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Grant, Kelly
From:Lima, Amanda
Sent:Wednesday, March 2, 2022 11:29 AM
To:Grant, Kelly
Subject:RE: UACC Stormwater Information
Hi Kelly, as we discussed, providing sustainable drainage infrastructure for continuous treatment is the key to success for
managing the water quality requirements in the Stormwater Regulations. I reviewed the response to ESS comments and
application material and have developed the following suggestions:
Pretreatment Requirement of 44% TSS removal
o As noted in ESS’s response letter, the Massachusetts Stormwater Handbook does not provide clear
direction if two deep sump catch basins/drain manholes in-line would receive the same TSS removal of
25%/each yielding the 44% TSS removal goal. With that being said, an additional pretreatment option
should be considered.
Option 1: Provide bi-annual sweeping of the parking lots areas. This would provide up to 10%
TSS removal.
Option 2: Substitute each drain manhole for a Stormceptor STC or equivalent oil/water
separator (Recommended Pretreatment Option by Massachusetts Stormwater Handbook).
While the handbook only assigns 25% TSS removal, Stormceptor performance testing
yields 76% to 93% TSS removal.
Option 3: DCE to perform TSS removal testing during a storm event at another site they have
designed and provide results to the commission.
Infiltration Rate
o The site’s test holes yielding 3-4’ deep of loamy sand and notes that these unsuitable soils will be
removed prior to construction of drainage. With the completion of this work, the infiltration rates
analyzed will be sufficient.
O&M Plan
o O&M plan dated 6/2021 notes that catch basin cleaning would occur once every two years under the
Estimated Operations and Maintenance Budget. This does not meet the Massachusetts Stormwater
Handbook guidelines, which states cleanings should occur four times a year or when the sump is 50%
full or 2’ as noted in the O&M plan. Understanding this may not be feasible, the Owner should provide
quarterly inspections and retain records to identify the depth of sediment below the outlet pipe. Based
on those results, the Owner should clean the catch basins upon 50% sediment depth or once every two
years.
o O&M also includes street sweeping, but it was not included in the TSS calculations. It notes that it will be
st
completed on or about April 1. The Massachusetts Stormwater Handbook guidelines suggests twice a
year, which is required to credit the 10% TSS removal noted in Option 1 above.
Thank you,
Amanda
Amanda Lima, P.E.
Yarmouth DPW -Town Engineer
Office (508)398-2231 Ext. 1253 - ALima@yarmouth.ma.us
From: Daniel A. Ojala, PE PLS \[mailto:downcape@downcape.com\]
Sent: Friday, February 18, 2022 12:51 AM
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