Glen Osborne City Zoning Code
ARTICLE VIII
Steep Slopes Regulations
§ 155-801 Purpose.
A.
To protect the public health and safety of Borough residents by mitigating potential hazards such as land subsidence that may arise due to the inappropriate development of lands with steep slopes or other sensitive natural resources.
B.
To safeguard the public welfare by guiding future development patterns to prevent potential detrimental impacts on the region's water and stream quality.
C.
To preserve the public health, safety, and welfare by protecting private property from potential damages that may occur due to uncontrolled development of lands with steep slopes, undevelopable soils, and other sensitive natural resources.
D.
To promote and protect the Borough's quality of life by restricting development on steep slopes.
§ 155-802 Intent.
The steep slope regulations herein are intended to supplement the requirements of general zoning districts wherever steep slopes are found in order to prevent loss of health, life, or property from landslides and to regulate uses and development on or near steep slopes.
§ 155-803 Steep slope regulations.
A.
A Slope and Soil Stability Analysis, as described and defined in § 804, shall be required for proposed developments on parcels of land that have existing slopes in excess of 8%.
B.
In areas of steep existing slopes (i.e., those over 8%), the following standards shall apply:
(1)
Existing slopes 8%–15%, no more than 60% of the areas shall be developed, regraded, or stripped of vegetation and a registered professional engineer experienced with slope and soil studies and duly licensed in the Commonwealth of Pennsylvania, must provide written certification to support the proposed work accompanied by a Slope and Soil Stability Study.
(2)
Existing slopes 15%–25%, no more than 40% of the areas shall be developed, regraded, or stripped of vegetation and a Geotechnical Engineering Site Investigation Report, prepared by a registered professional engineer licensed in the commonwealth with geotechnical experience, shall also be submitted along with a slope and soil stability analysis.
(3)
Existing slopes 25%–35%, no more than 20% of the areas shall be developed, regraded, or stripped of vegetation and a Geological Hazard Report and a Geotechnical Engineering Site Investigation Report, both prepared by a registered professional engineer licensed in the commonwealth with geotechnical and geological experience, shall also be submitted along with a Slope and Soil Stability Analysis.
(4)
Existing slopes 35% or more shall not be disturbed.
§ 155-804 Slope and soil stability analysis.
A.
A Slope and Soil Stability Analysis, prepared and sealed by a registered professional engineer licensed in the Commonwealth of Pennsylvania experienced in soil, slope, and foundation engineering, shall be submitted for any sites with existing slopes in the following categories: 8%–15%, 15%–25%, and 25%–35%.
B.
The Slope and Soil Stability Analysis shall include the following detailed factual information, analyses, and recommendations:
(1)
Surface features, including surface contours, rock outcrops, building and/or construction remnants, paving/roadways/cart-paths, watercourses, ditches, rills, ponds/lakes, wooded areas, filled-in areas, and recent and/or old landslides, rock-fall areas, wet or saturated ground surface areas, slumping and sloughing ground areas, potential mine subsidence depressions, ground tension cracks, retaining structures, and other relevant site elements and/or appurtenances of interest.
(2)
Hydronic features: the presence of seepage zones, depth to groundwater, surface or subsurface seeps and springs, and the possible fluctuations with the seasons.
(3)
Subsurface features.
(a)
A plotted, horizontal and vertical record of the stratification of the soil and rock deposits.
(b)
Information on the relative density of granular soils in the different strata and on the consistency of cohesive soils.
(c)
Information on the subsurface geological features and past mining activity, including thickness of total overburden (interval between mine roof and ground surface) and thickness of bedrock overburden (interval between mine roof and bedrock surface), as well as the apparent status of the mine (i.e., collapsed, partially collapsed, intact), and quality of the rock overburden strata. The project professional geotechnical engineer licensed in the Commonwealth of Pennsylvania shall provide an evaluation of the risk of structure damage due to potential mine subsidence. Further, test boring logs shall include the presence, if encountered, of subsurface boulders, obstructions, voids, conchoidal and other cracking/fracturing of bedrock, sometimes associated with mine subsidence, bedding planes, carbonaceous materials, pyritic and/or marcasitic materials, potentially-expansive soils and bedrock, high-plasticity (aka fat) clays, and delineations between strata and parent soil materials (i.e., fill, colluvium, residuum, alluvium, glacio-fluvium, etc.).
(4)
Exploration methods. Physical explorations can be carried out by several methods. Field explorations should follow the applicable standards, or the procedures and practices recommended by the American Society for Testing and Materials (ASTM). It is generally sufficient to secure soil samples at vertical intervals of three feet in depth or at intervals less than three feet to identify changes in subsurface materials. The intervals should be determined by such conditions as the soils encountered, proposed earthwork that is planned, and/or the type of proposed structure to be constructed, but should not be less than at three-foot vertical intervals. Soil samples shall be obtained from all borings for identification, classification, and logging purposes, as well as potential physical laboratory testing, as deemed necessary by the project professional geotechnical engineer licensed in the Commonwealth of Pennsylvania. Detailed boring logs/records shall be prepared and maintained by the geologist or engineer monitoring test borings during test drilling operations.
(5)
The spacing and depths of borings should also be based on site conditions and proposed construction. Maximum spacing between borings should not exceed 250 feet to 300 feet for proposed roadways, pavements, and proposed cut slopes and fill embankments. Borings drilled for proposed structures/buildings shall be spaced at 100 feet intervals, on average, and their placement determined by the project professional geotechnical engineer licensed in the Commonwealth of Pennsylvania. Further, two borings for the initial 6,000 square feet to 10,000 square feet of proposed building "footprint" area is the minimum for a three-story or greater structure. A minimum of two borings per structure is recommended for proposed one- to two-story single-family residences with a footprint no greater than 10,000 square feet. Larger proposed buildings shall include at least one additional boring for every additional 10,000 square feet of footprint area exceeding the initial 10,000 square-foot footprint area.
(6)
Groundwater measurements. Information is required on groundwater elevations, including depth of permanent and perched water tables. Water levels should be determined upon completing the boring and again approximately 24 hours later. Groundwater levels/elevations shall be included on the boring logs/records.
(7)
Classifications and descriptions. Direct observation of soils samples from various depths and locations will be required for correlation with the known geology of the area. Direct observations of boring operations must be carried out by a registered professional engineer or registered professional geologist in the Commonwealth of Pennsylvania. Classification and description of soils will be performed using the Unified Classification System (ASTM Specification D2487) and by the Visual Manual Identification Procedure (ASTM Specification D2488), although classifications can be supplemented via physical laboratory testing results (i.e., gradation analysis and plasticity testing).
(8)
Laboratory testing. The laboratory testing program should be dependent upon the characteristics of the soils and the anticipated geotechnical problems analysis. The project professional geotechnical engineer shall determine the required physical laboratory testing needed to facilitate the engineering analyses. Regardless, adequate laboratory testing, or other field testing means (such as the standard penetration test performed in accordance with ASTM D1586, or equal standardized testing procedure) shall be performed as necessary to characterize the strength properties, as well as other pertinent parameters, of subsurface soil strata.
(9)
The recommendations of all such investigations and reports of steep slopes and other identified soil or water condition hazards shall be reviewed by the Borough Engineer. Incorporation of said recommendations may be required as conditions for preliminary approval and/or final approval.
(10)
All public and private roads, bridges, utilities, and other facilities shall be located, designed, and constructed to avoid steep slope areas or to withstand any anticipated soil or rock movement.
(11)
Road and utility alignments and grades shall minimize cuts and fills.
(12)
Hazardous slope conditions, including, but not limited to, landslides, slumps, slough, and rock-falls, which may be present on a site must be corrected prior to completion of the development.
(13)
The location and dimensions of proposed cut-and-fill slopes shall be provided.
(14)
General. The setbacks and other restrictions specified by this section are minimum and may be increased by the Borough by the recommendation of a registered professional engineer or registered professional geologist licensed by the Commonwealth of Pennsylvania with the approval of the Borough Engineer if necessary for safety and stability or to prevent damage of abutting properties from sedimentation or erosion or to provide access for slope maintenance and drainage. Retaining walls may be used to reduce the required setbacks when approved by the Borough Engineer.
(15)
Setbacks from property lines. The tops of cuts and toes of fill slopes shall be set back from the outer boundaries of the area to be disturbed, including slope return areas and easements.
§ 155-805 Geotechnical engineering site investigation report.
A.
A Geotechnical Engineering Site Investigation Report, prepared and sealed by a registered professional engineer licensed in the Commonwealth of Pennsylvania experienced in soil, slope analysis, and foundation engineering shall be submitted for any sites with slopes in the following categories: 15%–25% and 25%–35%.
B.
The intent of a comprehensive Geotechnical Engineering Site Investigation Report is to determine the stability of proposed grading operations and to develop detailed engineered measures to provide for long-term slope stability. Test borings, extending to sufficient depths to evaluate proposed grading, shall be performed. Specifically, at a minimum, borings should be located at the toes (base) of proposed fill embankments supporting roads or structures, or are six feet or greater in height and will be graded to a slope steeper than four horizontal to one vertical. Sufficient borings, as determined by the registered professional engineer licensed in the Commonwealth of Pennsylvania, shall be located in cut slope areas supporting roads or structures, or that are greater than six feet in height and will be graded to a slope steeper than 4 1/2 horizontal to one vertical. The borings should extend at least to bedrock surface, but must also extend to a depth of at least five feet beyond the anticipated cut depth. At least some proposed cut slope area borings shall be located so that the full vertical cross-section of the soil mantle and bedrock zone within the proposed cut depth can be clearly identified.
C.
Standard penetration tests (SPTs) should be conducted in all test borings at no greater than three-foot vertical intervals in the soil mantle of all borings in compliance with the most current version of the American Society for Testing and Materials (ASTM) Test Designation: D1586. Where SPT refusal on bedrock is encountered prior to reaching the required depth, continuous NX, NQ, or NQ-2 rock cores should be procured as required for the engineering analysis. Thin-walled steel (Shelby) tube samples of relatively undisturbed soil samples should be procured from selected borings, if and where required for physical laboratory testing, to determine relevant soil properties for the engineering analysis, as determined by the registered professional engineer licensed in the Commonwealth of Pennsylvania.
D.
Groundwater encountered in each test boring should be recorded during drilling operations and 24 hours after completing each boring. This information shall be provided on the typewritten test boring logs/records accompanying the geotechnical engineering investigation report.
E.
The borings should be accurately located in the field. Ground surface elevations should be obtained at each boring. The final boring locations and their ground surface locations must be shown on a to-scale topographical survey, included with the geotechnical engineering investigation report, that includes existing contours and proposed site grading contours.
F.
A suitable typewritten boring log/record should be provided for each boring. At minimum, the logs should include: boring designation; SPT results; N values; depths of strata encountered; percent core recoveries and rock quality designations (RQDs) of rock cores; date boring was drilled; groundwater information (minimum zero-hour and twenty-four-hour readings); detailed types and descriptions of geomaterials encountered; delineations between strata, including parent material (i.e., fill, colluvium, residuum, alluvium, glacio-fluvium, etc.) boundaries; comments or notes regarding voids, boulders, obstructions, organics, construction rubble, or any other unusual or notable subsurface conditions encountered.
G.
A registered professional engineer licensed in the Commonwealth of Pennsylvania experienced in geotechnical engineering shall complete a quantitative slope stability analysis of proposed cut slopes and fill embankments. At a minimum, test boring and relevant laboratory soil or rock test results, site groundwater and surface water findings, anticipated surcharge, traffic, structure, and/or hydrostatic loads/conditions and any other factors affecting the proposed slopes should be included in the analysis. The slope stability analysis must be based on a method accepted by the geotechnical engineering community, and that has been published in an accepted engineering textbook, journal, or proceedings. The analysis should ultimately provide the minimum factor of safety (FS) against movement/failure of the proposed slope. A slope will generally be considered stable in the long term when the FS > 1.5, unless special circumstances, as approved by the Borough, should be allowed. Various slope/embankment construction scenarios can be analyzed by the engineer, but no proposed slopes/embankments indicating a FS less than that approved will be deemed acceptable. The side-slopes of proposed stormwater ponds/basins, and similar water-bearing features, shall also be subjected to slope stability analyses. The rapid drawdown condition for such features shall be included with the analysis. Slopes that may be potentially subjected to the rapid drawdown condition shall exhibit a minimum slope stability factor of safety of 1.2.
H.
The typewritten report, prepared and signed by the registered professional engineer licensed in the Commonwealth of Pennsylvania performing the slope stability analyses, shall be submitted to the Borough. The professional engineering seal for the authoring engineer shall be affixed to the report. The report shall, at a minimum, include the following:
(1)
A detailed description of the existing surface and subsurface site conditions.
(2)
A review of the site geology and geohydrology. United States Geological Survey (USGS) maps and resources relevant to areas that are susceptible to land sliding as well as such maps/references showing ancient, old, or recent landslides within the proposed development area shall be discussed in the report.
(3)
A discussion of any slope movements, sloughs, slumps, landslides, rock-falls, or mining on or adjacent to the site, and an evaluation of their existing and/or potential impact on the site.
(4)
Subsurface profile and cross-section drawings depicting all relevant parameters of the slopes that were analyzed.
(5)
A discussion of the slope stability analyses.
(6)
Conclusion(s) regarding the stability of proposed site grading.
(7)
The typewritten test boring logs/records and laboratory test results.
(8)
A copy of the calculations/computer output for the stability analyses.
(9)
The to-scale boring location plan described above.
(10)
With respect to slope stability, the report should also include recommendations, as required for:
(a)
Grades for stable cut slopes and fill embankments.
(b)
Drainage requirements.
(c)
Subgrade preparations.
(d)
Benching requirements.
(e)
Suitable fill material, compaction, loose-lift thickness, and moisture requirements.
(f)
Erosion protection requirements.
(g)
Retaining structures, if necessary.
(h)
Limitations or constraints to proposed slope construction.
§ 155-806 Geological hazard report.
A.
A Geological Hazard Report prepared and sealed by a registered professional engineer licensed in the Commonwealth of Pennsylvania experienced in soil, slope, geotechnical, and foundation engineering shall be submitted for any sites with slopes that are 25%–35%.
B.
The Geological Hazard Report shall include the following:
(1)
A map identifying all of the geological hazard areas found to exist based on an actual site investigation.
(2)
Topographic contour lines at two-foot intervals for the subject site before and after completion of the proposed development.
(3)
A soils survey and geologic evaluation, including a narrative description of any conditions or factors which are relevant to the possibility of landslides caused by development of the site.
(4)
A statement identifying whether the subject property, or any adjacent properties, have any history of landslides.
(5)
A recommendation as to whether the site can be made safe for the proposed use and development, including any specific recommended construction or control techniques.
(6)
If the recommendation is that the site is not safe, a plan and specifications detailing how the applicant proposes to make the site safe for the proposed use and protect adjacent properties from potential safety hazards must be included.