field guide to construction site dewatering
TRANSCRIPT
Field Guide to Construction Site DewateringFor individuals with sensory disabilities, this document is available in alternate formats upon request.
Please call or write to:
Storm Water Liaison, Caltrans Division of Environmental Analysis
MS 27, P.O. Box 942874, Sacramento, CA 94274-0001
(916) 653-8896 Voice or dial 711 to use a relay service.
iii
List of Tables ...................................................................................................................................................... vi
List of Abbreviations ........................................................................................................................................ viii 1. Introduction ............................................................................................................................................... 1-1
1.1 Overview ......................................................................................................................................... 1-1 1.2 Dewatering Operations Defined .................................................................................................... 1-2 1.3 Permits and Regulations that Apply to Dewatering Operations .................................................. 1-3
1.3.1 Federal Regulations ......................................................................................................... 1-3 1.3.2 California Regulations...................................................................................................... 1-3 1.3.3 Caltrans MS4 Permit ........................................................................................................ 1-3 1.3.4 Discharge of Accumulated Precipitation (Stormwater) ................................................. 1-4 1.3.5 Non-Storm Water Dewatering Operations ...................................................................... 1-4 1.3.6 Contaminated Groundwater ............................................................................................ 1-5 1.3.7 Utility Vault Dewatering.................................................................................................... 1-6
1.4 Dewatering Operations Requiring an NPDES Permit ................................................................... 1-7 1.5 Why are Dewatering Operations Regulated? ............................................................................... 1-7 1.6 What are Considered Pollutants? ................................................................................................. 1-7 1.7 Options for Managing Dewatering Operations ............................................................................. 1-8 1.8 What is the Resident Engineer’s Responsibility for Dewatering Permits Issued Prior to
Construction? ................................................................................................................................. 1-8 1.9 How to Use This Dewatering Guide ............................................................................................... 1-8
2. Selecting a Dewatering Management Option ......................................................................................... 2-1 2.1 Assess Water Quality ..................................................................................................................... 2-5 2.2 Estimated Discharge Parameters ................................................................................................. 2-7 2.3 Evaluate if the Discharge is an Authorized Non-Storm Water Discharge ................................... 2-9 2.4 Determine if the Discharge will be to a Waterbody or to the Land ............................................. 2-9
3. Dewatering Management Details ............................................................................................................ 3-1 3.1 Manage Water Containing Pollutants Other than Sediment ....................................................... 3-1
3.1.1 Definition .......................................................................................................................... 3-1 3.1.2 Implementation ................................................................................................................ 3-1 3.1.3 Advantages ....................................................................................................................... 3-1 3.1.4 Limitations ........................................................................................................................ 3-1
3.2 Manage Water within the Project Site .......................................................................................... 3-3 3.2.1 Definition .......................................................................................................................... 3-3 3.2.2 Implementation ................................................................................................................ 3-3 3.2.3 Water Quality .................................................................................................................... 3-3 3.2.4 Advantages ....................................................................................................................... 3-3
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3.4 Use at a Facility Owned by Others .................................................................................................3-7 3.4.1 Definition ...........................................................................................................................3-7 3.4.2 Implementation ................................................................................................................3-7 3.4.3 Water Quality ....................................................................................................................3-7 3.4.4 Advantages .......................................................................................................................3-7 3.4.5 Limitations ........................................................................................................................3-7 3.4.6 Requirements ...................................................................................................................3-7
3.5 Discharge to a Sanitary Sewer System .........................................................................................3-9 3.5.1 Definition ...........................................................................................................................3-9 3.5.2 Implementation ................................................................................................................3-9 3.5.3 Water Quality ....................................................................................................................3-9 3.5.4 Advantages .......................................................................................................................3-9 3.5.5 Limitations ........................................................................................................................3-9 3.5.6 General Requirements .....................................................................................................3-9
3.6 Off-Site Treatment ....................................................................................................................... 3-11 3.6.1 Definition ........................................................................................................................ 3-11 3.6.2 Implementation ............................................................................................................. 3-11 3.6.3 Water Quality ................................................................................................................. 3-11 3.6.4 Advantages .................................................................................................................... 3-11 3.6.5 Limitations ..................................................................................................................... 3-11 3.6.6 General Requirements .................................................................................................. 3-11
3.7 Discharge Accumulated Storm Water under the Construction General Permit ...................... 3-13 3.7.1 Definition ........................................................................................................................ 3-13 3.7.2 Implementation ............................................................................................................. 3-13 3.7.3 Water Quality ................................................................................................................. 3-13 3.7.4 Advantages .................................................................................................................... 3-13 3.7.5 Limitations ..................................................................................................................... 3-13 3.7.6 General Requirements .................................................................................................. 3-13
3.8 Discharge Authorized Non-Storm Water under the Construction General Permit ................... 3-16 3.8.1 Definition ........................................................................................................................ 3-16 3.8.2 Implementation ............................................................................................................. 3-16 3.8.3 Water Quality ................................................................................................................. 3-16 3.8.4 Advantages .................................................................................................................... 3-16
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3.10 Discharge Water to Land under the Statewide Low-Threat Discharge WDRS ......................... 3-18 3.10.1 Definition ........................................................................................................................ 3-18 3.10.2 Implementation .............................................................................................................. 3-18 3.10.3 Water Quality .................................................................................................................. 3-18 3.10.4 Advantages ..................................................................................................................... 3-18 3.10.5 Limitations ...................................................................................................................... 3-18 3.10.6 General Requirements................................................................................................... 3-18
Appendix A: Regional Board Dewatering Permit Requirements, Regional Board Contacts, Maps of Regional Boards and Caltrans District Boundaries ...................................................................... A
Appendix B: Sediment Treatment Options ....................................................................................................... B
Appendix C: Water Quality and Discharge Parameters Assessment Form, Dewatering Operations Form, Construction General Permit Forms ............................................................................................. C
Appendix D: Regional Board General NPDES Permits, WDRS, and Waivers that Regulate Dewatering ...... D
Appendix E: Defined Terms ................................................................................................................................E
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Figure 2-1. Dewatering Operations Management Flow Chart .....................................................................2-3
Figure 3-1. Accumulated Precipitation Discharge under the Construction General Permit ................... 3-15
Figure 3-2. General Dewatering Process under a Regional Board General NPDES Permit or Wavier ... 3-19
Figure A-1. Map of California showing Regional Board and Caltrans District Boundaries ........................ A-1
Figure B-1. Sediment Treatment Technology and Estimated Removal Efficiencies ................................. B-3
Figure B-2. Temporary Basin......................................................................................................................... B-7
Figure B-4. Tube Settlers............................................................................................................................. B-12
Figure B-6. Dewatering Tank Schematic Diagram ..................................................................................... B-14
Figure B-7. Gravity Bag Filter Schematic Diagram .................................................................................... B-16
Figure B-8. Sand-Media Filter Schematic Diagrams ................................................................................. B-18
Figure B-9. Bag/Cartridge Filters and Spent Bag/Cartridge Filters .......................................................... B-20
Figure B-10. Cartridge Filter Schematic ..................................................................................................... B-22
Figure B-11. Potential Treatment Schematic ............................................................................................ B-24
List of Tables Table 1-1. Caltrans Districts and Related Regional Board General Permits, WDRs & Waivers that
Regulate Dewatering ..................................................................................................................1-5
Table 1-2. Regional Board General Permits that Regulate Groundwater Extraction .................................1-6
Table 2-1 Water Quality Assessment Example .............................................................................................2-6
Table 2-2. Typical Pump Flow Rates .............................................................................................................2-7
Table 2-3 Discharge Parameter Calculation Sheet Example .......................................................................2-8
Table 3-1 Use Assessment: Manage Within the Project Site .......................................................................3-4
Table 3-2. Use Assessment: Use on Adjacent Land or Within the Caltrans Right-of-Way Outside Project Limits ................................................................................................................3-6
Table 3-3. Use Assessment: Use at a Facility Owned by Others ..................................................................3-8
Table 3-4. Use Assessment: Discharge to a Sanitary Sewer .................................................................... 3-10
Table 3-5. Use Assessment: Off-Site Treatment ........................................................................................ 3-12
Table B-1. Comparison of Sediment Treatment Technologies ................................................................... B-5
Table B-2. Example Desilting Basin Sizing ................................................................................................... B-6
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Table B-6. Typical Gravity Bag Filter Properties .......................................................................................... B-15
Table B-7. Typical Sand-Media Particulate Filter ....................................................................................... B-17
Table B-8. Typical Pressurized Bag Filter Specifications ........................................................................... B-19
Table B-9. Typical Cartridge Filter Specifications ....................................................................................... B-21
Table B-10. Potential ATS Components ....................................................................................................... B-24
Table B-11. Potential ATS Chemicals .......................................................................................................... B-24
Table C-1 Water Quality Assessment ............................................................................................................ C-3
Table C-2 Discharge Parameter Calculation Sheet ...................................................................................... C-4
Table D-1. Applicability of Regional Board General NPDES Permits, WDRs, and Waivers ........................ D-1
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CGP Construction General Permit
CWA Clean Water Act
DSA Disturbed Soil Area
ft feet
NAL Numeric Action Limit
NEL Numeric Effluent Limit
RE Resident Engineer
SWPPP Storm Water Pollution Prevention Plan
SWRCB California State Water Resources Control Board
TSS Total Suspended Solids
WQF Water Quality Flow
WQV Water Quality Volume
Introduction This Field Guide to Construction Site Dewatering (Dewatering Guide) provides information necessary to manage dewatering operations on Caltrans construction sites in compliance with federal and State water quality regulations.
1.1 Overview The purpose of this Dewatering Guide is to inform and guide intended users in selecting, implementing, and monitoring construction site dewatering operations. Intended users of this Dewatering Guide include Resident Engineers, Caltrans employees, and Caltrans contractors.
Special situations may warrant variation from the policies and guidelines contained within this Dewatering Guide. This Dewatering Guide is neither a textbook nor a substitute for engineering or technical knowledge, experience, or judgment.
The mention of any specific commercial product, process or service in this manual is not to be construed as either an actual or implied endorsement or recommendation by Caltrans. Caltrans makes no representation or warranty of any kind, whether expressed or implied, concerning products or processes discussed in this manual.
This Dewatering Guide is organized as follows:
Section 1 – Introduction: Provides an overview of what activities are considered dewatering; introduces the National Pollutant Discharge Elimination System (NPDES) permits that regulate dewatering in California; describes which dewatering discharges are regulated; and, identifies the pollutants that are of concern in dewatering discharges.
Section 2 – Selecting a Dewatering Management Option: Provides flow charts that guide the intended user through the process of determining if the dewatering operation is subject to an NPDES permit, Waste Discharge Requirements (WDRs), or waiver, and if so, under which permit or waiver the operation is regulated.
Section 3 – Dewatering Management Details: Identifies the specific regulatory requirements for each specific dewatering option as well as advantages or limitations of selecting a particular dewatering option.
Appendix A – Dewatering Permit Requirements: Presents a summary of NPDES permit requirements or waivers for dewatering discharges in each Regional Board jurisdiction; contains maps of the nine Regional Boards overlaid on the Caltrans District boundaries; and, provides Regional Board contacts for the relevant NPDES permit or discharge waiver.
Appendix B – Sediment Treatment Options: Contains brief descriptions, costs, and considerations for the following treatment technologies: desilting basins, sediment traps, weir tanks, gravity bag filter, sand media filter, pressurized bag filter, and cartridge filter. Also includes a brief description of the use of an Active Treatment System (ATS).
Appendix C – Assessment and Monitoring Forms: Contains forms for assessing dewatering options and recording decision making. Also contains forms for monitoring discharges from dewatering operations.
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Appendix D – Regional Board General NPDES Permit and Waiver Requirements: Presents general NPDES permits that regulate dewatering operations in each Regional Board. Also, some Regional Boards have waivers from waste discharge requirements and waivers from report of waste discharge. These waivers are included, where appropriate.
Appendix E –Defined Terms: Includes terms that relate to dewatering operations and permitting.
Appendix F – Endnotes and Relevant Citations: Contains endnotes for the Dewatering Guide. These endnotes contain additional information and citations that intended users may find helpful. Endnotes are indicated in the text with a superscript lower-case Roman numeral. Footnotes are indicated by a superscript Arabic numeral.
1.2 Dewatering Operations Defined Dewatering operations occur when accumulated precipitation or non-storm water must be removed from a work location so that construction may be accomplished. Figure 1-1 illustrates the construction-site dewatering process. Pollutants may be discharged during dewatering activities and for this reason, a number of NPDES permits regulate the discharge of dewatering waters.
Figure 1-1. General Construction Site Dewatering Process
The Construction General Permit1 governs water quality compliance for Caltrans construction or demolition activities that occur on project sites having equal to or greater than one acre of land surface disturbance. Waters generated from dewatering activities on these types of construction sites are considered authorized non-storm waters.i Typical sources of non-storm water from Caltrans construction site dewatering include groundwater, water from cofferdams, water diversions, and waters used during construction activities that must be removed from a work area.
Dewatering operations may occur during a wide range of activities on Caltrans construction sites including demolition of pavement or structures; grading (including cut and fill slopes); channel excavation; channel paving; trenching and underground drainage; installation of underground drainage facilities; drainage inlet modification; utility trenching; utility installation; structure excavation; bridge or structure construction; miscellaneous concrete work; sound or retaining wall construction; planting and irrigation; and, treatment best management practice (BMP) construction and maintenance.ii
The discharge of accumulated precipitation is also governed by the Construction General Permit. Discharge of accumulated precipitation is generally considered a stormwater discharge; however, accumulated precipitation may be commingled with non-storm water or impacted by construction
1 State Water Resources Control Board, National Pollutant Discharge Elimination System (NPDES) General Permit for Storm Water Discharges Associated with Construction Activities and Land Disturbances (CAS000002, Order No. 2009-0009-DWQ), issued September 2, 2009 (herein, “Construction General Permit”).
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materials or activities. Commingled accumulated precipitation is considered non-storm water. Because of this, the management of accumulated precipitation is described in the Dewatering Guide.
The Construction General Permit allows any of the nine Regional Water Quality Control Boards (Regional Boards) to regulate dewatering discharges using a general NPDES permit or site-specific permit.iii Eight Regional Boards have issued general NPDES permitsiv that regulate dewatering discharges. One Regional Board has issued WDRs that govern construction dewatering. Three Regional Boards have issued waivers of WDRs or waivers from reports of waste discharge (RWD) for construction dewatering.
On Caltrans construction sites, a dewatering and discharge work plan, meeting appropriate regulatory requirementsv must be prepared before dewatering operations occur.vi
1.3 Permits and Regulations that Apply to Dewatering Operations Dewatering operations are governed by federal and California law as implemented through California regulations. Although not specifically described by this dewatering guide, two types of permits may also apply on construction sites: groundwater extraction associated with cleanup of volatile organic and petroleum compounds and utility vault dewatering (see Section 1.3.6).
1.3.1 Federal Regulations Federal regulations for controlling discharges of pollutants from municipal separate storm sewer systems (MS4s), construction sites, and industrial activities were incorporated into the NPDES permit process by the 1987 amendments to the Clean Water Act (CWA) and by the subsequent 1990 promulgation of federal stormwater regulations by the U.S. Environmental Protection Agency (EPA). The EPA regulations require construction and stormwater discharges to comply with an NPDES permit. In California, the EPA delegated its NPDES permitting authority to the State Water Resources Control Board (SWRCB).
1.3.2 California Regulations California and the federal government define jurisdictional waters differently.vii This has important implications for the management of dewatering discharges. Federal regulations only govern discharges to Waters of the United States. Waters of the United States are surface waters and discharges to those waters are governed by an NPDES permit. The SWRCB and the associated Regional Boards implement the NPDES permit program in California.
California has a broader definition of waters subject to its jurisdiction. California regulates discharges to both surface waters and groundwater. California uses WDRs to regulate discharges that may impact groundwater. Thus, discharges solely to land are typically regulated using WDRs.
In addition to using WDRs or NPDES permits to regulate discharges, a Regional Board or the SWRCB may issue a waiver from WDRs or RWD for certain discharges. Region 5, Region 8, and Region 9 currently have such waivers and these waivers mostly regulate discharges to land. Additionally, the statewide low- threat discharge WDRs, discussed later, applies to certain discharges to land.
1.3.3 Caltrans MS4 Permit The current Caltrans MS4 Permit does not regulate Caltrans construction sites having a land disturbance area greater than or equal to one acre.viii For these sites, the Caltrans permit only “impose[s] electronic filing, notification, reporting, and contractor requirements for certain construction projects, and imposes limitations on types of materials that may be used during construction which may have an impact on post-construction discharges.”ix Caltrans construction sites having land disturbance area less than one acre are regulated by the Caltrans MS4 Permit and must implement appropriate BMPs.x
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1.3.4 Discharge of Accumulated Precipitation (Stormwater) Within each Regional Board jurisdiction, accumulated precipitation (accumulated stormwater) from Caltrans construction activities may be discharged to a storm drain or water body in accordance with the National Pollutant Discharge Elimination System (NPDES) General Permit for Storm Water Discharges Associated with Construction Activities and Land Disturbances (CAS000002, Order No. 2009-0009- DWQ), issued September 2, 2009 (Construction General Permit).xi This permit regulates storm water discharges from construction or demolition activities that result in a land disturbance of greater than or equal to 1 acre, except when such activities occur in the Lake Tahoe Hydrologic Unit.xii
Construction activities greater than 1 acre occurring in the Lake Tahoe Hydrologic Unit are governed by the General Waste Discharge Requirements and National Pollutant Discharge Elimination System Permit for Storm Water Discharges Associated with Construction Activity in the Lake Tahoe Hydrologic Unit, Counties Of Alpine, El Dorado, and Placer (CAG616002, Order No. R6T-2011-0019), issued April 14, 2011 (Lake Tahoe CGP).xiii Accumulated precipitation cannot be discharged from the construction site to a waterbody. However, discharges to land of dewatering waters are allowed if certain requirements are met.xiv
In the Lahontan Region, other than in the Lake Tahoe Hydrologic Unit, a separate permit regulates discharges of accumulated stormwater. This permit, the General Waste Discharge Requirements for Small Construction Projects, Including Utility, Public Works, and Minor Streambed/Lakebed Alteration Projects in the Lahontan Region Excluding the Lake Tahoe Hydrologic Unit (Board Order No. R6T-2003- 0004, Lahontan Small Construction Permit), covers construction sites having an area between 10,000 square feet and one acre. Like the Lake Tahoe CGP, the Lahontan Small Construction Project permit only allows discharges to land of accumulated stormwater if certain conditions are met.xv
1.3.5 Non-Storm Water Dewatering Operations Under the Construction General Permit, dewatering of uncontaminated non-storm water is an authorized non-storm water discharge.xvi The Construction General Permit regulates dewatering, unless a regional NPDES permit applies.xvii Non-storm water includes, but is not limited to, groundwater, dewatering of piles, water from cofferdams, water diversions, and water used during construction activities that must be removed from a work area.
Under the Construction General Permit, discharges must meet specific requirements of the Construction General Permit including meeting the prohibitions of the applicable Basin Plan, compliance with the prohibitions on discharges of toxics, implementing BMPs to prevent contact of dewatering waters with construction materials or equipment, and monitoring for and compliance with applicable numeric action levels (NALs), receiving water triggers, or numeric effluent limitations (NELs).xviii
General NPDES permits that regulate specific types of dewatering discharges are identified in Table 1-1 and are further discussed in Section 3.9. Copies of these permits are provided in Appendix D.
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General Permits, WDRs & Waivers that Regulate Dewatering
Caltrans District Regional Board Dewatering General Permit, WDRs & Waivers
1 Region 1 – General Permit R1-2009-0045 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145
2 Region 1 – General Permit R1-2009-0045 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145 Region 6 – General Permit R6T-2008-0023 & R6T-2003-0004
3 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145 Region 6 – General Permit R6T-2008-0023 & R6T-2011-0019
4
Region 1 – General Permit R1-2009-0045 Region 2 – No General Permit Region 3 – General Permit R3-2011-0223 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145
5 Region 2 – No General Permit Region 3 – General Permit R3-2011-0223 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145
6 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145 Region 6 – General Permit R6T-2008-0023 & R6T-2003-0004
7
8
9 Region 6 – General Permit R6T-2008-0023 & R6T-2003-0004
10 Region 2 – No General Permit Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145 Region 6 – General Permit R6T-2008-0023 & R6T-2011-0019
11 Region 7 – General Permit R7-2009-0300 Region 9 – General Permit R9-2007-0034 & R9-2008-0002, Resolution R9-2007-0104
12 Region 8 – General Permit R8-2009-0003 & R8-2007-0041, Resolution R8-2013-0015 Region 9 – General Permit R9-2007-0034 & R9-2008-0002, Resolution R9-2007-0104
1.3.6 Contaminated Groundwater Each Regional Board has general permits that regulate the cleanup of contaminated groundwater. Those permits that specifically include construction dewatering are included and described in this Dewatering Guide (i.e., Region 4 and Region 9). However, contaminated groundwater is sometimes encountered on Caltrans construction sites and for that reason, Table 1-2 is provided.
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Table 1-2. Regional Board General Permits that Regulate Groundwater Extraction
Caltrans District Regional Board Groundwater Extraction General Permit
1 Region 1 – General Permit R1-2011-0028 Region 5 – General Permit R5-2013-0074
2 Region 1 – General Permit R1-2011-0028 Region 5 – General Permit R5-2013-0073 & R5-2013-0075 Region 6 – General Permit R6T-2010-0024
3 Region 5 – General Permit R5-2013-0073 & R5-2013-0075 Region 6 – General Permit R6T-2010-0024
4
Region 1 – General Permit R1-2011-0028 Region 2 – General Permit R2-2012-0012 Region 3 – General Permit R3-2011-0222 Region 5 – General Permit R5-2013-0073 & R5-2013-0075
5 Region 2 – General Permit R2-2012-0012 Region 3 – General Permit R3-2011-0222 Region 5 – General Permit R5-2013-0073 & R5-2013-0075
6 Region 5 – General Permit R5-2013-0074 Region 6 – General Permit R6T-2010-0024
7
Region 3 – General Permit R3-2011-0222 Region 4 – General Permit R4-2013-00431 Region 5 – General Permit R5-2013-0073 & R5-2013-0075 Region 6 – General Permit R6T-2010-0024
8
Region 6 – General Permit R6T-2010-0024 Region 7 – General Permit R7-2009-0400 Region 8 – General Permit R8-2012-0027 Region 9 – General Permit R9-2007-00341 & R9-2008-00021
9 Region 6 – General Permit R6T-2010-0024
10 Region 2 – General Permit R2-2012-0012 Region 5 – General Permit R5-2013-0073 & R5-2013-0075 Region 6 – General Permit R6T-2010-0024
11 Region 7 – General Permit R7-2009-0400 Region 9 – General Permit R9-2007-00341 & R9-2008-00021
12 Region 8 – General Permit R8-2012-0027 Region 9 – General Permit R9-2007-00341 & R9-2008-00021
1…
Please call or write to:
Storm Water Liaison, Caltrans Division of Environmental Analysis
MS 27, P.O. Box 942874, Sacramento, CA 94274-0001
(916) 653-8896 Voice or dial 711 to use a relay service.
iii
List of Tables ...................................................................................................................................................... vi
List of Abbreviations ........................................................................................................................................ viii 1. Introduction ............................................................................................................................................... 1-1
1.1 Overview ......................................................................................................................................... 1-1 1.2 Dewatering Operations Defined .................................................................................................... 1-2 1.3 Permits and Regulations that Apply to Dewatering Operations .................................................. 1-3
1.3.1 Federal Regulations ......................................................................................................... 1-3 1.3.2 California Regulations...................................................................................................... 1-3 1.3.3 Caltrans MS4 Permit ........................................................................................................ 1-3 1.3.4 Discharge of Accumulated Precipitation (Stormwater) ................................................. 1-4 1.3.5 Non-Storm Water Dewatering Operations ...................................................................... 1-4 1.3.6 Contaminated Groundwater ............................................................................................ 1-5 1.3.7 Utility Vault Dewatering.................................................................................................... 1-6
1.4 Dewatering Operations Requiring an NPDES Permit ................................................................... 1-7 1.5 Why are Dewatering Operations Regulated? ............................................................................... 1-7 1.6 What are Considered Pollutants? ................................................................................................. 1-7 1.7 Options for Managing Dewatering Operations ............................................................................. 1-8 1.8 What is the Resident Engineer’s Responsibility for Dewatering Permits Issued Prior to
Construction? ................................................................................................................................. 1-8 1.9 How to Use This Dewatering Guide ............................................................................................... 1-8
2. Selecting a Dewatering Management Option ......................................................................................... 2-1 2.1 Assess Water Quality ..................................................................................................................... 2-5 2.2 Estimated Discharge Parameters ................................................................................................. 2-7 2.3 Evaluate if the Discharge is an Authorized Non-Storm Water Discharge ................................... 2-9 2.4 Determine if the Discharge will be to a Waterbody or to the Land ............................................. 2-9
3. Dewatering Management Details ............................................................................................................ 3-1 3.1 Manage Water Containing Pollutants Other than Sediment ....................................................... 3-1
3.1.1 Definition .......................................................................................................................... 3-1 3.1.2 Implementation ................................................................................................................ 3-1 3.1.3 Advantages ....................................................................................................................... 3-1 3.1.4 Limitations ........................................................................................................................ 3-1
3.2 Manage Water within the Project Site .......................................................................................... 3-3 3.2.1 Definition .......................................................................................................................... 3-3 3.2.2 Implementation ................................................................................................................ 3-3 3.2.3 Water Quality .................................................................................................................... 3-3 3.2.4 Advantages ....................................................................................................................... 3-3
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3.4 Use at a Facility Owned by Others .................................................................................................3-7 3.4.1 Definition ...........................................................................................................................3-7 3.4.2 Implementation ................................................................................................................3-7 3.4.3 Water Quality ....................................................................................................................3-7 3.4.4 Advantages .......................................................................................................................3-7 3.4.5 Limitations ........................................................................................................................3-7 3.4.6 Requirements ...................................................................................................................3-7
3.5 Discharge to a Sanitary Sewer System .........................................................................................3-9 3.5.1 Definition ...........................................................................................................................3-9 3.5.2 Implementation ................................................................................................................3-9 3.5.3 Water Quality ....................................................................................................................3-9 3.5.4 Advantages .......................................................................................................................3-9 3.5.5 Limitations ........................................................................................................................3-9 3.5.6 General Requirements .....................................................................................................3-9
3.6 Off-Site Treatment ....................................................................................................................... 3-11 3.6.1 Definition ........................................................................................................................ 3-11 3.6.2 Implementation ............................................................................................................. 3-11 3.6.3 Water Quality ................................................................................................................. 3-11 3.6.4 Advantages .................................................................................................................... 3-11 3.6.5 Limitations ..................................................................................................................... 3-11 3.6.6 General Requirements .................................................................................................. 3-11
3.7 Discharge Accumulated Storm Water under the Construction General Permit ...................... 3-13 3.7.1 Definition ........................................................................................................................ 3-13 3.7.2 Implementation ............................................................................................................. 3-13 3.7.3 Water Quality ................................................................................................................. 3-13 3.7.4 Advantages .................................................................................................................... 3-13 3.7.5 Limitations ..................................................................................................................... 3-13 3.7.6 General Requirements .................................................................................................. 3-13
3.8 Discharge Authorized Non-Storm Water under the Construction General Permit ................... 3-16 3.8.1 Definition ........................................................................................................................ 3-16 3.8.2 Implementation ............................................................................................................. 3-16 3.8.3 Water Quality ................................................................................................................. 3-16 3.8.4 Advantages .................................................................................................................... 3-16
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3.10 Discharge Water to Land under the Statewide Low-Threat Discharge WDRS ......................... 3-18 3.10.1 Definition ........................................................................................................................ 3-18 3.10.2 Implementation .............................................................................................................. 3-18 3.10.3 Water Quality .................................................................................................................. 3-18 3.10.4 Advantages ..................................................................................................................... 3-18 3.10.5 Limitations ...................................................................................................................... 3-18 3.10.6 General Requirements................................................................................................... 3-18
Appendix A: Regional Board Dewatering Permit Requirements, Regional Board Contacts, Maps of Regional Boards and Caltrans District Boundaries ...................................................................... A
Appendix B: Sediment Treatment Options ....................................................................................................... B
Appendix C: Water Quality and Discharge Parameters Assessment Form, Dewatering Operations Form, Construction General Permit Forms ............................................................................................. C
Appendix D: Regional Board General NPDES Permits, WDRS, and Waivers that Regulate Dewatering ...... D
Appendix E: Defined Terms ................................................................................................................................E
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Figure 2-1. Dewatering Operations Management Flow Chart .....................................................................2-3
Figure 3-1. Accumulated Precipitation Discharge under the Construction General Permit ................... 3-15
Figure 3-2. General Dewatering Process under a Regional Board General NPDES Permit or Wavier ... 3-19
Figure A-1. Map of California showing Regional Board and Caltrans District Boundaries ........................ A-1
Figure B-1. Sediment Treatment Technology and Estimated Removal Efficiencies ................................. B-3
Figure B-2. Temporary Basin......................................................................................................................... B-7
Figure B-4. Tube Settlers............................................................................................................................. B-12
Figure B-6. Dewatering Tank Schematic Diagram ..................................................................................... B-14
Figure B-7. Gravity Bag Filter Schematic Diagram .................................................................................... B-16
Figure B-8. Sand-Media Filter Schematic Diagrams ................................................................................. B-18
Figure B-9. Bag/Cartridge Filters and Spent Bag/Cartridge Filters .......................................................... B-20
Figure B-10. Cartridge Filter Schematic ..................................................................................................... B-22
Figure B-11. Potential Treatment Schematic ............................................................................................ B-24
List of Tables Table 1-1. Caltrans Districts and Related Regional Board General Permits, WDRs & Waivers that
Regulate Dewatering ..................................................................................................................1-5
Table 1-2. Regional Board General Permits that Regulate Groundwater Extraction .................................1-6
Table 2-1 Water Quality Assessment Example .............................................................................................2-6
Table 2-2. Typical Pump Flow Rates .............................................................................................................2-7
Table 2-3 Discharge Parameter Calculation Sheet Example .......................................................................2-8
Table 3-1 Use Assessment: Manage Within the Project Site .......................................................................3-4
Table 3-2. Use Assessment: Use on Adjacent Land or Within the Caltrans Right-of-Way Outside Project Limits ................................................................................................................3-6
Table 3-3. Use Assessment: Use at a Facility Owned by Others ..................................................................3-8
Table 3-4. Use Assessment: Discharge to a Sanitary Sewer .................................................................... 3-10
Table 3-5. Use Assessment: Off-Site Treatment ........................................................................................ 3-12
Table B-1. Comparison of Sediment Treatment Technologies ................................................................... B-5
Table B-2. Example Desilting Basin Sizing ................................................................................................... B-6
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Table B-6. Typical Gravity Bag Filter Properties .......................................................................................... B-15
Table B-7. Typical Sand-Media Particulate Filter ....................................................................................... B-17
Table B-8. Typical Pressurized Bag Filter Specifications ........................................................................... B-19
Table B-9. Typical Cartridge Filter Specifications ....................................................................................... B-21
Table B-10. Potential ATS Components ....................................................................................................... B-24
Table B-11. Potential ATS Chemicals .......................................................................................................... B-24
Table C-1 Water Quality Assessment ............................................................................................................ C-3
Table C-2 Discharge Parameter Calculation Sheet ...................................................................................... C-4
Table D-1. Applicability of Regional Board General NPDES Permits, WDRs, and Waivers ........................ D-1
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CGP Construction General Permit
CWA Clean Water Act
DSA Disturbed Soil Area
ft feet
NAL Numeric Action Limit
NEL Numeric Effluent Limit
RE Resident Engineer
SWPPP Storm Water Pollution Prevention Plan
SWRCB California State Water Resources Control Board
TSS Total Suspended Solids
WQF Water Quality Flow
WQV Water Quality Volume
Introduction This Field Guide to Construction Site Dewatering (Dewatering Guide) provides information necessary to manage dewatering operations on Caltrans construction sites in compliance with federal and State water quality regulations.
1.1 Overview The purpose of this Dewatering Guide is to inform and guide intended users in selecting, implementing, and monitoring construction site dewatering operations. Intended users of this Dewatering Guide include Resident Engineers, Caltrans employees, and Caltrans contractors.
Special situations may warrant variation from the policies and guidelines contained within this Dewatering Guide. This Dewatering Guide is neither a textbook nor a substitute for engineering or technical knowledge, experience, or judgment.
The mention of any specific commercial product, process or service in this manual is not to be construed as either an actual or implied endorsement or recommendation by Caltrans. Caltrans makes no representation or warranty of any kind, whether expressed or implied, concerning products or processes discussed in this manual.
This Dewatering Guide is organized as follows:
Section 1 – Introduction: Provides an overview of what activities are considered dewatering; introduces the National Pollutant Discharge Elimination System (NPDES) permits that regulate dewatering in California; describes which dewatering discharges are regulated; and, identifies the pollutants that are of concern in dewatering discharges.
Section 2 – Selecting a Dewatering Management Option: Provides flow charts that guide the intended user through the process of determining if the dewatering operation is subject to an NPDES permit, Waste Discharge Requirements (WDRs), or waiver, and if so, under which permit or waiver the operation is regulated.
Section 3 – Dewatering Management Details: Identifies the specific regulatory requirements for each specific dewatering option as well as advantages or limitations of selecting a particular dewatering option.
Appendix A – Dewatering Permit Requirements: Presents a summary of NPDES permit requirements or waivers for dewatering discharges in each Regional Board jurisdiction; contains maps of the nine Regional Boards overlaid on the Caltrans District boundaries; and, provides Regional Board contacts for the relevant NPDES permit or discharge waiver.
Appendix B – Sediment Treatment Options: Contains brief descriptions, costs, and considerations for the following treatment technologies: desilting basins, sediment traps, weir tanks, gravity bag filter, sand media filter, pressurized bag filter, and cartridge filter. Also includes a brief description of the use of an Active Treatment System (ATS).
Appendix C – Assessment and Monitoring Forms: Contains forms for assessing dewatering options and recording decision making. Also contains forms for monitoring discharges from dewatering operations.
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Appendix D – Regional Board General NPDES Permit and Waiver Requirements: Presents general NPDES permits that regulate dewatering operations in each Regional Board. Also, some Regional Boards have waivers from waste discharge requirements and waivers from report of waste discharge. These waivers are included, where appropriate.
Appendix E –Defined Terms: Includes terms that relate to dewatering operations and permitting.
Appendix F – Endnotes and Relevant Citations: Contains endnotes for the Dewatering Guide. These endnotes contain additional information and citations that intended users may find helpful. Endnotes are indicated in the text with a superscript lower-case Roman numeral. Footnotes are indicated by a superscript Arabic numeral.
1.2 Dewatering Operations Defined Dewatering operations occur when accumulated precipitation or non-storm water must be removed from a work location so that construction may be accomplished. Figure 1-1 illustrates the construction-site dewatering process. Pollutants may be discharged during dewatering activities and for this reason, a number of NPDES permits regulate the discharge of dewatering waters.
Figure 1-1. General Construction Site Dewatering Process
The Construction General Permit1 governs water quality compliance for Caltrans construction or demolition activities that occur on project sites having equal to or greater than one acre of land surface disturbance. Waters generated from dewatering activities on these types of construction sites are considered authorized non-storm waters.i Typical sources of non-storm water from Caltrans construction site dewatering include groundwater, water from cofferdams, water diversions, and waters used during construction activities that must be removed from a work area.
Dewatering operations may occur during a wide range of activities on Caltrans construction sites including demolition of pavement or structures; grading (including cut and fill slopes); channel excavation; channel paving; trenching and underground drainage; installation of underground drainage facilities; drainage inlet modification; utility trenching; utility installation; structure excavation; bridge or structure construction; miscellaneous concrete work; sound or retaining wall construction; planting and irrigation; and, treatment best management practice (BMP) construction and maintenance.ii
The discharge of accumulated precipitation is also governed by the Construction General Permit. Discharge of accumulated precipitation is generally considered a stormwater discharge; however, accumulated precipitation may be commingled with non-storm water or impacted by construction
1 State Water Resources Control Board, National Pollutant Discharge Elimination System (NPDES) General Permit for Storm Water Discharges Associated with Construction Activities and Land Disturbances (CAS000002, Order No. 2009-0009-DWQ), issued September 2, 2009 (herein, “Construction General Permit”).
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materials or activities. Commingled accumulated precipitation is considered non-storm water. Because of this, the management of accumulated precipitation is described in the Dewatering Guide.
The Construction General Permit allows any of the nine Regional Water Quality Control Boards (Regional Boards) to regulate dewatering discharges using a general NPDES permit or site-specific permit.iii Eight Regional Boards have issued general NPDES permitsiv that regulate dewatering discharges. One Regional Board has issued WDRs that govern construction dewatering. Three Regional Boards have issued waivers of WDRs or waivers from reports of waste discharge (RWD) for construction dewatering.
On Caltrans construction sites, a dewatering and discharge work plan, meeting appropriate regulatory requirementsv must be prepared before dewatering operations occur.vi
1.3 Permits and Regulations that Apply to Dewatering Operations Dewatering operations are governed by federal and California law as implemented through California regulations. Although not specifically described by this dewatering guide, two types of permits may also apply on construction sites: groundwater extraction associated with cleanup of volatile organic and petroleum compounds and utility vault dewatering (see Section 1.3.6).
1.3.1 Federal Regulations Federal regulations for controlling discharges of pollutants from municipal separate storm sewer systems (MS4s), construction sites, and industrial activities were incorporated into the NPDES permit process by the 1987 amendments to the Clean Water Act (CWA) and by the subsequent 1990 promulgation of federal stormwater regulations by the U.S. Environmental Protection Agency (EPA). The EPA regulations require construction and stormwater discharges to comply with an NPDES permit. In California, the EPA delegated its NPDES permitting authority to the State Water Resources Control Board (SWRCB).
1.3.2 California Regulations California and the federal government define jurisdictional waters differently.vii This has important implications for the management of dewatering discharges. Federal regulations only govern discharges to Waters of the United States. Waters of the United States are surface waters and discharges to those waters are governed by an NPDES permit. The SWRCB and the associated Regional Boards implement the NPDES permit program in California.
California has a broader definition of waters subject to its jurisdiction. California regulates discharges to both surface waters and groundwater. California uses WDRs to regulate discharges that may impact groundwater. Thus, discharges solely to land are typically regulated using WDRs.
In addition to using WDRs or NPDES permits to regulate discharges, a Regional Board or the SWRCB may issue a waiver from WDRs or RWD for certain discharges. Region 5, Region 8, and Region 9 currently have such waivers and these waivers mostly regulate discharges to land. Additionally, the statewide low- threat discharge WDRs, discussed later, applies to certain discharges to land.
1.3.3 Caltrans MS4 Permit The current Caltrans MS4 Permit does not regulate Caltrans construction sites having a land disturbance area greater than or equal to one acre.viii For these sites, the Caltrans permit only “impose[s] electronic filing, notification, reporting, and contractor requirements for certain construction projects, and imposes limitations on types of materials that may be used during construction which may have an impact on post-construction discharges.”ix Caltrans construction sites having land disturbance area less than one acre are regulated by the Caltrans MS4 Permit and must implement appropriate BMPs.x
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1.3.4 Discharge of Accumulated Precipitation (Stormwater) Within each Regional Board jurisdiction, accumulated precipitation (accumulated stormwater) from Caltrans construction activities may be discharged to a storm drain or water body in accordance with the National Pollutant Discharge Elimination System (NPDES) General Permit for Storm Water Discharges Associated with Construction Activities and Land Disturbances (CAS000002, Order No. 2009-0009- DWQ), issued September 2, 2009 (Construction General Permit).xi This permit regulates storm water discharges from construction or demolition activities that result in a land disturbance of greater than or equal to 1 acre, except when such activities occur in the Lake Tahoe Hydrologic Unit.xii
Construction activities greater than 1 acre occurring in the Lake Tahoe Hydrologic Unit are governed by the General Waste Discharge Requirements and National Pollutant Discharge Elimination System Permit for Storm Water Discharges Associated with Construction Activity in the Lake Tahoe Hydrologic Unit, Counties Of Alpine, El Dorado, and Placer (CAG616002, Order No. R6T-2011-0019), issued April 14, 2011 (Lake Tahoe CGP).xiii Accumulated precipitation cannot be discharged from the construction site to a waterbody. However, discharges to land of dewatering waters are allowed if certain requirements are met.xiv
In the Lahontan Region, other than in the Lake Tahoe Hydrologic Unit, a separate permit regulates discharges of accumulated stormwater. This permit, the General Waste Discharge Requirements for Small Construction Projects, Including Utility, Public Works, and Minor Streambed/Lakebed Alteration Projects in the Lahontan Region Excluding the Lake Tahoe Hydrologic Unit (Board Order No. R6T-2003- 0004, Lahontan Small Construction Permit), covers construction sites having an area between 10,000 square feet and one acre. Like the Lake Tahoe CGP, the Lahontan Small Construction Project permit only allows discharges to land of accumulated stormwater if certain conditions are met.xv
1.3.5 Non-Storm Water Dewatering Operations Under the Construction General Permit, dewatering of uncontaminated non-storm water is an authorized non-storm water discharge.xvi The Construction General Permit regulates dewatering, unless a regional NPDES permit applies.xvii Non-storm water includes, but is not limited to, groundwater, dewatering of piles, water from cofferdams, water diversions, and water used during construction activities that must be removed from a work area.
Under the Construction General Permit, discharges must meet specific requirements of the Construction General Permit including meeting the prohibitions of the applicable Basin Plan, compliance with the prohibitions on discharges of toxics, implementing BMPs to prevent contact of dewatering waters with construction materials or equipment, and monitoring for and compliance with applicable numeric action levels (NALs), receiving water triggers, or numeric effluent limitations (NELs).xviii
General NPDES permits that regulate specific types of dewatering discharges are identified in Table 1-1 and are further discussed in Section 3.9. Copies of these permits are provided in Appendix D.
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General Permits, WDRs & Waivers that Regulate Dewatering
Caltrans District Regional Board Dewatering General Permit, WDRs & Waivers
1 Region 1 – General Permit R1-2009-0045 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145
2 Region 1 – General Permit R1-2009-0045 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145 Region 6 – General Permit R6T-2008-0023 & R6T-2003-0004
3 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145 Region 6 – General Permit R6T-2008-0023 & R6T-2011-0019
4
Region 1 – General Permit R1-2009-0045 Region 2 – No General Permit Region 3 – General Permit R3-2011-0223 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145
5 Region 2 – No General Permit Region 3 – General Permit R3-2011-0223 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145
6 Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145 Region 6 – General Permit R6T-2008-0023 & R6T-2003-0004
7
8
9 Region 6 – General Permit R6T-2008-0023 & R6T-2003-0004
10 Region 2 – No General Permit Region 5 – General Permit R5-2013-0074, Resolution R5-2013-0145 Region 6 – General Permit R6T-2008-0023 & R6T-2011-0019
11 Region 7 – General Permit R7-2009-0300 Region 9 – General Permit R9-2007-0034 & R9-2008-0002, Resolution R9-2007-0104
12 Region 8 – General Permit R8-2009-0003 & R8-2007-0041, Resolution R8-2013-0015 Region 9 – General Permit R9-2007-0034 & R9-2008-0002, Resolution R9-2007-0104
1.3.6 Contaminated Groundwater Each Regional Board has general permits that regulate the cleanup of contaminated groundwater. Those permits that specifically include construction dewatering are included and described in this Dewatering Guide (i.e., Region 4 and Region 9). However, contaminated groundwater is sometimes encountered on Caltrans construction sites and for that reason, Table 1-2 is provided.
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Table 1-2. Regional Board General Permits that Regulate Groundwater Extraction
Caltrans District Regional Board Groundwater Extraction General Permit
1 Region 1 – General Permit R1-2011-0028 Region 5 – General Permit R5-2013-0074
2 Region 1 – General Permit R1-2011-0028 Region 5 – General Permit R5-2013-0073 & R5-2013-0075 Region 6 – General Permit R6T-2010-0024
3 Region 5 – General Permit R5-2013-0073 & R5-2013-0075 Region 6 – General Permit R6T-2010-0024
4
Region 1 – General Permit R1-2011-0028 Region 2 – General Permit R2-2012-0012 Region 3 – General Permit R3-2011-0222 Region 5 – General Permit R5-2013-0073 & R5-2013-0075
5 Region 2 – General Permit R2-2012-0012 Region 3 – General Permit R3-2011-0222 Region 5 – General Permit R5-2013-0073 & R5-2013-0075
6 Region 5 – General Permit R5-2013-0074 Region 6 – General Permit R6T-2010-0024
7
Region 3 – General Permit R3-2011-0222 Region 4 – General Permit R4-2013-00431 Region 5 – General Permit R5-2013-0073 & R5-2013-0075 Region 6 – General Permit R6T-2010-0024
8
Region 6 – General Permit R6T-2010-0024 Region 7 – General Permit R7-2009-0400 Region 8 – General Permit R8-2012-0027 Region 9 – General Permit R9-2007-00341 & R9-2008-00021
9 Region 6 – General Permit R6T-2010-0024
10 Region 2 – General Permit R2-2012-0012 Region 5 – General Permit R5-2013-0073 & R5-2013-0075 Region 6 – General Permit R6T-2010-0024
11 Region 7 – General Permit R7-2009-0400 Region 9 – General Permit R9-2007-00341 & R9-2008-00021
12 Region 8 – General Permit R8-2012-0027 Region 9 – General Permit R9-2007-00341 & R9-2008-00021
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