Not a direct translation but this place was described as a Rentendorf and there is a corresponding paragraph in EN which you may find helpful.

Things that spring to mind are transit camp, deportation camp, ghetto.

Nach dem deutschen Überfall auf Polen im September 1939 waren Kreis und Stadt Siedlce Teil des von Deutschland besetzten Generalgouvernement. Im Stadtzentrum wurde ein von der SS bewachtes "großes Ghetto" installiert, "in dem etwa 15.000 Juden lebten. In einem separaten Gebäudekomplex wurden 1941 westdeutsche Roma, die im Zuge der Mai-Deportation 1940 ins Generalgouvernement deportiert worden waren, festgehalten. Beide Gruppen hatten in der Stadt und ihrer Umgebung Zwangsarbeit zu leisten. Eine zweite Deportation von Roma - aus dem Kreis Siedlce - ins große Ghetto geschah im Juni 1942.[2] Am 19. August 1942 wurden die Juden aus Siedlce in das Vernichtungslager Treblinka abtransportiert. Dabei wurden auch Roma erschossen. Die überlebenden Roma wurden in das etwas außerhalb der Stadt gelegene kleine Ghetto überführt.[3] Im September 1942 kam es erneut zu, wie zeitgenössische deutsche Quellen berichten, "Greueltaten" eines deutschen "Sonderkommandos" in der Kreisstadt.[4] Während der Aktion Zamość, also des Germanisierungs- bzw. "Umvolkungs"versuchs im Kontext des Generalplans Ost wurde Siedlce als "Rentendorf" Unterbringungsstation für 350 zwangsausgesiedelte Familien aus dem Distrikt Lublin, die Volksdeutschen Platz zu machen hatten.[5] Ende Juli 1944 nahm die Rote Armee Siedlce ein. Die Einwohnerzahl betrug zu diesem Zeitpunkt noch 27.500, die Stadt war zur Hälfte zerstört.

http://de.wikipedia.org/wiki/Siedlce

The antisemitic persecutions perpetrated by the Black Hundreds in the last decades of Tsarist rule touched Siedlce with a pogrom in 1906, in which 26 Jews perished. In the wake of the First World War the town was affected by the Polish-Soviet War, being occupied by the Red Army in 1920 and taken over by the Polish Army in 1921. In 1939, Jews constituted some 37% of the town's population. Germans exiled some thousand Jews from elsewhere in Poland to Siedlce in 1940, especially from Łódź, Kalush and Pabianice. In March 1941 - still before the formal decision to implement the "Final Solution" of wholesale extermination the Jews - German forces rampaged for three days in Siedlce, killing many of its Jewish inhabitants. In August of the same year the town's Jews were herded into a ghetto and on October 1, 1941 were completely cut off from the outside world. In August 1942 some 10,000 of the Siedlce Jews were deported to Treblinka together with around 10 thousand gentile population for the Siedlce forced labour camps and murdered there. The town's remaining 7,000 Jews were sent off to extermination on November 25, 1942.

http://en.wikipedia.org/wiki/Siedlce

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Note added at 29 mins (2011-03-02 15:49:47 GMT)
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http://books.google.co.uk/books?id=h0oFGH81O7MC&pg=PA410&lpg...

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Note added at 39 mins (2011-03-02 15:59:56 GMT)
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Now what do you mean about 'dumping grounds'. The ghettos at this time were hardly picnics!

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Note added at 40 mins (2011-03-02 16:01:02 GMT)
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I imagine this Rentendorf was probably something like Drancy in Paris:

http://www.jewishvirtuallibrary.org/jsource/Holocaust/Drancy...

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Note added at 42 mins (2011-03-02 16:02:22 GMT)
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On ghettos during the Nazi period: http://en.wikipedia.org/wiki/Łódź_Ghetto

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Note added at 58 mins (2011-03-02 16:19:00 GMT)
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Please note that your own original context says that these camps were places from where people were transported to extermination camps. They are generally known as transit or deportation camps. There is undoubtedly a difference between ghettos and such camps but the ghettos were also cleared and people were deported/transported to be exterminated, too.

For what it is worth, the other suggestion of 'pensioners' camps' sounds like a translation to me and sounds much more like a holiday camp. For the purposes of comprehension, I would favour transit or deportation camp if your text makes such a distinction.