Cliffs, NJ, 1985.

6. Engineering Geology, USDA-SCS, NationalEngineering Handbook, Section 8, Chapter 1,1978.

Other SCS Standards and Specifications that mayapply with the installation of this practice include:Diversion (362), Filter Strip (393), GrassedWaterway (412), Lined Waterway or Outlet (468),Terrace (600) and Construction Specification 25.

Pennsylvania July 1990

PA 370-5

~'NKHOLE TREATMgj:!LOrainage Area lesl than 5 Acrel)

July 1990PATG Section IV Standards/Specifications Pennsylvania

PATG Section IV Standards/Specifications July 1990Pennsylvania