ILLINOIS URBAN MANUAL PRACTICE STANDARD

DEWATERING (no.) CODE 813

(Source: Illinois Urban Manual Technical Committee)

DEFINITION water, ground water, or other bodies of water. The controlled removal of water from construction sites. Where water pumping operations occur. PURPOSE Where the water table is intercepted. The purposes of this practice are as Where work is performed in-stream. follows: Where collected stormwater runoff is 1. To minimize construction impacts in removed from construction sites. areas with surface water or a high water table. Not for the removal of water that is polluted by chemicals, fuel, etc. This 2. To prevent sediment transport. standard only addresses a suspended 3. To provide work site safety. solid in the form of uncontaminated sediment. 4. To prevent pollution of groundwater or surface water from suspended soil CRITERIA particles carried in construction site dewatering operations. Dewatering shall consist of the removal 5. To preserve down-gradient natural of surface water and/or ground water by resources and property. diverting and/or removing water from construction sites to perform the CONDITIONS WHERE PRACTICE required construction in accordance with APPLIES the plans and specifications.

Construction sites, including any onsite Discharging sediment to upland and offsite excavated areas, where the vegetated areas shall not be used as a presence of water creates unsafe stand-alone sediment control practice conditions, potential damage, or during dewatering operations. restricts construction operations. Construction projects may be subject to Construction sites where water is local, county, state and federal rules present in any form, including stormwater runoff, stormwater ponding, and regulations. intermittent runoff, streams, standing

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Accumulated sediment from dewatering Sediment Control - All dewatering operations shall be disposed of in activities shall be performed in a accordance with all applicable laws and manner that does not negatively impact regulations. the water quality of the water table, cause erosion, or transport sediment to Diverting Surface Water – Cofferdams, wetlands, water bodies, water channels, sumps, flumes and temporary conveyance features, etc. on or off site. diversions shall be built and maintained, according to contract plans, In poorly drained soil areas where well specifications, and respective IUM dewatering is not practical, pumping Practice Standards. directly from construction trenches is permitted provided appropriate For the installation of cofferdams and sediment control practices are sumps, follow the requirements as incorporated with the pumping activity. outlined in Practice Standards COFFERDAM 803 and SUMP PIT 950. All outlets and drainage pathways for dewatering discharges shall be stable Excess surface runoff shall be diverted and protected from erosion. from the construction area as outlined in the IUM Practice Standards Sediment Removal Practices - TEMPORARY DIVERSION 955, Sediment removal shall be provided TEMPORARY SWALE 980, using the following practices, or DIVERSION 815 and DIVERSION DIKE combination of practices, depending on 820. the soil type, suitability of dewatering method, volume of sediment to be A permanent stream or other removed, location, and amount of concentrated flow shall be diverted dewatering. away from the construction area as outlined in Practice Standard Practice Standard. TEMPORARY TEMPORARY STREAM DIVERSION SEDIMENT TRAP 960 shall be used to 976. detain water and remove sediment from

Removing Water – Drains, sumps, pumping and diversion operations pumps, casings, well points and all where space is available. other practices required to dewater the site shall be furnished, installed and Practice Standard, PORTABLE maintained according to contract plans, SEDIMENT TANK 895 shall be used to specifications, and respective IUM retain sediment during dewatering Practice Standards. operations where there is limited space,

When dewatering by well points and deep wells is utilized, the wells shall be Practice Standards POLYACRYLAMIDE placed at intervals along the (PAM) FOR TURBIDITY REDUCTION construction area as necessary to AND SEDIMENT CONTROL 894. depress the groundwater table during construction. Monitoring wells shall be Pumps with Sediment Filtration Bags. installed where measurement of the pumping effectiveness is required. Well Where there is low, intermittent pumping point and deep well dewatering shall be activity, pumps with sediment filtration terminated and sealed immediately bags attached to pump discharges shall upon completion of the dewatering be used. Sediment filtration bags shall operation. be placed on a stabilized surface area. Sediment filtration bags shall not be

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placed, whole or partially, within aquatic CONSIDERATIONS areas (wetlands, streams, etc.), or water conveyance features (ditches, swales, Federal, State, County and local water quality requirements also need to be etc.). Sediment filtration bags shall be considered when choosing a dewatering raised above the supporting ground on method and may include requirements a surface, or material, that allows water for sampling and evaluating discharges to flow out of the bottom of the bag at for clarity. the respective design discharge rate for the sediment filter bag selected. The Base the location, method of pump discharge rate shall not exceed dewatering, and configuration on site conditions. The following items should the design discharge rate for the be considered when selecting the sediment filter bag. proper dewatering method:

Materials, structures, etc. that are used 1. Amount of water to remove. to ensure that water flows out of the 2. The amount of sediment to be bottom of a sediment filter bag must be removed. non-erodible and be placed atop a stabilized surface area. 3. Maintenance and operation required as a result of the construction The material for the sediment filtration operations. bag shall meet the requirements of 4. Length of time to complete the work. Material Specification 592 5. The space available in the work GEOTEXTILE, Table 2, Class I with a area. minimum tensile strength of 200 lbs, or 6. Ability to supervise pump operation. Table 1, Class 4 value. The sediment filter bag shall be sized per manufacturer recommendations and Evaluate function, need, velocity control, based on the size of the pump however, outlet stability, and site aesthetics. The the minimum bag size shall be 10 feet x location and capacity of temporary 15 feet with a usable surface drainage diversion and protective works should area of 300 square feet (10 x 15 x 2 ) sides, top & bottom) The largest be based on the characteristics of the diameter size pump hose to be used site, accessibility, and the potential for with a sediment filtration bag is 4-inch. off-site, or on-site damage during the Multiple hoses/pipes shall not be construction phase. attached to a single filtration bag inlet sleeve. Secondary Containment. Secondary sediment containment Removal of Dewatering Facilities - The temporary dewatering areas shall be practices may be required to ensure that removed after they have served their sediment from a dewatering activity purpose. The dewatering areas shall be does not adversely impact a particular graded where necessary, and stabilized body of water, wetland, or water with appropriate erosion control conveyance feature (ditch, swale, etc.). practices. Shall not create any Secondary containment may be obstruction of normal water flow, or any other interference with the operation of, required if the method of sediment or access to the permanent works. removal concentrates the sediment in one location or practice. Secondary containment measures shall be placed

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between the area of control and the Prevention Plan (SWPPP) and/or receiving area and/or aquatic resource. the erosion and sediment control plan, detailing the location of dewatering activities, presence of Winter conditions and freezing aquatic areas, equipment, fuel temperatures can impact the storage, and discharge point. effectiveness and functionality of 4. Any total maximum daily load sediment filter bags and anionic (TMDL) requirements for the polymers for sediment removal during receiving waters or turbidity dewatering. If dewatering activities are standards shall be stated on the likely to occur over winter, dewatering plan set. practices for sediment control should be 5. A brief narrative outlining a included in the development of the construction sequence for the Stormwater Pollution Prevention Plan dewatering operation. that can be effective in freezing 6. Drawing details for proper installation of the various temperatures. dewatering facilities as needed.

An analysis of the effects of dewatering All plans shall include installation, a site should also be considered. For inspection, and maintenance schedules example, permanent dewatering of a with the responsible party identified. site may cause subsidence of surface areas and settlement of foundations and Methods of dewatering shall be pavements, Additionally, temporary constructed to meet the requirements of dewatering may create dry areas during Construction Specification REMOVAL OF WATER 11. construction but the effect of allowing water tables to rise after construction may result in excess pressure on OPERATION AND MAINTENANCE subsurface structures, potentially causing damage and/or excessive sump The frequency of inspections shall pump cycling. depend on the dewatering method, amount of discharge, potential damage, PLANS AND SPECIFICATIONS and quality of the receiving bodies of water. The frequency of inspections, Plans and specifications for installing and building dewatering facilities shall responsible party and specific tasks be in keeping with this standard and shall be identified. shall describe the requirements for applying the practice to achieve its 1. Inspections shall be conducted to intended purpose. At a minimum ensure proper operation and include: compliance with all permits and water quality standards. 1. Approximate location and proposed type of dewatering method shown 2. Accumulated sediment shall be on plans. removed from the flow area and 2. Drawings, specifications, etc. for all temporary diversions shall be items of work as needed for repaired, as required. dewatering. 3. Outlet areas shall be checked and 3. Include the dewatering plan as part repairs shall be made in a timely of the Storm Water Pollution manner, as needed.

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4. Pump outlets shall be inspected for erosion, and sumps shall be inspected for accumulated sediment. 5. Sediment filtration bags shall be removed and replaced when half full of sediment, or when the design flow rate of the filter bag is no longer being maintained. 6. If the receiving area is showing any signs of turbid water, erosion, or sediment accumulation, discharges shall be stopped immediately once safety and property damage concerns have been addressed. 7.

REFERENCES

Maine Department of Environmental Protection, Bureau of Land and Water Quality. Maine Erosion and Sediment Control BMPs. G-3 Construction Dewatering. Augusta, ME. March 2003.

IDOT Erosion and Sediment Control Field Guide for Construction Inspection, July 1, 2010

January, 2019 urbst813.doc

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