I am often asked which community’s Eiruv is my favorite. I currently serve as an Eiruv consultant for more than sixty communities throughout North America, and I have seen more than a hundred Eiruvin on three continents. Which do I like best? Hands down, without a doubt, it is the Eiruv created and maintained by the Young Israel of Sharon, Massachusetts. Why is it my favorite? The answer is simple. The community aspires to attain the high Eiruv standards set by Rav Moshe Heinemann of Baltimore, meticulously maintains those standards, and in addition to regular rabbinic involvement, more than 45 lay members of the community regularly are involved in the ongoing weekly inspection and upkeep of the Eiruv. Among the issues in which the Sharon Eiruv adopts a high standard is the topic of Karpeif.
The Karpeif Issue
A potentially major obstacle in creating a viable community Eiruv is the existence of a Karpeif within the enclosed area, which may invalidate the Eiruv. A Karpeif is an area at least 100 Amot (between 150 and 200 feet) by 50 Amot (between 75 and 100 feet) that is not used for human habitation (Dirah) or other human needs. Accordingly, sports fields, playgrounds, and lakes used for boating do not constitute Karpeifiyot (plural of Karpeif). Chazal forbid carrying on Shabbat within a Karpeif even if it is enclosed by Mechitzot or Tzurot HaPetach and is therefore within a Reshut HaYachid. This is because the Mechitzot or Tzurot HaPetach must be built for the purpose of human habitation (Mukaf LeDirah) in order for carrying on Shabbat to be allowed within them. A wall or Tzurat HaPetach built to surround a very dense and impassable forest is not built for the sake of human habitation, so it does not permit people to carry on Shabbat within that forest.
Moreover, the presence of a Karpeif forbids carrying in the entire enclosed area surrounding it, because an area's walls or Tzurot HaPetach must be erected solely for human habitation. If they also encompass a Karpeif, however, they are erected for an area that is not entirely fit for human habitation. This issue arises much more often in suburban and rural areas than in urban areas, as an urban setting contains fewer undeveloped areas, making this a relatively rare advantage for an Eiruv in an urban setting. The Chazon Ish (Orach Chayim 88:25) writes that the only way to prevent a Karpeif from invalidating the rest of the Eiruv's area is to encompass the Karpeif with either Mechitzot or Tzurot HaPetach, thereby excluding it from the Eiruv. The community is then Mukaf LeDirah, while the uninhabited Karpeif is severed from it.
The lenient positions of some authorities might also solve this problem. The Bi’ur Halachah (358:9 s.v. Aval) cites one such approach from the Devar Shmuel. He rules that if a Karpeif is situated within a city and is only a small part of the city, carrying is allowed within that area. The Devar Shmuel reasons that in such a situation, the Karpeif is negligible compared to the rest of the city and may be ignored.
Halachic authorities have reacted to the Devar Shmuel's leniency with mixed feelings. On the one hand, the Chazon Ish (Orach Chaim 88:25) rejects this approach, as he sees no reason for a Karpeif within a city to differ from one in a more rural area. The Bi’ur Halachah expresses serious reservations concerning this leniency, but he seems to accept the conclusion of the Chacham Tzvi that the Devar Shmuel's opinion may be followed where it is impossible to construct an Eiruv otherwise.
This issue remains controversial, as some communities rely on the Devar Shmuel, while others do not. A number of Israeli rabbis have told this author that the practice of many large Israeli communities is to follow the lenient opinion of the Devar Shmuel (Bnei Brak, where the Chazon Ish resided, is a significant exception). This is hardly surprising, since Eiruvin in Israel often encompass entire cities, and it is exceedingly difficult to exclude every Karpeif within Israel's (Baruch Hashem) growing communities. Hence, in keeping with the approach of the Bi’ur Halachah, they rely on the Devar Shmuel's lenient ruling.
A number of authorities adopt a compromise approach that distinguishes between different types of Karpeifiyot. If a Karpeif beautifies the city, carrying is allowed. If, however, humans in no way benefit from the area, it must be excluded from the Eiruv.
Karpeif Exclusion in Sharon, Massachusetts
Sharon, Massachusetts is replete with many lush forest areas that seem to pose a Karpeif challenge. However, one must understand the community to appreciate how the forested areas are an integral part of the community.
In 2013, Money magazine ranked Sharon as the best place to live in the United States. Here is part of Money’s description of the town:
A half-hour train ride from Boston or Providence, this one-time summer resort has the natural beauty of a more remote place. Forty percent remains open space, and the town jewel, Lake Massapoag, offers a place for residents to swim, picnic, and enjoy concerts on Memorial Beach.
The open space in Sharon is clearly part of the Dirah! Moreover, a major part of the town culture is hiking and outdoor athletics. An incredibly high percentage of the population engages in outdoor activities including hiking in the town’s forested areas. The forests are very much integrated in the living space of the town and need not be regarded as Karpeifiyot.
Accordingly, the original Poskim for the Sharon Eiruv, Rav Shimon Eider zt”l and (Yibadeil LeChayim Aruchim) Rav Moshe Heinemann, required that only the most dense and watery of the forests be excluded from the Eiruv. In this manner, the Eiruv would not simply rely on the Devar Shmuel but would satisfy even those who adopt a strict attitude regarding Karpeifiyot. The Sharon community loyally and lovingly maintains these borders and excludes these areas from the Eiruv.
Regarding one of the excluded areas, though, the reality has been changing. It was decided by the relevant Rabbanim that it is no longer necessary to exclude the Hammershop Pond and the Ames Street playground from the Eiruv. In the past, this had been done because the pond area was deemed to be a Karpeif, but that has changed over the last year, as the town of Sharon has invested significantly into cleaning up the pond and its vicinity. During the winter of 2016-2017, a new dam was built to raise the water level, which makes it more conducive for boating, and a new path is currently being built so that the area can be used more regularly. Additionally, the hiking trails between the pond and Lake Massapoag have been better maintained by the local boy scouts.
All of these changes have made this area more fit for recreational usage and part of the Dirah. Upon my suggestion, Rav Noah Cheses (the Rav of the Young Israel of Sharon) even encouraged the community to use it for recreational purposes to further bolster its status as part of the Dirah. This Psak Din was made in consultation with Rav Moshe Heineman and Rav Willig. The recently retired long-term Rav of the community, Rav Meir Sendor, was also included in the decision and is supportive.
The Sharon Eiruv continues to maintain a high standard regarding the issue of Karpeif and many other areas of Halachic dispute regarding Eiruvin. Indeed, the Sharon, Massachusetts Eiruv serves as a model for Eiruvin worldwide of how the synergy between the local Rav, Poskim of stature, and a large percentage of lay community members creates and maintains a top-notch community Eiruv.
 See Eiruvin 23a-b and Shulchan Aruch, Orach Chaim 358.
 Rav Moshe Heinemann mentioned in a Shiur delivered to the Conference of Young Israel rabbis that sand traps and other hazards on a golf course do not constitute Karpeifiyot despite the fact that they are unused land. He explains that since the hazards are part of the game of golf, it is considered to be a useful portion of the golf course and part of the Dirah.
 For an analysis of the Karpeif's impact on the walls, see Bi’ur Halachah (358:9 s.v. HaZra'im).
 Also see the Bi’ur Halachah (358:9 s.v. Aval).
 Of course, the Devar Shmuel's leniency does not apply to Eiruvin that enclose very large forest areas that are not integrated into the local community, since his entire reason for leniency is that the Karpeif is negligible compared to the inhabited area. When this author many years ago sought to construct an Eiruv in a certain summer community in Connecticut, Rav Hershel Schachter ruled that the Eiruv could not be built because the Tzurot HaPetach would have had to encompass huge tracts of forest which were outside the area of habitation and not at all integrated into the living area. In fact, the deeply forested area would have occupied approximately ninety percent of the area encompassed by the proposed Eiruv. Rav Schachter also did not permit relying on the extraordinarily lenient views of Teshuvot Divrei Malki’el (cited in Melamed Leho'il 1:65) and Teshuvot Even Yekarah (Orach Chayim 16), which would have facilitated constructing this specific Eiruv, as these views are not accepted by most Halachic authorities. The many forests included in the Sharon Eiruv are not at all comparable to the Connecticut bungalow colony. The forests are very much integrated into the living area, as we shall discuss.
 Although the Devar Shmuel speaks of a city surrounded by walls, his ruling appears to apply equally to a city surrounded by Tzurot HaPetach; see Melamed Leho'il 1:65.
 Rav Aharon Gruman informs me that Rav Moshe Shternbuch permitted a community that otherwise could not reasonably exclude potential Karpeifim within its Eiruv to rely on the Devar Shmuel. Rav Shternbuch remarked that many communities rely upon the Devar Shmuel.
 In addition, Eiruvin Mehudarim in Israel exclude every Karpeif in accordance with the strict ruling of Rav Yosef Shalom Eliashiv.
 For example, according to information received from the Jerusalem Rabbinate in 1991, the circumference of Jerusalem's Eiruv is approximately 110 kilometers. One can only imagine that the size of the general Jerusalem Eiruv has considerably expanded since 1991.
 There is considerable debate regarding whether a cemetery constitutes a Karpeif. Rav Eliashiv (Kovetz Teshuvot 1:45) rules leniently, as people visit cemeteries, making it part of the Dirah. Rav Heinemann, though, reports that Rav Moshe Feisntein adopted a strict approach and did not regard a cemetery as part of the Dirah. The Passaic, New Jersey community excludes cemeteries from its Eiruv. An exception even according to the strict view might be cemeteries of special historic and/or national interest, such as Arlington National Cemetery.
 See Orchot Chayim (Ch. 358), Teshuvot Melameid Leho'il (1:65), and Teshuvot Har Tzvi (Orach Chayim vol. 2, Harari VaSadeh p. 249).
 Regarding watery areas, see Shulchan Aruch Orach Chaim 358:11. Rav Heinemann cites Rav Moshe Feinstein, who rules that in contemporary times, even water that is less than three Tefachim deep (approximately 9 to 11 inches) should be regarded as a Karpeif. Although the Mishnah Berurah (Bi’ur Halacha op. cit. s.v. VeHi) considers it a problem only if the water is at least three Tefachim deep, Rav Moshe feels that in contemporary society, unlike in the past (see, for instance, Yoma 77b and Ta’anit 23b), people do not walk through any body of water, even if it is very shallow; thus, no body of water is part of the Dirah.
 “Vietnam-like” density and inaccessibility is the way that one of the community members described the areas that are excluded from the Eiruv.