PA INC HARRISBURG NATIONAL DAN INSPECTION ...Lake Creek. Maple Lake Dam releases water into La Rue...

NATIONAL DAN INSPECTION REPORT. SUMMIT LAKE DAM INDI ID NUMBER -ETC(U)I -09 2 ANNETT

FLEMING CORDDRy AND CARPENTER

INC HARRISBURG PA F/6 13/13

JNLSI~ APR 79 DACW31-79-C-0015

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DENMYCVAbIArr

O NDl 11) NO. PA-00291DER 11D NO. 35-26

PENNSYLVANIA GAS AND WATER COWANY

Distribution UnlimitedApproved for Public ReleaseContract No. DACW3l-79-C-0015

Prepared by

GANNETT FLEMING CORDDRY AND CARPENTER, INC.D DConsulting EngineersD

o1 Harrsburg, Pennsylvania 17105FC (I P ALL D 9 1w8

For__" DEPARTMENT OF THE ARMYA

Coo- Baltimore District, Corps of Engineers\ Baltimore, Maryland 21203APRIL 1979 go17. /03

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JUSQUEHANNA RIVER BASINJUMMIT L CPEEK, cAwANNA COUNTY,

~~7) -'--...~ PENNSYLVANIAs

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SUMMIT 6AKE DAM

NDI ID -OO2 9/(D R -fD 35-26)/

PHASE I INSPECTION. EPORT-

NATIONAL DAM INSPECTION PROGRAM

Prepared By

GANNETT FLEMING CORDDRY AND CARPENTER, INC.Consulting Engineers

P.O. Box 1963Harrisburg, Pennsylvania 17105

For

DEPARTMENT OF THE ARMYBaltimore District, Corps of Engineers

Baltimore, Maryland 21203

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PREFACE

This report is prepared under guidance contained in the RecomendedGuidelines for Safety Inspection of Dams, for Phase I Investigations.Copies of these guidelines may be obtained from the Office of Chiefof Engineers, Washington, D.C. 20314. The purpose of a Phase Iinvestigation is to identify expeditiously those dams which maypose hazards to human life or property. The assessment of thegeneral condition of the dam is based upon available data and visualinspections. Detailed investigation, and analyses involving topo-graphic mapping, subsurface investigations, testing, and detailedcomputational evaluations are beyond the scope of a Phase I in-vestigation; however, the investigation is intended to identifyany need for such studies.

In reviewing this report, it should be realized that the reportedcondition of the dam is based on observations of field conditionsat the time of inspection along with data available to the in-spection team. In cases where the reservoir was lowered or drainedprior to inspection, such action, while improving the stabilityand safety of the dam, removes the normal load on the structureand may obscure certain conditions which might otherwise bedetectable if inspected under the normal operating environmentof the structure.

It is important to note that the condition of a dam depends onnumerous and constantly changing internal and external conditions,and is evolutionary in nature. It would be incorrect to assumethat the present condition of the dam will continue to representthe condition of the dam at some point in the future. Only throughfrequent inspections can unsafe conditions be detected and onlythrough continued care and maintenance can these conditions be pre-vented or corrected.

Phase I inspections are not intended to provide detailed hydrologicand hydraulic analyses. In accordance with the established Guide-lines, the spillway design flood is based on the estimated "ProbableMaximum Flood" for the region (greatest reasonably possible stormrunoff), or fractions thereof. The spillway design flood providesa measure of relative spillway capacity and serves as an aid indetermining the need for more detailed hydrologic and hydraulicstudies, considering the size of the dam, its general condition andthe downstream damage potential.

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SUSQUEHAINA RIVER BASIN

SUM1IT LAKE CREEK, LACKAWANNA COUNTY

PENNSYLVANIA

SUMMIT LAKE DAM

NDI NO. PA-00291

DER ID No. 35-26

PENNSYLVANIA GAS AND WATER COMPANY

PHASE I INSPECTION REPORT


APRIL 1979

CONTENTS

Description Page

SECTION 1 - Project Information . . . . . . . . . . . 1SECTION 2- Engineering Data . . . . . . . . .. . .. 6SECTION 3 - Visual Inspection. . . . . ........ 8SECTION 4 - Operational Procedures . . . . . . . . . . 10SECTION 5 - Hydrology and Hydraulics . . . . . . . . . 12SECTION 6 - Structural Stability . . . . . . . . . . 15SECTION 7 - Assessment, Recommendations, and

Remedial Measures . . . . . . . . . . . 18

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PLATES

Plate Title

1 Location Map2 Plan3 Sections and Outlet Works4 Spillway

APPENDICES

Appendix Title

A Checklist - Engineering Data.

B Checklist - Visual Inspection.

C Hydrology and Hydraulics.

D Photographs.

E Geology.

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BRIEF ASSESSMENT OF GENERAL CONDITION

AND

RECOMMENDED ACTION

Name of Dam: Summit Lake

NDI ID No. PA-00291/DER ID No. 35-26

Owner: Pennsylvania Gas and Water Company

State Located: Pennsylvania

County Located: Lackawanna

Stream: Summit Lake Creek

Date of Inspection: 26 October 1978

* Inspection Team: Gannett Fleming Corddry and Carpenter, Inc.Consulting EngineersP.O. Box 1963Harrisburg, Pennsylvania 17105

Based on visual inspection, available records,calculations and past operational performance, andaccording to criteria established for these studies,Summit Lake Dam is rated as unsafe, nonemergency,because the spillway capacity is seriously inadequate.The existing spillway can pass 26 percent of the ProbableMaximum Flood (PMF) without overtopping of the dam.The failure of the dam would cause an increased hazard toloss of life downstream. As a whole, the dam is judged tobe in fair condition.

If the top of the dam were raised 0.1 foot to itsdesign elevation, the spillway could pass 27 percent ofthe PMF. The spillway capacity would still be rated asseriously inadequate.

There is no evidence of stability problems withthe embankment. The masonry gravity section of the

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embankment has no significant deviations from the OCEguideline for stability, since the toe pressure is wellbelow the allowable.-r-

The following measures are recommended to beunder-taken by the Owner, in approximate order ofpriority, immediately:

(1) Perform additional studies to more accuratelyascertain the spillway capacity required for SummitLake Dam and the remedial measures required to make thespillway hydraulically adequate. Perform remedialmeasures as required. The studies should be performedby a professional engineer experienced in the designand construction of dams.

(2) Raise the embankment to the design elevationof the top of the dam.

(3) Monitor with any suitable means the saggingspillway cascade steps. If changes are noted, takeimmediate remedial measures.

(4) Clear the spillway approach channel of rocks.

(5) Repair the mortar in the spillway and masonry

gravity section. Repave the scoured area of the spillway.

(6) Replace the access bridge to the outlet worksintake with a sturdier structure.

(7) As part of the regular maintenance program,remove brush, trees, and debris from the downstreamtoe. Also, fill the burrowing animal holes.

In addition, it is recommended that the Ownermodify his operational procedures as follows:

(1) Develop a detailed emergency operation andwarning system for Summit Lake Dam.

(2) Provide round-the-clock surveillance ofSummit Lake Dam during periods of unusually heavyrains.

(3) When warnings of a storm of major proportionsare given by the National Weather Service, the Owner

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should activate his emergency operation and warningsystem procedures.

Submitted by:

GANNETT FLEMING CORDDRY t4 EAND CARPENTER, INC.

.

ALEST CHAPLES 0OOKEA. C. HOOKE E.Head, Dam Section 0 .'yDate: 30 April 1.979

Approved by:

DEPARTMENT OF THE ARMYBALTIMORE DISTRICT, CORPS OF ENGINEERS

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SUSQUEHANNA RIVER BASIN

SUMMIT LAKE CREEK, LACKAWANNA COUNTY

PENNSYLVANIA

SUMMIT LAKE DAM

NDI ID No. PA-00291DER ID No. 35-26




SECTION 1

PROJECT INFORMATION

1.1 General.

a. Authority. The Dam Inspection Act, PublicLaw 92-367, authorized the Secretary of the Army,through the Corps of Engineers, to initiate a programof inspection of dams throughout the United States.

b. Purpose. The purpose of the inspection is todetermine if the dam constitutes a hazard to human lifeor property.

1.2 Description of Project.

a. Dam and Appurtenances. Summit Lake Dam is ahomogeneous earthfill embankment with a masonry wallalong the downstream face. The wall extends up to thespillway crest elevation. The dam is 250 feet long and24 feet high at maximum section.

The spillway is at the right abutment of thedam. It is a rectangular masonry channel extending

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from the reservoir to the masonry wall, where a steppedmasonry cascade discharges flows into the stream. Therectangular channel is 12.2 feet wide. At the controlsection, the invert is 4.3 feet below the design topelevation of the dam.

The outlet works consists of an intake struc-ture and a 18-inch diameter cast-iron pipe. Access tothe intake structure is via a bridge extending from theembankment. A 20-inch gate valve and 3 "mud" (flap)valves are provided in the intake structure. Thevarious features of Summit Lake Dam are shown on thePlates at the end of the report and on the Photographsin Appendix D.

b. Location. The dam is located on Summit LakeCreek approximately 1.6 miles west of Chinchilla,Pennsylvania. Summit Lake Dam is shown on UgGS Quadrangl,Scranton, Pennsylvania, with coordinates N41 28'30" - W75 42'50"in Lackawanna County, Pennsylvania. The dam is 1.1miles upstream from Maple Lake Dam, which is on SummitLake Creek. Maple Lake Dam releases water into La RueReservoir, which is 0.3 mile downstream from Maple LakeDam. The location map is shown on Plate 1.

c. Size Classification. Small (24 feet high, 927acre-feet)-.

d. Hazard Classification. High hazard. Downstreamconditions indicate that a high hazard classification iswarranted for Summit Lake Dam (Paragraph 5.1c.).

e. Ownership. Pennsylvania Gas and Water Company,Wilkes-Barre, Pennsylvania.

f. Purpose of Dam. Water supply for Chinchilla,Pennsylvania and surrounding communities.

g. Design and Construction History. Summit Lake Damwas originally an earthfill embankment with a timber spill-way. It was constructed in 1875. There is no other in-formation available concerning this structure. Becauseof the large reservoir capacity, it is believed thatSummit Lake was originally a natural lake. However, thereis no information available to confirm this.

In 1884, the dam was enlarged by the ProvidenceGas and Water Company. The modification was designed

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by C. S. Weston, Consulting Engineer of Scranton. Themodifications altered the dam to its present configuration.

In 1910, a bulkhead was constructed acrossthe spillway crest to raise it to within 2.4 feet ofthe top of the embankment. The concrete intake structurewas also constructed at the same time.

In 1943, the bulkhead was removed and thespillway was returned to its post-1884 condition.

h. Normal Operational Procedure. The reservoiris normally maintained at spillway crest level. Thevalve on the outlet conduit is normally throttledpartially open to supply water to the Owner's distributionsystem downstream at Maple Lake and La Rue Dams.

1.3 Pertinent Data.

a. Drainage Area. (square miles). 1.3

b. Discharge at Damsite. (cfs).

Maximum known flood at damsite Unknown

Outlet works at maximum pool elevation 42

Spillway capacity at maximum pool elevation

Existing conditions 290

Design conditions 300

c. Elevation. (feet above msl).

Top of dam (design) 1383.7

Top of dam (existing) 1383.5

Maximum pool 1383.6

Normal pool (spillway crest) 1379.4

Upstream invert outlet works 1361.8

Downstream invert outlet works 1360.0

Streambed at toe of dam 1360.0

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d. Reservoir Length. (miles).

Normal pool 0.63

Maximum pool 0.64

e. Storage. (acre-feet).

Normal pool 645

Maximum pool 927

f. Reservoir Surface. (acres).

Normal pool 55.4

Maximum pool 69.6

g. Dam.

Type Homogeneous earth-fill with a mason-ry wall along thedownstream side

that extends up tospillway crest ele-vation.

Length (feet) 250

Height (feet) 24

Topwidth (feet) 8

Side Slopes

Upstream

Above spillway crest El. IV on 2.6HBelow spillway crest El. lV on 4.6H

Downstream

Above top of masonrywall 1V on 4.5H

Below toe of masonrywall Irregular, about

iV on 5H

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Zoning Homogeneous earth-fill.

Cutoff Masonry wall.

Grout Curtain None.

h. Diversion and Regulating Tunnel. None.

i. Spillway.

Type Rectangular masonrycontrol section.

Length of Weir (feet) 12.2

Crest Elevation 1379.4

Upstream Channel Rectangular mason-ry approach.

Downstream Channel Rectangular masonrychannel extendingto a steppedmasonry cascade thatdischarges into theexisting stream.

1. Regulating Outlets.

Type Tile clay pipe,18-inch diameter.A 20-inch intakeline extends to theintake structure.

Length (feet) 102

Closure 20-inch gate valveat intake structure.

Access Via bridge fromembankment.

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SECTION 2

ENGINEERING DATA

2.1 Design.

a. Data Available. Very little engineering datawere available for review for the original structuresor for the modifications to the dam. In a study performedin 1914 by the Pennsylvania Water Supply Commission, anaccount of design concepts, geology, constructionmaterials and methods, and design features was preparedfrom interviews with the Owner, visual inspection, andother sources. The available information is verylimited. The 1914 study also included analyses forhydrology and hydraulics. A summary of the results ofthe analyses is on file. No information pertinent tothe repairs accomplished in 1943 was available. Thismodification consisted of removing a previous modificationand was probably accomplished without plans or specifications.

b. Design Features. The dam and appurtenancesare described in Paragraph 1.2a. The design featuresare shown on the Plates at the end of the report andon the Photographs in Appendix D.

A plan of the dam is shown on Plate 2. Theembankment is shown on Photographs A and D. Typicalsections of the embankment, masonry section, and outletworks are shown on Plate 3. The downstream face of themasonry section is shown on Photograph B. The outletworks intake structure is shown on Photograph D; theoutfall is shown on Photograph C. The spillway isshown on Plate 4 and on Photographs E and F.

The plates are not design drawings. Theearliest drawing for the dam is dated 1901; accordingto information in the Pennsylvania Department of EnvironmentalResources (PennDER) files, some of the data on thedrawings was obtained from drawings dated before 1901.

c. Design Considerations. Almost nothing isknown about the design.

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2.2 Construction.

a. Data Available. Construction data availablefor review for the original structures were limited toinformation contained in the 1914 Report prepared bythe Pennsylvania Water Supply Commission. That in-formation was obtained by interviews with the Owner,and it gives very scant details of the constructionoperations. The report classifies the available infor-mation as "of little value and unreliable".

b. Construction Considerations. Since theavailable construction data is limited, the constructionmethods cannot be assessed.

2.3 Operation. There are no formal records of operation.Based on information from the Owner and the caretakerof the dam, all structures have performed satisfactorily.

2.4 Evaluation.

a. Availability. Engineering data were providedby the Bureau of Dam Safety, Obstructions, and StormWater Management, Department of Environmental Resources,Commonwealth of Pennsylvania (PennDER), and by theOwner, Pennsylvania Gas and Water Company. The Ownermade available both a senior construction supervisorand the caretaker for information during the visualinspection. The Owner also researched his files foradditional information upon request of the inspectionteam.

b. Adequacy. The type and amount of design dataand other engineering data are limited, and the assessmentmust be based on the combination of available data,visual inspection, performance history, hydrologicassumptions, and hydraulic assumptions.

c. Validity. There is no reason to question thevalidity of the available data. Conflicting data con-cerning the masonry gravity wall at the downstreamface of the embankment are discussed in Section 6.

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SECTION 3

VISUAL INSPECTION

3.1 Findings

a. General. The overall appearance of the dam isgood, with some deficiencies as noted herein. Thelocations of deficiencies are shown in Appendix B onPlate Bi. Survey data acquired during this inspectionare presented in Appendix B. On the day of the inspection,the pool was 3.4 feet below spillway crest elevation.

b. Embankment and Masonry Gravity Section. Thesod on the embankment is in excellent condition. Onthe upstream slope, the riprap does not extend to thetop of the dam. The riprap is washed out in some areasand deteriorated in others (Photograph D). On themasonry gravity section, the mortar is deteriorated.Downstream of this section, the slope is irregular.Small trees and burrowing animal holes were observed;debris, probably from the intake structure bridge asdiscussed hereafter, covers the area (Photograph B).The survey performed for this inspection reveals thatthe embankment slopes are generally in accordance withthe information shown on the Plates. The survey alsoreveals that approximately 50 percent of the top of theembankment is 0.1 foot below the design elevation(Appendix B). On the day of the inspection, no seepagewas observed at the dam.

c. Appurtenant Structures. The outlet works isin good condition. On the day of the inspection, theoutlet works valve was in a throttled position torelease water to the stream below. The configurationof the outlet works did not allow observation of conditionsat the outfall (Photograph C). The bridge extendingfrom the embankment to the intake structure is in poorcondition. The caretaker reported that the bridge is areplacement for a previous bridge that was damaged byvandalism and ice floes. The existing bridge is justabove the spillway crest elevation and it is not sturdy.The remains of the previous bridge have apparently beenplaced at the toe of the masonry gravity section.

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The spillway is in fair condition. Thebottom of the approach channel is covered with looserocks. The paved section between these rocks appearedto be somewhat irregular (Photograph E). The top of aconcrete cutoff wall is visible just upstream of thecontrol section. Near the control section, the bottompaving is cracked and a 1-foot by 3-foot area is eroded.The steps of the masonry cascade are sagging (PhotographF). The mortar in the entire spillway section isdeteriorated.

d. Reservoir Area. The reservoir has generallygentle slopes. The watershed has minor development. Acountry club with a golf course and some widely spacedsuburban development are within the watershed. Accessto the dam is via a short road, which parallels thereservoir *and is above it.

e. Downstream Channel. The stream flows fromthe dam for 0.1 mile by a poultry farm and then for 0.3mile by some dwellings within the floodplain. In theabove reach, the stream passes through some smallculverts under low roadway embankments. The streamthen flows for 0.9 mile along a reach within which areMaple Lake and La Rue Dams. Between Maple Lake Dam andLa Rue Dam are a few low lying homes. The stream thenflows 0.3 mile through part of Chinchilla to its confluencewith Leggetts Creek. In Chinchilla, some dwellings andcommercial establishments are directly adjacent to thestream, which passes through some small culverts.

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SECTION 4

OPERATIONAL PROCEDURES

4.1 Procedure. The reservoir is maintained at spillwaycrest, Elevation 1379.4, with excess inflow dischargingover the spillway and into the stream, which flows intoMaple Lake Reservoir 1.1 miles downstream. An 18-inchdiameter tile-clay pipe discharges water from thereservoir. Flows in the line are regulated by a 20-inch valve at the intake structure. Streamflows intoMaple Lake Dam can be increased by releases from SummitLake Dam. Since Maple Lake Dam functions as an intakereservoir, the valve on the Summit Lake water dischargeline is usually in the throttled position.

4.2 Maintenance of Dam. The dam is visited daily by acaretaker who records the reservoir elevation andadjusts the outlet works valves. Weekly reports aremailed to the Owner's Engineering Department. Thisinformation is used by the Owner's Engineering Departmentfor regulating flows in the distribution system. Thecaretaker is also responsible for observing the generalcondition of the dam and appurtenant structures and forreporting any changes or deficiencies to the Owner'sEngineering Department. A Pennsylvania Gas and WaterCompany engineer makes a formal inspection of the dameach year, and the records are filed and used fordetermining the priority of repairs. Informal inspectionsare also made when the engineer is on the site forother reasons. The grass on the embankment is mowedfrequently.

4.3 Maintenance of Operating Facilities. The valve onthe outlet works pipe is operated frequently. Inresponse to the Phase I Dam Inspection Program of theprevious year, the Owner is revising his maintenanceprocedures. Details of the procedures are still beingdeveloped.

4.4 Warning Systems in Effect. The Owner furnishedthe inspection team with a verbal description of thechain of command for Summit Lake Dam and of a generalized

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emergency notification list that is applicable for allof the Pennsylvania Gas and Water Company dams. TheOwner said that during periods of heavy rainfall,available personnel are dispatched to the dams toobserve conditions. All company vehicles are equippedwith radios, and the personnel can communicate witheach other and with a central control facility. Evaluationof risk is made by the Owner's Engineering Department.The Owner's Engineering Department is also responsiblefor notification of emergency conditions to the localauthorities. Detailed emergency operational procedureshave not been formally established for SummitLake Dam, but are as directed by the Owner's EngineeringDepartment.

4.5 Evaluation of Operational Adequacy. The maintenanceof the embankment is generally good. The maintenance pro-cedures for the outlet works valve are adequate. The pro-cedures used by the Owner for inspecting the dam are ade-quate, but some needed repairs have not been made. Ingeneral, the warning system is adequate, but it would bemore effective if it were more detailed.

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SECTION 5

HYDROLOGY AND HYDRAULICS

5.1 Evaluation of Features

a. Design Data. No design data were available forreview. During 1914, a report on the dam was made bythe Pennsylvania Water Supply Commission. This studyresulted in no recommendations. The spillway wasmodified to its present configuration in 1943. Ananalysis of the spillway modification by the PennsylvaniaWater Power Commission is available in the PennDERrecords. In this analysis, the spillway capacity wasestimated at 288 cfs with the embankment at designelevation. In a report, dated 1944, Thomas H. Wiggin,consulting engineer of New York City, estimated thedischarge capacity of the spillway at 225 cfs. As wasnoted in a review of the study by the Commonwealth, thedimensions used in the study do not agree with thedimensions of the existing spillway. Furthermore, thecoefficient of discharge used in the study was 1.5.Based on calculations made for this study, a spillwaydischarge capacity of 290 cfs for existing conditionsand 300 cfs for design conditions is used in thisreport (Appendix C).

b. Experience Data. The Owner has not reportedany hydraulic problems with the dam. He does not haveany experience data concerning flows during times offlood.

c. Visual Observations.

(1) General. The visual inspection ofSummit Lake Dam, which is descrited in Section 3,resulted in a number of observations relevant to hydrologyand hydraulics. These observations are evaluatedherein for the various features.

(2) Embankment. The low area on the top ofthe embankment reduces the spillway discharge capacity.The riprap not extending to the top of the dam presentsan erosion hazard when the pool is above spillway crestelevation. Judging by the washout and deterioration ofthe existing riprap, little protection is provided by

it.

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(3) Appurtenant Structures. Except for thecondition of the access bridge, no deficiencies wereobserved at the outlet works; upstream closure isprovided by the valve in the intake structure. Thecondition of the bridge indicates that it could bedamaged by high pool or ice floe conditions. Access tothe intake structure would then be difficult.

The conditions in the approach channelto the spillway will reduce spillway discharges whenthe pool is just above the spillway crest elevation.This would not significantly affect the higher spillwaydischarges.

(4) Reservoir Area. No conditions were ob-served in the reservoir area or watershed that mightpresent a significant hazard to the dam. The assessmentof the dam is based on existing conditions, and theeffects of future development are not considered.Access to the dam is good.

(5) Downstream Conditions. No conditionswere observed immediately downstream of the dam thatmight present a significant hazard to the dam. Thedownstream conditions indicate that many dwellingscould be flooded by a failure of Summit Lake Dam. BothMaple Lake and La Rue dams are sufficiently small thatthey would not provide significant mitigating effectsto floodflows originating upstream. Their failurewould not significantly increase the hazards caused bythe failure of Summit Lake Dam. The downstream conditionsindicate that a high hazard classification is warrantedfor Summit Lake Dam.

d. Overtopping Potential.

(1) Spillway Design Flood. According to thecriteria established by the Office of the Chief ofEngineers (OCE) for the size (Small) and hazard potential(High) of Summit Lake Dam, the spillway design flood(SDF) is between one-half of the probable maximum flood(PMF) and the PMF. Since there are at least 20 dwellingsdownstream, the PMF is selected as the SDF for SummitLake Dam.

(2) Description of Model. The watershed wasmodeled with the HEC-1DB computer program. The HEC-1DBcomputer program computes a PMF runoff hydrograph and routesthe flows through both reservoirs and stream sections.

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A, In addtion, it has the capability to simulate an overtoppingdam failure. The PMF inflow to Summit Lake was determinedand routed through the dam. Identical methods wereused for various percentages of the PMF.

(3) Summary of Results. Pertinent resultsare tabularized at the end of Appendix C. The Analysisreveals that Summit Lake Dam, with its existing topelevation of 1383.6, can pass approximately 26 percentof the PMF without overtopping.

If Summit Lake Dam were raised to itsdesign elevation of 1383.7, it would be able to passapproximately 27 percent of the PMF.

(4) Spillway Adequacy. The criteria used torate the spillway adequacy of a dam are described inAppendix C. Since the spillway cannot pass the 1/2 PMFwithout the overtopping of the dam, a furter analysiswas performed. It was assumed that Summit Lake Damwould develop an 80-foot wide breach 0.1 hour afterbeing overtopped by 0.3 foot. A breach of this sizeresults in a peak outflow of 32,600 cfs. The breachoutflow was routed downstream. It was assumed thatno runoff occurred downstream from Summit Lake Dam.The dam failure outflow would raise the stream depthabove the depth that would occur without failure of thedam by 5.1 to 10.2 feet. There is an increased hazardto loss of life. The spillway is rated as seriouslyinadequate.

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SECTION 6

STRUCTURAL STABILITY

6.1 Evaluation of Structural Stability.

a. Visual Observations.

(1) General. The visual inspection ofSummit Lake Dam, which is described in Section 3,resulted in a number of observations relevant to structuralstability. These observations are evaluated herein forvarious features.

(2) Embankments. Trees and brush growing atthe embankment are undesirable. Burrowing animal holesare also undesirable. The debris at the toe of themasonry gravity section is not a hazard to the damexcept that it hinders visual inspection. The top ofthe dam being slightly below the design elevation isprobably due to settlement. The deteriorated mortar inthe masonry gravity section is an indication of lack ofmaintenance.

(3) Appurtenant Structures. No deficienciesof structural significance were observed at the outletworks. Most of the deficiencies at the spillway are anindication of lack of maintenance. The sagging of thecascade steps is of some concern. It is believed thatthis could have been caused by poor construction practiceor foundation problems. As the construction informationis very limited, the cause cannot be ascertained withoutfurther investigation. The 1914 Pennsylvania WaterSupply Commission Report notes that in 1911 one of thewalls along the cascade had to be reset because it hadsettled. The Report indicated that the spillway cascadeis founded on earth.

b. Design and Construction Data. No record cfdesign data or stability analysis was available forreview. Analysis of the embankment stability is beyondthe scope of this study. Also, sufficient data on theengineering properties of the embankment material wouldhave to be acquired before the analysis could be performed.There is no evidence of stability problems with theembankment.

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The dimensions of the masonry gravity sectionare in doubt. The following is an excerpt from thePennsylvania Water Supply Commission Report.

"The information available on the originaldam, the changes made when the dam was increasedin height and the method of construction is oflittle value and unreliable. Mr. Cox tried toobtain information from several men who lived inthe vicinity of the dam, but was not successful,and on my last trip to Scranton I interviewedMr. C. S. Weston and even he remembered verylittle about what actually took place. He gave meto understand that a few sections of the wall thatwere traced from a drawing in his possession donot show how the wall was actually constructed andthat they were only proposed sections ........According to Mr. Weston, the wall was carrieddeeper and made heavier than shown on the drawingand, so far as he could recollect, it was foundedon hardpan. After a trench had been excavated inthe outer prism of the earthen embankment themasonry wall was built and the trench back filledwith selected material which was puddled andtamped. The reason for the odd location was tokeep down the amount of earth that had to behandled."

Mr. Weston was the designer of the 1884modification to the dam. Apparently the PennsylvaniaWater Supply Commission considered that the masonrygravity section was a corewall; it was never analyzedby them.

The highest section of the masonry go-avitywall that is shown on Plate 3 was analyzed for thisstudy. Plate 3 was drawn after 1909. It is unsurewhether the wall shown on the upper plate is the heaviersection referenced above. The stability analysis wasperformed for the wall, assuming a water level at thetop of the wall, full hydrostatic head and at-rest earthpressure on the upstream face, no tailwater, and upliftvarying from zero at the toe to two-thirds the headwaterat the heel. For this loading condition, the resultantis within the base, but outside of the middle third,about 1.8 feet from the toe, and both the factor ofsafety against sliding and the toe pressure are withinacceptable limits. The OCE guideline for stabilitystates that the resultant should be within the middle

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third. The resultant being outside the middle third isnot considered to be a significant deviation from theOCE guideline, since the toe pressure is well below theallowable.

Although information about the structure isuncertain, the available information indicates thatthe structure may be more massive than indicated; thiswould improve its stability. As such, there is noconcern about its stability.

c. Operating Records. There are no formalrecords of operation. According to the Owner, nostability problem3 have occurred over the operationalhistory of the dam.

d. Postconstruction Changes. As noted herein,very little information was available for the variousmodifications to the dam. However, the modificationswere made sufficiently long ago that the embankment, asit exists, is the basis for the evaluation.

e. Seismic Stability. Summit Lake Dam is locatedin Seismic Zone 1. Normally it can be considered thatif a dam in this zone has adequate factors of safetyunder static loading conditions, it can be assumed safefor any expected earthquake loading. However, sincethere are no formal static stability analyses, andsince there is the possibility of earthquake forcescracking the masonry gravity section, the theoreticalseismic stability of Summit Lake Dam is not known.

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SECTION 7

ASSESSMENT, RECOMMENDATIONS, ANDPROPOSED REMEDIAL MEASURES

7.1 Dam Assessment

a. Safety.

(1) Based on the visual inspection, availablerecords, calculations, and past operational performance,Summit Lake Dam is judged to be in fair condition.However, the existing spillway will pass only 26 percentof the PMF without overtopping of the dam. The failureof the dam will increase the hazard to loss of lifedownstream. The spillway is rated as seriously inadequate.According to criteria established for these studies,the dam must be rated as unsafe because the spillwaycapacity is seriously inadequate.

If the embankment were raised to itsdesign elevation, the spillway would be able to pass 27percent of the PMF. The spillway capacity would stillbe rated as seriously inadequate.

(2) There is no formal stability analysisavailable for Summit Lake Dam. However, there is noevidence of problems threatening the stability of theembankment. The masonry gravity section has its resultantoutside the middle third but within the base; this isnot judged to be a significant deviation from the OCEguideline, since the toe pressure is well below theallowable.

(3) The visual inspection revealed somedeficiencies, which are summarized below for the variousfeatures.

Feature and Location Observed Deficiencies

Embankment:Top Below design elevation.

Upstream slope Riprap does not extend tothe top of the dam; it isdeteriorated and washedout in areas.

~-18-

*4\.

Feature and Location Observed Deficiences

Downstream toe Brush, debris, and burrowinganimal holes.

Masonry gravity section Deteriorating mortar.

Outlet Works:Access bridge Insufficient strength.

Spillway:Approach channel Loose rocks.Control section Crack and scour.Cascade Sagging steps.Walls and paving Deteriorated mortar.

b. Adequacy of Information. The information availableis such that an assessment of the condition of the dam canbe inferred from the combination of visual inspection,past performance, and computations performed prior toand as part of this study.

c. Urgency. The recommendations in Paragraph 7.2should be implemented immediately.

d. Necessity for Further Investigations. Inorder to accomplish some of the remedial measuresoutlined in Paragraph 7.2, further investigations bythe Owner will be required.

7.2 Recommendations and Remedial Measures.

a. The following measures are recommended to beundertaken by the Owner, in approximate order of priority,immediately:

(1) Perform additional studies to moreaccurately ascertain the spillway capacity required forSummit Lake Dam and the remedial measures required tomake the spillway hydraulically adequate. Performremedial measures as required. The studies should beperformed by a professional engineer experienced in thedesign and construction of dams.

(2) Raise the embankment to the designelevation of the top of the dam.

(3) Monitor with any suitable means thesagging spillway cascade steps. If changes are noted,take immediate remedial measures.

I"

1. .

(4) Clear the spillway approach channel ofrocks.

(5) Repair the mortar in the spillway andmasonry gravity section. Repave the scoured area ofthe spillway.

(6) Replace the access bridge to the outletworks intake with a sturdier structure.

(7) As part of the regular maintenanceprogram, remove brush, trees, and debris from thedownstream toe. Also fill the burrowing animal holes.

b. In addition, it is recommended that the Ownermodify his operational procedures as follows:

(1) Develop a detailed emergency operationand warning system for Summit Lake Dam.

(2) Provide round-the-clock surveillance ofSummit Lake Dam during periods of unusually heavyrains.

(3) When warnings of a storm of major proportionsare given by the National Weather Service, the Ownershould activate his emergency operation and warningsystem procedures.

-20-

'.-


SUMMIT LAKE CREEK LACKAWANNA COUNTY

PENNSYLVANIA

SUMMIT LAKE DAM


PENNSYLANIA GAS AND WATER COMPANY



APRIL 1979

PLATES

4i;.

al

SUMMIT LAKE DAM--,,

SUMMITLAKE-.C REEK

MAPLELAKE DAM

2000 0 2000LA RUE DAM- -

SCALE. 1 IN.=2OO0 FT.PIIASE I INSPECTION REPORT

NATIONAL DAM INSPECTION PROGRAM/ SUMMIT LAKE DAMCHINCHILLA PENNSYLVANIA GAS AND WATER COMPANY

LOCATION MAP

1'APRIL 1979 PLATE I

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PHSE INPCINRPR

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OwIver orq/9na/ drawh.



SUMMIT LAKE DAM


SECTIONS AND OUTLET WORKS

APRIL 1979 PLATE 3

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PENNSYLVANIA

SUMMIT LAKE DAM





APRIL 1979

APPENDIX A

CHECKLIST - ENGINEERING DATA

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PENNSYLVANIA

SUMMIT LAKE DAM





APRIL 1979

APPENDIX B

CHECKLIST - VISUAL INSPECTION

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SUMMIT LAKE DAM





APRIL 1979

APPENDIX C

HYDROLOGY AND HYDRAULICS

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APPENDIX C

HYDROLOGY AND HYDRAUUCS

In the recommended Guidelines for Safety ispection of Dams,the Department of the Army, Office of the Chief of Engineers (OCE),established criteria for rating the capacity of spiliways. The recom-mended Spillway Design Flood (SDF) for the size (small, intermediate,or large) and hazard potential (low, significant, or high) classificationof a dam is selected in accordance with the criteria. The SDF forthose dams in the high hazard category varies between one-half of theProbable Maximum Flood (PMF) and the PMF. If the dam and spillwayare not capable of passing the SDF without overtopping failure, thespillway capacity is rated as inadequate. If the dam and spillway arecapable of passing one-half of the PMF without overtopping failure,or if the dam is not in the high hazard category, the spillway capacityis not rated as seriously inadequate. A spillway capacity is rated asseriously inadequate if all of the following conditions exist:

(a) There is a high hazard to loss of life from large flowsdownstream of the dam.

(b) Dam failure resulting from overtopping would significantlyincrease the hazard to loss of life downstream from the dam from thatwhich would exist Just before overtopping failure.

(c) The dam and spillway are not capable of passing one-halfof the PMF without overtopping failure.

cI

.4

APPENDIX C

S C2 6 U'.jv4 P, RiverBasin

Name of Stream: S v-,%T- Lv- Cte4

Name of Dam: , ecm-i L

NDS IDNo.: 0- 0o.9/

DER ID No.: 3"- C.

Latitude: q .j0, 2 8' .3 , longitude: -V 75" 2' 6O"

Top of Dam Oew-eveo Elevation: / _ 3, "7_._.

Streambed Elevation: 13j. - Height of Dam: ft

Reservoir Storage at Top of Dam Elevation: .. q 1 acre-ft

Size Category: StMAL..-

Hazard Category: H. ti. (see Section 5)

SpillwayDesignFlood: V2. / .2 m "P MF

UPSTREAM DAMSDistance Storage

from at top ofDam Height Dam Elevation

Name (miles) JM (acre-ft) Remarks

DOWNSTREAM DAMS Xwr" Po~,'kik,

l.. LAh/,zI _J7 2,0_ Z..-, 3S-.2

/S:, A' .. S pya 35 -.2

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US U ~Ek il Aijr4A RiverBasin

Name ofStream: fumui- LA-ie Cliggw.

Name of Dam: S ,- LALc..E .

Latitude: N H1 A l8'3" Lngtude: -/7S ° Li-t' 5-0"

DETERMINATION OF PM RAINFALL

For Area Aj.which consists of Subareas . j of /'. . sq. mile

Total Drainage Area /, 3 sq. mile

PMF Rainfall Index - , In., 24 hr., 200 sq. mile

Hydromet. 40 Hydromet. 33(Susquehanna Basin) (Other Basins)

Zone N/A .

Geographic Adjustment Factor . . 1.0Revised Index Rainfal hi - 4 -

RAINEALL 121QTRIBUTEDN (percent)

Time. PeAeVI

6 hours 112 hours )27

24 hours

48 hours I!1.V.72 hours / IC-3

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Data for Dam at Outlet of Subarea IL-.(see Sketch on Sheet C-.D

Name of Dam: S umg T LA - Sheet I of_

Height: -- L P (existing)

Spillway Data: Existing Design

Top of Dam Elevation 2385.4 / 3 3 :7

Spillway Crest Elevation /7?,t ,/j 79.1A

Spillway Head Available (ft) _. 2, A,

Type Spillway .R/rAtJC LJ. C-h7-o L. S&L:1i6

"C" Value - Spillway 2. Z , .. ". ,

Crest Length - Spillway (ft) Z..2 ' ,2,

iWiwAn Peak Discharge (cfs) A q A ViAuxiliary Spillway Crest Elevation NIF N 9M C

Auxiliary Spillway Head Available (ft) . ........ ......

Type Auxiliary Spillway ... . ...........

"C" Value - Auxiliary Spillway .. ... ...

Crest Length - Auxiliary Spillway (ft)_, . .....Auxiliary Spilway

Peak Discharge (of)

Combined Snilwav Discharge (ofs) Y , 9, yz

Spillway Rating Curve:

YIIAQ& SUilla (C ISAuxilia, 0S Dlwav (cWI) Gomi (aft)

.,, C 5C S

Data for Dam at Outlet of Subarea Al-Name of Dam: 5 J PAis L AKE Sheet 2 of_

Outlet Works Rating: Oue 1

Invert of Outlet _ _ 6 0_. '

Invert of Inlet _ _,.

Type -E C. -r

Diameter (ft) - D ., . .

Length (ft) - L _ _1

Area (sq. t) -A A-7 1.7 2.19

N .0/-6 1 ___1_LA J

K Entrance CAAMS.. .-( _ .2..5

K Exit - W IA

K Friction* 29.lN2L/R4 /3 -I.8.,. 7 4T x. o"Sum of K (.s" = K.,<(l/) 0 "5 - C .57 ___% ,. .uh,

Maximum Head (ft) - HM 2.7

Q " C A v2g(HM)(cfs) __).

Q Combined (cfs) -_.

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/003

* R = Hydraulic Radius - (Area/Wetted Perimeter) =D/4 for Circular Conduits.

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Data for Dam at Outlet of Subarea A .Name of Dam: - S-u" A& ty. " Sheet 3 of_

Storage Data:Atoreea

Area millon

_ ._ _ E LEV O* 0 0 0 . . ..

137.L1 ELEVl iA . -Si ____ Al./3Uo gf -____

/goo. 4, 2 ..

* ELEVO = ELEVI - (3S 1 /Al)

** Planimetered contour at least 10 feet above top of dam

AA&A. .Reservoir Area at .T-e-am is . . percent of watershed.Remarks: _ _ _ _ _ _ _ _ _ _ _ _

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Data for Dam at Outlet of Subarea A .Name of Dam: U vi"-A ir" it Sheet 4 of

Breach Data:

Sketch of Dam Profile (not to scale):

Sketch of Top of Dam (not to scale):

Soil Type from Visual Inspection: _ C.A 0 TShy .

Maximum Penrnmjible Velocity (Plate 28., EM 1110-2-1601) .. jfps(from Q CLH"" = V Aand depth - (2/3) x H) AtLeJ

HMAX - (4/9 V2/C 2 ) _ft., C -3.1/363.4

HMAX + Top of Dam Elev.- /-33 - FAILEL(Above is elevation at which failure would start)

Dam Breach Data:

BRWID = j0 ft (width of bottom of breach)Z = / (side slopes of breach)

ELBM - /360.0 (bottom of breach elevation,minimum of zero storage elevation)

WSEL = ' 37 9. A/ (normal pool elevation)

T FAIL - m mine

- O . hrs (time for breach to develop)

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S AudoV HANJ.A River BasinName of Stream: .Cuz;T L.Ak" C.Afi..

Name of Dam: Su f 'P L/iLC

Latitude: I V oif 28' 30" Longitude: .i/ - ' I' 5-0"

Drainage Area: ._,.__ _____sq. mile

Data for Subarea: / 1. (see Sketch on Sheet C-.._j)Name of Dam at Outlet of Subarea: Soli0%I LA A-L"

Drainage Area of Subarea: ,, 3 sq. mile

Subarea Characteristics:

Assumed Losses: 1.0-inch initial abstraction + 0.05 in/hr

The following are measured from outlet of subarea to thepoint noted:

L = Length of Main Watercourse extended to the divide =A / mile

LCA = Length of Main Watercourse to the centroid 0. ; mile

From NAB Data: Aaa IJ PA^'i ir

cp= 0,_6___

CT = /. _

TP C T x (Lx LCA) 0 3 = , (hrs)

Flow at Start of Storm = 1.5 cfs/sq. mile x Subarea D.A P ,0 O cfs

Computer Data:

QRCSN = -0.05 (5% of peak flow)

RTIOR = 2.0

Remarks:

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LAKE DAM

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SUSQUEHANNA RIVER BASINSUMMIT LAKE CREEK LACKAWANNA COUNTY

PENNSYLVANIA

SUMMIT LAKE DAM





APRIL 1979

APPENDIX D

PHOTOGRAPHS

ISti,

SUMMIT LAKE DAM

A. Emfbankment -ViewfrmSila

at Right Abutment

1I B.Downstream Masonryace

BIT D-1

SUMMIT LAKE DAM

C. Outlet Works Outfall

D. Upstream Slope and Valve House

TD-2

I-

SUMMIT LAKE DAM

E. Spillway - Looking Downstream

F. Spillway Cascade

D-3



PENNSYLVANIA

SUMMIT LAKE DAM





APRIL 1979

APPENDIX E

GEOLOGY

4'

SUMIIT LAKE DAM

APPENDIX E

GEOLOGY

1. General Geology. The damsite and reservoirare located inLackawanna County. Lackawanna Countywas completely covered with ice during the last con-tinental glaciation of Pleistocene time. The generaldirection of ice movement was S 35 - 40 W. Glacialdrift covers the entire County, except where subse-quent erosion has removed it. Thick deposits of glacialoutwash occur in many places along the LackawannaRiver, and are 50 to 100 feet thick near Dickson,Scranton, and Hoosic.

The only important structural feature inLackawanna County is the Lackawanna Syncline, whichtraverses the County in a southwesterly direction. Thesyncline enters the County at the northeast corner as anarrow shallow trough, gradually deepens and broadenstoward the southwest, and reaches its maximum developmentin Luzerne County. The rock formations exposed rangefrom the post-Pottsville formations (youngest) throughthe Pottsville, Mauch Chunk shale, Pocono sandstone tothe Damascus formation of the Catskill group (oldest).The rim rocks, the Pottsville formation ang Pocon8sandstone, have dips that rarely exceed 10 to 20 andform a rather simple syncline. The core rocks,the post-Pottsville formations, are folded into aseries of minor anticlines and synclines which trendabout N 700 E. The rocks in the northwestern andsoutheastern parts of the County, outside of the limitsof the Lackawanna Syncline, are generally horizontallystratified.

The Lackawanna River, in general, followsthe axis of the Lackawanna Syncline. Southeast ofthe Lackawanna River, the rise in terrain is quitegradual and the crests of the high mountains are severalmiles from the Lackawanna River. Streams, such as RoaringBrook, Stafford Meadow Brook, and Spring Brook, havecut deep canyons through the mountains and follow atorturous course to their confluence with the LackawannaRiver near Scranton. Northwest of Lackawanna River,

E-1

...... . . . I " I. . . . . . . .. . . l i I I I I1 1 l I r - I "I I I I i i

the mountains rise abruptly to a sharp ridge which inmost places is somewhat higher than the country to thenorthwest. Consequently, most of the drainage in thispart of the County flows westward by way of TunkhannockCreek. A few small tributary streams, however, such asLeggetts Creek, flow eastward from this area intoLackawanna River. In the area of interest, the LackawannaRiver streambed is founded in post-Pottsville formations.Proceeding uphill from the river, the older Pottsvilleformation, Mauch Chunk shale, Pocono sandstone, andCatskill continental group are encountered in turn.The tributary streams, in flowing down the mountains,have generally cut through or around the hard sandstoneand conglomerate members, and have eroded their stream-bed into the softer shales and glacial till. TheCatskill continental group of rocks underlies thegreater part of Lackawanna County.

2. Site Geology. Summit Lake Dam is founded onhardpan in the Catskill formation of late Devonian Age.The dam is situated on the Alleghany high plateau nearthe contact of the plateau and the valley and ridgeprovince. Structure in the area is primarily thatof a gently sloping dissected plateau. The Catskillformation is composed of dark red shale claystone, andsiltstone; gray, fine to medium grained sandstone, andcoarse grained conglomerates. Crossbedding, channelingand cut-and-fill features are common to the sandstoneand conglomerate units. Siltstone predominates in thelower part of the formation. Bedding is generally welldeveloped with thicknesses ranging from one foot toten to sixteen feet in the coarser more competent beds.

The available records did not yield in-formation pertinent to the foundation conditions atthe damsite, other than describing the bedrock ashardpan.

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PA INC HARRISBURG NATIONAL DAN INSPECTION ...Lake Creek. Maple Lake Dam releases water into La Rue...

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Transcript of PA INC HARRISBURG NATIONAL DAN INSPECTION ...Lake Creek. Maple Lake Dam releases water into La Rue...