Stormwater Infiltration
Investigation and
Regulation
Geoffrey M. Goll, P.E., SEO
ggoll@princetonhydro.com
PADEP MANUAL IN FINAL DRAFT
• Provides guidance on the final link for
implementation to the PADEP
Comprehensive Stormwater Management
Policy.
Act 167 Planning
Program
NPDES
Construction
Permits
Comprehensive
Stormwater
Management Policy
BMP Manual
NPDES Phase II
MS4s
COMPREHENSIVE STORMWATER
POLICY
• “A uniform approach to post-construction
stormwater management that emphasizes
groundwater recharge through infiltration
and discharge volume and rate control
with the goal of replicating infiltration and
runoff characteristics of the site prior to
development.”
BMP Recommendations
• The BMP Manual recommends removing
the difference in volume between the 2year storm, pre-development to postdevelopment or infiltrating the first 0.5
inches when 1.5 inches of rain are to be
captured and removed from runoff.
BMP Recommendations
• The BMP manual emphasizes controlling runoff from a
site using Low-Impact Development (LID) techniques to
maintain pre-development conditions as closely as
possible.
• However, at some point infiltration will be
required to meet the infiltration/recharge
deficit caused by development and the
creation of impervious surfaces.
To Infiltrate One Must Understand
the Underlying Soils and Geology
• 35% of the state soils contain less than
40” of soil overlying bedrock[i].
• 61% of the State’s soils are characterized
as Hydrologic Type C & D Soils[ii]
•
•
[i] Pennsylvania Association of Soil Scientists, “Take and Interactive Quiz on Pennsylvania Soils!”,
http://www.papss.org/PA%20soils%20quiz%20ques%202.htm\
[ii] PADEP BMP Manual
To Infiltrate One Must Understand
the Underlying Soils and Geology
Central Michigan University (2004), “ESC/BIO 334-Soil Science, How a Soil Forms”,
http://www.cst.cmich.edu/users/Franc1M/esc334/lectures/origin.htm
To Infiltrate One Must Understand
the Underlying Soils and Geology
Source: http://courses.missouristate.edu/ejm893f/creative/glg110/groundwater.html
To Infiltrate One Must Understand
the Underlying Soils and Geology
Source: http://courses.missouristate.edu/ejm893f/creative/glg110/groundwater.html
To Infiltrate One Must Understand
the Underlying Soils and Geology
GROUNDWATER MOUNDING CAN REDUCE REQUIRED
SEPARATION DISTANCES, FAIL A BASIN, AND CAUSE FLOODING
TO ADJACENT STRUCTURES.
Kaveh, Ph.D., Zamorodi, “Simplified Solutions for Groundwater Mounding Under
Stormwater Infiltration Facilities “, Dewberry, Fairfax, VA, Figure 2.
Recommended Testing in Addition
or as an Alternate to the BMP
Recommendations
• Installation of Shallow Wells or Piezometers
•In-situ Falling Head Permeability.
•Slug Testing.
• Open Pit Testing
•Basin Flood Tests.
•Pit Bail Testing.
Recommended Testing in Addition
or as an Alternate to the BMP
Recommendations
• In situations where groundwater mounding is a
concern, more complicated testing and analysis is
recommended:
•Installation of Monitoring Wells, and observation
wells.
•Aquifer stress testing (pump tests).
•Modeling mounding using techniques such as
ModFlow™.
Proposed Regulatory Incentives
Need incentive to engineers, developers and
governmental agencies to move away from “End-ofthe-Pipe” solutions to realistically meet objectives of the
Comprehensive Stormwater Management Policy and
intent of the BMP Manual.
One idea:
As infiltration techniques are proposed
closer and closer to the runoff source,
complex field testing and modeling
techniques could be relaxed.
Need Municipal Enforcement
• Once construction is complete and the developer
walks away, who will ensure on-lot infiltration
techniques are maintained in perpetuity??????
Rain gardens, drywells, infiltration trenches, porous
pavement, sandfilters, and bioretention, and
infiltration basins.
These are great ideas........................
.....if the property owner maintains them!!!
Need Municipal Enforcement
If the Township Maintains rights to these techniques,
easement can get cumbersome and onerous.
One idea comes from
Act 537, the Sewage Facilities Act.
Act 537, the Sewage Facilities Act
•Act 537 requires permitting of each septic system;
•A PADEP certified Sewage Enforcement Officer is
responsible for enforcing the Act;
•No easement or deeds necessary. Permits are
kept on file at the Township, County and State;
•Township via permit has right to enter property is
there is suspicion that system is not being
maintained.
Who Should Review Designs and
Enforce Functionality?
Who Should Review Designs and
Enforce Functionality?
•Soil Scientist
•Professional Geologist or Hydrogeologist
•Geotechnical Engineer
Above Professional would report Municipal Engineer or
Directly to Municipality.
Reimbursement Programs for
Enforcement
•Act 167 specifically provides for reimbursement of up
to 75% of the costs for the preparation of stormwater
management plans and actual administrative,
enforcement and implementation costs and revisions
to stormwater management plans required by the Act.
•The plan also reimburses the fees required for
special technical consultation concerning complex or
unusual stormwater management issues.
Thank you!