Common PCSM Plan Deficiencies

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Common PCSM Plan Deficiencies

• (Post Construction Stormwater Management
  Component of NPDES Permit)

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Common Deficiencies

• Stormwater Detention Basin Discharge Conveyance
  Is Not Clearly Detailed Or Has Been Determined To
  Be Not Adequate
• Page 56 of the ES Manual - "The discharge from a
  sediment basin must be to Waters of The
  Commonwealth or other approved alternative, and
  shall be designed, operated, and maintained
  without causing accelerated erosion or
  sedimentation.  Approved alternatives include
  stable constructed channels, storm sewers, and
  similar facilities that can accept the discharge
  with no erosion. This applies to PCSM basins
  also.
• If level spreaders are used, they should be
  designed according to the PA Stormwater BMP
  Manual section 6.8.1.

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Common Deficiencies

• Volume Control Guideline 1 (CG1) Is Applicable
  And Has Been Determined To Be Used But Has Not
  Been Properly Implemented
• Characteristics of the proposed project indicate
  that Volume Control Guideline 1 may be
  implemented. As indicated in Section 3.3.3 of
  the Pennsylvania Stormwater BMP Manual, the
  following three guidelines should be followed
• Do not increase the post-development total runoff
  volume for all storms equal to or less than the
  2-year/24-hour event.
• Existing (pre-development) non-forested pervious
  areas must be considered meadow (good condition)
  or its equivalent.
• Twenty (20) percent of the existing impervious
  area, when present, shall be considered meadow
  (good condition) in the model for existing
  conditions for redevelopment.

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Common Deficiencies

• Methodology For Calculating Runoff Volume Is Not
  Acceptable
• Please indicate which methodology was used to
  calculate Runoff Volume as well as Peak rate
  Runoff. Note the following
• For NPDES calculations, the Rational Method
  should only be used to predict the peak runoff
  rate for very small, highly impervious areas.
• The Modified Rational Method should not be used
  to calculate runoff volumes.
• Often a single, area weighted curve number is
  used to represent a watershed consisting of sub
  areas with different curve numbers. While this
  approach is acceptable if the curve numbers are
  similar, if the difference in curve numbers is
  more than 5 the use of a weighted curve number
  significantly reduces the estimated amount of
  runoff from the watershed. The runoff from
  different sub-areas should be calculated
  separately and then combined.
• Please refer to Chapter 8 of The Pennsylvania
  Stormwater BMP Manual for additional information
  on stormwater calculation methodology.

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Common Deficiencies

• Summary Table For Supporting Calculations
  Deficiencies
• Section C 2 of the submitted Notice of Intent
  (NOI) is either incomplete or filled out
  incorrectly. Please carefully read the
  instructions on page 5 of the NOI and make the
  appropriate changes.
• Summary Description of Post Construction
  Stormwater BMPs Deficiencies
• Section C 3 of the submitted Notice of Intent
  (NOI) appears to be either deficient or
  inconsistent with the information provided in
  section C 2. Please indicate the function(s) of
  each BMP. More than one function may be checked
  for a BMP. List the stormwater volume in
  acre-feet and area in acres that will be treated
  by each BMP. If a BMP is indicated as having
  more than one function, the volume and area
  treated must be listed for each function.
  Provide calculations in the Post Construction
  Stormwater Management Report supporting the
  volume of stormwater treated and the acres
  treated for each BMP and its associated
  function. The information in section C 2 and C
  3 will be compared for consistency.

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Common Deficiencies

• Project Description / Narrative Not Adequate
• Presenting DEP with a concise and comprehensive
  project description is crucial to the smooth
  processing of a NPDES permit application.
  Conversely, a vague description that does not
  accurately represent the proposal or a
  description that is in a state of flux makes
  processing unnecessarily time consuming. Extra
  time spent at the beginning of a project writing
  a good project description can save processing
  time. The post construction stormwater
  management plan narrative should address water
  quality, peak attenuation, and volume reduction
  of stormwater runoff increase due to construction
  activities. The type, location and performance
  of proposed BMPs should also be addressed in the
  narrative.

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Common Deficiencies

• Required Testing Data And Procedure For Proposed
  Infiltration BMPs Is Either Not Included Or Not
  Acceptable
• You have proposed infiltration BMPs. Please
  refer to Appendix C of the PA BMP Manual for
  guidance in providing details on your method of
  site evaluation and soil infiltration testing.
  In general, infiltration testing should be a
  multi-step process, which includes a background
  evaluation, test pit observation, infiltration
  testing, and design considerations. All
  infiltration testing data must be provided as
  well as a site map showing testing locations in
  relation to proposed infiltration BMPs.

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Common Deficiencies

• Operation And Maintenance Plan Not Acceptable
• The PCSM plan with operation and maintenance
  procedures provided along with ownership
  responsibilities for the proposed permanent
  stormwater BMPs must be submitted. The
  applicants name, company, government agency or
  entity that is to have ownership and
  responsibility for the PCSM BMPs should be
  specifically named.
• Note that home-owners associations should only be
  named as having ownership responsibilities of
  permanent stormwater BMPs under certain
  circumstances. The first circumstance would be
  that the Act 167 stormwater management plan for
  that watershed allows it. In which case a letter
  from the municipal engineer specifically stating
  that the home-owners association may be named as
  having ownership responsibilities of BMPs is
  required. The second circumstance would involve
  demonstrating that the home-owners association
  can take legal and financial responsibility for
  the proposed permanent stormwater BMPs.
  Demonstration may include but is not limited to
  recordable legal documentation, financial bonds
  and other applicable documentation.

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Common Deficiencies

• PNDI (PA Natural Diversity Inventory) Deficiency
• As part of the NPDES permit application, the
  applicant/consultant shall include documentation
  showing that he or she completed an online PNDI
  Environmental Review and attempted to resolve any
  conflicts with the required agencies before
  submitting the permit application to the Local
  Conservation district. PNDI searches are valid
  for one year from the date of the search. If a
  permit application is submitted more than one
  year after the initial search or conclusion of
  coordination with the jurisdictional agency
  (whichever is the later), then a new PNDI search
  is required.

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Common Deficiencies

• Act 167 Consistency Letter Requirement Deficiency
• Please provide a letter from either the local
  planning commission or the township/municipal
  engineer stating that the proposed plan is
  consistent with the an approved Act 167 Plan or
  in the absence of an approved Act 167 Plan, the
  applicable local storm-water ordinance.
• If the municipal engineer/planning commission has
  not yet reviewed the plan or is in progress of
  reviewing/commenting on the plan, please forward
  a copy of the letter to The Department after the
  plan has been approved.

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Common Deficiencies

• The Loading Ratio(s) For The Proposed
  Infiltration BMP(s) Exceed The Recommended
  Ratio(s) As Per The Pennsylvania Stormwater Best
  Management Practices Manual
• Recommended loading ratios are as follows
• 51 impervious drainage area to infiltration area
• 81 total drainage area to infiltration area
• 31 impervious drainage area to infiltration area
  for karst areas
• Please provide justification demonstrating that
  the receiving infiltration areas and soils can
  accept the proposed increased loading ratio(s).
  Justification may include but is not limited to a
  narrative, calculations, plans, reports, analyses
  and any other applicable documentation.
  Justification that should be included are
  geotechnical reports, soils analyses and/or other
  soils reports that are stamped and sealed by a
  Soils Scientist or a Professional Geologist
  (P.G.) with a narrative stating that the
  receiving infiltration areas and soils can accept
  the increased loading ratios without causing
  negative impacts along with the reasoning why.

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Questions?