Alewife Study Group > government > March. 14 2000, Cambridge Conservation Commission Search 

Oaktree Development
30 Cambridge Park Drive
Public Hearing

March. 14 2000, Ackerman Room, 2nd floor of Cambridge City Hall, Massachusetts Ave.

Oaktree is the developer for 30 Cambridge Park Drive (also written as CambridgePark Drive).

For ease of comparison to the printed version, page breaks in the original Microsoft Word report
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"Cambridge Conservation Commission
March 3, 2000 "
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Consultant's report

March 3, 2000

Ms. Julia Bowdoin
Conservation Administrator
Cambridge Conservation Commission BY EMAIL AND FIRST CLASS MAIL
City Hall Annex
57 Inman Street
Cambridge, MA 02139

RE: Review of Notice of Intent: 30 Cambridge Park Drive

Dear Ms. Bowdoin and members of the Conservation Commission:

The BSC Group, Inc. (BSC) has completed its review of the proposed project at 30 Cambridge Park Drive within the 100-year flood plain of Alewife Brook. This letter summarizes our findings and conclusions with respect to the three items the Commission requested assistance with:

As part of our review, we reviewed the following materials:


  1. BSC conducted research regarding Bordering Land Subject to Flooding (310

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    CMR 10.57) to determine policy and application of the performance standards set forth in the regulations. The primary question on which we focused revolved around the interpretation of the term "incremental". The applicant's position is that the term "incremental" does not require incremental compensation between elevations. As we understand their opinion, as long as incremental volume is compensated for, it does not necessarily have to provided at the same elevation from which it was lost (i.e. it can be directed to chambers, temporarily detained and released).

    Based on our review of DEP decisions and discussions with DEP regulators, it is BSC's opinion that loss of flood storage within bordering land subject to flooding is required to be compensated for at the incremental elevation from which it is lost.

  2. The drainage and flood plain calculations were reviewed and found to be largely accurate. We identified a few areas that required additional information or adjustment, which we discussed with the applicant's representatives. Technically, the project is designed using good engineering practice. The ability of the project to comply with DEP performance standard revolves around the regulatory interpretation of "incremental" and a decision on how the Commission will define existing conditions on the site. Should the project be reviewed assuming the "1950's building" demolished in December 1998 is still located on the site, the project is able to comply with the performance standards. If not, the project does not comply with the performance standards.

  3. Finally, the Commission requested assistance in its review of the demolition of the 1950's building in 1998. BSC has proposed a number of after-the-fact conditions that could be placed on the project. In addition, the Commission may wish to include several of the conditions as part of an enforcement provision included in the current permitting review.

Each of these is discussed in greater detail below.

Regulatory Interpretation of Bordering Land Subject to Flooding

The key question that needed addressing was whether compensatory flood storage needed to be created incrementally by volume or incrementally by volume between elevations, i. e. at each respective elevation where floodplain is lost. A secondary question was whether it is appropriate to re-grade portions of the existing flood plain to provide additional compensatory storage. In approaching these questions, BSC reviewed selected cases and discussed the cases with the DEP staff involved in the case. Because the cases were in the Northeast Region of the DEP and there is the possibility of an appeal directed to the same office, BSC did not discuss the specifics of the Cambridge case. We instead discussed the DEP approach to the cases reviewed and explained the applicant's position generally.

The regulations at 310 CMR 10.57 (4) (a) state, in part, "Compensatory storage shall be provided for all flood storage volume that will be lost as the result of a proposed project within Bordering Land Subject to Flooding.…Compensatory storage shall

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mean a volume not previously used for flood storage and shall be incrementally equal to the theoretical volume of flood water at each elevation, up to and including the 100-year flood elevation, which would be displaced by the proposed project. Such compensatory volume shall have an unrestricted hydraulic connection to the same waterway or waterbody."

The applicant represented that the regulations do not require an elevation to elevation comparison. In a letter to the Commission from Hutchins, Wheeler & Dittmar dated December 2, 1999, it was stated "What they (the regulations) require is that the volume of floodwater at each elevation up to and including the 100-year flood elevation must be equal in both pre and post development conditions. The increments referred to are between a level of no flooding and the particular flood in question, up to and including 100-year flood."

BSC does not agree with this statement. We base our conclusion on a reading of the regulations and discussions conducted with representatives of the DEP. The regulations read that flood storage shall be incrementally equal to the theoretical volume of flood water at each elevation. They do not say "equal to the theoretical volume of flood water" for each flood volume or flood event. In addition, the regulations specify that the compensatory flood volume include the flood elevations up to and including the 100-year flood elevation. Once again, the regulations do not state that compensatory flood volume include flood volumes or flood levels, they state flood elevations.

The applicant had provided to the Commission and to BSC three DEP cases which addressed compensatory flood storage, as well as copying a section of the Mass Audubon Society's A Guide to Understanding and Administering the Wetlands Protection Act. The three cases included In the Matter of Judith Sudduth, Trustee of Hesperus Avenue Realty (1993 WL 440477); In the Matter of Neponset Associates (1997 WL 825151) and In the Matter of Burkhard Corp (1999 WL 587155). In addition to reviewing the cases, BSC contacted Ms. Rachael Freed and Ms. Elizabeth Sabounjian, both analysts for the DEP and involved in the cases mentioned.

In the Matter of Sudduth, the relevant section appears to address one of the Commission's earlier concerns that portions of the compensatory flood storage could be provided by re-grading portions of the site that are already in the flood plain. Re-grading to enlarge flood storage capacity at increments that are not currently being used as flood storage meets the performance standards. This is also demonstrated in the Audubon reference. The relevant section of the case states that "…both the wetlands regulations and Sprague's testimony make clear that the performance standards are directed to incremental volume of storage, not lateral area covered." It is not clear whether the applicant interpreted this sentence to imply that as long as volume is stored incrementally, it does not need to be stored at the same elevation. In our opinion the issue discussed in this case is one of location of grading and flood storage within an existing flood plain, not of dismissing the increment by increment elevation requirement. Although I tried to reach Mr. Sprague to discuss this, I was not successful.

In the Matter of Neponset Associates, the relevant section also appears to address the

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earlier concern regarding the use of existing flood plain for compensatory storage through re-grading. The specific language is "…I infer that Mr. Pfischner intends to suggest that compensatory storage must be outside the flood plain. This reflects a misunderstanding of the regulatory standard. The Regulations require only that new storage be "a volume not previously used for flood storage."" The footnote associated with the sentence quotes Ms. Sabounjian's "understanding of the regulations and Department practice that compensatory storage can be placed within existing flood plain if the appropriate incremental volume, a three dimensional measurement, can be provided."" Once again, BSC is of the opinion that the discussion revolved around the re-grading of the existing flood plain, not the cumulative availability of compensatory flood storage or a dismissal of the elevation by elevation argument. An argument proposing otherwise could be viewed as taking the discussion out of context. Additionally, the case included a discussion regarding cumulative versus incremental storage. "Ms. Sabounjian calculated the total number of cubic feet which will be provided by the project up to elevation 102 to be 1, 156,490. She derived this figure by adding the flood storage to be provided at each elevation."

I was able to speak with Ms. Sabounjian regarding this case. She reaffirmed the requirement that compensatory flood storage be provided at each elevation.

Finally, in the Matter of Burkhard, the proposed project included approximately 800 cubic feet of vault storage, in addition to re-grading on the site. The proponent showed that the project compensated for lost flood storage at each one foot elevation. BSC read this to imply that each one-foot elevation was replaced, not the volume at each such elevation.

I was able to speak with Ms. Freed about this case and one other case in Cambridge she had worked on. In the Burkhard case and the other case, Genetics Institute case (DEP File #123-135), Ms. Freed indicated that compensatory storage is viewed on an incremental elevation basis, meaning between elevations, not on a volume basis. She indicated that the applicant's position that "The word "incrementally" in the regulations refers to each elevation, not between elevations" (Hutchins, Wheeler & Dittmar letter) is wrong.

In addition, the Burkhard case addressed the concern regarding unrestricted hydraulic connections. In the decision, floodwaters were designed to "flow unimpeded into and out of the vault, thus meeting the requirement that there be an unrestricted hydraulic connection from a compensatory storage area to the waterbody".

The 30 CambridgePark Place project is designed to allow backwater flooding from the 10-year storm event to enter the site, flooding that does not occur now. Larger, less frequent storms enter the site via lateral flooding extending from Alewife Brook and are, in part, directed to chambers beneath the building and parking lot. These chambers are designed to drain when the larger flood events have receded from the site. The elevation at which chamber drainage will be achieved is roughly equivalent to the theoretical 10-year flood. However, since the site will only flood during the 10-year flood by means of backwater flooding through the street drain system (under proposed conditions), the portions of the larger storm events that will be directed to

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the chambers and released at a theoretical controlled 10-year elevation are not provided an unrestricted hydraulic connection from the site to Alewife Brook. As designed, flood waters released from the larger events will be discharged to a small basin in the rear of the building and will either infiltrate to the ground or evaporate. The resultant inability of portions of the larger flood events to flow via an unrestricted hydraulic connection to Alewife Brook indicates that this performance standard is not met.

Given the information provided to BSC by DEP and applying BSC's interpretation of incremental as "between elevations", it is our opinion that a project must provide compensatory flood storage at the same elevation from which it is lost. Additionally, the Mass Audubon Guide (p. 276) states: "The plan in Figure 10-3b corrects the (previous) error, adequately compensating for the flood storage volume lost at each increment of elevation within the flood plain."

Technical Drainage Calculation Review

BSC engineers reviewed the drainage calculations provided with the Notice of Intent and met with the applicant's engineering team on three occasions. The engineering calculations conducted for the proposed project are accurate and follow good engineering practice. The proposed project provides compensatory flood storage at increasing flood levels by use of chambers located beneath the parking and building. However, as a result of the difference in opinion regarding the definition of "incremental", the project as presently proposed (assuming no building on the site) does not provide compensatory storage on an increment by increment elevation (between elevations), nor does it provide an unrestricted hydraulic connection to Alewife Brook.

The technical features of the drainage system proposed by the applicant's engineering team provide two mitigating functions - provision of compensatory flood storage and stormwater retention. In reviewing the compensatory flood storage approach by the applicant, we believe the applicant's engineer has made a reasonable attempt to address the technical aspects of providing compensatory flood storage.

The applicant provided the compensatory volume displaced at each elevation and reported the incremental volume in a summary table. The storage for various flood events was contained in chambers under the building and parking garage. Three chambers were proposed each with a weir structure that controlled the elevation of storage behind the chamber. The chambers were outlet through a discharge pipe at the bottom of the respective chamber. Technically and hydraulically, the proposed storage would function and provide the storage proposed.

However, our review found two flaws with the design approach, which are in conflict with the regulations. First, the storage of portions of the required compensatory flood volume was not being provided at the same elevation of the displaced storage, and second, the discharge pipe being outlet at a lower elevation than the flood elevation being stored did not, in our opinion, provide the unrestricted hydraulic connection for the portions of the less frequent, larger storm events that are directed to the chambers. An unrestricted hydraulic connection is required by the regulations.

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Our technical review also identified a volume measurement discrepancy of 1,200 cubic feet at elevation 8.0 to 8.2 (100-year flood elevation). The applicant's engineer concurred with our evaluation and corrected his calculations to adjust the incremental and the cumulative volumes calculated. The proposal for the use of chambers would require an additional chamber to store the additional 1,200 cubic feet controlled at the 8.2 elevation. The applicant has agreed to address the error in his calculations in this manner if the commission accepts the use of the chambers for compensatory flood storage. However, should the Commission decide to allow the applicant the credit for flood storage associated with the now-demolished building, the available flood storage provided by the additional volume from chambers will greatly increase flood storage capacity on the site beyond the amount that had been available with the now-demolished building. The Commission may, therefore, determine that the provision for the additional chamber is not necessary.

We noted that the bottom elevations of the proposed chambers were proposed to be open-bottom chambers allowing recharge to the ground. The elevations of the bottom were approximately at elevation 2.0 to 2.5. Based on the groundwater elevations provided by the applicant from their Geotechnical engineer, the groundwater elevations appear to fall within 12 to 18 inches of the bottom elevations of the chamber. Although this would appear to allow the recharge function of the chamber to function as proposed, there is a risk that the operation of the chamber may not perform as optimally as intended with the design. Also, the testing provided does not indicate any testing performed during the high groundwater season, which could and normally does result in a temporary elevation of the groundwater levels during that season. If the chambers were required to hold and release volumes from select storm events, as is currently proposed, it would be important to account for potential loss of flood storage volumes associated with seasonal high ground water filling part of the chamber. In that case, the design would have to account for the maximum groundwater elevation reasonably anticipated in order for the chambers to function as intended by the design.

If the Commission is interested in maintaining an absolute available volume within the chambers, it could consider engineering solutions to the groundwater issue. For example, if the bottom elevation of the chambers were to be maintained with the volume capacity currently proposed, one alternative could be to make the chambers watertight. A watertight chamber would provide the effective storage replacement without any groundwater intrusion. A sealed bottom, however, would negate the benefits of groundwater recharge from the chambers. Another alternative would be to raise the bottom elevation of the chamber to a reasonable distance above the maximum high groundwater elevation measured during the March-May period. This approach has the advantage of maintaining the groundwater recharge component of the design.

However, if the Commission allows the credit for the flood storage for the now-demolished building, the volume provided in the chambers could be permitted as additional storage required as part of after-the-fact review or an additional requirement for mitigation for unauthorized activities.

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After The Fact Demolition Review

The site supported a building constructed in the 1950's and associated parking and driveway until the building's demolition in December 1998. The regulations define Bordering Land Subject to Flooding as the FEMA 100-year flood plain. In this case, the FEMA report was prepared in 1982, subsequent to the construction of the building, meaning that the FEMA flood plain calculations did not include the volume displaced by the then-existing building to be part of the flood plain.

As part of receiving approval for demolition, the applicant asserts that the owner obtained all permits the owner believed to be necessary. Although ignorance cannot be excused, the owner was not provided guidance regarding the necessity that a permit was required from the Conservation Commission for work within the Bordering Land Subject to Flooding and does not appear to have acted willfully to avoid compliance with the Wetlands Protection Act. Given that the FEMA report was prepared subsequent to the construction of the building, removal of the building did not impact flood storage capacity. Conversely, the flood volume displaced by the then-existing building became an available part of the flood plain.

The Commission requested advice on methods to retroactively address this situation. One way to view this situation is to ask how the Commission would have reviewed and permitted a Request for Determination of Applicability or Notice of Intent to remove the building. Had the owner come to the Commission in December 1998, the Commission would likely have reviewed the proposed demolition in light of the presumptions of significance and performance standards associated with the Bordering Land Subject to Flooding.

Conditions the Commission could have imposed on the project may have included a goal to reduce the amount of impervious cover on the site, to include more green space and include plantings conducive to avian species known to populate the riverine/floodplain environment. These are goals similar to those stated in City planning documents. Would the Commission have conditioned future site conditions to assume no "reserve" of displaced flood volume? It is not unusual for a demolition project to be phased with a proposed redevelopment activity. As part of a future development proposal, the Commission may have imposed a condition that allowed future development but with required improvement of stormwater management and/or increased flooding capacity.

Under the existing permit process, the Commission can assert jurisdiction over the demolition and the proposed project in the same permit by including special conditions to address both the violation and the proposed activities. Conditions necessary to protect the interests of the Act are still a valid and necessary part of the review process for both the violation and the proposed project. These conditions could include an acknowledgement that the demolished building did displace flood storage, but could also require decreases in impervious cover, provision of more green space (plantings to be determined), allowance for an increase in infiltration to groundwater and, potentially, baseflow to the Brook and provision of an increase in the site's flood storage capacity. Several of these mitigating measures are currently

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proposed in the Notice of Intent, including provision of capacity for the 10-year flood (which flood currently does not access the site).

Conclusions and Recommendations

The Conservation Commission has two potential paths that it could follow.

As presently proposed, the project assumes the existing conditions to be a largely impervious but undeveloped site. In our opinion and interpretation of the regulatory requirements, under the undeveloped existing condition scenario, the project does not meet the performance standards as a result of its inability to provide increment by increment storage by elevation. However, until December 1998, the site did support a structure which displaced flood capacity on the site. That flood capacity was not included as part of the FEMA flood plain calculations. If one were to assume that the pre-existing building is the existing condition, or that a permit issued for the demolition would have allowed for a "reserved displacement volume" to credit toward future development, then the proposed project design is able to meet the performance standard of increment by increment compensatory flood storage by elevation. In addition, the site will maintain an unrestricted hydraulic connection to Alewife Brook. Under this scenario, the Commission could choose to permit the proposed project with conditions.

Special mitigating Conditions for unauthorized demolition and overall site improvement could include the following:

Alternatively, if the Commission determines that after-the-fact permitting review for the building demolition, or retroactive enforcement activity would not reserve displaced flood volumes from the now-demolished building, the project can be denied for failure to meet the performance standards for Bordering Land Subject to Flooding. However, subsequent to discussions with DEP, BSC believes that DEP would review as reasonable an evaluation that finds that the displaced flood volume associated with the now-demolished building could be used as a credit toward reconstruction on the parcel, if, after a review of all the circumstances, the Commission requires conditions requiring benefits to the interests of the act to the floodplain (on the site and therefore to the floodplain as a regional system) and can make a clear finding that there will be no increase in the horizontal extent and level of flood waters.

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If you have any questions or comments, please contact either one of us. In addition, once the Commission has determined its actions on the proposal and needs assistance in the issuance of Conditions, please let us know.

We look forward to your comments and questions concerning our review.


The BSC Group, Inc.

Ingeborg E. Hegemann                                                               James L. Fuda, P.E.
Vice President                                                        Senior Vice President

cc:     Gwen G. Noyes
          James F. McAuliffe
          Charles G. Samiotes, PE

Contact the Alewife Study Group, North Cambridge Massachusetts, by email at