Statutes, codes, and regulations
Delaware Administrative Code
Title 7 - Natural Resources and Environmental ControlDivision of Watershed Stewardship
Sediment and Stormwater Regulations
Section 5101-12.0 - Supplemental Requirements for Best Management Practices

7 Del. Admin. Code § 5101-12.0

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Current through Reigster Vol. 28, No. 6, December 1, 2024
Section 5101-12.0 - Supplemental Requirements for Best Management Practices
12.1 Soil Investigation Procedures for Stormwater Best Management Practices (BMPs)
12.1.1 All applicable federal, state and local laws, rules, regulations or permit requirements governing soil investigations shall be followed.
12.1.2 General Soil Investigations
12.1.2.1 Borings and pits shall be excavated to verify soil profile and to determine depth to limiting layer.
12.1.2.2 Soil Characterization
12.1.2.2.1 The minimum number of borings or pits shall be conducted for each BMP as follows:
12.1.2.2.1.1 For surface area BMPs, two (2) borings or pits required for the first 8,000 square feet, three (3) borings or pits required for up to 16,000 square feet, four (4) borings or pits required for up to 25,000 square feet and one (1) additional boring or pit required for each additional 25,000 square feet. Boring or pit locations shall be distributed within the facility and sufficient to determine variability.
12.1.2.2.1.2 For linear BMPs, two (2) borings or pits required up to 500 linear feet and one (1) additional boring or pit per 500 linear feet of trench, and sufficient to determine variability.
12.1.2.2.2 Borings or test pits must be advanced to the depth of the limiting layer or a minimum of three (3) feet below bottom of a proposed facility, whichever is encountered first.
12.1.3 Infiltration Testing Procedures
12.1.3.1 Planning and Design Phase
12.1.3.1.1 Any deviation from these procedures must be approved by the Department or Delegated Agency having jurisdiction.
12.1.3.1.2 Individuals in responsible charge of infiltration testing shall possess a Class D On-Site License issued by DNREC Division of Water Groundwater Discharges Section or be licensed in the State of Delaware as a Professional Engineer or Professional Geologist.
12.1.3.1.3 An initial screening of readily available data is required to determine feasibility of infiltration practices. Screening shall include at a minimum:
12.1.3.1.3.1 Site topography;
12.1.3.1.3.2 Soil characteristics as defined in the USDA NRCS Web Soil Survey;
12.1.3.1.3.3 Depth to groundwater and seasonal high water table; and
12.1.3.1.3.4 Historical groundwater level data from the nearest Delaware Geological Survey (DGS) monitoring well or wells.
12.1.3.1.4 Separation to a limiting layer such as bedrock or groundwater shall be at least two (2) feet.
12.1.3.1.5 Field Permeability Testing shall be done in accordance with ASTM-D5126 "Comparison of Field Methods for Determining Hydraulic Conductivity in the Vadose Zone".
12.1.3.1.5.1 Single Ring or Double Ring Infiltrometer are preferred test methods.
12.1.3.1.5.2 Cased Borehole Permeameter method is allowable only in cases where test pit excavation depths or site constraints pose safety or other concerns. Results from tests conducted using the Cased Borehole Permeameter method will only be accepted when approval is granted by the Department or Delegated Agency to use the Cased Borehole Permeameter method prior to conducting the test. Casing for Cased Borehole test shall have a minimum four (4) inch diameter.
12.1.3.1.6 The minimum number of field measured infiltration tests are based on the proposed facility's dimensions as follows:
12.1.3.1.6.1 For an infiltration trench with less than 10,000 square feet of impervious drainage area, one (1) test required up to 500 linear feet and one (1) additional test per 250 linear feet of trench, and sufficient to determine variability.
12.1.3.1.6.2 For an infiltration trench with greater than 10,000 square feet of impervious drainage area, one (1) test required up to 250 linear feet and one (1) additional test per 250 linear feet of system, and sufficient to determine variability.
12.1.3.1.6.3 For an infiltration trench used with roadway perforated pipe layouts, one (1) test required up to 500 linear feet and one (1) additional test per 500 linear feet of trench, and sufficient to determine variability.
12.1.3.1.6.4 For an infiltrating bioretention system, one (1) test required for the first 8,000 square feet, two (2) tests required for up to 16,000 square feet, three (3) tests required for up to 25,000 square feet and one additional test required for each additional 25,000 square feet. Test locations shall be distributed within the facility and sufficient to determine variability.
12.1.3.1.6.5 For a surface infiltration basin, one (1) test required for the first 8,000 square feet, two (2) tests required for up to 16,000 square feet, three (3) tests required for up to 25,000 square feet and one additional test required for each additional 25,000 square feet. Test locations shall be distributed within the facility and sufficient to determine variability.
12.1.3.1.6.6 For a subsurface infiltrating practice, one (1) test required per infiltration area with an additional test for every 8,000 square feet of infiltration area, and sufficient to determine variability.
12.1.3.1.7 A saturation period of one hour or a drop of 12 inches or 30.5 centimeters is required. The saturation period shall not be used in determining field verified infiltration rate.
12.1.3.1.8 After the saturation period, a minimum of two (2) test periods, are required. or until at least two (2) consecutive test periods are consistent. Each test period shall have a maximum reading interval of 15 minutes and meet one (1) of the following criteria:
12.1.3.1.8.1 A minimum of one hour,
12.1.3.1.8.2 A drop of at least 12 inches in 15 minutes or less for a minimum of 30 minutes, or
12.1.3.1.8.3 A stabilized infiltration rate as defined below:
12.1.3.1.8.3.1 A difference of 0.25 inches or less of drop between the highest and lowest reading of four (4) consecutive readings for infiltration rates greater than two (2.0) inches per hour.
12.1.3.1.8.3.2 A difference of 0.125 inches or less of drop between the highest and lowest reading of four (4) consecutive readings for infiltration rates equal to or less than two (2.0) inches per hour.
12.1.3.1.9 When using the constant head test method, the water level inside the casing shall be maintained at a constant level or refilled to the starting level after each reading throughout the test period at no more than 15 minute intervals.
12.1.3.1.10 When using the falling head test method each test period shall start with the same initial head of six (6) inches to normalize the effect of head on the measured drop.
12.1.3.1.11 The field verified infiltration rate shall be the final steady state reading of the test performed.
12.1.3.1.12 Reporting requirements shall be in accordance with Soil Investigation Report.
12.1.3.2 Construction Phase
12.1.3.2.1 For all infiltration facilities, confirmatory field verified infiltration testing shall be performed during facility construction. Unless recommended by a soil professional and approved by the Department or Delegated Agency prior to conducting the tests, the minimum number of confirmatory infiltration tests shall be in accordance with the original testing procedures used for design.
12.1.3.2.2 The confirmatory infiltration testing rate shall be no less than 150% of the approved design rate for the facility. If a deviation of less than 150% is observed, the design calculation for the facility shall be rerun by the design engineerbased upon 50% of the measured confirmatory infiltration testing rate to demonstrate that the facility will function as originally designed. The computations that confirm performance shall be provided with the Post Construction Verification Documents.
12.1.3.2.3 In addition to confirmatory infiltration testing, a hand auger shall be performed adjacent to the confirmatory infiltration test location or at locations recommended by the soils professional to a minimum depth of three (3) feet below the bottom of the facility to confirm that a limiting layer is not present and to log the soils conditions. If a limiting layer is observed at a depth less than two (2) feet, the licensed professional shall re-evaluate the design and submit recommendations and any required design changes to the Department or Delegated Agency for review and approval.
12.1.3.2.4 If confirmatory infiltration testing is not required by the Department or Delegated Agency, hand augers shall be performed within the proposed practice to log the soils and groundwater conditions within three (3) feet of the bottom of the practice.
12.1.4 Soil Investigation for Embankments
12.1.4.1 A detailed review of the existing site conditions and proposed embankment construction shall be performed by the responsible geotechnical engineer as part of the design process.
12.1.4.2 Site Investigation
12.1.4.2.1 The soil investigation for the embankment plan shall include the following:
12.1.4.2.1.1 Development of performance criteria, which may include but not be limited to allowable settlement, time available for construction, and seismic design requirements.
12.1.4.2.1.2 Identification of potential geologic hazards or areas of concern such as soft soils, and potential variability of local geology.
12.1.4.2.1.3 Identification of engineering analyses to be performed which may include but not be limited to: limit equilibrium slope stability analyses, liquefaction susceptibility, lateral spreading and slope stability deformations, and settlement evaluations.
12.1.4.2.1.4 Identification of engineering properties required for these analyses.
12.1.4.2.1.5 Determination of methods to obtain parameters and assess the validity of such methods for the material type.
12.1.4.2.1.6 Determination of the number of tests or samples needed and appropriate locations for them.
12.1.4.3 Methods of Subsurface Exploration
12.1.4.3.1 The subsurface exploration method shall be selected by the design professional based on the existing and proposed site conditions.
12.1.4.3.2 Minimum Number of Explorations
12.1.4.3.2.1 Embankments shall have explorations every 200 feet on center along the length of the embankment.
12.1.4.3.2.2 Pond bottom explorations shall follow the Soil Investigation Procedures. Exploration locations shall be distributed as uniformly as possible within the facility.
12.1.4.3.3 Minimum Depth of Explorations
12.1.4.3.3.1 Unless bedrock is encountered at a shallower depth, explorations shall be at a depth twice the proposed height from bottom of pond to top of embankment.
12.1.4.3.3.2 If bedrock is encountered, a minimum five (5) foot rock core shall be performed. If organic, plastic, or soils with an actual or estimated N-value less than four (4) are encountered, extended exploration to a depth of four (4) times the proposed embankment height.
12.1.4.3.4 If there is a potential for a significant groundwater gradient beneath an embankment or surface water levels are significantly higher on one side of the embankment than the other, the effect of reduced soil strength caused by water seepage shall be evaluated.
12.1.4.3.5 Seepage effects shall be considered when an embankment is placed on or near the top of a slope that has known or potential seepage through it.
12.1.5 Soil Investigation Report
12.1.5.1 Soil investigation reports shall include the following:
12.1.5.1.1 The signature, seal and date of a professional engineer or professional geologist experienced in soils licensed in the State of Delaware. Reports for embankments must be signed, sealed and dated by a professional engineer licensed in the State of Delaware.
12.1.5.1.2 A general description of the project, project elements, and project background.
12.1.5.1.3 Project site surface conditions and current use.
12.1.5.1.4 Regional and site geology.
12.1.5.1.5 Borehole or test pit logs must provide the following information:
12.1.5.1.5.1 Project name;
12.1.5.1.5.2 Name of individual collecting the field data;
12.1.5.1.5.3 Date field data was collected;
12.1.5.1.5.4 Type of boring or test pit excavation method and equipment used;
12.1.5.1.5.5 Air temperature and precipitation, including significant precipitation prior to investigation;
12.1.5.1.5.6 Elevation of boring location based on site benchmark;
12.1.5.1.5.7 Visual description of soil profile layers, and depths below grade encountered;
12.1.5.1.5.8 Sample numbers;
12.1.5.1.5.9 Depths of instability such as cave in, sloughing, flowing sands, or obstructions;
12.1.5.1.5.10 Blow counts if Standard Penetration Test (SPT) borings are performed;
12.1.5.1.5.11 Depth of seasonal high water table indicators such as mottling;
12.1.5.1.5.12 Depth of encountered free water during and after excavation;
12.1.5.1.5.13 Depth to bedrock if encountered;
12.1.5.1.5.14 General observations; and
12.1.5.1.5.15 Testing standards.
12.1.5.1.6 Depth and type of field testing performed. A summary of the laboratory testing conducted, if applicable.
12.1.5.1.7 Project soil and rock conditions shall include a description of the soil and rock units encountered, and how the units tie into the site geology.
12.1.5.1.8 Groundwater conditions shall be described, including the identification of any confined aquifers, artesian pressures, perched water tables, potential seasonal variations, if known, any influences on the ground water levels observed, and direction and gradient of groundwater, if known.
12.1.5.1.9 If rock slopes are present, the report shall discuss rock structure, including but not limited to the results of any field structure mapping using photographs as needed, joint condition, rock strength, and potential for seepage.
12.1.5.1.10 Summary of geological hazards identified and their impact on the project design, if any. Describe the location and extent of the geological hazard.
12.1.5.1.11 For analysis of unstable slopes including existing settlement areas, cuts, and fills, include background regarding the analysis approach, assessment of failure mechanisms, and determination of design parameters. A description of any back-analyses conducted, the results of those analyses, comparison of those results to any laboratory test data obtained, and the conclusions made regarding the parameters that shall be used for final design shall be included in this section.
12.1.5.1.12 Geotechnical recommendations for structural earthwork shall include:
12.1.5.1.12.1 Embankment design recommendations, if any are present, such as the slope required for stability, the need and extent of removal of any unsuitable materials beneath the proposed fills, and any other measures that need to be taken to provide a stable embankment, embankment settlement magnitude and rate.
12.1.5.1.12.2 Cut design recommendations, if any are present, such as the slope required for stability, seepage and piping control, erosion control measures needed, and any special measures required to provide a stable slope.
12.1.5.1.12.3 Determination of adequacy of excavated material for use as structural fill or spoil and include data for structural designs of BMP outlet works.
12.1.5.1.13 Long-term or construction monitoring needs if applicable. Provide recommendations on the types of instrumentation needed to evaluate long-term performance or to control construction, the reading schedule required, how the data should be used to control construction or to evaluate long-term performance, and the zone of influence for each instrument.
12.1.5.1.14 Address issues of construction staging, shoring needs and potential installation difficulties, temporary slopes, potential foundation installation problems, earthwork constructability issues, and dewatering, as applicable.
12.1.5.1.15 Appendices to support geotechnical recommendations.
12.1.5.2 Infiltration test reports shall include the following:
12.1.5.2.1 Description of approved infiltration testing method performed.
12.1.5.2.2 Summary table of location of test, depth of test, elevation of test if available and field verified infiltration rate.
12.1.5.2.3 Infiltration test log must state:
12.1.5.2.3.1 Name of individual performing test;
12.1.5.2.3.2 Date test was performed;
12.1.5.2.3.3 Type of test method;
12.1.5.2.3.4 Air temperature and precipitation;
12.1.5.2.3.5 Depth of test below ground surface and elevation;
12.1.5.2.3.6 Diameters of boring and casing;
12.1.5.2.3.7 Depth of casing penetration; and
12.1.5.2.3.8 Time and depth from reference point for each time increment.
12.1.5.2.4 Infiltration rate graph for each test. The graphs shall be field verified infiltration rate versus elapsed time of test. Appended to each graph shall be a table of the testing results.
12.1.5.2.5 Geotechnical recommendations shall be provided for each stormwater management facility, including design infiltration rate, impact of infiltration on adjacent facilities, effect of infiltration on slope stability, if the facility is located on a slope, stability of slopes within the facility, and foundation bearing resistance.
12.1.5.2.5.1 A minimum factor of safety of 2.0 shall be applied to field results from Single Ring or Double Ring Infiltrometer testing.
12.1.5.2.5.2 A minimum factor of safety of 2.5 shall be applied to field results from Cased Borehole Permeameter testing.
12.1.5.2.5.3 The report shall provide an elevation range over which the recommended design rates are applicable.
12.1.5.2.5.4 The maximum design infiltration rate shall be less than or equal to 15 inches per hour.
12.1.5.2.6 If steady state conditions for a given test are not achieved, the professional in responsible charge of infiltration testing shall provide an explanation as to why steady state could not be achieved and their professional opinion regarding the use of the results for design purposes. If steady state is not achieved for a given test and a reasonable professional opinion is not provided, the Department or Delegated Agency may require additional testing.
12.1.5.3 Geotechnical reports for embankments shall include the following:
12.1.5.3.1 Summary of design analyses, which provide the project description and basis of the design recommendations.
12.1.5.3.2 Summary of stability analysis, which provide the results of the stability analyses performed for the given embankment dimensions.
12.1.5.3.3 Summary of settlement analyses, including design assumptions and settlement results for above-grade embankments.
12.1.5.3.4 Design recommendations for embankment construction shall identify the following actions:
12.1.5.3.4.1 Construction procedures for placement of material in embankment widening areas;
12.1.5.3.4.2 Embankment cut-off and core trench materials for above-grade embankments;
12.1.5.3.4.3 Special notes for excavation of unsuitable material, with specific backfill requirements.
12.1.5.3.4.4 Specific measures required prior to placing embankment material.
12.1.5.3.4.5 Installation of appropriate erosion control and vegetative cover.
12.2 Setbacks
12.2.1 All applicable federal, state and local laws, rules, regulations or permit requirements governing setbacks shall be followed.
12.2.2 Where multiple setbacks exist, the greatest setback requirement shall apply.
12.2.3 Horizontal setback distances for all applicable best management practices (BMPs) shall be shown on the design plans with dimensions. The setback distances shall be measured from the BMP's water surface elevation for the Cv event to the following:
12.2.3.1 Center of a public or domestic well;
12.2.3.2 Closest point of a drainfield or components of a septic system;
12.2.3.3 Outer edge of pipe or conduit for utilities;
12.2.3.4 Outside edge of slabs or vertical walls of buildings or structures; and
12.2.3.5 Closest point of a property line.
12.2.4 Applicable Setbacks
12.2.4.1 Public and Domestic Wells
12.2.4.1.1 Setbacks from public and domestic wells are applicable to the following stormwater BMPs: infiltration practices, bioretention, permeable pavement systems, constructed wetlands, detention practices, and wet ponds.
12.2.4.1.2 The minimum setback from a public well as defined by the Office of Drinking Water shall be 150 feet.
12.2.4.1.3 The minimum by right setback from a domestic well as defined by the DNREC Water Supply Section shall be 100 feet.
12.2.4.1.4 In cases where the 100-foot setback cannot be met for a domestic well, the Department or Delegated Agency may consider an alternative method of compliance (AMC). The AMC shall consist of the following:
12.2.4.1.4.1 Developer shall notify owner of adjacent domestic well that a stormwater BMP is proposed on an adjacent property.
12.2.4.1.4.2 Developer shall offer to sample adjacent domestic well prior to installation of the stormwater BMP and two years after installation of the stormwater BMP.
12.2.4.1.4.3 Developer shall install a monitoring well between the proposed BMP and the adjacent well in accordance with Delaware regulations governing the construction and use of wells.
12.2.4.1.4.4 Prior to plan approval, developer shall perform a minimum of one (1) test of the groundwater from both the monitoring well and the adjacent domestic well, if access is granted. If accepted by the adjacent domestic well owner, developer shall perform a minimum of one (1) test of the groundwater from the adjacent domestic well two years after installation of the stormwater BMP.
12.2.4.1.4.5 All tests of groundwater shall monitor for the following constituents:
12.2.4.1.4.5.1 pH;
12.2.4.1.4.5.2 Total Dissolved Solids;
12.2.4.1.4.5.3 Total Phosphorus;
12.2.4.1.4.5.4 Total Chloride;
12.2.4.1.4.5.5 Specific Conductance;
12.2.4.1.4.5.6 Nitrate Nitrogen;
12.2.4.1.4.5.7 Total Nitrite/Nitrate;
12.2.4.1.4.5.8 Total Carbon(Particulate Total Carbon);
12.2.4.1.4.5.9 Total Organic Carbon;
12.2.4.1.4.5.10 Total Petroleum Hydrocarbons;
12.2.4.1.4.5.11 Turbidity;
12.2.4.1.4.5.12 Total Coliform;
12.2.4.1.4.5.13 Sodium;
12.2.4.1.4.5.14 Antimony;
12.2.4.1.4.5.15 Arsenic;
12.2.4.1.4.5.16 Barium;
12.2.4.1.4.5.17 Beryllium;
12.2.4.1.4.5.18 Cadmium;
12.2.4.1.4.5.19 Chromium;
12.2.4.1.4.5.20 Lead;
12.2.4.1.4.5.21 Nickel;
12.2.4.1.4.5.22 Selenium;
12.2.4.1.4.5.23 Silver;
12.2.4.1.4.5.24 Thallium;
12.2.4.1.4.5.25 Mercury;
12.2.4.1.4.5.26 Fluoride;
12.2.4.1.4.5.27 Nitrite Nitrogen;
12.2.4.1.4.5.28 Cyanide, Total;
12.2.4.1.4.5.29 Benzene;
12.2.4.1.4.5.30 Carbon Tetrachloride;
12.2.4.1.4.5.31 Chlorobenzene;
12.2.4.1.4.5.32 o-Dichlorbenzene;
12.2.4.1.4.5.33 p-Dichlorobenzene;
12.2.4.1.4.5.34 1,2-Dichloroethane;
12.2.4.1.4.5.35 1,1-Dichloroethene;
12.2.4.1.4.5.36 cis-1,2-Dichloroethylene;
12.2.4.1.4.5.37 trans--1,2-Dichloroethylene;
12.2.4.1.4.5.38 Dichloromethane;
12.2.4.1.4.5.39 1,2-Dichloropropane;
12.2.4.1.4.5.40 Ethylbenzene;
12.2.4.1.4.5.41 Styrene;
12.2.4.1.4.5.42 Tetrachloroethene;
12.2.4.1.4.5.43 Toluene;
12.2.4.1.4.5.44 1,2,4-Trichlorobenzene;
12.2.4.1.4.5.45 1,1,1-Trichloroethane;
12.2.4.1.4.5.46 1,1,2-Trichloroethane;
12.2.4.1.4.5.47 Trichloroethene;
12.2.4.1.4.5.48 Vinyl Chloride;
12.2.4.1.4.5.49 m-Xylene;
12.2.4.1.4.5.50 o-Xylene; and
12.2.4.1.4.5.51 p-Xylene.
12.2.4.1.4.6 Developer shall submit testing results of monitoring well and the adjacent domestic well, if applicable, to DNREC Source Water Assessment and Protection Program (SWAPP) and the Department Sediment & Stormwater Program or Delegated Agency.
12.2.4.1.5 The minimum setback distances for domestic wells with alternative method of compliance from applicable BMPs are as follows:
12.2.4.1.5.1 For Infiltration Practices, Bioretention, Permeable Pavement Systems, Constructed Wetlands and Wet Ponds into the water table:
12.2.4.1.5.1.1 50 feet for residential, commercial or institutional land uses.
12.2.4.1.5.1.2 100 feet for highway land uses.
12.2.4.1.5.2 For Detention Practices and Wet Ponds above the water table:
12.2.4.1.5.2.1 10 feet for residential, commercial or institutional land uses.
12.2.4.1.5.2.2 50 feet for highway land uses.
12.2.4.2 Septic Systems
12.2.4.2.1 Setbacks from septic system drainfields and components are applicable to the following stormwater BMPs: infiltration practices, bioretention, permeable pavement systems, constructed wetlands, detention practices, wet ponds, restoration practices, rooftop disconnection, vegetated channels, sheet flow, stormwater filtering systems, proprietary practices and afforestation.
12.2.4.2.2 The minimum setbacks for septic system drainfields and components from applicable BMPs shall be as follows
12.2.4.2.2.1 For Infiltration Practices, Bioretention, Permeable Pavement Systems, Detention Practices, Restoration Practices, Rooftop Disconnection, Vegetated Channels, Sheet Flow, Stormwater Filtering Systems, Proprietary Practices and Afforestation, the setback distances for both the drainfield and components shall be 10 feet.
12.2.4.2.2.2 For Constructed Wetlands and Wet Ponds, the setback distance shall be 50 feet for the drainfield and 25 feet for components.
12.2.4.3 BMPs shall not be located within a non-blanket utility easement unless a letter of no objection from the utility owner is provided. Utilities shall not impact existing BMPs unless a letter of no objection from the BMP owner is provided.
12.2.4.4 Buildings and Structures
12.2.4.4.1 Setbacks from buildings or structures are applicable to the following stormwater BMPs: Infiltration Practices, Bioretention, Permeable Pavement Systems (excluding sidewalks or minor linear paved areas), Detention Practices, Constructed Wetlands, and Wet Ponds.
12.2.4.4.2 BMPs shall be setback from buildings or structures having a below-grade crawl space or basement such that the below-grade crawl space or basement of the building or structure is outside of the calculated or assumed 4:1 phreatic zone of the BMP unless the building or structure is designed to be waterproof.
12.2.4.4.3 Building and structure setback distances shall be no less than that needed for maintenance.
12.2.4.5 Property line setback distances shall be no less than that needed for maintenance unless a shared use agreement exists between property owners.

7 Del. Admin. Code § 5101-12.0

22 DE Reg. 680 (2/1/2019) (Final)